Sixty-two knees that were replaced with Walldius prostheses and twenty-five knees with geometric replacements were studied prospectively. The follow-up ranged from twenty-four to 162 months (average, seventy-four months) for the knees with the Walldius prostheses and from twenty-four to seventyfive months (average, forty-seven months) for those with the geometric prostheses.

Using a 100-point clinical rating scale, the knees of patients who underwent Walldius replacement improved from their preoperative status by an average of 33 points (from 44 to 77 points) and those with geometric prostheses, an average of 24 points (from 54 to 78 points).

Twelve patients with twenty Walldius prostheses were followed for more than 100 months (average, 127 months). The greater average improvement (36 points) in this group was due primarily to the absence of any major complications.

Six patients underwent replacement of one knee with a Walldius prosthesis and one knee with a geometric implant. Although the ratings for the two knees were similar in each patient, four patients preferred the Walldius implant; one, the geometric replacement; and one had no preference.

Significant technical errors or complications (defined as those affecting the end result) occurred in 8 per cent of the knees with Walldius implants and in 12 per cent of the knees in the geometric group. There were two late infections in each group. One Walldius prosthesis was removed and the knee was fused. The other three prostheses (one Walldius and two geometric) associated with infection were salvaged.