Modification of a simplified hip joint simulator into an ISO 14242-1 compliant design and a comparison of wear test results

The ISO 14242-1 standard for hip joint simulator wear testing specifies a set of test conditions for the simulation of normal level walking in optimal conditions. Since some of the established simulators, such as the 12-station HUT-4, are not ISO 14242-1 compliant, the present study was carried out to answer the following question. Does wear produced in ISO 14242-1 conditions differ from that obtained earlier with the simplified HUT-4 hip joint simulator for similar specimens in normal level walking, optimal conditions? The HUT-4 hip joint simulator was made ISO compliant by an implementation of a number of modifications. One of the modifications was the design and construction of a novel servo-electric load actuator with proven dynamic response. The other modifications were related to the Euler sequence of motions, acetabular abduction angle, enclosure of the lubricant chamber, and temperature control. A 5 million-cycle wear test with thin, large-diameter VEXLPE liners resulted in a wear rate close to that obtained earlier with the HUT-4. The burnished bearing surface in both tests was in agreement with clinical retrieval studies. It appeared that a more simple, inexpensive hip joint simulator can reproduce clinical wear mechanisms. However, the simulator must meet certain basic requirements, such as the correct type of multidirectional relative motion, for which biaxial motion is sufficient. The present study was not intended to show a similarity in wear produced by the ISO 14242-1 and HUT-4 wear test systems.

Design and Evaluation of a Hip Joint Implant Wear Simulator

Every year a high number of total hip arthroplasty is reported worldwide and an increase in this number is expected. Several factors may cause hip wear, such as osteoarthritis, obesity, traffic accidents and sport practicing. Wear is a concern when considering hip prostheses, since a prosthesis presents finite life that in many cases is shorter than patient life, and leads to substitution. Also, research is constant and new developments have to be tested, which leads to the necessity of testing devices that reproduce real conditions of hip joint implant functioning. This work describes a low-cost device, according to the ISO 12242. The equipment was built, a set of three commercially available prostheses was tested and the results show wear values coherent with those found in literature. It was found a value of wear rate of (13.30 ± 3,81) mg/106 cycles; wear factor found was (0.41 ± 0,09) x 10-6 mm3 /Nm. After testing, the device was evaluated and no component presented significant wear. Keywords: Hip joint simulator; Prostheses; Wear; Arthroplasty; Test machine.

In Vitro Analysis of Wearing of Hip Joint Prostheses Composed of Different Contact Materials

Cobalt-chromium-molybdenum alloy (CoCrMo) and ceramic are the two most common materials for the femoral head in hip joint prostheses, and the acetabular liner is typically made from ultra-high molecular weight polyethylene (UHMWPE), highly cross-linked polyethylene (XLPE), or highly cross-linked polyethylene blended with Vitamin E (VEXLPE). The selection of suitable materials should consider both wear performance and cost-effectiveness. This study compared the wear rate between different friction pairs using a hip joint simulator and then recommended a suitable prosthesis based on the corresponding processing technology and cost. All wear simulations were performed in accordance with ISO 14242, using the same hip joint simulator and same test conditions. This study found that when using the same material for the femoral head, the XLPE and VEXLPE liners had a lower wear rate than the UHMWPE liners, and the wear rate of the XLPE liners increased after blending with Vitamin E (VEXLPE). There was no significant difference in the wear rate of XLPE when using a CoCrMo or ceramic head. Considering the wear rate and cost-effectiveness, a CoCrMo femoral head with an accompanying XLPE liner is recommended as the more suitable combination for hip prostheses.

Fatigue Life and Reliability Analysis of a Parallel Hip Joint Simulator

SUMMARY Aiming at 3SPS+1PS parallel hip joint simulator, the maximum stress of branched chains under the suggested trajectory is obtained by elastodynamic analysis. Based on Corten-Dolan fatigue damage theory and Rain-flow counting method, the dynamic stress of each branched chain is statistically analyzed. The fatigue life prediction shows that branched-chain A2P2C2 is the weakest component for the simulator. Finally, the fatigue reliability is analyzed and the fatigue life and reliability under different structural parameters are discussed. The study shows that the fatigue life of each branched chain can be increased or balanced by increasing structural parameters or exchanging initial motion parameters.

The Influence of Kinematic Conditions and Variations in Component Positioning on the Severity of Edge Loading and Wear of Ceramic-on-Ceramic Hip Bearings

Dynamic separation and direct edge loading of hip replacement bearings can be caused by many factors, including implant positioning, implant design, changes in device over time, surgical variations and patient variations. Such dynamic separation and direct edge loading can lead to increased wear. Different input kinematic conditions have been used for experimental hip simulator studies to produce clinically relevant elliptical contact wear paths between the bearings during gait. The aim of this study was to investigate the influence of input kinematics (two axes of rotation simulation conditions (without abduction/adduction) and three axes of rotation simulation conditions (with abduction/adduction and different loading profiles) and variations in component positioning (different levels of medial-lateral translational mismatch at standard and steep cup inclination angles) on the occurrence, severity of edge loading, dynamic separation and wear of size 36 mm ceramic-on-ceramic hip bearings on an electromechanical hip joint simulator. The results showed that, overall, either of the two axes or three axes input profiles were equally valid in providing a suitable preclinical testing method for assessing the occurrence and severity of edge loading and wear under edge loading conditions. In terms of component positioning, as cup inclination and medial-lateral translational mismatch increased, so did dynamic separation, axial load at the rim, severity of edge loading and wear.

RESEARCH ON FRICTION WEAR OF HIP JOINT ENDOPROSTHESES OF POLYETHYLENE-METAL MATERIAL COMBINATION ON HIP JOINT SIMULATOR

The article presents the results of friction wear tests of hip joint endoprostheses. The study comprised tests of endoprostheses, commercially available on the European market, used in total hip arthroplasty. The friction pair was formed by an actual cupacetabular cup made of ultra-high molecular weight polyethylene (PE-UHMW) along with a head having a diameter of 28 mm made of stainless steel FeCrNiMnMoNbN. The friction and wear tests were performed using an SBT 01.2 hip joint simulator of the authors’ own design, which was constructed taking into account the ISO 14242-1 standard. Bovine serum was used as the lubricant. The tests of each friction pair were made up to 5·106cycles of motion. During the tests, simulator operation was interrupted every 5·105 cycles to replace the lubricating liquid, and mass control was performed every 1·106 cycles. Prior to testing, the polyethylene cup was soaked in the lubricant to minimize liquid absorption during the test. Proper preparation of the cup and testing by taking into account a control group weight measurement allowed an accurate determination of the mass loss of the polyethylene cup.