Ion analysis has been used as one of the key indicators to assess the performance of MoM devices in patients. Modular devices, in particular having larger overall surface area (the stem and sleeve), and locking interfaces (head – bore, sleeve- taper and sleeve-bore, stem-taper surfaces) than other MoM devices are expected to release greater number of ions. Concerns have been expressed that the ion release at the taper junction might be a potential cause leading to the failure of the implant [Garbuz The aim of this study was to look into the wear and the associated ion release from the taper junction and the articulating surface of modular devices. For the first time a novel design has been used to isolate the taper junction on modular devices on the hip simulators in order to compare the wear at the taper junction and articulating surface. The taper junction has been isolated in a small gaiter, while the head and cup were contained in a large gaiter. CoCrMo sleeves having an offset of +8 mm have been used on 50 mm modular heads along with Ti6Al4V stems. The acetabular components were standard BHR cups. Three devices (Smith & Nephew, UK) have been tested with newborn calf serum as a lubricant (in the large gaiter) and also as the medium containing the taper junction (in the small gaiter). The serum samples from the articulating surface and taper junction were analysed using HR-ICPMS. The locking interfaces at the taper junction have been left intact throughout the duration of the test. Both the head and the cup have been tested under anatomical conditions using the standard implant development centre's (IDC) profile for 2 million cycles (Mc). The lubricant was newborn calf serum with 0.2% sodium azide diluted with de-ionised water to achieve protein concentration of 20 mg/ml. The flexion/extension was 30°/15° and 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. The frequency was 1 Hz, with an 8 hour stop after every 16 hours of testing.Introduction
Method
Metal-on-Metal devices generate significantly lower volumetric wear than conventional total hip replacements. However, clinically some patients may suffer some form of laxity in their joints leading to subluxation of the joint, which in turn may cause edge loading of an implant thereby increasing the chances of failure due to higher than expected wear. In this study, the effect of subluxation on MoM implant wear was investigated on a hip joint simulator. Two groups of 44 mm MoM devices were tested, n=3 in each group. The devices were subjected to 1 and 2 mm of subluxation. The flexion/extension was 30° and 15° respectively, internal/external rotation was ±10°, and cup inclination was 35°. The force was Paul type stance phase loading with a maximum load of 3 kN, with ISO swing phase load of 0.3 kN, run at 1 Hz. The test was carried out on a ProSim deep flexion & subluxation hip wear simulator (SimSol, UK). Rather than separating the head and the cup (microseparation), or reducing the swing phase load, this simulator is equipped with a novel mechanism to achieve translation of the head, while subjecting the devices to subluxation. During the swing phase, a controlled lateral force necessary for the translation of the head is applied by a cam mechanism, head retraction will then take place on heel strike. The lubricant used was new born calf serum with 0.2 wt. % sodium azide concentration diluted with de-ionised water to achieve average protein concentration of 20 g/l. Lubricant was changed every 250k cycles. Gravimetric wear measurements have been taken at 0.25 & 0.5 Mc stages. Tests conducted with 1mm (Group 1) and 2mm (Group 2) subluxation significantly increased volumetric wear compared to standard hip simulator tests [1]. At 0.5 million cycles, group 1 and 2 produced an average volume loss of 4.38±0.98 mm3 (95% CL) and 7.07±1.64 mm3 (95% CL) respectively.Materials & Methods
Results
Five pairs of 50 mm DefCom devices were tested in a ProSim hip wear Simulator for 5 million cycles (MC) at a frequency of 1 Hz. The lubricant was new born calf serum with 0.2% sodium azide diluted with de-ionised water to achieve protein concentration of 20 mg/ml. The flexion/extension was 30° and 15° and 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. Five standard 50 mm BHR devices were tested under the same testing conditions for comparison. Statistical analyses were performed at a 95% confidence level (CL) using the statistics function in Excel (Microsoft(r) Excel 2003).Introduction
Materials and Methods
All hip replacements depend upon good orientation and positioning to ensure that implants function well To investigate the correlation between edge loading and wear on retrieved implants through linear wear analysis and radiographic examination of implants Introduction
Aim
Hip implant research has been carried out for decades using hip simulators to reflect situations Three pairs of 50mm as cast (AC) and four pairs of 50mm double heat treated (DHT) CoCr MoM devices were tested in a ProSim hip simulator. In order to determine the frequency for testing, Patients' activities have been monitored using a Step Activity Monitor (SAM) device. The data showed a relatively slower walking pace (frequency) than that used in the hip simulator studies. The new frequency, along with stop/start motion and various kinetics and kinematics profiles have been used in putting together a more physiologically relevant hip simulator test protocol. The lubricant used in this study was new born calf serum with 0.2 % (w/v) sodium azide concentration diluted with de-ionised water to achieve an average protein concentration of 20 g/l. Gravimetric measurements have been taken at 0.5, 1, 1.5 & 2 million cycle (Mc) stages and ion analysis has been carried out on the serum samples.Introduction
Materials & Methods
Thromboprophylaxis in total hip replacement (THR) and total knee replacement (TKR) remains controversial, conspicuous by absence of consensus. Because of protracted and variable mobilisation, there is an extended risk of Venous Thromboembolism (VTE). We hypothesised that a combination of low molecular weight heparin and miniwarfarin would minimise the initial and extended risk. Therefore we evolved a protocol of enoxaparin sodium 40 mgs for 5 days starting preoperatively and miniwarfarin 1-2mg for 6 weeks following surgery. We undertook a retrospective study of total hip and knee replacements in a District General Hospital between January 2000 and December 2005 to determine the effectiveness of the protocol. We analysed the incidence of symptomatic VTE in 1307 patients, of who 681 underwent THR and 626 TKR. We evaluated the incidence of symptomatic DVT and PE between 0-6 weeks, 6 weeks-3months and 3-6 months following surgery.Aim
Methods
Scaphoid fracture is the most common undiagnosed fracture. Occult scaphoid fractures occur in 20-25 percent of cases where the initial X-rays are negative. Currently, there is no consensus as to the most appropriate investigation to diagnose these occult frctures. At our institution MRI has been used for this purpose for over 3 years. We report on our experience and discuss the results. All patients with occult scaphoid fractures who underwent MRI scans over a 3 year period were included in the study. There was a total of 619 patients. From the original cohort 611 (98.7%) agreed to have a scan, 6 (0.97%) were claustrophobic and did not undergo the investigation and 2 (0.34%) refused an examination. 86 percent of the cases were less than 30 years of age. Imaging was performed on a one Tiesla Siemen's scanner using a dedicated wrist coil. Coronal 3mm T1 and STIR images were obtained using a 12cm field of view as standard. Average scanning time was 7 minutes.Introduction
Materials and methods
