Measuring Motor Error During Physical Therapy in Young Children with Cerebral Palsy

Purpose/Hypothesis: Typical toddler movement is characterized by a high degree of error, with 17 falls per hour when learning to walk. Young children with cerebral palsy (CP) may not experience motor error as frequently as their peers with typical development because of lower physical activity levels or a limited ability to produce movements that challenge their balance - but this has not been quantified. Our objectives were to measure the type and amount of postural error during physical therapy in young children with CP and to determine if there was a relationship between error experience and gross motor function.

Number of Subjects: Fifteen toddlers with CP (6 boys, mean age 26.7 months, GMFCS I-IV) were included. Children were enrolled in a clinical trial (NCT#02340026) and could not take independent steps.

Materials/Methods: Participants were randomly allocated to “conventional” physical therapy (dose-matched control group) that prevented falls or to an intervention that encouraged (among other things) more error experience by not preventing falls and encouraging upright activities (experimental group). Participants were stratified by age and gross motor function to ensure equivalence at baseline. Videos of randomly selected biweekly 30-minute therapy sessions were manually coded to count losses of balance (118 videos total). All losses of balance were further coded as falls (child contacted the floor), rescues (fall prevented by therapist) or saves (child recovered their balance on their own). All videos were 20% double coded for reliability, and disagreements were reconciled for any video that didn’t reach 80% reliability. Differences between groups were assessed with Mann Whitney tests and the relationship to baseline level of gross motor function was quantified by Spearman correlation.

Results: Reliability for 78 videos (66%) exceeded 80% and consensus on disagreements was reached for the remaining 40 videos. Total losses of balance per session averaged 13.2 (SD 5.6) per session in the experimental group compared to 8.5 (SD 7.8) in the conventional therapy group. As intended, falls were significantly greater (p=0.038) in the experimental group (7.6, SD 4.1) compared to the conventional therapy group (1.6, SD 0.8). Neither rescues (experimental 4.7; conventional 6.8; p=0.27) nor saves, which were infrequent (experimental 0.9; conventional 0.2; p=0.19), differed between groups. In the whole sample combined, baseline gross motor function was related to the frequency of saves (r=0.58, p=0.032), but not falls (r=0.10, p=0.73) or rescues (r= -0.18, p=0.54).

Conclusions: Postural error experience resulting in falls may conventionally be lower in young children with CP than their peers with typical development but can be manipulated during physical therapy to approximate typical levels, even in children with significant motor impairment.

Clinical Relevance: Error experience through losses of balance may be an important ingredient in the acquisition of motor skill by promoting problem solving and introducing greater movement variability in young children with CP. Future work should investigate the relationship between error experience and rehabilitation outcomes.