APPROACH TO THE PATIENT: Back Pain TYPES OF BACK PAIN

Delineating the type of pain reported by the patient is the essential first step. Attention is also focused on identification of risk factors for a serious underlying etiology. The most frequent causes of back pain are radiculopathy, fracture, tumor, infection, or referred pain from visceral structures (Table 10-1).

Local pain is caused by injury to pain-sensitive structures that compress or irritate sensory nerve endings. The site of the pain is near the affected part of the back.

Pain referred to the back may arise from abdominal or pelvic viscera. The pain is usually described as primarily abdominal or pelvic, accompanied by back pain and usually unaffected by posture. The patient may occasionally complain of back pain only.

Pain of spine origin may be located in the back or referred to the buttocks or legs. Diseases affecting the upper lumbar spine tend to refer pain to the lumbar region, groin, or anterior thighs. Diseases affecting the lower lumbar spine tend to produce pain referred to the buttocks, posterior thighs, calves, or feet. Referred pain can explain pain syndromes that cross multiple dermatomes without evidence of nerve root compression.

Radicular pain is typically sharp and radiates from the low back to a leg within the territory of a nerve root (see “Lumbar Disk Disease,” below). Coughing, sneezing, or voluntary contraction of abdominal muscles (lifting heavy objects or straining at stool) may elicit the radiating pain. The pain may increase in postures that stretch the nerves and nerve roots. Sitting with the leg outstretched places traction on the sciatic nerve and L5 and S1 roots because the nerve passes posterior to the hip. The femoral nerve (L2, L3, and L4 roots) passes anterior to the hip and is not stretched by sitting. The description of the pain alone often fails to distinguish between referred pain and radiculopathy, although a burning or electric quality favors radiculopathy.

Pain associated with muscle spasm, although of obscure origin, is commonly associated with many spine disorders. The spasms are accompanied by abnormal posture, tense paraspinal muscles, and dull or achy pain in the paraspinal region.

Knowledge of the circumstances associated with the onset of back pain is important when weighing possible serious underlying causes for the pain. Some patients involved in accidents or work-related injuries may exaggerate their pain for the purpose of compensation or for psychological reasons.

A physical examination that includes the abdomen and rectum is advisable. Back pain referred from visceral organs may be reproduced during palpation of the abdomen (pancreatitis, abdominal aortic aneurysm [AAA]) or percussion over the costovertebral angles (pyelonephritis).

The normal spine has a cervical and lumbar lordosis and a thoracic kyphosis. Exaggeration of these normal alignments may result in hyperkyphosis of the thoracic spine or hyperlordosis of the lumbar spine. Inspection may reveal a lateral curvature of the spine (scoliosis). An asymmetry in the prominence of the paraspinal muscles suggests muscle spasm. Spine pain reproduced by palpation over the spinous process reflects injury of the affected vertebrae or adjacent pain-sensitive structures.

Forward bending is often limited by paraspinal muscle spasm; the latter may flatten the usual lumbar lordosis. Flexion at the hips is normal in patients with lumbar spine disease, but flexion of the lumbar spine is limited and sometimes painful. Lateral bending to the side opposite the injured spinal element may stretch the damaged tissues, worsen pain, and limit motion. Hyperextension of the spine (with the patient prone or standing) is limited when nerve root compression, facet joint pathology, or other bony spine disease is present.

Pain from hip disease may mimic the pain of lumbar spine disease. Hip pain can be reproduced by internal and external rotation at the hip with the knee and hip in flexion or by compressing the heel with the examiner’s palm while the leg is extended (heel percussion sign).

The straight leg–raising (SLR) maneuver is a simple bedside test for nerve root disease. With the patient supine, passive flexion of the extended leg at the hip stretches the L5 and S1 nerve roots and the sciatic nerve. Passive dorsiflexion of the foot during the maneuver adds to the stretch. In healthy individuals, flexion to at least 80° is normally possible without causing pain, although a tight, stretching sensation in the hamstring muscles is common. The SLR test is positive if the maneuver reproduces the patient’s usual back or limb pain. Eliciting the SLR sign in both the supine and sitting positions can help determine if the finding is reproducible. The patient may describe pain in the low back, buttocks, posterior thigh, or lower leg, but the key feature is reproduction of the patient’s usual pain. The crossed SLR sign is present when flexion of one leg reproduces the usual pain in the opposite leg or buttocks. In disk herniation, the crossed SLR sign is less sensitive but more specific than the SLR sign. The reverse SLR sign is elicited by standing the patient next to the examination table and passively extending each leg with the knee fully extended. This maneuver, which stretches the L2-L4 nerve roots, lumbosacral plexus, and femoral nerve, is considered positive if the patient’s usual back or limb pain is reproduced. For all of these tests, the nerve or nerve root lesion is always on the side of the pain.

The neurologic examination includes a search for focal weakness or muscle atrophy, focal reflex changes, diminished sensation in the legs, or signs of spinal cord injury. The examiner should be alert to the possibility of breakaway weakness, defined as fluctuations in the maximum power generated during muscle testing. Breakaway weakness may be due to pain or a combination of pain and an underlying true weakness. Breakaway weakness without pain is almost always due to a lack of effort. In uncertain cases, electromyography (EMG) can determine if true weakness due to nerve tissue injury is present. Findings with specific lumbosacral nerve root lesions are shown in Table 10-2 and are discussed below.

Laboratory studies are rarely needed for the initial evaluation of nonspecific acute (<3 months in duration) low back pain (ALBP). Risk factors for a serious underlying cause and for infection, tumor, or fracture, in particular, should be sought by history and exam. If risk factors are present (Table 10-1), then laboratory studies (complete blood count [CBC], erythrocyte sedimentation rate [ESR], urinalysis) are indicated. If risk factors are absent, then management is conservative (see “Treatment,” below)

Computed tomography (CT) scanning is superior to routine x-rays for the detection of fractures involving posterior spine structures, craniocervical and cervicothoracic junctions, C1 and C2 vertebrae, bone fragments within the spinal canal, or misalignment. CT scans are increasingly used as a primary screening modality for moderate to severe acute trauma. Magnetic resonance imaging (MRI) or CT myelography is the radiologic test of choice for evaluation of most serious diseases involving the spine. MRI is superior for the definition of soft tissue structures, whereas CT myelography provides optimal imaging of the lateral recess of the spinal canal and is better tolerated by claustrophobic patients.

Annual population surveys in the United States suggest that patients with back pain have reported progressively worse functional limitations in recent years, rather than progressive improvements, despite rapid increases in spine imaging, opioid prescribing, injections, and spine surgery. This suggests that more selective use of diagnostic and treatment modalities may be appropriate.

Spine imaging often reveals abnormalities of dubious clinical relevance that may alarm clinicians and patients alike and prompt further testing and unnecessary therapy. Both randomized trials and observational studies have suggested such a “cascade effect” of imaging may create a gateway to other unnecessary care. Based in part on such evidence, the American College of Physicians has made parsimonious spine imaging a high priority in its “Choosing Wisely” campaign, aimed at reducing unnecessary care. Successful efforts to reduce unnecessary imaging have typically been multifaceted. Some include physician education by clinical leaders and computerized decision support, to identify any recent relevant imaging tests and require approved indications for ordering an imaging test. Other strategies have included audit and feedback regarding individual rates of ordering and indications, and more rapid access to physical therapy or consultation for patients without imaging indications.

When imaging tests are reported, it may be useful to indicate that certain degenerative findings are common in normal, pain-free individuals. In an observational study, this strategy was associated with lower rates of repeat imaging, opioid therapy, and physical therapy referral.

Electrodiagnostic studies can be used to assess the functional integrity of the peripheral nervous system (Chap. 6). Sensory nerve conduction studies are normal when focal sensory loss confirmed by examination is due to nerve root damage because the nerve roots are proximal to the nerve cell bodies in the dorsal root ganglia. Injury to nerve tissue distal to the dorsal root ganglion (e.g., plexus or peripheral nerve) results in reduced sensory nerve signals. Needle EMG complements nerve conduction studies by detecting denervation or reinnervation changes in a myotomal (segmental) distribution. Multiple muscles supplied by different nerve roots and nerves are sampled; the pattern of muscle involvement indicates the nerve root(s) responsible for the injury. Needle EMG provides objective information about motor nerve fiber injury when clinical evaluation of weakness is limited by pain or poor effort. EMG and nerve conduction studies will be normal when sensory nerve root injury or irritation is the pain source.