ON THE USE OF BURMESTER CURVES TO EXPLAIN ATTACHMENT POINTS OF THE COLLATERAL LIGAMENTS.

The tibia, femur and two cruciate ligaments are often modeled as a four bar mechanism composed of rigid links. In general, four bar mechanisms consist of fixed and moving planes (the bones) along with two connecting links (cruciates) having revolute joints at each end. The connections between links are referred to as pivots and the moving pivots follow circular paths around the fixed (center point) pivots since they are connected by rigid links. A typical engineering problem is to design (synthesize) a linkage which causes the moving plane to pass through a series of prescribed positions. Synthesizing linkages for more than three positions was considered impossible until L. Burmester developed his theory about 1888. In 1977 Menschik used Burmester curves to explain the observed insertion sites of the collateral ligaments. It was Menschik's hypothesis that the attachment points of the collateral ligaments must be geometrically compatible with the motion produced by the four bar mechanism composed of the cruciate ligaments, the tibia, and the femur. This study had two objectives. First, to reproduce the Burmester curves reported by Menschik and determine if they are characteristic of the planar mechanism he used to approximate the knee. Second to compare curves computed using kinematic measurements made on human cadaveric knees with Menschik's curves, and to investigate the sensitivity of the shape of these curves to variations in kinematics induced by different loading conditions. These results bring into question the use of Burmester theory to explain the attachments of the collateral ligaments.