Direct examination of the ACL may cause a change of mind. ACL deterioration is gradual (as is the posterior extension of the tibial erosion), and it is sometimes difficult to determine the point at which the ACL has ceased to function adequately.
To increase the precision of the indications, we analysed retrospectively 820 OUKAs in which the state of the ACL had been recorded intraoperatively and graded as normal, synovial damage or longitudinal splits (Hamilton et al., 2016).
More marked macroscopic ACL damage was significantly associated with increasing age, male gender and a more extensive anteromedial tibial defect. At ten years, no difference in functional outcome or activity level was found between groups. However, compared to those with macroscopically normal ACL at ten years, a significantly greater improvement from baseline OKS and AKSS-Objective score was seen in patients with macroscopically ACL abnormalities. At fifteen years, no difference in implant survival, or failure mechanism, was detected between groups.
We therefore conclude that the macroscopic status of the ACL does not affect long term functional outcomes or implant survival providing the ACL is functionally intact.
In summary we have found that loss of synovial lining or longitudinal splits in the substance of the ligament are not contraindications. Knees in which the ligament is ruptured or its substance is demonstrably weak (friable and fragmented ACL) are unsuitable for OUKA.
A practical way to show that a ligament is ‘demonstrably weak’ is to insert a small tendon hook around the ACL and pull forcibly on it. If this test does not rupture the ACL, it is safe to proceed to OUKA; if it does, TKA is required.
Lateral compartment damage
Even through the small incision now used for OUKA, it is possible to see most of the articular surface of the lateral femoral condyle. Surface flaking and chondromalacia are very common and have been shown not to be significant. Occasionally, there is a medial ulcer on the lateral condyle. This can be ignored (see Chapter 5). Rarely, a full-thickness defect in the central weight-bearing cartilage is discovered. We treat this as a contraindication (although we have no evidence to support this practice).
