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-four percent had excellent clinical results. Thigh pain occurred in 23% of patients, but was severe in only two. "Cancelization" and rounding off of the calcar were noted in 83% of hips, whereas localized osteolysis 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 revision. Ultrahigh-molecular-weight polyethylene wear and plastic debris were 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 less. 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 alternate mechanism of proximal bone resorption.