Spondylolysis

  • Etiology: stress fracture from repetitive microtrauma of posterior vertebral elements at pars interarticularis which is weakest part of vertebra
  • Radiograph:
    — Early – sclerosis
    — Later – lucent pars interarticularis defect (“scotty dog”)
    — Contralateral pedicle often sclerotic due to stress – Wilkinson’s syndrome
  • Bone scan: needs to be done with SPECT for highest sensitivity, increased uptake
  • CT: incomplete ring sign with pars defect noted 10-15 mm above disk space
  • Clinical: uni- or bilateral (75%), most common at L5-S1, incidence is 5% of general population, usually asymptomatic, associated with hyperextension sports – gymnastics / diving / weight lifting / football / soccer / hockey / lacrosse

Cases of Spondylosis

Radiograph and bone scan of spondylosis
Lateral radiograph of the lumbar spine shows a lucency through the pars interarticularis of the L5 vertebral body (pars defect). Axial and coronal images from a nuclear medicine bone scan show increased radiotracer localization in the right L5 pars interarticularis.