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Other Names

  • Scotty Dog Fracture
  • Fracture in the pars interarticularis
  • "Spondy"
  • Pars stress fracture
  • Pars stress reaction
  • Spondylolytic stress fracture


  • This page refers to a fracture or bony defect of the pars interarticularis of the vertebral arch, most commonly referred to as spondylolysis


  • Stress reaction: sclerosis, incomplete disruption of pars
  • Spondylolysis: radiolucent defect in pars


  • Spondylolysis derivation: spondylos (vertebra) and lysis (defect)


  • Prevalence is up to 6% in the general population[1]
  • One of the most common causes of back pin in children, adolescents (need citation)
  • In athletes with low back pain, it is responsible for between 50% - 80% of cases[2][3]
  • Ratio of male to female is 2:1
  • Risk increasing from adolescence to adult hood, but does not appear to increase in patients as they continue to age[4]


  • Pathogenesis is controversial
    • Most widely accepted theory is repetitive micrtrauma in a congenitally weak or dysplastic pars
    • Often related to repetitive hyperextension, rotation of the lumbar spine
    • Cadaveric studies have shown the repetitive flexion-extension motions can contribute due large stress reversals on the pars interarticularis[5]
    • This leads to failure due to fatigue of the pars
    • Can also be due to acute trauma
  • Approximate 85-95% occur at the L5 level, 5=15% at the L4 level[6]
  • Bilateral defects are more common than unilateral[7]


  • Dysplastic
    • Involve congenital abnormalities (attenuated pars)
  • Isthmic
    • lesions in the pars interarticularis resulting from stress fractures or acute fractures
  • Degenerative
    • Degeneration of of intervertebral discs leading to segmental instability, alterations in articular process
  • Traumatic
    • Acute fractures in various areas of the neural arch, other than the pars
  • Pathological
    • involve various bone diseases, tumours or infections


  • Pars Interarticularis
    • Represents the junction of the pedicle, articular facets and lamina
    • Anterior-superior segment consists of vertebral body, pedicle, transverse process, superior articular process
    • Posterior-inferior segment consists of inferior articular process, laminae and spinous process

Associated Injuries

  • Spondylolisthesis
    • Especially in patients with bilateral spondylolysis due to anterior slippage of vertebrae
    • 50-80% of patients with spondylolysis have spondylolisthesis

Risk Factors

  • Sports involving repetitive back extension
    • Gymnastics[8]
    • Figure Skating
    • Diving
    • Football Lineman
    • Weightlifting
    • Wrestling
    • Dancers
    • Cricket[9]
    • Soccer
    • Basketball
  • Female athletic triad/relative energy deficiency in sport
  • Imbalance between activity and rest
  • Occupation
    • Drivers

Differential Diagnosis

Clinical Features

  • History
    • Often asymptomatic and found incidentally
    • When symptomatic, patients endorse low back pain
    • Can radiate into buttocks, proximal lower limb
    • Onset is usually insidious but can be acute if history of trauma
    • Pain is intense and worse after activity, hyperextension
  • Physical Exam: Physical Exam Back
    • Resting position may be exaggerated lordosis
    • Hamstring tightness is common, mechanism unknown[10]
    • Paraspinal muscle spasm is common[11]
  • Special Tests



  • Standard Radiographs Lumbar Spine
    • Can be seen on PA, lateral views
    • Dynamic and oblique views can also be helpful[12]
  • AP, lateral, 45° left/right oblique and collimated lateral view identify 96.5% of pars defects[13]
  • Oblique view identifies about 20% of pars defects
    • This is where the term "collar on the Scottie dog" originates
  • May be radiographically occult if stress fracture or reaction
  • Additional findings suggesting spondylolysis
    • Vertebral anisocoria
    • Lateral deviation of SP
    • Sclerosis of contralateral pedicle
  • Co-occuring Spondylolisthesis is common
    • Degree of spondylolisthesis correlates with degree of widening in the pars interarticularis


  • Best for evaluating fracture size, extent
  • Valuable as a follow up imaging modality


  • May detect changes in signal intensity even before fracture is visible on plain radiographs



Standaert and Herring Classification

  • Early
  • Progressive
  • Terminal



  • Most symptomatic cases do well with conservative care only
  • Between 9% and 15% of symptomatic spondylolysis require surgery (need citation)
  • Panteliadis et al review of outcomes in athletes following conservative or surgical management[14]
    • Duration of management ranges from 1.5 to 24 months
    • 344/390 patients reported good or excellent outcomes
    • Mean return to play was 3.7 months in conservative treatment
  • Michielsen et al found that among athletes, osseous healing is more likely to occur in unilateral active spondylolysis as compared to bilateral and pseudo-bilateral active spondylolysis[15]
    • 87% of athletes with unilateral defect healed
    • 87% of athletes with nonunion had bilateral defect


  • Cessation of aggravating activities
    • Especially true in athletes
  • Medications
    • NSAIDS might be considered controversial due to impaired bone growth, healing
    • In patients with osteoporosis or osteopenia, consider Bisphosphonate
  • Therapeutic modalities
  • Physical Therapy
    • Emphasis on isometric contractions of back muscles to promote increased blood flow
    • Core strengthening aimed at reducing lumbar lordosis
    • Treatment of tight/ contracted hamstrings
  • Bone Stimulator
    • Two case reports of excellent results[14]
  • Orthotics for 3-6 months
    • Goal is to prevent motion at the stress fracture, allow healing
    • One cited example is 3 months full time wear without followed by 3 months full time wear with sports[16]
    • Thoracolumbosacral Orthosis more commonly used
    • Lumbosacral Orthosis can also be considered


  • Indications
    • Failure of conservative measures after at least 6 months
    • Intractable pain
    • Progressive slip
    • Myelopathy
    • Segmental instability
    • Younger patient
  • Relative contraindications
  • Technique
    • Translaminar screw fixation
    • Cerclage wiring loop
    • Pendiculolaminar hook screws

Rehab and Return to Play


  • Needs to be updated

Return to Play

  • Patients with spondylolysis should rest 4 to 6 weeks and then demonstrate full range of motion and pain-free extension before RTP[17]


  • Nonunion
  • Neurologic deficits or myeloppathy
  • Pseudoarthrosis
  • Operative
    • Wound infection
    • Nonunion
    • Hardware malfunction

See Also


  1. Hu SS, Tribus CB, Diab M, Ghanayem AJ. Spondylolisthesis and spondylolysis. Instr Course Lect. 2008;57:431–445.
  2. McTimoney CA, Micheli LJ. Current evaluation and management of spondylolysis and spondylolisthesis. Curr Sports Med Rep. 2003;2:41–46.
  3. Iwamoto J, Sato Y, Takeda T, Matsumoto H. Return to sports activity by athletes after treatment of spondylolysis. World J Orthod 2010;1(1):26–30
  4. Brooks BK, Southam S, Mlady GW, Logan J, Rosett M. Lumbar spine spondylolysis in the adult population: using computed tomography to evaluate the possibility of adult onset lumbar spondylosis as a cause of back pain. Skeletal Radiol 2009;
  5. . Green TP, Allvey JC, Adams MA (1994) Spondylolysis. Bending of the inferior articular processes of lumbar vertebrae during simulated spinal movements. Spine 19:2683–2691
  6. Standaert DC, Herring S. Spondylolysis: a critical review. Br J Sports Med. 2000;34:415–422.
  7. Teplick JG, Lafley PA, Berman A, Haskin ME. Diagnosis and evaluation of spondylolisthesis and/or spondylolysis on axial CT. AJNR Am J Neuroradiol. 1986;7:479–91.
  8. Vrable A, Sherman AL. Elite male adolescent gymnast who achieved union of a persistent bilateral pars defect. Am J Phys Med Rehabil 2009;88(2):156–160
  9. Hardcastle PH. Repair of spondylolysis in young fast bowlers. J Bone Joint Surg Br 1993;75(3):398–402
  10. Anderson SJ. Assessment and management of the pediatric and adolescent patient with low back pain. Phys Med Rehabil Clin N Am. 1991;2:157–85.
  11. Garry JP, McShane J (1988) Lumbar spondylolysis in adolescent athletes. J Fam Pract 46:145–149
  12. Rodts MF. Disorders of the spine. Orthop Nurs. 2002;3:515–550.
  13. Amato M, Totty WG, Gilula LA. Spondylolysis of the lumbar spine: demonstration of defects and laminal fragmentation. Radiology. 1984;153:627–9.
  14. 14.0 14.1 Panteliadis, Pavlos, et al. "Athletic population with spondylolysis: review of outcomes following surgical repair or conservative management." Global spine journal 6.06 (2016): 615-625.
  15. Sys, J., et al. "Nonoperative treatment of active spondylolysis in elite athletes with normal X-ray findings: literature review and results of conservative treatment." European Spine Journal 10.6 (2001): 498-504.
  16. Steiner ME, Micheli LJ. Treatment of symptomatic spondylolysis and spondylolisthesis with the modified Boston brace. Spine. 1985;10:937–43.
  17. Eck JC, Riley LH., III Return to play after lumbar spine conditions and surgeries. Clin Sports Med. 2004;23:367-379
Created by:
John Kiel on 17 June 2019 16:44:34
Last edited:
5 October 2022 23:59:55