Postero-lateral rotatory instability in osteoarthritis of the knee.

Rotatory instability is well recognized following trauma to the knee, but it may also be seen in degenerative disease. The presence of chronic instability may affect the results of operative treatment of the osteoarthritic knee, as has been shown with postero-lateral rotatory instability in patients with varus deformity secondary to osteoarthritis. Recognition of these often subtle clinical entities is essential in order to improve patient selection when considering the various options for operation. An understanding of the pathomechanics of rotational instability in combination with abnormality of alignment in the joint will enable better classification of the changes which occur in osteoarthritis of the knee.