LOSS OF BONE STOCK WITH CEMENTLESS HIP-ARTHROPLASTY

One hundred four porous-coated anatomic cementless hip arthroplasties followed from 2 to 6.5 years (mean, 50 months) were studied. Ninety-fo ur percent had excellent clinical results. Thigh pain occurred in 23% of patients, but was severe in only two. ''Cancelization'' and roundin g off of the calcar were noted in 83% of hips, whereas localized osteo lysis occurred in 24 femurs and one acetabulum. Ten of these measured more than 10 mm, and all of those in the femur were located proximally . None of these patients were symptomatic and none have come to revisi on. Ultrahigh-molecular-weight polyethylene wear and plastic debris we re implicated as the cause of osteolysis. Lytic lesions were seen only after 3 years and occurred only in patients with 32-mm femoral heads in whom the outer diameter of the acetabular component was 52 mm or le ss. Use of excessively thin ultrahigh-molecular-weight polyethylene in these patients may have predisposed them to accelerated wear. Section modulus mismatch resulting in stress protection is considered as an a lternate mechanism of proximal bone resorption.