Gastrocnemius medialis muscle morphology and function one year after Vulpius gastrocsoleus lengthening surgery in adolescents with cerebral palsy.

BACKGROUND: Ankle plantarflexion contracture is common in cerebral palsy (CP). Surgical gastrocsoleus aponeurotic lengthening can improve ankle dorsiflexion, but the effects on muscle morphology and gait remain unclear. This study aimed to explore the effects of Vulpius lengthening on gastrocnemius medialis (GM) morphology and gait in CP. METHODS: GM morphology was assessed in eight adolescents with CP (13-20 years) before and one year after gastrocsoleus lengthening, using 3D ultrasonography at 0 and 4 Nm dorsiflexion moments. GM extensibility was defined as the length change between 0 and 4 Nm. In addition, gait kinematics and kinetics were evaluated using gait analysis. FINDINGS: Post-intervention, passive ankle dorsiflexion increased by 12.5° [0:55°] (median [min:max]). At 0 Nm, muscle belly length decreased by 4.1% [-23.6:0.2%] and fascicle length shortened by 14.2% [-44.7:-5.5%], while tendon length increased by 11.4% [5.6:32.6%]. The physiological cross-sectional area increased by 37.5% [7.2:85.7%]. Muscle belly and fascicle extensibility decreased, by 37.3% [-73.1:18.5%] and 20.8% [-77.9:-1.4%], respectively. During gait, on average knee extension in late stance/pre-swing increased by 3.9° [-1.3:22.8°], and ankle power absorption in loading response was reduced by 0.9 Watt/kg [0.007:1.5 Watt/kg]. INTERPRETATION: Orthopedic Vulpius lengthening increased passive ankle dorsiflexion and improved aspects of gait mainly by elongating the Achilles tendon, but led to a shorter muscle belly and fascicles. This study provides insight into GM morphological changes and gait adaptations one year after Vulpius lengthening, and underscores the need to consider muscle morphology and function, rather than just passive joint range of motion, when planning and evaluating musculoskeletal procedures.