The goal of this dissertation was to develop guidelines for treating crouch gait, a prevalent movement abnormality among children with cerebral palsy. The outcomes of orthopaedic surgeries to treat crouch gait are unpredictable and sometimes satisfactory. Interventions typically alter the lengths and/or moment arms of muscles— yet they are planned without quantitative descriptions of the musculoskeletal geometry. This work generated such descriptions in the form of graphics-based musculoskeletal models. These models were used to examine causes of the excessive knee flexion and hip internal rotation in persons with cerebral palsy.

Computer models of four subjects with cerebral palsy were constructed from magnetic resonance images. The accuracy of the models was evaluated by creating additional models of three lower limb specimens and comparing muscle moment arms estimated from these models to the moment arms measured on the specimens. A “deformable” model was developed to determine how the moment arms of muscles are altered by deformities of the femur. The subject-specific and deformable models were used in conjunction with kinematic data obtained from gait analysis to calculate the lengths and moment arms of the medial hamstrings, psoas, adductors, and gluteus medius during crouch gait.

Short hamstrings are reputed to cause excessive knee flexion, and persistent crouch is frequently treated by surgical lengthening of the hamstrings. Analyses of muscle lengths during crouch gait revealed that only 55% of the crouched limbs (33 of 60 limbs with knee flexion ≥ 15°) had hamstrings that were shorter than normal. Such analyses may help identify appropriate candidates for surgery.

Spastic medial hamstrings or adductors are presumed to contribute to excessive hip internal rotation, yet the rotational moment arms of these muscles during crouched, internally-rotated gait were discovered to be very small or external. Further investigation revealed that exaggerated hip flexion, which increases the internal rotation moment arm of the gluteus medius, or excessive femoral anteversion, which decreases abduction capacity, are more likely than the hamstrings or adductors to cause internal rotation.

This dissertation demonstrates the tremendous potential of biomechanical guidelines, based on accurate descriptions of musculoskeletal geometry, to improve treatment outcomes for persons with cerebral palsy.