Date of Award

5-2012

Degree Type

Thesis

Degree Name

Master of Science

Major

Biomedical Engineering

Major Professor

Jeffrey A. Reinbolt

Committee Members

William R. Hamel, J.A.M. Boulet

Abstract

Stiff knee gait is a prevalent and troublesome movement disorder among children with cerebral palsy, where peak knee flexion is diminished during swing phase. Rectus femoris transfer surgery, a common treatment for stiff-knee gait, reattaches the distal tendon of this biarticular, or two joint, muscle to a new site, such as the sartorius insertion on the tibia. Biarticular muscles play a unique role in motor control. As a biarticular muscle, rectus femoris may offer unrecognized benefits to maintain balance. This study uses musculoskeletal modeling and simulation to investigate the role of this biarticular muscle on balance recovery following support-surface translations. The hypothesis is that a preoperative simulation has increased balance recovery compared with two postoperative cases, and that a unilateral transfer simulation has improved balance recovery relative to a bilateral transfer.

The influence of rectus femoris transfer surgery on balance recovery was assessed with forward dynamic simulations of a patient with cerebral palsy. A 3-dimensional musculoskeletal model was scaled to represent the size of the patient using previously collected gait analysis data. This pre-surgical model was altered to represent unilateral and bilateral rectus femoris tendon transfers to the sartorius. The mechanism used to maintain balance was based on a muscle stretch-reflex control model, where reflex properties were found using optimization. Each 6s simulation included 0.25s of quiet standing, 0.35s of support-surface translation (6 cm in the anterior and posterior directions, with a peak velocity of 23 cm/s), and 5.4s of balance recovery. Balance recovery was evaluated by recording whole-body center of mass displacements relative to the support surface.

The preoperative simulations of balance recovery following support-surface translations maintained balance while both postoperative simulations did not. Moreover, the unilateral simulation maintained balance longer than the bilateral case in both support-surface translation directions. These findings support the hypothesis that the preoperative simulation has the best balance recovery, followed by the unilateral rectus femoris tendon transfer, and finally the bilateral transfer. This study’s results suggest that rectus femoris tendon transfer reduces balance recovery compared with the preoperative case, illustrating the biomechanical advantage that biarticular muscles have in motor control.

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