Mechanical loosening of the femoral head prosthesis in the Charnley total hip arthroplasty.

In 288 Charnley total hip arthroplasties, without sign of infection, loosening of the femoral component, defined as a radiolucent zone between the proximal lateral edge of the prosthesis and the cement, was recorded in 103 cases, or 36%. The zone usually occurred within a few years after the operation. The progression was most obvious in the first 2 years. Three-fourths of the hips with radiolucent zones were free of symptoms, but symptoms developed as the zone increased in thickness. Of hips with a zone 4 mm or more, half were painful and 8 hips have so far been replaced. Male sex, previous hip surgery, and improper cementing were more frequent in hips with signs of loosening, whereas body weight, diagnosis or the position of the prosthesis could not be demonstrated to influence loosening.