To compare the radiographic results of unicompartmental knee arthroplasty using a navigation system with those using a manual alignment system.

The results of 50 cases (46 patients) of unicompartmental knee arthroplasty using a navigation system (24 patients, 25 cases) and using a manual alignment system (22 patients, 25 cases) were evaluated. Knee anteroposterior, lateral, and weight-bearing full-length lower extremity radiographs before and after the arthroplasty were used for the measurements.

The mean postoperative femorotibial alignment was 3.6 ° of valgus in the manual alignment group and 5.4 ° of valgus in the navigation group. The postoperative mechanical axis measured using Kennedy and White's method was located at zone 1 in 4 cases (16%), at zone 2 or C in 21 cases (84%) in the manual group, and at zone C for all cases in the navigation group (p=0.001). In the coronal axis of the femoral component, 11 cases (44%) were excellent, 7 cases (28%) were good and, 7 cases (28%) were poor in the manual alignment group. In the navigation group, 15 cases (60%) were excellent and 10 cases (40%) were good and there were no poor results (p<0.05). In the coronal axis of the tibial component, 22 cases (88%) showed excellent results and 3 cases (12%) showed poor results in the manual alignment group. In the navigation group, all cases were showed excellent results (p>0.05). In the sagittal axis of the tibial component, 9 cases (36%) showed poor results in manual group and there were no poor results in the navigation group (p<0.05).

Unicompartmental knee arthroplasty using navigation produced better results in restoring the alignment of the prosthesis and the mechanical axis of the lower extremity than that using manual alignment.