Differential Diagnosis for Bony Protuberance on Medial Side of Bent Knee

• Single most likely diagnosis:
  • Osteochondroma: This is a common benign bone tumor that can cause a bony protuberance, especially on the medial side of the knee. It often presents as a hard, painless mass.
• Other Likely diagnoses:
  • Medial plica: This is a fold of synovial tissue in the knee joint that can become inflamed and cause a bony protuberance or a sensation of a mass on the medial side of the knee.
  • Medial meniscal cyst: A cyst that forms in association with a meniscal tear, which can cause a palpable mass on the medial side of the knee.
  • Bursitis (e.g., pes anserine bursitis): Inflammation of the bursa on the medial side of the knee can cause swelling and a palpable mass.
• Do Not Miss diagnoses:
  • Malignant bone tumor (e.g., osteosarcoma): Although rare, it is crucial to consider malignant bone tumors in the differential diagnosis, as they can present with a bony protuberance and have significant implications for treatment and prognosis.
  • Infection (e.g., osteomyelitis, septic arthritis): Infections of the bone or joint can cause swelling, pain, and a palpable mass, and require prompt diagnosis and treatment to prevent serious complications.
• Rare diagnoses:
  • Osgood-Schlatter disease: A condition that affects the tibial tubercle, causing a bony protuberance and pain, typically in adolescents.
  • Tibial spine avulsion fracture: A rare injury that can cause a bony protuberance on the medial side of the knee.
  • Synovial chondromatosis: A rare condition characterized by the formation of multiple cartilaginous nodules within the joint, which can cause a bony protuberance or a sensation of a mass on the medial side of the knee.