Introduction

The mobile-bearing (MB) total knee arthroplasty (TKA) design was introduced with the aim of reducing polyethylene wear and component loosening seen in the fixed-bearing (FB) design. A recent joint registry study has revealed increased risk for all-cause revision, but not revision for infection, in MB-TKA. We used the New Zealand Joint Registry (NZJR) to compare all-cause revision rates, and revision rates for aseptic loosening of MB-TKA compared with fixed bearing (FB) TKA.

Introduction

Autologous fat grafting has favourable potential as a regenerative strategy and is the current gold-standard to repair large contour defects, as needed in breast reconstruction after mastectomy and traumatic soft tissue reconstruction. Clinically, there is a limit on the volume of lipoaspirate which can be utilised to repair a soft-tissue defect. Surgical complications are the result of poor structural fidelity of lipoaspirate and graft resorption as a filling material and are hindered further by poor graft vascularisation. This study aims to develop injectable lipoaspirate-derived adipose tissue grafts with enhanced biologically and clinically-admissible structural and functional properties adopting light photocrosslinking of unmodified lipoaspirate.

INTRODUCTION

Stimulation of angiogenesis via the delivery of growth factors (GFs) like vascular endothelial growth factor (VEGF) is a promising strategy for the treatment of avascular necrosis (AVN). Tyraminated poly-vinyl-alcohol hydrogels (PVA-Tyr), which have the ability to covalently incorporate GFs, were proposed as a platform for the controlled delivery of therapeutic levels VEGF to the necrotic areas[1]. Nevertheless, PVA hydrophilicity and bioinertness limits its integration with the host tissues. The aim of this study was to investigated the effectiveness of incorporating gelatin, an FDA-approved, non-immunogeneic biomaterial with biological recognition sites, as a strategy to facilitate blood vessels invasion of PVA-Tyr hydrogels and to restore the vascular supply to necrotic tissues.

Introduction

The Oxford Unicompartmental Knee Replacement (OUKA) is the most popular unicompartmental knee replacement (UKR) in the New Zealand Joint Registry with the majority utilising cementless fixation. We report the 10-year radiological outcomes.

Femoral stem design affects periprosthetic bone mineral density (BMD), which may impact long term survival of cementless implants in total hip arthroplasty (THA). The aim of this study was to examine proximal femoral BMD in three morphologically different uncemented femoral stems designs to investigate whether one particular design resulted in improved preservation of BMD.

119 patients were randomized to receive either a proximally coated dual taper wedge stem, a proximally coated anatomic stem or a fully coated collarless triple tapered stem. Dual energy x-ray absorptiometry scans (Lunar iDXA, GE Healthcare, Madison, WI) assessed BMD across the seven Gruen zones pre-operatively, and post-operatively at 6-weeks, 1-year, and 2-years comparing the unoperated contralateral femur as a control.

BMD increased in zones one (2.5%), two (17.1%), three (13.0%), five (10%) and six (17.9%) for all stems. Greater preservation of BMD was measured on the lateral cortex (zone 2) for both the dual taper wedge and anatomic stems (p = 0.019). The dual taper wedge stem also demonstrated preservation of BMD in the medial calcar (zone 7) whilst the anatomic and triple taper stem declined in this region, however this was not statistically significant (p = 0.059). BMD decreased on average by 2.1% in the mid-diaphysis region, distal to the stem tip (zone 4) for all implants. All stems performed equivalently at final follow-up in all patient reported outcome measures.

Implant design was shown to impact BMD changes. All stems preserved bone at the metaphyseal level in early follow-up, which theoretically indicates favorable implant fixation. There was no significant stress shielding observed, however longer follow-up is required to elucidate the impact of this finding on implant survivorship.

Unicompartmental knee arthroplasty (UKA) is associated with a higher risk of revision compared with total knee arthroplasty (TKA). The outcomes of knee arthroplasty are typically presented as implant survival or incidence of revision after a set number of years, which can be difficult for patients and clinicians to conceptualise. We aimed to calculate the ‘lifetime risk’ of revision for UKA as a more relatable estimate of risk projection over a patient's remaining lifetime, and make comparisons to TKA. All primary UKAS performed from 1999 to 2019 (n=13,481) captured by the New Zealand Joint Registry (NZJR) were included. The lifetime risk of revision was calculated and stratified by age, gender and American Society of Anesthesiologists (ASA) status. The lifetime risk of revision for UKA was highest in the youngest patients (46-50 years; 40.4%) and lowest in the oldest patients (86-90 years; 3.7%). Lifetime risk of revision was higher for females (range 4.3%-43.4% cf. males 2.9%-37.4%) and patients with higher ASA status (ASA 3-4 range 8.8%-41.2% cf. ASA 1 1.8%-29.8%), regardless of age. The lifetime risk of UKA was two-fold higher than TKA (ranging from 3.7%-40.4% UKA, 1.6%-22.4% TKA) across all age groups. Increased risk of revision in the younger patients was associated with aseptic loosening in both males and females, and pain in females. Periprosthetic joint infections (PJI) accounted for 4% of all UKA revisions, in contrast to 27% for TKA; risk of PJI was higher for males than females for both procedures. The lifetime risk of revision is a more meaningful measure of arthroplasty outcomes and can aid with patient counselling prior to UKA. Findings from this study show the increased lifetime risk of UKA revision for younger patients, females and those with higher ASA status.

Source of the study: University of Auckland, Auckland, New Zealand and University of Otago, Christchurch, New Zealand

The Oxford Knee Score (OKS) is a 12-item questionnaire used to track knee arthroplasty outcomes. Validation of such patient reported outcome measures is typically anchored to a single question based on patient ‘satisfaction’, however risk of subsequent revision surgery is also an important outcome measure. The OKS can predict subsequent revision risk within two years, however it is not known which item(s) are the strongest predictors. Our aim was to identify which questions were most relevant in the prediction of subsequent knee arthroplasty revision risk.

All primary TKAs (n=27,708) and UKAs (n=8,415) captured by the New Zealand Joint Registry between 1999 and 2019 with at least one OKS response at six months, five years or ten years post-surgery were included. Logistic regression and receiver operating characteristics (ROC) curves were used to assess prediction models at six months, five years and ten years.

Q1 ‘overall pain’ was the strongest predictor of revision within two years (TKA: 6 months, odds ratio (OR) 1.37; 5 years, OR 1.80; 10 years, OR 1.43; UKA: 6 months, OR 1.32; 5 years, OR 2.88; 10 years, OR 1.85; all p<0.05). A reduced model with just three questions (Q1, Q6 ‘limping when walking’, Q10 ‘knee giving way’) showed comparable or better diagnostic ability with the full OKS (area under the curve (AUC): TKA: 6 months, 0.77 vs. 0.76; 5 years, 0.78 vs. 0.75; 10 years, 0.76 vs. 0.73; UKA: 6 months, 0.80 vs. 0.78; 5 years: 0.81 vs. 0.77; 10 years, 0.80 vs. 0.77).

The three questions on overall knee pain, limping when walking, and knee ‘giving way’ were the strongest predictors of subsequent revision within two years. Attention to the responses for these three key questions during follow-up may allow for prompt identification of patients most at risk of revision.

Source of the study: University of Auckland, Auckland, New Zealand and University of Otago, Christchurch, New Zealand

Outcomes following knee arthroplasty are typically defined as implant survivorship at defined timepoints, or revision incidence over time. These estimates are difficult to conceptualise, and lack context for younger patients with more remaining years of life. We therefore aimed to determine a ‘lifetime’ risk of revision as a more useful metric for total (TKA) and unicompartmental knee arthroplasty (UKA).

The New Zealand Joint Registry was used to identify 96,497 primary TKAs and 13,481 primary UKAs performed between 1999 and 2019. Patient mortality and revision incidence were also extracted. Estimates of lifetime risk were calculated using an actuarial lifetable method. The estimates were stratified by age and gender. Reasons for revision were categorised using previously published standardised definitions.

The lifetime risk of UKA revision was two-fold higher than TKA across all age groups (range 3.7-40.4% UKA, 1.6-22.4% TKA). Revision risk was higher for males with TKA (range 3.4%-25.2% males, 1.1%-20% females), but higher for females with UKA (range 4.3%-43.4% vs. 2.9%-37.4% for males). Revision due to infections were higher for TKA (1.5% males, 0.7% females) compared with UKA (0.4% males, 0.1% females). The increased risk in younger UKA patients was associated with higher incidence of aseptic loosening (UKA 2%, TKA 1%) and ‘unexplained pain’ (UKA 2%, TKA 0.2%).

The risk for UKA was two-fold higher than TKA, and this was partially explained by a higher proportion of revisions due to ‘unexplained pain’. For TKA, males had higher risk of revision, in contrast to UKA where females had higher risk; this gender difference was associated with higher incidence of infections with TKA. Younger age, gender and higher ASA status were also associated with increased lifetime risk of UKA revision. Lifetime risk of revision can provide a meaningful measure of arthroplasty outcomes to aid patient counselling.

Introduction: The mechanobiology and response of bone formation to strain under physiological loading is well established, however investigation into exceedingly soft scaffolds relative to cancellous bone is limited. In this study we designed and 3D printed mechanically-optimised low-stiffness implants, targeting specific strain ranges inducing bone formation and assessed their biological performance in a pre-clinical in vivo load-bearing tibial tuberosity advancement (TTA) model. The TTA model provides an attractive pre-clinical framework to investigate implant osseointegration within an uneven loading environment due to the dominating patellar tendon force.

A knee finite element model from ovine CT data was developed to determine physiological target strains from simulated TTA surgery. We 3D printed low-stiffness Ti wedge osteotomy implants with homogeneous stiffness of 0.8 GPa (Ti1), 0.6 GPa (Ti2) and a locally-optimised design with a 0.3 GPa cortex and soft 0.1 GPa core (Ti3), for implantation in a 12-week ovine tibial advancement osteotomy (9mm). We quantitatively assessed bone fusion, bone area, mineral apposition rate and bone formation rate.

Optimised Ti3 implants exhibited evenly high strains throughout, despite uneven wedge osteotomy loading. We demonstrated that higher strains above 3.75%, led to greater bone formation. Histomorphometry showed uniform bone ingrowthin optimised Ti3 compared to homogeneous designs (Ti1 and Ti2), and greater bone-implant contact. The greatest bone formation scores were seen in Ti3, followed by Ti2 and Ti1.

Results from our study indicate lower stiffness and higher strain ranges than normally achieved in Ti scaffolds stimulate early bone formation. By accounting for loading environments through rational design, implants can be optimised to improve uniform osseointegration. Design and 3D printing of exceedingly soft titanium orthopaedic implants enhance strain induced bone formation and have significant importance in future implant design for knee, hip arthroplasty and treatment of large load-bearing bone defects.

Source of the study: University of Auckland, Auckland, New Zealand and University of Otago, Christchurch, New Zealand

Patient reported outcome measures (PROMs) are predictors of knee arthroplasty revision. Unicompartmental knee arthroplasty (UKA) is effective for patients with the correct indications, however has higher revision rates than total knee arthroplasty (TKA). Different revision thresholds for the procedures have been postulated. Our aims were to investigate: 1) if PROMs could predict knee arthroplasty revision within two years of the score at six months, five years and ten years follow-up, and 2) if revision ‘thresholds’ differed between TKA and UKA.

All TKAs and UKAs captured by the New Zealand Joint Registry between 1999 and 2019 with at least one OKS response at six months (TKA n=27,708, UKA n=8,415), five years (TKA n=11,519, UKA n=3,365) or ten years (TKA n=6,311, UKA n=1,744) were included. were propensity-score matched 2:1 with UKAs for comparison of revision thresholds.

Logistic regression indicated that for every one-unit decrease in OKS, the odds of TKA and UKA revision decreased by 10% and 11% at six months, 10% and 12% at five years and 9% and 5% at ten years. Fewer TKA patients with ‘poor’ outcomes (≤25) subsequently underwent revision compared with UKA at six months (5.1% vs. 19.6%, p<0.001), five years (4.3% vs. 12.5%, p<0.001) and ten years (6.4%vs. 15.0%, p=0.02). Compared with TKA, UKA patients were 2.5 times more likely to undergo revision for ‘unknown’ reasons, bearing dislocations and disease progression.

The OKS is a strong predictor of subsequent knee arthroplasty revision within two years of the score from early to late term. A lower revision threshold was found with UKA when compared with a matched TKA cohort. Higher revision rates of UKA are associated with both lower clinical thresholds for revision and additional modes of UKA failure.

Due to shorter hospital stays and faster patient rehabilitation Unicompartmental Knee Replacements (UKR) are now considered more cost effective than Total Knee Joint Replacements (TKJR). Obesity however, has long been thought of as a relative contraindication to UKR due to an unproven theoretical concern of early loosening.

This study is a retrospective review of patient reported outcome scores and revision rates of all UKR with recorded BMI performed by the Canterbury District Health Board (CDHB) from January 2011 and September 2021. Patient reported outcome scores were taken preoperatively, at 6 months, 1 year, 5 years and 10 years post operatively. These included WOMAC, Oxford, HAAS, UCLA, WHOQOL, normality, pain and patient satisfaction. 873 patients had functional scores recorded at 5 years and 164 patients had scores recorded at 10 years. Further sub-group analysis was performed based on patient BMI of <25, 25-30, 30-35 and >35. Revision data was available for 2377 UKRs performed in Christchurch during this period.

Both obese (BMI >30) and non-obese (BMI <30) patients had significantly improved post-operative scores compared to preoperative. Pre-operatively obese patients had significantly lower functional scores except for pain and UCLA. All functional scores were lower in obese patients at 5 years but this did not meet minimum clinical difference. At 10 years, there was significantly lower HAAS, satisfaction and WOMAC scores for obese patients but no difference in Oxford, normality, WHOQOL, UCLA and pain scores. There was no significant difference in the improvement from pre-operative scores between obese and non-obese patients. All cause revision rate for obese patients at 10 years was 0.69 per 100 observed component years compared to 0.76 in non-obese. This was not statistically significant.

Our study proves that UKR is an excellent option in obese patients with post-operative improvement in functional scores and 10 year survivorship equivalent to non-obese patients.

Polyetheretherketone (PEEK) interbody fusion cages combined with autologous bone graft is the current clinical gold standard treatment for spinal fusion, however, bone graft harvest increases surgical time, risk of infection and chronic pain. We describe novel low-stiffness 3D Printed titanium interbody cages without autologous bone graft and assessed their biological performance in a pre-clinical in vivo interbody fusion model in comparison to the gold standard, PEEK with graft.

Titanium interbody spacers were 3D Printed with a microporous (Ti1: <1000μm) and macroporous (Ti2: >1000μm) design. Both Ti1 and Ti2 had an identical elastic modulus (stiffness), and were similar to the elastic modulus of PEEK. Interbody fusion was performed on L2-L3 and L4-L5 vertebral levels in 24 skeletally mature sheep using Ti1 or Ti2 spacers, or a PEEK spacer filled with iliac crest autograft, and assessed at 8 and 16 weeks. We quantitatively assessed bone fusion, bone area, mineral apposition rate and bone formation rate. Functional spinal units were biomechanically tested to analyse range of motion, neutral zone, and stiffness. Results: Bone formation in macroporous Ti2 was significantly greater than microporous Ti1 treatments (p=.006). Fusion scores for Ti2 and PEEK demonstrated greater rates of bone formation from 8 to 16 weeks, with bridging rates of 100% for Ti2 at 16 weeks compared to just 88% for PEEK and 50% for Ti1. Biomechanical outcomes significantly improved at 16 versus 8 weeks, with no significant differences between Ti and PEEK with graft.

This study demonstrated that macroporous 3D Printed Ti spacers are able to achieve fixation and arthrodesis with complete bone fusion by 16 weeks without the need for bone graft. These significant data indicate that low-modulus 3D Printed titanium interbody cages have similar performance to autograft-filled PEEK, and could be reliably used in spinal fusion avoiding the complications of bone graft harvesting.

Source of the study: University of Auckland, Auckland, New Zealand

Unicompartmental knee arthroplasty (UKA) is effective for patients with isolated compartment osteoarthritis, however the procedure has higher revision rates. Long-term survivorship and accurate characterisation of revision reasons are limited by a lack of long-term data and standardised revision definitions. We aimed to identify survivorship, risk factors and revision reasons in a large UKA cohort with up to 20 years follow-up.

Patient, implant and revision details were recorded through clinical and radiological review for 2,137 consecutive patients undergoing primary medial UKA across Auckland, Canterbury, Counties Manukau and Waitematā DHB between 2000 and 2017. Revision reasons were determined from review of clinical, laboratory, and radiological records for each patient using a standardised protocol. To ensure complete follow-up data was cross-referenced with the New Zealand Joint Registry to identify patients undergoing subsequent revision outside the hospitals. Implant survival, revision risk and revision reasons were analysed using Cox proportional-hazards and competing risk analyses.

Implant survivorship at 15 years was comparable for cemented fixed-bearing (cemFB; 91%) and uncemented mobile-bearing (uncemMB; 91%), but lower for cemented mobile-bearing (cemMB; 80%) implants. There was higher incidence of aseptic loosening with cemented implants (3-4% vs. 0.4% uncemented, p<0.01), osteoarthritis (OA) progression with cemMB implants (9% vs. 3% cemFB/uncemMB; p<0.05) and bearing dislocations with uncemMB implants (3% vs. 2% cemMB, p=0.02). Compared with the oldest patients (≥75 years), there was a nearly two-fold increase in risk for those aged 55-64 (hazard ratio 1.9; confidence interval 1.1–3.3, p=0.03). No association was found with gender, BMI or ASA.

Cemented mobile-bearing implants and younger age were linked to lower implant survivorship. These were associated with disease progression and bearing dislocations. The use of cemented fixed-bearing and uncemented mobile-bearing designs have superior comparable long-term survivorship.

Femoral stem design affects periprosthetic bone mineral density (BMD), which may impact long term survival of cementless implants in total hip arthroplasty (THA). The aim of this study was to examine proximal femoral BMD in three morphologically different uncemented femoral stems designs to investigate whether one particular design resulted in improved preservation of BMDMethods: 119 patients were randomised to receive either a proximally coated dual taper wedge stem, a proximally coated anatomic stem or a fully coated collarless triple tapered stem. All surgeries were performed via the posterior approach with mobilization on the day of surgery. Dual energy x-ray absorptiometry scans (Lunar iDXA, GE Healthcare, Madison, WI) assessed BMD across the seven Gruen zones pre-operatively, and post-operatively at 6-weeks, 1-year, and 2-years and compared to the unoperated contralateral femur as a control. Patient reported outcome measures of pain, function and health were also included at these corresponding follow-ups.

BMD increased in zones one (2.5%), two (17.1%), three (13.0%), five (10%) and six (17.9%) for all stems. Greater preservation of BMD was measured on the lateral cortex (zone 2) for both the dual taper wedge and anatomic stems (p = 0.019). The dual taper wedge stem also demonstrated preservation of BMD in the medial calcar (zone 7) whilst the anatomic and triple taper stem declined in this region, however this was not statistically significant (p = 0.059). BMD decreased on average by 2.1% inthe mid-diaphysis region, distal to the stem tip (zone 4) for all implants. All stems performed equivalently at final follow-up in all patient reported outcome measures.

This study demonstrated maintenance of femoral BMD in three different cementless femoral stem designs, with all achieving excellent improvements in patient reported outcomes. There was no significant stress shielding observed, however longer follow-up is required to elucidate the impact of this finding on implant survivorship.

This study aimed to examine the changing trends in the reasons for total hip replacement (THR) revision surgery, in one country over a twenty-one year period, in order to assess whether changes in arthroplasty practices have impacted revision patterns and whether an awareness of these changes can be used to guide clinical practice and reduce future revision rates.

The reason for revision THR performed between January 1999 and December 2019 was extracted from the New Zealand Joint Registry (NZJR). The results were then grouped into seven 3-year periods to allow for clearer visualization of trends. The reasons were compared across the seven time periods and trends in prosthesis use, patient age, gender, BMI and ASA grade were also reviewed. We compared the reasons for early revision, within one year, with the overall revision rates.

There were 20,740 revision THR registered of which 7665 were revisions of hips with the index procedure registered during the 21 year period. There has been a statistically significant increase in both femoral fracture (4.1 – 14.9%, p<0.001) and pain (8.1 – 14.9%, p<0.001) as a reason for hip revision. While dislocation has significantly decreased from 57.6% to 17.1% (p<0.001). Deep infection decreased over the first 15 years but has subsequently seen further increases over the last 6 years. Conversely both femoral and acetabular loosening increased over the first 12 years but have subsequently decreased over the last 9 years. The rate of early revisions rose from 0.86% to 1.30% of all revision procedures, with a significant rise in revision for deep infection (13-33% of all causes, p<0.001) and femoral fracture (4-18%, p<0.001), whereas revision for dislocation decreased (59-30%, p<0.001). Adjusting for age and gender femoral fracture and deep infection rates remained significant for both (p<0.05). Adjusting for age, gender and ASA was only significant for infection.

The most troubling finding was the increased rate of deep infection in revision THR, with no obvious linked pattern, whereas, the reduction in revision for dislocation, aseptic femoral and acetabular loosening can be linked to the changing patterns of the use of larger femoral heads and improved bearing surfaces.

Cementless fixation is an alternative to cemented unicompartmental knee replacement (UKR), with several advantages over cementation. This study reports on the 15-year survival and 10-year clinical outcomes of the cementless Oxford unicompartmental knee replacement (OUKR).

This prospective study describes the clinical outcomes and survival of first 693 consecutive cementless medial OUKRs implanted in New Zealand.

The sixteen-year survival was 89.2%, with forty-six knees being revised. The commonest reason for revision was progression of arthritis, which occurred in twenty-three knees, followed by primary dislocation of the bearing, which occurred in nine knees. There were two bearing dislocations secondary to trauma and a ruptured ACL, and two tibial plateau fractures. There were four revisions for polyethylene wear. There were four revisions for aseptic tibial loosening, and one revision for impingement secondary to overhang of the tibial component. There was only one revision for deep infection and one revision where the indication was not stated. The mean OKS improved from 23.3 (7.4 SD) to 40.59 (SD 6.8) at a mean follow-up of sixteen years.

In conclusion, the cementless OUKR is a safe and reproducible procedure with excellent sixteen-year survival and clinical outcomes.

Our objective was to examine revision rates and patient reported outcome scores (PROMS) for cemented and uncemented primary total knee joint replacement (TKJR) at six months, one year and five years post-operatively. Patients and Methods: This matched cohort study involved secondary analyses of data collected as part of a large prospective observational study monitoring outcomes following knee replacement in Christchurch, New Zealand. Cemented and uncemented TKJR participants (n = 1526) were matched on age (± 5 years), sex and body mass index (BMI). From this larger sample, PROMS data, Oxford Knee Score and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), out to five years post-operatively were analysed for a matched subset of participants (n = 252).

The average age of participants was 67.9 years (SD 9.4, range 38-94). There were no differences between cemented and uncemented cohorts on the basis of age, sex, BMI or comorbidities, revision rates or PROMS outcomes. Cemented procedures had greater skin to skin times than uncemented procedures (p < 0.01). Unadjusted outcomes comparing risk for revision across the two participant cohorts did not significantly differ. Overall rates for revision were low (cemented 3.2% v uncemented 2.7%, p=0.70). Propensity adjusted associations between baseline characteristics (age, sex, BMI, comorbidity, baseline Oxford and baseline WOMAC scores) also revealed no differences in risk for revision at any post-operative timepoint.

In this large multi-surgeon matched cohort study there were no significant differences in functional outcomes or revision rates, when outcomes following modern cemented and uncemented TKJR were compared out to 5-year follow up. Based on our findings, uncemented TKJR is predictable irrespective of patient's age, BMI or gender

Hypochlorous acid (HOCl) is a potent anti-bacterial agent which could reduce periprosthetic joint infection. Early infection complications in joint replacements are often considered to be due to local contamination at the time of surgery and result in a significant socioeconomic cost. Current theatre cleaning procedures produce “clean” operating theatres which still contain bacteria (colony forming units, CFU). Reducing this bacterial load may reduce local contamination at the time of surgery. HOCl is produced naturally in the human neutrophil and has been implicated as the primary agent involved in bacterial killing during this process. In vitro research confirms its efficacy against essentially all clinically relevant bacteria. The recent advent of commercial production of HOCl, delivered as a fog, has resulted in extensive use in the food industry. Reported lack of corrosion and high anti-bacterial potency are seen as two key factors for the use of HOCl in the orthopaedic environment. Prior work by the authors comparing human cell toxicity of HOCl, chlorhexidine and iodine solutions shows favourable results.

This study evaluates use of neutral HOCl applied as a dry room fog to decrease bacteria in the operating theatre environment. Using an animal operating theatre as the test site, bacterial swabs were taken from ten 100cm² sample areas before standard cleaning with detergent, after standard cleaning, and again after 60 minutes exposure to HOCl fog.

After standard cleaning, 6 of 10 sample sites recorded significant bacterial growth (>10 CFU/100cm²). After exposure to HOCl fog, growth in all 10 sites was below detection limits (<10 CFU/100cm²). This was repeated with specific exposure to Staphylococcus aureus and Escherichia coli.

We can conclude that HOCl is effective when used as a fogging agent to reduce bacterial loading within an operating theatre environment and as such has significant potential to reduce intraoperative contamination and periprosthetic infection.

Background

Reduced dislocation rates using lipped polyethylene (PE) liners in modular uncemented acetabular components has been shown, yet there may be increased wear because of impingement, which may lead to aseptic loosening. We used New Zealand Joint Registry (NZJR) data to compare survival rates, revision rates for dislocation and aseptic loosening between lipped and neutral liners.

Stress shielding has been a well-recognised problem with uncemented femoral components resulting in proximal bone loss and dysfunction, but less attention has been paid to the preservation of acetabular bone stock. Uncemented acetabular components often demonstrate reduced bone density on plain radiographs in the mid-portion of the cup (zone 2), which may be due to the rigidity of the outer shell. This study compares the change in bone density around three different cups with varying moduli of elasticity at a minimum of 2 years. Our hypothesis was that less rigid cups would be associated with improved bone density and less stress shielding.

This prospective randomised controlled trial compared the bone mineral content (BMC) adjacent to three different cups with marked differences in stiffness. Cup A was an all titanium shell, cup B was a titanium coated all polyethylene implant and cup C was a tantalum backed shell. All articulations used a 32mm ceramic femoral head. Cup B used polyethylene modified by treatment with vitamin E whereas cups A and C used a liner made of irradiated cross linked polyethylene.

Five regions of interest (ROI) were established adjacent to the cup, regions 2, 3 and 4 where similar to the DeLee and Charnley regions 1, 2 and 3. Bone density was measured using IDXA preoperatively, postoperatively, 6 months, 1 and 2 years and compared for each ROI and implant.

Precision measurements showed significant reliability. All areas showed a reduction in BMC following insertion of the acetabular cup. Bone loss was less in ROI 1 and 4 in the area of rim fit for all cups and the maximal bone loss was seen in ROI 2 and 3 at the dome of the cup. The more elastic cup (Cup B) produced the least bone loss in this area (p<0.05). Cup C produced the largest bone loss at ROI 2 (40%) which continued increasing at 2 years.

Cup stiffness is related to bone loss adjacent to the acetabulum, presumably due to a similar process of stress shielding as seen in the femur. All cups produced similar changes at the periphery of the cup but the more elastic cup retained bone density beneath the cup which continued past 2 years. This improvement in bone quality is likely to be associated with better acetabular bone stock into the future and more reliable long term cup fixation.

This study aimed to examine the changing trends in the causes for early revision of total hip replacements (THR) in one country over fifteen years to assess whether changes in arthroplasty practices have changed revision patterns.

The cause for revision within one year was extracted from the New Zealand Joint Registry for the period of January 1999 to December 2013. The results were grouped into three periods of 5 years (Period 1=1999–2003, Period 2=2004–2008 and Period 3 = 2009–2013). The causes were compared across the three periods and were adjusted for age, gender and ASA grade.

The rate of early revisions (within one year) rose from 0.86% to 1.30% per year. There was significant rise in revision for deep infection (14% increased to 21% of all causes, p<0.001) and femoral fracture (5% increased to20%, p<0.001), whereas revision for dislocation decreased (55% decreased to 35%, p<0.001). Adjusting for age and gender femoral fracture and deep infection rates remained significant for both (p<0.05). Adjusting for age, gender as well as ASA only remained significant for infection (P<0.05).

The reduction in revision for dislocation followed the registry trend for the use of larger femoral heads and cross linked polyethylene. The rise in early periprosthetic femoral fracture rates was directly associated (p<0.001) with the increased use of uncemented femoral prostheses. The worrying increase in infection rate was unexplained on the basis of registry data alone. It was related to ASA grade but the overall ratios of ASA grades remained consistent over the 15 years.

Aims

The primary aim of this independent prospective randomised trial was to compare serum metal ion levels for ceramic-on-metal (CoM) and metal-on-metal (MoM) bearing surfaces in total hip arthroplasty (THA). Our one-year results demonstrated elevation in metal ion levels above baseline with no significant difference between the CoM and MoM groups. This paper reviews the five-year data.

Polyethylene wear debris can cause osteolysis and the failure of total hip arthroplasty. We present the five-year wear rates of a highly cross-linked polyethylene (X3) bearing surface when used in conjunction with a 36 mm ceramic femoral head.

This was a prospective study of a cohort of 100 THAs in 93 patients. Pain and activity scores were measured pre- and post-operatively. Femoral head penetration was measured at two months, one year, two years and at five years using validated edge-detecting software (PolyWare Auto).

At a mean of 5.08 years (3.93 to 6.01), 85 hips in 78 patients were available for study. The mean age of these patients was 59.08 years (42 to 73, the mean age of males (n = 34) was 59.15 years, and females (n = 44) was 59.02 years). All patients had significant improvement in their functional scores (p < 0.001). The steady state two-dimensional linear wear rate was 0.109 mm/year. The steady state volumetric wear rate was 29.61 mm³/year. No significant correlation was found between rate of wear and age (p = 0.34), acetabular component size (p = 0.12) or clinical score (p = 0.74).

Our study shows low steady state wear rates at five years in X3 highly cross-linked polyethylene in conjunction with a 36 mm ceramic femoral head. The linear wear rate was almost identical to the osteolysis threshold of 0.1 mm/year recommended in the literature.

Cite this article: Bone Joint J 2015;97-B:1470–4.

This study reports on the first 150 consecutive Oxford cementless unicompartmental knee arthroplasties (UKA) performed in an independent centre (126 patients). All eligible patients had functional scores (Oxford knee score and high activity arthroplasty score) recorded pre-operatively and at two- and five-years of follow-up. Fluoroscopically aligned radiographs were taken at five years and analysed for any evidence of radiolucent lines (RLLs), subsidence or loosening. The mean age of the cohort was 63.6 years (39 to 86) with 81 (53.1%) males. Excellent functional scores were maintained at five years and there were no progressive RLLs demonstrated on radiographs. Two patients underwent revision to a total knee arthroplasty giving a revision rate of 0.23/100 (95% confidence interval 0.03 to 0.84) component years with overall component survivorship of 98.7% at five years. There were a further four patients who underwent further surgery on the same knee, two underwent bearing exchanges for dislocation and two underwent lateral UKAs for disease progression. This was a marked improvement from other UKAs reported in New Zealand Joint Registry data and supports the designing centre’s early results.

Cite this article: Bone Joint J 2015;97-B:1358–63.

Method.

We prospectively investigated the radiological outcomes of the uncemented Oxford medial compartment arthroplasty in 231 consecutive patients performed in a single centre with a minimum two year follow up.

There has been recent interest in the treatment of Dupuytren's disease by minimally invasive techniques such as needle fasciotomy and collagenase injection, but only few studies have reported the outcomes following open fasciotomy. This study attempts to address this gap, with a retrospective analysis of a large series of patients who underwent an open fasciotomy by a single surgeon over a five-year period. The aim of the study was to determine the requirement for re-operation in the cohort and to analyse the revisionary procedures performed.

Theatre coding data was used to identify a consecutive series of patients who underwent open fasciotomy over a five-year period between 2000 and 2005. Within this group medical records were obtained for those patients who underwent a secondary procedure for recurrence. All procedures were carried out by a single surgeon in a regional hand unit using an unmodified open technique.

A total of 1077 patients underwent open fasciotomy for Dupuytren's disease. Of these, 865 (80.3%) were male and 212 (19.7%) were female. The mean age at initial surgery was 64.4 years (range 21.7 to 93.7 years) for males and 68.3 (range 43.6 to 89.8 years) for females. Of the 1077 patients who underwent open fasciotomy, 143 patients (13.3%) subsequently underwent a second procedure for recurrence.

The medical records were available for 97 patients. The median time to re-operation in this group of patients was 42.0 months (95% CI, 8.3 to 98.0 months). The most common revision procedure being dermofasciectomy (54.2%), followed by fasciectomy (32.6%) and re-do open fasciotomy (13.2%). Mean pre-operative total extension deficit was 88 degrees (range 30–180 degrees) with intra-operative correction to a mean of 9.5 degrees (range 0–45 degrees).

There is no standard definition for recurrence after Dupuytren's surgery. We have looked at the rate of revision surgery after open fasciotomy, in a relatively fixed population serviced over a 5-year period by a single hand surgeon. A low re-operation rate has been identified, with good intra-operative correction achieved by secondary surgery.

Tibiotalocalcaneal (TTC) arthrodesis using a retrograde nail is a common salvage procedure for a range of indications. Previous work has suggested subtalar joint preparation is unnecessary to achieve satisfactory results. We examine the incidence of symptomatic subtalar nonunion following tibiotalocalcaneal fusion in a series of patients, all of whom had full preparation of the subtalar joint, and consider the possible contributing factors.

We performed a retrospective review of all patients who underwent TTC arthrodesis from 2004–2010. All fusions were performed by the same surgeon with full preparation of both tibiotalar and subtalar joints.

61 TTC arthrodeses were performed in 55 patients (mean age = 59 years) using an intramedullary retrograde nail. Mean follow-up was 18 months (6–48 months). Fifty-six ankles (92%) achieved satisfactory union. Five patients (8%) had symptomatic non-union: 4 patients of the subtalar joint - with 3 patients undergoing revision subtalar arthrodesis and 1 patient of the tibiotalar joint. Nine patients required removal of the calcaneal screw (16%) – all had evidence of isolated subtalar nonunion prior to metalwork failure. Eight of these patients achieved asymptomatic union following screw removal.

Subtalar nonunion following TTC fusion has resulted in recent changes to nail design to increase stability across the subtalar joint. Our results demonstrate a favourable overall nonunion rate with isolated subtalar nonunion making up the majority of cases. We also observed a significant rate of distal screw loosening, also associated with subtalar nonunion prior to screw removal, the significance of which merits further investigation.

In a double-blinded randomised controlled trial, 83 patients with primary osteoarthritis of the hip received either a ceramic-on-metal (CoM) or metal-on-metal (MoM) total hip replacement (THR). The implants differed only in the bearing surfaces used. The serum levels of cobalt and chromium and functional outcome scores were compared pre-operatively and at six and 12 months post-operatively.

Data were available for 41 CoM and 36 MoM THRs (four patients were lost to follow-up, two received incorrect implants). The baseline characteristics of both cohorts were similar. Femoral head size measured 36 mm in all but two patients who had 28 mm heads. The mean serum cobalt and chromium levels increased in both groups, with no difference noted between groups at six months (cobalt p = 0.67, chromium p = 0.87) and 12 months (cobalt p = 0.76, chromium p = 0.76) post-operatively. Similarly, the mean Oxford hip scores, Western Ontario and McMaster Universities Osteoarthritis index and University of California, Los Angeles activity scores showed comparable improvement at 12 months.

Our findings indicate that CoM and MoM couplings are associated with an equivalent increase in serum cobalt and chromium levels, and comparable functional outcome scores at six and 12-months follow-up.

Despite a large body of literature the optimal choice of bearing surface for total hip arthoplasty (THA) remains controversial. To avoid the brittleness and squeaking noted with ceramic-on-ceramic and the metal ion release associated with metal-on-metal (MOM) articulations, a novel hybrid coupling of ceramic-on-metal (COM) has been introduced. The purpose of this study was to compare changes in serum metal ion levels and the functional performance of COM and MOM bearing combinations.

Eighty-six patients (86 hips) undergoing THA between April 2009 and October 2010 were randomized to COM or MOM bearing couplings. All received identical uncemented acetabular shells and femoral components from two experienced surgeons using the same operative technique.

Demographic and peri-operative data were recorded. Serum cobalt and chromium levels, renal function and disease specific outcome scores (Oxford Hip, Harris Hip, UCLA activity) were assessed at baseline, 6 and 12 months post-operatively. Patients and outcome assessors remained blinded.

Mean age of the total cohort was 62.5 years. Randomization successfully matched groups for age, Body Mass Index, baseline serum Cobalt and Chromium levels, and pre-operative functional performance scores. One-year data is currently available for 25 of 44 COM and 26 of 42 MOM patients. No significant difference in serum cobalt (P value = 0.81) and chromium (P value = 0.66) levels between groups was noted. Improvements in outcome scores (Oxford Hip, Harris Hip, UCLA activity) were equivalent (P values 0.16 – 0.46).

At 1-year, COM and MOM hip arthroplasty articulations appear equivalent in terms of function and serum metal ion levels. Data collection out to 5-years post-surgery continues.

There has been limited research examining the effect training of orthopaedic trainees may have on patient outcomes. This paper aims to determine if there is a difference in revision rate and functional outcomes of total hip joint replacement performed by consultants compared to those performed by supervised and unsupervised trainees.

We reviewed all patient data since 2000 from the New Zealand National Joint Registry in patients undergoing total hip joint replacement (THJR) comparing the outcomes with the experience of the primary surgeon. The outcome measures were revision hip replacement and the Oxford Hip score at six months. We compared the reason for revision controlling for factors such as ASA, age and the index diagnosis. We also compared the six-month Oxford scores with the experience of the primary surgeon.

There were 35415 patients who underwent elective THJR, 30344 of which were performed by a consultant, 2982 by a supervised registrar and 1067 by an unsupervised registrar. There was an overall revision rate (RR) of 0.77 per 100 component years. The RR was 0.75 (95% CI 0.67–0.82) for consultants, 0.97 (95% CI 0.72 – 1.28) for supervised trainees and 0.70 (95% CI 0.36 – 1.22) for unsupervised trainees. There was no significant difference in revision rates between consultants and supervised trainees (p<0.077) or unsupervised trainees (p< 0.30). The most common cause for revision surgery was dislocation, occurring in 39% of cases. This was more common in supervised and unsupervised trainees (48% and 50%) however there was no significant difference between the three groups (p-value 0.24). The other causes for revision were; loosening of the acetabular or femoral component, deep infection, pain and fracture with no significant difference between the three groups. The mean OHS was higher for consultants at 40.7 compared to 38.95 and 38.23 for supervised and unsupervised trainees respectively (p <0.001)

The results of this study show no significant difference in the revision rate of THJR performed by trainees when compared to their consultants. Orthopaedic consultants do appear to have slightly better (1–2 points) OHS. These results are reassuring and show orthopaedic training does not adversely compromise patient outcomes.

Cell-scaffold based cartilage tissue engineering strategies provide the potential to restore long-term function to damaged articular cartilage. A major hurdle in such strategies is the adequate (uniform and sufficient) population of porous 3D scaffolds with cells, but more importantly, the generation of engineered tissue of sufficient quality of clinically relevant size. We describe a novel approach to engineer cartilage grafts using pre-differentiated micro-mass cartilage pellets, integrated into specifically designed 3D plotted scaffolds.

Expanded (P2) human nasal chondrocytes (HNCs) or bone marrow-derived mesenchymal stem cells (MSCs) from 3 donors (age 47–62 years) were micro-mass cell pellet cultivated at 5 × 105 cells/pellet for 4 days. Subsequently, pellets were integrated into degradable 3D Printed polymer (PEGT/PBT) scaffolds with 1mm fibre spacing. Constructs were cultured dynamically in spinner flasks for a total of 21 days. As a pellet-free control, expanded HNCs were spinner flask seeded into PEGT/PBT fibre plotted scaffolds. Constructs were assessed via histology (Safranin-O staining), biochemistry (glycosaminoglycan (GAG) and DNA content) and collagen type I and II mRNA expression.

After 4 days, micro-mass cultured pellets could be successfully integrated into the fibre plotted scaffolds. DNA content of pellet integrated constructs was 4.0-fold±1.3 higher compared to single seeded constructs. At day 21, cartilage tissue was uniformly distributed throughout pellet integrated scaffolds, with minimal cell necrosis observed within the core. GAG/DNA and collagen type II mRNA expression were significantly higher (2.5-fold±0.5 and 3.1-fold±0.4 respectively) in pellet versus single cell seeded constructs. Furthermore, compared to single cell, the pellet seeded constructs contained significantly more total GAG and DNA (1.6-fold±0.1 and 3.1-fold±1.0 respectively).

We developed a novel 3D tissue assembly approach for cartilage tissue engineering which significantly improved the seeding efficiency (∼100%), as well as tissue uniformity and integrity compared to more traditional seeding approaches using single cell suspensions. Furthermore, the integration of micro-mass cell pellets into 3D plotted PEGT/PBT scaffolds significantly improved the amount and quality of tissue engineered cartilage.

Bone mineral density (BMD) and bone mineral content (BMC) have not been previously assessed in unicompartmental knee replacement (UKR). We studied the early bone changes beneath the uncemented Oxford medial UKR. Our hypothesis was that this implant should decrease the shear stresses across the bone-implant interface and result in improved BMD and BMC beneath the tibial component.

Using the Lunar iDXA and knee specific software we developed 7 regions of interest (ROI) in the proximal tibia and assessed 38 patients with an uncemented Oxford UKR at 2 years. We measured the replaced knee and contralateral unreplaced knee using the same ROI and compared the BMD and BMC. The initial precision study in 20 patients demonstrated high precision in all areas.

There were 12 males and 16 females with an average age of 65.8 years (46–84 years). ROI 1 and 2 were beneath the tibial tray and had significantly less BMC (p=0.023 and 0.001) and BMD (p=0.012 and 0.002). ROI 3 was the lateral tibial plateau and this area also had significantly less BMC (p=0.007) and BMD (p=0.0001). ROI 4 and 5 immediately below the tibial keel had no significant change. These changes were independent of gender and age.

These results were surprising in that the universal loss of BMC and BMD suggested that bone loading of the proximal tibia was not improved even after a UKR. The better BMD and BMC adjacent to the keel confirms other studies that show improved bone in-growth around keels and pegs in the uncemented tibial component. A prospective longitudinal study has been developed to compare BMD and BMC changes over time to see whether these changes are dynamic.

C-type natriuretic peptide is the most abundant natriuretic peptide in the central nervous system. It has been implicated in neurogenesis and may have a significant role in spinal regeneration. We postulated that the spinal concentration of CNP would be reflected in the plasma concentrations of both CNP and the pro-hormone (NTproCNP) and this may be an indicator of repair potential in spinal injuries.

Concurrent plasma and CSF concentrations of CNP forms were measured in 51 subjects undergoing spinal anaesthesia for elective total hip and knee replacement. Associations with CNP activity and metabolism in CSF were sought by measuring CSF levels of cGMP and neprilysin respectively.

Elevated concentrations of NTproCNP (1045±359 pmol/L) were found in CSF and greatly exceeded those of CNP (7.9±3.2 pmol/L). The ratio of NTproCNP to CNP in CSF (145±55) was much higher than in plasma (31±27). A significant inverse relation was found between plasma and CSF CNP concentrations (r=−0.29, p<0.05). cGMP and neprilysin were unrelated to CNP levels in CSF

Despite markedly elevated levels of NTproCNP in CSF, it is unlikely that these contribute to systemic levels in healthy adults. Identifying NTproCNP as the dominant CNP form in CSF opens up the possibility of its use in future studies exploring CNP regulation within the CNS and possible applications in diagnosis and monitoring of healing in patients with spinal cord injury.

Determine if debridement, rather than staged revision is a more effective strategy in some patient subgroups with infected arthroplasty

We compiled a database comprising 154 proven infected knee replacements and 144 infected hip replacements in Christchurch over the last 10 years. This has given us the largest series in the literature. Cross referencing this database with the joint registry enabled us to compare the treatment of both acute and chronic infection in hip and knee arthroplasty with regard to both functional outcome and re-revision rate.

Patients treated with debridement had no statistically significant difference in re-revision rate or functional score when compared with patients undergoing staged revision.

Orthopaedic surgeons justifiably aim to eradicate infection in arthroplasty patients. A prosthesis retaining management strategy may be justifiable, especially in certain patient groups in whom multiple operations are best avoided.

Assessing the efficacy of cervical orthoses in restricting spinal motion has historically proved challenging due to a poor understanding of spinal kinematics and the difficulty in accurately measuring spinal motion. This study is the first to use an 8 camera optoelectronic, passive marker, motion analysis system with a novel marker protocol to compare the effectiveness of the Aspen, Aspen Vista, Philadelphia, Miami-J and Miami-J Advanced collars. Restriction of cervical spine motion was assessed for physiological and functional range of motion (ROM).

Nineteen healthy volunteers (12 female, 7 male) were fitted with collars by an approved physiotherapist. ProReflex (Qualisys, Sweden) infra-red cameras were used to track the movement of retro-reflective marker clusters attached to the head and trunk. 3-D kinematic data was collected from uncollared and collared subjects during forward flexion, extension, lateral bending and axial rotation for physiological ROM and during five activities of daily living (ADLs). ROM in the three clinical planes was analysed using the Qualisys Track Manager (Qualisys, Sweden) 6 Degree of Freedom calculation to determine head orientation relative to the trunk.

For physiological ROM, the Aspen and Philadelphia were more effective at restricting flexion/extension than the Vista (p<0.001), Miami-J (p<0.001 and p<0.01) and Miami-J Advanced (p<0.01 and p<0.05). The Aspen was more effective at restricting rotation compared to the Vista (p<0.001) and Miami-J (p<0.05). The Vista was least effective at restricting lateral bending (p<0.001). Through functional ROM, the Vista was less effective than the Aspen (p<0.001) and other collars (p<0.01) at restricting flexion/extension. The Aspen and Miami-J Advanced were more effective at restricting rotation than the Vista (p<0.01 and p<0.05) and Miami-J (p<0.05). All the collars were comparable when restricting lateral bending.

The Aspen is superior to, and the Aspen Vista inferior to, the other collars at restricting cervical spine motion through physiological ROM. Functional ROM observed during ADLs are less than those observed through physiological ROM. The Aspen Vista is inferior to the other collars at restricting motion through functional ROM. The Aspen collar again performs well, particularly at restricting rotation, but is otherwise comparable to the other collars at restricting motion through functional ranges.

Objective

To compare the effectiveness of the Aspen, Aspen Vista, Philadelphia, Miami-J and Miami-J Advanced collars at restricting cervical spine movement in the sagittal, coronal and axial planes.

We prospectively reviewed patients who had undergone a Revision Total Knee Replacement (TKR) to a mobile-bearing arthroplasty. We wanted to assess functional outcome and survival, and to determine whether the perceived advantages of a mobile-bearing arthroplasty could be expanded to the revision situation.

We divided the patients into two groups. Group 1 consisted of 40 patients who were revised to a rotating platform, with or without stems and augments, and group 2 consisted of 41 patients revised to a varus-valgus constrained mobile-bearing device that still allowed rotation of the bearing. All were assessed with Knee Society Knee Scores, WOMAC, and New Jersey Knee Scores and standard radiographs by an independent examiner.

Group 1 had an average age of 71 years at revision and a follow-up of 5–9 years. Seventy-six percent had excellent or good results with 89% survival at 9 years. Group 2 had an average age of 71 years at revision and a follow-up of 2–5 years. The patient satisfaction score was 8/10 and the normality score was 6.8/10. There was only one case of instability in both groups in a patient with a patellar fracture.

A mobile-bearing TKR can be used in the revision situation with acceptable clinical results and patient outcome without compromising the stability or survivorship in the short-term. It has proved to be a “patellar-friendly” procedure with reduced re-operation for patellar complications; however longer-term studies are required to determine whether the rates of polyethylene wear are reduced by the use of a more congruent articulation.

The purpose of this study was to investigate the surgical options for unicompartmental osteoarthritis (OA) in younger patients by comparing the survivorship and functional results of Total Knee Replacement (TKR) following osteotomy with the results for both primary TKR and revision of Unicompartmental Knee Replacement (UKR) to a TKR, and thereby recommend the most appropriate index procedure for this group of patients.

We reviewed the revision rate and functional outcome of all patients who had a total knee replacement (TKR) following an osteotomy or Unicompartmental Knee Replacement (UKR) on the New Zealand Joint Registry. We used this data to compare the results to primary TKR scores, including comparison of age-matched subgroups.

There were 711 patients who had undergone TKR as salvage for a failed osteotomy with a revision rate of 1.33 revisions per 100 component years and a mean Oxford knee score (OKS) of 36.9. 205 patients had failed UKR converted to TKR with a revision rate of 1.97 revisions per 100 component years and a mean OKS of 29.1. The revision scores of TKR for both failed osteotomy and failed UKR were significantly poorer than following primary TKR (p← 0.05). The mean OKS following revision of a UKR was significantly poorer than both primary TKR (p←0.001) and TKR for a failed osteotomy (p←0.001). There was no significant difference in mean OKS between primary TKR and TKR for a failed osteotomy, even amongst patients younger than 65 years (p=0.8).

This study has shown that if a surgeon is choosing between an osteotomy and a UKR in the younger patient than the better for any subsequent revision procedure will be achieved with an osteotomy. Revision of a failed osteotomy to a TKR has improved functional results compared to revision of a failed UKR. However, both yield poor survivorship rate compared to primary TKR.

The aim was to assess the wear rate of highly Cross Linked (X3) polyethylene with the use of 36mm femoral heads in total hip arthroplasty (THA). We have previously reported our early results and raised some concern regarding the potential excessive femoral head penetration rates. These results give the 2 year wear rates following this initial bedding-in phase.

There were 100 consecutive patients who had a THA with the same femoral and acetabular components using a 36mm femoral head and X3 polyethylene that were assessed prospectively. Validated computer software (Polyware) was used to assess linear and 3 dimensional wear using standardised x-rays. Examinations were performed at 2,12,18 and 24 months.

There were 40 hips that had completed the 2 year x-ray examination (average 2.4 years). The mean 2-dimensional linear wear rate was 0.17 mm/yr and the mean volumetric wear rate was 113.73 mm3/yr. Steady state wear was achieved after the 2 month and before the 1 year examination. The steady state wear rate was 0.001mm/yr. There was no difference in wear rate with the different sized cups used and wear rate was independent of liner thickness.

The early high wear rates reported have now settled into a more expected pattern of steady state wear similar to other results presented in literature with the use of smaller femoral heads. Using a 36 mm femoral head has not adversely increased the wear rates compared to smaller head sizes when used in conjunction with X3 polyethylene in the short term for THA. These results suggest that the wear rate of X3 is not compromised even with thinner liners and raise the possibility of safely using even larger head sizes with this polyethylene.

Replacement of damaged or diseased tissues with permanent metal implants based on stainless steel, cobalt chrome and titanium alloys has been at the forefront of classical biomaterials research and the orthopaedic medical device industry for decades. Biodegradable polymers have also reached the market but often have limited capacity in load bearing orthopaedic applications due to their low stiffness and poor mechanical properties. The development of biodegradable metals based on magnesium (Mg) could be heralded as a major breakthrough in the field of orthopaedic surgery. Degradable implants eliminate the time and cost associated with a secondary surgery to remove hardware, and reduces the period the implant is exposed to instability, fibrous encapsulation, stress shielding and inflammation. The metabolism of Mg and its excretion via the kidneys is a natural physiological process that is well understood, however, controlling the rapid degradation of Mg biomaterials in vivo is a major challenge yet to be resolved for the safe and effective use of Mg in orthopaedic implants.

In this study, we describe a novel manufacturing method for fabricating Mg/Mg alloy implants, as well as the development of an in vitro method for screening Mg/Mg alloy degradation rate by considering both their electrochemical corrosion behaviour and biological characteristics.

A range of Mg alloys with varying amounts of calcium (0.8–28%) and zinc (3–10%) were cast and then machined into Ø4mm and 15mm discs for biocompatibility (HETCAM) and parallel in vitro testing. Alloys were placed in various simulated body fluid (SBF) solutions in vitro (7–28 days) to determine effect of alloy composition on degradation rate. These potentiostatic and potentiodynamic tests were designed to simulate, to varying degrees, the in vivo environment, with the crucial factors (e.g. temperature, pH, serum proteins, CO2 level) controlled to ensure consistency across the test methods. The mechanisms of corrosion on the Mg/Mg alloy microstructure and the effect of protein adsorption all played key roles in dictating the corrosion of alloys in vitro. Specifically the inclusion of physiological levels of serum proteins decreased the corrosion rate up to 600% over more standard SBF solutions described in literature.

This work provides an improved understanding of the effects of corrosion variables on Mg alloys, while making major steps towards deciding the most appropriate screening tests for new alloys for their use as a biomedical material prior to moving to in vivo animal studies.

The aim of this study was to examine the results of medial opening wedge high tibial osteotomies in which TRISOITE (hydroxyapatite tricalcium phosphate composite) wedges have been used as bone graft substitute and to compare the histological results with the clinical outcome.

There were 36 medial opening wedge high tibial osteotomy performed in 33 patients with a mean age of 45 years. Medial compartment osteoarthritis with varus alignment was the indication in 32 patients. All were followed to union with a minimum follow up of 6 months (average 50 months).

The surgical technique involved creating an oblique upper tibial osteotomy at an angle of 60 degrees from distal-medial to proximal lateral, passing distal to the insertion of the patellar ligament and preserving the lateral cortex. The osteotomy was opened to the desired angle of correction and preformed Triosite wedges were inserted. Stabilisation was obtained with a contoured titanium T-plate (ENZTEC). Re-operation was required for metal removal or conversion to total knee replacement in 10 cases. All of these patients had a biopsy of the osteotomy site.

The clinical notes and x-rays were retrospectively reviewed. One patient developed a superficial infection post-operatively which was successfully treated with intravenous antibiotics. Bone grafting was required to achieve union in 1 case (2.8%). There were no cases of varus deformity recurrence as a result of graft collapse. Biopsies provided microscopic evidence of bony incorporation around the tricalcium phosphate with bone healing. Three patients were converted to total knee replacement with no problems at the osteotomy site.

Triosite wedges appear to be a reliable synthetic bone graft substitute to act as a scaffold for bone healing in opening wedge osteotomies. They reduce the morbidity associated with iliac crest bone graft.

This study reviewed the revision rate of fully cemented, hybrid and cementless primary total knee replacements (TKR) registered in the New Zealand Joint Registry from 1999 to May 2008 to determine whether there was any significant difference in the survival and reason for revision with these different types of fixation.

The percentage rate of revision was calculated per 100 person years (HPY) and compared to the reason for revision, type of fixation and the patient’s age.

Of the 28707 primary TKR registered, 522 underwent revision procedures requiring change of at least one component with a survival rate of 0.44 HPY (1.8%). The majority of revisions were for pain (153) followed by deep infection (133) followed by loosening of the tibial component (98). Overall the rate of tibial loosening was 0.07 HPY (0.3 %) in the cemented group vs 0.25 HPY (1%) in the cementless group (p < 0.001). There was no significant difference in the type of fixation used for the femoral component, but there was a significant difference in the different types of fixation when revised for pain, with the uncemented tibia performing the poorest. There was no significantly difference in the younger patient (< 55 years) with respect to tibial loosening (p=0.92).

Failure of the uncemented total knee replacement was due to pain and tibial loosening although the results in patients under 55 years were similar in all fixation groups. There was no difference in the fixation method of the femoral component.

To ascertain whether there is any relationship between the Oxford 12 scores gained six months post surgery and early revision for primary hip and knee arthroplasty.

The six month post surgery Oxford 12 scores were retrieved from the National Joint Registry (NJR) for the seven year period ending 31^st December 2006. These were analysed in relation to revision of primary hip and knee procedures using three methods of statistical analysis; logistic regression, receiver operating characteristic (ROC) curve and direct plotting of groups of scores against the proportion of hips revised for that same group.

Logistic regression: For every one unit increase in the Oxford score there was an 11% increased risk of revision (hips) and 12% (knees) within the first two years of surgery, 5 and 6% respectively between two and four years and 3 and 4% risk respectively between four and six years (p> 0.001).

The ROC Curve Analysis: demonstrated that a patient with a score greater than 20 (hips) or 28.5 (knees) or 24 (uni knees) has eight times the risk of needing a revision within two years compared to a person with a score equal or less than the above numbers. Alternatively the ROC analysis predicted 73% of the revisions within three years for all three arthroplasty groups.

Plotting Scores Against Revisions: Plotting scores in groups of five demonstrated an incremental increase in the risk during the first two years. A person with a score greater than 40 has; for hips 24 times, knees 27 times and uni knees 69 times the risk of a revision within two years compared to a person with a score between 16 and 20.

Monitoring of the six month post surgical Oxford 12 score is another tool in the surgeon’s armamentarium for deciding which patients need closer monitoring following arthroplasty surgery.

The early results with highly cross-linked polyethylene have been encouraging and have increased the ability to use larger head diameters to improve the range of motion and decrease the dislocation rate, the commonest cause of early complications following total hip arthroplasty (THA). Wear rates with 32 mls heads have been satisfactory however there have been very few independent studies looking at early polyethylene wear in 36 mm heads. This study assessed the rate of polyethylene wear of a 36mm ceramic femoral head and a highly cross-linked polyethylene (X3 Stryker) liner in THA.

This prospective study reviewed 100 consecutive THAs in young patients (mean age 58 years) who had undergone THA with the same 36mm ceramic femoral head and highly cross linked polyethylene liner. All patients received the same femoral stem (ABG, Stryker) and acetabular cup (Trident, Stryker). Two surgeons performed all procedures. Patients were assessed radiologically immediately postoperatively, at 10 weeks and at one year. Validated computer software (Polyware) was used to assess both volumetric and linear wear.

At one year the mean two-dimensional linear wear rate was 0.51 mm/yr. Mean three-dimensional linear vector wear rate was 0.59 mls per year with a mean volumetric wear rate of 322.6 mms per three years. Cup size ranged from 52–62 mms and the correlation coefficient between cup size and three-dimensional linear wear rate was −0.100. The correlation coefficient between cup size and volumetric wear rate was −0.009 confirming no significant correlation between cup size and wear.

Larger size femoral heads are associated with a higher volumetric wear compared to linear wear rate when using conventional polyethylene. This study demonstrated much higher early linear wear rates compared to other studies using 28 and 32 mms heads. This higher rate may be associated with the creep phenomenon and early bedding-in in the early stages after a THA and although this is of concern these results should be interpreted with caution.

Deterioration in knee joint proprioception has been postulated to occur following injury, resulting in further instability due to disruption of receptors and feedback mechanisms. Surgical reconstruction techniques may also influence post-operative proprioceptive ability (PA). We hypothesised that anterior cruciate ligament (ACL) reconstruction techniques which disrupt the knee capsule would result in a decrease in PA.

Following ethical approval, a total of 48 subjects (mean age: 28.1 ± 10.5, 34 male, 14 female) undergoing ACL reconstruction surgery were included in the study. Fifteen subjects underwent “open” capsule ACL surgery and patellar tendon graft, whereas 33 subjects had “closed” capsule surgery with a hamstring tendon graft. Knee proprioception was measured on a custom-designed test apparatus incorporating electromagnetic position sensors (Polhemus Fastrack) located on femoral and tibial landmarks to accurately track knee angle during flexion-extension (no load). Leg flexion-extension under partial weight-bearing (5kg) was also evaluated. Pre-operative PA was assessed bilaterally, and then again on operated joints at three, six and twelve months post-op. Proprioceptive ability was measured as the cumulative absolute error in knee angle (°) between five repeat measurements and a target angle.

We observed no significant difference in PA between injured and contralateral knees prior to ACL reconstruction. Post-operatively, no significant difference in PA was observed between “open” versus “closed” ACL techniques, irrespective of loading conditions. While trends indicated that PA during knee extension (no load) and leg flexion (partial weight-bearing) improved over the 12 months compared to pre-operative values in closed ACL surgery, these were not significantly different to open ACL results.

The proportion of subjects whose PA improved in at least two out of the three post-op evaluations was also similar (approx 50%) across all groups, irrespective of joint loading. The only difference was PA during leg flexion under partial weight bearing, where 27% of open ACL surgery patients showed improvement in two or more follow-up tests, as opposed to 58% of closed ACL surgery patients.

We present a method to determine pre- and postoperative PA during knee flexion/extension under no load as well as under partial weight-bearing. We saw no significant difference in PA of the knee under no-load versus load. We also saw no significant difference in postoperative PA following open capsule, patellar tendon graft versus closed capsule, hamstring tendon graft ACL reconstruction technique after 1 year follow-up.

There remains controversy as to whether computer-navigated TKA improves the overall alignment of the knee prosthesis. The aim of this study was to determine whether computer-assisted total knee arthroplasty provides superior prosthesis positioning when compared to a conventional jig-assisted total knee replacement.

A prospective controlled study comparing computer navigated and conventional jig-assisted total knee replacement in 23 patients who underwent bilateral TKA was undertaken to determine if there was any significant difference in component position. The 23 patients (46 knees) were randomised to receive one conventional jig-assisted total knee replacement, and a contra lateral computer-assisted total knee replacement. A single experienced knee surgeon performed all procedures.

A quantitative assessment of the spatial positioning of the implant in the 46 total knee replacements was determined using a low-dose dual-beam CT scanning technique. This resulted in six parameters of alignment that were compared. A blinded, independent observer recorded all radiological measurements.

Median external rotation of the femoral component relative to the trans-epicondylar axis was −2 degrees in the computer-assisted group and −3 degrees in the jig-assisted group. Median femoral component flexion was identical in both groups at 0 degrees. Median valgus angulation of the femoral and tibial components was +1 degree and 0 degree respectively for the computer-assisted group and 0 degree and −1 degree for the jig-assisted group. Median posterior tibial prosthesis slope was +5 degree in both the computer-assisted group and the jig-assisted group.

Computer-assisted implantation of total knee replacements does not offer a significant advantage in prosthesis alignment. Low dose dual-beam CT scanning provides a three dimensional model of the lower limb, allowing accurate measurement of prosthesis alignment.

Recent analysis of the Australian Joint Replacement Registry revealed the rate of revision of primary total hip arthroplasty was greater with cement-less fixation than with cemented fixation. The seven-year results of the New Zealand Joint Registry have also shown an increased revision rate with cement-less hip arthroplasty. The purpose of this study was to review the revision rate of cemented and cement-less total hip arthroplasty from those joint replacements registered with the New Zealand Joint Registry and to determine the cause for revision.

All 42 1000 primary total hip arthroplasties recorded in the New Zealand National Joint Registry since its establishment in 1999, until December 2006, were included in the study. The rate of revision of cemented and cement-less femoral and acetabular components was calculated for the study period, and for the first 90 days after the operation. The reasons for revision were evaluated and compared for different methods of fixation. Survival curves were constructed for each combination of femoral and acetabular component fixation.

Two hundred and eighty three cement-less (2.46%), 294 cemented (1.91%), and 321 cemented femoral with cement-less acetabular fixation (2.19%) primary total hip arthroplasties have been revised. The difference in revision rate between each group was statistically significant. There were only 573 primary total hip arthroplasties performed with cement-less femoral and cemented acetabular component, with 11 revised. The rate of revision was highest in the cement-less group (0.74% revised per year), and lowest in the cemented group (0.47%).

The predominant reason for revision in all three major groups was dislocation. Revision for loosening of the acetabulum was more common with cemented fixation. Revision for fractured femur was more common with cement-less fixation, and revision for deep infection was most common in the cemented group. These differences were all shown to be statistically significant. Revision for loosening of the femoral component and pain was more common in the cement-less group, but was not shown to be statistically significant.

In the first 90 days, there were a large number of revisions in the cement-less group (0.77%), compared to the cemented group (0.32%), and cemented femur with cement-less acetabulum group (0.57%). Dislocation was again the most common reason for revision. Revision for fractured femur was high in the cement-less group (0.19%) in the first 90 days. Excluding these early revisions, the number of revisions in the cemented and cement-less groups maintained a similar rate for the remainder of the study period.

This study confirmed that the revision rate for uncemented THA was higher than for cemented THA. The major difference was the early revision rate within 90 days. Addressing these problems would improve the overall early outcome.

Articular cartilage has a limited regenerative capacity. Tissue engineering strategies adopting seeding and differentiation of individual chondrocytes on porous 3D scaffolds of clinically relevant size remains a considerable challenge. A well documented method to produce small samples of differentiated cartilage tissue in vitro is via micro-mass (pellet) culture, whereby, high concentrations of chondrocytes coalesce to form. a spherical tissue pellet. However, pellet culture techniques are not applied clinically as it is only possible to produce small amounts of tissue (1–2mm). The aims of this study were to develop a method for mass-production of pellets, and investigate whether an alternative “pellet seeding” approach using smart 3D scaffold design would allow large numbers of spherical pellets to be fixed in place.

Chondrocytes were isolated from bovine articular cartilage via enzymatic digestion. Freshly isolated and expanded (passage 2) chondrocytes were placed in 96-well plates with round- or v-shaped wells at a range of densities from 0.1, 0.25 and 0.5 million cells per pellet, and centrifuged at 500g for 2 min. In order to assess pellet forming conditions, cells were treated with or without 300 mg/mL fibronectin (FN, Sigma) to improve cell-cell adhesion. Wells were also coated with or without silicone (Sigmacote) to prevent cell adhesion to wells. Pellets were cultured in vitro for up to 14 days and were assessed at various timepoints for size, shape, cell number (DNA assay) and cell differentiation capacity (histology). A robotic Bioplotter device was used to produce porous, biodegradable scaffolds by plotting −250μm polymer (PEGT/PBT) fibres in a layer-by-layer process. Scaffolds with specific 3D pore architecture were produced to allow spherical pellets to be press-fit in each pore thereby fixing them in place throughout the scaffold.

Primary and expanded chondrocytes plated at a density of 0.25 million cell/pellet in v-shaped 96-well plates without both FN and silicone treatment produced pellets with consistently better spherical shape and total cell number (as determined via DNA). Under these conditions, cell (re)differentiation and cartilage extracellular matrix formation was observed via positive staining for safranin-O. Mass production of pellets was achieved by culturing multiple 96-well plates in parallel. FN treatment promoted cell-cell adhesion, but also cell adhesion to well plates, irrespective of silicone treatment, resulting in irregular shaped pellets, as did the use of round-bottom shaped wells.

Smart scaffold design and layer-by-layer fabrication process allowed direct control over the fibre spacing and pore size (1.0–1.25mm). Multiple layers of spherical pellets (1.25–1.5mm) were press-fit in place, thereby limiting the need for direct cell adhesion to the scaffold. Continued culture of constructs containing pellets resulted in consistent tissue formation throughout the scaffold.

In this study, we describe an alternative approach to the design and seeding of scaffolds for cartilage tissue engineering. Current limitations involved with adherence and de-differentiation of single cell populations were avoided by taking advantage of smart 3D scaffold design and pellet-seeding and culture techniques. Further optimisation and automation of the process is necessary, however, such strategies could be beneficial for future scaffold-based cell therapies for repairing articular cartilage defects.

Squeaking is a rare complication of hard-on-hard hip bearings. Occasionally the noise is troublesome enough to warrant revision surgery. The purpose of this study is to contribute to the understanding of the mechanism(s) underlying squeaking.

We analyzed 10 alumina ceramic-on-ceramic bearings from squeaking hips collected at revision surgery. The reason for revision was given as squeaking (6 cases) or squeaking and pain (4 cases). Six of the 10 patients were male, average patient age was 48. Bearings were retrieved after an average of 23 months in service (11 to 61 months). There were 4 different designs of acetabular component from 2 different manufacturers. Nine have an elevated metal rim which is proud of the ceramic and one does not. Two bearings were 36mm in diameter, 6 were 32mm and 2 were 28mm.

All 10 bearings showed evidence of edge loading wear. Mean dimensions of the wear patch were 37mm by 12mm on the acetabular component and 32mm by 13mm on the femoral heads. Wear dimension was not related to bearing diameter. Seven of the 10 implants also had evidence of impingement of the femoral neck against the elevated metallic rim or the ceramic insert or both. There was no chipping or fracture of any of the ceramic components.

Squeaking is a recently recognized complication of hard on hard bearing surface. This retrieval study is the first of its kind, to our knowledge attempting to unravel the mechanism of this undesirable complication. Although impingement seems to be present in majority of cases, the latter does not seem to be necessary. Edge loading wear was the common factor in all cases and this may prove to be a critical mechanism.

We have examined the outcome of 400 consecutive patients who underwent total knee replacement with the Low Contact Stress mobile-bearing system between 1993 and 1994 and were followed up for a minimum of ten years. All operations were performed by surgeons in Christchurch, New Zealand, who used no other knee prosthesis during the study time.

At ten years after operation 238 patients (244 knees) remained for independent clinical and radiological assessment. There was a significant improvement (p < 0.001) in the postoperative knee scores at one, three, seven and ten years, although a slight deterioration in the score occurred between seven and ten years which did not reach statistical significance. The survival for polyethylene wear or loosening was 97% (95% CI 96 to 98) and survival using reoperation for any cause was 92% (95% CI 90 to 94) at 12 years. Polyethylene wear was more common in the meniscal-bearing component, with five knees requiring revision and a further eight demonstrating early wear. Osteolysis was not seen in the rotating platform component, but was present in three of the meniscal-bearing knees.

There was no association between the radiological alignment at one year and those knees that subsequently required revision. However, there was an association between the overall limb alignment and the Western Ontario McMasters University score (p < 0.001).

The Low Contact Stress mobile-bearing total knee replacement has proved to be a reliable implant at ten years when used in primary knee replacement irrespective of the deformity and diagnosis.

Recent studies have assessed operative skill in surgical trainees “objectively” based on patient outcomes by attempting to statistically separate many contributory variables. Compression hip screw fixation (CHS) for neck of femur fracture (#NOF) is a standard operation commonly performed by orthopaedic trainees of varying experience. Our aim was to determine if trainees could be assessed objectively on their efficiency and aptitude in performance of this operation. A secondary aim was to evaluate the predictors of fixation failure for CHS described in the literature.

Records and radiographs for all CHS performed by trainees of all levels for acute adult #NOF were examined retrospectively for 2 calendar years. Preoperative patient and fracture variables were scored. Outcome measures included operative time, scores of accuracy of fracture reduction and fixation, blood loss and complications. Failure of fixation was compared to the scores given to radiographs. Multivariate analysis was used to apportion variance between multiple contributing factors.

Three hundred and eight two eligible operations were performed by 26 trainees. Operative time was effected by fracture complexity, trainee level and trainee operator (all p< 0.05). “Tip apex distance”, a measure of depth and centrality of screw placement in the femoral head, known to predict screw cut out was associated with trainee operator. Other outcome scores of fixation on radiographs were not correlated with fracture, patient or operator variables. Blood loss and complications were not associated with operator. The rate of failure of fixation was low and associated with scores of reduction quality only (p< 0.05).

Trainees of variable experience perform CHS with a low overall complication rate and the most noticeable performance difference seems to be in speed of surgery.

The purpose of this study was to evaluate the results of simultaneous bilateral total hip and total knee arthroplasty performed in New Zealand during the first five years of the New Zealand National Joint Register and to determine whether this was an acceptable practice.

All total knee and total hip arthroplasties collected on the National Joint Register between 1999 and 2003 were divided into three groups – unilateral joint arthroplasty, staged bilateral joint arthroplasty and simultaneous joint arthroplasty. The Oxford 12 questionnaire results at six months were assessed as well as the patients self reported complications. All deaths that occurred within 6 months of the surgery were also recorded.

Analysis between the three groups was then performed using ANOVA tables comparing age, the Oxford scores and complications.

There was generally a significant difference (p< .001) in age between unilateral hip and knee replacement and staged or simultaneous bilateral replacement, with patients undergoing bilateral simultaneous replacement being younger.

There was a significant difference (p< .001) in the Oxford 12 scores between unilateral hip and knee replacement and both staged and simultaneous bilateral hip and knee replacement, with the bilateral simultaneous replacements scoring the best.

The death rate within the first 6 months was low in all groups with only 1 patient dying within 3 months of the surgery from an unrelated cause. The complication rate was low in all groups, in particular the DVT and pulmonary embolus rate, as reported by the patients, was not increased in either the sequential staged group or the simultaneous bilateral group.

The New Zealand National Joint Register has proven to be a valuable tool in gaining early information regarding the outcome following bilateral and staged lower limb total joint arthroplasty. The results clearly show that in the appropriate clinical situation performing simultaneous bilateral total knee or total hip arthroplasty is a safe and effective procedure.

The purpose of this paper is to review the first six months experience of using the ‘Time Out’ procedure to avoid wrong site/side surgery and to evaluate the usefulness of this procedure in the routine preoperative check.

Over a period of 18 months all elective surgical hospitals in Christchurch (both private and public) have coordinated to develop a pre-operative ‘Time Out’ check list to ensure that the correct surgical procedure is performed on the correct site. This procedure involves a final check of patient details, including surgical procedure and site, immediately prior to surgical preparation of the operative site.

All forms during this six month period were prospectively collected and evaluated, specifically looking for system errors, which could proceed to wrong site surgery.

There were a total of 10,330 procedures performed during this period within the three hospitals of which 9,098 (87.2%) completed time out forms were returned.

There were no wrong side or wrong site surgeries performed during this six month period. However, there were three ‘near miss’ situations which were captured by the time out procedure.

Analysis of the time out forms also revealed numerous consent issues, incorrect documentation and systems errors which could potentially have lead to serious errors in management and which will be discussed in detail.

During this period there were 109 objections (1.2%) to the time out procedure.

The time out procedure has been shown to be a useful tool for avoiding wrong site/side surgery and has gained acceptance amongst both medical and nursing staff as being a valuable check prior to surgery. It has accentuated the collective team responsibility for determining the correct site and side of surgery and as such is recommended for use in all centres to eliminate system errors resulting in incorrect site/side surgery.

We have assessed the comparative function of young patients with hip or knee replacement using a high level function score.

A high level function score was developed for assessing running, walking, stair climbing and recreational activity. This was used on a series of patients after a total of 153 joint replacements including 99 THR and 54 TKR.

The groups were comparable with respect to age (average 57 years), gender and follow-up. Comparison between the groups showed that there was no significant difference in walking, stair-climbing and recreational activity. Patients with THR scored better on running ability and overall total score. Other differences noted included lower scores in bilateral joint replaced patients and posterior cruciate sacrificed knees.

Young patients undergoing hip or knee replacement have similar functional outcomes using a high activity function score. There were trends towards superior running ability and overall scores in the THR group.

Our aim was to assess the clinical and radiological medium-term outcome of a series of 153 consecutive total hip arthroplasties performed by two surgeons in Christchurch using the ABG hydroxyapatite-coated femoral stem and Duraloc 100-series uncemented acetabulum.

An independent clinical review using interviews and patient notes and radiological review of immediate postoperative and most recent x-rays was carried out.

At six to eleven years with approximately 95% follow-up, there were no stem failures, but two revisions following a fracture from significant trauma. Two cups were revised for loosening and one cup bone grafted for osteolysis. A dislocation occurred in 4.7% of cases requiring two liner exchanges and one cup revision. A low incidence of thigh pain and excellent radiographic results of the stem with high rates of bony ingrowth and no incidence of significant loosening was a feature of this series.

We report excellent results at medium-term follow up for an unceme4nted HA- coated femoral stem.

The purpose of the study was to assess the use of the Internet for medical information, both in the Orthopaedic Outpatient population, and in practicing Orthopaedic Surgeons in New Zealand.

To identify any potential sites that may be of use to the patient in gaining reliable information on their orthopaedic problem. 300 questionnaires were distributed to Orthopaedic Outpatient Clinics (Public Trauma, Public Elective, and Private) in Christchurch. Each clinic had 100 questionnaires. A second questionnaire was sent out to all Orthopaedic Surgeons currently practising in New Zealand. A literature search was also performed.

Overall 18% of patients use the Internet to look up medical problems. Internet use was highest amongst the younger population. 68% of patients had a computer at home. 52% of patients thought recommended Internet sites would be useful. 91 % of patients stated they used their Doctor as their most common source of healthcare information, with only 5% stating the Internet. 76% of Orthopaedic Surgeons used the Internet for work purposes. 54% thought that the Internet misinformed patients. Only 50% of surgeons had accessed the NZOA web site.

The Internet is becoming an increasingly common source of healthcare information for patients and doctors. The NZOA site has huge potential for both surgeons and the public with regard to useful links. At present this site is largely under-utilised.

The purpose of this study was to establish whether retransfusion of blood collected in drains following total joint replacement was a safe and effective procedure. All patients undergoing a total joint arthroplasty, with no history of infection, between March and October 2001, were entered into the study. A single surgeon operated on all patients and no patient was excluded from the study. Informed consent was obtained and all blood drained into a recollection system within 6 hours of surgery was retransfused .A prospective protocol was filled out in all cases documenting the pre and postoperative haemoglobin, amount transfused and any extra transfusion requirements. A special note was made of any complications encountered during retransfusion. The results were then compared to previously known transfusion rates within the same hospitals.

There were 141 Total Joint Arthroplasties performed within the study period -12 were bilateral and 12 were revisions procedures. The average drainage was 655ml (60–3280ml) and the average amount of retransfused blood from the drains was 225ml (100–1822ml). There were a total of 9 (6.3%) subsequent blood transfusions. Four (3.8%) in primary and 5 (20.8%) in bilateral or revision procedures.

Transfusing patients with salvaged blood from the drains in total joint arthroplasty is a safe, reliable and cost effective practice, which significantly reduces the requirement for a subsequent blood transfusion. As a result of this study the Christchurch Orthopaedic Group has adopted a routine practise of retransfusing drained blood in all total joint arthroplasties.

Despite a variety of reports to the contrary it was felt by the Christchurch Orthopaedic group that the “wait” on the orthopaedic waiting list has been escalating rapidly to the point that a routine operation is now in the order of approximately 3 years from the time of GP referral.

A review of the time taken for GP referrals to be assessed by an Orthopaedic Surgeon was undertaken. The waiting lists from October 98 to May 02 were analysed, in addition to the operation outputs from the Burwood Hospital elective theatre records over the same period. Time taken from referral to be seen, time taken from been placed on the waiting list to receive an operation and volume of elective procedures were evaluated. A breakdown was made of those removed from the list vs those operated on. A major reduction in the waiting list over the last three years was secondary to 1/3 of the people on the list (1177) been “culled”. This was initiated in January 1999 and completed by January 2001. Since January 1999, 2538 patients had received their operations. The waiting list had dropped from 3303 to a low of 1164. It has since climbed to 2036. That waiting longer than 12 months for surgery, initially 64%, had dropped to 29% and has climbed back up to 40%. The figures have climbed dramatically since the waiting list initiative for arthroplasty was discontinued. The culling of the list has been responsible for removal of 1/3 of people off the original list without having an operation and has given a false sense of success in reducing the waiting list to various political interests. The criteria set for culling people assessed as requiring an operation has been set arbitrarily There is twice the number of patients waiting to see an orthopaedic surgeon than 2 years ago of which a proportion are requiring reassessment to be deemed eligible for an operation that they have already been assessed as requiring.

The waiting list initiative was effective as an addition to the regular DHB lists in maintaining the lists at a manageable level. Even if all those culled represented a group that no longer required their operation the current list cannot be considered to have such a group as they have all been recently reviewed and are in genuine need. There is an apparent lack of concern and denial over the current escalation in the numbers on the waiting list, and no plan instituted to address it.

Hypotheses:

A subject’s response to commonly used knee assessment scores is variable, even in the presence of a normal knee.

Methods: A group of 150 New Zealand subjects with normal knees were given three commonly used knee assessment questionnaires. There were three age groups with 50 subjects in each group: 20 to 40, 40 to 60 and above 60 years of age. All were examined to determine that each knee was objectively normal. This group was then compared with a similar group of Canadian subjects and the results were analysed.

Results: The results showed significant differences in expectation between the age groups, with the older age group less happy to score maximum points for their ‘normal’ knee. The Hospital for Special Surgery Knee Score scored the lowest followed by the Knee Society Knee Score. In the over 60 years group there was a significant difference between the New Zealand and Canadian subjects with the Canadians tending to score higher in all scores.

Conclusions: These results have implications when trying to compare results of total knee arthroplasty between different countries and age groups. This study has been expanded to include other countries in an attempt to find a mathematical formula to make future comparisons more relevant.

Aim: In 1990 the Christchurch Hospital Sarcoma Clinic established management guidelines for patients with suspected sarcomas, recommending referral prior to investigation, biopsy and excision. The aim of this study was to determine whether these guidelines are being followed.

Method: A review of the case notes of all sarcomas referred to the Sarcoma Clinic between 1990 and 1999 was performed.

Results: There were 53 referrals, 34 (22%) from orthopaedic surgeons, 56 (37%) from general surgeons, 16 (10%) from general practice and 47 (31%) from other specialties. Only 83 (54%) of the referrals had followed the guidelines. Twenty-five (74%) of the orthopaedic referrals, 19 (34%) of the general surgical, 10 (63%) of the general practice and 29 (62%) of the other specialties had followed the guidelines. Seventy (46%) of the referrals had failed to follow the guidelines. Thirty-four (49%) of these had undergone excision inadequate for sarcoma prior to referral, of which eight had been re-excised. Twenty-four patients had not been staged prior to excision despite having a positive fine needle aspiration (FNA) in four cases. Eighteen patients (26%) had FNA or biopsy prior to imaging or referral.

Conclusion: Forty-six percent of sarcoma patients had not been treated according to the recommended guidelines. Forty-nine percent of these had inadequate primary sarcoma excision and this may have compromised their outcome. Orthopaedic surgeons had the best record for following the guidelines at 74% of referrals but this could be further improved. Doctors and especially surgeons need to be more aware of the principle of early referral of patients with suspected sarcomas.

Aim: To compare the function in two groups of high demand patients with a total knee arthroplasty (TKA) – one group using a posterior cruciate sacrificing (PCS) prosthesis and the other a posterior cruciate retaining (PCR) prosthesis of similar design.

Method: Patients were eligible for the study if they were greater than two years from surgery, less than 65 years of age and without other co-existing morbidity to significantly decrease their physical activities. Group A underwent surgery by one surgeon who routinely retained the posterior cruciate ligament whereas Group B underwent surgery by one surgeon who routinely sacrificed the PCL. A mobile bearing TKA of similar design was used in each group. All patients were selected and assessed by an independent assessor using a questionnaire developed specifically to assess higher levels of activity not usually assessed by other knee scores.

Results: Group A (28 TKA in 20 patients) were matched with Group B (25 TKA in 19 patients) for age, length of follow-up and range of motion. The gross activity score was 3.36 in Group A compared with 3.12 in Group B. The combined walking, running and stair climbing score was significantly better in Group A (7.68 compared to 6.64 in Group B). Group B perceived their TKA was closer to a normal knee (2.00 compared to 2.32) with decreased anterior knee pain.

Conclusions: Retaining the PCL in TKA results in better function without significant complications.

A patient’s response to knee assessment questionnaires is often subjective and linked to age and cultural expectations.

In New Zealand 150 people, split into three groups of ages 20 to 40 years, 40 to 60 years and over 60 years, were given three commonly used knee assessment questionnaires. All were examined objectively to determine that their knees were normal. Scores in these groups were compared to similar groups of Canadian subjects and the results analysed.

The results show significant differences in expectations between the age groups. Older people were reluctant to score maximum points for their normal knees. The Hospital for Special Surgery’s knee score gave the lowest results, followed by the Knee Society score. In the over-60-year group there was a significant difference between scores in New Zealand and Canada, with Canadians tending to score higher in all scores.

These findings have implications when it comes to comparing results of total knee arthroplasty in different countries and age groups. This study has been expanded to include other countries in an attempt to find a mathematical formula that will make future comparisons more relevant.

Since its introduction in Christchurch in 1989, the mobile bearing LCS prosthesis has been used in over 3 500 total knee arthroplasty (TKA) procedures. The prosthesis is unique in that it has a mobile articulation not only at the tibiofemoral joint but also at the patellofemoral joint. The tibiofemoral articulation may be posterior cruciate retaining (meniscal bearings - MB) or sacrificing (rotating platform - RP).

Clinical and radiological assessment of 569 patients over three to nine years shows no significant difference between MB and RP groups with respect to Knee Society and New Jersey knees or the WOMAC functional score. In 93% of patients results were good or excellent. There were more early complications among MB patients, with five MB dislocations. However, four of these dislocations occurred in the early years this prosthesis and may reflect surgical inexperience. Clinical evidence of posterior cruciate laxity was present in 15% of the MB group, but there was no significant difference between knee scores of this group, the rest of the MB group, or the RP group.

When resurfaced patellae were compared to knees that were not resurfaced, there was no significant difference. Patellae with more than 4 mm of lateral subluxation were identified, but their knee scores were not significantly different.

The early to medium-term results of our continuing study of the LCS mobile bearing prosthesis are at least comparable to those of studies of fixed bearing prostheses. We continue to use this implant with confidence, but await long-term results.

We compared function in two groups of high demand patients who had undergone total knee arthroplasty (TKA), one group using a posterior cruciate sacrificing (PCS) prosthesis and the other a posterior cruciate retaining (PCR) prosthesis of similar design.

Patients were eligible for the study if surgery had been performed more than two years ago and they were under 65 years of age and had no coexisting morbidity that markedly decreased their physical activities. One surgeon operated on 28 patients in group A (20 TKAs), routinely retaining the posterior cruciate ligament (PCL). A second surgery operated on 19 patients in group B (25 TKAs) and routinely sacrificed the PCL. A mobile bearing prosthesis of similar design was used in each group. Patients were independently selected and assessed using a questionnaire specifically developed to assess higher levels of activity not usually assessed by other knee scores. Patients in the two groups were matched in terms of age, range of motion and follow-up

The gross activity score was 3.36 in group A and 3.12 in group B. The combined walking, running and stair-climbing score was in group A (7.68) than in group B (6.64). Patients in group B had decreased anterior knee pain and perceived their TKA closer to a normal knee (2.00 compared to 2.32).

We conclude that retaining the PCL in TKA results in better patient function without obvious complications.

We performed a prospective randomised trial on matched groups of patients with displaced tibial shaft fractures to compare conservative treatment with closed intramedullary nailing. The results showed conclusively that intramedullary nailing gave more rapid union with less malunion and shortening. Nailed patients had less time off work with a more predictable and rapid return to full function. We therefore consider that closed intramedullary nailing is the most efficient treatment for displaced fractures of the tibial shaft.

Fifty consecutive comminuted fractures of the femoral shaft were treated by closed unlocked intramedullary nailing. Twelve unstable fractures also had cast-bracing. There were no cases of infection or non-union, and satisfactory results were achieved in 38 fractures (76%). More severe comminution led to a higher incidence of unsatisfactory results, but malrotation deformity was seen more often in less comminuted fractures and appeared to be due to poor operative reduction. Shortening in severe comminution was the main complication and was not controlled by supplementary cast-bracing. Closed unlocked intramedullary nailing is effective for lesser grades of comminution, but fractures with no cortical continuity at reduction should be treated with a locking nail.

A new method of demonstrating sagittal laxity in the anterior cruciate-deficient knee is described. Seventy such knees were compared to 70 normal knees. Sagittal laxity was recorded as the average displacement of the medial and lateral femoral condyles. This displacement index was significantly different between the two groups of knees (P less than 0.0001). A range for normal and abnormal knees is discussed. Quantitative assessment of the degree of sagittal laxity by clinical evaluation is shown to be unreliable. Only the pivot-shift test demonstrated any significant correlation with the amount of sagittal displacement (P less than 0.05).

Blood flow in intact tendons in dogs was measured using 57Co-labelled microspheres and compared with the simultaneous clearance of a diffusible radionuclide, 85Sr, by the same tendons. Clearance was significantly greater than flow in all tendons, indicating that diffusion from surrounding tissues may be important in the nutrition of normal tendons.

Two cases of congenital pseudarthrosis of the ulna due to neurofibromatosis are reported. Similar radiographic changes in the ulna were found, with distortion of the capitulum and part of the trochlea and bowing of the radius. In one patient the head of the radius was dislocated and in the other it dislocated readily during pronation. A possible mechanism to explain the findings was suggested. On the basis of these and a review of the literature it is recommended that the main aim of treatment should be maintenance of the normal relative lengths of the radius and ulna by early excision of the pseudarthrosis to remove the restraining effect of the abnormal ulna. This will allow normal development of the lower end of the humerus and radius and prevent dislocation of the radial head.

The incidence of congenital dislocation of the hip in 156 children with infantile idiopathic scoliosis was 6.4 per cent, approximately 10 times its frequency in the general population. In both of these deformities there was a predominance of girls (eight girls: two boys). In unilateral dislocation of the hip the convexity of the thoracic scoliosis was on the same side as the dislocation. Eight out of the 10 children with both deformities also had plagiocephaly.