EARLY LOOSENING OF THE FEMORAL COMPONENT AT THE CEMENT-PROSTHESIS INTERFACE AFTER TOTAL HIP-REPLACEMENT

Between 1980 and 1990, 1941 total hip replacements were performed with use of the Iowa femoral component fixed,vith cement. Twenty-seven of these patients (twenty-nine hips) had early loosening of the femoral component two to ten years (average, five years) after the operation. The average age of these patients at the time of the operation was fifty-nine years (range, forty-one to seventy-seven years). The acetabular cup had been inserted without cement in seventeen hips, and the cup had been inserted with cement in twelve. The femoral stems had a matte finish; twenty had been precoated with polymethylmethacrylate and nine had not been precoated. The pattern of loosening of the femoral stem was unique: in each hip, the loosening was initially reflected by debonding (a superolateral lucency between the cement and the prosthesis in zone 1 of Gruen et al.), and this was followed by progressive loosening at the cement-prosthesis interface with maintenance of the bone-cement interface. In twenty hips, the debonding was followed by extensive osteolysis. Twenty patients (twenty-one hips) had a revision, and one was considering a revision at the time of writing. The average time from the onset of the symptoms to the revision for the nineteen hips for which this information was available was nine months. We believe that both the geometry (a cylindrical shape distal to the proximal cobra shape) and the surface finish of the Iowa femoral component were responsible for the pattern of progressive loosening. We suggest that once debonding develops, the cylindrical shape of this particular stem allows rotation, permitting the roughened surface finish to abrade the polymethylmethacrylate, which results in loosening and osteolysis.