Cementless Acetabular Revision with Rim Acetabular Defects: Experimental and FEA Investigation

2014-06-20T00:00:00Z (GMT) by Mark H. Gonzalez
Total Hip Arthroplasty (THA) has become a very popular procedure in the world today. As people are living longer and requiring improved function, the indications and frequency of performing total hip arthroplasty have expanded. As a result there are an increasing number of patients who have failed total hip arthroplasties that need revision. Failure generally occurs as a result of the biological response to wear particles. Polyethylene particles are generates by frictional wear both at the articulation between the femoral head and the polyethylene liner and between the liner and the metal cup. The particles are opsonized by macrophages initiating a cascade that causes acetabular bone loss as a result the acetabular implant loosens and has to be revised. The challenge to the surgeon is to place a new acetabular implant in the bone deficient acetabulum. Other causes of bone loss about the acetabulum include congenitally or developmentally dislocated hips and trauma about the hip. Our purpose is to better understand acetabular wall (rim) defects, and the acetabular bone cup interface stability and fixation. To this end several FEA models will be developed to investigate the different scenarios involved in THA in the presence of rim defects. The first step is to create and validate a FEA Model. A cadaver pelvis is implanted with acetabular cups bilaterally. On one side a defect is created in the pelvis. Each construct is loaded with a physiologic load followed by a supraphysiologic load and the micromotion of the cups noted. Based on Ct scans a model is created of both hemipelvis acetabular cups are implanted virtually. Boundary conditions are generated based on the previous literature and each pelvis is loaded with a profile identical to the experimental profile. Once the model is validated the model is used to examine three scenarios that will provide information to the hip surgeon contemplating hip revision in the case of bone deficiency. The scenarios are 1: The effect of the varying degrees of cup fixation on cup stability. 2: The effect of defect position on cup stability, 3: The effect of defect size and cup stability. The results show that the cup stability is sensitive to the degree of equatorial fixation. Decreasing the fixation especially on the rim side can greatly increase the micromotion of a cup under physiologic stress. The position of a defect is critical. Defects that are superior or inferior and are outside the anterior and posterior columns have a minimal effect on cup stability. Defects of the anterior or posterior columns create instability and are sensitive to size of defect.