OUTCOME OF CUSTOM DESIGNED TOTAL KNEE PROSTHESIS FOR KNEES WITH SEVERE DEFICIENCY OF BONE

Abstract

Purpose: To study the functional outcome and survivorship of custom designed knee implants for revision and primary total knee replacement surgery where off-the-shelf prosthesis were unsuitable.

Methods: We prospectively reviewed the clinical and radiological results of 20 patients with 23 custom designed total knee prosthesis from 1991 to 2000. The indications were bone loss due to multiple revisions of total knee prosthesis and debridement for infection; peri-prosthetic fractures; bone deformity with rickets and small bones of patients with juvenile chronic arthritis. All the patients had their knee designed and manufactured in the Centre for Biomedical Engineering, University College London Medical School, Stanmore, UK. There were 4 different designs of knee prosthesis used: Condylar knee of miniature size, CAD-CAM knee, Superstabiliser and Rotating Hinges. Patients were operated upon by one senior surgeon and the Hospital for Special Surgery score taken pre-operatively, at three months, and yearly by an independent research physiotherapist.

Results: Clinical and radiological results after an average of 62.5 months (range 22 to 118 months) showed that the average Hospital for Special Surgery Score improved significantly (p=0.025) from 13.5 points (range 0–48) pre-operatively to 86.5 points (range 62–96 points). Average maximum flexion post operatively measured 86.4 degrees (range 60–122 degrees). 16 knees had excellent, 5 good and 2 poor results. Three patients had an extension lag ranging from 15–25 degrees. Only one patient with juvenile chronic arthritis needed revision at five years after the index arthroplasty.

Conclusion: The clinical and radiological results compare favorably with those who had standard knee prosthesis with similar indications. Our results support the use of a custom designed knee implant as a salvage prosthesis and an alternative to arthrodesis or amputation.