Aims: The purpose was to assess the effect of discec-tomy surgery on postural control, lumbar perception and reßex activation of paraspinal muscles during sudden upper limb loading. Methods: The study included 20 patients selected for an operation for chronic low back pain due to disc herniation and 15 controls without chronic back pain. The paraspinal muscle responses for upper limb loading during unexpected and expected conditions were measured by surface EMG. The ability to sense lumbar rotation was assessed in a previously validated motorized trunk rotation unit in the seated position. The postural control was measured with a vertical force platform. Pain, disability and depression scores were recorded. Results: Patients had poorer lumbar perception (P=0.012) and postural control (P< 0.05) than healthy control subjects. The postural control remained unchanged but lumbar perception (P=0.054) and the lumbar feed-forward control (P=0.043) improved after the surgery. Conclusions: This study demonstrated impaired lumbar proprioception and postural control in sciatica patients. During short-term follow-up after operative treatment, postural control does not seem to change, but impaired lumbar proprioception and feed-forward control of paraspinal muscles seem to recover.

Aims: To assess the paraspinal muscle innervation and endurance in LSSMethods: Study included 25 patients with clinically and radiologically diagnosed LSS. Electromyography (EMG) of the paraspinal muscles was performed at the L3 to S1 levels bilaterally using a concentric needle. At least 20 insertions were analysed from each muscle to detect abnormal spontaneous activity associated with axonal damage (þbrillation potentials, positive sharp waves and complex repetitive discharges). Paraspinal muscle activity during trunk ßexion-extension movement and muscle endurance during dynamic isoinertial back endurance test were assessed by surface EMG. Muscle fatigue was calculated using mean power frequency (MPF) analysis. Results: Abnormal þndings in needle EMG of the paraspinal muscles were observed in 18 out of the 22 (81.8%) examined patients. Abnormal ßexionextension activation of the paraspinal muscles was observed in all examined patients. The MPF change was signiþcantly smaller than in previously evaluated healthy subjects and non-speciþc CLBP patients (P< 0.001) not suffering from symptoms of LSS. Para-spinal muscle fatigability was not associated with the denervation of the muscles. Conclusions: Denervation and abnormal activation of lumbar paraspinal muscles are frequent þndings in non-operated LSS patients. The paraspinal muscle endurance of the patients was unexpectedly good