Harvesting the quadriceps tendon graft. a. The proximal end of graft whipstitched using # 2 polyester suture. b. The sutured end of the graft was threaded through a hollow burr, which was attached to an oscillating compression air drill (Richard Wolf, Knittlingen, Germany). c. The cutting edge of a 9.4 mm hollow burr for graft harvesting. Two thirds of the circumference of this specific hollow burr had sharp teeth, while the other 1/3 was blunt. Using the hollow burr with in inner diameter of 9.4 mm, a cylindrical bone cylinder of 20 mm length could be harvested from the proximal aspect of the patella.