A technique for calculating in vivo ligament lengths with application to the human knee joint

Abstract

This analysis is concerned with the development and application of a technique for calculating in vivo ligament length patterns for human joints as they move through a range of arbitrary orientations. The basis of this method is an anthropometric scaling procedure whereby locations of soft tissue origins and insertions in an “inaccessible” human subjecy body segment are determined by mathematically transforming their locations from a dissected cadaver specimen to their respective positions in the human subject. A detailed mathematical development of the technique is presented with the procedure being adapted to the knee joint. The conceptual validity and mathematical accuracy of the method is examined by its application to simple blocks of known geometry. The basic scaling technique and subsequent ligament length calculations are further tested by substituting dry skeletal bones in place of cadaver and human subject limbs so that results obtained by direct measurement could be compared with those theoretically predicted. The in vivo procedure is then applied to human subjects. A parametric analysis is utilized to examine the sensitivity of the technique to the input data. A discussion of possible sources of error is presented.