Working Diagnosis:
Grade II sprain of proximal tibiofibular ligaments.

Treatment:
The athlete was placed in a tall controlled ankle motion (CAM) boot and was given crutches and permitted to bear weight as tolerated.

Outcome:
After 3 days, he was able to place partial weight on his left extremity. After 1 week, he was able to ambulate without crutches. Two weeks after the initial injury he was transitioned to an ankle stabilizing orthosis (ASO) brace and knee sleeve and worked with athletic trainers to a full recovery. He was able to participate in games with full activity three weeks after the initial injury.

Author's Comments:
This case highlights two learning opportunities. One, it is an uncommon presentation of knee pain in an athlete. Proximal tibiofibular sprains are not often seen, and the case highlighted the importance of relying on physical exam and history when creating a differential. Second, this case is a reminder to take everything into account when assessing an injury. This soccer player really had two injuries: a knee and ankle injury. but the emphasis was placed on the knee due to possibility of more severe injury and majority of the pain coming from the knee. This is a typical clinical scenario where it is possible to overlook the second diagnosis, the ankle injury.

Editor's Comments:
Injury to the proximal tibiofibular joint is a rare occurrence. The joint is most stable with the knee in extension as the lateral collateral ligament and bicep femoris tendon become taunt and stabilize the joint. The primary function of the proximal fibula is to dissipate torsional stresses applied at the ankle. Therefore, injuries to the joint occur when the knee is flexed and the leg or ankle is twisted. The lateral knee pain can mimic lateral meniscus tear and the diagnosis can often be missed. A thorough clinical examination is critical to make the diagnosis as radiological diagnosis can be difficult.

References:
Sarma A, Borgohain B, Saikia B. Proximal tibiofibular joint: Rendezvous with a forgotten articulation. Indian J Orthop. 2015;49(5):489-495.

Radakochi M, Malone T. The Superior Tibiofibular Joint: The Forgotten Joint. J Orthop Sports Phys Ther 1982;3(3):129-132.

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