Subject-specific musculoskeletal modeling of the lower extremities in persons with unilateral cerebral palsy

Abstract: The computational musculoskeletal models that are used to study muscle moment-generating capacities of persons with movement disorders and planning treatment options must be accurate, and take into account the inter-individual variability of musculoskeletal geometry.In Paper I the methods of creating the subject-specific musculoskeletal model of the lower extremities from magnetic resonance images (MRIs) were developed. The subject-specific model was used to analyze hip, knee and ankle muscle moment arms (MALs) and muscle-tendon lengths (MTLs) during gait in a subject with unilateral cerebral palsy (CP), and to evaluate the accuracy of widespread and commonly-used scaled generic model.It was found that the scaled generic model delivered accurate values for changes in MTLs in most muscles. However, the scaled generic and the subject-specific lower extremity musculoskeletal models showed substantial differences in MALs calculated during gait.In Paper II subject-specific musculoskeletal models of nine subjects with unilateral CP were created to study muscles volumes, MTLs and MALs; and to examine the accuracy of MALs calculated by the scaled generic models.It was shown that the scaled generic model significantly underestimated hip MALs discrepancies between the affected and the non-affected sides of the lower extremities. However, it significantly overestimated hip adduction/abduction of gluteus maximus, gluteus medius, gluteus minimus, tensor fascia latae and biceps femoris long head; and hip flexion of adductor longus and rectus femoris in the affected and the non-affected sides.It was also found that muscle volumes and hip abduction MALs in gluteus medius and gluteus minimus, hip flexion MALs in iliacus and hip rotation in gluteus maximus were smaller in the affected side of lower extremities. MTLs in the affected and the non-affected sides throughout the range of hip motion were similar.This thesis suggests the need for the subject-specific musculoskeletal models that can account for variability of muscle attachments and musculoskeletal geometry of persons with movement disorders. Based on inaccuracies of the scaled generic model reported here, the generic models that are used to guide treatment decisions must be tested, and interpreted with care.