There are 33 vertebrae in the human spine: 7 in the neck area (cervical), 12 in the chest area (thoracic), 5 in the lumbar (lower back), 5 fused vertebrae in the pelvic area (sacrum) and 4 fused vertebrae forming the tailbone (coccyx).
The cervical, thoracic and lumbar vertebrae are held in place, one above the next, by projections on each vertebra called superior and inferior processes. The inferior (lower) process of the top vertebra fit into the superior (upper) process of the lower vertebra, forming a joint that holds the vertebrae in place. Between each vertebra (except in the sacrum and coccyx) intervertebral (between the vertebrae) discs cushion and separate the vertebrae.
What is spondylolisthesis?
Spondylolisthesis is a Latin term meaning improper forward movement of a vertebra over the vertebra below it. Most often, this forward slip of the vertebra occurs in the lumbar area of the spine. This slippage and herniation (deformity) of the disc places pressure on the nerve roots associated with the affected vertebrae, causing pain and dysfunction. While the herniation of the disk causes pain, discectomy alone is unable to provide relief. The reduction in disk space height and abnormal amount of movement allowed by the joint also causes pressure on the nerves. This intervertebral space must be restored in order to provide adequate space for the nerves.
What causes spondylolisthesis?
Spondylolisthesis occurs only in people who are able to stand upright and walk, so is virtually nonexistent among newborns. The upright position of human walking seems to have a direct effect on the development. It is more common in persons who participate is sports such as diving, weight lifting, wrestling and gymnastics . All these activities require repetitive hyperextension, which can contribute to instability of the spine.
Can spondylolisthesis be prevented?
Good spinal care, both in developing good musculature and in preventing overuse or injuries, is key into reducing the chance of developing spondylolisthesis. Athletes, especially, need to be knowledgeable about body mechanics and the importance of both strengthening and resting the muscles of the back.
What treatment options are there for spondylolisthesis?
Anterior or posterior decompression with fusion cages
The goals of surgery are to remove pressure on spinal nerves (decompression), and to provide stability to the lumbar spine. Decompression involves removing the damaged structures that are causing the spondylolisthesis. In most cases of spondylolisthesis, lumbar decompression is accompanied by the uniting of one spinal vertebra to the next (spinal fusion) with spinal instrumentation (implants that are used to assist the healing process). Surgery can be performed from the back of the spine (posterior) or from the front of the spine (anterior). A structural graft is inserted into the place previously occupied by the removed structure. The purpose of this graft is to hold the disc space open until the fusion is complete. The graft is often held in place by a "cage" device, such as the BAK cage.
Laminectomy decompression with graft
In the laminectomy procedure, the spine is approached through a two-inch to five-inch incision in the midline of the back, and the left and right back muscles are detached from the lamina on both sides. The lamina are flat bone projections on each side of the vertebra. After this is accomplished, the lamina is removed (laminectomy), allowing the doctor to see the nerve roots. The facet joints, which are directly over the nerve roots, may then be trimmed to give the nerve roots more room. Once the nerve roots have adequate space made by the removed lamina and facet joint trimmings, pressure is eliminated, thereby alleviating pain. Bone graft chips may be placed between the vertebrae to create a solid section of bone, preventing motion that may detract from healing.
The posterolateral fusion involves placing bone graft in the posterolateral portion of the spine (behind and to one side of the spine).The surgical approach to the spine is from the back through a midline incision that is approximately three inches to six inches long. First, bone graft is obtained from the pelvis (the iliac crest). Most surgeons work through the same incision to obtain the bone graft and perform the spinal fusion.
Next, the harvested bone graft applied to the posterolateral portion of the spine. This region lies on the outside of the spine and is rich in blood to supply the nutrients for it to grow. A small extension of the vertebral body in this area (transverse process) is a bone that serves as a muscle attachment site. The large back muscles that attach to the transverse processes are elevated to create a bed to lay the bone graft on. The back muscles are then laid back over the bone graft, creating tension to hold the bone graft in place.
After surgery, the body uses a natural process to repair itself, which usually means growing bone. As the harvested bone graft grows and adheres to the transverse processes, the spinal fusion is achieved and motion at that segment is stopped. Spine surgery instrumentation (medical devices) is sometimes used as an adjunct to obtain a solid fusion.
Spinal instrumentation with pedicle screws
For spine operations to be successful, solid healing of bone across the spine must be achieved. The use of metal devices, also called instrumentation (screws, rods, plates, cables, wires) can help correct a deformed spine and will also increase the probability of obtaining a solid spinal fusion.
Spinal instrumentation can be placed in the front or in the back portion of the spine. The devices are usually made of metal, commonly stainless steel or titanium. In order to place this instrumentation into the spine, the spine is at first exposed by making a skin incision, and then gently clearing the muscles, ligaments and other soft tissues from the levels of the vertebrae to be fused. Specific tools are used to carefully prepare the bone in such a way to obtain good seating of the implants (screw, rod, wire, cable or other). When these devices are in the proper position, a rod (or plate) is positioned to link the implants together. Screws are inserted into the pedicles, which are part of the arch of the vertebra. This essentially forms a rigid scaffolding to hold the spine in the desired position. The bone graft which has been placed into the area of fusion gradually solidifies over several months. The spinal instrumentation is gradually covered by scar tissue and sometimes bone which the body lays down.
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