Histochemical changes in the multifidus muscle in patients with lumbar intervertebral disc herniation

Study Design. The histochemical changes in the multifidus muscle in 29 patients with L4-L5 lumbar intervertebral disc herniation were studied. Objectives. To clarify how nerve root impairment affects the histochemical properties of the lumbar multifidus muscle in patients with lumbar intervertebral disk herniation. Summary of Background Data. There have been several studies on histochemical changes in lumbar muscles in patients with nerve root impairment, but the findings concerning changes in muscle fiber sizes vary among investigators. Methods. Biopsy specimens were obtained intraoperatively from the L4 and L5 bands of the multifidus muscle on the affected and nonaffected sides. The specimens were stained with ATPase to evaluate the size of the fibers and structural changes. Results. In the L5 muscle band, the mean sizes of Type 1 and Type 2 fibers on the affected side were significantly smaller than those on the nonaffected side (Type 1: P < 0.01,Type 2: P < 0.001). The decrease in size was 6.4% for Type 1 and 9.8% for Type 2. Increased percentages of Type 1 fibers and a high incidence of small angular fibers and fiber type grouping were also shown on the affected side. In contrast, in the L4 muscle band, no side-to-side differences in the histologic findings were observed. There was no significant level-to-level difference in the mean size of Type 1 or Type 2 fibers on either the affected or the nonaffected side. Conclusions. These results suggest that nerve root impairment leads to atrophy of Type 1 and Type 2 fibers, with structural changes in the multifidus muscle only at the involved level. [Key Words: denervation, histochemistry, lumbar intervertebral disc herniation, multifidus muscle, myosin ATPase].