[Unicompartmental femorotibial arthroplasty and lateral gonarthrosis. Outcome of 52 prostheses implanted for more than 5 years].

The results of 52 Lotus unicompartmental knee implants with a follow up time exceeding 5 years are analysed. Forty-one prostheses with a mean follow-up of 6.5 years have given very good or good relief of pain. In almost all cases, flexion range exceeds 90 degrees and the preoperative motion has been most often clearly improved. Except for those due to prosthesis infection, all the poor and fair results in terms of pain, are explained by mechanical causes i.e. persistence of a frontal instability, loosening of the tibial component (2 cases) or narrowing of the nonprosthetic femorotibial space (11 cases). The latter is not related to the presence of any radiological chondrocalcinosis. These poor anatomical and clinical results appear to be preventable by a correct operative technique. In particular, the complete correction, by the prosthesis, or the angular deformity which has caused the lateral knee OA must be avoided. This is in contrast to what must be done in osteotomies. Unicompartmental prostheses thus have to stay in stress so that their long term future is uncertain. In the surgical management of lateral knee OA, these prostheses are not to be preferred to correction of frontal angular deformity by osteotomy, except in the elderly, when deformity cannot be completely corrected. Unicompartmental prostheses are particularly indicated in unstable knees in which osteotomies are known to be difficult to perform correctly.