|
The anatomy of intervertebral disc herniation is important in selecting and executing the appropriate operation. (See Spine Degeneration and Surgery: Basic Concepts) It should be noted that in the lumbar region the corresponding nerve root of a vertebral segment exits at the neural foramina just below the pedicle of the superior vertebral body of that segment. Thus at the L4/L5 level, the L4 nerve root exits through the foramen, hugging closely to the L4 pedicle. Because the disc space is somewhat below this level, any disc protrusion or herniation usually more commonly effects the nerve root sleeve as it originates from the main dural sac rather than the exact corresponding nerve root to that spinal level. Thus, in L4/ L5 disc herniations, the L5 nerve root is usually compressed much more commonly than the L4 root. For the L4 root to be involved, the disc herniation usually must occur more laterally out in the direct area of the neural foramen. As noted, the majority of acute disc herniations occur laterally on one side with corresponding radicular symptoms depending upon the nerve root compressed.
Usually for lateral disc herniations such as those described above, the first line of treatment is conservative, consisting of a limited period of time (approximately 72 hours) of bed rest and limitation of activities with use of nonsteroidal medication or low dose cortisone derivatives with appropriate analgesics. Investigational studies suggest that certain compounds released by the disc material during herniation cause inflammation of the nerve root that is responsible for a major a component of the pain as is the direct neural compression. Thus, many patients experience significant relief after this initial inflammation subsides. The length of the period of inflammation varies but it rarely exceeds six weeks, usually subsiding within a few days. This information serves as a useful guide in deciding how long to continue on conservative therapy. Compression of the nerve root can cause more chronic symptoms and these are often made worse with any standing or weight bearing where there is further protrusion of the disc material or any activity that increases intracranial pressure and compression of the nerve root sleeve against the herniated elements.
The central herniation in the lumbar region, including the sphincters and often severe motor and sensory involvement, is referred to as "cauda equina syndrome" and constitutes a surgical emergency. Rapid decompression of the depressed cauda equina is necessary for optimal restoration of function which once this occurs, may not be complete. In general, while the indications for surgery vary among practitioners, there are generally three recognized categories:
- Absolute indication for surgery is the compression of the cauda equina with signs described above.
- Relatively absolute indication for surgery is the development of significant weakness in the distribution of a nerve root. In such situations we recommend surgery unless there are overwhelming medical reasons against it.
- Relative indication is one where the patient's primary complaints are pain and the alteration of lifestyle that results from it. In such instances the decision whether to have surgery after all conservative measures fail is made by the patient depending on his/her assessment of the risk/benefit ratio of the surgery and on their philosophical inclination.
The same considerations apply to decisions regarding cervical spine disease and stenosis. (See Cervical Spinal Stenosis)Preoperative considerations for lumbar disc surgery generally follow the guidelines for other surgical procedures' so called pre-admission testing and consist of a full history and physical, baseline laboratory studies and evaluation of any known or discovered medical condition or concurrent illness. Blood type and cross match is performed although it is quite rare for transfusion to be required during a standard laminotomy and discectomy where the typical blood loss is quite low. Modern lumbar discectomy is performed with a small incision often measuring no more than 4 to 5 cm (1 1/2" - 2") in length and centered over the involved spinal level. In the lumbar region paraspinous musculature is retracted laterally and high-speed drills are used to perform a laminotomy which is followed by resection of the ligamentum flavum to expose the underlying thecal sac and nerve root exit zone. Using loop or microscope magnification, the neurosurgeon retracts the thecal sac and nerve root sleeve as little as possible to expose the disc space and herniated disc elements for their removal.
Care is taken to not remove disc which is still serviceable, yet to remove all or as much as possible of the degenerated nucleus. This principle is utilized in a procedure developed at our institution which is a modification of microdiscectomy and is called minimally invasive micronucleotomy. This technique allows for the surgery to be less invasive and lessens the likelihood of needing a fusion in the future. The recovery from surgery is usually also more rapid. The nucleotomy is accompanied in all instances by removing a small portion of the bone overlaying the nerve root as it traverses laterally towards the neural foramen. As such a "foraminotomy" is often performed not only to provide relief from the current symptoms but to guard against nerve root compression from osteophyte formation in the future. The standard one level procedure often requires one to two hours operative time although this can certainly vary due to complexity or if more than one disc space is exposed.
Other procedures may be used for the removal of a herniated
disc. A laminectomy used in the past should no longer be used for
this condition although it remains the procedure of choice for spinal
stenosis. "Arthroscopic microdiscectomy" or "open percutaneous microdiscectomy" are
usually used by orthopedic surgeons and are variations on the procedures
used in treatment of joints and use similar types of equipment. The
main difference from microdiscectomy and arthroscopic discectomy
is in that the surgeon does not see the operated structures directly
but rather on a television screen. It is performed through portals
which in congregate are no smaller than a microsurgical discectomy
and, as such, it does not have significant advantages in avoiding
muscle dissection. It has, however, some limitations in performing
foraminotomies or exploring more than one nerve root which, as can
be seen from our earlier discussion on anatomy, is often required
because overlooked fragment of disc material migrating above or below
the level of surgery will result in unsuccessful operation. "Closed
percutaneous discectomy" or "laser assisted percutaneous discectomy" performed
through a "thick needle" using an extraction device or a laser has
significant limitations and the results fall far below those of microdiscectomy.
This procedure cannot allow the removal of a fully herniated disc
fragment and great caution needs to be exercised when offering it
to the patients. It appears that at the present time a microsurgical
discectomy and its variations are the best treatment for an HNP without
instability.
[ top ]
|
|
|
