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.