Spontaneous atraumatic knee haemarthrosis.

Spontaneous knee haemarthrosis is a rare condition, most prevalent in the elderly with osteoarthritis. Recent reports have proposed that the source of bleeding is the peripheral arteries supplying the posterior horn of the lateral meniscus. In this case, a 62-year-old active man presented with acute postero-lateral left knee pain and swelling with limited weight bearing or movement of the knee. No recent history of trauma but history of lateral compartment dominant osteoarthritis and arthroscopic partial lateral meniscectomy of left knee. Aspiration showed a large haemarthrosis and following an MRI scan displaying large areas of full thickness chondral loss, complex tearing of lateral meniscus and loose bodies, the patient had an arthroscopy, washout, debridement of osteochondral tibial defect and diathermy of suspected bleeding point. This report supports the peripheral arteries supplying the posterior horn of the lateral meniscus as the source of bleeding in spontaneous haemarthrosis of the knee.