Accuracy of intramedullary alignment in total knee replacement.

The accuracy of a system of intramedullary alignment using 6 mm rods was assessed in 100 patients undergoing total knee replacements. Post-operative, full length weight-bearing X-rays were used; the mechanical axis from head was used as the reference axis. The method of calculating the errors produced by flexion and rotation of the limb in relation to the X-ray beam is described, the mean deviation from the mechanical axis in 100 cases being 0.67 degrees valgus with a standard deviation of 2.47 degrees. The maximum error was 6.68 degrees valgus and 4.62 degrees varus. The purpose of this study is twofold, first to assess the accuracy of this system of intramedullary alignment and, second, to develop a method of correcting for apparent radiological misalignment using standard radiographic equipment.