Degenerative Spondylolisthesis

Imaging Gallery

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Degenerative spondylolisthesis is anterolisthesis due to facet and disc degeneration with an INTACT pars interarticularis (distinguishing it from isthmic spondylolisthesis). Classic patient: female over 50 years at L4-5 level (sagittal facet orientation). Rarely exceeds Grade II. Key imaging: flexion-extension X-rays to assess instability (greater than 4mm translation or greater than 10° angulation = unstable). Management: trial conservative treatment for 6 months; surgery if refractory symptoms. Surgical treatment: decompression plus instrumented fusion - SPORT and Ghogawala trials generally favor fusion over decompression alone for better long-term outcomes.

Degenerative Spondylolisthesis (DS) is a disorder of segmental instability resulting in the forward slippage of a vertebra. Unlike isthmic spondylolisthesis, which involves a defect in the pars intra-articularis, DS results from the progressive degeneration of the facet joints and intervertebral discs. It typically occurs in the lumbar spine, representing a failure of the "three-joint complex" (the intervertebral disc and the two facet joints) to maintain alignment under load.

Epidemiology

Demographics

• Prevalence: 5-10% of the population over 60 years. Also termed "Pseudospondylolisthesis".
• Gender: Strongly Female predominant (F:M ratio ~5:1). This is thought to be due to hormonal changes (post-menopausal ligamentous laxity) and anatomical differences in pelvic incidence.
• Age: Peak incidence 50-70 years. It is extremely rare in patients under 40.
• Race: More common in African Americans (larger pelvic incidence).

Level of Involvement

• L4-5: 80% of cases. The L4 vertebra slips forward on L5. This level is most susceptible due to the transitional anatomy between the mobile lumbar spine and the stable lumbosacral junction.
• L3-4: Second most common.
• L5-S1: Rare (protected by iliolumbar ligaments and deep seating in pelvis below the intercristal line).

Risk Factors

• Anatomy: Sagittally oriented facet joints (allows forward slide).
• Hormonal: Post-menopausal state (ligament laxity decreases restraint).
• Medical: Diabetes (accelerated disc and facet degeneration).
• Pelvic Parameters: High Pelvic Incidence (PI) correlates with slip severity.
• Pregnancy: Multiple pregnancies may increase risk due to abdominal muscle stretching and hormonal laxity.

Biomechanics of Slip

The lumbar spine resists anterior shear forces through three primary mechanisms:

1. Disc: The annulus fibrosus provides tensile strength against slip.
2. Facets: The coronal orientation of the joint surfaces provides a "bony block" to anterior translation.
3. Ligaments: The iliolumbar and longitudinal ligaments provide tethering.

In Degenerative Spondylolisthesis, the failure is primarily at the Facet Joints. As the disc height is lost, the axis of rotation shifts posteriorly, loading the facets. The facets remodel, lose their coronal orientation, and become more sagittal. Once sagittal, they offer no resistance to the anterior shear force of gravity and body weight, allowing the slip to occur.

Pelvic Parameters (Spinopelvic Balance)

Recent literature emphasizes the role of sagittal balance:

• Pelvic Incidence (PI): A high PI is a predisposing factor. High PI requires high Lumbar Lordosis (LL) to balance.
• High Lordosis: Increases shear forces at the L4-5 level.
• Compensation: As the slip occurs, the patient compensates by retroverting the pelvis (increasing Pelvic Tilt) and flexing the knees (Simian stance) to maintain an upright posture despite canal stenosis.

The Degenerative Cascade

The process follows the Kirkaldy-Willis cascade of degeneration but with a specific vector of deformity (anterolisthesis).

1. Disc Degeneration: Loss of disc height leads to settling of the motion segment. The loss of turgor in the nucleus pulposus reduces its ability to resist shear forces.
2. Facet Loading: Loss of anterior column height transfers load to posterior elements (facets). The facet joints, which normally bear 20% of the load, now bear significantly more (up to 70%).
3. Facet Remodeling: Chronic loading causes cartilage wear and subluxation. The facets remodel from a coronal (resisting slip) to a sagittal orientation. Effusion develops in the joints.
4. Instability: The incompetent disc and sagittal facets allow the superior vertebra to slide anteriorly (anterolisthesis). The iliolumbar ligaments at L5 stabilize that level, making L4 the "victim" level above.
5. Stenosis: The "napkin ring" effect. The neural canal is tightened by:
   • Anteriorly: Disc bulge and osteophytes.
   • Posteriorly: Hypertrophied facets and buckling ligamentum flavum (due to height loss).
   • Result: Central canal stenosis (Claudication) and Lateral Recess Stenosis (Radiculopathy).

History

• Neurogenic Claudication: (90%). "Heaviness", fatigue, or pain in buttocks/legs when walking. Relieved by sitting or leaning forward ("Shopping Cart Sign"). This posture flexes the spine, opening the canal diameter and relieving venous congestion.
• Radiculopathy: (50%). Shooting leg pain in a specific dermatome.
  • L4-5 Slip: Usually causes L5 Radiculopathy. The L5 root is compressed in the lateral recess as it traverses the level.
• Back Pain: Mechanical, lower lumbar. Worse with extension (standing/walking) and relieved by flexion.
• Night Pain: Can be associated with instability as muscles relax during sleep.
• Worse with standing: Static standing is often worse than walking due to continuous extension load and venous engorgement.

Physical Examination

• Inspection: Flattening of lumbar lordosis ("Flat back"). Flexed posture. Simian stance (hips and knees flexed) to open the canal.
• Palpation: "Step-off" may be palpable. With L4 anterior slip, the L4 spinous process moves anteriorly (deep). The L3 spinous process remains posterior (prominent). The "step" is felt between L3 and L4.
• Neurology:
  • L5 Motor: Check EHL (Big toe extension) and Hip Abduction (Gluteus Medius).
  • Sensory: Dorsum of foot and first web space.
  • Reflexes: Hamstrings (L5) - difficult to elicit. Ankle (S1) usually normal.
• Provocative: Extension reproduces back/leg pain (Kemp's test). Femoral stretch test (L4) may be positive if significant foraminal stenosis.

Imaging Algorithm

1. Plain Radiographs

• Standing AP/Lateral: Essential. Assess grade of slip. Look for "sclerosis" of facets.
• Flexion/Extension Views: Critical for stability.
  • Instability Criteria: Greater than 4mm translation OR greater than 10 degrees angular motion.
  • Presence of instability dictates fusion.
• Spinous Process View: Look for Kissing Spines (Baastrup's disease).

2. MRI (Gold Standard)

• Assess central canal area (Critical stenosis less than 75mm2).
• Assess Lateral Recess (L5 root compression).
• Facet Effusion: T2 "Fluid Sign" indicates instability.
• Disc Quality: Pfirrmann grade.
• Pars Integrity: Can sometimes see marrow edema in pedicles (Pedicle stress reaction).

3. CT Scan

• Used to confirm Pars Integrity. If a defect is seen, diagnosis changes to Isthmic Spondylolisthesis.
• Pre-operative planning for pedicle screw trajectory.
• Assess facet tropism (asymmetry).

Case Examples

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AlgorithmConservativeSurgery

📊 Management Algorithm

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Conservative Care

First Line: For 3-6 months.

• Physiotherapy:
  • Core strengthening (Transversus Abdominis).
  • Pelvic tilt exercises.
  • Flexion-biased exercises (Williams).
  • Avoid extension (McKenzie) which closes the canal.
• Medication:
  • NSAIDs (short course) for acute flares.
  • Gabapentinoids (Pregabalin/Gabapentin) for claudication symptoms.
  • Paracetamol.
• Injections:
  • L4-5 Epidural Steroid Injection (ESI).
  • Can provide "window of relief" to allow rehab.
  • Diagnostic value: If pain resolves, confirms level.
• Lifestyle: Weight loss (unloads the spine), Smoking cessation (improves bone health).

Treatment success with conservative care is approximately 30-50%. It should be exhausted before considering surgery unless there is significant motor deficit.

Surgical Management

Indication: Failure of conservative care (6 months), progressive neuro deficit, Cauda Equina Syndrome (Emergency).

1. Decompression Alone?

• Pros: Less invasive, faster recovery, no hardware risks.
• Cons: Removal of midline structures (lamina/ligaments) destabilizes an already unstable segment. High recurrence of slip and worsening.
• Evidence: Generally inferior to fusion (Ghogawala 2016). Reserved for elderly, low-demand patients with STABLE slips (less than 2mm motion) on flexion-extension.

2. Decompression + Fusion (The Gold Standard)

• Posterolateral Fusion (PLF):
  • Standard laminectomy (decompression).
  • Pedicle screws placed into L4 and L5.
  • Bone graft (Autograft from laminectomy + Allograft/Synthetic) placed in lateral gutters (transverse processes).
  • High union rate (over 90%).
  • Pros: Familiar, effective.
  • Cons: Does not restore disc height effectively.
• Interbody Fusion (TLIF/PLIF):
  • Adds Anterior Column Support via a cage.
  • Restores Disc Height: This indirectly opens the foramen (Foraminal decompression).
  • Increases Fusion Surface Area: Endplate union is stronger than transverse process union.
  • Coronal/Sagittal Balance: Allows better correction of slip angle and lordosis.
  • Preferred for high grade slips or severe foraminal stenosis where disc height is collapsed.

Posterolateral (PLF) vs Interbody (TLIF) Fusion

Feature	Posterolateral Fusion (PLF)	Interbody Fusion (TLIF)
Target Fusion Area	Transverse Processes (Gutters)	Disc Space (Endplates) + Gutters
Indirect Decompression	Minimal (Direct only)	Significant (Restores foraminal height)
Slip Reduction	Moderate	Excellent (Cage leverage)
Operative Time	Shorter	Longer (Cage preparation)
Blood Loss	Less	More
Fusion Rate	85-90%	95-98% (Large surface area)
Clinical Outcome	Good (Effective for most)	Equivalent in low grades (Kim 2009)

3. Minimally Invasive (MIS-TLIF)

• Tubular retractors. Less muscle stripping.
• Less blood loss, faster early recovery. Same long-term outcome.
• Technical mastery required.

Final decision depends on bone quality (osteoporosis risks screw pullout) and patient comorbidities. A DEXA scan should be obtained in all women over 65 or with risk factors.

Post-Operative Rehabilitation Protocol

Adherence to a structured protocol prevents hardware failure and ensures fusion.

Phase 1: Protection (0-6 Weeks)

• Restrictions: No BLT (Bending, Lifting over 5kg, Twisting).
• Activity: Walking program (start 5-10 mins, increase daily).
• Bracing: Optional (Surgeon preference). Mostly for comfort/reminder.
• Wound: Keep dry for 2 weeks. Notify surgeon if discharge or redness.

Phase 2: Activation (6-12 Weeks)

• Imaging: X-ray at 6 weeks to check alignment/hardware.
• Physio: Start gentle core activation (Neutral spine).
• Hydrotherapy: Walking in water.
• Work: Return to sedentary work.

Phase 3: Strengthening (3-6 Months)

• Exercise: Progressive loading.
• Work: Return to light manual duties.
• Driving: When off opioids and can brake hard.

Phase 4: Return to Sport (6-12 Months)

• Conditioning: Sport specific.
• Contact Sport: Not recommended until fusion solid on CT (usually 9-12 months).

The Facet Joint (Z-Joint)

The zygapophysial joint is a synovial joint formed by the Superior Articular Process (SAP) of the level below and the Inferior Articular Process (IAP) of the level above.

• Capsule: Richly innervated (Same level and level above medial branch). Source of "Facetogenic Pain".
• Weight Bearing: Normally 20%. In disc degeneration, increases to 70%.
• Orientation:
  • Lumbar: Sagittal (flex-ext).
  • Thoracic: Coronal (rotation).
  • L5-S1: Coronally oriented (resists anterior shear).
  • L4-5: Sagittally oriented (susceptible to anterior shear).

Ligaments

• Iliolumbar Ligament: Connects L5 transverse process to Ilium.
  • Stabilizes L5 on the sacrum.
  • Explains why L5-S1 dysplastic slips are rare.
• Ligamentum Flavum: Elastic yellow ligament.
  • In height loss (disc collapse), it buckles anteriorly into the canal.
  • Major contributor to spinal stenosis along with the facet hypertrophy.

Vascular Anatomy

• The L4 nerve root exits below the L4 pedicle.
• The L5 nerve root traverses the disc space of L4-5.
• The Aorta and Vena Cava sit anterior to the disc. ALIF at L4-5 is dangerous due to the vascular anatomy (Iliac bifurcation). This is why PLIF/TLIF is preferred at L4-5.

Surgical Risks

• Dural Tear: Higher risk than simple stenosis due to adhesions and slippage. Incidence 5-10%. Repair primarily. Bed rest for 24 hours.
• Implant Failure: Screw loosening, pull-out. Common in osteoporotic bone. Use cement-augmented screws or fenestrated screws.
• Adjacent Segment Disease (ASD): 2-3% per year. Fusion increases stress on L3-4 (the level above). Can lead to new stenosis or instability requiring extension of fusion.
• Pseudarthrosis: Failure to fuse. Leads to loose hardware and recurrent pain. Risk factors: Smoking (Doubles risk), NSAIDs, Diabetes.
• Infection: 1-2%. Staph aureus / Epidermidis. PROMPT washout required.
• Neurology: L5 root injury during screw placement or reduction. Foot drop (L5) is the classic deficit to watch for.

Management Considerations

• Public System Coverage: Laminectomy, single level fusion, and pedicle screw instrumentation are covered under the public hospital system. Bone graft substitutes and cages are also covered under prostheses lists.
• Public vs Private: Public access to fusion surgery is restricted with wait times often exceeding 12 months for "Quality of Life" surgery such as DS. Private health insurance often covers the "gap" for instrumentation which can be thousands of dollars.
• Safety Guidelines: The Australian Commission on Safety and Quality (ACSQHC) lists lumbar fusion as a procedure requiring careful indication review due to practice variation across states.
• Rehabilitation Coverage: Post-op rehab protocols typically involve 6 weeks of restrictions (no bending/lifting/twisting) followed by graded physiotherapist-led mobilization, often covered by private health extras or Medicare Care Plans (EPC).
• Opioid Stewardship: Strict regulations in Australia regarding discharge opioids (limit 1 week supply) encourages multimodal analgesia strategies.

GP Referral Guidelines

General Practitioners play a crucial role in initial workup and referral.

• Imaging: Plain X-rays are the first line screening tool. Multi-slice CT can exclude pars defects. MRI availability via GP is restricted under Medicare (often no rebate for "back pain" alone, requires specific indications or specialist referral).
• When to Refer:
  • Red Flags: Immediate ED referral for Cauda Equina or progressive severe weakness.
  • Yellow Flags: Psychosocial barriers to recovery requiring multidisciplinary pain input.
  • Surgical Candidates: Patients with correlating MRI pathology who have failed 6 months of active physiotherapy.

Understanding Your Condition

What is a 'Slip'? It is not your spinal cord slipping, but the bone itself. This pinches the nerves running through the canal, causing the "heavy legs" feeling when walking.

Will it Paralyze me? Degenerative Spondylolisthesis rarely causes paralysis. However, if left untreated, the walking distance may decrease until you are housbound.

Recovery Timeline

• Hospital: 3-5 days.
• Walking: Immediately (Day 1).
• Driving: 4-6 weeks.
• Full Recovery: 6-12 months for the fusion to "knit" together.

Red Flags Go to Emergency if you experience:

• Loss of bowel or bladder control (Cauda Equina).
• Numbness in the saddle area (groin/buttocks).
• Weakness in the legs preventing walking.

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2. Ghogawala Z, Dziura J, Butler WE, et al. Laminectomy plus Fusion versus Laminectomy Alone for Lumbar Spondylolisthesis. N Engl J Med. 2016;374(15):1424-1434.
3. Försth P, Ólafsson G, Carlsson T, et al. A Randomized, Controlled Trial of Fusion Surgery for Lumbar Spinal Stenosis. N Engl J Med. 2016;374(15):1413-1423.
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7. Matsunaga S, Sakou T, Morizono Y, et al. Natural history of degenerative spondylolisthesis. Pathogenesis and natural course of the slippage. Spine. 1990;15(11):1204-1210.