Patient-specific computational tools for assessing muscle function in children with cerebral palsy

© 2011 Dr. Tomas Alexander CorreaCerebral palsy is a non-progressive neurologic disorder that is the most common cause of childhood disability in the developed world. Muscle and bone deformities displayed by children with cerebral palsy often require corrective surgical interventions. While many of these surgeries are successful, for some patients there may be little or no improvement. This may be partially attributed to surgery based on incorrect interpretations of individual patient conditions, particularly with regard to lower-limb muscle function. Computer models of the musculoskeletal system have the potential to address this issue by providing non-invasive quantification of the function of individual muscles. The goal of this dissertation was to improve current understanding of muscle function in children with cerebral palsy to improve patient outcomes through two objectives: the development of clinically suitable computational tools and a study of the two most common movement patterns associated with diplegic cerebral palsy. In this dissertation, existing modelling techniques were investigated for their accuracy and suitability for clinical usage. The 'scaled-generic' musculoskeletal modelling method was found to be suitably accurate and cost effective for assessments of muscle function in children with cerebral palsy. A novel scaling law was developed for estimating the strengths of individual muscles, which is particularly relevant for developing computer-based models of children. It is anticipated that this scaling law will be integrated into existing modelling software environments. In addition, several quantitative metrics of muscle function were assessed for reliability and suitability for those with neurological impairments. A 'unit-force' approach for assessing the potential or capacity of muscles to generate whole-body motion was found to be the most appropriate for the target patient group. These findings were used to formulate an analysis of the most common movement patterns typically associated with cerebral palsy, namely 'jump gait' and 'crouch gait'. Whilst both of these patterns are characterised by excessive hip and knee flexion, in jump gait there is excessive plantarflexion at the ankle, whilst in crouch gait there is excessive dorsiflexion at theankle. The study described the functional roles of individual muscles in these movement patterns, and found that in both jump gait and crouch gait, the gluteus medius muscle has a substantially reduced capacity for vertical support against gravity. Consequently, two treatments to address this issue were identified; one was a targeted muscle strengthening program, and the other, a surgical procedure. This knowledge may ultimately improvemobility for children displaying these gait abnormalities. This dissertation demonstrates that computational tools may be used to assess musculoskeletal disorders, such as those associated with cerebral palsy, in a manner previously unavailable to medical practitioners. The addition of such assessments to the practitioner's experience and traditional methods may positively influence the treatment of these disorders