Natural history of femoral focal osteolysis with proximal ingrowth smooth stem implant.

Focal femoral osteolysis has become a prominent cause of failure of total hip arthroplasty. Femoral focal osteolysis is studied in 185 hips with a patched porous-coated titanium femoral stem. Seventy-two hips had osteolysis and 113 did not. Seventy-one percent of osteolysis is evident on radiographs by 6 months to 5 years after surgery. The location is most commonly seen on an anteroposterior radiograph, with proximal osteolysis most common and the initial size of defects being greatest in zones 2, 3, 5, and 6. Progression of size is slow, with each focal defect averaging 0.89 mm/y. Progression of bone loss occurs more commonly with the occurrence of new defects rather than extension of an existing defect. Focal osteolysis was directly correlated with the amount of polyethylene wear. Osteolysis is more likely when linear polyethylene wear exceeds 0.2 mm/y or volumetric wear exceeds 150 mm3/y or when the patient is below age 60. Accelerated wear and osteolysis occur most often when the fixation of the arthroplasty is poor.