Gait in adolescent idiopathic scoliosis: kinematics and electromyographic analysis

Abstract

Adolescent idiopathic scoliosis (AIS) is a progressive growth disease that affects spinal anatomy, mobility, and left-right trunk symmetry. Consequently, AIS can modify human locomotion. Very few studies have investigated a simple activity like walking in a cohort of well-defined untreated patients with scoliosis. The first goal of this study is to evaluate the effects of scoliosis and scoliosis severity on kinematic and electromyographic (EMG) gait variables compared to an able-bodied population. The second goal is to look for any asymmetry in these parameters during walking. Thirteen healthy girls and 41 females with untreated AIS, with left thoracolumbar or lumbar primary structural curves were assessed. AIS patients were divided into three clinical subgroups (group 1 < 20 degrees, group 2 between 20 and 40 degrees, and group 3 > 40 degrees). Gait analysis included synchronous bilateral kinematic and EMG measurements. The subjects walked on a treadmill at 4 km/h (comfortable speed). The tridimensional (3D) shoulder, pelvis, and lower limb motions were measured using 22 reflective markers tracked by four infrared cameras. The EMG timing activity was measured using bipolar surface electrodes on quadratus lumborum, erector spinae, gluteus medius, rectus femoris, semitendinosus, tibialis anterior, and gastrocnemius muscles. Statistical comparisons (ANOVA) were performed across groups and sides for kinematic and EMG parameters. The step length was reduced in AIS compared to normal subjects (7% less). Frontal shoulder, pelvis, and hip motion and transversal hip motion were reduced in scoliosis patients (respectively, 21, 27, 28, and 22% less). The EMG recording during walking showed that the quadratus lumborum, erector spinae, gluteus medius, and semitendinosus muscles contracted during a longer part of the stride in scoliotic patients (46% of the stride) compared with normal subjects (35% of the stride). There was no significant difference between scoliosis groups 1, 2, and 3 for any of the kinematic and EMG parameters, meaning that severe scoliosis was not associated with increased differences in gait parameters compared to mild scoliosis. Scoliosis was not associated with any kinematic or EMG left-right asymmetry. In conclusion, scoliosis patients showed significant but slight modifications in gait, even in cases of mild scoliosis. With the naked eye, one could not see any difference from controls, but with powerful gait analysis technology, the pelvic frontal motion (right-left tilting) was reduced, as was the motion in the hips and shoulder. Surprisingly, no asymmetry was noted but the spine seemed dynamically stiffened by the longer contraction time of major spinal and pelvic muscles. Further studies are needed to evaluate the origin and consequences of these observations.

Figures

Fig. 1

Frontal viewing of a patient equipped with the cutaneous markers, the bipolar muscular electrodes, and the mask linked to the ergospirometer. The patient is walking on the motor-driven treadmill, suspended from the ceiling by a harness. The three solid black arrows represent the X–Y–Z axis in the three spatial planes. These axes served as reference to allow the computation of the 3D angular displacement and angular speed of shoulder, pelvis, hip, knee, and ankle

Fig. 2

Typical trace of shoulder (upper graphs), pelvis (middle graphs), and hip (lower graphs) kinematics in the frontal plane for a normal subject and a patient with idiopathic scoliosis selected from each subgroup. Angular displacements (°) are expressed as a function of the normalized gait cycle (%). The mean (±SD vertical bars—n = 10 consecutive strides) angular displacement is plotted in black for the left side of the normal subject and the convex side of patients. The mean (±SD vertical bars) angular displacement is plotted in thick gray for the right side of the normal subject and concave side of patients. The arrow represents the peak-to-peak amplitude of each joint, i.e. the maximum minus the minimum position

Fig. 3

Typical trace of hip (upper graphs), knee (middle graphs), and ankle (lower graphs) kinematics in the sagittal plane for a normal subject and a patient with idiopathic scoliosis selected from each subgroup. Angular displacements (°) are expressed as a function of the normalized gait cycle (%). The mean (±SD vertical bars—n = 10 consecutive strides) angular displacement is plotted in black for the left side of the normal subject and convex side of patients. The mean (±SD vertical bars) angular displacement is plotted in thick gray for the right side of the normal subject and concave side of patients. The arrow represents the peak-to-peak amplitude of each joint, i.e. the maximum minus the minimum position

Fig. 4

Typical trace of electromyographic activity of Quadratus Lumborum (QL), Erector Spinae (ES), Gluteus Medius (GM), and Semitendinosus (S) muscles for a scoliosis patient from each scoliosis group compared to a normal subject, expressed as a function of normalized stride (expressed in %). The horizontal black bars represent the phasic activity of the muscles for the left side of the normal subject and convex side of patients. The horizontal gray bars represent the phasic activity of the muscles for the right side of the normal subject and concave side of patients