Causes / typical injury mechanism: Any pathology involving the muscles / tendons / ligaments, facet or sacroiliac joints, vertebrae, or intervertebral disks can cause axial low back pain (LBP). This condition can arise acutely or can be caused by overuse / underuse, normal aging, or osteoarthritis (spondylosis). Often, there is no specific injury, with idiopathic etiologies representing up to 85% of cases.

This diagnosis is for back pain without radiculopathy. Back pain with radiculopathy is covered in lumbar radiculopathy and cervical radiculopathy.

Classic history and presentation: Most LBP cases are musculogenic and develop acutely. The classic history for musculogenic back pain is lumbosacral pain after repetitive bending at the waist. The patient will describe aching paraspinal pain and stiffness that is worse with activity. Pain may be unilateral or bilateral. Symptoms are often nonspecific.

Prevalence: LBP is the second most common cause for physician visits, second only to respiratory infections. Up to 80% of adults will experience LBP at some point in their lifetime, with an annual incidence of 15%-45%.

• Age – Occurs in all age groups but is most common in ages 35-55 years.
• Sex / gender – There is no difference in frequency between men and women.

Risk factors: Advanced age, obesity, smoking, alcohol use, osteoporosis, mental health disorders, physical inactivity, job dissatisfaction, other types of chronic pain, and occupations involving repeated lifting or twisting.

Pathophysiology: Broad, considering the variable etiology. Several structures can stimulate afferent pain fibers, resulting in nonspecific LBP.

• Musculogenic – Paraspinal muscle strain or spasm
• Discogenic – Implies that the source of pain is the intervertebral disk; this is controversial. However, decreased water content of the nucleus pulposus and deterioration of the collagen fibers of the annulus fibrosis contribute to degeneration of the lumbar spine (spondylosis).
• Mechanical – Wear in the disks, facet joints, and their supporting ligaments leads to micro- and macroinstability of the lumbar spine.
• Sacroiliac symptoms originate from the sacroiliac (SI) joints.
• See the Differential Diagnosis section for causes of back pain with neurogenic symptoms.

Grade / classification system:

• Acute – Sudden onset and resolves within 4 weeks.
• Subacute – Can arise suddenly or over time and resolves within 4-12 weeks.
• Chronic – Can arise suddenly or slowly, occurs daily, and persists longer than 12 weeks.

"Waddell signs" are a group of physical signs used to evaluate nonorganic causes of back pain, or pain with no direct anatomical etiology. The test is considered positive (ie, a higher likelihood of nonorganic pain) if 3 or more of the following signs are present:

• Superficial or nonanatomic tenderness on palpation
• Pain with axial loading of the spine or acetabular rotation
• Positive straight leg raise test but no pain during distraction (knee extension when the patient is in a seated position)
• Regional neurologic disturbances (stocking and glove paresthesias or weakness / cogwheeling that do not fit a dermatomal / anatomic pattern)
• Overreaction to stimulus