Proprioceptive-perception threshold is impaired in cerebral palsy and is associated with worse balance performance

Children with cerebral palsy (CP) have various motor impairments, but less is known about their possible proprioceptive deficits, and role of proprioception in the motor impairments1. There are no prior studies quantifying the proprioceptive-perception threshold in CP, but detection of passive movement event has either been intact2 or impaired3, predominantly in their more affected arm4. Joint-position replication performance has also been impaired in the more affected arm5 and bilaterally in the lower limbs6 in CP. To quantify proprioceptive-perception threshold for the ankle joint in adolescents with CP and their healthy peers and examine the association to standing balance performance. We recruited 12 participants with CP (age 16 ± 3.2 y, 11–26 y, 4 females, GMFCS I/III: 8/4) and 12 healthy peers (16.8 ± 4.8 y, 12–26 y, 3 females) after giving informed consent. The proprioceptive-perception threshold was quantified as ability to perceive light rotations of their more affected ankle joint in dorsiflexed position using a silent ankle-movement actuator (Fig. 1). In healthy peers, the tested left/right ankle was randomized. The participant pressed a response button when perceiving brief 2-s plantar flexions delivered every 4–12 s. Adaptive-test algorithm modified the angular velocity (<5 °/s) based on individual performance. The threshold was defined as the slowest angular velocity with >50% correctly perceived stimuli among ~30 rotations. The test was repeated twice to assess test-retest reproducibility. Postural sway using pressure plate recording was quantified in standing posture with hands held on hips in eyes open and closed conditions (60 s each). Fig. 1.Download : Download high-res image (215KB)Download : Download full-size image Proprioceptive-perception threshold was ~0–2.5 fold higher in participants with CP (mean ± SD 1.00 ± 0.39 °/s) compared to healthy peers (0.67 ± 0.13 °/s, p = 0.007, Mann-Whitney test). Test-retest reproducibility was excellent (ICC 0.90). No significant differences were detected between the groups in postural sway. However, the proprioceptive-perception threshold was correlated to the postural sway during eyes open (r = 0.645, p < 0.001, Spearman’s rho) and closed (r = 0.690, p < 0.001) tasks. Our results showed that the proprioceptive perception is impaired in CP. Incidence of marked proprioceptive impairment was 33% in our limited CP sample. These particular patients had ~2-fold higher threshold compared to healthy peers, their GMFCS was predominantly 3 (one with score 1) and showed the weakest postural balance. These results indicate that impaired proprioception may partially explain their motor impairments. Thus, our novel test may have high diagnostic value when planning and monitoring individualized rehabilitation in CP. The test directly quantifies perception, that is essentially a cortical process, and thus may provide highly relevant information when investigating patients with cortical lesions or deficits. Excellent test-retest reproducibility was also encouraging for long-term monitoring purposes.