Posteromedial Corner of the Knee: The Neglected Corner.

Lundquist et al. Radiographics. 2015 Jul-Aug;35(4):1123-37. [Link to free full text article]

This is the editor's interpretation of a paper published in the orthopaedic literature in 2015 - our attempt to make relevant medical articles accessible to lay readers. If you wish to read the original it is easy to ask your librarian to obtain a reprint for you from any medical library.

These authors point out that the anatomy of the rear of the knee is generally not well understood by the medical professionals dealing with problems that may involve this area. Although the outer or lateral side at the back of the knee is sometimes referred to as 'the dark side of the moon', this article points out that the anatomy of the inner or medial side at the back of the knee is even more so - and even less is published about the important anatomy here.


Why this area is important is that disruption of the anatomy on this medial side can lead to what is known as 'anteromedial rotatory instability'.

Damage to the posteromedial corner (PMC) seldom occurs in isolation, and there is often damage at the same time to the ACL or PCL (anterior or posterior cruciate ligaments). The danger is that if these important cruciate ligaments are repaired, but the PMC is left unstable, then it is highly possible that the cruciate repair itself will fail.


Anatomy of the Posteromedial Corner

The posteromedial corner contains the structures lying between the posterior margin of the longitudinal fibres of the superficial medial collateral ligament (MCL) and the medial border of the posterior cruciate ligament (PCL). Within these borders are the five major components of the PMC:


Key Takeaways

  • The semimembranosus is the main dynamic stabiliser of the posteromedial corner.
  • Isolated posteromedial corner injuries are uncommon and, as with isolated medial collateral ligament injuries, can be treated without surgery.
  • When posteromedial corner and medial collateral ligament injuries are both present, it is possible that surgery may be indicated.
  • Symptomatic, functional anteromedial rotatory instability in patients with ACL and posteomedial corner injury is an indication for surgical treatment of the PMC.
  • When both the PCL and posteromedial corner are injured, surgical repair of both ligaments is indicated.
  • Surgical repair of the posteromedial corner is also considered when multiligament (ACL, PCL, and MCL) injuries are present.

The paper is a very nice one, and rich with images. If you have a particular interest in the topic, there is a link at the top of this page to the free full online text with images..

Test for anteromedial rotatory instability (AMRI)

This video from Kostas Sakellariou shows how to test for anteromedial rotatory instability.

Posteromedial corner

Our illustration of the knee bones from the medial side, showing the semimembranosus tendon (SM) and its expansions (SME) [G:gastrocnemius, POL:posterior oblique ligament, MCL:medial collateral ligament.]