Lumbar discectomy is one of the most frequent operations in Neurosurgery. The success in the surgical treatment of lumbar disc herniation is subject to the individualized evaluation of the patient and the adequate correlation between the data obtained from the clinical history, the neurological examination and the diagnostic tests.
Most cases of sciatica resolve without surgical treatment or specialized medical attention, but in approximately 20% of cases the evolution of these methods is unfavorable and surgical treatment should be considered. 90% of patients who undergo lumbar discectomy feel complete relief of sciatic pain.
Causes of lumbar disc herniation
The origin of lumbar disc herniations is multiple. The spine is considered to be a structure poorly adapted to standing upright. This is why disc degeneration occurs, causing disc herniation, especially of the joints between the fourth and fifth lumbar vertebrae and the lumbo-sacral junction. Intense or less intense but successive lumbar trauma and postural overload are important in the development of the pathology. Other factors may be genetic and nutritional factors that act in a greater distension of the ligaments or a lower resistance of the annulus fibrosus.
Thus, the annulus fibrosus of the intervertebral disc may progressively tear, allowing first the protrusion of the nucleus pulposus, then the appearance of herniation and, finally, extrusion. This process is often accelerated by trauma or very intense overload.
Disc herniation is both mechanical and inflammatory: mechanical compression of the nerve root leads to the release of inflammatory mediators that irritate the nerve root, accentuating symptoms.
Symptoms of lumbar disc herniation, neurological examination
Lumbar disc herniations may be symptomatic or asymptomatic. The most frequent symptom is sciatica, consisting of lumbar pain that expands towards the back of the thigh, reaching the leg. Normally the pain is more intense in the leg than in the lumbar region, it intensifies with stretching movements of the nerve and with actions that increase venous and CSF pressure, it is relieved at rest and by flexing the leg on the thigh and the thigh on the hip. Herniated discs in the upper lumbar originate a picture of cruralgia with similar characteristics.
Lumbar disc herniation is the most frequent cause of sciatica, but it is not the only one. Therefore, when dealing with a patient with sciatica, special attention should be paid to the appearance of warning signs: weight loss, severe trauma, immunodeficiency, fever or personal history of cancer, among others, which may indicate a serious cause such as a fracture, vertebral tumors or spondylodiscitis.
Less frequently, lumbar disc herniation, especially in those that are central, bulky and in young patients, may present with cauda equina syndrome. This should be treated urgently because in its most severe form, the function of all the roots of this part of the spine may cease due to massive disc extrusion. In these cases, the consequences can be paraplegia, perineal and lower limb anesthesia along with sphincter dysfunction and sexual impotence. However, sciatic pain may or may not be present to varying degrees.
During the neurological examination, the heel and toe walking, the patient’s attitude, lumbar mobility and curvature, and antalgic scoliosis due to asymmetrical contracture of the vertebral muscles should be analyzed. In addition, palpation may show contractures and reproduce pain. Muscle strength of all lower limb muscles should be explored along with osteotendinous and plantar reflexes. Finally, the maneuvers that trigger pain in case of radicular entrapment are performed.
Even so, the neurological examination may reveal no major alterations or, on the contrary, indicate different degrees of second neuron motor deficit or superficial and deep sensitivity.
The effectiveness of disc herniation surgery depends on achieving an accurate diagnosis in which the clinical manifestations, the results of the neurological examination and the anatomical alterations obtained in neuroimaging coincide.
Herniated discs can be classified as central, lateral, foraminal and extreme lateral or extraforaminal, and in turn, usually show a caudal or cranial migration. In general, a herniated disc compresses the root that starts in a lower segment. As an exception, extreme lateral herniations compress the root arising at the same level.
Surgical treatment for herniation
Ninety percent of sciatica improves with conservative treatment during the first few weeks. Therefore, it is usual to wait at least four to six weeks before surgery is indicated, as long as no motor deficit or cauda equina syndrome is present.
In summary, three situations can be distinguished in which lumbar discectomy surgery is necessary:
- Cauda equina or cauda equina syndrome.
- Progressive neurological deficit
- Significant pain despite prolonged conservative treatment for two months.
Cases of isolated low back pain are not a decisive factor for discectomy. The best indicator is monoradicular sciatica as it predicts a greater response to radicular decompression. Other indicators are the levels of motor and sensory deficits.
On the other hand, the patient’s preference for recovery time should be carefully considered. The long-term results of microdiscectomy are similar to those of conservative treatment, when there are no neurological deficits, although recovery is significantly faster with surgical treatment.
Surgical techniques for lumbar disc herniation
A priori, any surgical intervention should be subject to four general principles:
- Be simple
- Be effective
- Respect the anatomy
- Be fast.
The reference technique is microdiscectomy, performed with the aid of an operating microscope and consisting of exposure of the space between the corresponding laminae underneath the periosteum, a tissue membrane attached to the outside of the bones. Subsequently, a hemiflavectomy is performed to remove the yellow ligament and, sometimes, the removal of a small portion of the lamina or the articular process. Once the root is detected, the fragment compressing it is removed and the annulotomy and removal of the nucleus pulposus is performed.
Another technique implemented in the last decade is the tubular discectomy, which consists of the introduction of a K-wire in a parasagittal situation (perpendicular to the floor and at right angles) at the level of the corresponding interlaminar space. Through this needle a succession of dilators of progressively larger diameter are introduced until finally the transmuscular retractor is introduced to be used as a working channel. The surgeon’s vision can be enhanced by means of a surgical microscope or endoscope.
The importance of posture in disc herniation
The aim of good posture is to decrease the pressure on the epidural venous plexuses, thus aiding respiratory mechanics, opening the spaces between laminae, allowing surgery and decreasing the risk of complications. The two options are: ventral decubitus with support, the patient is supported on his back with arms stretched and placed along the body, legs straight and placed parallel, and aligned with the spine and back. On the other hand there is the genupectoral, in which the patient is positioned face down and the trunk rests on the knees and chest. The patient must first rest on the knees on a surface and flex the waist so that the hips are up and the head is on the floor. These two postures are recommended, since they avoid abdominal compression by transferring the weight to another part of the body, other than the lumbar region. Many of the most serious complications of lumbar discectomy, such as blindness or neuropathies, are caused by an incorrect posture of the patient during surgery.
Results of the treatment of sciatica due to lumbar disc herniation
The main objective of surgical treatment is not the removal of the intervertebral disc, but to decompress and release the nerve root to relieve pain and facilitate the recovery of neurological deficits, if any. Secondarily, the nucleus pulposus is partially removed to prevent recurrence or recurrence of herniation.