Knee proprioception in children with spastic cerebral palsy: an observational study.

BACKGROUND: Proprioception, the sense of body position and movement, is vital for motor control but has been sparsely explored in children with cerebral palsy (CP), particularly in the lower extremities. This study explored proprioception as the capacity to reproduce and maintain a knee flexion angle in children with CP. METHODS: Fifty-seven children aged 6-18 years with spastic CP; 20 unilateral (USCP), and 37 bilateral (BSCP), at Gross Motor Function Classification System (GMFCS) I-IV, and 42 typically developing (TD) children participated. Three-dimensional motion analysis was used to capture knee movements during a joint position sense test performed in sitting with occluded vision. The test consisted of (i) the criterion angle (CA) trial; the leg was passively elevated to a knee flexion angle of 45 degrees (CA) by an examiner and the position was maintained by the child, and (ii) the reproduced angle (RA) trial; the angle was actively reproduced (RA) and maintained by the child. Joint position sense errors were evaluated as the difference between CA and RA. The children's capacity to maintain the leg position was measured as the difference in knee angles, fluctuations (root mean square error) and drift (linear regression). Data were analysed with non-parametric statistics. RESULTS: Joint position sense errors were greater in the USCP-group than the BSCP-group (p = 0.037), with a more extended knee in the USCP-group (p = 0.012). When maintaining the passively positioned knee angle for 2.5 s, the CP-group compared to the TD-group, showed increased knee flexion and greater movement fluctuations (p = 0.006). Within-group analysis showed increased knee flexion at the passively assumed position (CA vs. maintained for 2.5 s) compared to at the actively assumed position (RA vs. maintained for 2.5 s) in the BSCP-group (p = 0.015) and the GMFCS II-group (p = 0.028). The BSCP-group also showed increased drift over time towards knee flexion when the leg was passively compared to actively positioned (p = 0.040). CONCLUSIONS: The results reveal a divergence in proprioceptive function: while the USCP-group had greater difficulty than the BSCP-group in reproducing a knee angle, the BSCP-group demonstrated greater difficulty in maintaining the knee position during passive positioning of the lower limb. TRIAL REGISTRATION: This study was observational and was therefore not registered as a clinical trial.