Clinical Features of Low Back Pain
Of the symptoms of spinal disease (pain, stiffness, limitation of movement, and deformity), pain is foremost. Four types of pain may be distinguished: local, referred, radicular, and that arising from secondary muscular spasm. The origin of pain can often be discerned from the patient’s description, reliance being placed mainly on the character of the pain, its location, and conditions that modify it.
Local pain is steady and aching, but it may be intermittent and sharp, and, although not well circumscribed, is felt in or near the affected part of the spine. Local pain is caused by any pathologic process that impinges on structures containing sensory endings, including the periosteum of the vertebral body, capsule of apophyseal joints, annulus fibrosus, and ligaments. Destruction of the nucleus pulposus alone produces little or no pain but the annulus is innervated with small nerve fibers and, when disrupted, may produce considerable pain in the immediate region of the affected disc. Such local discomfort often accompanies the moment of disc rupture through the annulus, before the subsequent pain of nerve root compression arises. Pathologic change arising in spinal structures may also evoke discomfort in regions that share common innervation and thereby vaguely simulate the pain of radicular disease. These areas of referred projection may be considered similarly to the referred pain of the “sclerotomes” discussed in Chap. 7 and below.
Referred pain in reference to the spine may be projected from the spine to viscera and other structures lying within the territory of the lumbar and upper sacral dermatomes, or conversely, projected from pelvic and abdominal viscera to the spine. For example, pain caused by disease of the upper part of the lumbar spine may be referred to the medial flank, lateral hip, groin, and anterior thigh. This has been attributed to irritation of the superior cluneal nerves, which are derived from the posterior divisions of the first three lumbar spinal nerves and innervate the superior portions of the buttocks. Pain from the lower part of the lumbar spine is usually referred to the lower buttocks and posterior thighs and is a result of irritation of lower spinal nerves, which activate the same pool of intraspinal neurons as the nerves that innervate the posterior thighs. Pain of this type is usually diffuse and has a deep, aching quality, but it tends to be more superficially projected. In general, the intensity of referred pain parallels that of local pain and maneuvers that alter local pain have a similar effect on referred pain. McCall and colleagues and Kellgren have verified these areas of reference by the injection of hypertonic saline into the facet joints and the sclerotomes they determined are discussed in Chap. 7; however, as Sinclair and coworkers have pointed out, the sites of reference are inexact and cannot be relied on for precise anatomic localization.
The opposite situation, in which pain from visceral diseases is referred to the lumbar spine, is usually modified by the state of activity of the viscera and sometimes by assuming an upright or supine posture. What is notable in comparison to pain referred from the spine to the viscera is that the character and temporal relationship of the pain have little relationship to movement of the back.