When Lateral Impact Strikes An Unusual Medial Knee Injury

HISTORY: A 19 yo D3 offensive lineman presented to the training room two days after sustaining a L knee injury. During a blocking maneuver, an opposing player lost balance, and his helmet collided with the lateral aspect of the athlete’s knee, causing a forced valgus stress to the L knee. The athlete was unable to bear weight and required assistance off the field. Pain was localized primarily to the medial knee, with a rapidly developing effusion. Denied any sensations of clicking, catching, or instability. His medical history includes a L patellar dislocation in 2020. PHYSICAL EXAMINATION: 10/14 L Knee: Inspection: 1+ effusion Palp: TTP along the proximal aspect of MCL ROM: 10-80 deg ROM, limited by pain MMT: medial knee pain with extension Ligamentous: Pain with valgus stress and very slight laxity, neg Lachman/anterior drawer. Meniscal: Neg bounce home/joint line pain. McMurray deferred due to pain Neurovasc: Sensation intact throughout, 2 sec cap refill DIFFERENTIAL DIAGNOSIS: MCL sprain grade 1-3 Medial meniscus tear Osteochondral lesion Tendon rupture (Adductor magnus, quadriceps tendon)Bone contusion/fracture Patella dislocation TEST AND RESULTS: 10/14- XR L knee: Small knee effusion. Alignment is appropriate. There is a linear bone fleck displaced from the medial metaphysis. 10/28- MRI: MCL intact, rupture to the MPR, large complex joint effusion with a bony contusion to the lateral femoral condyle plus an avulsion of the periosteum at the medial supracondylar line of the femur where the adductor magnus inserts and vastus medialis originates. FINAL WORKING DIAGNOSIS: Avulsion of the vastus medialis origin and adductor magnus insertion TREATMENT AND OUTCOMES: This case is unique due to an avulsion at the shared insertion site of the adductor magnus and vastus medialis. The MPR rupture appears chronic, likely resulting from the athlete’s previous patella dislocation. This is supported by the bony contusion pattern on the lateral side (likely from the lateral blow to the knee), without any abnormality of the patella itself, and with no associated injury to the MCL, ACL, or PCL. Initially, the patient was placed in a hinged knee brace and began PT focused on strengthening, ROM, and BFRT. Now, at 3 weeks post-injury, he has started a return-to-activity progression, targeting a return to sport within 6-10 weeks.