Muscle contributions to vertical and fore-aft accelerations are altered in subjects with crouch gait

Abstract

The goals of this study were to determine if the muscle contributions to vertical and fore-aft acceleration of the mass center differ between crouch gait and unimpaired gait and if these muscle contributions change with crouch severity. Examining muscle contributions to mass center acceleration provides insight into the roles of individual muscles during gait and can provide guidance for treatment planning. We calculated vertical and fore-aft accelerations using musculoskeletal simulations of typically developing children and children with cerebral palsy and crouch gait. Analysis of these simulations revealed that during unimpaired gait the quadriceps produce large upward and backward accelerations during early stance, whereas the ankle plantarflexors produce large upward and forward accelerations later in stance. In contrast, during crouch gait, the quadriceps and ankle plantarflexors produce large, opposing fore-aft accelerations throughout stance. The quadriceps force required to accelerate the mass center upward was significantly larger in crouch gait than in unimpaired gait and increased with crouch severity. The gluteus medius accelerated the mass center upward during midstance in unimpaired gait; however, during crouch gait the upward acceleration produced by the gluteus medius was significantly reduced. During unimpaired gait the quadriceps and ankle plantarflexors accelerate the mass center at different times, efficiently modulating fore-aft accelerations. However, during crouch gait, the quadriceps and ankle plantarflexors produce fore-aft accelerations at the same time and the opposing fore-aft accelerations generated by these muscles contribute to the inefficiency of crouch gait.

Figure 1

Musculoskeletal model of an individual with cerebral palsy and crouch gait. Vertical and fore-aft accelerations of the mass center were calculated by analyzing muscle-driven simulations.

Figure 2

Average hip, knee, and ankle flexion angles and moments during unimpaired gait and mild, moderate, and severe crouch gait. The joint moments are normalized by body mass (kg).

Figure 3

The average (A) fore-aft and (B) vertical accelerations of the mass center during stance produced by each muscle and (C) the average muscle force during stance normalized by body weight (BW). Error bars are ± 1 standard error. A ‘*’ indicates a significant difference (p < 0.05) in the student’s t-test comparing unimpaired gait and crouch gait. An arrow indicates a significant change with crouch severity (p < 0.05) from a one-way ANOVA comparing mild, moderate, and severe crouch gait. In (B), ‘Gravity’ indicates the acceleration of the mass center when only gravity is applied to the mass center. The vertical acceleration provided by skeletal alignment is equal to 9.81 m/s² minus ‘Gravity.’

Figure 4

The fore-aft accelerations of the mass center produced by the vasti (gray line) and gastrocnemius (black line) during stance. The gray area shows the experimentally measured acceleration of the mass center (fore-aft ground reaction force normalized by body mass).