Some people have no problem regaining flexion during rehabilitation, but find that they are unable to regain full extension.
Difficulties regaining extension are commonly due to:
- tightness of the posterior capsule at the back of the knee.
In this region the capsule normally has soft folds, that can play out when the knee is fully extended and allow this range. If the knee is inflamed or held in a bended position for a long time, these folds may be lost and the tissues may become taut and painful as the knee is extended. This process can happen surprisingly quickly, which is why it is imperative to focus early on regaining full extension, equivalent to the good knee.
- scar tissue in the notch (cyclops lesion)
- cruciate ligament contracture from the knee being held bent
- hamstrings tightness and eventually muscle shortening.