ABSTRACT
Spinal fixation is a commonly used-procedure to manage spinal instability and mal-alignment as in spondylolisthesis and scoliosis. Restriction of the movement of the spinal segment is among its mechanical consequences. This restriction is assumed to reduce the proprioceptive output from the spine that is essential for proper postural control patterns. Was to investigate the parameters of the automatic postural response of the leg and trunk in patients who have undergone spinal fixation. Sixteen patients whose spine was fixed for management of spondylolisthesis and another 15 patients who had spinal fixation for idiopathic scoliosis were studied. Their automatic postural response parameters following backward perturbation of their erect stance, were compared with the response from 20 healthy volunteers. The study showed evidence supportive of significant deviation from normality of the automatic postural response of the patients' group. The abnormality was in the form of delayed erector spinae response latency as well as increased time gap between the trunk response and the leg response. Additionally, there was erector spinae response amplitude reduction in the patients' group. Finally, there was a statistical evidence of a tight link of the leg and trunk muscle response suggesting a stiffening pattern that was not observed among the control group. The results suggest a problem with the proprioceptive information coming out of the fixed spine that may probably be responsible for the response abnormality observed in the study. These abnormalities may put uncontrolled mechanical burden both on the trunk and the overall body balance