ANALYSIS OF THE KINEMATICS OF DIFFERENT HIP SIMULATORS USED TO STUDY WEAR OF CANDIDATE MATERIALS FOR THE ARTICULATION OF TOTAL HIP ARTHROPLASTIES

We developed an analytical technique to determine the paths traced by specific points on the femoral head against the acetabulum in the huma n hip joint during gait. The purpose of the study was to apply this te chnique to the mechanical hip simulators chosen to conduct wear tests on polymeric acetabular liners used in total hip replacements. These s imulators differ from one another in the type of motion produced, apar t from other variables such as type of lubricant and head position. Du e to the variation in the kinematics between the machines, the paths t raced by the points on the femoral head against the acetabular liner r anged from simple linear traces to figure-8 loops and quasi-elliptical paths during a single simulator cycle. The distances traveled by thes e points during the same period also varied appreciably among the diff erent hip simulator designs. These results are important when combined with other studies that have shown that kinematics can play an import ant role in the outcome of in vitro wear experiments. The kinematic di fferences quantified in this study can partially explain the substanti al differences in wear data reported from different simulator designs and also underscore the usefulness of the technique described in this study in judging the results from different hip simulator experiments.