A 58 year old man underwent TKR with computer navigation using our standard technique. His post operative course was characterized by thigh swelling and pain. He was discharged on postoperative day 3 with a range of movement of 0–30°. 3 days later he was readmitted with increasing thigh pain and swelling. A quadriceps haematoma was suspected and a computerized tomography scan with intravenous contrast was performed. This showed active bleeding into the femoral canal at the site of the pin tract from a branch of the profunda femoris artery as it entered the linea aspera and a large haematoma within the quadriceps muscle centred over the pin tract anteriorly. There was no extraosseous posterior haematoma. An 800ml haematoma was drained and two small fragment cortical screws were inserted into the pin tracts. Unicortical screws were used to minimize the risk of causing posterior bleeding. Arterial injury has not been reported before in this setting. The previously reported complications are: pin breakage, superficial wound infection, interference with line of sight, broken pelvic drill, prolonged operation time and prolonged tourniquet time.