The main indication for OUKA is significant symptoms and anteromedial osteo-arthritis defined as follows:
Physical signs
1. Pain severe enough to justify joint replacement.
Radiographic signs
2. Full-thickness cartilage loss with eburnated bone-on-bone contact in the medial compartment (Ahlback stage 2, 3, or 4) (Ahlback, 1968).
3. Full-thickness cartilage preserved in the lateral compartment, demonstrated on a valgus stress radiograph.
4. Intact medial articular surface at the back of the tibial plateau and of the femoral condyle, best seen on a lateral radiograph.
5. Intra articular varus deformity manually correctable (in 20° flexion), best seen on a valgus stress radiograph.
Intraoperative signs
6. Full-thickness cartilage preserved in the lateral compartment, demonstrated on a valgus stress radiograph.
7. Presence of an intact ACL (ignoring synovial damage and longitudinal splits).
8. Satisfactory appearance of the central weight-bearing articular cartilage of the lateral compartment.
Apart from the severity of the pain, all the indications that a knee is suitable for OUKA are anatomical; plain radiography and stressed films are the best ways to demonstrate them.
Many surgeons find it difficult to obtain good quality stress radiographs and therefore do not use them for assessing patients. This is not ideal as stress radiographs are the best way to assess patients and the only reliable way to assess the thickness of the lateral cartilage and the correctability of the deformity. We believe they should be used by all surgeons starting to implant the OUKA. However, many experienced surgeons believe, that if there is bone-on-bone medial OA with a functionally intact ACL and the central weight bearing area of the lateral femoral condyle is in good condition, it is acceptable to do an OUKA. Although this may be correct, we have no long term data to support it.
