Gait in thoracolumbar/lumbar adolescent idiopathic scoliosis: effect of surgery on gait mechanisms

Abstract

For patients whose scoliosis progresses, surgery remains the ultimate way to correct and stabilise the deformity while maintaining as many mobile spinal segments as possible. In thoracolumbar/lumbar adolescent idiopathic scoliosis (AIS), the spinal fusion has to be extended to the lumbar spine. The use of anterior spinal fusion (ASF) instead of the classic posterior fusion (PSF) may preserve more distal spinal levels in attempt to limit the consequences of surgery on trunk mobility. The effects of surgery on body shape, pain and the decompensation phenomenon have all been well evaluated. Very few studies have addressed the effect of ASF or PSF on basic activities, such as walking. Before any treatment, AIS patients already have reduced pelvis, hip and shoulder motion when walking at a normal speed compared with adolescents without scoliosis (control group). Additionally, they have longer contraction time of the lumbar and pelvic muscles leading to an excessive energy cost and reduced muscle efficiency. In addition, if these changes are associated with spinal stiffness, spinal fusion could further negatively affect this pre-surgical inefficient walk. The goals of this study were (a) to compare pre- and 1-year post-surgery conditions in order to assess the effects of spinal arthrodesis on gait parameters and (b) to compare the anterior versus the posterior surgical approaches. Nineteen young females with thoracolumbar/lumbar AIS were assessed by radiological and clinical examination and by conventional gait analysis before surgery and at almost 12 months after surgery. Seven subjects underwent surgery using ASF and 12 using PSF. Three-dimensional gait analysis was performed on a motor-driven treadmill at spontaneous self-selected speed to record kinematic, electromyographic (EMG), mechanical and energetic measurements synchronously. Although it was expected that the instrumentation would modify the characteristics of normal walking, this study showed that surgery does not induce asymmetric gait or any significant differences between the ASP and the PSF surgery groups. One year after surgery, the changes observed consisted of improvements in the gait and mechanical parameters. In the PSF group, 11-14 vertebrae were fused while only 3-4 were fused in the ASF group. In both AIS groups, step length was increased by 4% and cadence reduced by 2%. There was a slight increase in pelvis and hip frontal motion. Only the transverse shoulder motion was mildly decreased by 1.5 degrees . All the other gait parameters were left unchanged or were improved by surgery. Notably, the EMG timing activity did not change. The total muscular mechanical work (W (tot)) increased by 6% mainly due to the external work (W (ext)), i.e. the work performed by the body muscles to move the body in its surroundings. The energy cost, although showing a tendency towards a reduction, remained globally excessive, probably due to the excessive co-contraction of the lumbo-pelvic muscles.

Fig. 1

Back body subject fitted for gait analysis and post-surgery radiography. The left picture shows a postsurgical back shape of an adolescent idiopathic girl equipped with reflective cutaneous markers, surface electrodes, respiratory mask and preventive harness. The right illustration shows postsurgical radiological correction of the same AIS girl operated on with posterior instrumentation

Fig. 2

Typical trace of kinematics (left graphs) and energetics (right graphs) for a patient with idiopathic scoliosis compared to the norms. On the left panel, the graphs show transverse shoulder motion (upper graph), frontal pelvis (middle graph) and hip motion (lower graph). Angular displacements (°) are expressed as function of normalised gait cycle (%).The mean (±SD vertical bars––n = 10 consecutive strides) angular displacement is plotted in black solid line for AIS pre-surgery and in grey solid line for AIS post-surgery. The dash black line represents the mean of control matched group referenced in our previous study [22]. On the right panel, the graphs represent total mechanical work (W_tot, upper graph), energy cost (middle graph) and muscular efficiency (lower graph). The mean (vertical bar chart) ±SD (vertical bars) are drawn in pre-surgery condition (white bar chart) and in post-surgery condition (grey lined barchart) at the speed of 4 km h⁻¹. The black bar chart represents the mean of norms referenced in our previous study [22, 23]