A FINITE-ELEMENT ANALYSIS OF FACTORS INFLUENCING TOTAL HIP DISLOCATION

A previously validated three-dimensional finite element model was used to study how several total hip component design and surgical placemen t variables contribute to resisting the propensity for posterior dislo cation in the case of leg crossing in an erectly seated position. The computational formulation incorporated treatments of polyethylene mate rial nonlinearity and large displacement sliding contact. The primary outcome measures were the peak intrinsic moment developed to resist di slocation, and the ranges of motion before neck on lip impingement and before frank dislocation. Modifications of the acetabular liner desig n (chamfer bevel angle, lip breadth, head center inset) involved tradi ng off improved peak resisting moment for compromised range of motion and vice verse, Increases of head size led to substantial improvements in peak resisting moment, but if the head to neck diameter ratio was held constant, had almost no influence on the component range of motio n. For the leg crossing event studied, increased component anteversion , and even more so increased tilt (less net abduction), achieved impro vements in range of motion and in peak resisting moment, but these cha nges imply diminished resistance to anterior dislocation from extensio n and adduction motion inputs.