The possible causes of lower back pain are legion, including tumors, infection, complications from other systemic disease, and many musculoskeletal sources, such as bone disorders, osteoarthritis, ankylosing spondylitis, damage to facet joints or discs, and injury to muscles, ligaments or tendons.
However, in up to 40% of patients with chronic lower back pain, the lumbar discs are the primary source of pain. Pain with sitting that improves with walking and pain with back flexion without muscle tenderness suggests discogenic pain. Discogenic pain can be mechanical or chemical in origin and may result from several causes:
- Degenerative disc disease (DDD): DDD results in changes such as disc space narrowing, endplate osteophyte formation, endplate sclerosis, and gas formation within the disc space, which are easily seen on plain radiographs.
- Internal disc disruption (IDD): IDD is marked by altered internal disc structure and metabolic function. It is usually preceded by spinal trauma, but radiographs, CT scans, and myelograms are normal. Discogram is usually abnormal.
- Disc herniation, prolapse or rupture: Unlike IDD, in which the disc is intact externally, disc herniation, prolapse, or rupture alters the physical integrity of the discs.
- The natural aging process also results in degeneration of the intervertebral disc.
Painful discs often have tears and fissures in the anulus, which are innervated with unmyelinated nerve fibers (nociceptors). Stimulation of sensitized nociceptors near anular fissures plays an important role in discogenic pain.
In addition to understanding causal factors, it may be useful to review the patho-anatomy of discogenic lower back pain.