What is the appropriate initial management for a pars interarticularis defect (spondylolysis) in an adolescent or young adult with low back pain that worsens with extension or activity?

Initial Management of Pars Interarticularis Defect (Spondylolysis)

Begin with anteroposterior and lateral radiographs of the lumbar spine, and if clinical suspicion remains high despite negative radiographs, proceed to either MRI without contrast or SPECT bone scan to detect active stress injury, followed by conservative management with activity restriction, bracing for approximately 3 months, and structured physical therapy. 1

Diagnostic Imaging Algorithm

First-Line Imaging

• Obtain standing AP and lateral lumbar spine radiographs as the standard of care for initial evaluation, though these have limited sensitivity (low) for detecting spondylolysis without spondylolisthesis 1, 2
• Add oblique radiographic views specifically to better visualize pars interarticularis defects, as these significantly improve detection of the classic "Scotty dog" collar defect 1, 2
• Oblique views are particularly useful in this clinical scenario despite not being routinely recommended for general back pain 1

Advanced Imaging When Radiographs Are Negative

When radiographs are negative but clinical suspicion remains high (extension-based pain in young athlete), choose between:

Option 1: SPECT Bone Scan (Area of Interest)

• SPECT is the reference standard for detecting radiographically occult active spondylolysis in young patients 1
• Very sensitive for identifying stress reactions with increased radiotracer uptake in areas of increased bone turnover 1
• Can be performed with CT for improved localization (SPECT/CT), though the additional CT is not always necessary if findings won't change management 1
• Several authors support SPECT bone scan over MRI specifically for evaluating spondylolysis 1

Option 2: MRI Lumbar Spine Without Contrast

• Detects bone marrow edema in the pars or adjacent pedicle, indicating active stress injury 1, 2
• Provides better soft tissue resolution to identify disc degeneration, herniation, and vertebral marrow edema 1
• Useful if concerning clinical findings such as neurologic deficits are present 1
• Less sensitive than SPECT for detecting active spondylolysis but avoids radiation 1

Role of CT

• CT without contrast has increased sensitivity for detecting non-displaced fractures and established spondylolysis compared to radiographs 1, 2
• CT is less sensitive for detecting stress injuries involving the pars without complete lysis (frequently seen in pediatric patients) 1
• CT is complementary to SPECT and MRI for higher specificity and sensitivity when used together 1
• CT can be used for follow-up imaging of spondylolysis if clinically warranted 1, 2

Conservative Management Protocol (First-Line Treatment)

Activity Modification and Bracing

• Restrict activity and use a custom-fit thoracolumbar orthosis brace for approximately 3 months 3, 4
• This approach achieves excellent results in 84-95% of patients with spondylolysis 3, 4
• Activities involving repetitive hyperextension and/or extension rotation of the lumbar spine should be avoided, as these are painful in 98% of patients 3

Physical Therapy Program

• Follow bracing with an organized physical therapy program focusing on core strengthening, hamstring flexibility, and range of motion 3, 4
• All patients in one series returned to preinjury activity level with this protocol 4
• Conservative treatment is most effective with early diagnosis and treatment 5

Monitoring Response

• Monitor for resolution of bone marrow edema on MRI if obtained, as this suggests response to therapy and potential prevention of progression to complete fracture 2
• Back spasms should resolve and hamstring tightness should normalize with successful treatment 4

When Conservative Management Fails

Surgical Indications

• Surgery may be required if conservative treatment for at least 6 months fails to provide sustained pain relief for activities of daily living 5
• Only 5% of patients with spondylolysis required surgery in one large series 3
• Direct repair of the pars interarticularis can be effective in select patients who fail multimodality non-operative treatment, preserving anatomic integrity and motion of the affected segment 6

Critical Pitfalls to Avoid

Imaging Errors

• Do not rely solely on standard AP and lateral radiographs when clinical suspicion is high—radiography has low sensitivity for spondylolysis without spondylolisthesis 1
• Avoid complete spine imaging (radiography, CT, or MRI of entire spine) as stress injuries are typically localized to one segment 1
• Do not order oblique lumbar radiographs for general back pain, but they are specifically useful for visualizing pars defects 1

Management Errors

• Do not delay advanced imaging (SPECT or MRI) when radiographs are negative but clinical presentation is classic for spondylolysis (young athlete, extension-based pain) 1
• Ensure adequate duration of conservative treatment (3 months of bracing) before considering treatment failure 3, 4
• In patients with spondylolisthesis (slippage), obtain flexion-extension radiographs to assess for instability, which is essential for surgical planning 7

Special Considerations

• 85-90% of pars defects in athletes are located at L5 (the most caudad mobile vertebra), with L4 being the next most common 3
• Multiple-level or nonconsecutive pars fractures are rare but can occur; multiplane reconstruction CT and MRI are useful for planning treatment in these cases 8
• Low-intensity pulsed ultrasound (LIPUS) in addition to conservative treatment shows promise for achieving higher rates of bony union, though more supporting studies are needed 5