Abstract

Abstract

Cobalt chrome alloy is commonly used in joint replacement surgery. However, it is recognised that some patients develop lymphocyte mediated delayed type hypersensitivity (DTH) responses to this material, which may result in extensive bone and soft tissue destruction.

Phase 1. United Kingdom: From an existing database, we identified extreme phenotype patient groups following metal on metal (MoM) hip resurfacing or THR: ALVAL with low wearing prostheses; ALVAL with high wear; no ALVAL with high wear; and asymptomatic patients with implants in situ for longer than ten years. Class I and II HLA genotype frequency distributions were compared between these patients’ groups, and in silico peptide binding studies were carried out using validated methodology.

Phase 2. United Kingdom: We expanded the study to include more patients, including those with intermediary phenotypes to test whether an algorithm could be developed incorporating “risk genotypes”, patient age, sex and metal exposure. This model was trained in phase 3.

Phase 3. United Kingdom, Australia, United States. Patients from other centres were invited to give DNA samples. The data set was split in two. 70% was used to develop machine learning models to predict failure secondary to DTH. The predictions were tested using the remaining blinded 30% of data, using time-dependent AUROCs, and integrated calibration index performance statistics.

A total of 606 DNA samples, from 397 males and 209 female patients, were typed. This included 176 from patients with failed prostheses, and 430 from asymptomatic patients at a mean of >10 years follow up. C-index and ROC(t) scores suggested a high degree of discrimination, whilst the IBS indicated good calibration and further backed up the indication of high discriminatory ability. At ten years, the weighted mean survival probability error was < 4%.

At present, there are no tests in widespread clinical use which use a patient's genetic profile to guide implant selection or inform post-operative management. The algorithm described herein may address this issue and we suggest that the application may not be restricted to the field of MoM hip arthroplasty.

Introduction

We aimed to identify genes associated with the development of ALVAL at relatively low levels of wear.

Background

Some reports have suggested that debris generated from the head neck taper junction is more destructive than equivalent doses from metal bearing surfaces.

Introduction

Historical studies have reported incidences of taper corrosion in retrieved MoP hips of 20–50%. These studies relied on visual assessments, rather than using modern analytical techniques.

Introduction

In this study, we aimed to investigate the effect of the topography of the female taper surface on taper wear.

Background

Previous studies have suggested that the modular junction of metal on metal (MoM) total hip replacements (THR) is an important source of metallic debris.

Background

We have previously described the relationship between wear rates of MOM components and soft tissue necrosis. In this study we investigated the link between wear rates, metal ion concentrations and osteolysis.

Introduction

Total hip prostheses which use a ceramic head within a metal liner are a relatively recent innovation. As such, survivorship rates from independent centres alongside explant analysis are rare. The early clinical experience with this novel ceramic-on-metal (CoM) bearing couple is reported alongside explant analysis of failed devices.

INTRODUCTION

A detailed clinical examination and investigations are required to evaluate the cause of persisting groin pain following a metal on metal (MoM) hip replacement. Adverse reaction to metallic debris (ARMD) is an emerging problem with MoM hip replacements. It is an umbrella term encompassing metallosis, pseudo-tumors and aseptic lymphocytic vasculitis associated lesions (ALVAL). The role of imaging in the diagnosis of this complex problem is still unclear. A study was undertaken to evaluate the efficacy of ultrasound in diagnosis of ARMD following a MoM hip replacement.

Background

The failure and subsequent withdrawal of the ASR device in both its resurfacing and THR form has been well documented. The National Joint Registry report of 2010 quoted figures of 12–13% failure at five years. Adverse reaction to metal debris (ARMD) is a poorly understood condition and patients developing severe metal reactions may go unrecognised for sometime.

Introduction

Adverse reaction to metal debris (ARMD) is an increasingly recognised complication of metal-on-metal hip arthroplasty. A previous study described poor results following revision and recommended early intervention¹. We determined the outcome of revision for ARMD and present the largest case series to date.

Metal-on-metal hip resurfacing prostheses are a relatively recent intervention for relieving the symptoms of common musculoskeletal diseases such as osteoarthritis. While some short term clinical studies have offered positive results, in a minority of cases there is a recognised issue of femoral fracture, which commonly occurs in the first few months following the operation. This problem has been explained by a surgeon's learning curve and notching of the femur but, to date, studies of explanted early fracture components have been limited.

Tribological analysis was carried out on fourteen retrieved femoral components of which twelve were revised after femoral fracture and two for avascular necrosis (AVN). Eight samples were Durom (Zimmer, Indiana, USA) devices and six were Articular Surface Replacements (ASR, DePuy, Leeds, United Kingdom). One AVN retrieval was a Durom, the other an ASR. The mean time to fracture was 3.4 months. The AVNs were retrieved after 16 months (Durom) and 38 months (ASR).

Volumetric wear rates were determined using a Mitutoyo Legex 322 co-ordinate measuring machine (scanning accuracy within 1 micron) and a bespoke computer program. The method was validated against gravimetric calculations for volumetric wear using a sample femoral head that was artificially worn in vitro. At 5mm³, 10mm³, and 15mm³ of material removal, the method was accurate to within 0.5mm³. Surface roughness data was collected using a Zygo NewView500 interferometer (resolution 1nm).

Mean wear rates of 17.74mm³/year were measured from the fracture components. Wear rates for the AVN retrievals were 0.43mm³/year and 3.45mm³/year. Mean roughness values of the fracture retrievals (PV = 0.754, RMS = 0.027) were similar to the AVNs (PV = 0.621, RMS = 0.030), though the AVNs had been in vivo for significantly longer.

Theoretical lubrication calculations were carried out which found that in both AVN retrievals and in seven of the twelve cases of femoral fracture the roughening was sufficient to change the lubrication regime from fluid film to mixed. Three of these surfaces were bordering on the boundary lubrication regime. The results show that even before the femoral fracture, wear rates and roughness values were high and the implants were performing poorly.

Introduction

We conducted independent wear analysis of retrieved metal on metal (MoM) hip components from around the world. All patients with resurfaced hips who developed adverse reactions to metal debris (ARMD) were found to have increased wear of the bearing surfaces. This was untrue in patients with large diameter (?36mm) MoM total hip replacements. This led us to search for other factors leading to ARMD.

Introduction

Total hip prostheses which use a ceramic head within a metal liner are a relatively recent introduction. As such, survivorship rates from independent centres alongside explant analysis are rare. The early experience with this novel ceramic-on-metal (CoM) bearing couple is reported.

Background

The worldwide withdrawal of the DePuy Articular Surface Replacement (ASR) device in both its resurfacing and total hip replacement (THR) form on 26 August 2010, after 93,000 were implanted worldwide, has had major implications. The 2010 National Joint Registry for England and Wales quoted figures of 12-13% failure at five years; however these figures may be an underestimate.

Metal-on-metal hip resurfacing prostheses are a relatively recent intervention for relieving the symptoms of common musculoskeletal diseases such as osteoarthritis. While some short term clinical studies have offered positive results, in a minority of cases there is a recognised issue of femoral fracture, which commonly occurs in the first few months following the operation. This problem has been explained by a surgeon's learning curve and notching of the femur but, to date, studies of explanted early fracture components have been limited.

Tribological analysis was carried out on fourteen retrieved femoral components of which twelve were revised after femoral fracture and two for avascular necrosis (AVN). Eight samples were Durom (Zimmer, Indiana, USA) devices and six were Articular Surface Replacements (ASR, DePuy, Leeds, United Kingdom). One AVN retrieval was a Durom, the other an ASR. The mean time to fracture was 3.4 months. The AVNs were retrieved after 16 months (Durom) and 38 months (ASR).

Volumetric wear rates were determined using a Mitutoyo Legex 322 co-ordinate measuring machine (scanning accuracy within 1 micron) and a bespoke computer program. The method was validated against gravimetric calculations for volumetric wear using a sample femoral head that was artificially worn in vitro. At 5mm3, 10mm3, and 15mm3 of material removal, the method was accurate to within 0.5mm3. Surface roughness data was collected using a Zygo NewView500 interferometer (resolution 1nm).

Mean wear rates of 17.74mm3/year were measured from the fracture components. Wear rates for the AVN retrievals were 0.43mm3/year and 3.45mm3/year. Mean roughness values of the fracture retrievals (PV = 0.754nm, RMS = 0.027nm) were similar to the AVNs (PV = 0.621nm, RMS = 0.030nm), though the AVNs had been in vivo for significantly longer.

Theoretical lubrication calculations were carried out which found that in both AVN retrievals and in seven of the twelve cases of femoral fracture the roughening was sufficient to change the lubrication regime from fluid film to mixed. Three of these surfaces were bordering on the boundary lubrication regime. The results show that even before the femoral fracture, wear rates and roughness values were high and the implants were performing poorly.

Wear debris induced osteolysis is a recognized complication in conventional metal-on-polyethylene hip arthroplasty. One method of achieving wear reduction is through the use of metal-on-metal articulations. One of the latest manifestations of this biomaterial combination is in designs of hip resurfacing which are aimed at younger, more active patients. But, do these metal-on-metal hip resurfacings show low wear when implanted into patients?

Using a Mitutoyo Legex 322 co-ordinate measuring machine (scanning accuracy less than 1 micron) and a bespoke computer program, volumetric wear measurements for retrieved Articular Surface Replacements (ASR, DePuy) metal-on-metal hip resurfacings were undertaken. Measurements were validated against gravimetric calculations for volumetric wear using a sample femoral head that was artificially worn in vitro. At 5mm3, 10mm3, and 15mm3 of material removal, the method was shown to be accurate to within 0.5mm3.

Thirty-two femoral heads and twenty-two acetabular cups were measured. Acetabular cups exhibited mean volumetric wear of 29.00mm3 (range 1.35 - 109.72mm3) and a wear rate of 11.02mm3/year (range 0.30 - 63.59mm3/year). Femoral heads exhibited mean wear of 22.41mm3 (range 0.72 - 134.22mm3) and a wear rate of 8.72mm3/year (range 0.21 - 31.91mm3/year). In the 22 cases where both head and cup from the same prosthesis were available, mean total wear rates of 21.66mm3/year (range 0.51 - 95.50mm3/year) were observed.

Revision was necessitated by one of five effects; early femoral neck fracture (4 heads), avascular necrosis (AVN) (2 heads, 1 cup), infection (1 head, 1 cup), adverse reaction to metal debris (ARMD) (19 heads, 18 cups) or ARMD fracture (6 heads, 2 cups). Mean paired wear rates for the AVN and infection retrievals were 0.51mm3/year and 3.98mm3/year respectively. In vitro tests typically offer wear rates for metal-on-metal devices in the region of 2-4mm3.

Mean paired wear rates for ARMD and ARMD fracture were 17.64mm3/year and 68.5mm3/year respectively, significantly greater than those expected from in vitro tests. In the 4 cases of early fracture, only the heads were revised so a combined wear rate calculation was not possible. The heads exhibited mean wear rate of 8.26mm3/year. These high wear rates are of concern.

Introduction

Total knee replacements (TKR) are among the commonest operations performed in orthopaedic practice. Literature review showed that 10-30% of patients who underwent TKR needed 1-3 units of blood.

Tranexamic acid (TXA) has been popularised as an effective way to reduce blood loss and subsequent blood transfusion.

Our aim was to investigate the value of TXA in reducing blood loss and blood transfusion after TKR and other clinical outcomes such as deep venous thrombosis (DVT), pulmonary embolism (PE), ischaemic heart diseases and mortality.

Bearing diameter and acetabular component orientation have been shown to be important variables effecting blood metal ion levels following hip resurfacing arthroplasty. So far no studies on bilateral hip resurfacings have taken into account these variables.

We examined the serum ion results of patients under the care of two experienced hip resurfacing surgeons who carry out ion analysis as part of routine post operative care. Surgeon 1: Patients were implanted exclusively with a “third generation” resurfacing device. Surgeon 2: Patients were implanted with the same “third generation” device and also a low clearance “fourth generation” resurfacing device. Only ion results from patients who were 12 months post surgery were included. Bilateral patients were matched to unilateral patients according to the surgeon performing the operation; the resurfacing system implanted and cup inclination and anteversion angles. The ion data from each bilateral group was tested against the corresponding unilateral groups using the Mann Whitney U test for non parametric data. Significance was drawn at p<0.05.

Surgeon 1: There were 310 patients with unilateral joints and 50 with bilateral joints. There were no significant differences with regard to time to follow up, activity levels, joint sizes or cup orientations. Serum chromium (Cr) and cobalt (Co) concentrations were significantly greater in the bilateral group (p<0.001). Median ion levels were greater in the bilateral group by a factor of >2 in the smallest joint sizes and <2 in the largest joints. Surgeon 2: There were 11 patients with bilateral third generation resurfacing joints and 50 with unilateral joints of the same design. The same relationship as described above was identified. There was a notable difference in the fourth generation implant group (n=13 bilateral, n=100 unilateral). Median ion levels for patients receiving bilateral joints of sizes <47mm were ten times greater than in the corresponding unilateral group.

Bearing diameter and component design are critical factors in determining metal ion levels following bilateral hip resurfacings. Surgeons must consider the potential implications of gross increases in metal ion levels prior to performing bilateral hip resurfacings in smaller patients.

Objectives

To investigate the value of tranexamic acid (TA) in reducing blood loss and blood transfusion after TKR and other clinical outcomes such as deep venous thrombosis (DVT), pulmonary embolism (PE), ischaemic heart diseases and mortality.

PURPOSE OF STUDY

20-70% of patients need blood transfusion postoperatively. There remain safety concerns regarding allogenic blood transfusion. Tranexamic acid (TA) is a synthetic antifibrinolytic agent that has been successfully used to stop bleeding in other specialties. We applied TA topically prior to the wound closure to find out the effect on blood loss as well as need for subsequent blood transfusion. This method of administration is quick, easy, has less systemic side effect and provides a higher concentration at the bleeding site.

We conducted a systematic review and meta-analysis of randomised controlled trials evaluating the effect of tranexamic acid (TXA) upon blood loss and transfusion in primary total knee replacement. The review used the generic evaluation tool designed by the Cochrane Bone, Joint and Muscle Trauma Group. A total of 19 trials were eligible: 18 used intravenous administration, one also evaluated oral dosing and one trial evaluated topical use. TXA led to a significant reduction in the proportion of patients requiring blood transfusion (risk ratio (RR) 2.56, 95% confidence interval (CI) 2.1 to 3.1, p < 0.001; heterogeneity I² = 75%; 14 trials, 824 patients). Using TXA also reduced total blood loss by a mean of 591 ml (95% CI 536 to 647, p < 0.001; I² = 78%; nine trials, 763 patients). The clinical interpretation of these findings is limited by substantial heterogeneity. However, subgroup analysis of high-dose (> 4 g) TXA showed a plausible consistent reduction in blood transfusion requirements (RR 5.33; 95% CI 2.44 to 11.65, p < 0.001; I² = 0%), a finding that should be confirmed by a further well-designed trial. The current evidence from trials does not support an increased risk of deep-vein thrombosis (13 trials, 801 patients) or pulmonary embolism (18 trials, 971 patients) due to TXA administration.

Background: There is a paucity of published data with regard to the wear of failed metal on metal (MoM) resurfacing devices.

Materials and Methods: MoM components retrieved from patients from two independent centres experiencing failure secondary to ARMD were analysed using a Mitutoyo Legex 322 coordinate measuring machine (CMM) which has an accuracy of 0.8 microns. Between 4000 – 6000 points were taken on each explant, dependent on the size of the bearing surface. Maximum wear depths and total volumetric wear were calculated. These values were compared to those from control samples retrieved following uncomplicated fractures/femoral collapse secondary to avascular necrosis (after calculating equivalent yearly wear rates).

Results: 58 ARMD components were analysed. This included 22 36mm MoM THRs (DePuy Pinnacle), 28 DePuy ASRs and 8 Zimmer Duroms. There were 30 resurfacing fracture/avascular necrosis controls. Volumetric wear rates and maximum wear depths of ARMD resurfacing components were significantly greater than the resurfacing control group for both the ASR and Duroms (p< 0.05) however 2 ARMD components exhibited similar amounts of wear compared to controls. Wear rates of the ARMD THR group were significantly lower than the ARMD resurfacing group (p< 0.05).

Conclusions: Increased articular wear is associated with an increased incidence of local adverse effects including tissue necrosis, joint effusions and fractures. However, there are a minority of patients who can develop tissue necrosis in the absence of accelerated wear, implying a spectrum of sensitivity This is reflected in the incidence of ARMD in the patient groups at the main study centre: > 5% in the ASR group and approx 1% in the THR group. We believe this indicates a failure of adequate lubrication and the resultant negative effects in larger bearing devices.

Background: Definitive cup position for the reduction of blood metal ion levels has yet to be established.

Methods: Samples for serum metal ion analysis are taken routinely from patients under the care of the two senior authors of this paper. Both are high volume experienced hip resurfacing surgeons, one based in England, the other in Belgium. Metal ion results from two centres from patients with unilateral joints were correlated to size and orientation of femoral and acetabular components, UCLA activity score, age, time post surgery and post operative femoral head/neck ratios. EBRA software was used to assess cup inclination and anteversion on standing radiographs.

Cup orientation in vivo was compared to explant analysis of 60 retrieved resurfacing components using a coordinate measuring machine.

Results: Three resurfacing devices were studied. There were 620 results in total. Only femoral size and cup inclination/anteversion were found to have any effect on ion levels. In all devices, metal ion levels were inversely related to femoral size (p< 0.05). The device providing the smallest acetabular coverage arc was associated with the highest metal ion levels. Consistent throughout the implants, lowest ion levels were associated with cups with radiological inclination of 40–50° and anteversion 10–20°. Cup inclination angles lower than 40° were associated with posterior edge loading and likely sub-luxation of the femoral component.

Conclusion: The greater the coverage angle provided by the acetabular component, the greater the tolerance to suboptimal position. Lowest ion levels were found in well positioned lower clearance devices. Cup inclination/ante-version angles of 45/15+/−5° were associated with low ion levels in all three devices. We do not recommend cups to be placed with inclination angles below 40°.

Background: Blood metal ion levels have been shown to correlate with wear of retrieved components. Increased articular wear is associated with early failure. It is not clear what the management of patients with raised metal ions who remain asymptomatic should be.

Methods: A prospective study of the DePuy ASR resurfacing device was commenced in 2004 at our independent centre. Blood and serum metal ion analysis is carried out routinely. We assessed the clinical outcome of all patients with cobalt (Co) concentrations > 5μg/L (n=25). We consider this value to be a clear indicator of a poorly performing bearing surface. Patients who remained asymptomatic were brought back for repeat ions testing and clinical assessment. A parallel study was carried out to examine the relationship between the wear depth of retrieved explants (assessed using a coordinate measuring) and blood ion levels

Results: Increases in chromium(Cr) and Co levels from the second blood sample correlated with the first sample (p< 0.05). The four patients with the highest Cr Co levels went on to suffer spontaneous femoral neck fractures between 3 and 4 years post op (pseudotumours in two of these cases). Of the remaining 25, 5 were revised for worsening pain (large effusions and areas of tissue necrosis were seen at revision) and 10 were under investigation for new onset of pain. Wear depths correlated well with blood ion concentrations (p< 0.05) substantiating the results of another centre.

Conclusion: 60% of patients with raised metal ion levels went on to develop complications within two years of the blood test. This suggests patients may only have temporary tolerances to excessive concentrations of metal wear debris. One novel association appears to be spontaneous delayed femoral fracture. Results suggest increased ion concentrations associated with small joint size/sub optimal cup orientation will continue to rise and these patients should be followed up closely.

This report documents the clinical and histological findings, the operative management and the explant analyses of patients with early aseptic failure of large metal-on-metal (MonM) bearing joints.

Three hundred and fifty patients have been implanted with the ASR bearing surface (resurfacing or a modular THR) by a single surgeon at an independent centre since 2004. Six patients (all female) have been revised secondary to aseptic failure. All complained of severe groin pain exacerbated by straight leg raise and routine investigations were unable to establish a cause. Large amounts of sterile, highly viscous green fluid were aspirated from the hip joints in each case. Gross swelling of the pseudocapsule and a similar green fluid surrounding the implants were found at revision surgery. Histological examination of periprosthetic tissue samples showed changes consistent with ALVAL/metallosis, and analysis of the fluid revealed dense numbers of inflammatory cells. Symptoms in patients revised to ceramic-on-ceramic bearings improved post operatively. This was not the case with those reimplanted with MoM joints. Data from a subset of 76 patients (all unilateral resurfacings) showed that malaligned cups (anteverted > 20° +/− inclination angle > 45°) were associated with significantly higher whole blood metal ion levels than cups positioned within this range. All the patients with early aseptic failure had malaligned cups. Independent explant analysis revealed significant increases in the surface roughness values of the articular surfaces.

Our results suggest that some patients develop a significant inflammatory reaction to metal implants. This may be due to high levels of metal debris around the implant as a result of accelerated wear. Poor component alignment was found in all our patients with early aseptic failure.

Metal ion concentrations following metal on metal hip resurfacing arthroplasty remain a concern. Variables associated with increased metal ion concentrations need to be established. This study provides metal ion data from a consecutive cohort of the first 76 patients implanted with a fourth generation hip resurfacing prosthesis.

All patients agreed to post-operative blood metal ion sampling at a minimum of one year. Post-operative radiographic measurements of cup inclination and anteversion were obtained using the EBRA software. Mean whole blood chromium (Cr) and cobalt (Co) concentrations in patients receiving the smallest femoral implants (Ł51mm) were greater than in the patients implanted with the largest prostheses (ł53mm) by a factor of 3 and 9 respectively. Ion concentrations in the small femoral group were significantly related to acetabular inclination (R=0.439, P< 0.001 for Cr, R=0.372, P=0.004 for Co) and anteversion (R=0.330, P=0.010 for Cr, R=0.338, P=0.008 for Co). This relationship was not significant in the large implant group. Mean Cr and Co concentrations in patients with accurately orientated cups (inclination < 45°, anteversion < 20°) were 3.7μg/l and 1.8 μg/l respectively, compared to 9.1μg/l and 17.5μg/l in malaligned cups.

A reduced surface contact area caused by cup malalignment may increase contact stresses, resulting in a high wear rate if fluid film lubrication is inadequate. Improved fluid film lubrication has previously been found in larger heads in vitro. Accurate acetabular component positioning is essential in order to reduce metal ion concentrations following hip resurfacing.

Since the era of total knee replacement (TKR) began in the late 1960s, total knee replacement has become one of the commonest operations in orthopaedic practice.

TKR is frequently associated with transfusion of allogenic blood Benoni G 1995; Seppo T 1997. In our centre, 30 % of patients who had undergone TKR received allogenc blood transfusion perioperatively. Although, serological screening has reduced the risk for viral infection to a very low levelKlein HG 1995; Schreiber GB 1996, the public is still concerned about this potential serious complication. Allogenic blood transfusion can be also associated with other non infectious complications such as haemolysis, immunosuppression, transfusion-related acute lung injury and even death.Madjdpour C 2005 Therefore, further refinement of strategies to avoid exposure to allogeneic blood is needed.

Amongst the technologies to minimise the need for blood transfusion is the use of the anti-fibrinolytic drugs aprotinin, tranexamic acid (TXA), and epsilon amino-caproic acid (EACA).New Reference

Objectives: The purpose of this review is to investigate the evidence for the efficacy of Tranexamic acid in reducing peri-operative blood loss and blood transfusion after total knee replacement, and the evidence for any effect on clinical outcomes such as reduction in re-operation rates or increase in complication rates (e.g. deep venous thrombosis, pulmonary embolism, ischaemic heart diseases and mortality).

Method: Systematic review and metananalysis based on Cochrane guidelines of all randomised and quasirandomised trials.

Results: Fiften RCTs were included in the study; there has been a significant reduction of blood loss (P value 0.00001, I2 = 89%), blood transfusion without increase in systeanatic side effects such as ischaemic heart diseases, DVT, pulmondary embolisms. There was no singnificant difference in length of stay.

Background: There are no large comparative metal ion studies of commercially available hip resurfacing devices which have taken into account the effects of femoral size and cup inclination and anteversion.

Patients and methods: Metal ion analysis is carried out routinely at our independent centre. We present the metal ion results of 95 unilateral ASR patients and 70 unilateral BHR patients. For all patients, acetabular cup orientation was assessed using EBRA software. Patients with other metallic implants and those within 12 months of surgery were excluded.

Results: Whole blood/serum chromium (Cr) and cobalt (Co) concentrations were inversely related to femoral component size in both the ASR and BHR group (p< 0.05). Cr and Co levels were only seen to increase in the BHR group when the cup was implanted with an inclination greater than 55°. A significant relationship was identifed between the anteversion of the BHR cup and Cr and Co (p< 0.05 for Co, Spearman Rank correlation), with an increase in ions observed at anteversion angles > 17°. Cr and Co were more strongly influenced by cup position in the case of the ASR, with an increase in metal ions observed at inclinations greater than 45° and anteversion angles of < 10° and > 20°.

Discussion: The increased tolerance of the BHR cup to inclinations between 45–55° is likely due to the larger BHR cup providing greater protection against edge loading. When the cohort was divided by gender, the median Cr concentrations of the male ASR patients were significantly lower than those of the BHR males (p< 0.001). This suggests that in larger components positioned at more satisfactory angles of inclination and anteversion, the lower clearance of the ASR proves more significant than the extra coverage provided by the BHR cup. The BHR appears to be more sensitive to changes in anteversion than inclination.

Background: Resurfacing cups may produce significant clinical problems when placed at the extremes of version, including increased production of metal debris and psoas tendonitis.

Methods: We obtained the femoral and acetabular components of two unused ASR (Articular Surface Replacement) and BHR (Birmingham Hip Resurfacing) devices. The components were placed in moulds at varying degrees of inclination and anteversion in a grid to simulate pelvic landmarks and AP radiographic images were captured. The true radiological anteversion was determined by rotating the x-ray beam so that it was perpendicular to the acetabular axis and measuring the angle subtended by the cup rim and the vertical axis.

Five blinded orthopaedic registrars then used EBRA (Einzel-Bild-Roentgen-Analysis, University of Inns-bruck, Austria) software to determine the radiological anteversion from the AP films. Twenty-five ASR and twenty-five BHR images were analysed.

At the same time each observer was asked to grade the cups as “1” (< 10°) “2” (10–20°) “3” (20–30°) or “4” (> 30°) depending on the appearances of the cup vertices.

Results: Mean error for each observer was −0.7 (minimum) to 1.6° (maximum). The range of standard deviations of error for each observer was +/− 2.2 (minimum) to 3.5° (maximum). Retroverted cups were not identified in the majority of cases.

Cups graded as “1” or “4” showed high sensitivity and specificity for the true grade as determined on the lateral radiographs.

Conclusions: EBRA software can be used to calculate the anteversion of resurfacing cups to a clinically acceptable degree. The clinician must be aware of the limitations of the software most notably the difficulty in identifying a retroverted cup and errors arising from poor quality radiographs in terms of pelvic rotation. The presented clinical grading system can be used as a rapid assessment tool to identify cups at the extremes of anteversion.

Background: There is a paucity of published literature with regard to metal ion levels following bilateral hip resurfacings.

Method: Recent research has identified femoral component size and acetabular cup anteversion and inclination as important variables involved in metal ion release into the blood. We compared 13 patients with bilateral joints resurfaced using the ASR and 11 patients with bilateral BHRs to those with unilateral joints of similar size and cup inclinations/anteversions. Patients were excluded if the last procedure was within 12 months of blood sampling and if they had other metallic implants. Analysis of standing radiographs to determine cup orientation was carried out using EBRA software. Blood samples were analysed using ICPMS.

Results: Median whole blood Cr and Co values were higher in the BHR bilateral group when compared to the unilateral BHR group by a factor of 1.12 and 1.24 respectively. (5.17 vs 4.59 for Cr, 2.40 vs 1.93 for Co). The difference was significant for Co (p=0.030) but not for Cr (p=0.136). For the large ASR joints (53mm), median Cr and Co values were higher in the bilateral group by a factor of 1.5 and 1.85 respectively. (4.55 vs 2.97 (Cr) 2.83 vs 1.53 (Co)). The difference was significant for both Cr (p=0.001) and Co (p=0.022). For the small ASR joints (< 53mm), median Cr Co values were higher in the bilateral group by a factor of 1.95 and 2.30 respectively. (8.29 vs 4.25 (Cr), 6.78 vs 2.94 (Co)) (p=0.019 Co) (p=0.007 Co).

Conclusion: Metal ion concentrations are significantly greater in patients with bilateral resurfacings. The Cr Co concentrations observed in our patients with bilateral small ASR joints are double those in the published literature on bilateral 28mm metal on metal(MoM) joints implying that the lubrication achieved by small ASRs is sub optimal.

Introduction: Excellent medium term results have been reported with the BHR hip resurfacing implant. A number of modifications have been made to the latest designs in an attempt to preserve acetabular bone stock, improve function and prolong survival. We present the clinical and radiological results from the first independent series of ASR resurfacings.

Methods: The first consecutive series of 214 ASR hip resurfacings (192 patients) were followed up prospectively. No patients were lost to follow-up. The mean age of patients at implantation was 56 years and 40% were female. All patients had pre- and 2-year post-operative Harris Hip Scores (HHS) and UCLA activity scores. Radiographic and implant survival analysis was performed at 24–54 months following implantation.

Results: One hundred and seventy-three hips (87%) had an excellent Harris Hip Score (90 or above). Mean postoperative UCLA activity score was 7 and 92% were highly satisfied with the outcome. There were eleven revisions (5.1%). Four (1.9%) had femoral neck fractures (three had a femoral neck notch), two (0.9%) collapsed secondary to avascular necrosis and five (2.3%) were revised because of ongoing pain, as a result of metal wear debris.

Discussion: Although the fracture rate is similar to reports in the literature, the overall revision rate was higher. Rates of wear debris-related failure is concerning. Further investigation of specific implant failure is necessary.

In our independent centre, in the period from January 2003 to august 2008, over 1100 36mm MoM THRs have been implanted as well as 155 Birmingham Hip Resurfacing procedures, 402 ASR resurfacings and 75 THRs using ASR XL heads on SROM stems.

During this period we have experienced a number of failures with patients complaining of worsening groin pain at varying lengths of time post operatively. Aspiration of the hip joints yielded a large sterile effusion on each occasion. At revision, there were copious amounts of green grey fluid with varying degrees of necrosis. There were 11 failures of this nature in patients with ASR implants (10 females) and 2 in the 36 MoM THR group (one male one female).

Tissue specimens from revision surgery showed varying degrees of ‘ALVAL’ as well as consistently high numbers of histiocytes. Metal debris was also a common finding.

A fuller examination of our ASR cohort as a whole has shown that smaller components placed with inclinations > 45° and anteversions < 10 or > 20° are associated with increased metal ion levels. The 11 ASR failed joints were all sub optimally positioned (by the above definition), small components.

Explant analysis using a coordinate measuring machine and out of roundness device confirmed greater than expected wear of each component. The lower number of failures in the 36mm MoM group, as well as the equal sex incidence, suggests that the majority of these failures are due to the instigation of an immune reaction by large amounts of wear debris rather than adverse reactions to well functioning joints. It is likely that small malpositioned ASRs function in mixed to boundary lubrication, and this, combined with the larger radius of these joints compared to the 36mm MoM joints, results in more rapid wear.

Introduction: There are ongoing concerns regarding metal wear debris following the use of metal-on-metal (MonM) bearings for hip surface and total arthroplasty. A Type IV Hypersensitivity reaction to MonM articulations has previously been identified (aseptic lymphocyte dominated vasculitis associated lesion, ALVAL) but little is known of its incidence, diagnosis or management. Persisting groin pain in MonM patients may be undiagnosed ALVAL. At our single centre we have reviewed and compared three types of MonM articulations to examine the incidence of ALVAL and to identify trends.

Methods: The resurfacing group comprised 250 patients with the ASR prosthesis. In the resurfacing hybrid total hip replacement (THR) group there were 86 patients implanted with an ASR head on a stem. The final group comprised of 625 patients with a MonM THR using a 36mm Pinnacle head. Both the S-ROM and the Corail stems were used in the THR groups. Patients with persisting and activity-restricting groin pain had tests for infection. Patients were counselled and revision was offered if ALVAL was suspected from the clinical picture, blood results and the aspiration result. Specimens for microbiological and histological analysis were taken at the time of revision.

Results: We found 5 cases of histologically proven ALVAL in the absence of infection in 961 patients. The incidence was: 1.2% in the resurfacing group, 2.3% of Resurfacing Hybrid THR group and 0 in the 36 mm THR group. All 5 cases were in female patients. Only 1 case had any radiological abnormality. One patient was initially revised from a resurfacing to a 36mm MonM THR without clinical success. All patients have now been revised to ceramic-on-ceramic bearings with improvements in outcome.

Discussion: ALVAL may be under-diagnosed. The 5 patients we describe showed good clinical recovery following their primary procedure. However, activity levels decreased and pain increased at 6–12 months post-op. All described non-specific systemic symptoms. On examination, a painful straight leg raise was a characteristic finding. This may result from the significant effusion found around the hip at each revision. Fluid aspirated from these hips was of a characteristic colour (green grey) and viscosity. The failure of the revision of a resurfacing to a smaller MonM bearing highlights the problem of sensitisation to the metal debris. Any subsequent revision to a MonM bearing is unlikely to improve clinical outcome. This finding is consistent with previous reports in the literature. Our results suggest the incidence of ALVAL may be higher that previously thought. We suggest all patients with significant groin pain should have inflammatory markers tests and a hip aspiration performed. In the absence of infection, revision to an alternative bearing surface may be indicated.

Introduction: Potential problems resulting from metal-on-metal hip wear debris are well known. Previous studies have shown an association between high cup angles and raised metal ion levels, but a link to clinical outcome has yet to be established. We aim to show the relationship between high cup angles, raised metal ion levels and pain following hip resurfacing.

Methods: This analysis comprised the first 250 Depuy ASR hip resurfacings performed by a single surgeon (senior author) over a 3 yr period at an independent centre. Patients were followed up, examined and x-rayed at regular intervals. We measured Harris Hip Score (HHS) and pain. The acetabular cup inclination angles were measured from standardised pelvic radiographs. A subgroup of 80 patients had serum and whole blood chromium and cobalt measurements performed. This subgroup comprised patients with a similar sex split, age, activity level, follow-up and cup angle profile to the parent group.

Results: HHS improved from 51.6 pre-operatively to 94.6 post-operatively. Males had a significantly higher post-op HHS (97.1) compared with the females (91.0). 2.1% of male patients had pain compared with 8.7% of females. High cup angles were associated with pain in females. This relationship did not occur in males. In patients with cup angles of 48° and above there were no males with pain compared to 15.4% of females. Females under 48° had a HHS of 93.7 compared to 88.0 for those over 48°. When we analysed metal ion levels there was a similar relationship. Patients with cup angles of 48° and above had significantly higher serum and whole blood chromium and cobalt levels compared with lower cup angles. Three patients with cup angles over 50° developed ALVAL (aseptic lymphocyte dominated vasculitis associated lesion) based on histological findings. All were female.

Discussion: High cup angles are associated with increased pain and elevated metal ion levels. Women seem to be more intolerant of an higher cup angle than men. This may be a consequence of the smaller prostheses in females. Cups implanted lower than 48° had a better clinical outcome and less metal ion wear. Like other 4th generation designs, the ASR cup is not a complete hemisphere (unlike the BHR) and may be susceptible to edge loading at lower inclination angles than previously thought. We believe the current recommendation of 45° +/−5° is too high based on our findings. We recommend an inclination angle that does not exceed 48°.

Optimal cup orientation for metal-on-metal hip resurfacing has yet to be established. Guidance is based on hip replacement data and in vitro studies. We sought to determine the influence of component size and positioning on early clinical outcome.

This study comprises a consecutive series of 200 hip resurfacings. All had Harris Hip Scores (HHS) at one-year review. Acetabular inclination angles were measured on pre-operative radiographs, and cup inclination/anteversion angles on 3-month post-operative films using EBRA. Restoration of anatomy was defined as placement of the cup within +/−5 degrees of pre-operative inclination. The difference between pre-operative acetabular and post-operative cup inclination was termed cup-angle difference (CAD).

HHS inversely correlated with CAD (P=0.023) and anteversion (P=0.003), and directly correlated with femoral head size (P< 0.001). In patients with restoration of inclination anatomy mean HHS at one year was significantly higher at 98.7 compared with cups placed outside the normal anatomy restoration limits (93.8, P=0.003). Patients with anteversion > 20 degrees had a significantly lower HHS (P=0.010) compared with cups anteverted < 20 degrees. 96% of patients with HHS < 90 had malaligned cups (inclination over 45 degrees, anteversion over 20 degrees).

Restoring pre-operative cup inclination, anteverting the cup < 20 degrees and using large femoral heads improves early clinical outcome following MonM hip resurfacing. We recommend accurate pre-operative planning and meticulous attention to intra-operative cup positioning with these results in mind.

Resurfacing metal-on-metal hip arthroplasty is currently showing promising clinical results. However there are concerns related to such implants, including the elevated levels of metal ions typically seen in patients. Valuable data can be obtained from explanted prostheses but due to their recent introduction few retrieval studies on resurfacing hip prostheses have been published.

Five ASR hip resurfacing prostheses were revised due to pain. From two patients, head and cup were available for independent explant analysis. In the other three cases only femoral components were available. All were removed from female patients and all were revised to ceramic-on-ceramic hip prostheses. Post-operative radiographic measurements of cup inclination and ante-version were obtained using the EBRA software. The surface roughness values of the articulating surfaces of the explants were measured using a non-contacting profilometer. A co-ordinate measuring machine was used to measure the diameter of the head and the cup and thus the diametral clearance. The same measurements were then taken from a new unused ASR prosthesis and compared. Using elastohydrodynamic theory the minimum effective film thickness of the implant was calculated. In turn this allowed the lubrication regime to be determined.

The average roughness values of the head and the cup of one implant were found to be 0.135microns and 0.058microns respectively, with a diametral clearance of 110microns. These results indicated that, at the time of removal, the prosthesis would have operated in the boundary lubrication regime. Other explants showed evidence of localised contact between the head and the rim of the acetabular cup, and these showed articulating surfaces with typical roughness values of between 0.025microns and 0.050microns. The new ASR had head and cup surface roughness values of 0.010microns and 0.012microns respectively and a diametral clearance of 87microns, implying that a new implant would operate under fluid film lubrication. All cups five were implanted with inclination angles over 45 degrees and anteversion over 25 degrees.

These results suggest that components with high inclination and anteversion angles display greater than expected wear and may operate in boundary rather than fluid film lubrication which may eventually lead to early failure.

Introduction: Patient selection has been critical to the excellent medium-term clinical results following hip resurfacing. Hypersensivity to metal ion debris has been described in previous generations of metal-on-metal bearings. This may also be a problem that affects modern designs. Characteristic histological changes have been identified (ALVAL). There are few studies that include large female numbers, and show separate outcome and implant survival.

Methods: Eighty-one female hips at a mean of 23 months (11–43) had an ASR hip resurfacing procedure at a single-surgeon independent centre. Mean age was 55 years (28–69). Harris Hip Scores (HHS) were recorded at one-year follow-up. Failures were analysed.

Results: HHS improved from 46.4 (11–77) to 90.2 (27–100). Overall, there was a 7.4 % revision rate. There were 3 femoral neck fractures. In the entire series of 98 female patients there were 3 cases of severe pain requiring revision (3.1%). All three patients had HHS < 50 at one year follow-up. Patients had groin pain, reduced flexion and a painful straight leg raise. Blood results were not suggestive of infection. Aspiration of the hip joint in each case revealed copious amounts of milky green grey aseptic fluid. All had similar macroscopic changes at revision. There were characteristic histological changes in keeping with ALVAL. All 3 patients were revised to THRs with ceramic bearings.

Discussion: The failure rate of 7.4% in the older female group is poor at this early stage following hip resurfacing. The incidence of metal hypersensitivity in our series suggests this complication may be more common than previously thought. Patients with persisting pain of unknown aetiology following resurfacing at other centres may have metal hypersensitivity.

Introduction: Experimental studies in anatomic full size hip models indicate that larger femoral heads offer potential in providing greater hip range of motion and joint stability. We studied the effects of increasing head diameter from 28mm to 36 mm in total hip replacement (THR) on the range of flexion and abduction.

Methods: 243 patients who underwent primary total hip replacement with S ROM prosthesis between July 1996 and June 2004 were studied. 151 patients (77 male and 74 female) underwent THR with 28 mm head and 92 patients (38 male and 54 female) underwent THR with 36 mm head. The range of flexion and abduction were studied and statistical analysis was performed using the Student t-test. We monitored the dislocation rate in both groups.

Results: The mean flexion is 87.0 for the 28 mm group and 89.6 for the 36 mm group. The mean abduction is 27.77 and 27.98 for 28mm and 36mm groups respectively. Even though there is a slight increase in the mean flexion and abduction from the 28mm to 36mm group, this increase in not found to be statistically significant. For flexion (2.6 (−0.85 to 3.2); p=0.377), and for abduction (0.02 (−2.37 to 1.94); p=0.847). Three hips dislocated in the 28mm group (2%) but none of the hips in 36mm group has dislocated.

Discussion: Even though experimental studies indicate improvement in range of motion with increasing head diameter in THR, this effect is not reflected in our clinical study. But there is improvement in the joint stability by using a prosthesis with larger head diameter as evidenced by a reduction in the dislocation rate.

Introduction: EMG recording from lumber spine muscles can be a reliable discriminator and predictor of low back pain (LBP). Multi variant analysis shows age influences these variables.

Aim: to determine in a longitudinal study if age is a significant factor.

Method: EMG recording from 9 subjects was carried out at time1 and 12 years afterwards (time 2);

at the same load and

Results: At the same load there was no significant change in the Mean Half Width (HW) from time1 (M=45.9, SD=19.1) to time 2 (M=51.4, SD=18.7), t(8)= −0.98, p=0.36. No difference was observed when the load set at time 1 was used at time 2 (M=51.4, SD=18.7) and compared with a load set from the MVC obtained at time 2 (M=45.9, SD=12.0), t(8)=1.75, p=0.118.. There was no statistically significant difference between Initial Median Frequency (IMF) at time1 (M=50.6, SD=12.0) and time 2, either using the same load (M=51.7, SD=8.6), t(8)=− 0.273, p=0.79) or the load based on current MVC.

Discussion: In this 12 year longitudinal study, age did not appear to affect the HW or IMF measurement. Both of these variables might be used in long term studies.

Introduction: Pain after total hip arthroplasty (THA) can be caused by infection, aseptic loosening, heterotopic ossification, and referred pain. Psoas tendonitis is a rare cause of groin pain after THA and resurfacing arthroplasty. It is believed to be caused by psoas tendon impingement against a malpositioned acetabular component due to defective anteversion or centring and the use of oversized cups. We report 4 cases of psoas tendonitis following resurfacing arthroplasty and hybrid surface arthroplasty.

Methods: Between April 2004 and June 2005, we diagnosed 4 cases (3 female and 1 male) of psoas tendonitis among 152 cases of resurfacing arthroplasty and hybrid surface arthroplasty (2.6%). 116 patients had a hip resurfacing with ASR prosthesis (2 cases, 1.7%) and 36 patients had hybrid surface arthroplasty with ASR unipolar head on S ROM stem (2 cases, 5.6%). All these patients presented 2–5 months postoperatively with severe groin pain which was exaggerated when moving from the sitting position to the upright position and when going up stairs. Common causes of pain after hip arthroplasty, infection and loosening were ruled out. Radiological and ultrasound examination were performed.

Results: Ultrasound examination revealed thickening of psoas tendon in all cases and fluid collection around the tendon in one case. All cases were treated with corticosteroid injection under ultrasound guidance. Significant but temporary symptomatic relief was achieved in all cases.

Discussion: Psoas tendonitis should be considered in the differential diagnosis of groin pain after hip resurfacing procedures. Ultrasound examination is the initial investigation of choice and corticosteroid injection around the tendon is initial method of treatment. Computerized tomography and surgical options of management should be considered in resistant cases.

Introduction: Design of the prosthesis is an important factor in the successful outcome and longevity of total hip replacement. The purpose of the present study is to evaluate the minimum six-year results of primary total hip replacement using LX cemented prosthesis.

Methods: We prospectively studied 177 patients (60 male and 117 female) who underwent 197 hip replacements, between 1996 and 1999, using LX cemented prosthesis comprising a femoral component with cylindrical cross section of the stem and an acetabular component of ultrahigh molecular weight polyethylene. The average follow up was 7.3 years (6.1–9.6years). Clinical (Harris Hip Score) and radiological assessments (Barrack’s grading of cementation, subsidence, debonding, radiolucent lines and osteolysis) were performed.

Results: The average Harris Hip Score is 85.53 (28–99) compared to the preoperative score of 59.28. 28 cases (14.2%) developed progressive radiolucent lines around the stem. Sinking and debonding of the stem was noted in 18 cases (9.1%). 15 hips (7.6%) have dislocated and 11 were recurrent dislocations. Revision hip replacement was carried out in 12 cases (6%) for subsidence and debonding of stem, cement fracture and recurrent dislocation. The femoral stem components were found to be loose at the time of surgery.

Discussion: We believe that design of the prosthesis is an important factor in the high incidence of subsidence and debonding of the femoral stem. Both the geometry (cylindrical shape) and the rough surface finish (Ra value 100 microinches) were responsible for the pattern of progressive loosening. Lack of progressive increase in the offset with increase in the size of femoral component from 1 to 2 is one of the factors which contributed to high incidence of dislocation.

Introduction: Experimental studies in anatomic full size hip models indicate that larger femoral heads offer potential in providing greater hip range of motion and joint stability. We studied the effects of increasing head diameter from 28mm to 36 mm in total hip replacement (THR) on the range of flexion and abduction.

Methods: 243 patients who underwent primary total hip replacement with S ROM prosthesis between July 1996 and June 2004 were studied. 151 patients (77 male and 74 female) underwent THR with 28 mm head and 92 patients (38 male and 54 female) underwent THR with 36 mm head. The range of flexion and abduction were studied and statistical analysis was performed using the Student t-test. We monitored the dislocation rate in both groups.

Results: The mean flexion is 87.0 for the 28 mm group and 89.6 for the 36 mm group. The mean abduction is 27.77 and 27.98 for 28mm and 36mm groups respectively. Even though there is a slight increase in the mean flexion and abduction from the 28mm to 36mm group, this increase in not found to be statistically significant. For flexion (2.6 (−0.85 to 3.2); p=0.377), and for abduction (0.02 (−2.37 to 1.94); p=0.847). Three hips dislocated in the 28mm group (2%) but none of the hips in 36mm group has dislocated.

Discussion: Even though experimental studies indicate improvement in range of motion with increasing head diameter in THR, this effect is not reflected in our clinical study. But there is improvement in the joint stability by using a prosthesis with larger head diameter as evidenced by a reduction in the dislocation rate.

Introduction: The distorted anatomy in Developmental Dysplasia of the Hip (DDH) makes a total hip arthroplasty (THA) a challenging procedure. The purpose of the current study is to report the midterm results after uncemented primary hip arthroplasty using S ROM prosthesis in a prospective series of patients with hip dysplasia.

Methods: We performed 22 uncemented total hip replacements using S ROM prosthesis in 21 (12 female and 9 male) patients with hip dysplasia. The means age at the time of hip surgery was 41.8 (22 to 64) years. The mean follow-up was 6.3 (3.8 to 9.6) years. In 9 (40.9%) patients the operative treatment of DDH was performed during the early childhood (femoral osteotomy in 6 and pelvic osteotomy in 3). All patients were evaluated clinically and radiologically. The femoral head displacement prior to THA surgery was classified according to Crowe at al. classification (4 hips were type1, 2 type2, 10 type3 and 6 type 4).

Results: The average Harris Hip Score improved from 29.48 to 72.76 (44 to 99) and the average Oxford hip score is 31.22 (12 to 47). The range of flexion is 60°–120° (average 83.23) and abduction is 10°–40°(average 22.94). None of the hips has dislocated. Radiolucent lines were noted around the femoral stem in one case. None of the cases have developed osteolysis around femoral prosthesis. In one patient (4.5%), revision hip surgery was done for aseptic loosening of cemented acetabular cup.

Discussion: The midterm results of total hip replacement in DDH using S ROM uncemented prosthesis are promising. We recommend this modular prosthesis for hip replacement in dysplastic hips.

Introduction: Revision total hip replacement has high rates of failure which appears to be due, in part, to deficient bone stock that does not provide an adequate environment for fixation of the implant. Cementless modular implant offers the possibility of restoration of bone stock in conjunction with adequate fixation, thus re-establishing the function of the hip without the use of additional cement. This study reviews patients treated with the S-ROM system, assessing clinical outcomes, implant stability and osseous response to the hip revisions.

Methods: Sixty two cementless revision hip arthroplasties were performed using the S-ROM prosthesis between 1996 and 2001. Fifty four were available for follow up evaluation at 3 to 8 years (median 4.5 years). Radiological analysis, patient satisfaction and Harris hip scores were assessed pre and post operatively then at average of 4.5 years later.

Results: Eighty-five percent of patients were satisfied with the result of surgery. Clinical scores improved from a preoperative value 34 to 80 points post-operatively and were maintained on further assessment at average of 4.5 years. Forty-three stems had solid bony ingrowth, nine had mild subsidence initially averaged 6.4 mm then stabilized. Two had marked initial subsidence, which also later stabilised. There was gradual filling of the osteolytic defects in 32 of the 37 (86.5%) femoral lesions.

Discussion: With improvement of the postoperative hip score by more than 50 points and absence of definite implant instability at the final follow up, the results of use of S-ROM prosthesis in the revision cases of this study seems to be successful. The follow up is relatively short, but the experience derived from this work confirms the versatility of the S-ROM prosthesis in the complex hip revision situations as well as its favourable mechanical and biologic impact on the adjacent osseous structures.

To assess the performance of calcium sulphate pellets as a bone graft substitute in an Orthopaedic Oncology practice using clinical and radiological outcomes.

Between 1998 and 2001, calcium sulphate pellets were used in cavitary defects in 38 procedures in 34 patients with bone tumours. In 29 calcium sulphate pellets were used alone, in 8 allograft and in 1 autograft bone was added. The diagnosis was unicameral bone cyst in 13, giant cell tumour in 11, non-ossifying fibroma in 2, chondroblastoma in 2, benign fibrous histiocytoma in 2 and another pathology in 8 procedures. The femur was involved in 12 procedures, the humerus in 8, the radius in 5, the tibia in 4, the fibula in 3, the calcaneus in 2, and one procedure each in the tarsal cuboid, a metatarsal, the talus, and the middle phalanx of a finger.

Median follow up was 14 months (3 to 48). Seven patients had wound complications. Pellets had absorbed completely in 26/28 (93%) evaluable procedures by 3 months. Healing of the defect occurred in 24/28 (86%) evaluable procedures by 6 months. In 6 cases, the healed defect contained cystic areas simulating local recurrence. In 3 cases, there was collapse of the defect.

In cavitary defects, calcium sulphate pellets reliably absorb. Some patients have wound complications, especially where the cavity is relatively superficial. The pellets do not provide mechanical stability where there is attenuated cortical bone. Cysts within the healed defect may simulate recurrence.