The multifidus is a group of deep spinal muscles spanning several vertebral segments, primarily in the lumbar region. These muscles extend the vertebral column and, when contracting on one side, contribute to lateral flexion and rotation of the spine. They play a role in maintaining posture, stabilizing the vertebrae, and supporting spinal movement. Atrophy refers to the shrinking or wasting of muscle tissue. Multifidus atrophy is a common finding in individuals experiencing persistent low back pain, indicating a weakening of these specific muscles rather than being the pain itself.
Causes of Multifidus Atrophy
Multifidus atrophy often results from several interconnected factors. Persistent pain signals from the back can lead to arthrogenic muscle inhibition, where the nervous system reduces neural drive to muscles surrounding an injured joint. This inhibition causes the multifidus to become less active, leading to muscle wasting over time. This lack of full spontaneous recovery may contribute to the frequent recurrence of low back pain.
Inactivity and a sedentary lifestyle also contribute to disuse atrophy. When spinal movement is avoided due to fear of pain or prolonged sitting, the multifidus muscles are not adequately challenged, leading to their weakening. This is also observed with prolonged bed rest, where multifidus muscles quickly decrease in size.
Multifidus atrophy is frequently a secondary consequence of other spinal issues. Conditions such as disc herniation, facet joint arthritis, or spinal stenosis can disrupt normal muscle function by causing nerve compression or altering spinal mechanics. For instance, a disc herniation can lead to a reduction in the cross-sectional area and fatty infiltration of the multifidus on the affected side. Lumbar foraminal stenosis, where intervertebral spaces narrow, can also impede nerve function and induce multifidus atrophy.
Direct trauma to the back or the recovery period following spinal surgery can also lead to multifidus atrophy. Injuries, including muscle strains or sprains, may cause the multifidus to weaken due to disuse or direct nerve damage. The healing process after surgery might also involve reduced movement or altered muscle activation patterns.
Recognizing the Symptoms
Individuals experiencing multifidus atrophy often report a persistent, deep, and dull ache in the low back, rather than a sharp, acute sensation. This discomfort can be consistent, indicating an ongoing issue with spinal support. The pain may not always be localized to one small spot but can spread across the lower back region.
A common sensation is that of spinal instability, described as a feeling that the back is weak, might “give out,” or lacks proper support during daily movements. This instability arises because the multifidus muscles are less able to provide their segment-by-segment stabilizing action. Patients might perceive a lack of control over their spine, especially during transitions or when bearing weight.
Symptoms often worsen during specific activities that demand more spinal stabilization. Prolonged sitting or standing can aggravate the discomfort, as these positions require sustained multifidus activity. Bending forward or lifting objects also tend to increase pain, as these movements place greater strain on the compromised muscles, which are unable to provide adequate support.
How Multifidus Atrophy Is Diagnosed
A healthcare professional typically begins the diagnostic process with a thorough physical examination. During this assessment, a physical therapist or physician may use palpation to identify areas of tenderness or reduced muscle bulk. Functional tests are also performed to observe the patient’s ability to consciously contract these deep muscles and assess spinal stability during various movements. These tests help determine if the multifidus is activating appropriately or if there is a delay or weakness in its engagement.
Imaging techniques are central to confirming multifidus atrophy and assessing its extent. Magnetic Resonance Imaging (MRI) is considered the most effective method for visualizing the multifidus muscles. MRI can clearly show changes in muscle size, including reductions in cross-sectional area, and reveal fatty infiltration. Fatty infiltration, where muscle tissue is replaced by non-contractile fat, is a significant indicator of chronic atrophy and appears as areas of increased signal intensity on MRI scans.
Rehabilitative ultrasound imaging (RUSI) offers another diagnostic approach, allowing clinicians to view the multifidus muscle contracting in real-time. This technique can measure muscle thickness changes during activation, providing immediate visual feedback on muscle function and helping to identify asymmetry or reduced ability to thicken during contraction. While less precise than MRI for detailed structural changes, RUSI is valuable for assessing muscle activity and guiding rehabilitation efforts.
Rehabilitation and Treatment Approaches
The primary goal of treating multifidus atrophy extends beyond general “core strengthening” to specific neuromuscular re-education. This approach aims to reactivate the atrophied muscle, helping the brain regain control over its specific contraction patterns. Successful rehabilitation focuses on restoring the precise, localized function of the multifidus rather than simply building overall strength in superficial muscles.
Treatment begins with very specific, low-load exercises designed to isolate and activate the deep multifidus muscles. These exercises often involve learning to gently contract the multifidus without recruiting larger, more superficial back muscles. Examples include subtle movements like tilting the pelvis or performing a modified “bird dog” exercise, where the focus is on maintaining a neutral spine and controlled, minimal movement. The objective is to swell the muscle beneath a therapist’s fingers without visible spinal movement, ensuring the correct muscle is targeted.
The guidance of a physical therapist is beneficial in this process. Therapists can provide tactile cues, placing their fingers on the multifidus to help patients feel the muscle activating, and offer verbal instructions to ensure proper technique. They can help differentiate multifidus contraction from the activation of other muscles, which is a common challenge for individuals with atrophy. General exercises like crunches or planks, while strengthening the global core, often fail to specifically target the deep multifidus and can sometimes be counterproductive if they promote compensatory movement patterns.
As patients gain better motor control, treatment progresses from basic activation to integrating the multifidus into more complex, functional movements. This staged progression involves gradually increasing the load and complexity of exercises, such as incorporating the multifidus into squatting, lifting, and walking patterns. The aim is to build the muscle’s endurance and strength so it can consistently provide stability during daily activities, ultimately restoring spinal function and reducing the likelihood of recurring pain.