The Muscle Behind Spine Surgery: Why the Multifidus Matters

-Sukanya Rao

We focus on discs, nerves, bone, and alignment but what happens to the muscle that stabilizes the spine?

Spine surgery is often planned around clearly defined pathology: neural compression, disc degeneration, instability, deformity, and bony anatomy. Yet posterior lumbar surgery also involves another important component of the functional spine the paraspinal musculature.

Among these muscles, the multifidus plays an important role in segmental stabilization and control of lumbar motion (1).This raises a relevant surgical question: when we treat the pathology, what happens to the muscle supporting the segment?

Why Does This Muscle Matter?

Located deep within the posterior paraspinal musculature, the multifidus has short fascicles spanning individual lumbar segments. While it contributes to spinal movement, its architecture is particularly suited to segmental stabilization and control of lumbar motion (1).

Muscle quality can also change over time. Aging, degenerative disease, chronic pain, and reduced activity may be accompanied by atrophy and fatty infiltration. By the time a patient reaches surgery, the posterior musculature may therefore already reflect the effects of the underlying condition. Surgical exposure can introduce an additional source of change.

What Happens During Posterior Lumbar Surgery?

Posterior lumbar exposure may require varying degrees of muscle dissection, detachment, splitting, and retraction. These maneuvers can contribute to direct tissue injury, reduced perfusion during prolonged retraction, and disruption of the neural supply to the paraspinal musculature.

Researchers have examined these effects using biochemical and imaging measures. Creatine kinase (CK) can indicate acute muscle injury, while MRI can identify structural changes. Cross-sectional area reflects muscle quantity, whereas fatty infiltration provides information about muscle composition and quality.

A study published in the European Spine Journal in 2010 demonstrated measurable muscle changes following one-level posterior lumbar interbody fusion (2). Both conventional open and minimally invasive approaches were associated with changes in the posterior musculature, although the magnitude of acute muscle injury and subsequent structural change was greater with the more extensive open exposure (2).The findings highlighted an important aspect of posterior surgery: the route used to reach the spine can influence the muscle surrounding the operative segment.

Do These Muscle Changes Matter Clinically?

The clinical significance of paraspinal muscle health is increasingly being investigated.A systematic review published in the European Spine Journal in 2020 found that lower preoperative fatty infiltration was associated with greater improvement in low back pain and disability after surgery for degenerative lumbar disease, while associations involving muscle cross-sectional area were less consistent (3). 

This distinction is important because muscle quality and muscle size do not necessarily provide the same information. Fatty infiltration reflects changes in muscle composition that may not be captured by cross-sectional area alone.Taken together, the evidence points to two related considerations. Muscle quality may already be altered in patients presenting for lumbar surgery, while posterior surgical exposure can produce additional measurable changes in the paraspinal musculature. How these factors relate to postoperative pain, function, and recovery remains an evolving area of investigation.

Why the Muscle Deserves Attention

The multifidus is not the primary surgical target, but it is part of the functional anatomy surrounding that target.Its role in segmental stability, its susceptibility to changes associated with posterior surgical exposure, and the emerging relationship between paraspinal muscle quality and clinical outcomes make this musculature increasingly relevant to how we understand lumbar surgery and recovery.

As evidence continues to develop, the question is no longer simply whether the muscle changes after lumbar surgery, but how much those changes matter for postoperative function and recovery.

References

1. Ward SR, Kim CW, Eng CM, Gottschalk LJt, Tomiya A, Garfin SR, et al. Architectural analysis and intraoperative measurements demonstrate the unique design of the multifidus muscle for lumbar spine stability. J Bone Joint Surg Am. 2009;91(1):176–85. 

2. Fan S, Hu Z, Zhao F, Zhao X, Huang Y, Fang X. Multifidus muscle changes and clinical effects of one-level posterior lumbar interbody fusion: minimally invasive procedure versus conventional open approach. Eur Spine J. 2010;19(2):316–24. 

3. Jermy JE, Copley PC, Poon MTC, Demetriades AK. Does pre-operative multifidus morphology on MRI predict clinical outcomes in adults following surgical treatment for degenerative lumbar spine disease? A systematic review. Eur Spine J. 2020;29(6):1318–27.