Tibial torsion measurement by surface curvature.

BACKGROUND Tibial torsion is the angle between the transverse axes of the proximal and distal tibial articular surfaces. It measures the degree of twisting of the tibia around its own longitudinal axis. The accurate measurement on the magnitude of tibial torsion is of great use in monitoring derangements. It is also useful as a baseline in the event of surgical intervention. Various methods have been developed but none of them have gained wide acceptance. Even the CT scan technique, which is considered the "gold standard", produces varying results when executed by different researchers. A quick, objective and non-invasive method is thus very much needed for the effective monitoring of tibial torsion in clinical environments. METHODS Eighteen adult men's lower legs were scanned by a laser scanner to give the surface coordinates of the leg surfaces. By calculating curvature maps of legs from the 3D coordinates, stable anatomical landmarks such as the lateral and medial malleoli can be located. The angle indicating the degree of tibial torsion can then be derived from these landmarks. FINDINGS The objective determination of the various anatomical landmarks results in a reproducible measure of tibial torsion. The results obtained in this study are generally in agreement with the measurements reported previously. INTERPRETATION The reproducibility of the results allows for the objective observation, monitoring and comparison of tibial torsion over time and across subjects. It allows also for the development of a system of measurement that is fast, convenient, accurate and radiation-free.