Clinical Cases |
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Laminectomy
A laminectomy (etymology: -ectomy= removal: laminectomy= removal of the lamina) is a surgical procedure performed by orthopedic and neurosurgeons in which the laminae of a vertebra are removed. As you can see in the images below, the laminae form the posterior aspect of the vertebral bony arch that forms the spinal canal. The spinous process extends posteriorly from where the two laminae meet each other, and the transverse processes extend laterally from where the laminae meet the pedicles. A complete laminectomy, like the one performed by medical students in gross anatomy, requires the cutting of the laminae where they meet the transverse processes and removal of both laminae along with the spinous process.
Spinal laminectomy is done to relieve back pain that is caused by impingement or compression of the spinal cord or a spinal nerve. The spinal nerves exit the vertebral column via the spinal foramina, which are created by the pedicles and laminae, and are held open by the intervertebral disks. Any spinal injury or degeneration that narrows or occludes the spinal foramina can also compress the spinal nerve as it is exiting the vertebral column, leading to back pain and symptoms of neuropathy along the affected dermatome. Common conditions that result in spinal nerve compression are:
- Herniated disk - The intervertebral disk is made of a fibrous outer ring called the anulus fibrosus, which surrounds and contains a gelatinous inner core called the nucleus pulposus. With aging and overuse, the anulus fibrosus can weaken, allowing the nucleus pulposus to herniate through and enter the spinal canal where it compresses the spinal cord or spinal nerves.
- Spinal osteoarthritis - The intervertebral disks help to keep the spinal foramina open enough for the spinal nerves to pass through unimpeded. If the disks begin to degenerate and lose their size and suppleness, they allow the vertebrae to rest more closely to each other and so reduce the size of the spinal foramina. This can lead to compression of the spinal nerves.
- Osteophytosis - Another complication of spinal arthritis is the formation of osteophytes, or bone spurs. As the intervertebral disks degenerate, they allow adjacent vertebral bodies to rub against each other. This agitation can lead to a compensatory overgrowth of hard bone tissue, which forms an osteophyte. If these osteophytes grow into the spinal canal or foramina, they can impinge on the spinal nerves or the cord itself (see clinical case "Osteophytosis").
The vertebrae and disks of the lumbar spine are particularly prone to injury because of their important role in weight bearing. The force exerted on the spine when one is bending is supported primarily by the intervertebral disks between L3-L4 and L4-L5. As an indicator of how prone the lower lumbar vertebrae and disks are to overuse injury, approximately 95% of spinal disk operations are performed on L4 and L5.
An open laminectomy begins with a single straight incision over the affected vertebra. The deep back muscles and connective tissue are moved aside and the laminae are exposed at their junction with the transverse processes. The supraspinous ligament is cut above and below the spinous process which is to be removed. The laminae are then both cut, and the posterior aspect of the vertebral arch, including the laminae, spinous process, supraspinous ligament, and interspinous ligament are removed. This exposes the ligamenta flava, which is next cut to expose the spinal canal and the compressed nerve. At this point the surgeon is able to see what is causing the compression (typically a herniated disk, disk fragment that has entered the spinal canal, an osteophyte, or a tumor). The laminectomy therefore helps to decompress a spinal nerve via two mechanisms:
It enables the surgeon to directly see and fix whatever is causing the compression.
- By removing the laminae, the spinal foramina are enlarged, giving the spinal nerve more room to leave the vertebral column unobstructed.
Removing the entire posterior aspect of one or more vertebrae in a spine that is likely already weakened by overuse, injury, or arthritis can result in a dangerously unstable vertebral column. This is why many patients who receive a laminectomy also have several vertebrae fused after a procedure in order to help stabilize their spine. The classic spinal fusion involves taking a small piece of bone from the patient's hip and attaching it to the bodies of the affected vertebrae using metal plates and screws.
The movie file below is the CT scan of cadaver 33492. Move the scan to time=68, K12 and M12. At this point you can see the 12th rib coming off of T12. Begin moving the scan downward (advancing the time forward) while keeping track of your level on the lumbar spine by counting the spinous processes as they come into view. Notice that just below L3 (time= 75, K13 and M13) two large screws come into view. These screws can be seen entering the vertebra at the base of the transverse processes and extending through the pedicles into the vertebral body. Continue scanning down and you will notice that just below the 4th lumbar spinous process is a metal plate spanning the distance laterally across the posterior aspect of the vertebral column. Scan a little bit further (time= 79, L13) and you will see that the laminae and spinous process of L5 are missing entirely, leaving the spinal canal open posteriorly. Also at this level are another set of screws that can be seen entering the superior articular facet of the sacrum.
This laminectomy and spinal fusion were likely done for this patient to alleviate back pain that resulted from spinal cord or nerve compression in the lower lumbar spine. Examine the vertebral bodies of the lower lumbar spine and notice how bony outgrowths (osteophytosis) are visible on L3-L5 vertebral bodies. This is a sign of spinal osteoarthritis. See the clinical case "Osteophytosis" for more information.