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.