Maladaptive plasticity: effect of obligatory mirroring on knee extensor strength in spastic cerebral palsy.

Research Report
Population: Pediatric

Eileen Greenan Fowler, PT, PhD, Director of Research and Education, UCLA Center for Cerebral Palsy, University of California, Los Angeles

Loretta Staudt, MS, PT, Research PT, University of California, Los Angeles

Marcia Greenberg, MS, PT, Research PT, University of California, Los Angeles

Kent Heberer, MS, Engineer, University of California, Los Angeles

Keywords: Plasticity, Cerebral palsy, Spasticity, Voluntary Motor Control


TITLE: Maladaptive plasticity: effect of obligatory mirroring on knee extensor strength in spastic cerebral palsy

ABSTRACT BODY: Purpose/Hypothesis: Mirror movement is obligatory simultaneous movement of a homologous contralateral joint that occurs during voluntary movement. Obligatory mirror movement may develop following neurological insult in children with spastic cerebral palsy (CP). Upper extremity mirroring in spastic hemiplegic CP is believed to result from the preservation of ipsilateral corticospinal tracts. Animal studies suggest that early motor training may reestablish normal corticospinal connections and function following unilateral brain injury. Lower extremity mirroring is one aspect of reduced selective motor control in children with spastic CP that is assessed using Selective Motor Control Assessment of the Lower Extremity (SCALE) but its effect on the production of voluntary movement has not been studied. Hypothesis: Inhibition of obligatory contralateral knee mirroring will reduce maximal voluntary knee extensor torque.

Participants: Eleven participants (4 females and 7 males) with spastic diplegic (n=9) or hemiplegic (n=2) cerebral palsy (CP) (mean age=9.4±2.6, range=5.6-13.2 years) participated. GMFCS levels (n): I (2), II (3), III (5) and IV (1).

Materials/Methods: SCALE was performed (score range=0 (absent)-10 (normal)) and obligatory mirroring of the contralateral knee was documented. Ten repetitions of maximum effort knee extensor torque (Biodex II isokinetic dynamometer) at 90 deg/s was collected while the contralateral limb was 1) unconstrained allowing mirroring and 2) constrained: held in hip flexion/abduction and knee flexion. Peak and average torques for the two conditions were compared using paired t-tests.

Results: For 7 participants who exhibited obligatory mirroring during SCALE, a significant reduction in peak (.66±.18 vs .39±.11 Nm/kg, p=.004) and average (.48±.16 vs .28±.10 Nm/kg, p=.007) knee extensor torque occurred during the constrained condition. For 4 participants without obligatory mirroring, peak (1.13±.13 vs 1.17±.27 Nm/kg) and average (.90±.18 vs .83±.18 Nm/kg) torques were similar for unconstrained and constrained conditions, respectively. Average limb SCALE scores were higher for the group without obligatory knee mirroring (7.3 vs 3.4).

Conclusions: Inhibition of mirroring resulted in a 41% deficit in peak motor output. These findings support our hypothesis and suggest that mirroring is a form of maladaptive corticospinal tract plasticity that negatively affects ipsilateral voluntary control mechanisms.

Clinical Relevance: Knee extension with contralateral knee flexion occurs during functional tasks such as walking and kicking. The influence of obligatory mirroring on the acquisition and performance of these tasks is an important area for research.

References: 1) Farmer SF et al. Neurology 41:1505-1520, 1991. 2) Martin JH et al. Neurosci Biobehav Rev 31:1125-1135, 2007. 3) Friel K et al. J Neurosci 32:9265-9276, 2012. 4) Fowler EG et al. Dev Med Child Neurol 51:607-614, 2009.

Fowler, Eileen Greenan, PT, PhD; Staudt, Loretta , MS, PT; Greenberg, Marcia , MS, PT; Heberer, Kent , MS. Maladaptive plasticity: effect of obligatory mirroring on knee extensor strength in spastic cerebral palsy.. Poster Presentation. IV STEP Conference, American Physical Therapy Association, Columbus, OH, July 17, 2016. Online.