What is needed for a diagnosis of spondylolysis?

Diagnosis of Spondylolysis

Start with plain radiographs (anteroposterior and lateral views) of the symptomatic spine region as the initial screening tool, followed by MRI without contrast if radiographs are negative but clinical suspicion remains high, or to detect early stress reactions before fracture occurs. 1

Initial Imaging Approach

• Plain radiographs serve as the first-line screening modality with a sensitivity of 77.6% for detecting spondylolysis using standard AP and lateral views 1
• The combination of negative radiographs and negative clinical examination has a negative predictive value of 0.81, meaning approximately 1 in 5 cases may still have the condition 1
• Oblique views should NOT be obtained as they double radiation exposure without significantly increasing diagnostic sensitivity 1

Advanced Imaging When Radiographs Are Negative or Equivocal

MRI Without Contrast (Preferred Next Step)

MRI is the most appropriate advanced imaging modality for suspected spondylolysis, particularly in pediatric and adolescent patients, as it avoids radiation exposure while providing high diagnostic accuracy 1

• MRI demonstrates 92% sensitivity for detecting pars interarticularis injuries 2
• Fat-suppressed and fluid-sensitive sequences (T2-weighted with fat saturation) are essential to identify bone marrow edema in the pars interarticularis or adjacent pedicle, which indicates active stress reaction even before a visible fracture line develops 1
• MRI can detect early stress reactions (grade 1 lesions) that are invisible on CT, allowing earlier intervention and potential prevention of progression to complete fracture 1, 2
• MRI provides the added benefit of evaluating for alternative diagnoses including disc herniation, apophyseal injuries, intraspinous ligamentous injury, and nerve root compression 1
• Contrast is NOT indicated for evaluation of mechanical back pain due to spondylolysis 1

CT Spine (Adjunctive Role)

• CT has high sensitivity for detecting established pars defects and is superior to radiographs for visualizing bony detail 1
• CT is primarily used as an adjunct to confirm fractures suggested on other imaging or when MRI is contraindicated 1
• Modern dose-reduction techniques allow CT to be performed with radiation exposure similar to plain radiographs 1
• Important limitation: CT may miss early stress reactions without a visible fracture line, which MRI can detect 1

Bone Scan with SPECT (Alternative Advanced Imaging)

There is ongoing debate about whether MRI or bone scintigraphy with SPECT is superior for diagnosing spondylolysis, with evidence supporting both modalities 1:

• Some studies show SPECT bone scan is more sensitive than MRI for detecting active spondylolysis 1
• SPECT has the advantage of whole-body imaging, which can identify multifocal disease 1
• However, bone scan exposes patients to significant ionizing radiation and has high false-positive and false-negative rates 3, 4
• In chronic spondylolysis with wide separation and smooth margins, bone scans may be falsely negative 1
• Bone scan may show increased uptake from stress reaction when CT shows no abnormality 1

Clinical Context for Imaging

Imaging should be reserved for patients with persistent back pain lasting 4 weeks or more, particularly those with clinical red flags including constant pain, night pain, radicular symptoms, or abnormal neurologic examination 1

• Children with back pain of short duration, normal physical examination, and minor or no trauma history typically do not require imaging 1
• Spondylolysis is the most common cause of overuse-related chronic back pain in children and adolescent athletes 1

Key Diagnostic Algorithm

1. Obtain AP and lateral radiographs (no oblique views) of the symptomatic spine region 1
2. If radiographs are positive: Consider MRI to assess for active stress reaction, evaluate healing potential, and identify nerve root compression 1
3. If radiographs are negative but clinical suspicion remains high: Proceed directly to MRI with fat-suppressed sequences 1, 2
4. CT may be added if MRI shows abnormality and precise bony detail is needed for surgical planning, or if MRI is contraindicated 1

Common Pitfalls to Avoid

• Do not rely on oblique radiographs, as they provide no additional diagnostic value while doubling radiation exposure 1
• Do not skip MRI in favor of CT alone in pediatric patients, as MRI detects earlier stress reactions and avoids radiation 1, 2
• Do not order MRI with contrast for suspected mechanical back pain from spondylolysis, as contrast adds no diagnostic value 1
• Do not assume negative radiographs exclude the diagnosis, as sensitivity is only 77.6% and early stress reactions are radiographically occult 1