Slipped Vertebrae (Spondylolisthesis)

Anterior subluxation (slippage) of one vertebral body on another. Most commonly the upper vertebra slips forward. The most common is slippage of L5 over S1. Next common is L4 over L5.

Types of spondylolisthesis:

• Type 1: dysplastic congenital: upper sacrum or arch of L5 permits the slip. No pars defect. Associated with spina bifida occulta
• Type 2: isthmic (spondylolysis) defect of pars interarticularis
  Three subtypes
  Lytic- fatigue or insufficiency fracture of pars- common in athletes/ gymnasts
  Elongated but intact pars
  Acute pars fracture
• Type 3: degenerative- common at L4/5- due to facet joint laxity; no break in pars
• Type 4: traumatic-fractures in areas other than pars
• Type 5: pathological- generalized or local bone disease

Meyerding grading of spondylolisthesis:

• Grade 1: less than 25% slip
• Grade2: 25-50% slip
• Grade3: 50-75% slip
• Grade4: 75-100% slip
• Spondyloptosis: greater than 100% slip i.e. complete