Listhesis (Spondylolisthesis)

Directional Types

Classification (Newman-Wiltse-McNab) — Six Types

1. Dysplastic (Congenital) — congenital vertebral anomalies
2. Isthmic — defect in the pars interarticularis (spondylolysis); most common at L5–S1
3. Degenerative — disc degeneration and facet joint arthropathy; most common at L4–L5
4. Traumatic — acute fractures (e.g., Hangman's fracture = traumatic spondylolisthesis at C2–C3)
5. Pathologic — bone disease (tumor, Paget's, etc.)
6. Iatrogenic (Post-surgical)

Grading (Meyerding) — Based on % of Vertebral Body Width Displaced

Spondylolysis vs. Spondylolisthesis

• Spondylolysis — a defect/fracture in the pars interarticularis (the "neck" of the Scotty dog on oblique X-ray). A fatigue fracture from repetitive hyperextension (common in gymnasts, football linemen). Isolated spondylolysis actually elongates the spinal canal.
• Spondylolisthesis — the actual forward slippage that may result from bilateral spondylolysis, degeneration, or other causes. Causes segmental canal narrowing.

Clinical Presentation

• Low back pain aggravated by extension
• Hamstring tightness, palpable step-off
• Altered gait ("pelvic waddle")
• Severe slips: L5 radiculopathy, cauda equina dysfunction, kyphosis at the lumbosacral junction, "heart-shaped" buttocks

• Extension-provoked low back pain (posterior element compression)
• L5 nerve root radiculopathy (from fibrocartilaginous Gill nodule at the pars)

• Neurogenic claudication (central stenosis) — leg heaviness/cramping, relieved by flexion ("shopping cart sign")
• L5 nerve root compression (traversing root in lateral recess)
• Bowel/bladder dysfunction (uncommon)

Key Measurements

• Pelvic Incidence (PI): Normally ~50°; patients with spondylolisthesis typically have PI of 70–80°. Higher PI demands more lumbar lordosis for sagittal balance.
• Slip angle: Normally <0° (lordosis at L5–S1); abnormal kyphosis at the lumbosacral junction is a risk marker.
• Sacral inclination: Normally >30°.
• PI does not predict progression of listhesis.

Imaging

• Plain X-ray (lateral): detects 80% of pars lesions; shows degree of slippage
• Oblique X-ray: "Scotty dog" sign — defect in the dog's neck = spondylolysis
• CT: best for bony detail, pars defect characterization
• SPECT: increased uptake = acute/healing lesion with potential to heal
• MRI: identifies pars defect, bony edema ("stress reaction"), Gill nodule, and neural compression

Treatment

• Activity restriction, flexion-based exercises, bracing, NSAIDs, hamstring stretching, core strengthening

• Grade I/II: in situ posterolateral L5–S1 fusion
• Grade III–V: L4–S1 fusion; foraminal decompression
• Reduction controversial — risk of L5 nerve root palsy

• Decompression + posterolateral fusion ± instrumentation
• SPORT trial (4-year follow-up): operative treatment significantly better than nonoperative for pain and disability outcomes