Lengths of hamstrings and psoas muscles during crouch gait: effects of femoral anteversion.

Recent studies of muscle lengths measured by means of gait analysis data and musculoskeletal models have suggested that in many cases of crouch gait in patients with cerebral palsy, the hamstrings are of normal length and the psoas muscles are short. In these studies, however muscle lengths were calculated by applying kinematic data from a child's joint to a normal adult model. Children with cerebral palsy and other disorders generally do not have normal bone architecture but instead have muscle attachment points and muscle paths altered by osseous deformities. In this study, we explored the consequences of using normal adult musculoskeletal models to calculate hamstring and psoas lengths for children with cerebral palsy. Specifically, for a group of subjects with cerebral palsy who walk with a crouch gait, we investigated the changes in muscle lengths that arise when a patient-specific representation of clinically measured femoral anteversion was added to a model of normal musculoskeletal geometry. The calculation of psoas muscle length was found to be very sensitive to femoral anteversion whereas the calculation of hamstrings length was found to be relatively insensitive to this osseous deformity.