Lower back pain is a common diagnosis with an estimated 80% of people having at least 1 episode of low back pain during their lifetime.¹ Furthermore, lower back is the fifth most common reason for all physician visits in the United States.² To define the scope of this chapter, lower back pain will be described as the perception of pain within the vertebrae, joints, tendons, and ligaments of the lumbosacral spine as well as the muscles, subcutaneous tissue, and skin overlying this region. Most patients (˜85%) who present to primary care with a chief complaint of lower back pain have symptoms that cannot be reliably attributed to a specific disease or anatomic abnormality (thus termed nonspecific low-back pain),³ and most patients recover without significant medical intervention within a few weeks.⁴

As with all musculoskeletal complaints it is important to include in the location, duration, details of any prior back pain, severity of the pain and any palliative or provocative features. Although the majority of patients presenting to primary care with a chief complaint of lower back pain will not have a serious condition, it is important to ensure consideration of more concerning causes in your evaluation. For example, pain that fails to improve with 1 month of therapy, unexplained weight loss, and previous history of cancer are associated with high specificity (90%) for cancer.⁵ In patient with a history of cancer, sudden onset, severe pain should raise concern for a pathologic fracture. Spinal infections such as vertebral osteomyelitis or epidural abscess are modestly associated with a history of intravenous drug use or urinary tract or skin infections (sensitivity of 40%)⁶ and may have associated symptoms such as fever and malaise. Other concerning findings by history include diminished sensation, weakness, and/or bowel/bladder incontinence, as these raise the threshold of suspicion for neurologic injury such as an acute radiculopathy or cauda equina syndrome. Bladder incontinence, in particular, is very sensitive for the detection of cauda equina syndrome (90%).⁷

The mechanism of injury for lower back pain can provide insight into possible pain generators in lower back pain. Acute pain after a lifting injury may indicate a soft tissue sprain or strain or possibly an acute disc herniation. An elderly/osteoporotic individual reporting acute-onset back pain after a bumpy car ride, coughing/sneezing, or mild trauma would be concerning for vertebral
compression fracture. Conversely, chronic lower back pain in overweight individuals who spend most of their time at work sitting with poor posture may indicate discogenic pain (see Table 19-1).

Pain location and radiation characteristics may help in making an accurate diagnosis (Figure 19-1). Patients with lumbosacral spondylosis (zygapophysial or facet joint arthropathy) may report a deep achy pain radiating in a band across the lower back and/or radiation into the buttock or thigh, with radiation below the knee being rare.⁸

Sacroiliac joint pain, a common source of nonradicular axial back pain, tends to be located at the lumbosacral-gluteal junction with referral into the ipsilateral lower extremity and/or groin. In general, sacroiliac joint pain causes pain at and below the waistline, whereas those with lumbar facet arthropathy will tend to localize their pain at and above the waistline.

Lumbar or sacral radicular pain is described as sharp/shooting/lancinating pain felt both superficially and deep that radiates down the leg.⁹ In the absence of objective neurologic deficits this pain is called radiculitis. Radicular pain may occur secondary to mechanical factors causing impingement upon a nerve root (such as neural foraminal stenosis or a disc bulge) or owing to chemical irritation secondary to exposure of the nerve roots to herniated nucleus pulposus (which is enzymatically active and irritating to the nerve roots). This pain, with the possible exception of the S1 nerve root, does not reliably follow a specific dermatomal pattern when patients describe their symptoms.¹⁰ Conversely, a lumbar or sacral radiculopathy is characterized by objective signs of neurologic deficits such as diminished sensation, strength, or reflexes in a dermatomal and/or myotomal pattern congruent with a nerve root distribution.

In any complaint of lower back pain, it is important to evaluate for any objective findings of neurologic deficit with examination of strength, sensation, and reflexes in the lower extremities. This can be accomplished efficiently but thoroughly with an understanding of lumbosacral dermatomes, myotomes, and reflexes. A sufficient examination for screening strength would include assessment of hip flexion (L2), knee extension (L3), ankle dorsiflexion (L4), great toe extension (extensor hallucis longus, L5), and ankle plantar flexion (S1). A screening sensory examination should include the L2-S2 dermatomes (see Figure 19-2 for reference). Reflex examination should include patellar reflexes (primarily L4), medial hamstring reflexes (L5), and Achilles reflexes (S1), with particular attention being paid to asymmetry from side to side. In addition, assessment for upper motor neuron signs in the lower extremity should be included, as injury at/above the level of the conus medullaris (generally ˜L1) may cause an up going great toe on plantar response (Babinski sign) and/or clonus on ankle jerk.

Pain primarily located in the soft tissues of the lower back/buttock region may represent myofascial pain. This is conventionally defined as regional pain originating from exquisitely tender taut bands of muscle (trigger points) and may exist in isolation or as a response to postural or muscular accommodations for an underlying anatomic process such as degenerative disc disease, lumbar facet arthropathy, or scoliosis.¹¹