Crouched postures reduce the capacity of muscles to extend the hip and knee during the single-limb stance phase of gait

Abstract

Many children with cerebral palsy walk in a crouch gait that progressively worsens over time, decreasing walking efficiency and leading to joint degeneration. This study examined the effect of crouched postures on the capacity of muscles to extend the hip and knee joints and the joint flexions induced by gravity during the single-limb stance phase of gait. We first characterized representative mild, moderate, and severe crouch gait kinematics based on a large group of subjects with cerebral palsy (N=316). We then used a three-dimensional model of the musculoskeletal system and its associated equations of motion to determine the effect of these crouched gait postures on (1) the capacity of individual muscles to extend the hip and knee joints, which we defined as the angular accelerations of the joints, towards extension, that resulted from applying a 1N muscle force to the model, and (2) the angular acceleration of the joints induced by gravity. Our analysis showed that the capacities of almost all the major hip and knee extensors were markedly reduced in a crouched gait posture, with the exception of the hamstrings muscle group, whose extension capacity was maintained in a crouched posture. Crouch gait also increased the flexion accelerations induced by gravity at the hip and knee throughout single-limb stance. These findings help explain the increased energy requirements and progressive nature of crouch gait in patients with cerebral palsy.

Figures

Figure 1

The 3D musculoskeletal model in poses corresponding to single limb stance (14–50% of the gait cycle) for normal gait (A) and severe crouch gait (B). The musculoskeletal model has 10 segments, 13 degrees of freedom, and 92 muscle paths. Although an upper body segment was included in our analysis of crouch gait, it is omitted from the figure. We assumed normal trunk kinematics in the crouch groups since upper body motion data was not available for most subjects with crouch gait.

Figure 2

Average joint kinematics for normal and crouch gait. The gray line and bands show the mean values ±1 SD for a group of 83 able-bodied children walking at self-selected speed. The black solid and dashed lines show mean kinematics for subjects with cerebral palsy who walked in a crouch gait, classified as mild (N = 89), moderate (N = 127), or severe (N = 100) based on knee flexion angle at initial contact. All angles are in degrees. The three crouch groups had significantly greater than normal hip flexion (B), knee flexion (C), ankle dorsiflexion (D), and internal hip rotation (E) when averaged over the gait cycle (p

Figure 3

The effect of crouch gait on the capacity of muscles to extend the hip (A) and knee (B). Each bar graph shows the capacity of the major leg muscles to accelerate the hip and knee joints per 1 N muscle force, averaged over the single limb stance period, for normal and crouch gait. Darker shades of gray represent more severe crouch. Extension capacities are positive. The muscles shown include gluteus maximus (GMAX), hamstrings (HAMS), the posterior compartment of gluteus medius (GMEDP), vasti (VAS), soleus (SOL), gastrocnemius (GAS), rectus femoris (RF), tensor fascia latae (TFL), and psoas (PSOAS). Results for the other muscles in the model are available as an online supplement (Appendix A).

Figure 4

The effect of crouch gait on the capacity of the hamstrings to extend the hip and knee, throughout single limb stance, for normal gait and for mild, moderate, and severe crouch gait.

Figure 5

The effect of crouch gait on the flexion accelerations induced by gravity at the hip (A) and knee (B) vs. the gait cycle for normal gait and for mild, moderate, and severe crouch gait. Flexion acceleration is positive.

Figure 6

The effect of tibial torsion on the capacity of muscles to extend the hip (A) and knee (B) in normal and moderate crouch gait during single limb stance. The muscles shown, including gluteus maximus (GMAX), the posterior compartment of gluteus medius (GMEDP), and soleus (SOL), are the stance phase extensor muscles that are substantially affected by tibial torsion (Hicks et al. 2007). The solid white bars show the average extension capacity during normal single limb stance for each muscle in a model with 0°, 30°, and 60° of tibial torsion. The grey bars show the average extension capacity during moderate crouch gait single limb stance, for a model with 0°, 30°, and 60° of tibial torsion.