椎間板ヘルニア l:はじめに

Intervertebral disc herniation occurs when the nucleus pulposus, the gel-like inner core, protrudes through a tear or weakness in the annulus fibrosus, the outer fibrous ring. Most herniations result from degenerative disc changes where aging reduces disc hydration and elasticity. Trauma, heavy lifting, or repetitive twisting can precipitate herniation, especially in individuals with risk factors like obesity, smoking, or improper lifting techniques.

The lumbar spine is most frequently affected, particularly at the L4–L5 and L5–S1 levels, due to the high mechanical load these segments bear. Cervical herniations are the second most common, occurring at C5–C6 and C6–C7. Thoracic spine involvement is rare. The lumbar region's susceptibility stems from its role in supporting body weight and facilitating movement.

Radiculopathy is nerve root pain that develops when displaced disc material compresses nearby spinal nerve roots. This compression causes pain, tingling, weakness, and sensory changes along the affected nerve's distribution pathway. Radiculopathy is the hallmark symptom of intervertebral disc herniation and varies depending on which nerve roots are compressed and the herniation's location.

Lumbar herniations typically produce sciatica, with pain radiating from the lower back into the buttock, leg, or foot, often accompanied by weakness in knee extension, dorsiflexion, or plantarflexion depending on the affected nerve level. Cervical herniations cause neck pain radiating into the shoulder, arm, or hand, with weakness in biceps or triceps muscles. Both conditions may include sensory loss and reflex changes specific to the compressed nerve root.

Cauda equina syndrome is a severe complication of lumbar disc herniation causing bilateral leg weakness, saddle anesthesia (numbness in the perineal region), and bladder or bowel dysfunction. It represents a medical emergency because it can lead to permanent neurological damage, including sexual impairment and loss of bowel or bladder control, if not treated urgently. Immediate surgical intervention is typically required to decompress the nerve roots.

Risk factors include aging, which reduces disc hydration and elasticity; occupations involving frequent bending or twisting; high-impact sports such as wrestling; improper lifting techniques; repetitive strain; sedentary lifestyle; obesity; smoking; prolonged driving; and congenital factors like ligament laxity. Trauma or mechanical strain can precipitate herniation in individuals with these predisposing conditions.

Cervical myelopathy results from severe spinal cord compression caused by disc herniation, producing upper motor neuron signs below the lesion and lower motor neuron signs at the compression level. Unlike radiculopathy, which affects individual nerve roots, myelopathy causes progressive gait difficulty, loss of coordination, sensory changes, and bladder dysfunction. It represents a more serious condition requiring urgent intervention to prevent permanent spinal cord damage.