How does artificially reduced rectus femoris primered knee extensor muscle force alters the gait biomechanics in children with cerebral palsy?

Stiff knee gait (SKG) is a common gait abnormality in children with spastic cerebral palsy (SCP) (1). The rectus femoris (RF) muscle is the most targeted treatment of SKG with surgical and neurological interventions (2,3). There is no study in the literature, as we are aware of, investigating the temporary effects of RF muscle weakness on gait in children with SPC. How does artificially reduced rectus femoris primered knee extensor muscle force alters the gait biomechanics of children with SCP? 4 children with SCP (GMFCS Level I-II; 3 females; 2 bilateral, 2 unilateral CP; age:12.75 ± 4.65 y.o., weight: 37.50 ± 12.44 kg, height: 143.88 ± 16.15 cm) were included in the study. To reduce the RF maximal isometric voluntary muscle contraction force (MIVMCF) temporarily, a stretching protocol (135 sec×13 repetitions with 5 sec. resting) was performed (4,5,6). Stretching severity is set as 7/10 discomfort level according to the visual analog scale. 3D gait analysis system (VICON, 6xVantage 5 + 2xAMTI force plates) was utilized before (BS) and after (AS) stretching. MIVMCF of knee-extensor muscles were measured in BS and AS conditions with a hand-held dynamometer (Lafayette 01165 A, US) 3 times at 30-second resting intervals in a sitting position. Interested kinematic and kinetic gait alterations were statistically compared with the paired statistical parametric mapping (SPM{t}) using MATLAB (p<0.05). The MIVMCF of knee-extensor muscles decreased by 15.59% (from 133.91 ± 59.89 N to 113.04 ± 46.35 N) in the AS period. No significant difference was observed between walking speeds (p=0.353). According to the SPM{t} analysis of the sagittal plane parameters of the knee between AS and BS, a significant difference was observed in the initial contact, loading response, and swing sub-phases. All interested gait parameters were compared in Table-1. Download : Download high-res image (255KB)Download : Download full-size image The stretching methodology was effective enough to temporarily reduce the MIVMCF of the knee extensors in children with SPC. As the first in the literature, the gait alterations of rectus femoris primered knee extensor muscle weakness in three planes were determined for children with SCP. As expected, the peak knee flexion and range improved in AS, although the peak knee flexion delay-related parameters did not significantly change. Although 2 of the 4 stiff knee parameters were improved, anterior pelvic tilt was not significantly reduced which may be related to stretching methodology partially involving other knee extensors such as three vastii. Therefore, this study demonstrated that, although the stretching methodology may be improved by surface EMG, it is capable to generate MIVMCF reduction to predict treatment on the knee extensors such as the application of neural agents or orthopedic surgery for SCPs.