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Roles of Reflex Activity and Co-contraction During Assessments of Spasticity of the Knee Flexor and Knee Extensor Muscles in Children With Cerebral Palsy and Different Functional Levels

SR Pierce, PT, PhD, NCS, is Research Physical Therapist, Shriners Hospitals for Children, Philadelphia, Pennsylvania, and Assistant Professor, Institute for Physical Therapy Education, Widener University, One University Place, Chester, PA 19013 (USA)
MF Barbe, PhD, is Professor, Physical Therapy Department, College of Health Professions, and Professor, Department of Anatomy and Cell Biology, School of Medicine, Temple University, Philadelphia, Pennsylvania
AE Barr, PT, DPT, PhD, is Chair and Professor, Department of Physical Therapy, Jefferson College of Health Professions, Thomas Jefferson University, Philadelphia, Pennsylvania
PA Shewokis, PhD, is Associate Professor, College of Nursing and Health Professions, Drexel University, Philadelphia, Pennsylvania
RT Lauer, PhD, is Assistant Professor, Physical Therapy Department, College of Health Professions, Temple University, and Research Engineer, Shriners Hospitals for Children, Philadelphia, Pennsylvania

Address all correspondence to Dr Pierce at: srpierce{at}mail.widener.edu

Background and Purpose: Spasticity is a common impairment in children with cerebral palsy (CP). The purpose of this study was to examine differences in passive resistive torque, reflex activity, coactivation, and reciprocal facilitation during assessments of the spasticity of knee flexor and knee extensor muscles in children with CP and different levels of functional ability.

Subjects: Study participants were 20 children with CP and 10 children with typical development (TD). The 20 children with CP were equally divided into 2 groups: 10 children classified in Gross Motor Function Classification Scale (GMFCS) level I and 10 children classified in GMFCS level III.

Methods: One set of 10 passive movements between 25 and 90 degrees of knee flexion and one set of 10 passive movements between 90 and 25 degrees of knee flexion were completed with an isokinetic dynamometer at 15°/s, 90°/s, and 180°/s and concurrent surface electromyography of the vastus lateralis and medial hamstring muscles.

Results: Children in the GMFCS level III group demonstrated significantly more peak knee flexor torque with passive movements at 180°/s than children with TD. Children in the GMFCS level I and level III groups demonstrated significantly more repetitions with medial hamstring muscle activity, vastus lateralis muscle activity, and co-contraction than children with TD during the assessment of knee flexor spasticity at a velocity of 180°/s.

Discussion and Conclusion: Children with CP and more impaired functional mobility may demonstrate more knee flexor spasticity and reflex activity, as measured by isokinetic dynamometry, than children with TD. However, the finding of increased reflex activity with no increase in torque in the GMFCS I group in a comparison with the TD group suggests that reflex activity may play a less prominent role in spasticity.