This study investigates whether primary knee arthroplasty (KA) restores health-related quality of life (HRQoL) to levels expected in the general population. This retrospective case-control study utilises two sources: patients undergoing primary KA from a University Teaching hospital; and individual-level data from the Health Survey for England which was used to represent the General Population. Propensity score matching was used to balance covariates (sex, age and body mass index (BMI)) and facilitate group comparisons. Two matched cohorts with 3029 patients each were obtained for the adjusted analyses (median age 70.3 interquartile range (IQR) 64–77; Female sex 3233 (53.4%); median BMI 29.7 IQR 26.5-33.7). HRQoL was measured using the three-level version of the EuroQol 5-Dimensions’ (EQ-5D-3L) Index and EQ-VAS scores.Abstract
INTRODUCTION
METHODOLOGY
Instability accounts for approximately 20% of revision total knee arthroplasty (TKA) operations, however, diagnostic tests remain relatively subjective. The aim of this examination was to evaluate the feasibility of using pressure mat analyses during functional tasks to identify abnormal biomechanics associated with TKA instability. Five patients (M = 4; age = 69.80±7.05 years; weight = 79.73±20.12 kg) with suspected TKA instability were examined compared to 10 healthy controls (M = 4; age = 44.6±7.52 years; weight = 70.80±14.65). Peak pressure and time parameters were measured during normal gait and two-minute bilateral stance. Side-to-side pressure distribution was calculated over 10-second intervals during the second minute. Mann-Whitney tests compared loading parameters between groups and side-to-side differences in TKA patients (significance level = p<0.05). Pressure distribution was expressed relative to bodyweight. Notable differences were seen during bilateral stance. Uneven side loading was greater – favouring the non-operated limb – in TKA patients during bilateral stance compared to controls. This was significantly different at 30s (p=0.0336) and 60s (p=0.0336). Gait analyses showed subtle pressure distribution differences in unstable TKA patients. Stance time was indifferent. TKA patients tended to exhibit longer heel contact time (0.76s vs. 0.64s and reduced weight acceptance (50.75% vs. 56.75%) on the operated limb compared to the non-operated limb. Side-to-side differences in peak toe-off forces were significantly more pronounced in TKA patients versus controls (9.25% +/− 1.5% vs. 1.67% +/−5.79%; p=0.0039). Conclusion: This feasibility work demonstrates subtle differences in limb loading mechanics during simple clinical tests in unstable TKA patients that might be invisible to the naked eye. In the long-term, pressure analyses may be a useful diagnostic tool in identifying patients that would benefit from revision surgery for TKA instability.
Instability accounts for approximately 20% of all revision total knee arthroplasty (TKA), however diagnostic tests remain crude and subjective. The aim of this examination was to evaluate the feasibility of pressure mat (SB Mat, TekScan) analyses of functional tasks to differentiate instability in a clinical setting. Five patients (M = 4; age = 69.80±7.05 years; weight = 79.73±20.12 kg) with suspected TKA instability were examined compared to five healthy controls (M = 1; age = 46.80±7.85 years; weight = 71.54±16.17 kg). Peak pressure and time parameters were measured during normal gait and two-minute bilateral stance. Side-to-side pressure distribution was calculated over 10-second intervals during the second minute. Pressure distributions were expressed relative to bodyweight (%BW). T-tests compared loading parameters between groups (significance level = p<0.05). Analyses showed subtle differences in pressure distribution in unstable TKA patients versus healthy controls. Stance time during gait was indifferent. TKA patients tended to exhibit longer heel contact time (0.76 vs. 0.64 sec) and reduced weight acceptance (50.75% vs. 56.75%) on the operated versus non-operated limb. Side-to-side differences in toe-off forces were significantly more pronounced in TKA patients versus controls (9.25% vs. 3.75%;
Patient reported outcomes have become validated objective measures of success in research studies. They take time and effort to develop and administer. However, to remain relevant and universal PROMS should be gathered routinely and used to manage evidence-based change in healthcare systems. To ensure that they are adopted individual clinician involvement is key however a framework for comparison and relevance promotes engagement. Several examples will be presented of system change using PROMS and PREMS as well as using routine data to defend patient selection. How and what we present depends on whom we are expecting to influence.
To investigate the validity of threshold values for the Oxford Hip and Knee Score (OHS and OKS) for treatment success 12 months after total knee or hip replacement. Questionnaires were administered to patients undergoing total hip (THA) or knee (TKA) replacement before and 12 months after surgery alongside questions assessing key accepted aspects of treatment success (satisfaction, pain relief, functional improvement) to form a composite criterion of success and assessed using receiver operator characteristic (ROC) analysis. Thresholds providing maximum sensitivity and specificity for predicting treatment success were determined for the total sample and subgroups defined by pre-surgery scores.Aim
Methods
To evaluate the association of BMI and improvement in patient-reported outcomes after TKA. Knee replacement outcome data for procedures carried out over an eight month period was extracted from a regional arthroplasty register in the UK. Data was available before surgery and 12 months after. We analysed the impact of overweight on post-operative change in the Forgotten Joint Score − 12 (FJS-12) measuring joint awareness and the Oxford Knee Score (OKS) measuring pain and function using five BMI categories (A: <25, B: 25–29.9, C: 30–34.9, D: 35–39.9 and E: >40).Aim
Methods
Obese patients undergoing total knee arthroplasty (TKA) face increased risks of complications such as joint infection and early revision. However, the influence of obesity on measures of patient function following TKA is poorly defined. Knee arthroplasty outcome data for procedures carried out over an eight month period was extracted from a regional database in the UK. We analysed the impact of weight categories (BMI<30, BMI=30–34.9, and BMI≥35) on the Forgotten Joint Score – 12 (FJS-12) and Oxford Knee Score (OKS). Data was available preoperatively and 12 months postoperatively. Physical and mental health was assessed with the SF-12 one year after surgery. Data from 256 patients were available. 49.6% had a BMI<30, 27.4% had a BMI 30–34.9 and 23.1% had a BMI≥35. Mean FJS-12 results at 1-year were 48.7 points for patients with a BMI<30, 40.7 points for patients with a BMI=30–34.9 and 34.0 points for patients with a BMI≥35. Effect sizes for change from baseline to 12-month post-op were 3.0 (Cohen's d) in patients with BMI<30 and d=2.2 in patients with BMI≥35. Mean OKS results at 1 year were 36.9 (BMI<30), 33.7 (BMI=30–34.9) and 32.0 (BMI≥35) respectively. Effect sizes for change from baseline to 12-month was d=2.1 (BMI<30) and d=1.9 (BMI≥35). Differences between BMI groups with regard to post-operative change were statistically significant for the FJS-12 (p=0.038) but not for the OKS (p=0.229). This study highlights that outcome scores may differ in their ability to capture the impact of obesity on patient function following TKA. The FJS-12 showed significant differences in outcome based on patient obesity category, whereas the OKS did not detect between group differences.
Patient function is poorly characterised following revision TKA. Modern semi-constrained implants are suggested to offer high levels of function, however, data is lacking to justify this claim. 52 consecutive aseptic revision TKA procedures performed at a single centre were prospectively evaluated; all were revision of a primary implant to a Triathlon total stabiliser prosthesis. Patients were assessed pre-operatively and at 6, 26, 52 and 104 weeks post-op. Outcome assessments were the Oxford Knee Score (OKS), range of motion, pain rating scale and timed functional assessment battery. Analysis was by repeated measures ANOVA with post-hoc Tukey HSD 95% simultaneous confidence intervals as pairwise comparison. Secondary analysis compared the results of this revision cohort to previously reported primary TKA data, performed by the same surgeons, with identical outcome assessments at equivalent time points. Mean age was 73.23 (SD 10.41) years, 57% were male. Mean time since index surgery was 9.03 (SD 5.6) years. 3 patients were lost to follow-up. All outcome parameters improved significantly over time (p <0.001). Post-hoc analysis demonstrated that all outcomes changed between pre-op, 6 week and 26 weeks post-op assessments. No difference was seen between primary and revision cohorts in OKS (p = 0.2) or pain scores (p=0.19). Range of motion and functional performance was different between groups over the 2 year period (p=0.03), however this was due to differing pre-operative scores, post-hoc analysis showed no difference between groups at any post-operative time point. Patients undergoing aseptic revision TKA with semi-constrained implants made substantial improvements in OKS, pain scores, knee flexion, and timed functional performance, with the outcomes achieved comparable to those of primary TKA. High levels of function can be achieved following revision knee arthroplasty, which may be important considering the changing need for, and demographics of, revision surgery.
This study assessed whether patient satisfaction with their hospital stay influences the early outcome of total knee replacement (TKR). During a five year period patients undergoing primary TKR at the study centre had prospectively outcome data recorded (n=2264). Patients with depression (p=0.04) and worse mental wellbeing (p<0.001), according to the short form (SF)-12, were more likely to be dissatisfied with their hospital stay. Decreasing level of satisfaction with their hospital stay was associated with a significantly worse post-operative OKS (p<0.001) and SF-12 score (p<0.001). Multivariable regression analysis confirmed that the patients perceived level of satisfaction with their hospital stay was an independent predictor of change in the OKS (p<0.001) and SF-12 score (p<0.001) after adjusting for confounding variables. Patient satisfaction with their TKR was significantly influenced by their hospital experience, decreasing from 96% in those with an excellent experience to 42% in those with a poor experience. Food, staff/care, and the hospital environment were the most frequent reasons of why patients rated their hospital experience as fair or poor. A patient's perception of their inpatient hospital experience after surgery is an important modifiable predictor of early functional outcome and satisfaction with TKR.
Service industry metrics (the net promoter score) are being introduced as a measure of UK healthcare satisfaction. Lower limb arthroplasty, as a ‘service’, scores comparably with the most successful commercial organisations. Satisfaction with care is important to both the patient and the payer. The Net Promoter Score, widely used in the service industry, has been recently introduced to the UK National Health Service as an overarching metric of patient satisfaction and to monitor performance. This questionnaire asks ‘customers’ if they would recommend a service or products to others. Scores range from −100 (everyone is a detractor) to +100 (everyone is a promoter). In industry, a positive score is well regarded, with those over 50 regarded as excellent. Our aims were to assess net promoter scores for joint arthroplasty, to compare these scores with direct measures of patient satisfaction, and to evaluate which factors contributed to net promoter response.Summary Statement
Background
Using current analysis/methodology, new implant technology is unlikely to demonstrate a large enough change in patient function to impact on the cost-effectiveness of the procedure. Cost effectiveness is an increasingly important metric in today's healthcare environment, and decisions surrounding which arthroplasty prosthesis to implant are not exempt from such health economic concerns. Quality adjusted life years (QALYs) are the typical assessment tool for this type of evaluation. Using this methodology, joint arthroplasty has been shown to be cost effective, however studies directly comparing the QALY achieved by differing prostheses are lacking.Summary Statement
Purpose
Many psychological factors have been associated with function after joint replacement. Personality is a stable pattern of responses to external conditions and stimuli. The aim of this study was to investigate the relationship between personality, joint function, and general physical in patients undergoing total hip (THR) and knee replacement (TKR). We undertook a prospective cohort study of 184 patients undergoing THA and 205 undergoing TKA. Personality was assesed using the Eysneck Personality Questionaire, brief version (EPQ-BV). Physical health was measured using the EuroQol (EQ-5D). Joint function was measured using the relevant Oxford Score. Outcomes were assessed at six months. Multivariable models were constructed. The stable introvert personality was most common. Unstable introverts had poorer pre-operative function with hip arthrosis, but not knee arthrosis. Personality was not directly associated with post-operative function – the only independent predictors were pre-operative function (p=0.002) and comorbidity (p<0.001). While satisfaction after TKR was associated with personality (p=0.026), there was no association after THR (p=0.453). The poorest satisfaction was in those with the unstable introvert personality type. Personality was a predictor of preoperative status. It did not have a direct association with postoperative status, but may have as preoperative function was the main predictor of postoperative function, personality may have had an indirect effect. Personality was also a predictor of satisfaction after TKR. This suggests that predicting satisfaction after knee replacement is more complex. Therefore certain patient may benefit from a tailored preoperative education to explore and manage expectations.
Expectations of patients requiring knee arthroplasty surgery have become higher than in the past, with more strain being put on modern prostheses by fitter and younger patients. The objective of this study was to analyse the survivorship of primary knee arthroplasties at a minimum of ten years, with end points of revision and death. Patients who had a total (TKA) or unicompartmental (UKA) knee arthroplasty performed at a university teaching hospital were identified from the local arthroplasty database. Electronic and operative records were analysed to determine parameters including operative indication, subsequent revision surgery, and patient mortality. Results were collated and analysed using PASW software. A total of 1023 patients were recruited, with 566 (55%) female and 457 (45%) male. Minimum follow up was 10.1 years, with an average of 12.1 years (S.D 0.87). 64.9% of patients were alive at follow up, with an average age of 79.7 years (S.D 8.7). 92.8% were operated on for osteoarthritis (OA), 6.6% for rheumatoid arthritis (RA) and 0.6% for other indications. Kaplan–Meier analysis estimated survival of 94% (S.D 0.008) at eleven years, with no statistical difference found in survivorship of knees operated on for OA or RA. Similarly no statistical difference was found between survivorship of UKA or TKA implants. Of those that died by follow up, 95.2% did so with their original implant. We conclude that both TKA and UKA offer a lasting solution for patients, with excellent outcomes achieved in both rheumatoid and osteoarthritic patients.
Nerve damage is a complication of THA and TKA procedures. The incidence of subclinical nerve injury following arthroplasty is unknown. The aim was to determine the prevalence of asymptomatic nerve deficits in an arthroplasty population group, and the incidence of post-operative changes in nerve function. A Secondary aim was to identify the nature of any deficits. And the association between nerve deficits and history of backache. A non-randomised prospective series of patients undergoing lower limb arthroplasty for osteoarthritis were studied at a single hospital. The peroneal nerve was investigated using nerve conduction in forty patients. Twenty patients had upper limb testing to differentiate between a polyneuropathy or isolated lower limb neuropathy. Nerve function deficits were detected in the peroneal nerve in fifteen patients pre-operatively and fifteen post-operatively, of those twelve had A waves detected suggestive of a generalised neuropathy. Ten patients who had upper limb testing had a conduction defect (five had asymptomatic Carpal tunnel). There was a positive correlation between presence of post-operative deficit and age(r=0.389, p=0.013). A negative correlation was found for presence of post-operative A waves and BMI(r=−0.370, p=0.019). The prevalence of pre-operative subclinical peroneal neuropathy is much higher than expected in this group (37.5%) of arthroplasty patients. There is a strong correlation between presence of post-operative conduction abnormalities and age. There is no relationship between peripheral neuropathy and history of backache or residual post-operative deficit.
The aim was to perform a cost-utility analysis of total joint replacement in the current environment. Arthritis is a disabling condition that leads to long-term deterioration in quality of life. Total joint replacement, despite being one of the greatest advances in medicine in the modern era, has come under recent scrutiny. The National Health Service (NHS) has competing demands and resource allocation is challenging in times of economic restraint. Patients undergoing total hip (n=348) and knee arthroplasty (n=323), from January to July 2010, were entered into a prospective arthroplasty database. A health utility score was derived from the Euroqol (EQ-5D) score preoperatively, and at one year, and was combined with individual life expectancy to derive the Quality-Adujusted-Life-Years (QALYs) gained. Predicted need for revision surgery was Incorporated in the model. The 2011–12 Scottish Tariff was used. Two-way analysis of variance was used to compare QALYs gained between procedures, while controlling for baseline differences. The number of QALYs gained was higher in THR versus TKR (6.53 vs 4.04 years, p<0.001). The cost per QALY for THR was £1371 (95% CI £1194 to £1614) compared with £2101 (£1762 to £2620) for TKR. Predictors of an increase in QALYs gained were poorer health prior to surgery (p<0.001) and younger age (p<0.001). General health (EQ-5D VAS) showed greater improvement in THR versus TKR (p<0.001). This study provides up to date cost-effectiveness data for total joint replacement. THR and TKR are both extremely clinically and cost-effective interventions, with costs that compare favourably with other medical interventions (e.g. laparoscopic hernia repair vs open: £55,548 per QALY; CHD primary prevention with statins: £21,000).
Many prosthetic design changes have been introduced in attempt to improve outcomes following TKA; however there is no consensus as to whether these changes confer benefits to patients. This study aimed to assess whether patients treated with a modern implant design had an enhanced patient outcome compared to a traditional model in a double blind randomised controlled trial. 212 consecutive patients were prospectively randomised to receive either a modern (Triathlon) or a traditional (Kinemax) TKA (both Stryker Orthopaedics). 6 surgeons at a single unit performed all procedures in a standardised manner. A single researcher, blinded to implant allocation, performed all assessments. Patients were assessed pre-operatively, and at 6, 26, 52 weeks post-surgery with the Oxford Knee Score (OKS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score, goniometry, timed functional assessment, lower limb power (Leg Extensor Power Rig) and pain numerical rating scales (NRS). Change in scores and between group differences were assessed with Two-Way Repeated Measures ANOVAs.Introduction
Methods
Patient expectations and their fulfilment are an important factor in determining patient-reported outcome and satisfaction of hip (THR) and knee replacement (TKR). The aim of this prospective cohort study was to examine the expectations of patients undergoing THR and TKR, and to identify differences in expectations, predictors of high expectations and the relationship between the fulfilment of expectations and patient-reported outcome measures. During the study period, patients who underwent 346 THRs and 323 TKRs completed an expectation questionnaire, Oxford score and Short-Form 12 (SF-12) score pre-operatively. At one year post-operatively, the Oxford score, SF-12, patient satisfaction and expectation fulfilment were assessed. Univariable and multivariable analysis were performed. Improvements in mobility and daytime pain were the most important expectations in both groups. Expectation level did not differ between THR and TKR. Poor Oxford score, younger age and male gender significantly predicted high pre-operative expectations (p < 0.001). The level of pre-operative expectation was not significantly associated with the fulfilment of expectations or outcome. THR better met the expectations identified as important by patients. TKR failed to meet expectations of kneeling, squatting and stair climbing. High fulfilment of expectation in both THR and TKR was significantly predicted by young age, greater improvements in Oxford score and high pre-operative mental health scores. The fulfilment of expectations was highly correlated with satisfaction.
Osteoarthritis continues to be a major cause of pain and disability. The pathological processes leading to the end-stage of joint degeneration remain poorly understood. Advances in radiological imaging have the potential to improve understanding of the structural and functional changes observed in OA. The aim of this study was to describe the microarchitecture of the femoral head in osteoarthritis. Twenty osteoarthritic femoral heads underwent micro-computed tomography scanning at 30µm. Four parameters of micro-architecture and structure were determined: bone volume ratio (BV:TV), trabecular thickness, structural model index and degree of anisotropy. The femoral head was divided into 27 cubic volumes of interest. Analysis of variance (ANOVA) was used to assess differences between regions. Cystic and sclerotic changes were assessed qualitatively.Introduction
Methods
There is limited literature regarding the outcome of hip and knee arthroplasty (THR and TKR) in the Super-Elderly (≥80yrs). The aim is to compare the outcome of THR and TKR in the Super-Elderly with a standard-age cohort of patients. From January 2006 to August 2008; 1290 TKR and 1344 THR were performed at the study institute. Comorbidity, length of stay, patient satisfaction, Oxford knee or hip scores, and SF12 scores were recorded prospectively. The Oxford Score and SF12 were recorded at one year. The mode age range was 65-74yrs for TKR (n=492) and THR (n=495), deemed the standard cohort. 185 TKR and 171 THR were performed in the Super-Elderly. Outcome in this cohort was compared to the standard. The standard cohort had a greater absolute improvement in Oxford knee scores (15.8 and 14.7.p=0.2). Improvement of absolute Oxford hip scores revealed no difference (20.0 and 20.2.p=0.8), but the Super-Elderly had a greater improvement in pain components (11.0 vs.12.0.p=0.05) with a lesser improvement of the functional components (9.0.vs.8.2.p=0.05). There was a greater improvement in the physical component of the SF-12 score in the standard cohort for both TKR and THR (10.6.vs.7.9.p=0.05 and 14.4.vs.10.4.p=<0.01, respectively). No significant difference was seen in comorbidities, but the Super-Elderly patients had a longer hospital stay for TKR (6.2.vs.8.3.p=0.01) and THR (5.9.vs.9.0.p=0.01). The Super-Elderly were more satisfied with their surgery (p=0.05). Super-Elderly patients have comparable outcomes to their younger counterparts and are more satisfied with their surgery, but they may require a longer length of stay.
To investigate the incidence, types and trends in diagnosis of venous thromboembolic events (VTE) in patients undergoing total knee arthroplasty (TKA) over a ten-year period. Data from 5100 consecutive TKAs performed in our unit between April 1996 and March 2006 were prospectively collected by the Scottish Arthroplasty Project (SAP). This database contains data on 100% of arthroplasty cases in Scotland. We retrospectively reviewed casenotes of these patients to identify thromboprophylaxis given, the diagnosis of VTE, treatment and adverse outcomes.Aim
Methods
There is widespread appreciation amongst orthopaedic surgeons of the importance of thromboprophylaxis. However much of the evidence is based on surrogate outcomes of clinical end-points. This population-based study aims to identify the incidence and trends in venous thromboembolic disease (VTE) following total hip (THR) and knee arthroplasty (TKR) with death or readmission for VTE up to two years following surgery for all patients in Scotland as the primary outcome. We used the Scottish Morbidity Record (SMR01) system to identify all patients undergoing hip or knee arthroplasty over the ten-year period from 1992 to 2001. Patients undergoing cataract surgery over the same period were identified as a control group. Record linkage for all patients to subsequent SMR01 and Registrar General records provided details of further admissions due to DVT or non-fatal PE and deaths within Scotland up to two years after the operation. The cause of death was determined from the Registrar General Records. The incidence of VTE (including fatal pulmonary embolism (PE)) three months following primary THR was 2.27% and primary TKR was 1.79%. The incidence of fatal PE within three months of THR was 0.22% and TKR was 0.15%. The majority of events occurred in the interval from hospital discharge to six weeks after surgery. There was no apparent trend over the period. An apparent reduction in the overall mortality within 365 days of surgery appears to be due to a reduction in the incidence of acute myocardial infarct. The data support the current advice that prophylaxis should be continued for at least six weeks following surgery. Despite increased uptake of prophylaxis regimens and earlier mobilisation, there has been no apparent change in the incidence of symptomatic VTE over the ten-years from 1992 to 2001.
We compared the outcome of arthroscopic repair of the rotator cuff in 32 diabetic patients with the outcome in 32 non-diabetic patients matched for age, gender, size of tear and comorbidities. The Constant-Murley score improved from a mean of 49.2 (24 to 80) pre-operatively to 60.8 (34 to 95) post-operatively (p = 0.0006) in the diabetic patients, and from 46.4 (23 to 90) pre-operatively to 65.2 (25 to 100) post-operatively (p = 0.0003) in the non-diabetic patients at six months. This was significantly greater (p = 0.0002) in non-diabetic patients (18.8) than in diabetics (11.6). There was no significant change in the mean mental component of the Short-Form 12, but the mean physical component increased from 35 to 41 in non-diabetics (p = 0.0001), and from 37 to 39 (p = 0.15) in diabetics. These trends were observed at one year. Patients with diabetes showed improvement of pain and function following arthroscopic rotator cuff repair in the short term, but less than their non-diabetic counterparts.
Following hip arthroplasty carried out using the Slooff-Ling impaction grafting technique micro-motion of the acetabular cup is frequently seen within the bone graft bed. In some cases this can lead to gross migration and rotation of the acetabular cup, resulting in failure of the arthroplasty. The movement of the cup is thought to be due to the irrecoverable deformation of bone graft under shear and compressive forces. Previous experimental studies have addressed ways in which the behaviour of the bone graft material may be improved, for example through washing and the use of improved particle size distribution. However there has been a limited amount of research carried out into assessing the behaviour of the acetabular construct in-vivo. This study presents a 3D finite element model of the acetabular construct and hemi-pelvis following impaction grafting of a cavitory defect. A sophisticated elasto-plastic material model was developed based on research carried out by the group to describe the bone graft bed. The material model includes the non-linear stiffness response, as well as the shear and consolidation yield response of the graft. Loading associated with walking, sitting down, and standing up is applied to the model. Distinct patterns of migration and rotation are observed for the different activities. When compared in a pseudo-quantitative manner with clinical observations results were found to be similar. Walking is found to account for superior migration, and rotation in abduction of the acetabular cup, while sitting down and standing up are found to account for posterior migration, and lateral rotation. The developed 3D model can be used in the assessment of cup designs and fixation devices to reduce the rate of aseptic failure in the acetabular region.
Previous experimental studies of the pelvis have been carried out on cadaveric samples stripped of soft tissue. Investigations of the stress concentrations present in the pelvis due to the application of force through the hip joint have been conducted with the superior iliac crests cast in resin or cement. Thus stress concentrations are observed towards the superior iliac crests, and to some extent the pubic symphysis (these being the areas in which force transfer can occur). Due to the rigid fixing of the pelvis in these experiments, the pelvic bone has become viewed as a ‘sandwich beam’ acting between the sacro-iliac and the pubic joints. Numerical models employing similar fixed conditions have shown good agreement with the experimental studies. However it is clear that these experiments, and the accompanying computational models are not representative of the in-vivo situation, in which the muscles and ligaments of the pelvis and hip joint provide resistance to movement, and in the case of muscles place additional forces on the pelvis, not addressed in the experimental studies. This study presents a finite element model of the pelvis in which novel techniques have been used to include the pelvic ligaments, and hip joint muscles using realistic attachment areas on the cortex, providing a more realistic comparison to the in-vivo environment. Joint interactions at the pubic symphysis and sacro-iliac joints are also simulated. A fixed boundary condition model is also presented for comparison. The resulting stress concentrations in the pelvis for single leg stance observed in the in-vivo boundary condition model are dramatically different to those presented in studies in which the pelvis is rigidly fixed in place. The abductor muscles are seen to play a significant role in reducing stress concentrations towards the sacro-iliac joints and superior to the acetabulum, in comparison to fixed boundary condition analyses. Stress reductions away from the acetabulum are also observed in the underlying trabecular bone for the in-vivo boundary condition model. Similar stresses are observed within the acetabular region for the fixed, and in-vivo boundary condition models.
Morsellised cortico-cancellous bone (MCB) is used extensively in impaction grafting procedures, such as the filling of cavitory defects on the femoral and acetabular sides during hip arthroplasty. Several experimental studies have attempted to describe the mechanical behaviour of MCB in compression and shear, and it has been found that it’s properties can be improved by washing and rigorous impaction at the time of surgery. However their focus has not been on the development of constitutive models that can be used in computational simulation. The results of serial confined compaction tests are presented and used to develop constitutive models describing the non-linear elasto-plastic behaviour of MCB, as well as its time dependent visco-elastic behaviour. It is found that the elastic modulus, E of MCB increases linearly with applied pressure, p, with E achieving a value of around 30 MPa at a pressure of around 1 MPa. The plastic behaviour of MCB can be described using a Drucker Prager Cap yield criterion, capable of describing yielding of the graft in shear and compression. The time dependent visco-elastic behaviour of MCB can be accurately modelled using a spring and dashpot model that can be numerically expressed using a fourth order Prony series. The role of impaction in reducing subsequent plastic deformation was also investigated. The developed relationships allow the constitutive modelling of MCB in finite element simulations, for example of the acetabular construct following impaction grafting. The relationships also act as a gold standard against which to compare synthetic graft and graft extender materials.
If an arthroplasty patient presents with wound breakdown, sinus formation or a hot, red joint the diagnosis of infection is straightforward. However, most total joint replacement (TJR) infections are difficult to distinguish from aseptic loosening. It is imperative to know if a painful TJR is infected to plan appropriate management. In this prospective study of 204 patients we analysed the diagnostic accuracy of various tests for infection: Inflammatory Markers (CRP/ESR); Aspiration Microbiology; and the Polymerase Chain Reaction (PCR) – a novel technique in this situation. We used international criteria as the gold standard for infection, applied at the time of revision surgery. Any of – a sinus; frank pus in the wound; positive intra-operative microbiology; positive histology – classified the patient as infected. The sensitivity (Sens), specificity (Spec), positive predictive value (PPV) and negative predictive value (NPV) of each test were calculated. 52 patients with an original diagnosis of inflammatory arthritis were excluded, as histology may be inaccurate. The results for the remaining 152 patients are: CRP >
20mg/l: Sens 77%; Spec 76%; PPV 49%; NPV 92%. ESR >
30 mm/hr: Sens 61%; Spec 86%; PPV 57%; NPV 87%. Aspiration Microbiology: Sens 80%; Spec 83%; PPV 71%; NPV 88%. PCR: Sens 71%; Spec 78%; PPV 43%; NPV 89%. Few patients with negative CRP/ESR were found to be infected; if positive, there was a 50/50 chance that the joint was infected. Positive aspiration microbiology was associated with underlying infection 3 times out of every 4, and negative results were correct 9 times out of 10. PCR was no more accurate than existing tests. All patients with painful TJR’s should have inflammatory markers checked – if negative the clinician can be relatively reassured that the implant is not infected. If positive or suspicion remains, further investigation should be undertaken. Joint aspiration for microbiology is currently the best available second line investigation.
Using established emboli criteria 10 (50%) patients had true cerebral emboli with a range from 1 to 550 signals (median 2.5 interquartile range (IQ) 2 to 12.5). S-100B levels increased from a pre-operative median (IQ) of 0.15 microg/L (0.12 to 0.20) to a peak immediately following surgery of 1.88(1.36 to 4.24) returning to 0.26(0.18 to 0.37) by 48 hours (normal range: 0.03–0.15). Plotted scatter charts indicated no correlation between embolic load and cognitive dysfunction or with S-100B levels following surgery.
Morsellised bone graft is used extensively in revision arthroplasty surgery. The impaction technique at the time of surgery has a significant effect on the subsequent elastic and inelastic properties of the bone graft bed. Differences in values reported in the literature for the mechanical properties of morsellised cortico-cancellous bone (MCB) can be attributed to the different loading histories used during testing. We performed serial confined compaction tests to assess the optimum compaction strategy. Compaction of the samples was carried out using repeated standardised loading cycles. Optimal preparation of MCB is dependant on the force and frequency of compaction. The maximum compactive pressure the samples were subjected to was 3 N/mm2 based on the clinical experience of Ullmark &
Nilsson MCB was also found to exhibit significant visco-elastic response, with stress relaxation under displacement controlled loading continuing for several hours following initial load application. Bone graft substitutes do not at present exhibit a similar beneficial shock absorbing visco-elastic response. Our experiments indicate that the material properties of MCB are dependent on the force of impaction and the number of impactions applied with a hammer at the time of surgery. A minimum of 10 to 20 compaction episodes, or hammer blows are required for MCB to achieve 60 to 70% of its long term predicted stiffness.
We recommend that all patients with painful TJRs have inflammatory markers checked as a screening test – if negative then the clinician can be relatively reassured that the implant is not infected. If positive, further investigation should be undertaken. Joint aspiration for microbiology is currently the best available second line investigation.
This population-based study investigated the incidence and trends in venous thromboembolic disease after total hip and knee arthroplasty over a ten-year period. Death or readmission for venous thromboembolic disease up to two years after surgery for all patients in Scotland was the primary outcome. The incidence of venous thromboembolic disease, including fatal pulmonary embolism, three months after surgery was 2.27% for primary hip arthroplasty and 1.79% for total knee arthroplasty. The incidence of fatal pulmonary embolism within three months was 0.22% for total hip arthroplasty and 0.15% for total knee arthroplasty. The majority of events occurred after hospital discharge, with no apparent trend over the period. The data support current advice that prophylaxis should be continued for at least six weeks following surgery. Despite the increased use of policies for prophylaxis and earlier mobilisation, there has been no change in the incidence of venous thromboembolic disease.
We investigated the use of PCR (the Polymerase Chain Reaction) to detect the presence of infection in a group of patients undergoing revision arthroplasty for loose TJR (total joint replacement), compared to internationally agreed criteria used as the ‘gold standard’ for infection. We prospectively tested samples taken from 108 patients undergoing revision arthroplasty (76 hips, 32 knees). Antibiotics were omitted prior to obtaining samples. DNA was extracted by 2 methods – a previously published technique ( Using the published DNA extraction technique PCR had a sensitivity of 50%, specificity of 93%, positive predictive value of 67% and negative predictive value of 88%. Using commercial extraction the sensitivity improved to 60%, specificity to 98%, positive predictive value to 90% and negative predictive value to 90%. The previous report stated that PCR had a high sensitivity but a low specificity for detecting low grade infection. However, when using the published technique we found the opposite results – a moderate sensitivity and a high specificity. Introduction of a new DNA extraction technique improved the sensitivity. The refined PCR technique had a high accuracy, but further work is needed to improve sensitivity before we would recommend this method for routine clinical use.
Four cases are described of localised endosteal bone lysis in the femur occurring in association with cemented femoral components that were not obviously 'loose' radiologically. In each, the area of lysis was shown at operation to be related directly to a region in which there was a local defect in the cement mantle surrounding the stem. Via the space between the stem and cement, such defects provide a route through which the contents of the joint cavity may reach the endosteal surface of the femur, subsequently leading to localised bone lysis, and later to frank loosening.
Intramedullary locking nails have proved to be of considerable advantage when treating complex, comminuted or segmental femoral shaft fractures. We have reviewed 117 patients with 120 femoral shaft fractures treated with the Strasbourg device. These included 20 compound fractures, 13 pathological fractures and two non-unions. Rehabilitation and union rates have been very satisfactory and there have been no serious infections in the series. Comminution of the proximal femur has occurred in six patients and there have been three femoral neck fractures, but all of these have healed without further complications.
One hundred and twenty-seven consecutive patients with displaced subcapital fractures of the femoral neck (Garden Grade III or IV) all under 80 years of age and independently mobile, were randomly allocated to fixation with either double divergent pins or a single sliding screw-plate device. The incidence of non-union and infection in the sliding screw-plate group was significantly higher, and we believe that when internal fixation is considered appropriate multiple pinning should be used. Mobility after treatment was disappointing in about half of the patients, and we feel that internal fixation can only be justified in patients who are physiologically well preserved and who maintain a high level of activity.
Torsion and subsequent ischaemia is a well-recognised cause of symptoms and morbidity in general surgery. We present three cases of solitary pigmented villonodular tumours of the knee which were found to have undergone torsion. We believe these to be the first intra-articular tumours in which torsion has been reported.