Clinical medium-term results with the cementless unconstrained total knee replacement (Type Natural Knee) in comparison with sledge prosthesis for unicompartmental knee replacement (Type Wessinghage).

Aim: In the present study, we performed a follow-up investigation comparing middle-term results after unicompartmental and bicompartmental knee arthroplasties. Material and Methods: We used matched pairs with 18 patients in each group. The first group was treated with the unicompartmental slegde prosthesis (Type Wessinghage), the second with the cementless nonconstrained bicondylar prosthesis (Type Natural knee). The mean time of follow-up was 4.5 years. (SD +/- 0.6). The average age of the patients in both groups was 59 years (SD +/- 3). Both groups included 12 female and 8 male patients. All patients suffered from primary medial osteoarthritis of the knee. In all cases, the contralateral knee also had signs of manifest osteoarthritis. The determination and evaluation of the results of the investigation were made according to the score of the American Knee Society. We also reviewed the radiological findings concerning placement of the prosthesis, radiolucent lines, and patella position in the femoral shield. Results: At follow-up examination, there were no significant differences in the knee score between the patients undergoing unicompartmental or total knee replacement. However, patients with the Wessinghage sledge tended to show better results. The mean knee score was 94.3 +/- 4.9 in the Wessinghage group and 91.9 +/- 8.3 in the Natural knee group. Evaluation of the radiographs revealed radiolucent lines in the group with total replacement. In contrast, in 7 of 18 patients with the unicompartmental prostheses we found radiolucent lines at the tibial component of 1 mm or more, which, however, did not cause clinical symptoms. Conclusion: Our results show, that the unicompartmental arthroplasty is still an effective method for the treatment of the osteoarthritis, especially concerning the conditions for possibly needed revisions.