Greater trochanteric pain syndrome (GTPS) is common, yet the impact on function and quality of life has not been measured. The aim of this study was to quantify the impact on function and quality of life, comparing the results to people with severe hip osteoarthritis and an asymptomatic control group.

Forty two people with GTPS – including 11 not actively seeking treatment and 11 seeking surgical treatment, 20 with severe hip osteoarthritis (OA), and 23 age and sex matched asymptomatic participants (ASC) where recruited from public and private hospitals, and the community. Upon confirming meeting inclusion and exclusion criteria participants were interviewed. Exclusion criteria included lumbar nerve root signs; inflammatory, neoplastic and metabolic disorders. Measured used were the Harris hip score (HHS); the Oswestry disability index (ODI); the Australian quality of life instrument (AQoL); the Functional co-morbidity index (FCI); and fulltime work assessments.

No difference was found between the GTPS and the OA group on the HHS, ODI, AQoL or the FCI measures. Both symptomatic groups were significantly more disabled than the ASC group on the HHS and ODI (p<0.001). The GTPS and OA groups had lower AQoL than the ASC group (p<0.001); and higher FCI results than the ASC group (GTPS vs ASC, p=0.005; OA vs ASC, p=0.019). GTPS participants were least likely to be in full time work; full time work participation probability (95% C.I.): GTPS Prob=0.288 (0.160 to 0.463), OA Prob= 0.518 (0.273 to 0.753); ASC group of Prob=0.676 (0.439 to 0.847).

People with GTPS have similar levels of pain, disability and quality of life, but are less likely to be in full time employment than people with severe hip OA which puts them at risk of economic hardship. Research on conservative and surgical treatments should measure pain, disability and work participation.

INTRODUCTION

Studies have suggested that there is a reduction in head-neck-ratio (HNR) associated with MoMHRA. A reduction in HNR at operation would decrease range of movement and increase impingement risk. Impingement could lead to 20 edge loading, increasing wear. Serum ion levels of Chromium (Cr) and Cobalt (Co) are surrogate markers of wear. Although acetabular component orientation has been shown to contribute to wear and PT development, the role of a decrease in HNR has only been highlighted in PT development. This study aimed to measure changes in HNR that occur at resurfacing and determine any gender- and component size-specific differences. In addition it aimed to determine whether changes in HNR could be associated with increased wear.

Purpose

No knee-specific outcome measures have demonstrated reliability, validity or responsiveness in patients with multiligament knee injuries. Furthermore, the content validity of existing questionnaires has been challenged and remains unknown for patients with concomitant neurovascular injury. As a first step in developing a disease-specific outcome measure, the objective of this study was to identify items from existing knee questionnaires pertinent to patients with multiligament knee injuries using established a priori criteria.

INTRODUCTION

Although simulation studies have shown superior wear properties of metal-on-metal articulations, increased concern exists regarding the excess in-vivo wear of a small number of Metal-on-Metal-Hip-Resurfacing (MoMHRA) implants. Serum ion levels of Chromium (Cr) and Cobalt (Co) are surrogate markers of wear. Risk factors associated with increased wear include female gender, small components, dysplasia, cup orientation outside safe zone and femoral head downsize during surgery with an associated decrease in Head-Neck-Ratio (HNR). However, these factors are interlinked. This study aims to identify the factors that are most important for subsequent wear of MoMHRA, by performing a multivariate analysis.

The treatment of osteochondral lesions in the ankle joint remains a challenging problem. While debridement and drilling or microfracture of the lesion reduce symptoms initially, long-term stability of the fibrous repair tissue is questionable. Osteochondral transplantation or mosaicplasty provide hyaline cartilage and repair the bony defect at the same time. However, an open arthrotomy with medial, lateral or anterior osteotomy is necessary to repair lesions of the talus. Lesions of the distal tibia cannot be reached. Matrix Associated Chondrocyte Implantation (MACI) has been shown to produce hyaline like cartilage repair tissue, and the implantation can be performed arthroscopically. Long term follow up studies (up to 10 years) in the knee demonstrate promising results.

The purpose of this study was to assess the efficacy of arthroscopic MACI for the treatment of osteochondral lesions in the ankle joint. We reviewed all patients (n=20) who had arthroscopic MACI treatment (n=22) between February 2006 and November 2008 clinically (Foot Function Index, AAOS Foot and Ankle Questionnaire, AOFAS-Hindfoot Score) and with MRI (3 Tesla Siemens MRI).

The clinical results and MRI findings up to three years after MACI were compared to pre-operative data. Possible correlations with the individual history and the nature, size or location of the lesion will be discussed. The surgical technique will be described. The results of the procedure are promising.

The increasing rate of fragility fractures in the developed world is now well- documented and presents a significant challenge to Orthopaedics. Although guidelines exist for the management of osteoporosis, both before and after fracture events, little work has yet been done to measure the effect of interventions on reducing the rate of second fractures in the at-risk population. The longitudinal study, begun at The Canberra Hospital, aims to compare rates of second fractures in two populations of patients over 40 years who have sustained a low-impact, minor trauma fracture.

A retrospective study of medical records provides baseline information on current intervention rates for osteoporosis. Secondly, a prospective study population is recruited from patients presenting to Fracture Clinic at The Canberra Hospital.

Patients presenting to clinic will, after consent, undergo a screening process including blood test and DEXA scans, to confirm or reject a diagnosis of osteoporosis. Those diagnosed will be referred for medical management as well as non-pharmacological interventions.

Follow-up will be conducted at 12 months with repeat testing for bone density to determine whether the interventions have produced measurable improvement and patients will be followed up for five years to establish the rate of re-fracture.

A progress report will be presented to the conference advising on findings from the retrospective arm, scheduled for completion in September 2009, and results to date of the prospective arm. The study is a current work-in-progress, and will provide a basis for future research in this area.

The standard approach for kinematic analysis of knee joints has been roentgen stereophotogrammetry (RSA). This approach requires implanting tantalum beads during surgery so pre- and post-surgery comparisons have not been conducted. CT- fluoroscopy registration is a non-invasive alternative but has had accuracy and speed limitations. Our new algorithm addresses these limitations.

Our approach to the problem of registering CT data to single-plane fluoroscopy was to generate a digitally reconstructed radiograph (DRR) from the CT data and then filter this to produce an edge-enhanced image, which was then registered with an edge-enhanced version of the fluoroscopy frame. The algorithm includes a new multi-modal similarity measure and a novel technique for the calculation of the required gradients.

Three lower limb specimens were implanted with 1 mm tantalum beads to act as fiducial markers. Fluoroscopy data was captured for a knee flexion and femur and tibia CT data was registered to the fluoroscopy images.

A previous version of our algorithm (developed in 2008) showed good accuracy for in-plane translations and rotations of the knee bones. However, this algorithm did not have the ability to accurately determine out-of-plane translations. This lack of accuracy for out-of-plane translations has also been the major limitation of other single-plane 2D-3D registration algorithms. Fregly et. al. and Dennis et. al. reported standard deviations for this measurement of 5.6 and 3.03 mm respectively. The latest version of our algorithm achieves error standard deviations for out-of-plane translations of 0.65 mm. The algorithm includes a new similarity measure, which calculates the sum of the conditional variances (SCV) of the joint probability distributions of the images to be registered. This new similarity measure determines the true 3D position of the bones for a wider range of initial disparities and is also faster than the cross-cumulative residual entropy (CCRE) measure used in the 2008 version. For a set of initial 3D positions ranging from ± 5 pixels and ± 5 degrees the proposed approach successfully determined the correct 3D position for 96% of cases–whilst the approach using CCRE was successful for only 49% of cases. The algorithm also required 60% less iterations than the previous CCRE approach.

The new registration algorithm developed for the project provides a level of accuracy that is superior to other similar techniques. This new level of accuracy opens the way for a non-invasive mechanism for sophisticated kinematic analysis of knee joints. This will enable prospective, longitudinal and controlled studies of reconstruction surgery.

The quality of bone in the skeleton depends on the amount of bone, geometry, microarchitecture and material properties, and the molecular and cellular regulation of bone turnover and repair. This study aimed to identify material and structural factors that alter in fragility hip fracture patients treated with antiresorption therapies (FxAr) compared to fragility hip fracture patients not on treatment (Fx).

Bone from the intertrochanteric site, femoral head (FH: FxAr = 5, Fx = 8), compression screw cores and box chisel were obtained from patients undergoing hemi-arthroplasty surgery, FxAr (6f, 2m, mean 79 and range [64–89] years), and Fx (7f, 1m, age 85 [75–93] years). Control bone was obtained at autopsy (9f, 4m, 77 [65–88] years). Treated patients were on various bisphosphonates. Samples were resin-embedded, for quantitative backscattered electron imaging of the degree of mineralisation and assessment of bone architecture. Trabecular bone volume fraction (BV/TV) and architectural parameters were not significantly different between FxAr and Fx groups.

Both groups showed normal distributions of weight (wt) % Ca; however, the FxAr was less mineralised than the Fx and the control group (mean wt % Ca: FxAr = 24.3%, Fx = 24.8%, Control = 24.9%). When comparing the FH specimens only, we found that BV/TV in the FxAr was greater than the Fx group (18% vs 15%). All other parameters were not significantly different. In addition, the mineralisation was greater in the FxAr group compared to the Fx group (25.5 % vs 25.0%) but was not significantly different.

Collectively, these data suggest the effect on bone of antiresorptives may be different for patients on antiresorptive treatment that do not subsequently fracture. Assessment of bone material property data together with other bone quality measures may hold the key to better understanding of antiresorptive treatment efficacy.

This study aims to investigate femoral blood flow during Metal-on-Metal Hip Resurfacing (MMHR) by monitoring oxygen concentration during the operative procedure.

Patients undergoing MMHR using the posterior approach were evaluated. Following division of fascia lata, a calibrated gas-measuring electrode was inserted into the femoral neck, aiming for the supero-lateral quadrant of the head. Baseline oxygen concentration levels were detected after electrode insertion 2-3cm below the femoral head surface and all intra-operative measures were referenced against these. Oxygen levels were continuously monitored throughout the operation. Data from ten patients are presented.

Oxygen concentration dropped most noticeably during the surgical approach and was reduced by 62% (Std.dev +/-26%) following dislocation and capsulectomy. Insertion of implants resulted in a further oxygenation decrease by 18% (Std.dev +/-28%). The last obtained measure before wound closure detected 22% (Std.dev +/-31%) of initial baseline oxygen levels. Variation between subjects was observed and three patients demonstrated a limited recovery of oxygen levels during implant insertion and hip relocation.

Intra-operative measurement of oxygen concentration in blood perfusing the femoral head is feasible. Results in ten patients undergoing MMHR showed a dramatic effect on the oxygenation in the femoral head during surgical approach and implant fixation. This may increase the risk of avascular necrosis and subsequent femoral neck fracture. Future experiments will determine if less invasive procedures or specific positioning of the limb can protect the blood supply to femoral neck and head.

Introduction: Metal-on-metal-hip-resurfacing-arthroplasty (MoMHRA) has been associated with the development of inflammatory pseudotumours(IP), especially in females. IPs have been linked to wear debris, which can be related to metal-ion blood levels. Acetabular component position has been shown to influence wear. We have identified an optimum component orientation minimising IP risk around an inclination/anteversion of 40°/20°±10°. Our aim was to see if this optimal position results in lower metal ions and to identify the boundary of an optimal placement zone for low wear.

Methods: A cohort of 104 patients(60M:44F) with unilateral MoMHRA was studied. Blood tests were obtained at a mean follow up of 3.9 years and serum Co/Cr levels were measured(ICPMS). High metal ion concentrations were defined as Co> 4.1ppb and Cr> 5.2ppb. Radiographic cup inclination/anteversion were measured using EBRA. The differences in ion levels between different orientation zones were investigated. Three orientation zones were defined centered on 40°/20°: Z1-within ±5°, Z2-outside ±5°/within ±10° and Z3-within ±10°.

Results: There was a wide range of cup placements. Females had significantly (p< 0.001) smaller components(mean:51, 44–60) than males(mean: 56, 52–64). Cr levels, but not Co, were higher in females(p=0.002) and those with small femoral components(< 50mm, p =0.03). Patients with cups within Z1 (n=13) had significantly lower Co(p=0.005) and Cr(p=0.001). Males with cups within Z3(n=27) had lower ion levels in comparison to those outside, which were significantly lower for Co(p=0.049) but not Cr(p=0.084). Females had similar ion levels within and out of Z3(Cr/Co: p=0.83/0.84). Co levels were significantly lower in Z1(n=13) in comparison to Z2(n=33)(p=0.048) but Cr levels were not different (p=0.06).

Discussion: MoMHRA cups placed within ±5° of the optimum(40°/20°) had significantly lower metal ions indicating lower wear within this narrow zone. This safe zone, could extend to ±10° for males only. The narrower safe zone coupled with smaller components implanted are possible factors contributing to the increased IP incidence seen in females.

Introduction: The use of highly cross-linked polyethylene (HXLPE) is now commonplace for total hip arthroplasty, however there is no long-term data to support its use. Hip simulator studies suggest that the wear rate of some types of HXLPE is ten times less than conventional polyethylene (UHMWPE). The outcomes of hip simulator studies are not always reproduced in vivo and there is some evidence that HXLPE wear may increase between 5 and 7 years.

Method: A prospective double blind randomised control trial was conducted using Radiostereometric Analysis (RSA). Fifty-four subjects were randomised to receive hip replacements with either UHMWPE liners or HXLPE liners. All subjects received a cemented CPT stem and uncemented Trilogy acetabular component (Zimmer, Warsaw, IN, USA). The 3D penetration of the head into the socket was determined to a minimum of 7 years.

Results: The total liner penetration was significantly different at 7 years (p=0.005) with values of 0.33 mm (SE 0.05 mm) for the HXLPE group and 0.55 mm (SE 0.05 mm) for the UHMWPE group. The steady state wear rate from 1 year onwards was significantly lower for HXLPE (0.005 mm/yr, SE 0.007 mm/yr) than for UHMWPE (0.037 mm/yr, SE 0.009 mm/yr) (p=0.007). The direction of wear was supero-lateral.

Discussion: We have previously demonstrated that the penetration in the first year is creep-dominated, from one year onwards the majority of penetration is probably due to wear. This study confirms the predictions from hip simulator studies which suggest that the wear rate of this HXLPE approaches that of metal-on-metal and ceramic-on-ceramic articulations. HXLPE may have the potential to reduce the need of revision surgery, due to wear debris induced osteolysis. It may also enable surgeons to use larger couples, thus reducing the risk of impingement and dislocation.

Introduction: Metal on metal hip resurfacing arthroplasty(MoMHRA) is an alternative option to THR in the treatment of young adults with OA. A recognised MoMHRA complication is the development of an inflammatory pseudotumour(IP). Diagnosis is made with the aid of US and/or MRI. To-date, no radiographic indication of the presence of IP has been identified. Neck thinning is a recognised phenomenon in MoMHRA hips not associated with any adverse clinical events. Its pathogenesis is considered multi-factorial. Our aim was to establish whether excessive neck narrowing is associated with the presence of a pseudotumour.

Methods: Twenty-seven hips (26 patients) with IP confirmed clinically, radiologically, intra-operatively and histologically were matched for sex, age, pre-operative diagnosis, component size and follow-up with an asymptomatic MoMHRA cohort (Control n=60). For all patients, prosthesis-neck-ratio(PNR) was measured on plain AP pelvic radiographs post-operatively and at follow-up as previously described and validated.

Results: All IP patients (4M:23F) and all (12M:48F) but two controls had a posterior approach at the time of MoMHRA. Post-operatively, there was no difference in the PNR between the two groups (p=0.19). At an average follow up of 3.5 years (range:0.7–8.3), IP patients(mean 1.26, 1.10–1.79) had a significantly higher (p< 0.0001) PNR in comparison to their controls(mean 1.14, 1.03–1.35). Greater neck narrowing occurred in both genders. IP necks had narrowed by an average of 8% (range:3–23). The degree of neck narrowing was correlated with length of survival of implant (p=0.001).

Discussion: This study shows a strong association between IP and neck narrowing. Processes such as impingement and increased wear are considered to be involved in the pathogenesis of both IP and neck narrowing. Furthermore, the presence of an IP, could lead to altered vascularity via a mass effect and further contribute to neck narrowing. Neck narrowing in symptomatic MOMHRA patients should alert surgeons of the possible presence of IP.

Metal on metal hip resurfacing (MMHR) is a popular procedure for the treatment of osteoarthritis in young patients. Several centres have observed masses, arising from around these devices, we call these inflammatory pseudotumours. They are locally invasive and may cause massive soft tissue destruction. The aim of this study was to determine the incidence and risk factors for pseudotumours that are serious enough to require revision surgery.

In out unit, 1,419 MMHRs were performed between June 1999 and November 2008. All revisions were identified, including all cases revised for pseudotumour. Pseudotumour diagnosis was made by histological examination of samples from revision. A Kaplan-Meier survival analysis was performed, Cox regression analysis was used to estimate the independent effects of different factors.

The revision rate for pseudotumour increased with time and was 4% (95% CI: 2.2% to 5.8%) at eight years. Female gender was a strong risk factor: at eight years the revision rate for pseudotumours in men was 0.5% (95% CI 0% to 1.1%), in women over 40 it was 6% (95% CI 2.3% to 10.1%) and in women under 40 it was 25% (95% CI 7.3% to 42.9%) (p< 0.001). Other factors associated with an increase in revision rate were, small components (p=0.003) and dysplasia (p=0.019), whereas implant type was not (p=0.156).

We recommend that resurfacings are undertaken with caution in women, especially those younger than 40 years of age, but they remain a good option in men. Further work is required to understand the patho-aetiology of pseudotumours so that this severe complication can be avoided.

Introduction: Pseudotumours (soft-tissue masses relating to the hip joint) following metal-on-metal hip resurfacing arthroplasty (MoMHRA) have been associated with elevated serum and hip aspirate metal ion levels, suggesting that pseudotumours occur when there is increased wear. This study aimed to quantify in vivo wear of implants revised for pseudotumours and a control group of implants revised for other reasons of failure.

Methods: A total of 30 contemporary MoMHRA implants in two groups were investigated in this Institutional Review Board approved study:

8 MoMHRA implants revised due to pseudotumour;

The linear wear of retrieved implants was measured using a Taylor-Hobson Roundness machine. The average linear wear rate was defined as the maximum linear wear depth divided by the duration of the implant in vivo.

Results: In comparison with the non-pseudotumour implant group, the pseudotumour implant group was associated with:

significantly higher median linear wear rate of the femoral component: 8.1um/year (range 2.75–25.4um/year) vs. 1.79um/year (range 0.82–4.15um/year), p=0.002; and

Similarly, differences were also measured in absolute wear values. The median absolute linear wear was significantly higher in the pseudotumour implant group:

21.05um (range 2.74–164.80um) vs. 4.44um (range 1.50–8.80um) for the femoral component, p=0.005; and

Wear on the acetabular cup components in the pseudotumour group always involved the edge, indicating edge-loading of the bearing. In contrast, edge-loading was observed in only one acetabular component in the non-pseudotumour group of implants. The deepest wear was observed well within the bearing surface for the rest of the non-pseudotumour group. The difference in the incidence of edge-loading between the two groups was statistically significant (Fisher’s exact test, p=0.03).

Discussion: Significantly greater linear wear rates of the MoMHRA implants revised due to pseudotumour support the in vivo elevated metal ion concentrations in patients with pseudotumours. This study provides the first direct evidence to confirm that pseudotumour is associated with increased wear at the MoM articulation. Furthermore, edge-loading with the loss of fluid film lubrication may be the dominant wear generation mechanism in patients with pseudotumour.

Introduction: The use of second generation highly cross-linked polyethylene (HXLPE) is now commonplace for total hip arthroplasty, however there is no long-term data to support its use. Hip simulator studies suggest that the wear rate of HXLPE is ten times less than conventional polyethylene (UHMWPE). The outcomes of hip simulator studies are not always reproducible in vivo. Long term clinical data is required, as there is emerging clinical data, which suggests that some types of second generation HXLPE may have increased wear after 5 years.

Method: A prospective double blind randomised control trial was conducted using Radiostereometric analysis (RSA). Fifty-four subjects were randomised to receive hip replacements with either UHMWPE liners or HXLPE liners. All subjects received a cemented CPT stem and uncemented Trilogy acetabular component (Zimmer, Warsaw, IN, USA). The 3D penetration of the head into the socket was determined to a minimum of 7 years.

Results: The total liner penetration was significantly different at 7 years (p=0.01) with values of 0.33mm (SD 0.17mm) for the HXLPE group and 0.51mm (SD 0.14mm) for the UHMWPE group. The steady state wear rate from 1 year onwards was significantly lower for HXLPE (0.003 mm/yr, SD 0.04 mm/yr) than for UHMWPE (0.03 mm/yr, SD 0.03 mm/yr) (p=0.01). The direction of wear was in the antero-medial direction in both groups.

Conclusion: We have previously demonstrated that the penetration in the first year is creep-dominated, from one year onwards the majority of penetration is due to wear. The wear rate of this second generation HXLPE approaches that of metal on metal bearings. Second-generation HXLPE may have the potential to reduce the risk of revision surgery, due to wear debris induced osteolysis.

Introduction: Metal-on-metal hip resurfacing arthroplasty (MoMHRA) has gained popularity as an alternative to THR for younger patients with osteoarthritis. A growing concern has been the association of MoMHRA with the development of inflammatory pseudotumours (IP), especially in women. These have been linked to metal-on-metal wear, which can be related to metal ion concentrations. Elevated metal wear debris levels may result from impingement, rim contact and edge loading. Head-neck ratio (HNR) is a predetermining factor for range of movement and impingement. Neck thinning is a recognised phenomenon post-MoMHRA and we have found an association of IP with increased neck thinning based on a case control study. Our aims were to identify HNR changes a hip undergoes when resurfaced and at follow up; and whether greater neck thinning at follow-up could be associated with the presence of elevated metal ions.

Methods: A cohort of 91 patients (57M:34F) with unilateral MoMHRAs were included in this study. Blood tests were obtained at a mean follow up of 3.9 years (range 1.7–7 years) and serum (Co:Cr) ion levels were measured (ICPMS). High metal ion concentrations were defined as Co> 4.1ppb and Cr> 5.2ppb. For all patients, head-neck ratio (HNR) was measured on plain anterio-posterior pelvic radiographs pre-operatively, immediately post-operatively and at follow-up.

Results: Female patients had significantly bigger HNR pre-op (mean=1.35, range:1.22–1.64) compared to males(mean=1.22, range:1.05–1.38) (p< 0.01). Immediately post-op, female HNRs (mean: 1.26, range: 1.14–1.34) were not different to male patients(mean=1.24, range=1.11–1.38) (p=0.11). At follow-up HNR was once again significantly bigger (p< 0.01) in females (mean=1.35, range: 1.21–1.49), compare to males (mean=1.27, range:1.11–1.38). HNR alterations with operation (p=0.00) and at follow-up (p< 0.01) were significantly bigger in female patients. Furthermore, there was a significant correlation between high ion levels and HNR change at follow-up for both Co (p=0.02) and Cr (p< 0.01).

Conclusion: This study identified gender-specific changes in HNR that resurfaced hips undergo, not previously documented. Female hips have greater HNR pre-operatively, compared to male hips, and appear to be biomechanically disadvantaged when resurfaced. A decrease in HNR with resurfacing could result in impingement and lead to processes, known to be more prevalent in females, such as neck thinning, increased wear and IP development. In addition, we highlight a correlation between high ion levels and greater neck thinning at follow-up. Increased neck thinning in symptomatic MoMHRA hips could be secondary to increased wear and should be investigated further radiologically for the presence of IP.

Introduction: Metal-on-metal hip resurfacing arthroplasty (MoMHRA) has gained popularity as an alternative to THR for younger patients with osteoarthritis. A growing concern has been the association of MoMHRA with the development of inflammatory pseudotumours (IP), especially in women. These have been linked to metal-on-metal wear, which can be related to metal ion concentrations. Although cup orientation has been shown to influence wear, the optimum cup position has not been clearly defined. We have identified an optimal cup orientation to minimise IP risk, based on a case controlled study, for inclination/anteversion within ±10° of 40°/20°. Our aim was to see if this optimal position results in lower metal ions, and to identify the boundary of an optimal placement zone for low wear.

Methods: A cohort of 104 patients (60M: 44F) with unilateral MoMHRA was included in this study. Blood tests were obtained at a mean follow up of 3.9 years (range 1.7–7 years) and serum Co and Cr ion levels were measured (ICPMS). High metal ion concentrations were defined as Co> 4.1ppb and Cr> 5.2ppb. Radiographic cup inclination and anteversion were measured using EBRA. The differences in ion levels between different cup orientation zones were investigated. Three orientation zones were defined centered on the target orientation of 40°/20°: Z1 within ±5°, Z2 outside ±5°/within ±10° and Z3: within ±10°.

Results: There was a wide range of cup placements; mean inclination/anteversion were 46.3°(21.5°–64.6°)/15°(2.7°–35.6°). Cr levels, but not Co, were higher in female patients (p=0.002) and those with small femoral components (< 50mm, p =0.03).

For the whole cohort, there was no significant difference in ion levels (Cr: p=0.092. Co=0.075) between cups positioned within Z3 (n=58) versus those outside (n=46 mean). Male patients with cups within Z3 (n=27) had lower ion levels in comparison to those outside Z3, which were significantly lower for Co (p=0.049) but not Cr (p=0.084). Female patients had similar levels within and out of Z3 for both ions (Cr: p=0.83, Co: p=0.84). However, patients with cups within Z1 (n=13) had significantly lower Co (p=0.005) and Cr (p=0.001) than those outside Z1 (n=95). Interestingly, Co levels were significantly lower in Z1 (n=13) in comparison to Z2 (n=33) (p=0.048) but Cr levels were not different (p=0.06).

Discussion: MoMHRA cups placed with ±5° of the ideal position of 40°/20°gave rise to significantly lower metal ions indicating lower wear within this narrow zone, in both sexes. This safe zone, could be extended to ±10° for male patients only. Gender specific factors, such as pelvic anatomy and joint flexibility, could be responsible for the narrower ‘safe’ zone seen in females. The narrower safe zone coupled with smaller components implanted are factors contributing to higher ion levels and hence the increased incidence of IP seen in females.

Introduction: The development of Inflammatory Pseudotumour (IP) is a recognised complication following Metal on Metal Hip Resurfacing Arthroplasty (MoMHRA), thought to occur secondary to wear and elevated ion levels. Studies have shown that acetabular component orientation influences the wear of metal-on-metal hip replacement bearings. The aims of this study were to investigate the significance of cup orientation in the development of IP, and to identify a ‘safe-zone’ for cup placement with lower-risk for IP development.

Methods: Twenty six patients (n=27 hips) with IP confirmed radiologically, intra-operatively and histologically were matched for sex, age, pre-operative diagnosis, component size and follow-up with a cohort of asymptomatic MoMHRA patients (Control n=58). Radiographic acetabular anteversion and inclination were measured using EBRA. We calculated the distance in degree space of each acetabular component from the optimum position of 40° inclination and 20° anteversion, recommended by the designers, and thus compared acetabular component position between the two groups. Three different zones were tested as possibly optimum for acetabular placement. These were Lewinneck’s Zone (LZ) (inclination/anteversion; 30–50°/5–25°), and two zones defined by ±5° (Zone 1) or ± 10° (Zone 2) about the suggested target of 40°/20°. An optimal placement zone was determined based on a significant difference in IP incidence between components in the zone versus those outside.

Results: There was a wide range in cup orientations; mean inclination and anteversion were similar in the two groups: IP 47.5° (10.1°–80.6°)/14.1° (4.1°–33.6°) Vs Control 46.1° (28.8°–59.8°)/15.6° (4.3°–32.9°). Acetabular components in the IP group were significantly further away from the optimum position of 40°/20° in comparison to the controls (p=0.023). There was no difference in IP incidence between cups positioned within (IP:13/27, Control:35/58) or out of LZ (p=0.09) and within (IP: 2/27, Control: 10/58) or out of Zone 1 (p=0.156). Cups placed in Zone 2 (IP:6/27, Control:27/58) had significantly lower IP incidence versus those outside this zone (p=0.01). The odd’s ratio of developing IP when the cup is positioned out-of Zone 2 was 3.7.

Discussion: This study highlights the importance of ace-tabular component orientation in IP development. On the whole, patients with pseudotumour had acetabular components that were further away from the optimum position in comparison to the controls. However, a small number of IP patients had well-placed components implying that additional factors, possibly patient and/or gender specific, are involved in the development of pseudotumour. Furthermore, we defined an optimum, ‘safe-zone’ of ±10° around the cup position of 40°/20°. Patients with acetabular components outside this safe zone have an increased risk of IP development.

Roentgen Stereophotogrammetric Analysis (RSA) can predict long-term outcome of prostheses by measuring migration over time. The Exeter femoral stem is a double-tapered highly polished implant and has been shown to subside within the cement mantle in 2 year RSA studies. It has a proven track record in terms of long-term survivorship and low revision rates. Several studies have demonstrated excellent clinical outcomes following its implantation but this is the first study to assess stem migration at 10 years, using RSA.

This is a single-centre study involving 20 patients (mean age: 63 years, SD=7) undergoing primary total hip replacement for degenerative osteoarthritis using the lateral (Hardinge) approach. RSA radiographs were taken with the patient bearing full weight post-operatively, at 3, 6, 12 months and at 2, 5 and 10 years follow-up. The three-dimensional migration of the Exeter femoral stem was determined.

The mean Oxford Hip Score at 10 years was 43.4 (SD=4.6) and there were no revisions. The stems subsided and rotated internally during a 10-year period. The mean migrations of the head and tip of the femoral stem in all three anatomic directions (antero-posterior, medio-lateral & supero-distal) were 0.69 mm posterior, 0.04 mm lateral and 1.67 mm distal for the head and 0.20 mm anterior, 0.02 mm lateral and 1.23 mm distal for the tip. The total migration at 10 years was 1.81 mm for the head and 1.25 mm for the tip.

The Exeter femoral stem exhibits migration which is a complex combination of translation and rotation in three dimensions. Comparing our 10 year with our previous 2 year migration results, the Exeter stems show continued, but slow distal migration and internal rotation. The subsidence continues to compress the cement and bone-cement interface which maintains secure fixation in the long term.

Introduction: Symptomatic abnormal soft-tissue masses relating to the hip joint, such as those described as pseudotumours, are being increasingly reported following metal-on-metal hip resurfacing arthroplasty (MoMHRA). These were found to be locally destructive, requiring revision surgery in a high proportion (75%) of patients. Lymphocyte infiltrations seen in pseudotumours were similar to aseptic lymphocyte vascular associated lesion (ALVAL), which is thought to represent a T-lymphocyte-mediated delayed type hypersensitivity. Therefore, a delayed hypersensitivity reaction to nickel (Ni), chromium (Cr) or cobalt (Co) has been suggested to play a role in pseudotumour aetiology. In patients with bilateral MoMHRA who presented with symptoms on one side, subsequent scans have demonstrated pseudotumours both on the symptomatic and asymptomatic side. Thus, there are concerns that there may be an appreciable number of asymptomatic pseudotumours that surgeons are unaware of and these may eventually become symptomatic.

Aim: The aims of this study were:

to determine the prevalence of asymptomatic pseudotumours after MoMHRA; and

Methods: A total of 201 MoMHRA implanted hips in 158 patients (97 male, 61 female) with a mean age of 56 years (range 33–73 years) were evaluated. The mean follow-up was 61 months (range 13–88 months). Resurfacing devices implanted included 128 Birmingham Hip Resurfacing, 66 Conserve Plus and seven ReCap. The control groups included additional 20 patients, 10 male and 10 female (a mean age 68 years, range 57–80 years) with metal-on-polyethylene total hip arthroplasty and a further 22 age-matched patients (a mean age 55 years) without any metal implants. Ultrasound was used as the initial imaging modality and MRI was used to assess the extent of the identified masses. Patients with a soft-tissue mass had ultrasound-guided aspiration or core biopsy performed. Venous blood samples were collected in all patients for serum cobalt and chromium ion levels analysis using Inductively-Coupled Plasma Mass Spectrometer and lymphocyte transformation tests (LTT). The Oxford Hip Score (OHS) was used to measure the functional outcomes of patients. Acetabular component abduction angle was measured from standardised anteroposterior pelvis radiographs.

Results: Prevalence – Pseudotumours were found in 7 patients (6 female and 1 male). The overall prevalence of asymptomatic pseudotumours was 4%, with a relatively very high (30%) prevalence in females with bilateral implants. Histological examinations showed extensive necrosis of connective tissue, in which there were scattered aggregates of metal particles and a diffuse lymphocyte infiltrate.

Metal Ion Levels – The presence of pseudotumour was associated with significantly higher median serum cobalt levels (9.2mg/L vs. 1.9mg/L, p< 0.001), chromium levels (12.0mg/L vs. 2.1mg/L, p< 0.001), hip aspirate cobalt levels (1182 mg/L vs. 86.2mg/L, p=0.003), and aspirate chromium levels (883mg/L vs. 114.8mg/ L, p=0.006), as well as with inferior functional scores (OHS 41 vs. 47 p< 0.001). There was no significant difference in acetabular cup inclination angle (p=0.51). Lymphocyte Reactivity: A higher incidence and level of enhanced lymphocyte reactivity to Ni (p=0.001), but not to Co or Cr (the principal elements in the CoCr alloy used in metal-on-metal hip resurfacing implants), was found in patients with MoMHRA compared to the patients without MoM implants. However, lymphocyte reactivity to Co, Cr and Ni did not significantly differ in patients with pseudotumours compared to those patients without pseudotumours.

Conclusion: The prevalence of asymptomatic pseudotumours in females was high, especially in females with bilateral MoMHRA implants (30%). The patients with ‘asymptomatic’ pseudotumours were in fact mildly symptomatic. Lymphocyte reactivity to Co, Cr and Ni did not differ in patients with pseudotumour compared to those patients without pseudotumours, suggesting that systemic hypersensitivity type IV reactions, mediated by lymphocyte reactivity to these metals, is not the dominant mechanism in pathogenesis of the soft tissue pseudotumours. Furthermore, pseudotumours were not detected in those patients who had normal levels of cobalt and chromium ions. This suggests that pseudotumours do not occur if MoM articulations are well functioning. Therefore, pseudotumours are likely to be a biological consequence of the large amount of metal debris generated in vivo due to excessive wear.