Misunderstood Multifundus
Key Player in Spinal Health
By Jennifer Bresnick, PT, DPT
Monday June 8, 2009
The spine consists of stacked vertebrae separated by cartilaginous discs, with ligaments and muscles holding the whole arrangement together. Although the design may seem simple at first, closer inspection reveals its complexity.“There are a number of biomechanical factors that contribute to spinal health, each contributing in both a unique and collective fashion,” says Chad Cook PT, PhD, MBA, OCS, FAAOMPT, associate professor and coordinator of clinical research in adult spine at Duke University in Durham, N.C.“Bone integrity loss and changes in soft tissue structures, such as disc herniation, arthritic changes to the facet joints, and calcification of a ligamentous complex, may lead to architectural changes of the spine, whereas neuromuscular components may lead to impaired strategies in segmental control,” he explains. “Good spinal health requires a balanced relationship between both groups of factors.”Just as the relationship between bone, cartilage, and muscle must be balanced, so too must individual muscles be in harmony with others. This balance between muscle length, strength, and activation is another important factor that contributes to spinal health, says Heidi Prather, DO, associate professor and chief of section, physical medicine and rehabilitation at Washington University School of Medicine in St. Louis.Precarious Balance
The delicate balance of spinal health is often disrupted by musculoskeletal dysfunction, trauma, or injury. “It is proposed that controlled spinal movement is a complex pattern that involves active structures [muscles], passive structures [bones, capsule, and ligaments], and the neuromuscular subsystems,” Cook says. “Any alteration in the active subsystems responsible for stabilization during movement causes delayed, inefficient deep muscle activity, poor segmental stabilization, compensatory strategies from patients, and increased risk of recurrence of future spinal pain episodes.”Prather adds, “Muscles will adapt to injury and establish substitution patterns. Over time, these patterns of movement can become as debilitating as the original structural injury.”Roy Bechtel, PT, PhD, assistant professor, department of physical therapy and rehabilitation science at the University of Maryland School of Medicine in Baltimore, explains the effects of an impaired musculoskeletal system: “Somatic dysfunction has been shown to both inhibit and facilitate muscles of the spine, depending on the primary tissues and muscles involved. Usually, local muscles like multifidus are inhibited, and global muscles, like psoas, are facilitated. Several studies have shown that pain, which can be associated with trauma of surgery or injury, can inhibit local muscles like [multifidus and] transversus abdominus. This is a problem because local muscles are responsible for stabilizing the spine. If they are inhibited, the risk of injury and dysfunction increases.”Despite its relatively small size, the multifidus muscle group may be more important than previously thought. “The multifidus is one of the local stabilizing muscles of the spine. It stabilizes every segment, but is best-developed in the lumbar spine,” says Bechtel, who specializes in spinal orthopedics. “Studies have shown that an inhibited multifidus does not automatically return to health when back pain goes away. Patients with an inhibited multifidus are several times more likely to have a recurrence of their back pain than patients who have specifically rehabilitated the multifidus using exercises designed for that purpose.”Cook agrees, adding, “The multifidi have been shown to atrophy or exhibit a delayed response in patients with reports of spinal pain and after resolution of spinal pain. Dysfunction in this muscle has been implicated for the high recurrence rates of patients with acute spinal pain.”Muscle Recruitment
Because the multifidus is located so deeply, it can be difficult for therapists to palpate through the overlying musculature. “Direct palpation of multifidus adjacent to the spinous process is possible and often gives good information. Feeling the multifidus lift your finger dorsally during contraction is a quick verification of activity,” Bechtel says. “The key to activating multifidus, after disinhibiting it with mobilization or manipulation at the involved spinal segment, is to work the muscle against gravity in prone or supine, and add stress to the thoracolumbar fascia via diagonal extremity movement.”But actual muscle fiber recruitment can be difficult to verify through simple palpation. “Real-time ultrasound is now becoming less cost-prohibitive and has been shown to be valid and reliable in monitoring multifidus function,” Bechtel says.Although research has yet to show which specific multifidus exercises are superior in terms of outcomes, “At present, targeted interventions specific to the multifidi have demonstrated benefit when compared to no activity,” Cook says. “Further investigation is needed to determine if recovery of this deep muscle group occurs through basic or complex exercise prescription.”Resources
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* Koppenhaver SL, Hebert JJ, Fritz JM, Parent EC, Teyhen DS, Magel JS. Reliability of rehabilitative ultrasound imaging of the transversus abdominis and lumbar multifidus muscles. Arch Phys Med Rehabil. 2009;90(1):87–94.
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Jennifer Bresnick, PT, DPT, is a medical writer for the Gannett Healthcare Group. To comment, e-mail pteditor@gannetthg.com.
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