Subluxating biceps femoris tendon: an unusual case of lateral knee pain in a soccer athlete. A case report.

A 24-year-old male medical student had a 6-year history of bilateral knee pain, worse on his left side than on his right, which had increasingly limited his activities, preventing him from playing soccer. The pain was localized to the lateral aspect of his knees and was accompanied by a catching sensation. His symptoms were exacerbated with activity, particularly descending stairs and rising from a squat. There was no history of antecedent trauma. Physical examination revealed normal knee motion, ligamentous stability, normal knee alignment, and excellent hamstring flexibility. Specifically, there was no evidence of lateral collateral ligament instability, posterolateral laxity, or fibular head instability. The fibular heads were extremely prominent in both knees. During knee extension from a flexed position, the long head of the biceps femoris muscle displaced over the fibular head, left more evident than right, reproducing his symptoms (Fig. 1). This phenomenon occurred in the extremes of flexion between 80° and 100° and only with the tibia internally rotated. The snapping or subluxation could be dampened and eliminated by manually compressing the distal biceps musculature. Radiographs demonstrated bilaterally prominent fibular heads but were otherwise unremarkable. No arthritis of the proximal tibiofibular joint was observed. Despite nonoperative treatment with antiinflammatory medication and home physical therapy, his left knee symptoms worsened, and operative exploration of the left knee was performed. Intraoperatively, while the patient was under anesthesia, the subluxation was reproduced. It occurred only with the lower leg internally rotated between 80° and 110° of knee flexion. When a tourniquet placed around the distal thigh musculature was inflated, we could not reproduce the subluxation in internal rotation, effectively confirming our previous result with direct manual compression. The tourniquet was released and the subluxation reconfirmed. A 4.5-inch incision was placed slightly anterior to the long head of the biceps tendon and the common peroneal nerve was identified. Under direct visualization, we observed the subluxation of the tendon anteriorly in extension and reduction of the subluxation with knee flexion (Fig. 1), but we noted no apparent anatomic anomaly of the tendon. We had been prepared to transfer a portion of the biceps tendon if it was abnormally inserted on either the tibia or the fibular head. Instead, we performed a partial resection of the fibular head prominence, removing a 1 3 1.5 cm piece without detaching the biceps tendon or violating the lateral collateral ligament or popliteal fibular ligament (Fig. 2). This procedure eliminated the snapping sensation intraoperatively when the knee was assessed in the provocative positions. The operation was performed on an outpatient basis. Early motion and progression to full weightbearing was allowed. The patient noted immediate resolution of the snapping, regained full motion of his knee, and returned to soccer. At follow-up 1.5 years after the operation, the left knee remained asymptomatic. The right knee biceps * Address correspondence and reprint requests to Bernard R. Bach, Jr., MD, Department of Orthopedic Surgery, Rush-Presbyterian–St. Luke’s Medical Center, 1725 West Harrison Street, Suite 1063, Chicago, IL 60612. No author or related institution has received any financial benefit from research in this study. 0363-5465/101/2929-0093$02.00/0 THE AMERICAN JOURNAL OF SPORTS MEDICINE, Vol. 29, No. 1 © 2001 American Orthopaedic Society for Sports Medicine