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Lumbar Disc Disease

Background

The intervertebral discs are cartilaginous plates surrounded by a fibrous ring which lie between the vertebral bodies and serve to cushion them. Through degeneration, wear and tear, or trauma, the fibrous tissue (annulus fibrosus) constraining the soft disc material (nucleus pulposus) may tear. This results in protrusion of the disc or even extrusion of disc material into the spinal canal or neural foramen. This has been called herniated disc, ruptured disc, herniated nucleus pulposus, or prolapsed disc.

This disc herniation may become significant if a nerve root is compressed. Irritation of the nerve root produces pain in the distribution of that nerve, typically down the back of the leg, side of the calf, and possibly into the side of the foot. For this reason, a herniated lumbar disc characteristically produces sciatica but not back pain per se. If sensory function of the impinged nerve root is impaired, numbness will result. The exact area of numbness is determined by the particular root, and may be in the inner ankle, the great toe, the heel, the outer ankle, the outer leg, or a combination of these. Impairment of motor function of the root will cause weakness which again depends on the particular root, and may include weakness of bringing the ankle upward or downward or raising the great toe.

 

Manifestation  Level of Disc Herniation 
L3-4  L4-5  L5-S1 
Root Compressed  L4  L5  S1 
Weakness  quadriceps, tibialis anterior  extensor hallicus longus (extension of great toe)  gastrocnemius (ankle plantarflexion) 
Reflex Involvement  knee jerk  none significant  Achilles 
Sensory Loss  medial ankle  great toe  lateral foot & heel 
Pain Distribution  anterior thigh  back of thigh  back of thigh, lateral calf 

Table 1. The most common clinical manifestations of lumbar disc herniation.

Table 1 summarizes the major lumbar disc herniation syndromes. Note that the L5-S1 disc is involved 45-50% of the time, L4-5 40-45%, and L3-4 about 5%. Disc herniation at the other lumbar levels is rare. The root compressed is the one exiting the level below, in the vast majority of cases. However, if the herniation is lateral, into the foramen, then the root compressed will be the one above. This is known as a far lateral disc herniation and occurs in about 3-10% of cases. It is also important to note that while these signs are helpful in the diagnosis and decision regarding type of treatment, not all of the signs and symptoms associated with a root may be present in an individual, and multiple root signs may even be present.

Diagnosis

The diagnosis should be suspected from the history and physical examination. Radiographic studies should be done to make the diagnosis and define its location and configuration. Generally, an MRI scan is preferred because it is noninvasive (no needle punctures or injections are required) while providing excellent detail. CT scan, while inferior to MRI in soft tissue detail, are superior in bony detail, and are faster and less expensive. For this reason, a good quality CT scan is often sufficient in an uncomplicated herniated lumbar disc. Myelography with CT has long been the gold standard, because of its excellent definition of the spaces around the nerve roots. Its disadvantage is that it requires injection of contrast dye through a lumbar puncture. It has to a large extent been supplanted by MRI, but it should be viewed as a complementary rather than an alternative test, and in many cases it is indispensable.

Treatment

The mainstay of therapy for herniated lumbar disc is conservative treatment, that is, nonsurgical. This is for the simple fact that in the majority of patients the symptoms resolve or subside to a level allowing normal activity within 2 weeks. If bedrest fails, surgery should be considered.

Surgery for removal of a herniated lumbar disc is one of the most commonly performed procedures in this country. An incision is made vertically along the midline of the back, usually about 2 inches long. Some of the muscle overlying the bone which forms the back of the spinal canal, called the lamina, is separated off the bone. A small window is drilled in the laminae overlying the disc herniation. The nerve root is identified and gently retracted away to expose the offending disc herniation. The disc material is then removed and the wound is closed in a way which restores the normal anatomic layers.

Postoperative recovery is relatively short. Patients are up walking the same night or the next morning and discharged home in 3 to 5 days. The vast majority of patients experience permanent relief of pain. Recovery of motor function is variable.


 

 

 

 

 

 

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