Degenerative disease can affect the cervical, thoracic, or lumbar spine and is usually associated with aging. It is a chronic disease that can range from being asymptomatic to presenting acutely.
“Spondylosis” is a non-specific term that can be used to refer to degenerative spine disease. Common causes include disc herniation, spondylolisthesis, and spinal stenosis, which are discussed below. Other causes include the formation of bony protrusions known as osteophytes, which may compress nerve roots, and facet joint abnormalities. Complications include radiculopathy, defined as numbness, pain, and/or weakness in the arms or legs due to spinal nerve impingement; and myelopathy, which has similar symptoms due to spinal cord compression. Neurogenic claudication is painful cramping or weakness in the arms or legs due to nerve impingement or inflammation in the spine.
The intervertebral disc forms a fibrocartilaginous joint between two vertebrae and is comprised of 2 components: an outer, fibrous ring known as the annulus fibrosus, and a gel-like inner core, called the nucleus pulposus.
Most disc herniations are due to protrusion of the nucleus pulposus through the annulus fibrosis. Normal aging entails dehydration, fissuring, and fragmentation of the nucleus pulposus, which predisposes to herniation. Complications arise when the posterior longitudinal ligament is torn, which allows the disc to herniate into the spinal canal and compress either the spinal nerve root or spinal cord. Disk herniations can be median, paramedian, lateral, foraminal and extra-foraminal. Paramedian and lateral disk herniations are most usual. Foraminal disk herniations are usually associated with severe arm or leg pain depending on their location in the spine.
Symptoms depend on the spinal cord level. Disc herniation in the cervical spine typically causes unilateral pain shooting from the neck down the shoulder/arm and possibly into the hand. It is worsened by certain neck motions.
Thoracic disc herniation is rare, accounting for 0.25% of all disc herniation. It can cause pain along the chest wall or, more seriously, gait disturbance, loss of rectal tone, and lower extremity hyperreflexia and clonus.
Lumbar disc herniation involves shooting pain in the legs. Sciatica is a common presentation classically described as shooting pain down the back of the leg. However, pain distribution associated with a lumbar disc herniation may alternatively entail the front or side of the leg. Low back pain may occur concurrently.
For most cases of disc herniation, patients will respond to conservative management with partial or complete resolution of symptoms. This entails non-steroidal anti-inflammatory drugs (NSAIDs) for pain control, exercise, physical therapy, and weight control. For those who experience continued symptoms, epidural corticosteroid injection is a non-surgical alternative to provide immediate to moderately long-lasting relief. Patients may be able to achieve pain control utilizing a combination of conservative management and epidural injection every several months.
The final, definitive step in management is surgical intervention. Patients with unremitting pain or otherwise intolerable symptoms are appropriate candidates.
Cases that involve emergent signs including loss of bowel or bladder function, significant leg weakness especially of acute onset known as caudaequina syndrome – should be taken to surgery immediately.
Surgical approach and procedure is tailored to the spinal level involved.
In the cervical spine, anterior discectomy with or without fusion is most commonly done, where the disc is evacuated from an anterior approach and the spinal column is fused as needed. Modern surgery includes replacing the resected disk with a disk prosthesis. If the operated level is unstable, a fusion is recommended after the disk is resected.
Approach varies for thoracic disc herniation depending on location and quality, where anterior is most commonly used for midline or broad-based herniations or densely calcified discs and posterolateralis recommended for lateral or soft disc herniations. Laminectomy, a direct posterior approach, is not recommended for thoracic disk herniation as it risks to herniate the thoracic cord and cause serious complications. The lamina is a large segment of the bone that forms the boundary of the spinal canal from the posterior aspect.
In the lumbar spine, microdiscectomy is a commonly used, where a herniated disc is removed from a posterior approach under the microscope. Open discectomy is an alternative for severe cases that usually necessitates a laminectomy for better visualization of the disc. These procedures may also involve fusion for stabilization of the spinal column, as needed.
Spinal stenosis is narrowing of the spinal canal or intervertebral foramina. It may have congenital and degenerative etiologies, the latter of which is more common and will be the focus. Loss of intervertebral disc height and protrusion, facet joint arthropathy, osteophyte formation, and hypertrophy of the ligamentumflavumoccur along a continuum. Each of these processes may result in spinal stenosis. Patients commonly present in the 6th and 7th decades of life.
Symptoms depend on the spinal level involved and are similar to those discussed for disc herniation. In the cervical spine, nerve radiculopathy includes arm pain, paresthesias, and weakness. Lumbar radiculopathy may cause low back pain radiating to the leg, whereas neurogenic claudication causes painful leg cramping. Symptoms of myelopathy, which is discussed in greater detail below, include bowel or bladder incontinence, sudden leg weakness, and gait disturbance. This is an emergent condition that requires immediate surgical decompression. Otherwise, conservative management should be tried, with NSAIDs, physical therapy, and exercise for overweight individuals.
Surgery for lumbar spinal stenosis entails laminectomy for decompression with or without fusion. The presence of spondylolisthesis (discussed below) favors concomitant fusion. Cervical spinal stenosis may also be treated with laminectomy. Alternatively, a corpectomy (Vertebrectomy) may be undergone, which involves an anterior approach with removal of the vertebral body and any osteophytes. A bone graft, known as a strut graft, is then used to replace the space created by removal of the vertebral body.
Myelopathy is by definition neurologic dysfunction related to direct spinal cord damage. In the degenerative setting, myelopathy is caused by compression secondary to spinal stenosis. Disc herniation, osteophyte formation, and ligamentous hypertrophy may all cause stenosis and myelopathy. Degenerative myelopathy is frequently seen in the cervical spine, known as cervical spondylotic myelopathy. This is the most common type of spinal cord dysfunction in patients older than 55 years. Aside from direct cord compression, microtrauma related to neck flexion and extension and vascular injury may also cause cervical spondylotic myelopathy.
An early sign of cervical spondylotic myelopathy is gait disturbance, often with lower extremity weakness or stiffness. Difficulty running is a common complaint. Cord damage can cause upper motor neuron findings, including hyperreflexia and spasticity in the limbs. With compression of the cervical spine, this would be expected to be pronounced in the legs, while the arms would be prone to lower motor neuron signs, including weakness and hyporeflexia.
If signs of acute compression are present, such as sudden-onset, severe weakness or gait disturbance, or any bowel or bladder incontinence, the patient should be taken to surgery immediately. Otherwise, conservative management with NSAIDs, restriction of high risk activities (such as action sports and heavy lifting), bed rest, and prolonged immobilization with rigid cervical bracing is suggested. Myelopathy that does not respond to nonoperative management or patients with severe symptoms should undergo surgery.
Surgical approach depends on myelopathic etiology. A posterior approach is preferred when ossification of the posterior longitudinal ligament (OPLL) is involved. A laminectomy either alone or in conjunction with instrumentation/fusion, or laminoplasty, may be undergone. Laminectomy alone has a higher incidence of late kyphotic deformity. Laminoplasty may be done should the patient have myelopathic symptoms without axial neck pain.An anterior approach is preferred for correcting kyphotic deformities. The procedure options entail anterior cervical discectomy and fusion (ACDF), corpectomy (removal of the vertebral body) and fusion, or a combination of both.