For most of my career, I was content to blame chronic low back pain on the usual suspects: discs, joints, nerve roots, and the ever-mysterious soft tissue. That was the prevailing wisdom, and I’ll admit, it served me well enough for a long time. But as both the literature and my years in the clinic have evolved, I’ve had to acknowledge a less obvious but essential player: the lumbar spine’s multifidus muscle. This unassuming muscle is actually the spine’s primary stabilizer. When its precise control falters, chronic back pain often follows. The encouraging news is that we now have the tools to assess, retrain, and even directly stimulate the multifidus.
Today, musculoskeletal ultrasound is a bedside tool that lets physicians evaluate the multifidus’ structure and dynamic function. With real-time ultrasound, we can now measure muscle thickness at rest and during contraction, providing a meaningful contraction ratio rather than just a static measurement. Recent studies suggest these ultrasound measures are reliable across sessions, rather than relying on a single snapshot.
Comparative studies suggest ultrasound can grade fatty infiltration about as accurately as MRI, though it still falls short in measuring exact cross-sectional area. Use MRI or CT for the initial structural assessment of fat infiltration and atrophy, then rely on ultrasound for functional, in-office, and follow-up evaluations. This practical combination fits well into a busy clinic.
A recent 2025 study took things a step further by using shear-wave elastography alongside MRI fat-water imaging to look at lumbar multifidus stiffness and contraction ratios at L4-L5 and L5-S1 in patients with and without chronic low back pain. This adds a biomechanical angle (muscle stiffness) that our usual size-based measures completely miss. It helps explain why some patients with only modest atrophy on imaging still have significant functional deficits, and why the reverse can also be true. The study also echoes what earlier ultrasound literature has shown: Multifidus atrophy in chronic low back pain is usually localized to the lower lumbar levels, not spread throughout, and is often paired with a measurable drop in the muscle’s ability to contract voluntarily.
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Motor control exercise (MCE) is probably the most studied approach for targeting the multifidus. The idea is simple: Rather than just telling patients to do general strengthening, we teach them to isolate and activate the multifidus and transversus abdominis with low-load, precise movements. I can vouch for this from both my clinical experience and my own time in the gym. It is harder than it sounds for most people at first, me included. But the payoff, in terms of function and pain relief, is well worth the effort.
Systematic reviews and meta-analyses consistently show that MCE reduces pain and disability in chronic nonspecific low back pain, with benefits seen at follow-up rather than fading immediately after the program ends. A 2025 randomized controlled trial comparing core stabilization exercises to conventional physiotherapy found greater improvements in multifidus cross-sectional area and fat infiltration grade with the stabilization approach, along with better pain and disability outcomes.
The most significant recent development is not in exercise science, but in implantable technology. The ReActiv8 system is currently the only FDA-approved restorative neurostimulation device for chronic low back pain linked to multifidus dysfunction. Unlike spinal cord stimulators, which mainly reduce pain, this device targets the medial branch of the dorsal ramus to trigger episodic, isolated multifidus contractions. In effect, it overrides the neuromuscular inhibition that keeps the muscle from firing and helps restore active spinal control over time.
Two-year results from the ReActiv8-B pivotal trial showed that 76 percent of participants had substantial, clinically meaningful improvement in pain, disability, or both. The benefits grew stronger the longer patients were treated, rather than leveling off early. This study supports a rehabilitative model, not just a palliative one. The device seems to help produce lasting neuromuscular and structural changes, rather than merely masking pain.
In October 2024, ICD-10-CM code M62.85 formally recognized multifidus dysfunction as a distinct disease entity. A 2025 International Society for the Advancement of Spine Surgery (ISASS) guideline update consolidated five-year pivotal trial data, randomized controlled evidence, and payer coverage, including a favorable coverage decision from a major national payer. Case series in patients with prior failed spine surgery have also reported lower complication rates and high patient satisfaction scores, showing a role even in populations who are not surgical candidates and have exhausted conservative care.
It is worth noticing where restorative neurostimulation fits within the wider category of peripheral nerve stimulation (PNS), as the terminology overlaps. A 2023 systematic review of PNS for low back pain, including 29 studies and roughly 1,000 patients, grouped several modalities: conventional PNS targeting the lumbar medial branch nerves, peripheral nerve field stimulation, and restorative neuromuscular stimulation of the multifidus. All three produced mild to moderate pain improvement, but they vary significantly in mechanism and durability, a distinction a 2025 literature update confirms. Most conventional PNS systems use temporary or semi-permanent leads placed percutaneously for weeks to months and work through a sensory, palliative pathway similar in spirit to spinal cord stimulation. In contrast, the implantable restorative device is intended as a permanent motor therapy: It delivers brief, cyclical stimulations to the multifidus over months to years, explicitly aiming to reverse muscle inhibition rather than gate pain signals.
A recent scoping review focused on this distinction, describing neurostimulation as distinct from ablative therapies, spinal cord stimulation, and temporary PNS because it targets underlying motor pathophysiology rather than pain sensation itself. That review also noted a gradual recovery pattern, consistent with rehabilitation rather than an immediate palliative effect.
The strongest evidence remains the RESTORE trial, a randomized head-to-head comparison of the implantable restorative device against optimal medical management, which includes the pharmacologic and interventional therapies most of us already use, including temporary PNS where appropriate, in patients with an average eleven-year history of chronic low back pain and confirmed multifidus dysfunction. Over one year, restorative neurostimulation was statistically significantly better than continued optimal medical management, with a safety profile dominated by expected implant-site issues such as pocket pain and, less commonly, lead fracture. Another real-world cohort study of multifidus and medial branch stimulation similarly found consistent reductions in pain intensity, with adverse event rates comparable to those of other established neurostimulation therapies and no reported lead migrations at the longest follow-up.
We still lack a large, randomized trial directly comparing temporary PNS to the permanent restorative implant in the same patient population. However, the practical takeaway is this: PNS is a reasonable, lower-commitment option for axial mechanical pain without confirmed multifidus dysfunction, while the implantable restorative device is the better-supported choice once multifidus dysfunction is clearly diagnosed and conservative care, including physical therapy and maybe even a course of PNS, has failed.
In summary, the evidence points us toward a stepped clinical approach. Start with ultrasound or MRI to get a baseline sense of multifidus atrophy and function. Next, a structured motor control exercise program with biofeedback should be our first-line rehabilitation. Depending on patient response, consider temporary peripheral nerve stimulation for those with axial mechanical pain but without confirmed multifidus dysfunction. The implantable restorative neurostimulation device should be reserved for patients with persistent disability and clear multifidus dysfunction who have not improved with conservative care and are not candidates for surgery. As always, it comes down to matching the right tool to the right patient, a lesson I keep learning, even after all these years.
Francisco M. Torres is an interventional physiatrist specializing in diagnosing and treating patients with spine-related pain syndromes. He is certified by the American Board of Physical Medicine and Rehabilitation and the American Board of Pain Medicine and can be reached at Florida Spine Institute and Wellness.
Dr. Torres was born in Spain and grew up in Puerto Rico. He graduated from the University of Puerto Rico School of Medicine. Dr. Torres performed his physical medicine and rehabilitation residency at the Veterans Administration Hospital in San Juan before completing a musculoskeletal fellowship at Louisiana State University Medical Center in New Orleans. He served three years as a clinical instructor of medicine and assistant professor at LSU before joining Florida Spine Institute in Clearwater, Florida, where he is the medical director of the Wellness Program.
Dr. Torres is an interventional physiatrist specializing in diagnosing and treating patients with spine-related pain syndromes. He is certified by the American Board of Physical Medicine and Rehabilitation and the American Board of Pain Medicine. He is a prolific writer and primarily interested in preventative medicine. He works with all of his patients to promote overall wellness.
