Lumbar disc herniation is a primary cause of lower back pain in adults. Typically, lower lumbar disc herniations occur at L4/5 and L5/S1 segments due to the load bearing forces exerted at these levels. Under 10% of lumbar disc herniations occur at L3/4 and above.
The spine is stabilised by local muscles, and have additional functions of controlling the spinal curvature, and maintaining its mechanical stability. The lumbar multifidus muscle group specifically acts to maintain segmental stability of the spine, controls facet joint movement, and helps to distribute load and pressure between the vertebrae. Interestingly, the nerve supply to multifidus is very primitive given its important role in spinal stability.
Recent studies have found a link between lumbar disc herniation and multifidus muscle degeneration. MRI of the lumbar spine will often indicate fatty deposits within the multifidus muscle group when lumbar disc herniation has occurred. Typically, this was observed in the lower lumbar region, but more recently, it has been apparent in the upper lumbar spine.
Patients will often report pain centrally in the upper lumbar region, with or without radicular pain into the hips or legs. Some may report feelings of pins and needles, numbness or power loss in the legs. The release of inflammatory factors may lead to multifidus muscle degeneration and a decline in function. A contributing factor will be the protective muscle spasm that restricts lumbar movement, whereby the multifidus will be unable to function leading to disuse atrophy. The longer the symptoms persist, the more marked the degeneration of multifidus, meaning greater instability of the lumbar spine.
Multifidus fatty infiltrate can be prevented through lumbar muscle strength training, indicating the need for prompt spinal mobilisation and pain reduction to allow for effective stabilisation.