_________________________________________________________________________ Neck Pain in Adults
Herniated Nucleus Pulposus Herniated nucleus pulposus is localized displacement of the nucleus, cartilage, or fragmented annular tissue beyond the intervertebral disk space. Most cases of herniated nucleus pulposus involve the annulus fibrosus. The four herniated nucleus pulposus subtypes are [51]: • Disk protrusion: The nucleus pulposus herniates through annular fibers but is confined within the annular margin. • Disk extrusion: Nucleus pulposus herniation extends beyond the annular margin. • Disk sequestration: A nucleus pulposus fragment separates from the extruded disk. • Disk migration: Disk material displaces from the extrusion site. Herniated nucleus pulposus results from repetitive cervical stress but seldom from a single traumatic incident. Increased risk may accrue with vibrational stress, heavy lifting, prolonged sedentary position, whiplash accidents, or frequent acceleration/deceleration [51]. Disk bulge, whereby disk margins extend past the margins of adjacent vertebral end plates, is not considered a true herniation [51]. Degenerative Disk Disease Cervical degenerative disk disease involves degenerative annular tears, loss of disk height, and nucleus pulposus degradation. It is commonly age-related and affected by poor nutrition, smoking, atherosclerosis, job-related activities, and genetics. It is important to remember that degenerative disk changes seen by x-ray may reflect natural aging and not painful pathology [51]. Internal Disk Disruption Internal disk disruption describes pathologic annular fissuring within the disk, without external disk deformation. Internal disk disruption can result from cervical trauma-related nucleus pulposus degradation, cervical flexion/rotation-induced annular injury, or whiplash [51].
Chemical Radiculitis Herniated or degenerated nucleus pulposus releases inflammatory promoters (e.g., phospholipase A2, prostaglandin E2, proteoglycans, cytokines, tumor necrosis factors) and mediators (e.g., substance P, bradykinin, potassium, histamine). This inflammatory cascade can cause chemical radiculitis, characterized by intense chemical irritation of cervical spine nerve roots, radicular pain, and most herniated nucleus pulposus pain [24; 51; 58]. Cervical Radiculopathy In cervical radiculopathy, compression or irritation of a cervical spine nerve root, typically by herniated disk material, chemical radiculitis, or stenosis, results in radiating pain, weakness, or numbness [22; 23; 58]. Most cervical radiculopathies involve C7 or C6 nerve root levels, but all root levels exhibit motor, sensory, and reflex abnormalities that follow specific dermatomal or myotomal distribution patterns in the neck and upper extremities ( Table 1 ) [2; 22; 56]. Mechanical compression induces nerve deformation and malfunction when external pressure exceeds intraneuronal pressure. This results in conduction block, interruption of axonal flow, vascular sequelae (e.g., hypoxia), and accumulation of metabolic byproducts [22; 58]. Nerve root compression alone may not be painful unless inflammation is present. Narrowing of the foraminal space (foraminal stenosis) encroaches on the exiting spinal nerve, and foraminal stenosis from disk or facet joint degeneration accounts for many cervical radiculopathy cases [51]. Cervical Spinal Stenosis In the C3–C7 spinal canal, the normal anteroposterior diameter is 17–18 mm. The spinal cord requires 10–11 mm; an anteroposterior diameter <10 mm is absolute spinal canal stenosis, and 10–13 mm is relative stenosis [59; 60].
TYPICAL DISTRIBUTION OF SENSORY AND MOTOR WEAKNESS IN CERVICAL RADICULOPATHY a Affected Nerve Root (Frequency) Sensory Deficits/Pain Location Muscle Weakness Abnormal Reflexes C4 (<10%) Lower neck, cape-like distribution in upper shoulder None None C5 (10%) Lateral arm Deltoid Biceps C6 (20% to 25%) Radial forearm, radial two digits Biceps, wrist extension Brachioradialis C7 (45% to 60%) Middle finger Triceps, wrist flexion Triceps C8 (10%) Ulnar two digits Finger flexors Finger flexors a Pain referral patterns can vary among patients. Source: [2; 22; 56] Table 1
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