What is the management approach for L5 pars interarticularis defects with mild subluxation?

Management of L5 Pars Interarticularis Defects with Mild Subluxation

Begin with anteroposterior and lateral radiographs of the lumbar spine as the standard initial imaging, adding oblique views to better visualize the pars defect, and initiate conservative management with activity restriction, bracing, and physical therapy for 3-6 months before considering surgical intervention. 1, 2

Initial Diagnostic Approach

Imaging Strategy

• Obtain AP and lateral lumbar spine radiographs first as these remain the standard of care for initial evaluation, though sensitivity for detecting spondylolysis without spondylolisthesis is limited 1
• Add oblique radiographic views specifically to better visualize pars interarticularis defects, as these significantly improve detection of the classic "Scotty dog" collar defect 1
• Consider advanced imaging if radiographs are negative but clinical suspicion remains high:
  • MRI without contrast can detect bone marrow edema in the pars or adjacent pedicle, indicating active stress injury, and is especially useful for detecting early spondylolysis before frank fracture occurs 1
  • SPECT bone scan with area-of-interest imaging has high sensitivity (77.6% for plain films alone) and can identify active stress reactions with increased radiotracer uptake 1
  • CT without contrast has increased sensitivity for detecting non-displaced fractures and established spondylolysis compared to radiographs, and can be used for follow-up imaging if clinically warranted 1

Conservative Management Protocol (First-Line Treatment)

Treatment Components

• Restrict activities involving repetitive hyperextension and extension-rotation of the lumbar spine (the painful movements in 98% of cases), particularly sports like gymnastics, football, and weightlifting 2
• Prescribe antilordotic bracing to reduce stress on the pars defect during the healing period 3, 2
• Implement a flexion-based exercise program focusing on:
  • Abdominal strengthening with curl-ups
  • Posterior pelvic tilts
  • Avoidance of lumbar extension exercises 3
  • Note: Flexion exercises show superior outcomes compared to extension exercises, with only 19% having moderate-to-severe pain at 3-year follow-up versus 67% in extension exercise groups 3

Duration and Expected Outcomes

• Continue conservative treatment for a minimum of 3-4 months before considering it a failure 3, 2
• Expect 84% excellent results in spondylolysis patients treated conservatively with this protocol at average 4.2-year follow-up 2
• 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 1

Surgical Indications

When to Consider Surgery

• Persistent disabling low back pain after 3-6 months of appropriate conservative management including activity restriction, bracing, and physical therapy 4, 5, 2
• Progressive spondylolisthesis beyond grade I-II despite conservative care 3, 2
• Positive staged pars interarticularis infiltration test with bupivacaine 0.5% confirming the pars defect as the pain generator 5

Surgical Options

• Direct pars repair with screw fixation and bone grafting is preferred in young patients with:

  • Intact disc height
  • Minimal or no spondylolisthesis
  • Desire to preserve motion segments 4, 5, 6
  • This approach achieves excellent results in most surgically treated patients at mean 34-month follow-up 5

• Posterolateral fusion with instrumentation is indicated for:

  • Grade II or higher spondylolisthesis
  • Failed direct repair
  • Degenerative disc disease at the affected level 3, 2
  • Note: 60% of spondylolisthesis patients required surgery versus only 15% of spondylolysis patients 2

Critical Pitfalls to Avoid

• Do not rely solely on plain radiographs in young athletes with typical symptoms as 8 patients in one series had normal radiographs but abnormal bone scans 2
• Avoid extension-based exercise programs as these show significantly worse outcomes (67% with moderate-to-severe pain) compared to flexion programs (19% with moderate-to-severe pain) 3
• Watch for hypoplasia of the neural arch on imaging, as this anatomic variant is associated with higher non-union rates after direct repair 4
• Do not rush to surgery as 84-85% of spondylolysis patients achieve excellent results with conservative management alone 2