Predisposing Factors in Fixation Failure of Femoral Prostheses Following Primary Charnley Low Friction Arthroplasty. A 10- to 20-year Followup Study

To identify factors affecting radiologically detected loosening of the Charnley femoral prosthesis, 326 femoral prostheses with 10- to 20-year followup were studied. After observation of postoperative radiological changes, the criteria for fixation failure detected radiologically, of femoral prostheses were defined as progression or accompanying occurrences of subsidence, demarcation, separation of the prosthesis from cement, cement fracture, or endosteal cavitation. Sixteen femoral prostheses (4.9%) developed radiologically detected fixation failure. Male gender, low canal flare index, low femoral score, large medullary canal width, low implant (cement and stem)/canal ratio, low stem/canal ratio, and varus orientation of the stem affected fixation failure. Inadequate cementing techniques such as low implant/canal and stem/canal ratios and varus stem orientation might be within the surgeon's control and should be avoided. An unfavorable canal geometry (stovepipe canal) and osteopenia of the femur, indicated by a low femoral score, are risk factors that might be out of the surgeon's control, and require future research.