Definition

Lumbar strain or sprain is a term used by clinicians to describe an episode of acute low back pain. The patients report pain in the low back at the lumbosacral region accompanied by contraction of the paraspinal muscles (hence, the expression “muscle sprain” or “strain”). The definite cause is unknown in most cases. It most likely is secondary to a chemical or mechanical irritation of the sensory nociceptive fibers in the intervertebral discs, facet joints, sacroiliac joints, or muscles and ligaments at the lumbosacral junction area.

Low back pain is a prevalent condition associated with work absenteeism, disability, and large health care costs [1]. Episodes of low back pain constitute the second leading symptom prompting patients to seek evaluation by a physician [2]. It is estimated that 50% to 80% of adults experience at least one episode of acute low back pain in their lives [3,4]. The incidence of radiculopathy is reported to be much lower than the incidence of axial back pain at 2% to 6% [5]. Patients who experience acute back pain usually see improvements and are able to return to work within a month [6,7]. However, 2% to 7% of patients have chronic back pain [8,9]. Several studies suggest that 90% of patients with an acute episode of low back pain recover within 6 weeks [10–12]. In contrast, some well-conducted cohort studies demonstrate a less optimistic picture, providing short-term estimates of recovery ranging from 39% to 76% [13,14]. Pengel and colleagues [6] published a meta-analysis investigating the course of acute low back pain, concluding that both pain and disability improve rapidly within weeks (58% reduction of initial scores in the first month) and recurrences are common. On the other hand, more recently, Menezes and associates [1] demonstrated that the typical course of acute low back pain is initially favorable, with a marked reduction in mean pain and disability in the first 6 weeks. After 6 weeks, improvement slows, and only small reductions in mean pain and disability are apparent for up to 1 year. By 1 year, the average measures of pain and disability for acute low back pain were very low, suggesting that patients can expect to have minimal pain or disability at 1 year.

Clinicians encounter a number of patients who convert from acute pain to chronic pain. In a recent review involving 10 studies and more than 4000 participants, Hallegraef and coworkers [15] investigated adults with acute and subacute nonspecific low back pain. The odds that patients with negative recovery expectations will remain absent from work because of progression to chronic low back pain was two times greater than for those with more positive expectations.

Consequently, the goals of the clinician evaluating patients with an episode of acute low back pain are to have a working differential diagnosis of the condition and its etiology, to rule out radiculopathy or other serious medical causes, to have a rehabilitation plan that aims to prevent recurrence of this episode, to educate the patient about the pathologic process, and to formulate a management plan if the condition does not improve promptly.

Symptoms

The pain develops spontaneously or acutely after traumatic or strenuous events such as sports participation, repetitive bending, lifting, motor vehicle accidents, and falls. Pain is predominantly located in the lumbosacral area (axial) overlying the lumbar spinous processes and along the paraspinal muscles. There may be an association with pain in the lower extremities; however, the lower extremity pain is less intense than the low back pain. Pain is usually described as sharp and shooting in character accompanied by paraspinal muscle tightness.

Trunk rotation, sitting, and bending forward usually exacerbate pain. Lying down with application of modalities (heat or ice) usually mitigates it.

Red flags that require prompt medical response are outlined in Table 48.1.

Discogenic pain due to degenerative disc disease is the most common known cause of axial pain. The pain from the intervertebral discs is located in proximity to the degenerated disc. Multiple inflammatory products are found in the painful disc tissue that may increase the excitability of the sensory neurons. The pain is referred from the disc to the surrounding paraspinal and pelvic girdle muscles.

Facet (zygapophyseal) joint arthropathy is another source of axial pain, present in about 30% to 50% of patients describing axial pain in the lumbar as well as in the cervical spine [16–18]. The facets are paired synovial joints adjacent to the neural arches. Pain is predominantly in the paraspinal area and is accompanied by contractions of the muscles that guard around the facet joints. The pain from the facet joints can be unilateral or bilateral.

Sacroiliac joint arthropathy is a cause of axial back pain as well. The pain is located in the lumbosacral-buttock junction with referral to the lower extremity and to the groin area. Painful conditions of the sacroiliac joint are known to result from spondyloarthropathies, infection, malignant neoplasms, pregnancies, and trauma and even to occur spontaneously.

Radicular Pain

Predominant buttocks area pain is a common presentation of lumbar radicular pain. Nerve roots can be affected secondary to mechanical pressure and inflammation. Mechanical pressure is usually secondary to disc protrusion (herniation) or due to spinal stenosis. Disc herniations involve all age groups, with predominance in the young and middle aged. Spinal stenosis, on the other hand, predominantly affects the elderly; it is a combination of disc degeneration, ligamentum hypertrophy, and facet arthropathy or spondylolisthesis. In radiculopathy, symptoms are present along a nerve root distribution. Sensory symptoms include pain, numbness, and tingling that follow the distribution of a particular nerve root. The symptoms may be accompanied by motor weakness in a myotomal distribution. Diagnosis and treatment of radiculopathy are discussed in Chapter 47.

Myofascial Pain

There are different theories explaining muscular reasons for acute low back pain, but they remain unproved [19,20]. These theories include inflammation—failure at the myotendinous junction and the production of an inflammatory repair response; ischemia—postural abnormalities causing chronic muscle activation and ischemia; trigger points secondary to repetitive strain of muscles (this theory remains the most attractive) [20]; and muscle imbalance.

The currently most accepted theory for muscle pain is related to the myofascial pain syndrome, which is a common reported disorder in chronic conditions but can be present in the acute conditions as well [21