The effect of Demi Plié in ballet on children with spastic cerebral palsy：A cross-sectional observational study

Background Demi Plié is the most basic movement in classical ballet. Previous studies have shown that Demi Plié may be beneficial for maintaining the posture of patients with cerebral palsy. However, studies also reported that Demi Plié caused injury. The aim of this study was to observe the angles and moments of the lower limb joints of cerebral palsy at different foot turn-out angle of Demi Plié. Methods A cross-sectional observational study was conducted and divided into two group. Joint angles and moments were collected during Demi Plié at progressive foot turn-out angles (30°, 60°, 90° and 120°). Results With the increase of foot turn-out angles, the external rotation and eversion angles of the ankle increased( P  < 0.001), and the eversion moments of ankle increased while the external rotation moments of ankle decreased( P  ≤ 0.001). The external rotation angles of tibia increased with increasing turn-out angles ( P  < 0.001). The extension moments of knee in cerebral palsy group was less than that in the typically developing group ( P  = 0.021). Hip abduction angles and hip external rotation angles in both groups increased with the increase of turn-out angles( P  < 0.001), while hip extension moments and hip abduction moments decreased( P  < 0.05). Pelvis rotation angles were greater in cerebral palsy group compared to typically developing group. Conclusions A large turn-out angle (90° or 120°) may cause excessive stress to lower limb joints, leading to injury in cerebral palsy patients, especially those who have a crouching gait with hyperflexion of the knee and hip and deformities associated with ankle eversion. Trial Registration The trial was registered with the full protocol accessible through Chinese Clinical Trial Registry (ChiCTR) website(https//www.chictr.org.cn/) on February 23rd, 2021. Trial registration number ChiCTR2100043593.