Aims

Several different designs of hemiarthroplasty are used to treat intracapsular fractures of the proximal femur, with large variations in costs. No clinical benefit of modular over monoblock designs has been reported in the literature. Long-term data are lacking. The aim of this study was to report the ten-year implant survival of commonly used designs of hemiarthroplasty.

In order to emulate normal knee kinematics more closely and thereby potentially improve wear characteristics and implant longevity the Medial Pivot type knee replacement geometry was designed. In the current study the clinical and radiographic results of 50 consecutive knee replacements using a Medial Pivot type knee replacement are reported; results are compared to the Australian Orthopaedic Associations National Joint Replacement Registry. The patients' data were crossed checked against the registry to see if they had been revised elsewhere. After a mean follow-up of 9.96 years results show that the Medial Pivot Knee replacement provides good pain relief and functional improvement according to KSS and Womac scores and on subjective patient questionnaires. There was one minor revision; insertion of a patella button at 6.64 years FU. There were no major revisions; all implants appeared to be well fixed on standard radiographic examination. While the revision rate for the Medial Pivot knee according to the Australia Joint Registry results is higher compared to all other types of knee replacements in the registry, and to what is reported in the literature on the medial pivot knee, it is not in the current series. Revision rate was similar to what is reported on in the literature, but after a longer follow-up period. However, long term follow-up is required to draw definitive conclusions on the longevity of this type of implant.

Post-operative peri-prosthetic femoral fracture (PO-PPFF) is one of the most relevant complications in primary Total Hip Arthroplasty (pTHA), accountable for a significant clinical and socio-economic burden both in revision and fixation settings. We retrospectively reviewed of our series of 1586 cementless total hip arthroplasty performed between 1999 and 2019 (achieving a minimum of 5-years follow-up) with different short stems. We have observed a cumulative low incidence of PO-PPFF of 0,33% (5 cases): we divided Po-PPFF in two groups: fracture occurred around a short stem (A) and around a standard shortened stem (B), according to French Hip & Knee Classification of Short Stems. Despite the length of observed period (mean follow-up 12 years, min 5 years max 24 years) a total of 1512 cases (mean age at surgery 61 years, max 74, min 40 years) were available to clinical and radiographic follow-up, being this population enrolled in elective surgery clinical protocols. Our data exceed the low incidence of post-operative femoral fracture around bone -preserving previously reported by Kim in 2018 (12 fracture out of 1089 cases:1.1%). No correlation have been observed among occurrence of PO-PPF age of the patient and no fracture occurred around cemented short stems despite patient's characteristics were unfavourable in term of age and bone quality. This result is not unexpected, giving the lower incidence of peri-prosthetic fracture even cemented conventional stems, as reported in all registry and systematic reviews. A similar behaviour was reported in 2020 Australian Joint Registry, where Post-operative periprosthetic femoral fracture showed a steep curve in early period, but remaining firmly below 1% during the following 12 years. Our clinical data seems to confirm previous studies by Jones (conducted on synthetic bone and fresh-frozen cadaveric femurs) where higher fracture angles and higher fracture torque were detected in short hips compared to standard stems

Patients ≤ 55 years have a high primary TKA revision rate compared to patients >55 years. Guided motion knee devices are commonly used in younger patients yet outcomes remain unknown. In this sub-group analysis of a large multicenter study, 254 TKAs with a second-generation guided motion knee implant were performed between 2011–2017 in 202 patients ≤ 55 years at seven US and three European sites. Revision rates were compared with Australian Joint Registry (AOANJRR) 2017 data. Average age 49.7 (range 18–54); 56.4% females; average BMI 34 kg/m2; 67.1% obese; patellae resurfaced in 98.4%. Average follow-up 4.2 years; longest follow-up six years; 27.5% followed-up for ≥ five years. Of eight revisions: total revision (one), tibial plate replacements (three), tibial insert exchanges (four). One tibial plate revision re-revised to total revision. Revision indications were mechanical loosening (n=2), infection (n=3), peri-prosthetic fracture (n=1), and instability (n=2). The Kaplan-Meier revision estimate was 3.4% (95% C.I. 1.7% to 6.7%) at five years compared to AOANJRR rate of 6.9%. There was no differential risk by sex. The revision rate of the second-generation guided motion knee system is lower in younger patients compared to registry controls

Introduction. Patients ≤ 55 years have a high primary TKA revision rate compared to patients >55 years. Guided motion knee devices are commonly used in younger patients yet outcomes remain unknown. Materials and Methods. In this sub-group analysis of a large multicenter study, 254 TKAs with a second-generation guided motion knee implant (Journey II Bi-Cruciate Stabilized Knee System, Smith & Nephew, Inc., Memphis) were performed between 2011–2017 in 202 patients ≤ 55 years at seven US and three European sites. Revision rates were compared with Australian Joint Registry (AOANJRR) 2017 data. Results. Average age 49.7 (range 18–54); 56.4% females; average BMI 34 kg/m. 2. ; 67.1% obese; patellae resurfaced in 98.4%. Average follow-up 4.2 years; longest follow-up six years; 27.5% followed-up for ≥ five years. Of eight revisions: total revision (one), tibial plate replacements (three), tibial insert exchanges (four). One tibial plate revision re-revised to total revision. Revision indications were mechanical loosening (n=2), infection (n=3), peri-prosthetic fracture (n=1), and instability (n=2). The Kaplan-Meier revision estimate was 3.4% (95% C.I. 1.7% to 6.7%) at five years compared to AOANJRR rate of 6.9%. There was no differential risk by sex. Discussion. Reasons for high TKA revision rates in younger patients remain unknown. Conclusion. The revision rate of the second-generation guided motion knee system is lower in younger patients compared to registry controls

At the present time, there is no bearing in total hip arthroplasty that a surgeon can present to a younger and/or more active patient as being the bearing that will necessarily last them a lifetime. This is the driver to offering alternative bearings (crosslinked polyethylene with either a CoCr or ceramic head, resurfacings, and ceramic-on-ceramic) to patients. Each of these bearings has pros and cons, and none has emerged as the clear victor in the ongoing debate. Ceramic-on-ceramic (CoC) bearings have been available for decades. Earlier generation CoC bearings did encounter problems with rare fractures, however, with a greater understanding and improvement in the material, the fracture incidence has been significantly reduced. However, what has emerged in the past few years is an increasing reporting of significant squeaking. The incidence of squeaking, reported in the literature in various series, has varied from less than 1% to over 20%, depending on the definition used. The primary reasons that ceramic-on-ceramic is not truly the articulation of choice for younger patients are: 1) There is absolutely no evidence that this bearing has a lower revision rate. Data from the Australian joint registry actually shows that at 15 years it has a significantly increased rate of revision (7.2%) compared with using a highly crosslinked liner with either a ceramic (5.1%) or a CoCr (6.3%) head; 2) This bearing is by far the most costly bearing on the market. In 2017 with significant constraints on health care systems across the globe, this is a significant concern; 3) This bearing has unique complications including squeaking and both liner and head fracturing. While ceramic-on-ceramic can be considered a viable alternative bearing in total hip arthroplasty, it can be in no way considered the articulation of longevity for the younger patient

There is limited evidence in the literature suggesting that ceramic-on-ceramic (CoC) THA is associated with lower risk of revision for prosthetic joint infection (PJI) than other bearing combinations especially metal-on-polyethylene (MoP) and metal-on-metal (MoM). Pitto and Sedel reported hazard ratios of 1.3 – 2.1 for other bearing surfaces vs. CoC. Of interest, the PJI rate was not significantly lower in the first 6 months, when most infections occur, but only became significant in the long term. While factors such as patient age, fixation, mode, O.R. type, use of body exhaust suits, and surgeon volume were considered in the multivariate analysis, BMI, medical comorbidities, and ASA class were not. This is a major weakness that casts doubt on the conclusion, since those three factors are MAJOR risk factors for PJI AND all three factors are more likely to be unevenly distributed, much more likely present in groups other than CoC. The data was also limited by the fact that it was drawn from a retrospective review of National Registry data, The New Zealand Joint Registry. While similar findings have recently been reported from the Australian Joint Registry, the danger in attributing differences in outcomes to implants alone is possibly the single greatest danger in interpreting registry results. While device design can impact implant survival, other factors such as surgical technique, surgeon, hospital, and especially patient factors have a far greater likelihood of explaining differences in observed results. A recent report from the same New Zealand joint registry reported that obesity, ASA class, surgical approach, and trainee operations all were associated with higher PJI and all would be more likely in non-CoC THAs. Accuracy of diagnosis is also a major concern. Revision for trunnionosis is more common in non-CoC THA and is frequently misdiagnosed as PJI. Numerous non-registry studies and reviews have compared PJI in CoC vs. other bearing and none have concluded than the incidence of PJI differed significantly

At the present time, there is no bearing in total hip arthroplasty that a surgeon can present to a younger and/or more active patient as being the bearing that will necessarily last them a lifetime. This is the driver to offering alternative bearings (crosslinked polyethylene with either a CoCr or ceramic head, resurfacings, and ceramic-on-ceramic) to patients. Each of these bearings has pros and cons, and none has emerged as the clear victor in the ongoing debate. Ceramic-on-Ceramic (CoC) bearings have been available for decades. Earlier generation CoC bearings did encounter problems with rare fractures, however, with a greater understanding and improvement in the material, the fracture incidence has been significantly reduced. However, what has emerged in the past few years is an increasing reporting of significant squeaking. The incidence of squeaking, reported in the literature in various series, has varied from less than 1% to over 20%, depending on the definition used. The primary reasons that Ceramic-on-Ceramic is not truly the articulation of choice for younger patients are:. 1). There is absolutely no evidence that this bearing has a lower revision rate. Data from the Australian joint registry actually shows that at 15 years it has a significantly increased rate of revision (7.2%) compared with using a highly crosslinked liner with either a ceramic (5.1%) or a CoCr (6.3%) head. 2). This bearing is by far the most costly bearing on the market. In 2017 with significant constraints on health care systems across the globe, this is a significant concern. 3). This bearing has unique complications including squeaking and both liner and head fracturing. While Ceramic-on-Ceramic can be considered a viable alternative bearing in total hip arthroplasty, it can be in no way considered the articulation of longevity for the younger patient

There is limited evidence in the literature suggesting that ceramic-on-ceramic (CoC) THA is associated with lower risk of revision for prosthetic joint infection (PJI) than other bearing combinations especially metal-on-poly (MoP) and metal-on-metal (MoM). Pitto and Sedel reported hazard ratios of 1.3 – 2.1 for other bearing surfaces versus CoC. Of interest, the PJI rate was not significantly lower in the first 6 months, when most infections occur, but only became significant in the long term. While factors such as patient age, fixation, mode, OR type, use of body exhaust suits, and surgeon volume were considered in the multivariate analysis, BMI, medical comorbidities, and ASA class were not. This is a major weakness that casts doubt on the conclusion, since those three factors are MAJOR risk factors for PJI AND all three factors are more likely to be unevenly distributed, and much more likely present in groups other than CoC. The data was also limited by the fact that it was drawn from a retrospective review of National Registry data, The New Zealand Joint Registry. While similar findings have recently been reported from the Australian Joint Registry, the danger in attributing differences in outcomes to implants alone is possibly the single greatest danger in interpreting registry results. While device design can impact implant survival, other factors such as surgical technique, surgeon, hospital, and especially patient factors have a far greater likelihood of explaining differences in observed results. A recent report from the same New Zealand joint registry reported that obesity, ASA class, surgical approach, and trainee operations all were associated with higher PJI and all would be more likely in non-CoC THAs. Accuracy of diagnosis is also a major concern. Revision for trunnionosis is more common in non-CoC THA and is frequently misdiagnosed as PJI. Numerous non-registry studies and reviews have compared PJI in CoC vs. other bearings and none have concluded than the incidence of PJI differed significantly

Total knee arthroplasty is a successful procedure with good long-term results. Studies indicate that 15% – 25% of patients are dissatisfied with their total knee arthroplasty. In addition, return to sports activities is significantly lower than total hip arthroplasty with 34% – 42% of patients reporting decreased sports participation after their total knee arthroplasties. Poor outcomes and failures are often associated with technical errors. These include malalignment and poor ligament balancing. Malalignment has been reported in up to 25% of all revision knee arthroplasties, and instability is responsible for over 20% of failures. Most studies show that proper alignment within 3 degrees is obtained in only 70% – 80% of cases. Navigation has been shown in many studies to improve alignment. In 2015, Graves examined the Australian Joint Registry and found that computer navigated total knee arthroplasty was associated with a reduced revision rate in patients under 65 years of age. Navigation can improve alignment, but does not provide additional benefits of ligament balance. Robotic-assisted surgery can assist in many of the variables that influence outcomes of total knee arthroplasty including: implant positioning, soft tissue balance, lower limb alignment, proper sizing. The data on robotic-assisted unicompartmental arthroplasty is quite promising. Cytech showed that femoral and tibial alignment were both significantly more accurate than manual techniques with three times as many errors with the manually aligned patients. Pearle, et al. compared the cumulative revision rate at two years and showed this rate was significantly lower than data reported in most unicompartmental series, and lower revision rates than both Swedish and Australian registries. He also showed improved satisfaction scores at two years. Pagnano has noted that optimal alignment may require some deviation from mechanically neutral alignment and individualization may be preferred. This is also likely to be a requirement of more customised or bi-cruciate retaining implant designs. The precision of robotic surgery may be necessary to obtain this individualised component alignment. While robotic total knee arthroplasty requires further data to prove its value, more precise alignment and ligament balancing is likely to lead to improved outcomes, as Pearl, et al. and the Australian registry have shown. While it is difficult to predict the future at this time, I believe robotic-assisted total knee arthroplasty is the future and that future begins now

My involvement in the DEFENSE side of MoM hip litigation has allowed me the luxury of reflection and continued study of the basic and clinical science and voluminous medical and scientific literature concerning this particular wear couple. Much of what I have learned is relevant to other articular couples, and might help you in your next THR. While useful, in vitro laboratory testing cannot wholly replicate or predict in vivo behavior of a particular wear couple. (Mother Nature always has something new to teach us!). Although MoM implants underwent rigorous pre-market testing and evaluation by the industry and appropriate regulatory approval in both the US and EU, the process cannot assure the clinical safety or success of new designs and materials for all implant recipients. Two year results obtained in pre-market (IDE) studies are of insufficient follow-up for accurate evaluation of the short, and certainly medium, or long-term clinical performance of new materials or designs, as demonstrated by the two year data from the Australian Joint Registry. In certain populations, MoM bearings have performed satisfactorily (to date) in individuals for whom traditional bearings were a poor option. Conclusions. Be conservative. Use appropriate clinical judgment and careful informed consent if you recommend new designs or materials to your patient

It is estimated that 15 % of the population is allergic to metal, most commonly to Nickel, which is a common component of the alloys in most knee and hip arthroplasties. It would therefore be expected that allergy to metal is a frequent form of implant failure – but very little is reported in the literature. With the recent concerns about metal-on-metal bearings and metal ion issues, there has been renewed interest in metal allergy – with the Australian Joint Registry 2010 reporting it as a causative factor in 7 % of Hip Resurfacing revisions. With over 200 BHR and 571 ASR Hip Resurfacing arthroplasties in my series from 2001, I have identified only 1 patient with implant failure due to metal allergy. In 2010 two Total Knee Arthroplasty patients presented with pain and strongly positive Melisa allergy tests – these patients were revised to Titanium coated implants resulting in a complete relief of symptoms. This paper will analyse the problem of metal sensitivity, the investigation and management of the allergic patient who has, or requires, joint arthroplasty

Femoral stems with exchangeable necks are a recent development in hip arthroplasty. They are proposed to be better in restoring offset and leg length while not compromising the fixation in the femoral canal. Few studies have been published on the clinical and functional outcome of modular neck hip system. The Australian Joint registry data was analysed to evaluate the outcome after modular neck hip arthroplasties with the diagnosis of primary osteoarthritis. Only prostheses with data for more than 50 patients were studied. The indications for revision were identified. A comparison of outcomes with conventional hip arthroplasties was done. The analysis confirmed that femoral stems with exchangeable necks have a significantly higher risk of revision compared to all other primary total conventional hip replacement (adj HR=2.13; 95% CI (1.88, 2.42), p<0.001). With the exception of three, all femoral stems with exchangeable necks have a higher rate of revision compared to primary total conventional hip replacement. The three exceptions have a short follow up. There is an increased incidence of revision for loosening and dislocation. The recent registry data suggests that with end point being revision, the outcome of exchangeable neck hips are worse than conventional hips in patients with primary osteoarthritis of hip

AIM. Tibial component design has be been scrutinized in a number of studies in an attempt to improve tibial coverage in total knee arthroplasty. However, very few have controlled for both component rotation and resultant changes to posterolateral tibial tray overhang and posteromedial underhang. We hypothesize that asymmetrical tibial components can provide greater coverage than symmetrical trays without increasing overhang. METHODS. The 6 most commonly used tibial trays on the Australian Joint Registry (2009) were superimposed on MRI slices of normal knees to assess tibial component overhang, underhang and percent coverage. Rotational alignment in this analysis was based upon the line joining the junciton of the medial and middle 1/3 of the patellar tendon and the PCL insertion. RESULTS. The popliteus tendon was on average 1 mm from the posterior tibial cortex. Only 28.2% of all tibial trays showed optimal posterolateral fit and 48.8% were oversized enough to cause popliteus impingement. NexGen symmetric tray had the largest number of optimally fitting trays on the posterolateral corner (33.7%, the difference was significant against the Genesis II and Triathlon only). The asymmetric Genesis II had the largest percentage of overhang greater than 1 mm. All 6 tray designs had over 80% tibial bone coverage. The Genesis II had the greatest amount of coverage at 88% (paired t test, p<0.001 for each comparison). CONCLUSION. Asymmetric trays in the analysis appear to offer improved bone coverage at the expense of tray overhang when compared to symmetric tray designs thus rejecting our hypothesis

We report long-term results of the first non-designer study of the HA coated Unix UKR. 85 consecutive UKR's were carried out between 1998 and 2002 using the Unix cementless HA coated UKR. 7 were lost to follow up, 6 were deceased and 6 had undergone revision. The remainder had a mean follow-up of 10 years (range 8–13). Oxford Knee Scores, WOMAC questionnaire and radiological assessment were carried out. Average age at surgery was 65 years. The mean Oxford Knee Score was 38.56 (13–48) with 67% scoring over 40, the mean WOMAC Score was 20.16 (0–72) with 58% scoring under 15. Survivorship analysis showed a survival rate of 95% with aseptic loosening as the end-point. Radiographic assessment was carried out by the senior author and an independent radiologist and showed lysis around the tibial base plate in 6% of patients with no lysis evident around the central fin region. The Unix UKR has the unique design of a central horizontal fin inserting under the tibial spine. The survivorship results from this study confirm those of Epinette's showing 100% survivorship at 13 years. Australian Joint Registry data shows high revision rates for UKR's mainly due to tibial loosening. Approximately 70% of the force is transmitted through the medial compartment and recreating this in a UKR results in large forces in the antero-medial proximal tibia. Simpson et al found that with either a central fin or HA coating on the lateral wall, the strain levels in the proximal tibia fell by approximately 66%. We feel that the central fin design is key to dissipating large forces throughout the proximal tibia, resulting in low levels of tibial loosening reported in both the Unix UKR series to date

Joint Registries are a valuable resource for defining the survivorship of prostheses and procedures undertaken for the treatment of joint disease. However, the use of this data as a basis for advocating specific implant designs is controversial because of the confounding effects of variations in patient selection, the training, skill and experience of surgeons, and the priorities of individual patients. Despite these challenges, the Australian Joint Registry has utilized its early survivorship data to identify specific designs that are expected to exhibit lower than average durability in the long term. The aim of this study was to assess the accuracy of this practice in identifying implants providing inferior long-term performance. Over the period 2004–8, the Australian Registry identified 48 prosthetic components used in primary THA, HRA, TKA or UKA which exhibited a statistically significant increase in the early revision rate. For each of these components, we compared the rate of revisions per 100 “component-years” when it was first identified by the Registry, to its ultimate fiveyear cumulative survival in 2008. These survival parameters were also compared to average values based on procedure (eg.THR) and fixation method (i.e. cemented, cementless, hybrid). Regression analysis was performed to determine the accuracy of initial relative revisions per 100 OCY as a predictive measure of eventual component revision rate. Five year survival data was available on 30 of the 48 implants identified by the registry. There was a strong correlation (R2=0.9614) between initial revisions per 100 component-years and the 5-yr survival of the identified designs. 29 of 30 designs (97%) exhibited lower than average survivorship at 5 years. Six designs (20%) had failure rates within 2% of average values, and 7 (23%) had a 5–year failure rate less than 50% above average values. Although, when identified by the Registry, 80% of identified components exceeded the average rate of revision by 100%, only 60% displayed more than twice the cumulative revision rate at 5 years post-op. These results demonstrate that early data collected by Joint Registries can form the basis of accurate identification of designs which ultimately prove to be clinically unsuccessful. Predictions made by the Australian Registry concerning inferior designs have an accuracy of approximately 80%. Further work is recommended to enhance the valuable potential of Registry data in predicting the outcome of both implants and procedures

Introduction: The ten-year survivorship of Oxford Unicompartmental Knee Arthroplasty (OUKA) has ranged from 98% in the hands of the developers to only 82–90% in reports from independent centers and national registries. This study was performed to investigate the effects of surgeon training and correct patient selection on the expected outcome of this procedure. Methods: We created a computer-simulated joint registry consisting of 20 surgeons who performed OUKA on 1,000 patients. Mathematical models of the patient and surgeon populations and corresponding hazard functions were formulated using data from the Swedish and Australian joint registries. The long-term survivorship of UKA was assumed to average 94% at 10 years and was modeled as the product of hazard functions quantifying risk factors under the surgeon’s control, risk factors presented by the patient, and the inherent revision risk of the procedure. We performed four simulations looking at the effect of surgeon training by pairing surgeons and patients based on surgeon experience and patient risk factors. Results: When experienced surgeons (> 40 cases) performed OUKA on low risk patients (bottom quintile), the revision rate dropped from 6.0% to 4.5%. The same surgeons had a revision rate of 7.5% when assigned to the highest risk patient group (top quintile). Conversely, when the least experienced surgeons (< 10 cases) selected the least fit patients, the revision rate increased from 6% to 8.25%. However, when these surgeons were assigned to the lowest risk group, only 5.25% of patients were revised. Taken simultaneously, these results indicate that the overall revision rate of this procedure can vary between 4.5% to 8.25%, depending upon the experience of the surgeon and the patients selected. Conclusions:. Mathematical models of patients and surgeons can be built using joint registry data. These models can then be used in a computer simulation yielding results comparable to what has been reported in the literature. The outcome of Oxford UKA is primarily determined by the skill of the surgeon in selecting suitable patients rather than operative experience. Attempts to expand indications for new procedures should be moderated by concerns that the favorable results from pioneering centers may be due to the judgment and experience of the developers as much as their technical skill in performing the procedure

Introduction: Although Hip Resurfacing Arthroplasty (HRA) has become a popular alternative to THR, the outcome of these procedures varies extensively between centres. This has been attributed to variations in patient selection, surgical experience, and patient volume. In this study we examine the effect of hospital volume on the outcome of hip resurfacing using a national database. Methods: We examined data collected by the Australian Joint Registry between September 1999 and December 2006 relating to 8945 hip resurfacing procedures performed in 196 hospitals. Survivorship of the implanted components was calculated with revision as the end-point. The cumulative rate of revision at 4 years was compared between hospitals as a function of the number of cases performed during the study period (< 25, 25–49, 50–100, > 100 procedures). Using the log-rank test, differences in the risk of revision, corrected for age and sex of patients, were compared for low (< 25 cases) vs. higher volume centres (> 25 cases). We also estimated the number of cases/year of each centre and examined its apparent impact on revision rate. Results: The majority (74%) of hospitals reporting performed less than 30 resurfacing procedures over the 7 year study period, with 64% of procedures performed at 16 “high volume” hospitals (> 100 cases), Overall, 249 of the 8945 resurfacing procedures (2.9%) were performed for revision of the original components. At 4 years, the cumulative revision rate dropped from 5.8% for hospitals performing less than 50 cases to 4.7% (50–99 cases) and 2.7% (> 100 cases) for larger volume centres. When adjusted for differences in patient age and sex, the risk of revision was 66% higher in hospitals performing < 25 cases. Based on the available data, the gap in revision rate between high and low volume centres is reduced by 50% once a surgeon’s operative volume exceeds 6 cases per year. On average, this corresponds to a learning curve of approximately 5 cases. Conclusions: In this study, hospital volume is primarily a reflection of the operative experience of individual surgeons. Our results show that the outcome of hip resurfacing is strongly dependent on the experience of the surgeon and hospital performing the procedure. Even when adjusted for age and sex of the patients, the risk of revision increased by 66% when cases were performed at low volume centres. This supports the need for increased training of surgeons before undertaking hip resurfacing

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

While Oxidized Zirconium (OxZr) femoral heads matched with highly cross-linked polyethylene (XLPE) have demonstrated the lowest rate of revision compared to other bearing couples in the Australian National Joint Registry, it has been postulated that these results may, in part, be due to the fact that a single company offers this bearing option with a limited combination of femoral and acetabular prostheses. The purpose of this study was to assess clinical and radiographic outcomes in a matched cohort of total hip replacements (THR) utilizing an identical cementless femoral stem and acetabular component with either an Oxidized Zirconium (OxZr) or Cobalt-Chrome (CoCr) femoral heads at a minimum of 10 years follow-up. We reviewed our institutional database to identify all patients whom underwent a THR with a single cementless femoral stem, acetabular component, XLPE liner and OxZr femoral head with a minimum of 10 years of follow-up. These were then matched to patients who underwent a THR with identical prosthesis combinations with CoCr femoral head by gender, age and BMI. All patients were prospectively evaluated with WOMAC, SF-12 and Harris Hip Score (HHS) preoperatively and postoperatively at 6 weeks, 3 months, 1 and 2 years and every 2 years thereafter. Charts and radiographs were reviewed to determine the revision rates and survivorship (both all cause and aseptic) at 10 years for both cohorts. Paired analysis was performed to determine if differences exist in patient reported outcomes. There were 208 OxZr THRs identified which were matched with 208 CoCr THRs. There was no difference in average age (OxZr, 54.58 years, CoCr, 54.75 years), gender (OxZr 47.6% female, CoCr 47.6% female), and average body max index (OxZr, 31.36 kg/m2, CoCr, 31.12 kg/m2) between the two cohorts. There were no significant differences preoperatively in any of the outcome scores between the two groups (WOMAC (p=0.449), SF-12 (p=0.379), HHS(p=0.3718)). Both the SF12 (p=0.446) and the WOMAC (p=0.278) were similar between the two groups, however the OxZr THR cohort had slightly better HHS compared to the CoCr THR cohort (92.6 vs. 89.7, p=0.039). With revision for any reason as the end point, there was no significant difference in 10 years survivorship between groups (OxZr 98.5%, CoCr 96.6%, p=0.08). Similarly, aseptic revisions demonstrated comparable survivorship rates at 10 year between the OxZr (99.5%) and CoCr groups (97.6%)(p=0.15). Both THR cohorts demonstrated outstanding survivorship and improvement in patient reported outcomes. The only difference was a slightly better HHS score for the OxZr cohort which may represent selection bias, where OxZr implants were perhaps implanted in more active patients. Implant survivorship was excellent and not dissimilar for both the OxZr and CoCr groups at 10 years. Therefore, with respect to implant longevity at the end of the first decade, there appears to be no clear advantage of OxZr heads compared to CoCr heads when paired with XLPE for patients with similar demographics. Further follow-up into the second and third decade may be required to demonstrate if a difference does exist