Neurosurgical Consultants: Spine Disorders: Degenerative Spine Conditions: Herniated Lumbar Disc

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LUMBAR SPINAL STENOSIS

"Stenosis" means "narrowing". In this context, it is the narrowing of the Spinal Canal. This narrowing is occasionally seen as a "congenital phenomenon". It is more commonly identified consequent to a progression of the "Degenerative Disc Disease" which also affects the related Spine structures. As "Disc Disease" progresses, the Disc becomes dehydrated and progressively collapses to a point where it is no longer an effective "cushion" between the Vertebrae and no longer functions as a "spacer" to keep those bones apart. As a result of this progressive collapse of the Disc Space, the Lumbar Facet Joints begin to over ride one another. As the Facet Joints "over ride", their joint surfaces are subjected to abnormal "wear". The bone and joint's response to this attempt to "wear out" is to FORM MORE BONE, the result of which is a much larger Facet which then encroaches upon the Spinal Canal and the Neural Foramena to produce STENOSIS.

Figure 1: Diagrams of the Lumbar Spine

The Role of the Lumbar Facet Joints

Facet Joints (See Figure 1), as part of the Spinal Column's weight bearing mechanism, are particularly subject to vertical pressure as they participate in the "weight bearing" function of the Spinal Column. The Facet Joints are also structures where motion occurs between the adjacent Vertebrae. In time, this motion together with the consequences of "weight bearing" produces excessive "wear and tear". When Spinal Joints are involved in this "wear-and-tear" process, they react in a characteristic method in an attempt to "protect" themselves from wearing out (as ball bearings would in the joints of some machines.) The Facet Joint's surfaces react to produce more bone in an attempt to halt the wearing away. This "new bone" formation results in an overgrowth (Hypertrophy) which eventually encroaches on the Spinal Canal (where the Spinal Nerves reside) making the Spinal Canal (and the Neural Foramen) narrower.

One of the paraphenomenon of "Degenerative Arthritis" of the Spine is the progressive "collapse" (or narrowing) of the Disc Space. Among the consequences of this Disc Space "collapse" is that the Facet Joint surfaces overlap to a greater than "normal". This, too, adds to the pathological pressures upon the Facet Joints resulting in further Degenerative changes.

This bone process is called "Degenerative Arthritis" or "Osteoarthritis". The new bone often has the appearance of "spurs" (also called "Osteophytes.") The process of Degenerative Arthritis is usually a very slow one. It is, to a degree, inevitable in everyone. Some people, for many of the reasons outlined previously, encounter it earlier and to a greater degree than others do. Despite a well-advanced case, some people are not significantly affected either by pain or neurological injury, whereas others can be incapacitated by it. Unfortunately, there are no medications or treatments that can reverse this "degenerative" process. Anti-inflammatory drugs are usually helpful in reducing the pain associated with an acute flare-up of joint inflammation.

Occasionally this process of progressive abnormal bone formation results in a very substantial stenosis (narrowing) of the Spinal Canal. This narrowing is consequent to the overgrowth of the Facet Joints as well as the Ligamentum Flavum (Yellow Ligament). This special ligament is part of the normal stabilizing structure of the Spine and lies beneath each Lamina connecting one Lamina to its immediate neighbor above and the one below. The Ligamentum Flavum is subject to stresses just as the Facet Joints are and as a result it participates in this counter-productive degenerative process which ultimately results in a pathological thickening (hypertrophy) of the Ligament.

Once the Ligamentum Flavum and Lumbar Facet Joints have become sufficiently overgrown to seriously compromise the diameter of the Spinal Canal and Neural Foramina, substantial pressure is exerted upon the Spinal Nerve Roots.

Figure 2: The LIGAMENTS of the LUMBAR SPINE.

Figure 3A (Left): Lumbar Myelogram (Postero-anterior View)
Figure 3B (Right): Lumbar Myelogram (Lateral View)
Both views show the "high grade" narrowing of the Spinal Canal at the L4,5 level.
The "blockage" to the flow of Myelographic "dye" is indicated by the ABSENCE of the "dye" which is a "water-soluble" substance that mixes with the Cerebrospinal Fluid.

SYMPTOMS

Neurogenic Intermittent Cauda Equina Claudication

The most frequent symptom experienced by patients with Spinal Stenosis is SEVERE PAIN OR CRAMPING IN THE LEGS when trying to walk some distance, a condition called "NEUROGENIC INTERMITTENT CLAUDICATION". It is this Spinal Canal narrowing that squeezes the Nerve Roots within the Spinal Canal that causes this severe pain.

There is another (and probably more common) cause of "Claudication". In those patients the pain is a result of a decrease in the actual blood supply to the large muscles of the lower extremities. The deceased blood supply is due to a progressive narrowing of the main arteries supplying the leg muscles by a condition known as "Atherosclerosis" (or "Hardening of the Arteries".)

Since the symptom of Claudication tends to occur in the elderly and both causes (Spinal Stenosis consequent to "Degenerative Osteoarthritis" as well as decreased blood supply resulting from Atherosclerosis) also occur with advancing age, it is imperative to differentiate between the two in order to arrive at an accurate diagnosis. Most often these problems can be evaluated by simple methods. Occasionally a more detailed examination is required. (See the "DIAGNOSIS" section below for a discussion on the investigation of these patient problems.)

In patients suffering from Claudication resulting from Spinal Stenosis there is usually neither isolated muscle weakness nor sensory loss as commonly occurs with Herniated Lumbar Disc situations. However the presence of "tingling", "numbness" and/or weakness DOES NOT PRECLUDE THE DIAGNOSIS of CLAUDICATION consequent to STENOSIS. (Also see the next paragraph) Once the Claudication is severe and the pain becomes a major factor impairing the quality of life, then treatment becomes necessary.

Figure 4: Post-myelographic CT Scan (Same patient as Figure 3)
High grade stenosis indicated by the minimal amount of myelographic "dye" (the "white material") within the narrowed Spinal Canal (Vertical Arrow). The "small black dots" within the "white dye" are the Spinal Nerve Roots being tightly squeezed.
The Facet Joints (Horizontal Arrows) are overgrown.
The Hypertrophic Ligamentum Flavum (the "Dark" space between the "Dye" and the bone of the Lamina indicated by the Bi-directional Arrows) results in compression of the nerves from posteriorly.

OTHER SPINAL CONDITIONS ACCOMPANYING SPINAL STENOSIS

Herniated Disc

A "Herniated Disc" can also occur in conjunction with the "Stenosis" described above. In these cases, there is significantly less room within the Spinal Canal and Neural Foramena resulting in substantially greater pressure upon the Nerve Root(s) and a lesser likelihood of recovery without surgical intervention.

Once again it is a matter of degree of Neurological Injury and extent of Nerve Root (and/or Spinal Cord) compromise that will help to decide the appropriate form of treatment. When too much pressure is exerted on the Spinal Nerves as they are squeezed against the bone of the Spinal Canal, the pressure can be sufficient to injure the Nerve Root (and/or the Spinal Cord) as well as the small blood vessels supplying these vital structures. The characteristic response by the Nerve Root to this type of injury is for it to "swell". Unfortunately as it swells against the hard bone surface of the Spinal Canal, this produces further pressure on the Nerve Root and its blood supply, which results in more injury to the Nerve Root and progressively more swelling. THIS IS A VISIOUS CYCLE THAT MUST BE INTERUPTED in order to preserve Neurological function.

Figure 5A (Left): Lumbar Spine MRI Scan (Sagittal View). Large Herniated (Extruded) L4,5 Disc with Inferior Migration (Curved Arrow). In addition, the Spinal Canal is narrowed by the Hypertrophic Ligament Flavum (Straight Arrows).
Figure 5B (Right): Lumbar Spine MRI Scan (Axial View just below the L4,5 Disc Space). The Herniated Disc is in the Center (Vertical Arrow) of the Stenotic Spinal Canal. The Hypertrophic Facet Joints (Oblique Arrows) and the Ligamentum Flavum (indicated by the Bi-directional Arrows and appearing as "Dark" objects) are compressing the Cerebrospinal Fluid ("White" in the center of the Spinal Canal) and Nerve Roots.

Synovial Cysts

The "Synovium" is the "lining" of "joint surfaces". This "joint lining" is subject to "degenerative" changes resulting from the "trauma" that affects the particular Facet Joint. As the Synovium of the Lumbar Facet Joint undergoes "degenerative" change, it also becomes "hypertrophic" (increases in size). These "Degenerative" changes may take several forms. This includes "Cyst" formation as well as pathological "calcification". The "Cyst" may become a significant "mass" within a Spinal Canal that is already compromised by the Spinal Stenosis (initially caused by the Facet and Ligamentum Flavum hypertrophy.) Oftentimes the Cyst becomes quite adherent to the Dura Mater overlying the Nerve Root, making its removal at surgery technically difficult.

Figure 6A (Left): Post-myelographic Lumbar CT Scan (Axial View) in a 70 year old Male. The Hypertrophic Ligamentum Flavum (the dark grey structure within the narrowed Spinal Canal indicated by the Bi-directional Arrow) combined with the Degenerative Hypertrophic Facet Joints (Horizontal Arrows) has resulted in severe Spinal Stenosis as demonstrated by the paucity of myelographic "dye" ("white" substance within the Spinal Canal indicated by the Vertical Arrow).
A Synovial Cyst (round object within the Spinal Canal indicated by the Side-curved and Oblique Arrows) on the Left side of the Spinal Canal adds to the considerable pressure on the Nerve Roots.
Figure 6B (Right): MRI Scan (Sagittal View) in a 72 year old Female. This is a SYNOVIAL CYST (Oblong object at the end of the Oblique Arrows) producing severe Spinal Stenosis. Compare the Spinal Canal Diameter above and below the Stenotic level (indicated by the Bi-directional Arrows.)

Scoliosis

Scoliosis ("twisting" of the Spinal Column) is a condition that frequently begins in adolescence and progresses at variable rates in the affected individuals. The purpose of bringing this to our discussion in this section relates to its association with advanced Degenerative Osteoarthritis and resulting Spinal Stenosis. "Rotoscoliosis" is the term applied to a variation of "Scoliosis" which incorporates "rotation" with "twisting" of the Spinal Column (See Figures 11-13 for examples of this condition.)

The presence of Scoliosis, by definition, means that the weight-bearing mechanism of the Spinal Column is ABNORMAL. The consequence is that the Vertebral Joints, Ligaments and Discs will be subjected to ABNORMAL pressures due to this disturbance in the normal Spinal Alignment. Over a life-time this will result in more extensive and rapidly progressive Degenerative changes of these structures which often leads to severe Spinal Stenosis since the "Degenerative" response is ALWAYS associated with an INCREASE IN SIZE of the Facet Joints and the Ligament. This, again, is the body's way to defend itself from "wearing out" (such as ball bearings would do in a mechanical joint.)

Figure 7A (Left):MRI Scan (Coronal View) 73 year old Female. A "central" Vertical Line drawn from the T11 Vertebra demonstrates the serpentine configuration of this "Scoliotic" Spine.
Figure 7B (Right): MRI Scan (Axial View-Same Patient) Severe stenosis (Vertical Arrow points to the "light grey" central Spinal Canal) at L4,5 with massive Facet (Horizontal Arrows) and Hypertrophic Ligamentum Flavum (Bi-directional Arrow points to this "Black" ligament.)

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This page last edited on 6/23