Osteophytes
Osteophytes are commonly seen at the margins of all the articular surfaces. Their presence around the lateral and patellofemoral surfaces does not necessarily indicate damage to the weight-bearing areas of these compartments. The presence of osteophytes at certain sites should be noted so that they can be removed at surgery.
On the lateral projection, there is often an osteophyte on the posterior margin of the medial tibial plateau which makes delivery of the plateau difficult (Fig. 4.12). Those on the back of the medial femoral condyle are sometimes large and may contribute to the flexion deformity by ‘tenting’ the posterior capsule. They can also impinge against the bearing in flexion and cause dislocation.
An osteophyte may be seen arising from the intercondylar region of the tibia, anterior to the attachment of the ACL. It can impinge against the femur in extension and constitute a block to the recovery of full extension. The osteophyte is typically ‘anvil’ shaped and is often seen on a lateral radiograph.
Figure 4.12 Radiograph of posterior tibial osteophyte.
Mediolateral subluxation
When there is significant loss of bone from the medial compartment (varus greater than 10°), the AP standing and the varus-stressed films may show lateral subluxation of the femur on the tibia (Fig. 4.13). If the valgus-stressed film shows complete reduction of the subluxation and the varus, both will be corrected by the operation and the subluxation can be ignored. If the subluxation persists on the valgus- stressed film, there is usually ACL deficiency and it is a contraindication to OUKA.
Figure 4.13 Varus stress radiograph (a) showing mediolateral subluxation which is corrected by valgus stress (b).
Intraoperative observations
The clinical and radiographic examinations described above can predict the suitability of a knee for OUKA with an accuracy of greater than 90%. However, the final decision, whether to proceed with unicompartmental or total replacement, is best taken on the operating table when the joint has been opened.
