Type of Surgery
Last updated: 02/17/2009
Structure of the spine
In order to understand why removal of a piece of bone from the arch of a vertebra relieves pain, it is helpful to have a brief description of the structure of the spinal column and the vertebrae themselves. In...
humans, the spine comprises 33 vertebrae, some of which are fused together. There are seven vertebrae in the cervical (neck) part of the spine; 12 vertebrae in the thoracic (chest) region; five in the lumbar (lower back) region; five vertebrae that are fused to form the sacrum; and four vertebrae that are fused to form the coccyx, or tail-bone. It is the vertebrae in the lumbar portion of the spine that are most likely to be affected by the disorders that cause back pain.
The 24 vertebrae that are not fused are stacked vertically in an S-shaped column that extends from the tail-bone below the waist up to the back of the head. This column is held in alignment by ligaments, cartilage, and muscles. About half the weight of a person's body is carried by the spinal column itself and the other half by the muscles and ligaments that hold the spine in alignment. The bony arches of the laminae on each vertebra form a canal that contains and protects the spinal cord. The spinal cord extends from the base of the brain to the upper part of the lumbar spine, where it ends in a collection of nerve fibers known as the cauda equina, which is a Latin phrase meaning "horse's tail." Other nerves branching out from the spinal cord pass through openings formed by adjoining vertebrae. These openings are known as foramina (singular, foramen).
Between each vertebra is a disk that serves to cushion the vertebrae when a person bends, stretches, or twists the spinal column. The disks also keep the foramina between the vertebrae open so that the spinal nerves can pass through without being pinched or damaged. As people age, the intervertebral disks begin to lose moisture and break down, which reduces the size of the foramina between the vertebrae. In addition, bone spurs may form inside the vertebrae and cause the spinal canal itself to become narrower. Either of these processes can compress the spinal nerves, leading to pain, tingling sensations, or weakness in the lower back and legs. A lumbar laminectomy relieves pressure on the spinal nerves by removing the disk, piece of bone, tumor, or other structure that is causing the compression.
Causes of lower back pain
The disks and vertebrae in the lower back are particularly vulnerable to the effects of aging and daily wear and tear because they bear the full weight of the upper body, even when one is sitting quietly in a chair. When a person bends forward, 50% of the motion occurs at the hips, but the remaining 50% involves the lumbar spine. The force exerted in bending is not evenly divided among the five lumbar vertebrae; the segments between the third and fourth lumbar vertebrae (L3-L4) and the fourth and fifth (L4-L5) are most likely to break down over time. More than 95% of spinal disk operations are performed on the fourth and fifth lumbar vertebrae.
Specific symptoms and disorders that affect the lower back include:
- Sciatica. Sciatica refers to sudden pain felt as radiating from the lower back through the buttocks and down the back of one leg. The pain, which may be experienced as weakness in the leg, a tingling feeling, or a "pins and needles" sensation, runs along the course of the sciatic nerve. Sciatica is a common symptom of a herniated disk.
- Spinal stenosis. Spinal stenosis is a disorder that results from the narrowing of the spinal canal surrounding the spinal cord and eventually compressing the cord. It may result from hereditary factors, from the effects of aging, or from changes in the pattern of blood flow to the lower back. Spinal stenosis is sometimes difficult to diagnose because its early symptoms can be caused by a number of other conditions and because the patient usually has no history of back problems or recent injuries. Imaging studies may be necessary for accurate diagnosis.
- Cauda equina syndrome (CES). Cauda equina syndrome is a rare disorder caused when a ruptured disk, bone fracture, or spinal stenosis put intense pressure on the cauda equina, the collection of spinal nerve roots at the lower end of the spinal cord. CES may be triggered by a fall, automobile accident, or penetrating gunshot injury. It is characterized by loss of sensation or altered sensation in the legs, buttocks, or feet; pain, numbness, or weakness in one or both legs; difficulty walking; or loss of control over bladder and bowel functions. Cauda equina syndrome is a medical emergency requiring immediate treatment. If the pressure on the nerves in the cauda equina is not relieved quickly, permanent paralysis and loss of bladder or bowel control may result.
- Herniated disk. The disks between the vertebrae in the spine consist of a fibrous outer part called the annulus and a softer inner nucleus. A disk is said to herniate when the nucleus ruptures and is forced through the outer annulus into the spaces between the vertebrae. The material that is forced out may put pressure on the nerve roots or compress the spinal cord itself. In other cases, the chemicals leaking from the ruptured nucleus may irritate or inflame the spinal nerves. More than 80% of herniated disks affect the spinal nerves associated with the L5 vertebra or the first sacral vertebra.
- Osteoarthritis (OA). OA is a disorder in which the cartilage in the hips, knees, and other joints gradually breaks down, allowing the surfaces of the bones to rub directly against each other. In the spine, OA may result in thickening of the ligaments surrounding the spinal column. As the ligaments increase in size, they may begin to compress the spinal cord.
Factors that increase a person's risk of developing pain in the lower back include:
- Hereditary factors. Some people are born with relatively narrow spinal canals and may develop spinal stenosis fairly early in life.
- Sex. Men are at greater risk of lower back problems than women, in part because they carry a greater proportion of their total body weight in the upper body.
- Age. The intervertebral disks tend to lose their moisture content and become thinner as people get older.
- Occupation. Jobs that require long periods of driving (long-distance trucking; bus, taxi, or limousine operation) are hard on the lower back because of vibrations from the road surface transmitted upward to the spine. Occupations that require heavy lifting (nursing, child care, construction work, airplane maintenance) put extra stress on the lumbar vertebrae. Other high-risk occupations include professional sports, professional dance, assembly line work, foundry work, mining, and mail or package delivery.
- Lifestyle. Wearing high-heeled shoes, carrying heavy briefcases or shoulder bags on one side of the body, or sitting for long periods of time in one position can all throw the spine out of alignment.
- Obesity. Being overweight, particularly if the extra pounds are concentrated in the abdomen, adds to the strain on the muscles and ligaments that support the spinal column.
- Trauma. Injuries to the back from contact sports, falls, criminal assaults, or automobile accidents may lead to misalignment of the vertebrae or a ruptured disk. Traumatic injuries may also trigger the onset of cauda equina syndrome.
Laminectomy is a spine operation to remove the portion of the vertebral bone called the lamina. There are many variations of laminectomy, in the most minimal form small skin incisions are made, back muscles are pushed aside rather than cut, and the parts of the vertebra adjacent to the lamina are left intact. The traditional form of laminectomy (conventional laminectomy) excises much more than just the lamina, the entire posterior backbone is removed, along with overlying ligaments and muscles. The usual recovery period is very different depending on which type of laminectomy has been performed: days in the minimal procedure, and weeks to months with conventional open surgery.
Surgery for removal is generally advised for patients with limited cancer elsewhere in the body and a single brain metastasis.
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