Fibular Collateral Ligament–Biceps Femoris Calcific Bursitis Causing Flexion Contracture in the Knee, External Rotation in the Leg, and Equinus Deformity in the Ankle

ObjectiveThe fibular collateral ligament (FCL)–biceps femoris (BF) bursa is not a commonly known location for calcific bursitis. A case of FCL-BF calcific bursitis is presented.Clinical FeaturesAn 18-year-old man had a blunt trauma on the lateral side of his right knee approximately 1 year before his examination. The pain and physical distortion developed in the trauma region over time. Physical examination revealed a 30° flexion contracture and slight valgus deformity in the right knee. There was 30° of external rotation in the leg and a 15° equinus deformity in the ankle. The patient had toe-toe gait. There was a tender swelling 3 × 4 cm in size on the posterolateral aspect of the right knee.Intervention and OutcomePlain radiography and computed tomography revealed a calcific mass, approximately 1.5 × 4 cm in size, between soft tissues adjacent to the posterolateral side of the right lateral femoral condyle. There were articular cartilage thinning and joint space narrowing at the lateral site of the knee joint, and magnetic resonance imaging showed bone marrow edema at the lateral condyles of the tibia and femur. The enlarged calcified bursa was excised. A segment of the contracted iliotibial tract was excised, and a fractional lengthening was performed on the BF tendon.ConclusionThis case report revealed that calcific bursitis can occur in the FCL-BF bursa, which may lead to complications when neglected.