A Hybrid System for Simulation of Athletic Activities Related to Lower Extremity Biomechanics

In this dissertation, the design and development of a hybrid robotic system that
simulates dynamic biomechanical tasks of the lower extremity with emphasis on knee
and hip joints are presented. The hybrid system utilizes a mechanical hip and a cadaveric
knee/ankle component and can accelerate the whole complex towards the ground. This
system is used to simulate complex athletic movements such as landing from a jump at
various anatomical orientations of the lower extremity with muscle action. The dynamic
response of the lower extremity is monitored and analyzed during impulsive contact
between the ground and the cadaveric leg. The cadaveric knee is instrumented to measure
strain of the Anterior Cruciate Ligament (ACL) during simulated high impact sports
activities. The mechanical hip allows various kinematics of the hip including flexion as
well as abduction. In addition to the flexion and abduction of the mechanical hip, the
controlled flexion and extension of the cadaveric knee allows for simulation of complex
tasks such as landing from a jump. A large number of tests were performed at various anatomical positions utilizing this device to simulate landing from a jump. ACL strain
was measured during these tasks using a Differential Variance Resistance Transducer
(DVRT). Ground Reaction Force and muscle forces were measured and monitored using
AmCell load cells recorded using the LabView software. one-inch and 6-inch jump
landing heights were used for all the simulations. The tests were performed at differing
angles of hip flexion (0°, 30°, 45°, 60°) and at two different ankle positions. Plantar
flexion and flat-footed landing conditions were simulated and compared in all degrees of
hip flexion. These tests were repeated with and without hip abduction in order to study
the effects of these landing positions on ACL strain. Hip flexion was found to effect ACL
strain: as angle of hip flexion increases, ACL strain decreases. This occurred in both
abducted and non-abducted hip positions. Ankle landing position had an effect only in
small drop heights, while hip abduction had an effect in large drops. Future tests must be
completed to further study these effects. These studies showed that the robotic system can
simulate dynamic tasks, apply muscle forces, and move the cadaveric tissue in three
dimensional biomechanical positions.