Multifidus

Multifidus Atrophy Associated with Lumbar Disc Herniation

In order to observe effects of pathologies such as intervertebral disc herniation (IDH) at the cellular level, there have been several studies on chemical changes of lumbar muscles in patients with nerve root impairment.

However, the findings with concern to changes in muscle fiber size vary among investigators, and often report conflicting results. 

To clarify this issue, a study investigated how nerve root impairment affects the histochemical properties of the lumbar multifidus muscle in patients with lumbar IDH. Biopsy specimens were obtained from the L4 and L5 bands of the multifidus muscle on the affected and nonaffected sides of patients with lumbar IDH. The specimens were stained to evaluate the size of the fibers and structural changes.

In the lumbar multifidus muscle, the mean size of Type 2 fibers was significantly smaller than that of Type 1 fibers in all biopsy sites. The mean size of type 1 and type 2 fibers on the affected side were compared with those on the nonaffected side. In the L4 muscle band, there was no side-to-side difference in the mean sizes of either fiber type. In the L5 muscle band, the mean sizes of both types on the affected side, where denervation changes could be expected to occur, were significantly smaller than those on the nonaffected side. There was no significant level-to-level difference in the mean sizes of type 1 and type 2 fibers on either the affected or the nonaffected side.

The authors suggest that significant decreases in the size of type 1 and type 2 fibers, along with structural changes, were demonstrated in the L5 muscle band on the affected side. Nerve root impairment caused by herniated discs may lead to atrophy of both fiber types. Patients with lumbar intervertebral disc herniation may need strength training at a fast velocity and endurance training to improve atrophy of fast- and slow-twitch muscles.

Yoshihara K, Shirai Y, Nakayama Y, et al. Histochemical changes in the multifidus muscle in patients with lumbar intervertebral disc herniation. Spine 2001:26(6), pp. 622-626.

Pathologic Changes in the Multifidus in Lumbar Disc Herniation

Compression forces generated by lumbar disc herniation (LDH) on nerve roots can cause low back pain, leg pain, muscle spasm, and restriction of trunk movement. Dysfunction of the back muscles can also result, although little data report on the histochemical and morphologic features of the paraspinal muscles from diseased vs.normal sides in LDH patients.

The authors of this study note two purposes to their research: to compare the differences and changes in fiber types in the multifidus muscle between diseased and normal sides; and to analyze the relationship between these parameters and the straight leg raising test, low back pain, and the transverse location of the herniated mass. Bilateral samples from the multifidus muscle were harvested from 19 patients (13 men, 6 women) with LDH, then examined using quantitative histologic and histochemical methods. Results showed that:

* Type I (slow-twitch) and Type II (fast-twitch) fibers were significantly smaller in the diseased side compared with the normal side.

* Pathologic changes such as fiber type grouping, group atrophy, internal nuclei, and the presence of small, angulated fibers were more obvious in the diseased side vs. the normal side.

* There was a decrease in the number and cross-sectional area of Type II fibers in the diseased side, leading to diminished Type II muscle strength.

* Abnormal straight leg raising test results correlated with small Type I and Type II fibers on the diseased side.

* Size of Type I and II fibers did not differ between diseased/normal sides in patients with unilateral and bilateral low back pain; however, Type I fibers were significantly smaller when patients had symptoms of central low back pain.

Zhao Wei-Ping, Kawaguchi Y, Matsui H, et al. Histochemistry and morphology of the multifidus muscle in lumbar disc herniation. Spine 2000:25(17), pp2191-2199