Isolated Deep MCL tear: an easily missed injury and cause of persistent medial side knee pain

INTRODUCTION: The usual treatment of medial collateral ligament (MCL) grades I / II injuries is conservative, with good healing rates reported in the literature. Isolated deep MCL tears are reported rarely in literature, possibly due to under diagnosis. The usual reported mechanism is rapid external rotation of tibia at knee during sports. METHODS: We report here 14 cases (all males, age range 21 - 35 years) of deep MCL tears with intact superficial MCL. All Patients were level 6 (recreational sports) on the Tegner- Lysholm activity scale. Diagnosis was done by grade 1 valgus stress test at 30-degree flexion, normal on 0 degrees. Confirmation was done by MRI imaging showing deep MCL fibers rupture on coronal T2 images. All of these patients had medial sided knee pain. Ten had associated knee injuries (10 had ACL tears, 5 had medial meniscus tears, 3 had lateral meniscus tears). Nine patients were diagnosed retrospectively on MRI due to symptom persistence; five were diagnosed preoperatively. Deep MCL repair was done in five patients. The dMCL was found to be avulsed from the femoral origin underneath an intact sMCL in all the cases. The repair was done over a suture anchor and was checked with intraoperative correction of the valgus stress test to normal. The Average follow-up duration was 10 months. RESULTS: Five patients, diagnosed preoperatively, had medial sided knee pain resolution and no laxity complaints. The other nine patients reported slight pain on medial knee side at follow-up, for which local depomedrol and lignocaine injections were given under ultrasound guidance. The pain was resolved immediately and remains reduced at the time of last follow-up. The patient with repaired dMCL had better symptom resolution as compared to the patients managed with local steroid injections. Although there were no symptoms of laxity in any of the patients, even though the conservatively managed patients had valgus stress test grade 1 positive in 30 degree flexion, at the time of last follow-up. CONCLUSION: Isolated deep MCL tears are reported sparsely in literature. They can be a cause of persistent medial sided knee pain at follow-up, compromising the result of associated ligament reconstructions. The long-term outcomes of such injuries in terms of media laxity are not known, but a timely diagnosis can allow repair of the dMCL and better patient satisfaction.