Muscle contracture in cerebral palsy and stroke : an MRI investigation

Muscle contracture is a loss in joint range of motion caused by changes in the passive mechanical properties of muscle. Contractures are prevalent in cerebral palsy and stroke and are often debilitating. The mechanisms of contracture are poorly understood, partly due to limitations of previous techniques used to measure muscle architecture. This thesis used novel imaging techniques to investigate muscle adaptations in contracture following cerebral palsy and stroke. Anatomically-constrained diffusion tensor imaging and mDixon scans were used to measure fascicle lengths, muscle volumes, physiological cross-sectional areas, pennation angles and intramuscular fat fractions in the medial gastrocnemius muscles of children with hemiplegic cerebral palsy, adults who have had a stroke, and age-matched control participants. In children with cerebral palsy, reduced dorsiflexion range on the more-affected side compared to the less-affected side (13 degrees) was accompanied by medial gastrocnemius muscles with shorter fascicles (13%), smaller volumes (35%), smaller physiological cross-sectional areas (26%) and higher fat fractions. Compared to typically developing children, dorsiflexion range was also reduced (10 degrees), and more-affected muscles had shorter fascicles (11%), smaller volumes (33%), smaller physiological cross-sectional areas (7%) and higher fat fractions. Muscles on the less-affected side of children with cerebral palsy were architecturally similar to typically developing muscles but had elevated fat fractions. In people who have had a stroke, reduced dorsiflexion range on the paretic side compared to the non-paretic side (11 degrees) was accompanied by medial gastrocnemius muscles with smaller muscle volumes (15%). Compared to control participants, dorsiflexion range was reduced (6 degrees) and paretic muscles had smaller volumes (16%) and higher fat fractions. Muscles on the non-paretic side were architecturally similar to control muscles but had elevated fat fractions. In cerebral palsy and stroke, reduced dorsiflexion range was accompanied by reduced muscle volume and elevated intramuscular fat fractions. Intramuscular fat did not correlate with range of motion, suggesting (but not proving) that intramuscular fat does not cause contracture. In cerebral palsy, range of motion may be limited by short muscle fascicles. In contrast, muscle fascicle lengths appear to be unchanged following stroke, suggesting that mechanisms of contracture may be different in cerebral palsy and stroke. Muscle contracture in the medial gastrocnemius muscles of children with cerebral palsy may be explained by relatively short fascicles. If short muscle fascicles cause contracture, therapy should be designed to lengthen muscle fascicles. This thesis presents a series of cross-sectional studies. Cross-sectional studies cannot explain how contractures develop over time. Longitudinal studies are needed to understand better the progression of contracture. The MRI techniques used here are likely to be useful for future muscle architecture and intramuscular fat measurements, because these techniques overcome many of the limitations faced by conventional techniques used to make muscle architecture and intramuscular fat measurements