Kinematics of the human knee using an open chain cadaver model.

There continues to be controversy about the kinematics of the human knee. This study used seven knees from cadavers moved by pulling on the quadriceps tendon in an open chain fashion using video motion analysis to determine the instantaneous helical axis of movement. Computed tomography scans of the specimens allowed the axes to be related to condyles. The parameter beta was defined by the relationship of the helical axis to the center of the condyle (pure spinning motion) and the contact point of the condyle on the tibia (pure rolling motion). Axes above the center of the condyle represent countertranslation, those between the center and the contact point combined spinning and rolling, and those below represent concordant translation. If the motion of the knee is guided by the crossed four-bar link then this model, that allows the knee to 'seek its own path' throughout the range of motion, should show the rollback that commonly is thought to be an important feature of knee motion. The results of this study show that the medial side of the knee stays stable in spinning kinematics whereas the lateral side has a rolling motion in full flexion progressing to a spinning motion in midflexion and counter-translation near full extension. The kinematics that would be expected from rollback were not observed.