Fibular Head Dislocation: An Uncommon Cause of Knee Pain
The patient is a male in his 20s who was playing soccer and felt a pop in his left knee followed by pain in his left knee. He has not been able to ambulate since the injury. He has an obvious deformity to the lateral aspect of his left knee. His x-ray was read as normal. Given his pain and mechanism, there was concern for fibular head dislocation so a CT of the knee was ordered. This showed an anterior, inferior subluxation of the fibular head.
Management of Fibular Head Dislocation
Dislocation of the proximal fibular head is an uncommon injury and can be missed on plain x-rays, as was the case in the patient above.  The injury usually happens when force is applied to a slightly flexed knee while the foot is plantar flexed and rotated. Soccer, long jump, parachuting, and snowboarding have all been reported to cause this injury pattern.  Anterolateral dislocation is the most common injury while the subluxation pattern seen in the patient above is actually common in preadolescent girls and classically associated with hyper-mobility of the joint.  This diagnosis is made clinically and should be suspected when there is a lateral knee deformity with pain that is aggravated by ankle movement.  CT can make the definitive diagnosis and is often used when clinical suspicion is high with a negative plain x-ray.  Closed reduction of the injury by applying pressure to the fibular head while reversing the injury pattern is immediate treatment. There is controversy in the literature whether the patients should be immobilized in the ED or be allowed early mobility as tolerated.  Neither approach is considered incorrect but all fibular head dislocations should see an orthopedic surgeon as there is risk for hypermobility of the joint if repeatedly injured.
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