Lumbar spinal stenosis (LSS) is a narrowing of the spinal canal. Though LSS may occasionally occur congenitally with symptoms presenting in the thirties and forties, by far the largest number of patients with LSS acquire the disease later in life and are over 60 years of age. The spinal canal is narrowed as a result of degenerative changes. It is estimated that as many as 400,000 Americans may suffer from this disease the majority of which have not been diagnosed. The treatment is a decompressive lumbar laminectomy.

Anatomy

• The lumbar spine and pelvis, the low back, supports the entire body. The lumbar spine allows bending forward and backward and to twist at the waist
  
• The normal lumbar spine is composed of five building blocks called vertebrae that sit on the sacrum, which is the back part of the pelvic bone. (Figure 1)
  
• Each vertebra is constructed of a body, lamina, and pedicles, which surround an opening, the spinal canal.(Figure 2)
  
• A spinous process extends posteriorly (towards the back) from the lamina in the midline. Through the spinal canal pass the nerve roots that emerge from the end of the spinal cord and go to form the nerves to the legs. (Figure 3)
  
• Each root exits the spinal canal through a 'hole' in the side of the canal formed by two adjacent vertebrae called a foramen
  
• The roots float in fluid and are contained within a fibrous sac called the dura
  
• Separating any two vertebral bodies is a soft elastic material called a disk. The disk is composed of two parts, a soft center called the nucleus and a tough outer band called the annulus. (Figure 4). There are five lumbar disks
  
• On each side of the back of the spinal canal and linking one vertebra to the next are a series of small joints called facets
  

Figure 1 - The lumbar spine is composed of five vertebra separated by disks.	Figure 2 - Cross-section of a lumbar vertebrae showing the various parts.

Figure 3 - Cross-section showing the spinal canal and nerve roots.	Figure 4 - Cross-section showing a disk.

• With advancing age, several changes occur in the bone, disk, joints and ligaments of the lumbar spine. (Figure 5)
  
  1. Bones. The bones tend to loose water and become less dense (spondylosis). Because of degenerative changes near the disk margins, an overgrowth of bone may occur producing bony spurs (osteophytes) that may encroach on the exiting foramina with compression of the enclosed nerve roots
     
  2. Disk. The disks also loose water and compress thus narrowing the disk space. The spacing between the vertebrae likewise narrows resulting in further narrowing of the foramina
     
  3. Joints. Along with the other degenerative changes, there develops a degenerative arthritis of the facet joints that causes the joints to enlarge. Sometimes the lining of the joint (synovium) enlarges or becomes cystic. This combination of events results in narrowing of the spinal canal and increasing stiffness of the spine. If the joints degenerate such that the fibrous capsule loosens, then one vertebrae may slip over the one below causing further narrowing of the canal and instability
     
  4. Ligaments. With advancing age the ligaments tend to stretch and thicken. This further encroaches on the spinal canal and foramina
     
• The above combination of changes results in nerve roots being compressed within the spinal canal or as the roots exit from the spinal canal through the foramina
  

Figure 5 - Cross-section of the lumbar spine showing stenosis caused by an overgrowth of the facets and thickening of the ligaments.	Click image above to view animation

History and Exam

• Individuals with spinal stenosis may complain of:
  1. Back pain. A fairly constant complaint is lower back pain. The pain is usually described as dull or aching but occasionally the pain may be sharp and severe
  2. Nerve root pain. Irritation or compression of the nerve roots in the lumbar spinal canal or foramina produce this pain. (All the roots together in the lumbar spinal canal are called the cauda equinae.) The pain may begin in the low back and go to the buttocks, thighs and down the legs. In most cases the pain goes to both sides but in many sufferers the pain is only on one side
  3. Numbness and tingling or pins and needles feeling. This is type of discomfort is also caused by irritation or compression of the nerve roots
  4. Loss of bowel or bladder function. This is caused by severe compression of the cauda equinae
  5. Pain on standing or walking (neurogenic claudication). This is the most classic symptom of LSS
  • The deep aching pain begins when standing or walking. Frequently the patient complains of not being able to walk to the mailbox or around the block
  • The patient may find relief by bending forward at the waist while walking, thus the patient may be seen leaning forward on a shopping cart in the grocery or mall
  • Sitting down relieves the pain. This may be mistaken for a similar pain on walking but due to narrowing of the arteries going to the legs (vascular claudication)
• On examination, the physician may find few abnormalities
  1. The reflexes on tapping the knee or ankle may be depressed
  2. There may be a mild weakness of the legs
  3. The response to pin or touch may be less than normal
  4. The pulses in the legs are normal

Tests

• Special tests are necessary in making the correct diagnosis. These are:
  
• X-ray of the lumbar spine. The x-rays may show collapse of the disk spaces with narrowing of the foramina, bony spurs, scoliosis, slippage of one vertebrae over another (spondylolesthesis) and degenerative changes in the facet joints
  
• CT (computerized tomography) scan. This test images the lumbar spine by X-ray as a series of cross-sections. The changes in the bone and joints can be evaluated as to the degree of spinal canal narrowing
  
• MRI (magnetic resonance imaging) scan. This test images the lumbar spine though the use of a magnetic field and radar waves. The soft tissues such as the ligaments are imaged better than bone. This test also can be used to determine the degree of narrowing (Figure 6A,B)
  
• Lumbar myelogram. This test involves the injection of an X-ray contrast material containing iodine into the fluid that surrounds the cauda equinae. Regular X-rays as well as a CT scan are then obtained. This test usually gives the clearest picture of the degree of spinal narrowing and the number of spinal levels involved (Figure 7)

Figure 6a - MRI showing stenosis of the lumbar spine.	Figure 6b - MRI showing spinal canal narrowing at the level of the disk space (between arrows).

Figure 7 - CT myelogram of the lumbar spine showing spinal stenosis.

Non-surgical Treatment

• Surgery is usually not the first treatment of choice.
  
• Pain and anti-inflammatory medication such as aspirin, ibuprofen, acetaminophen and naproxen may be of benefit particularly in early cases of LSS
  
• Physical therapy. Exercises for strengthening and stretching the back and abdominal muscles may help
  
• Epidural cortisone injection. Cortisone is injected into the spine between the bone and the dura. This sometimes may reduce inflammation and reduce pain. Injections of steroids should be used cautiously since any long term series of injections can have adverse side effects

Indications

• Surgery is indicated when:
  
• Pain medication and physical therapy do not help
  
• The back and leg pain is severe enough to limit an individuals everyday activities or quality of life
  
• There is a neurologic deficit such as weakness in the legs, loss of sensation in the legs or loss of bowel or bladder control
  
• There is significant pain on walking
  
• The tests confirm the diagnosis of LSS
  

Surgical Procedure

• Decompressive lumbar laminectomy is the procedure most commonly carried out for LSS. The procedure is carried out in the following manner:
• The number of vertebra that are involved is determined and an incision is made extending from one vertebrae above to one vertebrae below the vertebra to be operated upon
• The muscles are elevated off of the spinous processes and lamina of the vertebra and held apart with an instrument called a retractor
• The spinous processes and lamina of the involved vertebra are then carefully removed under magnification (magnification loupes or operating microscope).
• These structures are removed using an air or electrically driven burr and small bone biting instruments called rongeurs (Figure 8)
• Using the same instruments, the overgrowth of the facet joints and the bone pushing in on the foramina are removed as necessary
• The overgrown and stretched ligaments are also removed
• All bleeding is stopped and the wound is sutured
  

Figure 8 - Cross-section of the lumbar spine showing removal of the lamina and the return of the dural sac to normal.

Other procedures

• Some surgeons may prefer to perform multiple partial laminectomies instead of the more extensive complete laminectomy
  1. In this case, only the lower one-half of the lamina and ligaments are removed on each side of the involved vertebra
  2. Using the same instruments, the overgrowth of the facet joints and the bone pushing in on the foramina are also removed as necessary
  3. The overgrown and stretched ligaments are also removed
  4. This may preserve the stability of the involved structures
     
• Unilateral decompressive laminectomy
  
  1. Used In cases in which the pain and bone overgrowth are unilateral (one sided) (Figure 9)
     
  2. A laminectomy is carried out on the side of the overgrowth. The lamina above and below the narrowing may be partially or completely removed
     
  3. An important part of the procedure is the removal of the medial (towards the midline) portion of the overgrown facet, the part that traps the nerve root
     
• Bilateral decompressive laminectomy through a unilateral approach
  1. This minimally invasive procedure uses an endoscope or operating microscope for improved visualization and approaches the stenosis from one side thus minimizing trauma to the back muscles
  2. A partial laminectomy of the involved vertebra is performed on the side on which the patient has the more severe symptoms
  3. The overgrowth of the facet joints and the bone pushing in on the foramina are also removed as necessary
  4. The lower part of the spinous process is removed to allow access to the opposite side
  5. Most or all of the lower half of the lamina of the opposite side is then removed followed by the overgrown ligaments (Figure 10)
• Spinal fusion
  
  1. In a few individuals with LSS, there is an associated spinal instability because of destruction of the facet joints. In these cases it is necessary to add a fusion to the procedure
     
  2. Decompressive laminectomy alone is not an indication for fusion. If there is instability, there will be a noticeable shift in alignment of one vertebra over the one below (spondylolesthesis) on flexion and extension X-rays of the lumbar spine
     
  3. Fusion is not indicated in elderly patients with only a small shift
     
  4. A second opinion is warranted if spinal fusion is being considered in addition to the decompressive laminectomy
     
  5. The fusion is accomplished through the same incision
     
  6. Bone taken from the iliac crest (hip bone) is used for the fusion. The bone is laid down lateral to the pedicles and over the transverse processes. If there is considerable instability, the addition of screws and rods may be necessary

Figure 9 - MRI of unilateral overgrowth of the facets (arrowheads) trapping a nerve root (arrow).

Figure 10a - (Left) Cross-section CT scan before surgery through the L3 disc space showing spinal stenosis (arrowheads).	Figure 10b - (Right) Similar CT scan after decompressive laminectomy through a right unilateral approach showing relief of the stenosis (arrowheads).

Complications

While decompressive laminectomy is a relatively safe procedure. Despite even the greatest care, complications do occur.

• Hemorrhage. Hemorrhage may cause compression of the nerve roots with resulting weakness or paralysis in the legs, loss of feeling and loss of bowel or bladder control
  
• Tearing of the dura over the nerve roots. This problem occurs because the ligaments may be stuck to the dura, and can lead to injury to the nerve roots, pain, and leakage of cerebrospinal fluid (the fluid that surrounds the nerve roots). If leakage occurs, this must be corrected to prevent later infection
  
• Infection of the wound
  
• Direct injury to the nerve roots causing weakness or paralysis in the legs, loss of feeling and loss of bowel or bladder control. Tears in the dura and injury to the nerve roots are minimized by the use of magnification at the time of surgery
  
• Deep venous thrombosis with pulmonary embolism. This is a very serious problem. In some patients, blood clots will form in the veins of the legs or pelvis. These clots may come loose from the vein wall and travel to the lungs causing severe difficulty with respiration and even death
  
• Since this surgery is most often performed on an older population, the patient may also be subject to complications related to to heart or lung disease, diabetes, or hypertension

After Surgery Care

• After surgery the patient is given instructions for care at home until seen in the doctor's office
  
  1. The doctor should be contacted if there is any:
     
  2. Redness or discharge from the wound
     
  3. Fever
     
  4. Weakness or numbness in the legs or
     
• Trouble with urination
  
• Most patients are discharged from hospital on the first or second post-operative day
  
• Elderly patients with heart, lung, kidney or other diseases such as diabetes may require additional hospital stay