METHOD FOR PREDICTING IN VIVO LIGAMENT LENGTHS FOR THE KNEE.

The proposed technique for in vivo calculation of ligament lengths is based upon an anthropometric scaling procedure (Lew, Lewis-1976) whereby locations of soft tissue origins and insertions are transformed from a dissected cadaver limb to an inaccessible human subject limb. The proposed method may be used to study such topics as the effect of prosthesis orientation for total knee arthroplasties, a force analysis of the knee joint, and the efficacy of reconstructive procedures for internal derangements of the knee. The proposed technique is described and its accuracy examined by several methods. It is then applied to normal human subjects for flexion of the knee. To demonstrate possible applications, the technique was applied to knee flexion to 90 degree for eight human subjects in a series of fourteen trials. Means and standard deviations of changes in ligament lengths are presented. Length changes follow the same pattern as human subject 1, but standard deviations are larger in nearly every case. This implies that ligament length changes differ from person to person, depending upon their bony geometry.