During the past five years, fifty patients have been seen who presented the clinical picture of "chronic tibial collateral ligament strain".

Although it was not suggested by the history or demonstrated by the usual clinical tests, internal derangement of the medial meniscus was suspected.

Exploration of the knees of thirty patients confirmed the suspicion of derangement. The degree and type of derangement varied from patient to patient, but the symptom-producing mechanism was essentially the same in all. That is, part or all of the middle third of the medial meniscus was deformed as well as displaced or herniated out of the medial joint space and wedged beneath the tibial collateral ligament. It was therefore assumed that displacement of the meniscus had caused either overstretch of the fibers of the adjacent ligament or irritation of the ligament and its bursa.

Because of this assumption the medial meniscus of each patient was removed. None has had recurrence of his symptoms. This would seem to substantiate the conclusion that medial meniscus derangement, though not demonstrated clinically, was responsible for the tibial collateral ligament syndrome in each patient and that the treatment of choice is arthrotomy with removal of the medial meniscus.