The posteromedial corner includes the posterior oblique ligament, semimembranosus tendon and its expansions, and the posteromedial capsule, working with the MCL to resist valgus and rotational forces. Posteromedial corner injuries often accompany ACL and MCL injuries and contribute to anteromedial rotatory instability when not addressed.
| Origin | Medial tibial condyle, medial femoral condyle, and medial meniscus |
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| Insertion | Semimembranosus expansion, posterior capsule, and medial structures |
| Actions | Resists valgus stress and internal tibial rotation at the knee; static medial stabiliser complementing the MCL |
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Isolated posteromedial corner injuries are uncommon but occur as part of multi-ligament knee injuries. The posterior oblique ligament is the primary static posteromedial stabiliser and its repair during medial-sided reconstruction significantly improves outcomes compared to MCL reconstruction alone in complex knee instability.
Posterior oblique ligament and posteromedial capsule disruption producing anteromedial rotatory instability accompanying ACL and MCL injuries, requiring combined reconstruction for optimal stability.
