59.2 Spinal Conditions: Spinal Stenosis, Spondylolisthesis & Compression Fractures

Lumbar Spinal Stenosis: Pathoanatomy & Biomechanics

Lumbar Spinal Stenosis (LSS) is a degenerative anatomical condition characterized by the progressive narrowing of the central spinal canal, the lateral recesses, or the neural foramina of the lumbosacral spine. This narrowing results in mechanical compression and vascular compromise of the traversing and exiting nerve roots of the cauda equina. LSS is the single most common indication for spinal surgery in adults over 65 years of age.

The Degenerative Triad of Spinal Stenosis

Acquired degenerative stenosis results from a predictable cascade of aging and biomechanical wear involving three contiguous anatomical structures:

1. Intervertebral Disc Degeneration: With advanced age, the nucleus pulposus dehydrates and loses proteoglycan content, resulting in loss of intervertebral disc height. The annulus fibrosus develops radial and concentric fissures, bulging diffusely into the anterior aspect of the central spinal canal and neural foramina.
2. Facet Joint Hypertrophy: Disc collapse shifts excessive axial compressive and shear loads onto the posterior paired zygapophyseal (facet) joints. In response to chronic mechanical stress, the facet joints develop severe osteoarthritis characterized by synovial inflammation, joint space narrowing, capsule laxity, osteophyte proliferation, and subchondral bony overgrowth. The superior articular process hypertrophies anteriorly into the lateral recess, while the inferior articular process hypertrophies medially into the central canal.
3. Ligamentum Flavum Thickening & Inward Buckling: The paired ligamenta flava, which line the posterolateral wall of the spinal canal between adjacent lamina, lose elastic fibers and undergo progressive fibrosis and collagenous hypertrophy. As disc height collapses, the ligamentum flavum loses longitudinal tension and buckles inward toward the thecal sac during axial loading.

                  CROSS-SECTIONAL ANATOMICAL ZONES OF SPINAL STENOSIS

   Anatomical Zone   Anatomical Boundaries                    Compressive Elements & Neural Structures Affected
   ═════════════════════════════════════════════════════════════════════════════════════════════════════════════
   Central Canal     Bound anteriorly by disc / PLL;          Bulging disc, inferior facet hypertrophy, and
                     laterally by pedicles; posteriorly by    ligamentum flavum buckling compress the THECAL SAC
                     laminae and ligamentum flavum            and CAUDA EQUINA (bilateral symptoms)
   ─────────────────────────────────────────────────────────────────────────────────────────────────────────
   Lateral Recess    Bound anteriorly by posterior vertebral  Superior facet hypertrophy, posterolateral disc bulge
   ('Trefoil Zone')  body; laterally by pedicle; posteriorly  compress the TRAVERSING NERVE ROOT (e.g., L5 root
                     by superior articular process of facet   compressed at L4-L5 level)
   ─────────────────────────────────────────────────────────────────────────────────────────────────────────
   Neural Foramen    Bound superiorly/inferiorly by pedicles; Foraminal disc herniation, superior facet tip overgrowth,
                     anteriorly by vertebral body/disc;       loss of disc height compress the EXITING NERVE ROOT
                     posteriorly by ligamentum flavum/facet   (e.g., L4 root compressed at L4-L5 level)
   ═════════════════════════════════════════════════════════════════════════════════════════════════════════════

Anatomical Dimensions: In an average adult, the normal sagittal (anteroposterior) diameter of the central lumbar canal is 15 to 25 mm. An AP diameter of 10 to 12 mm defines relative central stenosis, whereas <10 mm defines absolute central stenosis. On cross-sectional axial MRI, a dural sac area <100 mm² indicates moderate stenosis, and <75 mm² defines severe stenosis.

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Neurogenic Claudication: Clinical Hallmarks & The "Shopping Cart Sign"

Pathophysiology: Posture-Dependent Neuroischemia

The pathognomonic clinical manifestation of lumbar spinal stenosis is Neurogenic Claudication (historically termed pseudoclaudication). The underlying pathophysiology is dynamic, posture-dependent neurovascular ischemia:

• Spinal Extension (Aggravating Factor): When the patient stands erect, walks upright, or extends the lumbar spine (as in walking downhill), the lumbar lordosis increases. This lordotic extension forces the intervertebral discs to bulge posteriorly, shifts the inferior facet processes downward, and causes the hypertrophic ligamentum flavum to buckle anteriorly into the spinal canal. Consequently, spinal canal cross-sectional area decreases by 16% to 20%.
• Venous Engorgement & Microvascular Stasis: Increased mechanical pressure inside the narrowed canal exceeds the low intravascular pressure of the epidural and radicular veins (normally ~15-20 mmHg). This venous outflow obstruction produces secondary capillary congestion, relative ischemia of the lumbosacral nerve roots, and ectopic axonal firing, manifesting as bilateral leg pain, heaviness, and numbness.
• Spinal Flexion (Relieving Factor): When the patient flexes the spine forward (stooping, sitting down, squatting, or leaning forward), lumbar lordosis is flattened. Forward flexion increases interlaminar spacing, pulls the ligamentum flavum taut against the dorsal canal, and opens both the central canal and neural foraminal areas by up to 25%. Venous perfusion is instantly restored, rapidly clearing metabolic waste products and abolishing the neural symptoms.

Clinical Features & The "Shopping Cart Sign"

• Symptom Complex: Patients report bilateral (or asymmetric) aching discomfort, numbness, tingling, burning dysesthesias, muscle cramping, or profound heaviness ("legs feel like rubber or lead") originating in the buttocks or low back and radiating down the posterior and lateral thighs into the calves and feet.
• The "Shopping Cart Sign": Patients discover empirically that they can walk significantly longer distances without leg pain if they lean forward over a grocery shopping cart, a rolling walker, or a stroller. Leaning forward holds the lumbar spine in continuous flexion, maintaining canal patency.
• Incline Discrepancy: A classic clinical clue on board exams is that walking uphill is much easier and tolerated for longer distances than walking downhill. Climbing uphill naturally forces the patient into forward trunk flexion, opening the canal; walking downhill forces the spine into extension and lordosis, promptly precipitating neurogenic symptoms.

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Neurogenic vs. Vascular Claudication: Detailed Differential Diagnosis

Distinguishing neurogenic claudication from peripheral artery disease (PAD)-induced vascular claudication is a frequent board scenario and a pivotal clinical distinction in family medicine.

                  DIFFERENTIAL DIAGNOSIS: NEUROGENIC VS. VASCULAR CLAUDICATION

   Feature                 Neurogenic Claudication (Spinal Stenosis)   Vascular Claudication (Peripheral Artery Disease)
   ═════════════════════════════════════════════════════════════════════════════════════════════════════════════
   Primary Pathophysiology Mechanical compression & venous ischemia   Inadequate arterial blood flow to exercising muscle
                           of cauda equina / lumbosacral nerve roots  relative to metabolic demand

   Triggering Factor       Posture-dependent: Standing upright,       Exertion-dependent: Walking a fixed, reproducible
                           walking, and lumbar spine extension        distance; independent of spinal posture

   Relieving Factor        Spinal flexion: Sitting down, stooping     Stopping exertion: Standing completely still;
                           forward, leaning on a shopping cart        relief occurs without sitting or bending

   Time to Pain Relief     Slow: Requires 5 to 20 minutes of flexion  Rapid: Resolves promptly within 1 to 5 minutes
                           to relieve venous congestion               of halting muscle work

   Walking Uphill vs Down  UPHILL IS EASIER (trunk flexes forward);   DOWNHILL IS EASIER; UPHILL IS HARDER
                           downhill causes severe pain (extension)    (higher metabolic muscle work)

   Quality of Sensation    Aching, burning, numbness, tingling,       Intense muscle cramping, tight aching, or squeezing
                           heaviness ("rubber legs"), weakness        typically confined to calf muscles (or thigh/buttock)

   Distribution of Pain    Diffuse: Buttocks, posterior thighs,       Well-localized: Calf (femoral-popliteal disease);
                           calves, feet; often dermatomal or patchy   buttock/thigh (aortoiliac disease / Leriche)

   Peripheral Pulses       NORMAL, bounding dorsalis pedis and        DIMINISHED or ABSENT pedal/posterior tibial pulses;
                           posterior tibial pulses                    presence of femoral bruits

   Skin & Trophic Changes  Absent; normal skin color, temperature,    Trophic changes: Thin shiny skin, loss of leg hair,
                           and normal hair growth on toes/legs        thickened nails, pallor on elevation, rubor

   Bicycle Test            NEGATIVE (No pain): Can bicycle long       POSITIVE (Pain elicited): Pedaling induces
   (van Gelderen)          distances because spine is held flexed     ischemic calf cramping regardless of spinal posture

   Ankle-Brachial Index    NORMAL (ABI 0.91 to 1.30)                  ABNORMAL (ABI <= 0.90 confirms arterial disease)
   ═════════════════════════════════════════════════════════════════════════════════════════════════════════════

[!TIP] THE BICYCLE TEST OF VAN GELDEREN To confirm neurogenic versus vascular claudication at the bedside or in clinic, perform the Bicycle Test of van Gelderen. Have the patient pedal a stationary bicycle while leaning forward over the handlebars. A patient with neurogenic claudication can pedal indefinitely without lower extremity pain because the flexed spinal posture maintains canal diameter. Conversely, a patient with vascular claudication will develop ischemic calf cramping after pedaling a predictable distance, because pedaling increases skeletal muscle oxygen demand regardless of trunk posture.

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Diagnostic Imaging for Lumbar Spinal Stenosis

• Lumbar Spine MRI without IV Contrast: The gold-standard, definitive imaging modality. Sagittal and axial T2-weighted sequences provide exquisite anatomic resolution of soft tissue and bony compression: demonstrating disc bulging/herniation, facet arthropathy, ligamentum flavum hypertrophy, dural sac effacement (dural sac cross-sectional area <75 mm² confirms severe stenosis), and obliteration of the perineural fat surrounding exiting roots in the neural foramina.
• Lumbar Spine Plain Radiographs (AP, Lateral, Flexion-Extension): Initial baseline evaluation to assess overall spinal alignment, intervertebral disc height loss, osteophytosis, and dynamic segmental instability (spondylolisthesis slipping >3-4 mm between flexion and extension).
• CT Myelography (Post-Myelogram CT): Indicated when MRI is contraindicated (non-MRI-conditional cardiac pacemakers, severe claustrophobia, metallic hardware artifacts). Lumbar puncture is performed, iodinated contrast is instilled into the subarachnoid space, and high-resolution CT is acquired. Demonstrates osseous detail, canal diameter, and contrast column cutoff with high accuracy.

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Conservative, Interventional & Surgical Management of LSS

1. Conservative Management

• Flexion-Based Physical Therapy: Physical therapy centered on Williams flexion exercises (pelvic tilts, knee-to-chest stretches, abdominal core muscle strengthening, hamstring stretching) to decrease lumbar lordosis. Extension-based protocols (such as McKenzie extension exercises) must be avoided, as extension exacerbates canal narrowing. Conditioning via stationary upright cycling is highly encouraged.
• Oral Pharmacotherapy: First-line analgesia includes scheduled or intermittent NSAIDs (e.g., naproxen 500 mg BID, celecoxib 200 mg daily) or acetaminophen for axial low back pain. For patients with prominent radicular dysesthesias, burning nerve pain, or neurogenic paresthesias, neuropathic agents such as gabapentin (titrated from 300 mg at bedtime to 300-900 mg TID) or pregabalin (75 to 150 mg BID) provide modest symptom relief. Systemic corticosteroids provide no durable benefit. Long-term opioids are strongly discouraged.

2. Interventional Management: Epidural Steroid Injections (ESI)

• Fluoroscopically guided epidural corticosteroid injections (interlaminar, transforaminal, or caudal approaches) deliver targeted corticosteroid (e.g., triamcinolone, dexamethasone) and local anesthetic around compressed thecal sac and nerve roots.
• Evidence: ESIs provide modest, short-term pain relief (lasting 2 to 6 weeks) during acute neurogenic or radicular flares, allowing participation in physical therapy. However, large randomized sham-controlled trials (e.g., LESS trial, Friedly et al., NEJM 2014) demonstrate that ESIs do not improve long-term physical function, walking distance, or decrease the ultimate rate of surgical decompression.

3. Indications for Surgical Decompression

• Emergency Indications (Cauda Equina Syndrome): Immediate emergency neurosurgical or orthopedic spine referral for emergent surgical decompression (within 24-48 hours) is mandated if the patient develops saddle anesthesia, acute urinary retention or overflow incontinence, fecal incontinence, or progressive bilateral motor weakness.
• Elective Indications: Surgical referral is indicated for patients with:
  1. Progressive or severe motor deficit (e.g., foot drop due to L5 nerve root impingement);
  2. Intractable, debilitating neurogenic claudication or radicular pain refractory to at least 3 to 6 months of comprehensive conservative therapy;
  3. Substantial impairment in ambulation and activities of daily living confirmed by corresponding MRI evidence of moderate-to-severe stenosis.
• Surgical Procedures: Lumbar Laminectomy (decompression of central canal and unroofing of lateral recesses by resecting the lamina, spinous process, and thickened ligamentum flavum). If the patient has concomitant spondylolisthesis or scoliosis (segmental spinal instability), instrumented posterolateral spinal fusion is performed concurrently to prevent post-decompression slip progression.

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Spondylolisthesis: Classification, Biomechanics & Management

Spondylolisthesis refers to the translation (subluxation) of one vertebral body relative to the subjacent vertebra, most commonly an anterior slippage (anterolisthesis).

                  THE MEYERDING CLASSIFICATION OF SPONDYLOLISTHESIS

   Grade              Percentage of Vertebral Body Slippage    Clinical Severity & General Approach
   ═════════════════════════════════════════════════════════════════════════════════════════════════════════════
   Grade I            1% to 25% displacement                   Low-grade; conservative physical therapy
   Grade II           26% to 50% displacement                  Low-grade; conservative unless progressive or symptomatic
   Grade III          51% to 75% displacement                  High-grade; surgical evaluation frequently indicated
   Grade IV           76% to 100% displacement                 High-grade; structural instability, surgical stabilization
   Spondyloptosis     > 100% (vertebral body completely slips  Catastrophic slip off the sacral promontory;
                      anterior and inferior to sacrum)         requires complex reconstructive fusion
   ═════════════════════════════════════════════════════════════════════════════════════════════════════════════

The Two Dominant Etiologic Types

                  COMPARISON: DEGENERATIVE VS. ISTHMIC SPONDYLOLISTHESIS

   Clinical Feature        Degenerative Spondylolisthesis              Isthmic Spondylolisthesis
   ═════════════════════════════════════════════════════════════════════════════════════════════════════════════
   Primary Mechanism       Facet joint osteoarthritis, disc space      Fatigue stress fracture or fibrous non-union
                           collapse, and ligamentous laxity            of the PARS INTERARTICULARIS (spondylolysis)

   Neural Arch Integrity   NEURAL ARCH INTACT (No pars defect)         PARS INTERARTICULARIS FRACTURED / DEFECTIVE

   Typical Patient         Older adults (> 50-60 years); Female > Male Young athletes (gymnasts, football linemen, divers)
                           (3:1 ratio); associated with obesity        performing repetitive hyperextension

   Predominant Level       L4 on L5 (L4-L5 level; > 80% of cases)      L5 on S1 (L5-S1 level; > 90% of cases)

   Radiographic Sign       Intact neural arch, facet remodeling,       "SCOTTY DOG WITH A COLLAR" (radiolucent break
                           anterior translation on lateral X-ray       in the neck of the dog on 45° oblique X-rays)

   Nerve Root at Risk      L5 root (compressed in lateral recess)      L5 root (compressed beneath fibrous pars defect)

   Associated Pathology    Severe central lumbar spinal stenosis       Tight hamstrings, flattened buttocks, waddling gait
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• Management of Spondylolisthesis:
  • Low-grade (Grade I and asymptomatic Grade II): Conservative management with core stabilization physical therapy, hamstring stretching, avoidance of repetitive hyperextension, and short-term lumbar bracing during acute symptomatic episodes in young athletes.
  • High-grade (Grade III-IV), progressive slippage on serial radiographs, intractable mechanical back pain, or persistent neurological deficit: Instrumented surgical decompression and posterolateral fusion.

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Osteoporotic Vertebral Compression Fractures (VCF)

Vertebral compression fractures (VCFs) are the most common osteoporotic fragility fractures, affecting over 700,000 patients annually in the United States. Many fractures occur silently, but acute clinical presentations require prompt identification and structured management.

Clinical Presentation

• Acute Midline Pain: Sudden, acute onset of severe, deep, sharp, or dull aching back pain localized directly over the mid-thoracic or thoracolumbar spine (T8 through L2 are the most frequent levels). Pain is triggered by minimal mechanical force—such as bending forward, lifting a modest object (e.g., a bag of groceries), stepping off a curb, coughing, or sneezing—or occurs spontaneously during routine activities.
• Aggravating Factors: Pain is sharply exacerbated by standing, walking, coughing, or rolling over in bed, and partially improved by lying completely flat supine.
• Physical Examination: Focal, pinpoint midline spinous process tenderness elicited by gentle direct percussion over the involved vertebra. Marked paravertebral muscle spasm is common. Neurological examination is typically normal in uncomplicated fragility fractures (radicular symptoms or spinal cord/cauda equina compression are rare and suggest retropulsion of bone fragments or malignant collapse).

Diagnostic Imaging

• Plain Radiography (Standing AP and Lateral Thoracolumbar Spine): Initial imaging modality. Cardinal hallmark is the anterior wedge deformity, defined as a reduction in anterior vertebral body height of >=20% or >=4 mm compared to the posterior vertebral body height. Biconcave ("codfish") and crush deformities may also be seen.
• Magnetic Resonance Imaging (MRI): The modality of choice to determine fracture chronicity and etiology:
  • Fracture Acuity: Acute or subacute fractures (<6 to 12 weeks old) demonstrate intense bone marrow edema characterized by low signal on T1-weighted images and high signal (bright) on T2/STIR (short tau inversion recovery) sequences. Healed, chronic fractures exhibit normal marrow signal.
  • Ruling Out Pathologic Fractures: MRI is essential to distinguish benign osteoporotic fractures from pathologic fractures secondary to multiple myeloma or metastatic cancer. Red flags for malignancy on MRI include: involvement of the posterior vertebral elements (pedicles, lamina), an associated soft-tissue or epidural mass, convex posterior vertebral body cortex bulging into the spinal canal, and multiple non-contiguous marrow abnormalities.

                  EVIDENCE-BASED MANAGEMENT OF OSTEOPOROTIC VCF

   Management Domain       Clinical Intervention                  Clinical Directive & Evidence Base
   ═════════════════════════════════════════════════════════════════════════════════════════════════════════════
   Activity & Mobilization • Minimize strict bed rest             LIMIT BED REST TO <= 24-48 HOURS; prolonged immobility
                           • Early protected ambulation           accelerates bone loss, DVT/PE risk, and deconditioning
   ─────────────────────────────────────────────────────────────────────────────────────────────────────────
   Acute Analgesia         • Acetaminophen + Short-term NSAID     First-line oral analgesics; monitor renal function
                           • Short-term low-dose Opioid (3-5 days) Reserved strictly for severe pain preventing mobilization
                           • INTRANASAL SALMON CALCITONIN         200 IU nasal spray daily; unique endorphin-mediated
                                                                  analgesic effect reducing acute bone pain (first 2-4 wks)
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   Biomechanics / Orthosis • Thoracolumbosacral Orthosis (TLSO)   Semirigid or rigid brace during sitting and ambulation;
                                                                  restricts flexion and offloads anterior column (4-6 wks)
   ─────────────────────────────────────────────────────────────────────────────────────────────────────────
   Vertebral Augmentation  • Percutaneous Vertebroplasty /        Reserved strictly for severe, intractable pain failing
                             Balloon Kyphoplasty                  conservative therapy after 2 to 4 weeks; sham trials
                                                                  show mixed results; risk of adjacent level fractures
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   Secondary Prevention    • Bone Mineral Density (DXA Scan)      Presence of fragility VCF confirms severe osteoporosis
                           • Calcium (1,200 mg) & Vitamin D       regardless of T-score; prompt initiation of
                           • Antiresorptive / Anabolic Agent      bisphosphonates (zoledronic acid) or teriparatide
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