What is the most common pain generator in low back pain?

Most Common Pain Generator in Low Back Pain

The intervertebral disc is the most common pain generator in low back pain, with internal disc disruption (IDD) being the leading cause of chronic low back pain. 1

Pathophysiology of Discogenic Pain

• Disc degeneration leads to nociceptive pain (discogenic pain) through stimulation of nerve endings in the anulus fibrosus, which can be triggered by both mechanical and inflammatory processes 2

• The degenerative cascade begins with an imbalance between catabolic and anabolic processes in the intervertebral discs, leading to extracellular matrix degradation 3

• As disc degeneration progresses, pathological changes include:

  • Ingrowth of vessels and nerve fibers into deeper layers of the anulus fibrosus 2
  • Release of inflammatory mediators including tumor necrosis factor and interleukins 2
  • Loss of nucleus pulposus and water content with subsequent loss of disc height 3

Clinical Presentation of Discogenic Pain

• Discogenic pain typically presents as axial midline low back pain with or without non-radicular referred leg pain in a sclerotomal distribution 4

• Pain commonly increases with weight-bearing activities and certain movements due to abnormal mechanical stimulation of nociceptors 2

• Nonspecific low back pain is defined as "pain occurring primarily in the back with no signs of a serious underlying condition, spinal stenosis, radiculopathy, or another specific spinal cause" 5

• Degenerative changes on lumbar imaging are usually considered nonspecific as they correlate poorly with symptoms 5

Other Pain Generators in Low Back Pain

• When disc degeneration leads to herniation, it can affect adjacent nervous system structures (nerve roots or dorsal root ganglion), causing neuropathic pain 2

• Facet joints can be direct sources of pain due to their rich innervation, while their degenerative changes can cause compression of nerve roots in lateral recesses and neural foramina 1

• Degenerative instability is a common and often misdiagnosed cause of axial and radicular pain 1

• Spinal stenosis can cause neurogenic claudication, characterized by leg pain and weakness on walking or standing, relieved by sitting or spinal flexion 5

Diagnostic Considerations

• Clinical assessment of pain source can be challenging due to the complex anatomy and function of the spine 1

• Advanced imaging methods are often insufficient for definitive diagnosis as similar findings may be present in both symptomatic and asymptomatic individuals 1

• A clinical correlation is always mandatory, and therapy cannot rely solely on imaging abnormalities 1

• Red flags that warrant immediate attention include:

  • Cauda equina syndrome (urinary retention, fecal incontinence, saddle anesthesia) 6
  • Signs of spinal infection (fever, recent infection, IV drug use) 6
  • Malignancy indicators (history of cancer, unexplained weight loss, failure to improve after 1 month) 6

Management Implications

• Both nociceptive and neuropathic pain can be modulated at higher centers, both at spinal and supraspinal levels (central sensitization) 2

• The altered magnitude of perceived pain (neural plasticity) plays a critical role in the evolution of chronic pain 2

• Psychological aspects may also influence the nervous system response in patients with chronic low back pain caused by disc degeneration 2

• Understanding the pathophysiology of degenerative disc disease is important for developing innovative techniques to address the degenerative processes 3