Designer hips

Longitudinal Analysis and Latent Growth Modeling of the Modified Hip Dysfunction and Osteoarthritis Outcome Score for Joint Replacement (HOOS-JR)

The Hip Dysfunction and Osteoarthritis Outcome Score for Joint Replacement (HOOS-JR) was developed as a short-form survey to measure progress after total hip arthroplasty (THA). However, the longitudinal validity of the scale structure pertaining to the modified five-item HOOS-JR has not been assessed. Therefore, the purpose of this study was to evaluate the structural validity, longitudinal invariance properties, and latent growth curve (LGC) modeling of the modified five-item HOOS-JR in a large multi-site sample of patients who underwent a THA. A longitudinal study was conducted using data from the Surgical Outcome System (SOS) database. Confirmatory factor analyses (CFAs) were conducted to assess the structural validity and longitudinal invariance across five time points. Additionally, LGC modeling was performed to assess the heterogeneity of the recovery patterns for different subgroups of patients. The resulting CFAs met most of the goodness-of-fit indices (CFI = 0.964-0.982; IFI = 0.965-0.986; SRMR = 0.021-0.035). Longitudinal analysis did not meet full invariance, exceeding the scalar invariance model (CFIDIFF = 0.012; χ2DIFF test = 702.67). Partial invariance requirements were met upon release of the intercept constraint associated with item five (CFIDIFF test = 0.010; χ2DIFF = 1073.83). The equal means model did not pass the recommended goodness-of-fit indices (CFIDIFF = 0.133; χ2DIFF = 3962.49). Scores significantly changed over time, with the highest scores identified preoperatively and the lowest scores identified at 2- and 3-years postoperatively. Upon conclusion, partial scalar invariance was identified within our model. We identified that patients self-report most improvements in their scores within 6 months postoperatively. Females reported more hip disability at preoperative time points and had faster improvement as measured by the scores of the modified five-item HOOS-JR.

The ethics of explantation

BACKGROUND

With the increased use of implanted medical devices follows a large number of explantations. Implants are removed for a wide range of reasons, including manufacturing defects, recovery making the device unnecessary, battery depletion, availability of new and better models, and patients asking for a removal. Explantation gives rise to a wide range of ethical issues, but the discussion of these problems is scattered over many clinical disciplines.

METHODS

Information from multiple clinical disciplines was synthesized and analysed in order to provide a comprehensive approach to the ethical issues involved in the explantation of medical implants.

RESULTS

Discussions and recommendations are offered on pre-implantation information about a possible future explantation, risk-benefit assessments of explantation, elective explantations demanded by the patient, explantation of implants inserted for a clinical trial, patient registers, quality assurance, routines for investigating explanted implants, and demands on manufacturers to prioritize increased service time in battery-driven implants and to market fewer but more thoroughly tested models of implants.

CONCLUSION

Special emphasis is given to the issue of control or ownership over implants, which underlies many of the ethical problems concerning explantation. It is proposed that just like transplants, implants that fulfil functions normally carried out by biological organs should be counted as supplemented body parts. This means that the patient has a strong and inalienable right to the implant, but upon explantation it loses that status.

Early subsidence of shape-closed hip arthroplasty stems is associated with late revision. A systematic review and meta-analysis of 24 RSA studies and 56 survival studies

BACKGROUND AND PURPOSE

Few studies have addressed the association between early migration of femoral stems and late aseptic revision in total hip arthroplasty. We performed a meta-regression analysis on 2 parallel systematic reviews and meta-analyses to determine the association between early migration and late aseptic revision of femoral stems.

PATIENTS AND METHODS

Of the 2 reviews, one covered early migration data obtained from radiostereometric analysis (RSA) studies and the other covered long-term aseptic revision rates obtained from survival studies with endpoint revision for aseptic loosening. Stems were stratified according to the design concept: cemented shape-closed, cemented force-closed, and uncemented. A weighted regression model was used to assess the association between early migration and late aseptic revision, and to correct for confounders. Thresholds for acceptable and unacceptable migration were determined in accordance with the national joint registries (≤ 5% revision at 10 years) and the NICE criteria (≤ 10% revision at 10 years).

RESULTS

24 studies (731 stems) were included in the RSA review and 56 studies (20,599 stems) were included in the survival analysis review. Combining both reviews for the 3 design concepts showed that for every 0.1-mm increase in 2-year subsidence, as measured with RSA, there was a 4% increase in revision rate for the shape-closed stem designs. This association remained after correction for age, sex, diagnosis, hospital type, continent, and study quality. The threshold for acceptable migration of shape-closed designs was defined at 0.15 mm; stems subsiding less than 0.15 mm in 2 years had revision rates of less than 5% at 10 years, while stems exceeding 0.15 mm subsidence had revision rates of more than 5%.

INTERPRETATION

There was a clinically relevant association between early subsidence of shape-closed femoral stems and late revision for aseptic loosening. This association can be used to assess the safety of shape-closed stem designs. The published research is not sufficient to allow us to make any conclusions regarding such an association for the force-closed and uncemented stems.

Early proximal migration of cups is associated with late revision in THA: a systematic review and meta-analysis of 26 RSA studies and 49 survivalstudies

BACKGROUND AND PURPOSE

The association between excessive early migration of acetabular cups and late aseptic revision has been scantily reported. We therefore performed 2 parallel systematic reviews and meta-analyses to determine the association between early migration of acetabular cups and late aseptic revision.

METHODS

One review covered early migration data from radiostereometric analysis (RSA) studies, while the other focused on revision rates for aseptic loosening from long-term survival studies. Thresholds for acceptable and unacceptable migration were classified according the Swedish Hip Arthroplasty Register and the Australian National Joint Replacement Registry: < 5% revision at 10 years.

RESULTS

Following an elaborate literature search, 26 studies (involving 700 cups) were included in the RSA review and 49 studies (involving 38,013 cups) were included in the survival review. For every mm increase in 2-year proximal migration, there was a 10% increase in revision rate, which remained after correction for age, sex, diagnosis, hospital type, continent, and study quality. Consequently, proximal migration of up to 0.2 mm was considered acceptable and proximal migration of 1.0 mm or more was considered unacceptable. Cups with proximal migration of between 0.2 and 1.0 mm were considered to be at risk of having revision rates higher than 5% at 10 years.

INTERPRETATION

There was a clinically relevant association between early migration of acetabular cups and late revision due to loosening. The proposed migration thresholds can be implemented in a phased evidence-based introduction, since they allow early detection of high-risk cups while exposing a small number of patients.

Early migration of tibial components is associated with late revision: a systematic review and meta-analysis of 21,000 knee arthroplasties

PURPOSE

We performed two parallel systematic reviews and meta-analyses to determine the association between early migration of tibial components and late aseptic revision.

METHODS

One review comprised early migration data from radiostereometric analysis (RSA) studies, while the other focused on revision rates for aseptic loosening from long-term survival studies. Thresholds for acceptable and unacceptable migration were determined according to that of several national joint registries: < 5% revision at 10 years.

RESULTS

Following an elaborate literature search, 50 studies (involving 847 total knee prostheses (TKPs)) were included in the RSA review and 56 studies (20,599 TKPs) were included in the survival review. The results showed that for every mm increase in migration there was an 8% increase in revision rate, which remained after correction for age, sex, diagnosis, hospital type, continent, and study quality. Consequently, migration up to 0.5 mm was considered acceptable during the first postoperative year, while migration of 1.6 mm or more was unacceptable. TKPs with migration of between 0.5 and 1.6 mm were considered to be at risk of having revision rates higher than 5% at 10 years.

INTERPRETATION

There was a clinically relevant association between early migration of TKPs and late revision for loosening. The proposed migration thresholds can be implemented in a phased, evidence-based introduction of new types of knee prostheses, since they allow early detection of high-risk TKPs while exposing only a small number of patients.

RSA and registries: the quest for phased introduction of new implants

INTRODUCTION

Although the overall survival of knee and hip prostheses at ten years averages 90%, recent problems with several hip and knee prostheses have illustrated that the orthopaedic community, industry, and regulators can still further improve patient safety. Given the early predictive properties of roentgen stereophotogrammetric analysis (RSA) and the meticulous follow-up of national joint registries, these two methods are ideal tools for such a phased clinical introduction. In this paper, we elaborate on the predictive power of RSA within a two-year follow-up after arthroplasty and its relationship to national joint registries. The association between RSA prosthesis-migration data and registry data is evaluated.

METHODS

The five-year rate of revision of RSA-tested total knee replacements was compared with that of non-RSA-tested total knee replacements. Data were extracted from the published results of the national joint registries of Sweden, Australia, and New Zealand.

RESULTS

There was a 22% to 35% reduction in the number of revisions of RSA-tested total knee replacements as compared with non-RSA-tested total knee replacements in the national joint registries. Assuming that the total cost of total knee arthroplasty is $37,000 in the United States, a 22% to 35% reduction in the number of revisions (currently close to 55,000 annually) could lead to an estimated annual savings of over $400 million to the health-care system.

CONCLUSION

The phased clinical introduction of new prostheses with two-year RSA results as a qualitative tool could lead to better patient care and could reduce the costs associated with revision total knee arthroplasty. Follow-up in registries is necessary to substantiate these results and to improve post-market surveillance.

Hybrid total knee arthroplasty: 13-year survivorship of AGC total knee systems with average 7 years followup

A retrospective study of 201 anatomic graduated component total knee arthroplasties implanted with hybrid fixation at the authors' center was performed in response to conflicting data in the literature concerning the benefits of a hybrid method. Selection for hybrid fixation was nonrandomized and based on femoral component fit. Survivorship analysis was performed, and rates of radiolucent lines surrounding the femoral component and occurrence of osteolysis were noted. At 7 and 13 years, survivorship with tibial or femoral revision as the end point was 0.9926 and 0.9732, respectively. Radiolucencies were found adjacent to 15 femoral components at final followup (seven in Zone 1, three in Zone 2, five in Zone 3, one in Zone 4, two in Zone 5, zero in Zone 6). Osteolysis was observed in one knee after secondary evaluation. Hybrid fixation in a selected patient population can result in excellent results in middle to long-term followup.

Compliant layer acetabular cups: friction testing of a range of materials and designs for a new generation of prosthesis that mimics the natural joint

Total joint replacements (TJRs) have a limited lifetime, but the introduction of components that exhibit good lubricating properties with low friction and low wear could extend the life of TJRs. A novel acetabular cup design using polyurethane (PU) as a compliant layer (to mimic the natural joint) has been developed. This study describes a series of friction tests that have been used to select the most appropriate material, optimize the design parameters, and fine-tune the manufacturing processes of these joints. To determine accurately the mode of lubrication under which these joints operate, a synthetic lubricant was used in all these tests. Friction tests were carried out to assess the lubrication of four PU bearing materials. Corethane 80A was the preferred material and was subjected to subsequent testing. Friction tests conducted on acetabular cups, manufactured using Corethane 80A articulating against standard, commercially available femoral heads, demonstrated friction factors approaching those for full-fluid-film lubrication with only approximately 1 per cent asperity contact. As the joint produces these low friction factors within less than half a walking cycle after prolonged periods of loading, start-up friction was not considered to be a critical factor. Cups performed well across the full range of femoral head sizes, but a number of samples manufactured with reduced radial clearances performed with higher than expected friction. This was caused by the femoral head being gripped around the equator by the low clearance cup. To avoid this, the cup design was modified by increasing the flare at the rim. In addition to this the radial clearance was increased. As the material is incompressible, a radial clearance of 0.08 mm was too small for a cup diameter of 32 mm. A clearance of between 0.10 and 0.25 mm produced a performance approaching full-fluid-film lubrication. This series of tests acted as a step towards the optimization of the design of these joints, which has now led to an in vivo ovine model.

Effect of radiation, heat, and aging on in vitro wear resistance of polyethylene

Radiation cross-linking increases the wear resistance of polyethylene used in total hip replacement. Radiation also generates residual free radicals, which are detrimental to long-term properties of polyethylene. Two approaches are used to stabilize the residual free radicals and terminally sterilize the components. One is postirradiation annealing with gas sterilization and the other is postirradiation melting with gamma sterilization in nitrogen. The hypothesis of the current study is that postirradiation annealing followed by gamma sterilization in nitrogen will result in more free radicals in polyethylene than gamma sterilization either in air or in nitrogen alone. To test this hypothesis, concentration of residual free radicals was quantified in polyethylene that was annealed and gamma sterilized in nitrogen and control polyethylenes gamma sterilized in air versus in nitrogen. Three crosslinked polyethylenes that were melted and gas sterilized also were included in the study. The effects of residual free radicals were studied by accelerated aging. Oxidation levels and weight loss in bidirectional pin-on-disk tests were determined before and after aging. Polyethylene that was subjected to postirradiation annealing and gamma sterilization resulted in 58% more residual free radicals than control polyethylenes. Weight loss of the annealed polyethylene increased by 16-fold on accelerated aging and had three times higher oxidation levels than that measured in control polyethylenes after aging. In contrast, polyethylenes that were stabilized with postirradiation melting and terminally gas sterilized showed no detectable residual free radicals. Accelerated aging did not affect the weight loss and oxidation levels of melted polyethylenes.

Use of explicit criteria for total hip joint replacement fixation techniques

We developed a tool to judge the appropriateness of indications and fixation mechanisms for total hip joint replacement (THJR) and applied it to a sample of patients. Criteria were developed using a modified Delphi panel judgment process, following the RAND methodology (RAM). We recruited, during 1 year, patients with a diagnosis of osteoarthritis undergoing THJR in five public hospitals. The appropriateness of the THJR intervention and the fixation mechanism was judged by the explicit criteria developed by a panel of experts. Of the 216 scenarios scored by the panel for the use of each of three fixation mechanisms, the cemented fixation was considered inappropriate in 69.5%, versus just 33.3% for the non cemented. Of those scenarios considered appropriate, the most appropriate mechanism of fixation was considered to be non cemented (74.4%), while cemented (17.8%) and hybrid (7.8%) scenarios were scored as appropriate less often. The previous explicit criteria were applied to 583 real patients. After evaluation of the interventions, 30% of the fixation mechanisms used were considered appropriate, while 21.8% inappropriate. Appropriate use of fixation mechanisms varied among hospitals. RAM can provide explicit criteria to help in clinical decision making and evaluating indications for a THJR intervention. Nevertheless, in the case of the appropriateness of fixation mechanisms, due to the lack of evidence, the panel criteria were biased towards the non cemented technique, which had important implications for the evaluation of some hospitals.

Innovation and regulation in human implant technologies: developing comparative approaches

Human implant technologies are subject to continual innovation and proliferation, raising important issues for technology testing, healthcare sciences, clinical performance and risk assessment, and regulation. The regulatory environment of medical devices is being shaped by harmonisation of standards in the European Union. The aim of this paper is to compare the histories and current regulatory environment of two technologies, breast implants and artificial hips, and to consider the implications of this comparison for a sociological healthcare research agenda to investigate the issues raised. The main focus is upon developments in the United Kingdom. Major points of contrast between the two technologies include the institutional contexts in which clinical evidence has been marshalled for government attention; the relative importance of strategic alliances between clinicians and manufacturers in the innovation process; the degree of public controversy evident; the varying definitions of an 'adverse incident' within medical device vigilance systems; and in the UK the presence of a national register for breast implants but not for hip implants. Inter-national contrasts in these dimensions are noted. The analysis suggests that improved understanding is required of the institutional, organisational and professional processes involved in implant technology innovation and regulation. A comparative research agenda is proposed, focusing upon: innovativeness and proliferation; safety and technological standards; clinical and social outcomes; and consumer/user information and choice. It is concluded that research in these areas will enhance the 'evidence-base' for the evaluation of human implant technologies in the context of their innovatory and regulatory environments.

Early failure of modern cemented stems

In the late 1970s, improved cement technique was introduced in an attempt to address the problem of early cemented stem loosening. Subsequently, numerous centers reported stem survival rates of >95% beyond 10 years. Long-term cemented stem fixation was believed widely to be consistently obtainable in most patients. Despite the widespread clinical success of these early cemented stems, numerous changes were introduced in stem design and cement technique. In more recent years, a surprising number of series of early failures of cemented stems have been reported. Some designs consistently have had a high early failure rate. Others have failed infrequently, but the failures have occurred early and with extensive osteolysis. Numerous causes have been proposed, including poor cement technique, undersized broaches, increased stem offset, decreased stem length, rough surface finish, and circular stem cross-section. Failures often are multifactorial and defy a simple explanation based on a single parameter. Results of cemented stems are more variable than previously appreciated. There are nuances of cemented stem design, cement technique, and patient selection that can lead to early failure and that are not understood completely at present. Given the availability of many cemented designs with proven records of clinical success, new design features should be introduced prudently with extensive premarket testing, limited clinical release, and careful postmarket surveillance.

Can shared care deliver better outcomes for patients undergoing total hip replacement? A prospective assessment of patient outcomes and associated service use

OBJECTIVES

To assess whether shared care for patients undergoing total hip replacement delivers better outcomes compared to care as usual.

DESIGN

Prospective, observational cohort study.

SETTING

Two regions in The Netherlands where different organisational health care models have been implemented: a shared care setting (experimental group) and a care as usual setting (control group).

PATIENTS

One hundred and fifteen patients undergoing total hip replacement: 56 in the experimental group and 59 in the control group.

MAIN MEASURES

Functional health status according to the sickness impact profile, hip function, patient satisfaction and use of health care services.

RESULTS

Two weeks before hip replacement both groups were comparable concerning patient characteristics, hip function and health status. The mean improvement of the total sickness impact profile score between two weeks before hip replacement and six months after was -1.92 in the shared care group, compared to -5.11 in care as usual group, a difference in favour of the control group (p=0.02). The mean length of hospital stay was comparable in both settings: 12.8 days in the shared care group and 13.2 days in the care as usual group. After hip replacement, compared to care as usual, patients in the shared care group received more homecare, with a higher frequency, and for a longer period of time. No differences in patient satisfaction between the two groups were found.

CONCLUSIONS

Six months after hip replacement, the health status of patients in the care as usual group, using significantly less home care, was better than the status of patients in the shared care group.

DISCUSSION

The utilisation of home care after hip replacement should be critically appraised in view of the need to stimulate patients' independence.

The value of short and simple measures to assess outcomes for patients of total hip replacement surgery

OBJECTIVES

To evaluate the performance of a patient assessed outcome measure, the Oxford Hip Score, in a national study of primary hip replacement surgery.

DESIGN

A survey of patients' health status before undergoing primary hip replacement surgery and three months and one year after surgery.

SETTING

143 hospitals in three NHS English regions.

PATIENTS

7151 patients admitted for primary total hip replacement surgery over a period of 13 months from September 1996.

MAIN MEASURES

For patients, Oxford Hip Score and satisfaction with hip replacement and, for surgeons, American Anesthesiologists' Society (ASA) classification of physical status.

RESULTS

The response rates to the postal questionnaire at three and 12 months follow up were 85.2% and 80.7%, respectively. Including all three administrations of the questionnaire, all except two items of the Oxford Hip Score were completed by 97% or more respondents and only one item at one administration appeared marginally to reduce the reliability of the score. The effect sizes for changes in the score from baseline to three months was 2.50 and to 12 months was 3.05. Patients rated by surgeons as being healthy preoperatively by the ASA classification were somewhat more likely to return a completed questionnaire at three months (79.4% versus 75.3%) and 12 months (72.4% versus 70.3%) than those rated as having poorer health.

CONCLUSIONS

Overall there was little evidence of difficulties for patients in completing the Oxford Hip Score or of unreliable data, except in relation to one questionnaire item. The instrument was very responsive to change over time and score changes for the Oxford Hip Score related well to patients' satisfaction with their surgery. The instrument is an appropriate measure in terms of validity, responsiveness, and feasibility for evaluating total hip replacement from the

Revision hip arthroplasty activity in a single UK health region: an audit of 1265 cases

Revision hip arthroplasty is an operation which is steadily increasing in number and can often be technically challenging. We have utilised a regional hip register (the Trent Regional Arthroplasty Study) to analyse the epidemiology of revision hip arthroplasties in a single UK health region. The study shows that of the large number (1265) of procedures performed over a 7-year period (1991-1997), the majority were performed by general orthopaedic surgeons, with 91 different surgeons performing the operation and only two surgeons performing more than 20 procedures per year. Of more than 100 prosthetic combinations used for the procedure, the Charnley prosthesis was the most common (38.3% of acetabular revisions and 37.5% of femoral revisions). The same component was also the most commonly explanted (43%). There was an even geographical spread across the region with revision hip arthroplasty being performed in all hospitals with an orthopaedic in-patient facility. Prospective audit of this large and varied cohort is necessary to determine differences in outcome (if any) between 'specialist' hip surgeons and general orthopaedic surgeons.

How long should patients be followed-up after total hip replacement? Current practice in the UK

Some 1000 postcard questionnaires were sent to Fellows of the British Orthopaedic Association (BOA) to establish current follow-up practice of primary total hip replacement (THR) patients. For cemented THRs, 50% of surgeons saw their patients for under 1 year, 78% under 5 years with indefinite follow-up being performed by 14%. There was significantly more follow-up of uncemented and hybrid prostheses with the proportions being 25%, 56% and 30% respectively (chi 2, P < 0.0001). This study has revealed a wide variation in practice between individual surgeons and has shown over one-third of surgeons feel they are prevented from performing as much follow-up as they would wish by the availability of clinic resources. Higher follow-up rates of uncemented components may reflect a lack of confidence in their long-term performance.

Economic evaluations in the hip arthroplasty literature: lessons to be learned

Readers are increasingly encountering articles dealing with health economic evaluations that compare various surgical strategies, leaving orthopaedists with the challenge of determining which program is cost-efficient and truly pertains to their setting. This study carries out a systematic review of the literature to appraise the quality, quantity, and type of economic evaluation as it pertains to the hip arthroplasty literature. To identify all relevant articles, we conducted a comprehensive computerized bibliographic search of Medline from 1966 to 1996. This search produced 1,611 abstracts that were screened. Studies that were incorporated met the following inclusion criteria: i) formal economic analysis, ii) an intervention specific to hip arthroplasty, and iii) the perspective of the study was evident (ie, patient, provider, society). These studies were appraised with regards to methodologic soundness based on 8 established economic principles. Only 68 articles from the 138 retrieved met the study criteria. Only 2 of the 68 articles met all 8 criteria of a comprehensive economic evaluation. The hip arthroplasty literature is deficient in methodologically sound economic evaluations. Several guidelines are introduced to aid orthopaedists in appraising the various economic studies, and recommendations are made to improve the quality of these studies in the orthopaedic literature. We suggest that the generation of such information should rank high on the priority list of the orthopaedic profession, granting agencies, and governments.

The costs and benefits of primary total hip replacement. How likely are new prostheses to be cost-effective?

Many new hip prostheses are now available for use in total hip replacement. The majority remain untested relative to standard prostheses; however, many new prostheses are substantially more costly. We examine how much more effective new prostheses must be, in terms of reducing the need for revision operations, in order to justify this increased cost.

Current practice in primary total hip replacement: results from the National Hip Replacement Outcome Project

As part of the National Study of Primary Hip Replacement Outcome, 402 consultant orthopaedic surgeons from three regions were contacted by postal questionnaire which covered all aspects of total hip replacement (THR). There was a 70% response rate of which 71 did not perform hip surgery, a further 33 refused to take part, leaving 181 valid responses. Preoperative assessment clinics were used by 89% of surgeons, but anaesthetists and rehabilitation services were rarely involved at this stage. Of respondents, 99% used routine thromboprophylaxis, with 79% using a combination of mechanical and chemical methods. Of surgeons, 84% routinely used stockings, whereas 95.5% used chemical prophylaxis, 63% employed low molecular weight heparins. Theatre facilities were shared with other surgical specialties by 6% of surgeons and 18% regularly used body exhaust suits for THR. Antibiotic loaded cement was used by 69% of surgeons, the majority (65%) used a single brand of normal viscosity cement with 9% using reduced viscosity formulations. Modern cementing techniques were commonly used at least in part, 87% used a cement gun and 94% a cement restrictor for femoral cementing. On the acetabulum, 47% pressurised the cement. In all, 36 different femoral stems and 35 acetabular cups were in routine use, but the majority of surgeons (55%) used Charnley type prostheses. Of the surgeons, 57% performed only cemented THR, while 3% exclusively used uncemented THR. Of consultants, 21% followed up their patients to 5 years, the majority discharge patients within the first year. Of concern is a large proportion of surgeons using low molecular weight heparins despite a lack of evidence with regard to reducing fatal pulmonary embolism, and also the small number of surgeons using prostheses of unproven value. Third generation cementing techniques have yet to be fully adopted. The introduction of a national hip register could help to resolve some of these issues.

Total hip replacement: a case history

The history of total hip replacement in the U.S. demonstrates that health care providers can reduce costs while improving quality. Nationwide, the cost of total hip replacements has declined dramatically while quality has improved. This article describes 14 clinical and management innovations ranging from patient education to competitive bidding.

The Stanmore total hip arthroplasty. A 15- to 20-year follow-up study

An ongoing study was made of 804 primary Stanmore total hip prostheses implanted in 839 patients between 1973 and 1991. The earliest surviving implants were brought back for radiologic and clinical review in 1995 at an average of 17 years after surgery. The remainder of the patients still living were sent a questionnaire to assess their current status. Survivorship was 95% at 10 years, 85% at 15 years, and 73% at 20 years. The average Merle d'Aubigné-Postel score was excellent up until 14 years. Patient satisfaction remained high until 22 years. Overall, 10% of the prostheses had failed. The results of this study suggest that the Stanmore prosthesis is capable of producing satisfactory long-term results that compare favorably with those of other cemented prostheses.

The problem of 'noise' in monitoring patient-based outcomes: generic, disease-specific and site-specific instruments for total hip replacement

OBJECTIVES

To compare the performance of three types of patient-based health status instrument--generic, disease-specific and site-specific--in assessing changes resulting from total hip replacement (THR).

METHODS

A two-stage prospective study of patients undergoing surgery for THR involving an assessment at a pre-surgical clinic and a follow-up clinic at 6 months. 173 patients with a diagnosis of arthritis and being admitted for unilateral THR were recruited in the outpatient departments of a specialist orthopaedic hospital and peripheral clinics within Oxfordshire. Patients' health status was assessed using the 12-item Oxford Hip Score, the Arthritis Impact Measurement Scales (AIMS) and SF-36 general health questionnaire together with their surgeons' assessment using Charnley hip score obtained before and 6 months after surgery.

RESULTS

Effect sizes, used to compare change scores, revealed that pain and function domains changed most following THR on both the AIMS and the SF-36. 71 patients (41%) were assessed as having symptoms or problems currently affecting lower limb joints other than the hip recently replaced. Change scores were compared between these patients and all other patients who reported no current problems with other joints. The Oxford Hip Score found no significant difference between change scores for these two groups of patients while both AIMS and SF-36 physical and pain dimensions recorded significant differences of similar magnitude (physical P < 0.01, pain P < 0.05). Likely reasons for this were apparent on closer inspection of the item content of each instrument.

CONCLUSIONS

Assessment of outcomes in THR is necessarily long-term. Within studies of this kind, a hip-specific instrument (Oxford Hip Score) is likely to be more able to distinguish between symptoms and functional impairment produced by the index joint, as compared with other joints and conditions, than either a disease-specific instrument (AIMS) or a generic health status measure (SF-36). This is important given the high probability of existing and subsequent co-morbidity affecting such populations of patients. This consideration is likely to be relevant to any long-term assessment programme following treatment for a condition which threatens bilateral expression over time.

Comparison of measures to assess outcomes in total hip replacement surgery

OBJECTIVES

To compare the performance of a disease specific and a general health questionnaire in assessing changes resulting from total hip replacement.

DESIGN

Two stage prospective study of patients undergoing total hip replacement surgery involving an assessment at a clinic before and six months after surgery. 60(32%) patients were followed up by post.

SETTING

Outpatient departments at a specialist orthopaedic hospital and peripheral clinics within Oxfordshire.

PATIENTS

188 patients admitted for unilateral total hip replacement between February and mid-August 1994.

MAIN MEASURES

Patients' self assessed scores with the 12 item Oxford hip score and SF-36 general health questionnaire together with surgeons' assessment with Charnley hip score obtained before and again at six months after surgery.

RESULTS

186 patients were followed up six months after total hip replacement; a subsample (n=60) by post. Of the 60 postal patients, 59(98.3%) fully completed the Oxford hip score compared with 44(73.3%) who fully completed the SF-36. For the followup sample as a whole, post operative changes in scores produced a large effect size of 2.75 on the Oxford hip score, compared with -1.89 physical function (SF-36), -2.13 pain (SF-36). With the exception of physical function and role (physical), postoperative SF-36 scores were shown to be similar to or better than those found by two population surveys on patients of comparable age. The responsiveness of a disease specific questionnaire, the Oxford hip score, and relevant sections of a general questionnaire, SF-36, were found to be similar as assessed by three different criteria.

CONCLUSIONS

A disease specific questionnaire, the Oxford hip score, and a general state of health questionnaire, SF-36, performed similarly in assessing outcomes of total hip replacement except that the disease specific questionnaire resulted in a higher completion rate and greater responsiveness in some sections. On the other hand the general health questionnaire drew attention to broader problems of physical function not considered by the Oxford hip score. The health questionnaires examined here offer a valid and practical means of monitoring outcomes of hip replacement surgery.

Total hip replacement: the way forward

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Roentgen stereophotogrammetric analysis for assessing migration of total hip replacement femoral components

A new Roentgen stereophotogrammetric analysis system, using a biplane technique, has been developed to determine the migration and rotation of total hip replacement (THR) femoral components in three dimensions. Stainless steel marker balls were injected into the femur during the operation. The patients stood within a calibration frame during the X-ray. The two exposures were taken consecutively allowing radio-opaque shutters to be moved in front of the films to prevent fogging. Studies with a model demonstrated that the system was capable of measuring the position of an implant to better than 0.11 mm (2 SD). In vivo measurements demonstrated that the migration rate of the different parts of the femoral component could be determined with an accuracy of 0.25 to 0.50 mm/year. By considering the accuracy determined in different ways, methods for improving the system have been identified. The migration and rotation rate of 58 Hinek cemented femoral components was studied for four years. Migration was three to five times greater (p < 0.001) during the first year than subsequently. The prosthesis head moved the most during the first year (0.94 mm). A better understanding of the cause of implant failure could be obtained by studying the early migration of different types of prosthesis and comparing this with their clinical results and design features.

Orthopaedic and trauma surgery

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Prevalence of total hip replacement: how much demand has been met?

OBJECTIVE

To determine the prevalence of completed elective total hip replacements in a defined elderly population.

DESIGN

Cross sectional postal questionnaire survey with additional data and validation from general practice and hospital records.

SETTING

Six general practices in the English counties of Avon, Somerset, and Oxfordshire.

SUBJECTS

A total of 7806 patients aged 65 years and over (94.7% response).

RESULTS

The overall prevalence (95% confidence intervals) of elective total hip replacement was 5.3 (4.8,5.8)% Age and sex specific prevalences were 2.7 (2.0,3.5)% in men and 4.1 (3.3,4.9)% in women aged 65-74 years, and 5.2 (4.0,6.5)% in men and 8.8 (7.6,10.0)% in women aged 75 years and over. Of the 415 patients who had received elective total hip replacement, 28.2% had required bilateral surgery, 20% had received at least one operation privately, and 13% had required revision surgery.

CONCLUSION

Our results show an increased level of satisfied demand for total hip replacement in elderly people compared with earlier estimates. The increasing prevalence of hip replacement is an indicator of increasing potential demand for revision procedures. Population based surveys are required to establish the level of unmet demand for primary procedures. Differences in past surgical activity may be important in interpreting the wide variation in current surgical rates.