Abstract
Spastic cerebral palsy (SCP) affects neural control, deteriorates muscle morphometrics, and may progressively impair functional walking ability. Upon passive testing, gastrocnemius medialis (GM) muscle bellies or fascicles are typically shorter, thinner, and less extensible. Relationships between muscle and gait parameters might help to understand gait pathology and pathogenesis of spastic muscles. The current aim was to link resting and dynamic GM morphometrics and contractile fascicle behavior (both excursion and velocity) during walking to determinants of gait. We explored the associations between gait variables and ultrasonography of the GM muscle belly captured during rest and during gait in children with SCP [n = 15, gross motor function classification system (GMFCS) levels I and II, age: 7–16 years] and age-matched healthy peers (n = 17). The SCP children’s plantar flexors were 27% weaker. They walked 12% slower with more knee flexion produced 42% less peak ankle push-off power (all p < 0.05) and 7/15 landed on their forefoot. During the stance phase, fascicles in SCP on average operated on 9% shorter length (normalized to rest length) and displayed less and slower fascicle shortening (37 and 30.6%, respectively) during push-off (all p ≤ 0.024). Correlation analyses in SCP patients revealed that (1) longer-resting fascicles and thicker muscle bellies are positively correlated with walking speed and negatively to knee flexion (r = 0.60–0.69, p < 0.0127) but not to better ankle kinematics; (2) reduced muscle strength was associated with the extent of eccentric fascicle excursion (r = −0.57, p = 0.015); and (3) a shorter operating length of the fascicles was correlated with push-off power (r = −0.58, p = 0.013). Only in controls, a correlation (r = 0.61, p = 0.0054) between slower fascicle shortening velocity and push-off power was found. Our results indicate that a thicker gastrocnemius muscle belly and longer gastrocnemius muscle fascicles may be reasonable morphometric properties that should be targeted in interventions for individuals with SCP, since GM muscle atrophy may be related to decreases in walking speed and undesired knee flexion during gait. Furthermore, children with SCP and weaker gastrocnemius muscle may be more susceptible to chronic eccentric muscle overloading. The relationship between shorter operating length of the fascicles and push-off power may further support the idea of a compensation mechanism for the longer sarcomeres found in children with SCP. Nevertheless, more studies are needed to support our explorative findings.
Highlights
Spastic cerebral palsy (SCP) is a neuromuscular disorder due to a nonprogressive brain lesion occurring early in infancy or before (Graham et al, 2016)
The peak push-off power in individuals with SCP is likely affected by the fascicle forcelength relationship, while in typically developing (TD) individuals the force-velocity relationship could instead be decisive
Concerning fascicle lengths, these findings are somewhat in line with biomechanical
Summary
Spastic cerebral palsy (SCP) is a neuromuscular disorder due to a nonprogressive brain lesion occurring early in infancy or before (Graham et al, 2016). Alterations of the musculoskeletal system, e.g., muscle weakness, restricted joint range of motion (RoM), and increased passive joint stiffness, are partly attributable to altered muscle-tendon properties (Barber et al, 2012) This likely contributes to limited mobility and restricted participation in daily life (Damiano et al, 2000). Examinations on microscopic level demonstrated longer sarcomeres (Lieber and Friden, 2002; Ponten et al, 2007; Smith et al, 2011; Mathewson et al, 2014; Mathewson and Lieber, 2015) and reduced serial sarcomere number (Lieber and Friden, 2018) These alterations likely limit muscle force output and excursion, which may in turn deteriorate walking
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