Low back pain

What it is

Back pain divides into a mechanical cause and an inflammatory cause, and telling the two apart is the first task.

Causes and risk

Ankylosing spondylitis, one subset of the broader diagnostic category of axial spondyloarthritis, is the diagnosis to look for behind inflammatory back pain.

Mechanical low back pain has a differential of its own, and each part carries a share:

• Lumbosacral muscle strains and sprains, 70%: often following isolated traumatic incidents or repetitive use; pain worse with movement, relieved by rest; examination may reveal restricted range of motion, muscle tenderness, or trigger points.
• Lumbar spondylosis, 10%: more common in persons older than 40 years; pain may be present in or radiate from the hips; pain is worse with activity and may worsen with lumbar spine extension or rotation; neurologic examination is usually normal.
• Disk herniation, 5% to 10%: most often involves the L5 or S1 nerve root, at L4-L5 or L5-S1 in 90% to 95% of cases; symptoms may include pain, paresthesia, sensory change, loss of strength or reflexes depending on the affected nerve root.
• Spondylolysis, less than 5%: common in young athletes; symptoms often develop insidiously; pain with activities involving lumbar extension; imaging is diagnostic, but early imaging in the absence of red flags is typically not necessary; usually occurs in a lower lumbar vertebra, most often L5.
• Vertebral compression fracture, 4%: the fracture may occur slowly over time or acutely with mild trauma; acute episodes usually resolve in four to six weeks, but abnormal healing or additional fractures may result in chronic pain and functional impairment; it presents as localized back pain that is worse with flexion, often with point tenderness on palpation; risk factors include increased age, history of trauma, chronic steroid use, and osteoporosis; plain radiography should be obtained to confirm the diagnosis.
• Spondylolisthesis, 3% to 4%: pain often radiates into the buttocks or posterior thigh; leg pain may be worse than back pain; often presents as paresthesias, numbness, or weakness; occurs at L5 in 90% of cases.
• Spinal stenosis, 3%: presents as back pain, sometimes with sensory loss or weakness in the legs, and calf pain with ambulation that is relieved with rest or sitting, that is pseudoclaudication; neurologic examination findings are normal; imaging is diagnostic.