Cozen's Phenomenon After Repair of a Medial Collateral Ligament Periosteal Avulsion in a Pediatric Athlete: A Case Report.

CASE: A 13-year-old boy sustained an acute, grade III medial collateral ligament (MCL) distal periosteal avulsion injury while playing noncontact football. Treatment consisted of diagnostic knee arthroscopy with open physeal-sparing MCL repair. At approximately 1-year follow-up, new development of genu valgum in the operative extremity was noted. After 8 months of nonoperative treatment with deformity progression, the patient underwent correction with proximal medial tibial hemiepiphysiodesis.

CONCLUSION: Although Cozen's phenomenon commonly occurs after a proximal metaphyseal tibial fracture in children aged 2 to 7 years, it can occur as a rare complication of MCL injury/repair and remains a possible outcome in skeletally immature patients.