INTRODUCTION. Analysis of retrieved ceramic components have shown areas of localized ‘stripe wear’, which have been attributed to joint laxity and/or impingement resulting in subluxation of the head, causing wear on the edge of the cup. Studies have been conducted into the effects of mild subluxation, however few in vitro tests have looked at severe subluxation. The aim of this study was to develop a more clinically relevant subluxation protocol. MATERIALS & METHODS. Seven (Subluxation n=4; standard test n=3) of 36mm Biolox Forte (R3, Smith & Nephew) ceramic devices were tested for 0.5m cycles (mc). Two of the subluxed joints were further tested to 1 Mc. The devices were subjected to subluxation under standard testing conditions. The flex/ext was 30° and 15° respectively, with internal/external rotation of ±10°. The force was Paul type stance phase loading with a maximum load of 3 kN, and a standard ISO swing phase load of 0.3 kN at 1 Hz. The test was conducted on a ProSim hip joint wear simulator (SimSol, UK). The simulator is equipped with a novel mechanism to achieve translation of the head, to achieve subluxation. During the ISO swing phase load of 0.3kN, a controlled lateral force required for the translation of the head is applied by a cam mechanism, head retraction then occurs during heel strike. The lubricant used was new born calf serum diluted with de-ionised water to achieve average protein concentration of 20 g/l, with 0.2 wt % concentration NaN3, and changed every 250k cycles. Measurements have been taken at 0.5 & 1 mc stages. RESULTS. Linear wear measurements conducted on the subluxed joints resulted in stripe wear similar to that reported in vivo. Average length, width and depth dimensions were 25.34±1.96 mm, 8±1.60 mm and 16.95±3.87 μm (± 95% CL) respectively. Linear wear at 0.5 Mc for standard joints, were undistinguishable from the original profile. Gravimetrically, weight loss was undetectable for joints tested under standard conditions. The volume loss of the joints under subluxation was 1.9± 0.7 mm3 at 0.5 mc. Two joints tested to 1mc generated an average volume loss of 3.1±2.3 mm3. The stripe wear length, width and depth at 1 Mc were 25.30±3.33mm, 8±3.92mm and 35±17.07 μm respectiveley. DISCUSSION. The current study presents test results of a hip joint simulator with a novel subluxation mechanism to simulate severe and clinically relevant hip joint. Past techniques have had to reduce the swing phase load to achieve stripe wear patches of varying size and depth. The subluxed joints produced significantly higher volumetric wear than the standard joints. Dimensional measurements in terms of length, width and depth of wear patches of subluxed joints generated similar results to that which have been observed following retrieval analysis. Tests that can simulate different types of activity in hip joint simulators will help to improve the design and understanding of implant behaviour in vivo

Aims. Will Hydroxyapatite hip (HA) arthroplasty associated with ceramic bearings produce uncomplicated function in younger, active patients’ The incidence of aseptic loosening, dislocation and broken implants has been particularly investigated. Debris disease from plastic debris contributes to aseptic loosening. Hard-Hard bearings should obviate this problem. Metal-metal will release ions which might be deleterious. Experience with metal-metal resurfacing has high lighted problems including pseudo-tumours. Ceramic bearings may fracture but otherwise appear free of complications. Methods. This is a study extending over 19 years of 626 HA hip arthroplasties with ceramic bearings. Annual review using Harris Hip Score to assess pain and function and X-rays to check osseointegration has been performed. Alumina ceramic was inserted in 467 hips. The newer Zirconia Toughened Alumina (ZTA) has been inserted in 169 hips. There are 118 hips still under review at 10 or more years. Results. Aseptic loosening is unusual (one stem, two acetabulae (3 of 1252 components, 0.24%) Failure from mal-orientation with repeated dislocation occurred in six hips (0.96%). Three alumina heads (0.48%) and two alumina liners (0.32%) broke. There has been no failure of ZTA ceramic. No patients have thigh pain. Osteolysis and debris disease have not arisen. Harris Hip Scores show 91.2% scoring over 90 or 100. Lower scores mostly relate to other joint and medical problems. Conclusions. Assessments confirm that patients remain well. Aseptic loosening of HA hips is rare at 0.24%. Failure from broken alumina components is unusual. Alumina has now been superseded by ZTA for implantation. Ceramic on ceramic is a reliable selection for bearing surfaces in patients of any age and either sex

Introduction. One of the most common complications of ceramic on ceramic hip replacement is squeaking. The association of Accolade stem and Trident acetabular system has been reported to have squeaking incidence of up to 35,6%. There is doubt if this phenomenon occurs due to: the stem titanium alloy, the V40 femoral neck, the recessed liner of the trident cup or even the mal-seating of the trident insert on the cup. Objectives. Primary: The purpose of the present study was to determine the incidence of squeaking in association with the use of Exeter stem and Trident ceramic acetabular system. Secondary: Analysis of the correlation of the cup abduction angle and squeaking. Methods. During the period from March 2004 to December 2008, two surgeons performed 87 total hip arthroplasties in 77 patients with use of a ceramic-on-ceramic bearing (Exeter stem, alumina head, Trident ceramic acetabular system). Seventy six patients (86 THA) were available for review after at least 18 months follow-up. The incidence of squeaking and other noises was analyzed. Cup abduction angle was measured. The Pearson correlation coefficient was used to determine if a correlation existed between the cup abduction angle and squeaking. Results. The incidence of squeaking was 2,63% (2 patients). Both patients reported a “click” noise in hyperextension of the hip. The mean abduction angle was 44 degress (35–60), and 48 degrees (46 and 50) on the squeaking group. There was no statistically significant difference in the in the mean cup inclination between squeaky and quiet hips. Conclusion. The incidence of squeaking in association with the use of Exeter stem and Trident ceramic acetabular system was 2,63%. There was no correlation of the cup abduction angle and squeaking