Introduction: Dislocation remains one of the most common orthopaedic complications of hip replacement. Surgical technique, implant design and patient factors have been suggested as risk factors. The 2005 AOA Joint Registry recorded data on 101, 952 hip procedures between 1999 and 2004. We analyzed risk factors for early revision in this group of patients.

Methods: Ethics approval was obtained then a formal application was made to the Australian Joint Registry to release the required data. All primary hip replacements between 1/09/1999 – 31/12/2004 were studied. Statistical analyses of traditional risk factors including initial diagnosis, sex, age and head size were performed. We also studied the effect of fixation method on revision for dislocation.

Results: A total of 65,992 primary hip replacements across all diagnoses groups recorded were investigated with regard to diagnosis. The only initial diagnoses with significantly increased relative risk (RR) of revision for dislocation compared to osteoarthritis was fractured neck of femur (RR 2.25, p< 0.0001) and rheumatoid arthritis (RR 1.9, p< 0.01).

58,109 primary hip replacements for osteoarthritis were investigated for effect of age group, sex and fixation method. Age group and sex were not significant risk factors in revision for dislocation. Studying fixation method, cementless acetabular components were implanted more frequently (49,027, 84%) than cemented (9,082, 15.6%). In total, there were 428 (0.7%) revisions for dislocation, 369(0.8%) with a cementless acetabulum and 59 (0.6%) with cemented. Relative risk (cementless v cemented acetabulum adjusted for age group, sex and head size) of 1.59 (CI 1.19 to 2.12, p< 0.01). Head sizes of > 30mm, 28mm, 26mm and 22mm had significantly increasing relative risk (p< 0.001).

Discussion: The results from this large database indicate rheumatoid patients and those after fractured neck of femur have increased risk of revision for dislocation compared to osteoarthritis. Many of the traditional groups thought to be at higher risk of dislocation were not associated with an increased risk of revision for dislocation. These included age group, sex, avascular necrosis, developmental dysplasia and failed internal fixation. Cementless acetabuli have a higher rate of revision for dislocation. This has not been previously reported. Further investigation is needed to identify the cause of this finding.

Introduction and Aims: Nine countries have established national joint replacement registries. The first population-based national registry, the Swedish Knee Registry, was established in 1975 with the most recent, the UK National Joint Registry (UK NJR), beginning in 2003. We identify commonalities and differences in the structure, function and methods of reporting among these national registries.

Method: Data was collected from the annual reports of the various registries, published literature and personal contact with registry coordinators and directors.

Results: Commonalities include registry ownership, source of funding, procedure types collected, method of data collection and validation of data. Most registries are owned by the national Orthopaedic Association or a government agency. The most common source of funding is government; membership fees and a mandated implant levy are also used. Most national registries collect total hip and knee replacements, primaries and revisions. Hemiarthroplasties are not commonly collected, though some registries collect additional joints (including shoulder, elbow, wrist, finger, ankle and toe). The most common method of data collection is paper-based, usually from theatre, with subsequent data entry at the registry. Electronic data collection is used to supplement the paper-based system in some countries, while the Swedish Hip Registry and the UK NJR utilise a web application for the submission of data. Most registries attempt to validate their data against hospital inpatient data held by government. Differences include reporting of rates, cost per registration and definitions. Failures of primary implants may be reported as cumulative proportions, true incidence rates or survival probabilities. This leads to difficulties in comparison of data among the national registries. The cost of registering a procedure varies up to five-fold across countries.

Conclusion: There are obvious opportunities for collaboration between national joint replacement registries, however some issues need to be addressed. These include definitions of what is collected, for example hemiarthroplasties, and methods of analysis and reporting, especially revision rates.

Introduction and Aim: Following the establishment of the Australian Orthopaedic Association National Joint Replacement Registry, the Australian orthopaedic community has quality prosthesis specific information on knee replacement. This presentation details the demographics of primary total knee replacement, types of prostheses used, methods of fixation and the incidence of, and reasons for, early revision.

Results: Over 36,000 primary total knee replacements with almost 400 subsequent revisions were recorded. Primary total knee replacements were undertaken more commonly in females (56.4%), mostly for osteoarthritis (95.9%), with a mean subject age of 69.6 years.

The Registry recorded 56 different knee prostheses with the 10 most common accounting for 85.5% of all procedures. The patella was not replaced in the majority of cases (58.5%), however this varied considerably with prosthesis type and method of fixation. Cement fixation of the tibial component occurred in 76.9% of cases and the femoral component in 49.5%. Most commonly the insert was fixed (71.3%) and minimally stabilised (86.7%). Posterior stabilised inserts were used in 12.8% of primary cases. The cumulative revision rate at one year was 1.0% and 2.1% at two years. Early revision was minor in 54.1% of cases and major in the remainder. The most common reasons for minor revision were patello-femoral pain (27.1%) and infection (21.7%); for major revision, early loosening (40.2%) and infection (27.5%). Prosthesis type, patella use, method of fixation, degree of constraint and the use of fixed, rotating and/or sliding inserts did not significantly affect revision rates at this early stage.

Conclusion: Although variation is seen in early revision rates depending on the prosthesis type, patella use, method of fixation and other prosthesis specific characteristics, these differences are currently not significant.

Introduction and Aims: The use of resurfacing hip replacements has increased dramatically in recent years. The aim of this study was to compare the early results of this treatment with conventional cemented, cementless and hybrid primary total hip replacement in Australia.

Method: The data used for this report included all conventional primary total hip and resurfacing procedures, as well as any subsequent revisions of those procedures which had been undertaken and reported to the Australian Orthopaedic Association National Joint Replacement Registry (AOA NJRR) before 31 December 2002. Analysis included the determination of demographics, components used and method of fixation. Early revision rates and reasons for failure were also assessed. The AOA NJRR commenced data collection in September 1999 and has had national coverage since 2002, therefore any results reported at this stage are early outcomes.

Results: Almost 33,000 primary total hip replacements were recorded, of these 2130 were resurfacing procedures (6.5%). This proportion of resurfacing was consistent across states with the exceptions of Victoria (11%) and Tasmania (0.6%). Cementless hip replacement was the most common form of primary total hip replacement (41%) with hybrid (34%) and cemented (18.2 %) less common. There was marked state variation in the proportion of cemented and cementless fixation with NSW having a low proportion of cement fixation (4.5%). Early revision rates for cemented conventional primary total hip replacement are significantly less compared to cementless and hybrid hips (cemented v cementless) hazard ratio (adjusted for age and sex) 2.13; 95% CI (1.49, 3.05) p< 0.0001) (cemented v hybrid) hazard ratio (adjusted for age and sex) 1.94; 95% CI (1.37, 2.77) p=0.0002). There was no difference between cementless and hybrid hips. The most common reason for early revision was dislocation and the risk of this was related to head size with larger sizes showing a reduced risk. Although revisions per 100 observed component years were higher for resurfacing hip replacements than for conventional hips (1.73 v 1.18), this difference was not statistically significant. The principal reason for early failure of resurfacing hips was fracture.

Conclusion: The AOA NJRR has identified prosthesis specific differences in early outcomes and failure mechanisms following primary total hip replacement. Continued monitoring of existing and new prostheses will provide surgeons with independent quality information to assist in the selection of the most appropriate prostheses for particular clinical situations.

Introduction and Aims: Austin Moore and Thompson hemiarthroplasties are commonly used for the management of subcapital neck of femur fractures, particularly in the frail elderly. There are no published studies that directly compare the results of these two procedures. The Australian Orthopaedic Association National Joint Replacement Registry (AOA NJRR) has reviewed outcomes for these prostheses.

Method: Data from the AOA NJRR collected from participating hospitals between September 1999 and December 2002 were used to test for differences in revision rates between these two prostheses. Mortality data from the National Death Index were used to censor the time of follow-up and to compare mortality rates following surgery. Further analyses were undertaken to examine the effects of age, gender, diagnosis and regional variation.

Results: The Registry recorded 4080 Austin Moore and 1111 Thompson hemiarthroplasties. Of these, 4023 (98.6%) Austin Moore prostheses were cementless and 1010 (90.9%) Thompsons were cemented. The distributions of age and gender were similar for the two prostheses. There were regional differences in the use of monoblock prostheses during the data collection period. In Victoria, all partial monoblock prostheses used were Austin Moore (N=1560). This contrasts to Queensland and Western Australia where 62.8% and 75.8% respectively of all partial monoblock hip replacements were Thompsons. The cementless Austin Moore prosthesis had a significantly higher rate of revision (122/4023, 3%) than the cemented Thompson prosthesis (9/1010, 0.9%). A Cox model yielded a hazard ratio, adjusted for age and gender, of 3.94 (95% CI: 2.00, 7.76; p < 0.001). None of the 57 cemented Austin Moore and four of the 101 (4%) cementless Thompsons required revision. The cumulative mortality rates for the period to 2001 were similar for the two prostheses (Austin Moore 23.3% and Thompson 24.0%). In the states where sufficient numbers of both types of prostheses were used the difference in outcomes were consistent with the overall results.

Conclusion: The use of the cementless Austin Moore prostheses is associated with an almost four-fold increase in the rate of revision when compared to the cemented Thompson prosthesis.

With increasing primary joint replacement procedures and an ageing population surviving longer, the rate of revision surgery will increase. Revision surgery, however, is associated with increased morbidity and mortality and has a far less successful outcome than primary joint replacement. The mid- to long-term survival rate of the large variety of replacement prostheses remains unknown. Inadequate outcomes data for the majority of prostheses, as well as variability related to different surgical techniques and diagnostic groups, have made it difficult for surgeons to identify the relative effectiveness of different prostheses and treatments. The Federal Government provided funding to the Australian Orthopaedic Association (AOA) to establish the National Joint Replacement Registry (NJRR) in March 1998. The AOA has appointed a committee to manage the Registry and has contracted with the Data Management and Analysis Centre at the University of Adelaide to establish and manage the data systems for the Registry.

The primary aim of the AOA NJRR is to evaluate the effectiveness of different types of joint replacement prostheses and surgical techniques at a national level.

Implementation methods, aspects of database design and early progress in data collection are presented.