Angiogenesis and osteogenesis are essential for bone growth, fracture repair, and bone remodeling. VEGF has an important role in bone repair by promoting angiogenesis and osteogenesis. In our previous study, endothelial progenitor cells (EPCs) promoted bone healing in a rat segmental bone defect as confirmed by radiological, histological and microCT evaluations (Atesok, Li, Schemitsch 2010); EPC treatment of fractures resulted in a significantly higher strength by biomechanical examination (Li, Schemitsch 2010). In addition, cell-based VEGF gene transfer has been effective in the treatment of segmental bone defects in a rabbit model (Li, Schemitsch et al 2009); Purpose of this study: Evaluation of VEGF gene expression after EPC local therapy for a rat segmental bone defect. Rat bone marrow-derived EPCs were isolated from the rat bone marrow by the Ficoll-paque gradient centrifuge technique. The EPCs were cultured for 7 to 10 days in endothelial cell growth medium with supplements (EGM-2-MV-SingleQuots, Clonetics). and collected for treatment of the rat segmental bone defect. EPCs were identified by immunocytochemistry staining with primary antibodies for CD34, CD133, FLK-1, and vWF. A total of fifty six rats were studied. A five millimeter segmental bone defect was created in the middle 1/3 of each femur followed by mini plate fixation. The treatment group received 1×106 EPCs locally at the bone defect and control animals received saline only. Seven control and seven EPC treated rats were included in each group at 1, 2, 3 and 10 weeks. Animals were sacrificed at the end of the treatment period, and specimens from the fracture gap area were collected and immediately frozen. Rat VEGF mRNA was measured by reverse transcriptase-polymerase chain reaction (RT-PCR) and quantified by VisionWorksLS. All measurements were performed in triplicate.Purpose
Method
Hip wear simulator test results could be affected by many non-bearing related factors such as fixation surface conditions, equipment calibration and component set-up. In an effort to improve the accuracy, reliability and repeatability of hip simulator test, a quality management system has been established at the IDC hip tribology laboratory, which has been accredited by UKAS (United Kingdom Accreditation Service) in accordance with the recognised international standard ISO17025. This study demonstrates that under well-controlled laboratory and testing conditions, satisfactory repeatability can be achieved during hip simulator studies. Between 2008 to 2010, ten 50 mm Birmingham Hip Resurfacing (BHR) devices were tested by the IDC tribology laboratory using two ProSim hip wear simulators in three different tests (T1, T2 and T3). All tests were performed following the same IDC testing protocols at 1 Hz frequency for 5 million cycles (Mc) or until after a steady state was reached. Paul type stance phase loadings with a maximum load of 3 kN and a swing phase load of 0.3 kN was used. The flexion and extension angles were 30 and 15 degree. The internal/external rotation angel was ±10 degree. Wear was measured gravimetrically using an analytical balance (Mettler, Toledo xp504) with an accuracy of 0.1 mg.INTRODUCTION
METHODS
Whilst there is a great deal of research on hip implants, few studies have looked at implant orientation and the subsequent effect upon the wear performance of a hip resurfacing. This study aimed to measure implantation angles through radiographic analysis and linear wear for retrieved acetabular cups in order to investigate possible causal links between wear and implant orientation. Seventy Birmingham Hip Resurfacing (Smith & Nephew, UK) cups with known time in vivo were analysed. Linear wear of retrieved cups were assessed using a Talyrond 290 roundness machine. Deviations from the characteristic manufactured profile, was identified as a region of wear. Polar measurements across the wear region were taken to determine wear. The linear wear rate (LWR) of a component was defined as the linear wear (μm) divided by the duration of the implant life in vivo (years). Cups which showed the wear crossing over the edge of the cup were classified as edge loaded (EL). For all non-edge loaded (NEL) cups, the wear area was within the bearing surface. Cup orientation angles were conducted for 31 cups. This was determined by superimposing BHR models of appropriate size, generated by CAD ProEngineer Wildfire 4, onto anterior-posterior x-rays. Anatomical landmarks and specific features of the BHR were used as points of reference to determine cup version and inclination angles.INTRODUCTION
MATERIALS & METHODS
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
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. 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.INTRODUCTION
MATERIALS & 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
osteoblast-hVEGF, fibroblast-hVEGF, Osteoblasts alone, and Fibroblasts only. The cultured cells were harvested at 1, 3 and 7 days after the transfection. The total mRNA was extracted (TRIZOL); both hVEGF and rat VEGF mRNA were measured by reverse transcriptase-polymerase chain reaction (RT-PCR) and quantified by VisionWorksLS.
The in vivo abduction angle and version angle of the cup were determined by superimposing the BHR models onto the radiographs (ProEngineer Wildfire 4 with ISDX II extension software) using anatomical references and specific features of the BHR.
Cup orientation: The abduction angles of the two non-edge loaded cups were 31° and 39°, and their version angles were 12 and 16° respectively. These angles were within recommended orientation for the BHR. In contrast, the adduction angles and/or version angles of all edge loaded devices were outside the recommended orientation. Their abduction angle varied from 40° to 66° and version angle from 5° to 46°. The edge loaded devices with higher inclination angles and/or higher version angels generally had higher linear wear. There is strong correlation between the cup orientation and the linear wear of the implant.
One R3 joint and one BHR device were friction tested in a ProSim hip friction simulator at 0, 3 and 5 million cycles of wear testing. The test was conducted in new born calf serum with added carboxy methyl cellulose (CMC) to generate viscosities of 1 to 100 cP. The loading cycle was set at maximum loads of 2 kN and minimum load of 0.1 kN. The flexion/extension was 30° and 15°, and the frequency was 1 Hz.
Friction: The coefficient of friction (COF) of the R3 joint varied from 0.08 to 0.14 depending on the viscosity of the serum and cycles of wear simulation test. Under physiologically relevant lubricant conditions (1, 3 and 10 cP), the COF for the R3 device tested was comparable to that of the standard BHR device. Wear: The R3 devices generated typical characteristics of wear to the BHR devices, with a higher wear rate during the initial running in period (0 – 0.5 Mc) followed by a low steady state wear rate after 0.5 Mc. The average wear rate at 0.5 Mc was 1.86 mm3/Mc for the R3 and 1.80 mm3/Mc for the BHR devices. The wear rate during the steady state for the R3 and the BHR devices was reduced to 0.09 mm3/Mc and 0.12 mm3/Mc respectively. The difference in average wear rates between the BHR and R3 devices during the running in and steady states were not statistically significant (p >
0.05).
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.