Preoperative assessment aims to determine, as precisely as possible, whether a particular knee has anteromedial OA.
Clinical examination
Pain
Pain is usually felt near the medial joint line but it may be anterior, posterior, and even on the lateral side of the knee. Its localisation is not a reliable sign. Pain is felt on standing and walking, but is usually absent while sitting (when the intact articular surfaces at the back of the medial compartment are in contact) and when lying down (when the damaged surfaces are unloaded).
Severity of pain, limitation of walking distance and compromised quality of life are the factors that decide the need for operation. The criteria are similar to those used to justify TKA.
Physical signs
The principal physical signs were briefly described in the previous section.
1. Varus deformity of the leg is best seen when the patient is standing. Varus is seldom less than 5° on presentation and rarely more than 15°. A ‘lateral thrust’ of the knee is often seen on walking and is not a contraindication.
As already noted, the intra-articular varus deformity corrects spontaneously when the patient is seated with the knee flexed to 90° (Figs. 4.3(c) and (d)), and it can be manually corrected, by applying a valgus force, with the knee flexed 20° or more to relax the posterior capsule (Figs. 4.3(e) and (f)).
Figure 4.3 Diagrammatic explanation of the physical signs of anteromedial OA in the right knee (see text).
2. Usually the knee will not fully extend. If the ACL remains intact and functional, the fixed flexion deformity is rarely more than 15°.
3. Flexion range is usually limited but is rarely less than 110°. Flexion less than 110° is a relative contraindication to OUKA because of the difficulty it presents at surgery. However, more flexion can usually be achieved under anaesthesia than in the clinic, particularly if the limitation is due to severe pain rather than stiffness of the joint.
4. Moderate synovial swelling and joint effusion are common, and there is often tenderness to palpation over the medial joint line.
It should be noted that the ‘pivot shift’, the drawer test, and other manoeuvres designed to assess the cruciate ligaments after trauma are of much less value in the arthritic knee. Erroneous conclusions may result from false instability, due to intact ligaments being rendered slack by loss of articular cartilage height, or from false stability, due to interpenetration of the damaged articular surfaces, or the presence of large osteophytes, which mask ligament insufficiency. These tests are not used in preoperative decision-making.
