201by lumbar disc herniation. For this purpose, we assessed the CSAs of these muscles using magnetic resonance imaging (MRI). Based on the results, we suggest possible remedies to hasten the recovery after lumbar disc surgery. MATERIALS AND METHODS Patient populationWe retrospectively analyzed data obtained from 76 consecutive patients who underwent conventional open microdiscectomy for severe leg pain caused by lumbar disc herniation in 2005, of which 39 patients (51.3%) had a symptom duration of 1 month or less (group A), and 37 (48.7%) had a symptom duration of 3 months or more (group B). The inclusion criteria of group A were as follows : 1) single-level lumbar disc herniation at L4-5 level on computed tomography and/or MRI; 2) severe leg pain that was consistent with the radiologic findings; 3) leg pain that did not respond to conservative treatment; and 4) interval from symptom onset to surgery of 1 month or less. Patients with chronic low back pain, motor weakness, and/or previous history of lumbosacral spinal surgery were excluded. Group A comprised 27 men and 12 women with a mean age of 42.2±7.9 years (range, 25-58 years). The mean symptom duration INTRODUCTIONSciatica is characterized by radiating pain in an area of the leg typically served by one nerve root in the lumbar or sacral spine. The most common cause of sciatica is lumbar disc herniation. The clinical course of sciatica is considered favorable, with resolution of leg pain via conservative treatment in a majority of the patients 15) . However, atrophy of the ipsilateral multifidus or psoas muscles has been reported in cases of sciatica caused by lumbar disc herniation 2,3,10) . Dangaria and Naesh 3) noted a significant reduction in the cross sectional area (CSA) of the ipsilateral psoas in patients with unilateral lumbar disc herniation. Hyun et al. 10) reported a significant decrease in the CSA of the ipsilateral multifidus in patients with unilateral lumbosacral radiculopathy.The aim of the current study was to investigate whether asymmetry of the multifidus and psoas muscle occurred and whether it was related to the duration of the unilateral sciatica caused Department of Neurosurgery, Wooridul Spine Hospital, Seoul, KoreaObjective : To quantitatively evaluate the asymmetry of the multifidus and psoas muscles in unilateral sciatica caused by lumbar disc herniation using magnetic resonance imaging (MRI). Methods : Seventy-six patients who underwent open microdiscectomy for unilateral L5 radiculopathy caused by disc herniation at the L4-5 level were enrolled, of which 39 patients (51.3%) had a symptom duration of 1 month or less (group A), and 37 (48.7%) had a symptom duration of 3 months or more (group B). The cross-sectional areas (CSAs) of the multifidus and psoas muscles were measured at the mid-portion of the L4-5 disc level on axial MRI, and compared between the diseased and normal sides in each group. Results : The mean symptom duration was 0.6±0.4 months and 5.4±2.7 months for groups A and B, respectively (p<0.001). There were no dif...