Knee-joint configuration analysis by bi-plane X-ray photogrammetry (1st report, Presentation of calculation method of rotational angles)

This paper investigates the three dimensional rotation between the tibia and femur, which constitute the femorotibial joint, using the bi-plane photogrammetric system developed by the authors. Calculation method of rotational angles is presented based on the corrective rotation of tibial coordinates (r, a, s) to the femoral coordinates (R, A, S). Experiments are performed on two fresh human normal left joints (died at 53 years and 57 years). Internal and external torques of 2.5 N·m are applied to intact and anterior cruciate ligament (ACL) cut joints at flexions ranging from 0° to 80° and their 3-D rotational angles are measured. Known clinical facts relating to the present experiment of ACL cut from normal knee are : (1) By the application of the internal torgue, it causes the increase of the internal rotation at flexions ranging from 0° to 40°. (2) It has no effect on the adduction-abduction of the knee. Comparing the present results with the clinical ones, it is concluded that the proposed calculation method is adequate.