Density of lumbar muscles 4 years after decompressive spinal surgery.

Results of decompressive surgery for lumbar spinal stenosis vary. We evaluated the density of lumbar muscles by computed tomography (CT) at the L2-L4 levels in patients 4 years after they had undergone surgery for lumbar spinal stenosis. Twenty of these patients had an excellent outcome clinically, and 16 patients had very poor outcome. The residual stenosis and density of lumbar muscles in Hounsfield units were measured on CT images. The clinical evaluation of outcome also included the Oswestry questionnaire and a walking test. The density of lumbar flexors was higher in the group with excellent results than in the group with poor results. The density of lumbar extensors showed a marked decrease in the operated area. These results suggest that the decrease of muscular density can be partially explained by disuse or inactivity. The decrease in the operated area probably reflects muscular atrophy caused by muscle denervation.