Incarcerated Pes anserinus around a proximal tibial osteochondroma: a rare extra-articular cause of locked knee

Background: Osteochondroma is the most common benign skeletal neoplasm and is found most often in long bones, especially in the distal femur and proximal tibia. They usually present as painless swelling near the joint and can be complicated by mechanical irritation, compression or injury of adjacent structures, fracture, malignant transformation, and post-operative recurrence. Locking of the knee refers to flexion of the knee without complete extension and passive extension is limited resulting in significant pain. Excision is a successful form of the treatment for symptomatic osteochondromas. Case Report: A case of osteochondroma of the proximal tibia illustrates extra-articular cause of locked knee secondary to the incarceration of pes anserinus tendons by the lesion. Conclusion: Surgical excision of the bilobed pedunculated posteromedial proximal tibia osteochondroma and restoration of the gracilis and semitendinosis to its normal anatomic position resulted in the complete resolution of symptoms.