TOTAL KNEE ARTHROPLASTY AFTER A PREVIOUS PATELLECTOMY

We performed a retrospective, matched-control analysis of the results of total knee arthroplasty with cement in twenty-two patients who had had a previous patellectomy for either a fracture of the patella (sixteen patients) or severe patellofemoral osteoarthrosis or chondromalacia patellae (six patients), Nine of the patients were men and thirteen were women, The average age at the time of the total knee arthroplasty was sixty-nine years (range, fifty-nine to seventy-four years). The average time front the patellectomy to the total knee arthroplasty was eight years (range, two to fourteen years). The patients were divided into two groups according to the type of implant that had been used, Group A (nine patients) had had insertion of a posterior stabilized prosthesis (a posterior cruciate-sacrificing implant) and Group B (thirteen patients) had had insertion of a posterior cruciate-sparing implant, Two computer-generated matched groups of patients who had had a total knee arthroplasty with insertion of implants that were identical to those in the study groups but who had not had a previous patellectomy served as controls, Group C consisted of patients who had had insertion of the same type of implant as that used in Group A, and Group D consisted of patients who had had insertion of the same type of implant as that used in Group B. All patients were evaluated before the arthroplasty and five years postoperatively with use of the rating system of the Knee Society The mean over-all preoperative knee score was 43 points, There was no significant difference between Group A (mean, 45 points) and Group B (mean, 47 points), The mean over-all postoperative score was 76 points; this was a significant improvement compared with the preoperative score (p < 0.01), The mean postoperative score for Group A (89 points) was significantly better than that for Group B (67 points) (p < 0.01), The mean postoperative scores for Groups C and D were not significantly different from the score for Group A, Five knees had a pain score of 30 points or less, and all were in Group B, At the time of the followup examination, seven (32 per cent) of the twenty-two knees that had had a patellectomy had a measurable loss of active extension; six of the seven were in Group B. On the basis of the evaluation of the specific implants used in this small series, we concluded that total knee arthroplasty provides predictably good results in selected patients who have had a previous patellectomy, Use of a posterior stabilized prosthesis provides predictably good results, in terms of both function and relief of pain, in patients who have had a patellectomy for a fracture, Use of a posterior cruciate-sparing implant in patients who have had a previous patellectomy provides less predictable results than the posterior stabilized prosthesis with respect to over-all function postoperatively, Total knee arthroplasty in patients who have had a patellectomy for patellofemoral osteoarthrosis or chondromalacia patellae does not offer predictably good relief of pain.