Peter A. Huijbregts, MSc, MHSc, PT, OCS, MTC, CSCS
Abstract: This article reviews research on the effects of manipulation, traction, and McKenzie exercises on the position of herniated nuclear material in lumbar intervertebral discs. Conclusions based on this research are discussed as well as clinical relevance and avenues for future research.
Key Words: Disc, Herniation, Manipulation, Traction, McKenzie
“Disc herniation” is a collective term, describing a process in which the rupture of anular fibers allows for a displacement of the nucleus pulposus within the intervertebral space, most commonly in a posterior or posterolateral direction1. Weber1 subdivides disc herniations into three categories: protruded, extruded, and sequestered. He visualizes a protrusion as a bulging disc with the anular wall still intact and an extrusion as a disc in which the nucleus pulposus has penetrated the outer anular fibers. With a sequestration, one or more fragments of the nucleus have broken free from the herniated mass and have escaped into the spinal canal.
All nociceptively innervated structures are theoretically a source of pain if afflicted by an appropriate disease or disorder2. Because the periphery of the disc is nociceptively innervated, the degenerative and/or traumatic process of disc herniation may produce discogenic pain by excessive mechanical strain on the outer anular fibers2. Inflammatory products following trauma to these anular fibers may cause pain by chemical irritation of the nociceptive nerve fibers2. Disc herniation can also cause compression of nociceptively innervated extradiscal structures, such as the posterior longitudinal ligament, the dural sleeves of the nerve roots, and possibly the dural covering of the spinal cord2.
Disc herniation can also cause radicular pain. Dorsal root ganglia have been shown to be sensitive to mechanical compression2 (normal nerve roots are not sensitive to such compression2). However, the venous system of the nerve root is very vulnerable: even minor compression may lead to edema formation, resulting in intraneural inflammation and making the nerve root highly mechanosensitive1. Penetration of the outer anular fibers may also release endogenous chemicals from within the disc, thus increasing nerve hyperexcitability and susceptibility to compression1; these chemicals may also cause pain by chemical irritation of any other nociceptively innervated structures with which they come into contact2.
The goal of physical therapy with disc herniation (as with any other disease or dysfunction) is to restore or maximize patient function. Disc herniation is hypothesized to result in the patient’s symptoms by mechanical or chemical irritation of discal and extradiscal structures. Decreasing the mechanical component by restoring the displaced nuclear material to its normal, or a more normal, place within the disc is one possible method for decreasing symptoms and restoring function. Physical therapists use several interventions in the treatment of disc protrusion or extrusion, justifying these choices by stating these interventions may alter the position of nuclear material. This article reviews research on the ability of the physical therapist to affect nuclear position in the lumbar spine by manipulation, traction, and McKenzie exercises. To establish the effect of such interventions on nuclear position research uses imaging techniques that give information on that nuclear position pre- and post-intervention, such as epidurography, discography, CT scan and MRI. I will also discuss possible conclusions drawn from these research findings, the relevance of these conclusions for physical therapy practice, and suggestions for future research.