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Abstract
This study presents a scheme to evaluate the functional integrity of the knee based on a mechanical model. The model is a two-link system articulated by a linear torsional spring and damper. By providing the appropriate dimensions, inertial properties, and spring-damper coefficients of the model, the equations of motion can be written for the model during the stance and swing phases of gait. The angular acceleration of the leg-foot or distal segment can be calculated from these equations and then integrated twice to find the angular displacement of the segment.
The inertial properties of the leg-foot complex are determined from a geometrical model of the leg-foot. This model uses sixteen anthropometric measurements of a subject's leg and foot in order to calculate the inertia tensor and principal moments of inertia at the centroid and knee joint of the model. The output from this model has been validated by comparing the model's results to experimental measurements of fresh cadaver limbs.
The mechanical coefficients of the model are determined from two tests which monitor the oscillation of the knee in relaxed and unrelaxed conditions. These tests identify increases in stiffness in a small sample of older male subjects when compared to younger adult male subjects. A statistically significant increase in damping is identified in the older group during unrelaxed oscillations at 45(DEGREES) of knee flexion. While there is no significant difference in damping among the other tests, there is a tendency toward increased damping among the older group.
The simulated angular motion of the knee determined from the equations of motion based on these input parameters compare favorably to actual knee motion monitored by high speed cinematography. Arbitrary increases in the model's stiffness result in changes in the simulated data.
Strength of the Quadriceps Femoris muscle is a standard clinical measure of knee function. Therefore a correlational analysis is used to identify a relationship between knee extension strength and the coefficients of stiffness and damping. No correlation is found between these parameters.
