What is Spondylolysis?
Spondylolysis is a defect or stress fracture of the pars interarticularis (the bony bridge between the upper and lower facet joints of a vertebra), most commonly occurring in the lumbar spine at L5 and L4 levels 1, 2, 3.
Pathophysiology and Etiology
The condition represents either a developmental defect or an acquired stress fracture resulting from repetitive mechanical loading and chronic low-grade trauma to the pars interarticularis 4. The etiology is multifactorial, involving:
- Repetitive stress injury: Chronic hyperextension and rotational forces on the lumbar spine
- Genetic predisposition: Familial tendency toward structural weakness
- Biomechanical stress: Particularly from athletic activities involving repetitive spinal loading 1
The defect can be unilateral or bilateral, with bilateral lesions carrying higher risk for progression to spondylolisthesis 1.
Clinical Significance and Natural History
In children with bilateral spondylolysis, approximately 75% will develop spondylolisthesis (forward slippage of the affected vertebra) 5. This progression risk is particularly relevant during growth periods when skeletal maturity has not been achieved.
Key Clinical Points:
- Most common age: Peak incidence around 15 years old, following normal distribution 6
- Athletic association: Particularly prevalent in young athletes participating in football, baseball/softball, gymnastics, wrestling, weightlifting, and track and field 7, 6
- Sport-specific patterns: Different activities create distinct injury patterns (e.g., soccer players develop multilevel spondylolysis from compressive running forces, while baseball players sustain injuries from high rotational/torsional forces) 7
Clinical Presentation
Many patients with spondylolysis are asymptomatic. When symptomatic, patients typically present with:
- Low back pain: Exacerbated by activity, particularly extension-based movements
- Neurogenic claudication: In cases with associated stenosis
- Radiculopathy: When nerve root compression occurs
- Mechanical back pain: Worsened by repetitive hyperextension activities 8, 4
Diagnostic Imaging Considerations
The 2025 ACR Appropriateness Criteria provide clear guidance on imaging approach 7:
Initial Imaging:
- Radiography is first-line but has low sensitivity for detecting spondylolysis without spondylolisthesis
Advanced Imaging When Radiographs Are Negative:
- MRI is preferred for pediatric patients: Detects early stress reactions with bone marrow edema before fracture line develops; avoids radiation exposure 7, 4
- CT without contrast: Most accurate for visualizing the bony pars defect and assessing osseous healing; higher sensitivity than radiography for nondisplaced fractures 7
- SPECT (area of interest): Very sensitive for identifying active spondylolysis through radiotracer uptake in areas of increased bone turnover; useful when radiography negative with high clinical suspicion 7
Important caveat: CT is less sensitive than MRI for detecting stress injuries involving the pars interarticularis without lysis (pre-fracture stress reaction), which is frequently seen in pediatric patients 7.
Relationship to Spondylolisthesis
Spondylolysis must be distinguished from spondylolisthesis, though they are related:
- Spondylolysis: The pars defect itself
- Spondylolisthesis: Forward slippage of vertebra that can result from bilateral spondylolysis
- Progression risk: Two-thirds of children with acute pediatric spondylolysis achieve bony union with early activity restriction; one-fourth of those with non-union will develop spondylolisthesis 1
When spondylolisthesis is present with stenosis, imaging becomes particularly important to identify spinal canal or neural foraminal narrowing and guide treatment decisions 7.