'Complex' or 'multi-ligament' instability of the knee implies damage to more than one stabilising structure, often giving considerable difficulty in diagnosis and management.

The damage may include tears of both cruciates, or one or more cruciates and a collateral - plus or minus one or more structures of the posterolateral corner (to the outer side of the back of the knee).

A multi-ligament instability is very much super-specialist territory. Remember than the KNEEguru website maintains a list of knee surgeons around the world, which you can find from the main menu under 'Specialists'.

Syndromes of complex instability include -


Unhappy Triad of O'Donoghue

This particular multi-ligament knee injury has earned itself the infamous name of 'The unhappy triad of O'Donoghue'! 

In fact much more common is -

  • torn anterior cruciate ligament (ACL)
  • torn medial collateral ligament (MCL)
  • torn lateral meniscus (if the medial meniscus is torn, the lateral one is usually torn also)

Popliteus tendon

Postero-lateral Rotatory Instability

This is a particular multi-ligament injury involving damage to the structures of the posterolateral corner -

The ACL is frequently also torn, in which case a Segond fracture (bony attachment of the lateral capsular ligaments torn off) may be apparent. This is definitely a condition requiring super-specialist attention.