1. What Is Spinal Stenosis

Lumbar spinal stenosis is a condition involving any type of narrowing of the spinal canal or nerve-root canals.¹

1.1 Definition and Classification

There are many forms of lumbar spinal stenosis. The most common is degenerative stenosis, occurring in virtually the entire adult population as a result of the natural process of aging.

Lumbar Spinal Stenosis is classified as follows:^*2

1. Congenital-developmental stenosis
   1. Idiopathic (hereditary)
   2. Achondroplastic
2. Acquired stenosis
   1. Degenerative
   2. Combined congenital and degenerative stenosis
   3. Sponylolytic/spondylolisthetic
   4. Iatrogenic
      1. Post laminectomy
      2. Post fusion
      3. Post chemonucleolysis
   5. Posttraumatic
   6. Metabolic
      1. Paget's disease
      2. Fluorosis

* Modified from Arnoldi CG, Brodsky AE, Cauchoix J, et al; Clin Orthop 1976; 115-4-5.

Lumbar Spinal Stenosis is a degenerative narrowing of the spinal canal, nerve root canals and/or intervertebral foramina caused by bone and/or ligament hypertrophy in local, segmental or generalized regions. The narrowing results in compression of spinal nerves and nerve roots, causing a constellation of symptoms, including lower back pain, neurogenic claudication and lower extremity pain.

Congenital lumbar stenosis is relatively rare and usually presents at an early age, often between 30 and 40. Acquired LSS is more common and generally develops when patients are in their 60s or older. It is a puzzling condition that can neither be predicted nor prevented. It does not distinguish by sex, race, or ethnicity. Nor is it associated with any particular occupation or any particular body type.

Symptoms include:

• Dull to severe aching pain in the lower back or buttocks - develops with walking or other activities.
• Pain radiates into one or both thighs and legs (60% bilateral pain).
• Numbness, weakness or paraesthesia involving the lower extremities.
• Symptoms relieved by bending forward, sitting or lying down.

1.2 The Normal Aging of the Spine; The Degenerative Cascade

Complex changes in the vertebral structures and ligaments of the spine contribute to the development of acquired lumbar spinal stenosis. As the body dehydrates with age, bones become less dense and the discs of the spine lose mass. The discs compress, causing tilting, slippage and rotation of vertebral bodies. This results in compression of the spinal sac and nerve roots. In some cases, bone growth is stimulated and osteophytes form in the lateral recess and intervertebral foramina as the spine tries to stabilize itself. This can cause compression of nerve roots as they exit through the foramina to the lower back and legs, leading to chronic back pain and intermittent weakness and numbness in the legs.

At the same time, hypertrophy of the spinal ligaments (ligamentum flavum) can reduce the space available for the spinal sac, causing further compression of the nerve roots. These ligaments stiffen with age and begin to buckle into the spinal canal, creating additional points of compression and pain. Arthritis often compounds the problem by increasing the stiffness and inflexibility of the ligaments and joints.

In addition to the body's dehydration with age, the physiological changes responsible for LSS are thought to have their genesis in four areas. Listed from most common to rare:

• Degenerative causes such as spondylosis, spondylolisthesis, hypertrophy of the ligamentum flavum, and synovial cysts are the main etiology of LSS by far.
• Traumatic causes such as vertebral fractures and subluxation, complications following laminectomy such as epidural fibrosis and herniated discs.
• Skeletal causes such as metastatic cancer of the spine, rheumatoid arthritis, Paget's disease, ankylosing spondylitis and diffuse idiopathic skeletal hyperstosis (DISH).
• Metabolic and endocrine causes such as acromegaly, pseudogout, renal osteodystrophy, hypoparathyroidism or, in rare cases, Cushing's disease.

The clinical presentation and diagnosis of lumbar spinal stenosis are described below.

1.2.1 Clinical Presentation of Lumbar Spinal Stenosis - A Puzzle

The posture of patients with lumbar spinal stenosis while walking is typically kyphotic. Patients will sometimes describe how they can walk for longer periods in a store only by leaning forward supported by a shopping cart. Extension of the spine will often provoke symptoms while flexion will relieve them. Thus, many patients will stop walking, and bend over or squat to relieve their pain. The patients may only be able to walk a few hundred meters but may be able to ride a bicycle for several kilometers.³

Although more variation exists in the complaints of patients with spinal stenosis than any other syndrome producing low back pain, there are four primary sub-syndromes:

1.2.1.1 Neurogenic Intermittent Claudication

Pseudoclaudication is a syndrome unique to spinal stenosis and also its most common symptom. Intermittent claudication is defined as pain in the buttocks, thighs, and legs brought on by either prolonged standing or exercise in the erect posture. This symptom typically is relieved by various maneuvers that flex the lumbar spine such as bending forward, either in a sitting or lying position.

1.2.1.2 Radicular Pain (Sciatica)

Peripheral symptoms are classically those of sciatica, which is described by patients as pain in the lower back and hip, radiating down the back of the thigh into the leg. A history of numbness, and associative weakness, or tingling is suggestive of a radiculopathy.

1.2.1.3 Atypical Leg Pain

Atypical leg pain occurs with non-radicular distribution, vague localization, and inconsistencies in location and presentation.⁴

1.2.1.4 Cauda Equina Syndrome

Cauda equina syndrome due to massive lumbar disc prolapse must be positively diagnosed or dismissed prior to any successful course of treatment for symptoms of lumbar spinal stenosis. Considered rare (occurring in 1 in 100,000 to 1 in 33,000 of adults)⁵ the important features of this syndrome are:

1. rapid progression of neurologic signs and symptoms in a patient with a known disc herniation;
2. bilateral leg pain and neurologic symptoms that frequently accompany it;
3. presence of caudal anesthesia;
4. presence of genitourinary dysfunction manifested by overflow incontinence or retention; and
5. loss of rectal sphincter tone sometimes accompanied by fecal incontinence.

It is important to assess the presence of cauda equina syndrome quickly in patients presenting symptoms of lumbar spinal stenosis. Delayed surgical intervention may result in persistent neurologic dysfunction.

1.2.2 Diagnosis of Lumbar Spinal Stenosis

The first diagnosis of lumbar spinal stenosis may have come as early as 1900⁶ but it was not until the availability of axial imaging, as provided by computed tomography and magnetic resonance imaging, that there was a rapid increase in reported cases. The effect of this dramatic improvement in medical technology can be seen in the rapid increase in clinical literature concerning this condition after 1976.

Because the neurologic compression that triggers LSS can be located in many different places on the spine, symptoms can vary.

In many cases, patients change their lifestyles to manage their pain and often fail to mention key symptoms that would help their general practitioner arrive at a definite diagnosis. These factors make it necessary for the diagnosing physician to obtain an excellent history, perform a complete physical examination and obtain proper imaging studies when indicated.

Typically X-rays are taken to assess the alignment of the spine and the extent of any degenerative changes. A CT scan is excellent in showing the shape and dimensions of the canal, ligamentum flavum hypertrophy, facet arthropathy and disc bulges and herniation. MRI has limitations in defining bone detail, but is good in defining nerve root impingement. As with any diagnosis of spinal disorders, radiological evidence of stenosis must be correlated with the patient's symptoms before the diagnosis can be confirmed.

Observe the patient for:

• Posture. LSS patients tend to bend forward at the waist to relieve the pain.
• Gait disturbance
• Decreased range of motion of the lumbar spine.

Conduct a neurologic exam:

• Straight leg raising
• Strength of musculature of hip, leg, ankles, toes
• Sensory exam
• Deep tendon reflexes (knee and ankle jerks)
• Check peripheral pulse

Red Flags

Patients whose symptoms suggest LSS instead may be suffering from other serious, even life-threatening conditions. It is important for practitioners to look for these red flags when evaluating a patient:

• Fever
• Unexplained weight loss
• Severe pain when recumbent
• Recent trauma as indicator of fracture
• Presence of severe or progressive neurological deficit

IF ANY OF THESE RED FLAGS ARE PRESENT, IMMEDIATE NEUROLOGICAL EVALUATION IS RECOMMENDED.