Randomized Clinical Trial of Medial Unicompartmentel Versus Total Arthroplasty for Medial Tibio-femoral OA.

• Purpose OA of the knee can be debilitating and may require insertion of a knee prosthesis. In many cases there will be widespread degenerative changes of the knee, and in these cases it is necessary with the insertion of a complete prosthesis (total knee replacement, TKA) replacing all of the surfaces of the knee. However, there are cases in which the degenerative arthritis is found only between the thigh bone and the shin bone on the inner side of the knee, termed medial unicompartmental osteoarthritis (herein abbreviated to mu-OA). In situations of isolated mu-OA, it is possible to insert a complete prosthesis, as in the case of widespread OA of the knee, but it is also possible to insert a partial knee replacement (medial unicompartmental knee replacement, mUKA). There is not today enough information to decide which of the two types of prosthesis gives the best result in the event of mu-OA.

Supporters of TKA state that the treatment provides a predictable and good result, while supporters of mUKA say that it is not necessary to remove the good cartilage and mUKA provide even better results. If the inserted prosthesis become worn or loose, then it will be relatively easy to carry out a new operation after a mUKA, while a second surgery after TKA can be problematic. This is a further argument for mUKA. The costs of the two types of treatments are only poorly studied, and there are no comparative analyzes.

The aim of this study is to compare the results, in terms of 1) patient-reported outcomes, 2) clinical results including prosthetic survival of and 3) costs.

• Subjects All Danish citizens with isolated MU-OA referred to an orthopedic department at Gentofte, Næstved, Vejle, Århus and Aalborg hospital will be offered participation in the trial. The following exclude from participation in the study: under 18years of age, non-Danish speaking, alcohol or drug abuse, severe psychiatric disorder, severe systemic illness, employment in an orthopedic department, and major hip or back condition.

There will be 350 patients in the study. In 2014, the total numer of knee replacements at the participating centres was 3005 distributed at Gentofte (796 (112)), Århus (410 (152)), Vejle (629(138)), Aalborg/Farsø (381 (9)) Slagelse / Næstved (789(86)). Assuming an unchanged number of MUKA, 90% of which are suitable and a 50% participation accept-rate, we can expect an annual inclusion of approximately 220 patients. With an alternative assumption that about 25% of primary operations are suitable for mUKA, that 90% of these are suitable for the trial, and that 50% accept participation we can expect an annual inclusion of approximately 340. It is reasonable to expect that the total number of patients will be included within 12 to 19 months.