The aim of the following study was to find out how much a previously implanted unicondylar prosthesis affects the clinical and functional outcome of a total knee arthroplasty in case of revision surgery.
A matched-pair comparative analysis was performed on 28 patients (group A) who required bicondylar knee arthroplasty following failed unicondylar arthroplasty and 28 patients (group B) with primary bicondylar knee arthroplasty. Both groups were matched according to age, sex, weight, height, type of prosthesis, and follow-up time after bicondylar arthroplasty. The patients' evaluation was based on the Knee Society Score and the WOMAC Score. Radiographs (AP weight-bearing and lateral) were taken of the knee. The average follow-up time after bicondylar arthroplasty was 55+/-15 months in group A and 56+/-13 months in group B.
The knee score was 71.8+/-18 and 80.4+/-10 points (p=0.01) and the function score 56.1+/-15 and 64.1+/-19 points (p=0.1) for group A and group B, respectively. The subjective assessment according to the WOMAC Score was statistically significant in terms of the functional outcome. Increased postoperative range of motion of 109 degrees +/-11 degrees was noticed for group B in comparison with group A (101 degrees +/-8 degrees ; p=0.004). Patients revised from an unicondylar arthroplasty required a significantly thicker polyethylene inlay (12.9+/-3 mm) compared with the primarily implanted group (10.3+/-3 mm; p=0.004).
Revision of an unicondylar to a bicondylar knee replacement showed inferior functional results in comparison to primary bicondylar knee arthroplasty. Patients are satisfied after conversion of an unicondylar to bicondylar prosthesis, but not quite as much as patients who received a primary bicondylar arthroplasty. However, in the small number of patients where revision surgery after failed unicondylar prosthesis is required, the patient had already been successfully treated for many years.