Causes of stenosis development
Narrowing of the spinal canal is in the overwhelming majority of cases a consequence of age-related degenerative changes. Basic contributing factors include intervertebral disc protrusions, ligamentous hypertrophy, and the formation of bone overgrowths known as osteophytes. Spondylolisthesis, in which one vertebral body slips relative to another, serves as an additional cause of compression.
Significantly less often, the pathology is congenital in origin. Rheumatoid arthritis also acts as a specific trigger: in this condition, narrowing of the canal lumen occurs due to pathological synovial overgrowth and the development of spondylolisthesis caused by facet joint damage.
Anatomy and root exit topography
At each level of the spinal cord, sensory (dorsal) and motor (ventral) neurons merge. The resulting nerve roots leave the canal through the lateral intervertebral foramina. The topography of their exit follows strict rules depending on the spinal region:
- Cervical spine: the nerve trunk exits above the pedicle of the corresponding vertebra. For example, the C6 nerve is located between the C5 and C6 vertebrae.
- Thoracic and lumbar spine: the root passes below the pedicle of its vertebra. For example, the L2 nerve exits between the L2 and L3 vertebrae.
- Transitional zone: the C8 root forms between the C7 and T1 (Th1) vertebrae, ensuring a smooth transition to the thoracic anatomical structure.
Features of disc herniation compression
The key difference between the spinal regions lies in the direction of the nerve fibers' course. This determines precisely which nerve root will be affected when an intervertebral disc herniation or other space-occupying lesion occurs.
In the cervical spine, nerve trunks depart horizontally. Because of this, any herniation at a specific level—whether central or lateral—will compress the exact same nerve. Thus, a C5/C6 disc herniation will inevitably lead to compression of the C6 root.
In the lumbar spine, nerve roots descend distally in a vertical direction. They run alongside the spinal cord for an entire segment before turning laterally. Consequently, herniations at the L4/L5 level cause different consequences:
- Lateral (foraminal) herniation compresses the exiting L4 root located directly in front of the foramen.
- Central (paracentral) herniation compresses the traversing L5 root headed downward to exit at the level below.
Clinical presentation: myelopathy
For a long time, cervical stenosis can remain asymptomatic. As degenerative processes progress, myeloradiculopathy (myeloradiculopathy) develops—a combined affliction of these structures. An accurate diagnosis requires a comprehensive approach: medical history, physical examination, and neuroimaging data.
The initial signs of myelopathy often include neck pain or stiffness. Sensory disturbances (tingling, numbness) are bilateral and do not correspond to the innervation zones of specific dermatomes (non-dermatomal distribution). Symptoms initially appear in the upper extremities and subsequently spread to the lower extremities. Motor deficits include muscle weakness, impaired coordination, and loss of fine motor function. In severe cases, urinary incontinence and pronounced gait instability are observed.
During a neurological examination, the physician may reveal:
- Hyperreflexia (hyperreflexia);
- Reduced speed when performing rapid alternating movements;
- Difficulty with heel-to-toe walking (impaired heel-toe walking);
- Impaired proprioception (abnormal proprioception), which is clearly noticeable during the finger-to-nose test with eyes closed.
Specific reflexes and radiculopathy
Two important clinical signs serve to confirm spinal cord compression:
- Hoffmann sign (Hoffmann sign): a sharp, flicking tap downward on the nail phalanx of the patient's middle finger elicits involuntary flexion or adduction of their thumb.
- Babinski sign (Babinski sign): in response to stroking the lateral border of the sole, the big toe involuntarily extends (extensor response). In healthy adults, the toes should flex downward, whereas in infants up to 2 months old, a positive Babinski sign is considered a physiological norm.
If radiculopathy (radiculopathy) develops, the clinical picture changes. Pain, stiffness, and paresthesias radiate down the arm in strict accordance with the affected dermatome (dermatomal distribution). Depending on the entrapped root, specific neurological weakness and abnormal reflexes are identified:
- C5: weakness of the deltoid (m. deltoideus) and biceps (m. biceps brachii) muscles, diminished biceps reflex.
- C6: weakness of the brachioradialis muscle (m. brachioradialis) and impaired wrist extension. Diminished brachioradialis reflex.
- C7: weakness of the triceps brachii muscle (m. triceps brachii) and impaired wrist flexion. Diminished triceps reflex.
- C8: marked weakness of the intrinsic muscles of the hand.
Briefly: answers to topical questions
What surgical treatment methods (types of decompression) are used for severe spinal canal stenosis?
The choice of a specific surgical procedure depends on the exact localization of symptomatic neural compression. The following types of decompressive interventions are used:
- Laminectomy (laminectomy) is the surgical removal of the vertebral lamina.
- Expanded decompression — involves resection of the articular processes (facet joints), which requires supplementing the surgery with surgical spinal fusion.
- Laminotomy (laminotomy) — removal of only a small portion of the vertebral lamina (a less invasive alternative).
- Foraminotomy (foraminotomy) is decompression at the level of the intervertebral foramen.
- Interspinous distraction (interspinous distraction) is the placement of an implant between the spinous processes.
What clinical symptoms are characteristic of cauda equina syndrome in lumbar stenosis?
Cauda equina syndrome is characterized by the development of marked bilateral neurological deficits and pelvic organ dysfunction. The clinical picture includes the following symptoms:
- Pain syndrome — acute pain in both legs.
- Sensory disturbances — numbness in the legs and anogenital region (saddle anesthesia).
- Motor disturbances — pronounced bilateral motor deficit of the lower extremities.
- Pelvic organ dysfunction — bowel and bladder dysfunction (urinary and fecal incontinence).
Cervical roots exit ABOVE their corresponding vertebra (C6 above the C6 vertebra), while thoracic and lumbar roots exit BELOW their corresponding vertebra (L2 below the L2 vertebra).
Class and exam questions
What is the difference between the symptoms of cervical myelopathy and radiculopathy?
In radiculopathy, numbness and pain are localized within a single dermatome on one limb. Myelopathy, however, causes bilateral sensory disturbances that are not tethered to dermatomes and affect the arms first, followed by the legs.
Why can an L4/L5 disc herniation in the lower back affect different roots?
In the lumbar spine, nerve roots descend vertically. A central herniation at the L4/L5 level will compress the traversing L5 root running below, whereas a lateral herniation will affect the L4 root exiting directly into that foramen.
Does a positive Babinski sign always indicate pathology?
In adults, extension of the big toe in response to plantar stroking definitively indicates spinal cord compression. However, for infants under 2 months of age, this response is a physiological norm.
What else to study on this topic
- Pathophysiology of myeloradiculopathy development
- Method for testing proprioception and assessing gait
- Topographic anatomy of upper extremity dermatomes (from C3 to T1)
- Effect of rheumatoid arthritis on facet joints
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