SHOULDER WEAR SIMULATOR FORINVESTIGATION OF WEAR OF GLENOIDCOMPONENT

摘要

Wear of polyethylene glenoid component is one of main complications in totalshoulder arthroplasty. Glenoid component wear can be the result of not properly selectedmaterials for articular surfaces. Therefore, wear of glenoid component should be evaluated invitro to select a proper material for load-bearing application. Several studies have been donefor wear testing of total hip and knee replacements. However, no experimental wear study hasbeen performed to investigate influence of the component material and geometry on wearperformance of glenoid prosthesis yet. The aim of the study is to develop a shoulder wearsimulator, which will be used for wear testing of the currently used and alternative glenoidcomponents.Wear testing device is developed to simulate the abduction/adduction movement of theshoulder joint. During the movement a physiologically-correct loading will be applied to theprosthetic components. The humeral head abduction/adduction movement is realized bystepper-motor. The axial loading is realized by force controlled pneumatic actuator. Themovement and loading are computer controlled. The glenoid component is mounted in thespecial holder. The humeral head is mounted on the rotated axis. A new born calf serum isused as a lubricant. The lubricant temperature is maintained at 37oC using thermocouple.Wear of the glenoid component is measured gravimetrically according to ASTM standard.The shoulder wear simulator allows also for obtaining the friction factor between articulatedprosthetic materials during the wear test.Before using the device for actual material testing, initial preliminary tests were done toensure that the device was operating properly under test condition. Good repeatability andaccuracy performances of the motor and cylinder have been found. Then, the preliminarywear test for polyethylene glenoid component and metal humeral was performed. The test ranfor 2 millions cycles under loads, which changed from 150N to 750N during each cycle. Afterthe test was completed, the glenoid component was inspected for wear. The calculatedvolumetric wear rate was of about 40 mm3/yr. The maximum wear depth was of about0.2 mm.This test method is developed for in vitro evaluating the friction and wear properties ofcombinations materials that are being considered for use as the bearing surfaces of humanjoint replacement under physiological load/motion/lubrication conditions. Flexibility of thedevice allows programming of many different motion and loading configurations. Throughthe preliminary wear test, the device proved effectiveness at reproducing the desired motionsand loads, and initiating wear.