What is the likely diagnosis of a 13-year-old girl with lower back pain along the fourth lumbar (L4) vertebrae and pain along the left lower back, who stands with her right hip and knee flexed to 90° and her back hyperextended?

Likely Diagnosis: Spondylolysis

The most likely diagnosis is spondylolysis (stress fracture of the pars interarticularis at L4), given the characteristic presentation of a 13-year-old with localized lumbar pain and a positive one-legged hyperextension test.

Clinical Reasoning

Pathognomonic Physical Examination Finding

• The described stance—standing on the left leg with right hip and knee flexed to 90° while hyperextending the back—is the one-legged hyperextension test (Stork test), which is highly suggestive of spondylolysis when it reproduces the patient's pain 1
• This maneuver loads the pars interarticularis on the side of the standing leg (left side in this case), reproducing pain at the site of the stress fracture 1
• The localization of pain to L4 with left-sided symptoms correlates with the biomechanical stress pattern typical of spondylolysis 2, 3

Age and Epidemiology Support This Diagnosis

• Spondylolysis is the most common cause of low back pain in adolescent athletes, accounting for approximately 50% of pediatric back pain cases in athletic patients 1, 3
• The lesion typically presents during the adolescent growth spurt (ages 10-15), precisely matching this patient's age of 13 years 4, 3
• Spondylolysis represents a stress fracture of the pars interarticularis caused by repetitive hyperextension and rotational forces on the spine 5, 2

Clinical Presentation Pattern

• The typical presentation includes low back pain aggravated by activity, often with minimal physical findings on routine examination 1
• Pain is frequently localized to the lumbar region and may radiate to the buttocks or posterior thighs without neurologic deficit 4
• Sports involving repetitive spinal hyperextension (gymnastics, weightlifting, wrestling, soccer, track and field, baseball, tennis) predispose to this injury 6

Differential Considerations to Exclude

Red Flags Requiring Urgent Investigation

While spondylolysis is most likely, you must actively exclude more serious pathology given the ACR guidelines on pediatric back pain 6:

• Infection (discitis/osteomyelitis): Look for fever, night pain, elevated inflammatory markers (ESR, CRP, leukocytosis), decreased range of motion, and irritability 6, 7
• Neoplasm: Assess for persistent nighttime pain refractory to rest, progressive neurologic symptoms, unintentional weight loss, and pain duration >4 weeks 6
• Inflammatory spondyloarthropathy: Evaluate for morning stiffness, systemic symptoms, and family history of autoimmune disease 6, 8

Less Likely Diagnoses in This Presentation

• Muscle strain would not produce a positive one-legged hyperextension test 1
• Disc herniation typically presents with radicular symptoms and neurologic deficits, which are absent here 6
• Scheuermann disease presents with thoracic kyphosis and wedging of vertebral bodies, not focal L4 pain with this specific physical finding 9

Diagnostic Imaging Algorithm

Initial Imaging: Radiographs First

• Obtain AP and lateral radiographs of the lumbar spine as the initial imaging study 6, 8
• Radiographs can identify spondylolysis in up to 24% of children with back pain, particularly when spondylolisthesis is present 6, 9
• Avoid oblique views—they double radiation exposure without increasing diagnostic yield 7

Critical Limitation of Radiographs

• Plain radiographs have low sensitivity for detecting early spondylolysis (stress fracture stage) without spondylolisthesis 6, 1
• Negative radiographs do NOT exclude spondylolysis and should not delay further imaging if clinical suspicion remains high 6, 8, 1

Advanced Imaging When Radiographs Are Negative or Equivocal

For suspected spondylolysis with negative radiographs, proceed with:

• MRI lumbar spine without contrast as the preferred next imaging modality 6

  • MRI detects marrow edema indicating acute stress injury before frank pars fracture develops 6
  • MRI identifies associated soft tissue pathology and excludes other serious diagnoses (infection, tumor, disc pathology) 6
  • MRI demonstrated definitive diagnosis in an additional 34% of pediatric patients with back pain after negative radiographs 6

• Bone scan with SPECT or SPECT/CT is an alternative when MRI is contraindicated or unavailable 6

  • SPECT has high sensitivity for detecting metabolically active pars stress fractures 6
  • CT can be complementary to SPECT for higher specificity in confirming pars defects 6

Management Implications

Conservative Treatment (First-Line)

• Activity restriction with temporary discontinuation of aggravating sports is the cornerstone of treatment 2, 3
• Bracing may be beneficial, particularly for early-stage lesions, though healing can occur without bracing 2
• Conservative treatment is successful in controlling symptoms and restoring function in the majority of patients 5, 2, 3
• Early diagnosis and treatment prevent progression to more significant defects requiring aggressive intervention 1

Surgical Indications

• Surgery is reserved for patients with symptoms unresponsive to at least 6 months of conservative treatment 5
• Patients with grade III or IV spondylolisthesis (>50% slip) may require surgical intervention due to high risk of progression and symptom persistence 4, 3

Common Pitfalls to Avoid

• Do not misdiagnose as "lumbosacral strain" and delay imaging—this is the most common error in managing adolescent spondylolysis 1
• Do not rely solely on plain radiographs to exclude spondylolysis—early stress fractures are radiographically occult 6, 1
• Do not ignore a positive one-legged hyperextension test—this finding has high clinical utility for early diagnosis 1
• Do not delay advanced imaging if red flags are present (night pain >4 weeks, fever, neurologic deficits, systemic symptoms) 6, 8, 7