Isolated MCL I and MCL II lesions evidence good recovery of integrity and function under non-operative modes of treatment. Isolated MCL III lesions may also be treated by non-operative management, but with the expectation of a slightly less successful result. However, there is an 80% incidence of concomitant ligament injury with this grade of lesion. The prognosis following injury to the MCL is significantly influenced by the presence of concurrent compromise of other ligaments, particularly that of the anterior cruciate ligament. Resolution of knee instability and dysfunction following a mixed MCL injury of any grade severity is best accomplished through operative intervention. Therefore, it is the authors' opinion that isolated MCL III and all mixed MCL lesions are best managed with operative treatment. Because of the apparent influence compromise of other ligament structures have on the recovery of MCL function, an attempt must be made to repair all acutely injured structures at the time of surgery. The keystones of a satisfactory result are early and accurate diagnosis, prompt treatment, and when indicated, complete surgical repair.
Fetto et al. (1978) studied this question.