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Spondylolysis


KEY FACTS

Terminology

  • Defects in pars interarticularis (PI) thought to result from repetitive stress injury

    • Pars is junction of pedicle, lamina, and facet

Imaging

  • Most common at L5: 80-90%

  • Discontinuity in neck of “Scotty dog” on oblique plain films

  • Elongation of spinal canal at level of pars defects on axial imaging

  • Incomplete-ring sign on axial imaging

Top Differential Diagnoses

  • Acute traumatic fracture of posterior elements

  • Facet arthropathy with marrow edema

  • Septic facet with marrow edema

  • Bone tumor with marrow edema

  • Pedicle stress fracture

  • Congenital defect with pars cleft

Pathology

  • Repeated microfractures of PI lead to fatigue fracture

Clinical Issues

  • 6-8% in general population

  • 10-20 years old is typical age range

  • Symptoms of chronic low back pain

  • Conservative measures in grade 1-2 spondylolisthesis

  • Wide variety of practice patterns for treatment

    • 50% of surgeons agreed on surgical treatment

    • No consensus on optimum surgical strategy

Diagnostic Checklist

  • L5-S1 IS stand-alone ALIF failure has been reported

  • Look for integrity of PI on sagittal MR and pars/pedicle marrow edema

Lateral graphic shows chronic L5 spondylolisthesis
and spondylolysis
with defect in the pars interarticularis (PI) and resultant foraminal stenosis.

Coronal oblique radiograph shows a thin lucency
in the right L5 PI with adjacent bony sclerosis.

Lateral radiography shows a defect and mild angulation in L5 PI
with anterolisthesis of L5 on S1. There is disc height loss at L5-S1 with associated sclerotic endplate changes
.

Sagittal bone CT reformation shows L5 pars defect
without anterolisthesis.

TERMINOLOGY

Synonyms

  • Isthmic spondylolysis (IS)

Definitions

  • Unilateral or bilateral defects in pars interarticularis (PI) thought to result from repetitive stress injury

    • Pars is junction of pedicle, lamina, and facet

IMAGING

General Features

  • Best diagnostic clue

    • Bony defect or cortical discontinuity in PI

  • Location

    • Most common at L5: 80-90%

    • L4 2nd most common

    • 10-15% unilateral defects

      • –

        Unilateral healing or union of fractures that were initially bilateral

  • Morphology

    • Horizontal orientation on axial imaging

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