Functional morphologic features of the human knee: an evolutionary perspective

The complex functional morphologic characteristics of the knee are of ancient origin. The multiple asymmetries of anatomy can be traced back more than 300 million years to the pelvic appendages of Sarcoptorigian lobe-finned fish. The knee functions as a biologic transmission with ligaments acting as sensate linkages and the menisci acting as sensate, mobile bearings. Cine-computed tomography and magnetic resonance imaging studies of intact knees from cadavers reveal a combined rolling and gliding motion, with posterior displacement of the femorotibial contact point with increasing flexion. The posterior displacement of the femorotibial contact point is greater in the lateral compartment by approximately a factor of two. The anatomy of the lateral compartment, including the inferior sloping of the posterior tibial plateau, reflects and accommodates this greater motion. This asymmetry of kinematics between the medial and lateral compartment, an established characteristic of human and many other extant mammalian knees, results in an internal rotation of the tibia relative to femur with increasing flexion. By taking into account the complexities of functional morphologic features of the knee, the design of joint replacements and bracing systems may be improved.