Spondylolisthesis

Spondylolisthesis is the forward or anterior displacement of one vertebra over another. Backward displacement is referred to as retrolisthesis. Most common is L5 on S1, next most common is L4 on L5.

A hangman's fracture is a specific type where the C2 is displaced anteriorly relative to C3 due to fracture of the C2's pedicles.

Classification

By Causes

• Dysplastic/type 1: congenital abnormalities of the upper sacral facets or inferior facets of L5. No pars defect. 94% are associated with spina bifida. Some of these may progress (no way to identify these).
• Isthmic/spondylolytic/type 2: defect in pars interarticularis or elongated pars (the neck of the "Scotty dog" on oblique LS-spine X-ray). May be seen in 5-20% of spine X-rays.
  • Lytic: fatigue fracture or insufficiency fracture of pars. In the pediatric age group may occur in athletes (especially gymnasts or football players); exacerbation of pre-existing defect v. repetitive trauma.
  • Elongated but intact pars: repetitive fractures and healing
  • Acute fracture of pars
• Degenerative/type 3: a result of facet arthritis and joint remodeling. More likely in women, persons older than fifty, and African Americans. Usually at L4-L5.
• Traumatic/type 4: acute fractures in the neural arch, other than pars.
• Pathologic/type 5: infection v. malignancy v. osteogenesis imperfecta
• Iatrogenic/type 6: surgical complication

By Location

• A: pars fatigue fracture
• B: pars elongation due to multiple healed stress effects
• C: pars acute fracture

By Severity

Meyerding grading of subluxation in the sagittal plane:

• Grade I: 0-25%
• Grade II: 25-50%
• Grade III: 50-75%
• Grade IV: 75-100%
• Grave V: > 100%