Assessing the accuracy of a prototype drill guide for fibular graft placement in femoral head necrosis.

A prototype drill guide was developed to improve the accuracy of surgical placement of fibular grafts for the treatment of femoral head necrosis. To document performance, two tantalum beads, one placed on the lateral femoral shaft and the other embedded in the superior portion of the head, were used to define the desired graft tract in a series of seven surrogate femurs. Two orthogonal x-rays of the drill guide mounted on each surrogate femur were taken both before and after drilling. After stylus digitization of each x-ray pair, a computer program calculated the achieved accuracy of the drill. The mean of the absolute error between the desired versus obtained position of the drill tip was 3.68 mm (s.d. 1.24 mm), and the random component of the error was 1.98 mm (s.d. 0.89 mm).