Instability in the knee is the feeling that you cannot confidently trust the joint, which may feel wobbly or give way suddenly, and the term may also apply to the kneecap which can sublux or dislocate.

Sherman Type 2 ACL tearWith a torn anterior cruciate ligament, even after all pain and swelling have settled, the patient may still experience abnormal feelings of shifting of the bones when bearing weight, and a need to taughten the thigh muscles to improve stability.
menisco-tibial avulsion or floating meniscusAn avulsed meniscotibial ligament may leave the patient with an unstable feeling when performing twisting activities, and the knee may suddenly buckle.

 

Tibiofemoral instability

Knee instability (as opposed to kneecap instability) is the uncomfortable subjective experience of the knee catching, buckling (giving way), moving abnormally front-to-back, rotationally or sideways. It may be challenging to describe. The cause may be found to be -

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Patello-femoral instability

A number of conditions may cause the kneecap to feel untrustworthy, where it might suddenly catch painfully or feel as if it is jumping out from its usual position, or even dislocate. These include both injury to the stabilising structure of the kneecap and abnormal anatomy between the patella and its underlying groove, including -

 

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Dr Sheila Strover (Editor)
BSc (Hons), MB BCh, MBA

See biography...