Knee Moment-Angle Characteristics and Semitendinosus Muscle Morphology in Children with Spastic Paresis Selected for Medial Hamstring Lengthening

Abstract

To increase knee range of motion and improve gait in children with spastic paresis (SP), the semitendinosus muscle (ST) amongst other hamstring muscles is frequently lengthened by surgery, but with variable success. Little is known about how the pre-surgical mechanical and morphological characteristics of ST muscle differ between children with SP and typically developing children (TD). The aims of this study were to assess (1) how knee moment-angle characteristics and ST morphology in children with SP selected for medial hamstring lengthening differ from TD children, as well as (2) how knee moment-angle characteristics and ST morphology are related. In nine SP and nine TD children, passive knee moment-angle characteristics and morphology of ST (i.e. fascicle length, muscle belly length, tendon length, physiological cross-sectional area, and volume) were assessed by hand-held dynamometry and freehand 3D ultrasound, respectively. At net knee flexion moments above 0.5 Nm, more flexed knee angles were found for SP compared to TD children. The measured knee angle range between 0 and 4 Nm was 30% smaller in children with SP. Muscle volume, physiological cross-sectional area, and fascicle length normalized to femur length were smaller in SP compared to TD children (62%, 48%, and 18%, respectively). Sixty percent of the variation in knee angles at 4 Nm net knee moment was explained by ST fascicle length. Altered knee moment-angle characteristics indicate an increased ST stiffness in SP children. Morphological observations indicate that in SP children planned for medial hamstring lengthening, the longitudinal and cross-sectional growth of ST muscle fibers is reduced. The reduced fascicle length can partly explain the increased ST stiffness and, hence, a more flexed knee joint in these SP children.

Glycine receptor subunit-ß -deficiency in a mouse model of spasticity results in attenuated physical performance, growth and muscle strength

“…reduced quality). The observation that spastic muscle has a smaller physiological crosssectional area is in line with data from children with spasticity, as spastic children in general show a reduced physiological cross-sectional area (Haberfehlner et al 2016;Bandholm et al 2009;Moreau et al 2010). To the best of our knowledge, for the SO muscle of children, there is no data available regarding physiological cross-sectional area.…”

“…However, several studies have shown increased tendon lengths in children with spasticity, while similar tendon lengths in typical developing children and children with spasticity have been reported as well (c.f. Barber et al 2011;Herskind et al 2016;Malaiya et al 2007;Mohagheghi et al 2008;Barber et al 2012;Gao et al 2011;Wren et al 2010;Haberfehlner et al 2016). This indicates that in spastic muscle-tendon complex, the tendon likely does not contribute to the increased muscle stiffness.…”

“…Children with spasticity show steeper relationships between ankle and knee joint angles and external applied moments compared to typical developing children (Haberfehlner et al 2016;Bénard et al 2010). This means that in children with spasticity, the resistance to joint extension is higher.…”

“…The underlying mechanism for this may be an impaired longitudinal muscle fiber growth as has been shown during development in children with SP (Barber et al 2012;Haberfehlner et al 2016), which indicates that serial sarcomere number must be likely lower in these fascicles.…”

Outcome of medial hamstring lengthening in children with spastic paresis: A biomechanical and morphological observational study

“…The ST, one of the hamstring muscles, is presumed to contribute to ROM limitation of the knee in children with SP and its tendon is, therefore, frequently lengthened [ 2 – 4 ]. In children with SP, ST has been shown to have a shorter muscle belly and lower volume than in typically developing children [ 12 – 16 ]. Also stiffer fascicles, sarcomeres that operate at higher length, and lower muscle fiber cross-sectional area compared to typically developing children have been reported [ 17 ].…”