Definition: the slipping forward of one vertebra upon another. Incidence is approximately 6% of population. Common in gymnasts, football players, weightlifters.
Spondylolysis is the presence of a bony defect at the pars interarticularis, the space between the superior and inferior facet, and can lead to spondylolysthesis

Etiology (Wiltse classification):

  • Type I = dysplastic deficiency of superior sacral facet, inferior 5th lumbar facet, or both
  • Type II = isthmic type, defect in pars interarticularis (types I & II most common)
  • Type III = degenerative form, mostly L4-5
  • Type IV = traumatic form
  • Type V = pathologic form, caused by neoplasm


  • May be asymptomatic
  • Back pain
  • Leg pain
  • Radicular pain, bowel or bladder symptoms rare
  • Isthmic spondylolisthesis commonly presents between 10-15 years
  • Extent of slippage may not correlate with pain
  • L5 slippage on sacrum is most common


  • Lateral view shows defect
  • Oblique view demonstrates “Scottie dog” with “collar” or “broken neck” sign indicating pars defect

Axial CT image of a 17-year-old demonstrating unilateral spondylolysis with sclerosis of the contralateral pars.


  • Slip angle = measure of lumbosacral kyphosis, helps determine likelihood and presence of progression on younger patients
  • Meyerding’s classification
  • Grade I = 1-25% slippage
  • Grade II = 26-50% slippage
  • Grade III = 51-75% slippage
  • Grade IV = 76-100% slippage


  • Grades I and II managed conservatively by restricting aggravating activities, bracing to reduce lumbar lordosis, physical therapy
  • Grade III & IV slips are at risk for progression, especially in skeletally immature patients, and fusion is recommended
  • Fusion indications are: demonstrate progression of slip, greater than 50% slip, fail to respond to conservative measure, and skeletal immaturity
  • Combined spinal decompression and fusion are indicated if neurological findings present (numbness, weakness, bowel or bladder compromise
  • Pars repair possible in young patients with minimal slip