Introduction: The accepted method of assessing wear following a hip simulator test has been to use a precision balance. As the MoM devices produce significantly less weight loss than hard-on-soft bearings, the measurements of MoM devices are now almost at the detection limit of many balances. There is a need for a method that can be used in conjunction with gravimetric analysis that will provide an accurate assessment of ion concentration levels that will support the gravimetric measurements.

Aim: To develop a method to assess wear using metal ion analysis in order to support gravimetric measurements of metal on metal devices.

Materials and methods: Hip simulator test: Three pairs of 50 mm diameter as cast CoCr MoM devices were tested in a ProSim hip wear simulator (SimSol Stockport/UK) under physiologically relevant conditions. The lubricant was new born calf serum with 0.2 % sodium azide concentration diluted with de-ionised water for protein concentration of 20 g/l. Stop-start motion was implemented every 100 cycles. Lubricant changed every 125 k cycles. The frequency was 0.5 Hz. Wear was assessed gravimetrically at every 0.5 million cycles (Mc) interval.

Ion analysis: Serum was collected from test station and allowed to settle for 12 hours. An aliquot of 20 ml from lubricant was collected. Each sample was centrifuged at 2500 g-force for 10 minutes. A 10 ml aliquot was collected from each sample and was further centrifuged at 2500 g-force for 10 minutes. 1.5 ml aliquot was collected and stored at −20 °C. A high resolution inductively-coupled plasma mass spectrometry instrument (ELEMENT, ThermoFinnigan MAT, Bremen/Germany) was then used for the analysis of metal ions.

Results and Discussion: The average cumulative metal ion levels at 0.5, 1 and 1.5 Mc showed similar trends in wear to that of the average cumulative weight loss assessed gravimetrically. There were similar biphasic wear trends in both metal ion levels and gravimetric weight losses. Other studies have also shown similar correlation between volume loss and ion concentration levels. The percentage distribution of Co, Cr and Mo in the metal ion samples are in close agreement with nominal chemical composition of the material tested.

Conclusion: This study showed that metal ion measurements can help to confirm gravimetrically measured material loss.

Introduction: To develop a more physiologically relevant hip simulator test protocol and study the effect of microstructure on the wear performance of as-cast (AC) and double heat treated (DHT) devices under the new protocol.

Methods: Three pairs of AC and four pairs of DHT 50 mm CoCr metal-on-metal (MoM) devices were tested. The lubricant used was bovine serum. Stop-start motion was implemented between the two sets of kinetics and kinematics that alternated every 100 cycles throughout the test. Condition one: The flexion/extension was 30° and 15° respectively. The internal/external rotation was ±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. Condition two: The flexion/extension was ±22°. The internal/external rotation was ±8°. The force was a maximum stance phase load of 2.2 kN and a swing phase load of 0.24 kN at 0.5 Hz frequency. Wear was assessed gravimetrically.

Result: The masking effect of 1 Hz speed and uninter-rupted motion, in providing exaggerated lubrication regime, was exposed under more physiologically relevant test conditions. The AC devices have significantly reduced wear when compared to the DHT devices. It can also be seen that from 0.5 to 2 Mc the divergence in wear has increased.

Conclusion: A more physiologically relevant hip simulator test protocol was successfully developed and implemented, in showing the effect of microstructure on wear as seen in vivo, where high wear of DHT devices has been observed. 295

Introduction: The purpose of this study was to determine the effects of edge loading on in vivo wear of hip resurfacings from retrievals.

Methods: The wear of retrieved BHR heads and cups was assessed using a Taylor-Hobson Talyrond 290 roundness machine. The maximum deviation of the profile from an ideal circle was taken as the maximum linear wear. Edge loaded devices (Figure 1a) were classified as cups which showed the maximum area of wear crossing over the edge of the cup. For all non-edge loaded pairs (Figure 1b), the wear area on the cup was within the sphere of the cup. In this study 50 pairs (diameter size 38 mm to 54 mm) were analysed.

Results: 28 pairs were classified as edge loaded, and 22 were not. Edge loaded pairs display greater linear wear than non-edge loaded components (Table 1). Edge loaded components showed no correlation between time in vivo and linear wear.

Discussion: Edge loaded pairs have a far greater range of linear wear which may be due to the variation of the angles of the components in vivo. Edge loading may be caused by an open cup, impingement and/or high combined anteversion angle of both the head and cup. The success of a hip resurfacing depends strongly upon articulation occurring within the sphere of the cup, which is reliant upon good component orientation.

Hip simulators have been used for ten years to determine the tribological performance of large-head metal-on-metal devices using traditional test conditions. However, the hip simulator protocols were originally developed to test metal-on-polyethylene devices. We have used patient activity data to develop a more physiologically relevant test protocol for metal-on-metal devices. This includes stop/start motion, a more appropriate walking frequency, and alternating kinetic and kinematic profiles.

There has been considerable discussion about the effect of heat treatments on the wear of metal-on-metal cobalt chromium molybdenum (CoCrMo) devices. Clinical studies have shown a higher rate of wear, levels of metal ions and rates of failure for the heat-treated metal compared to the as-cast metal CoCrMo devices. However, hip simulator studies in vitro under traditional testing conditions have thus far not been able to demonstrate a difference between the wear performance of these implants.

Using a physiologically relevant test protocol, we have shown that heat treatment of metal-on-metal CoCrMo devices adversely affects their wear performance and generates significantly higher wear rates and levels of metal ions than in as-cast metal implants.

Introduction: Cementless cup designs in metal-on-metal (MoM) hip resurfacing devices generally depend on a good primary press-fit fixation which stabilises the components in the early post-operative period. Pressfitting the cup into the acetabulum generates non-uniform compressive stresses on the cup and consequently causes non-uniform cup deformation. That in turn may result in equatorial contact, high frictional torque and femoral head seizure. It has been reported that high frictional torque has the potential to generate micromotion between the implant and its surrounding bone and as a result adversely affect the longevity of the implant. The aim of this study was to investigate the effects of cup deformation on friction between the articulating surfaces in MoM bearings with various clearances.

Materials and methods: Six Birmingham Hip Resurfacing (BHR) devices with various clearances (80 to 306 μm) were tested in a hip friction simulator to determine the friction between the bearing surfaces. The components were tested in clotted blood which is the primary lubricant during the early post-operative period. The joints were friction tested initially in their pristine conditions and subsequently the cups were deflected by 25– 35 μm using two points pinching action before further friction tests were carried out.

Results and Discussions: It has been reported that reduced clearance results in reduced friction. However, none of the previous studies have taken cup deflection into consideration nor have they used physiologically relevant lubricant. The results presented in this study show that for the reduced clearance components, friction was significantly increased when the cups were deflected by only 30 μm. However, for the components with higher clearance the friction did not change before and after deflection. It is postulated that the larger clearances can accommodate for the amount of distortion introduced to the cups in this study.

Arthroscopic surgery is a common intervention for osteoarthritis of the knee. However, the benefits from such an intervention are not clear. The purpose of the study was to perform a questionnaire survey of orthopaedic surgeons of Wales to analyse the practice of arthroscopy for osteoarthritic knee.

Over a three-month period, a postal survey was conducted of all hospital orthopaedic consultants in Wales. Of a total of 62 questions sent we received a reply of 37. 31 surgeons perform arthroscopic lavage or debride-ment. 4 surgeons perform arthroscopic surgery for symptomatic meniscal tear only. There was no defined protocol regarding the management. Early OA was the commonest indication (18). Arthroscopic lavage (17) was equally popular to lavage and debridement (16). 6 respondents like to perform the surgery themselves while the majority would allow a middle grade surgeon to operate with or without supervision. 26 surgeons felt that the results of the procedure are unpredictable, but still continued to perform it. Only 6 surgeons felt a continued relevance of the procedure.

Arthroscopic surgery is a commonly performed symptomatic treatment for arthritic knee. It bears a significant financial commitment. 266 arthroscopic knee surgery were performed annually in a district general hospital, of whom 115 were arthroscopic washout. Average cost of each operation is £1000. The physiological basis for arthroscopic washout is not clear. A majority of the Welsh surgeons have reservations about this procedure. In spite of evidence of limited usefulness, it is still performed widely.

To evaluate one-year mortality rate of hip fractures treated surgically and assess the influence of medical status and ASA grade on this parameter. 212 patients above 65 years (range 65–100, mean 82.7): There were 104 (49.1%) intertrochanteric and 108 (51.9%) femoral neck fractures. A number of surgical procedures, (sliding/compression screw 104 (49.1%), hemiarthroplasty 81 (38.2%), cannulated screws 18 (8.5%) and total hip replacement (4.2%) were used. The one - year mortality rate was obtained from computerised records, case notes and General Practitioners.

One-year mortality rate for the whole group was 28.8% with an exponential increase corresponding to ASA grade. The relationship between ASA grade and mortality for the whole group (P< 0.001), younger age group of 65 – 84 years (P< 0.001), older age group of 85– 100 years (P=0.002), early operation group < 2 days (P=0.001), females (P=0.000), intertrochanteric fractures (P=0.007), femoral neck fractures (P=0.022) and sliding/compression screw (P=0.007) was highly significant. The type of operation per se and time of operation had no predictive value.

Conclusion: Statistically significant mortality is neither dependent on age, nor type of fracture, time of surgery and type of surgery per se, but is essentially a reflection of ASA status.

The extensive dominant influence of ASA grade is a highly significant predictive determinant and final arbiter of surgical risk and mortality in hip fracture.

Introduction: Osteoid Osteomas are not uncommon, benign bone tumours which have well-defined clinical, radiological and pathological characteristics. These tumours can potentially affect any bone in the body, but show a predilection for long tubular bones. The clinical presentation can easily be confusing, if the site in question is rare and the presentation atypical. Lesions occurring in the foot often pose particular problems in diagnosis, often leading to delays in treatment. Although there have been accounts of the post traumatic presentations of osteoid osteomas, no direct link has been established between trauma and its incidence.

Case Report: A 38 year old gentleman was referred by his GP with an eighteen month history of right midfoot pain after a football injury which forced his right foot into hyperextension and abduction. Initial radiographs after the injury were normal. The pain did not respond to non-steroidal anti-inflammatory drugs (NSAIDs) and there were no nocturnal exacerbations. Examination at presentation showed an antalgic gait with medial mid-foot tenderness centred over the first tarso-metatarsal joint (TMTJ). Repeat radiographs showed mild degenerative changes in the first TMTJ. A bone scan showed a hot spot over the right cuneiform bones. Subsequent computed tomography (CT) showed an osteoid osteoma, with a characteristic central calcific nucleus within the nidus, of the medial border of the lateral cuneiform bone. The osteoma was treated with en-bloc excision and the diagnosis was confirmed by histology.

Conclusion: Despite the advances in its treatment, osteoid osteoma of the foot can pose a difficult diagnostic puzzle. This condition should always be kept in mind when faced with persistent, post-traumatic foot pain, even in the absence of roentgenographic findings. In such cases a high index of suspicion and a low threshold for appropriate imaging can lead to the timely diagnosis and treatment of this tumour.