In a 60‑year‑old woman with chronic pelvic instability since childbirth, does a flamingo view showing a 3.3 mm vertical asymmetry of the superior pubic rami indicate pubic symphyseal insufficiency fracture or instability?

Flamingo View Findings Consistent with Pubic Symphyseal Instability

A 3.3 mm vertical asymmetry of the superior pubic rami on flamingo views is below the threshold for definitive instability and does not confirm pubic symphyseal insufficiency fracture in this patient. The imaging findings suggest relatively preserved pelvic ring stability despite her chronic symptoms.

Understanding the Diagnostic Threshold

The flamingo view (single-leg stance radiograph) is specifically designed to detect pathologic motion at the pubic symphysis by stressing the anterior pelvic ring 1. However, the 3.3 mm vertical displacement observed in your patient falls well below established thresholds for instability:

• Vertical displacement <11 mm indicates rotational stability in the flexion-extension plane and suggests intact pelvic ring integrity 2
• Displacement >22 mm reliably indicates loss of pelvic flexion resistance and instability 2
• The 11-22 mm range represents an indeterminate zone requiring additional clinical correlation

Your patient's 3.3 mm displacement places her firmly in the stable category from a biomechanical standpoint.

Clinical Context: Postpartum Pelvic Instability

While the imaging doesn't confirm acute instability, chronic postpartum pelvic dysfunction is a recognized entity 1, 3. The key distinction here is between:

• Acute structural failure (fractures, significant ligamentous disruption requiring fixation)
• Chronic functional instability (muscular weakness, minor ligamentous laxity, pain without structural failure)

The absence of acute fracture on the report and minimal displacement on stress views suggests this patient has chronic functional instability rather than structural failure requiring surgical intervention.

Recommended Diagnostic Approach

Since flamingo views are inconclusive for her symptoms:

1. Obtain MRI of the pelvis without contrast - This is the gold standard for detecting:

   • Occult insufficiency fractures of the pubic rami or sacrum 4, 5
   • Bone marrow edema indicating stress injury
   • Posterior pelvic ring involvement that may not be apparent on radiographs 1

2. Evaluate for pregnancy-related insufficiency fractures - In a 60-year-old woman with symptoms dating to childbirth, consider:

   • Postpartum sacral stress fractures (often missed on plain films) 6
   • Chronic pubic symphysis changes from prior diastasis 6
   • Pregnancy-associated osteoporosis as an underlying risk factor 4, 5

3. Assess posterior pelvic ring - CT may be useful if MRI is contraindicated, as posterior ring involvement often accompanies anterior instability and drives treatment decisions 1

Management Implications

Given the minimal displacement on stress views:

• Initial conservative management is appropriate: pelvic orthosis, activity modification, physical therapy focusing on pelvic floor strengthening 1, 3
• Surgical fixation is NOT indicated based on current imaging - Guidelines recommend pubic symphysis plating only for diastasis >25 mm in acute trauma 7, and this patient has neither acute injury nor significant displacement
• If MRI reveals occult fractures with significant bone marrow edema, protected weight-bearing and reassessment would be warranted 4, 5

Critical Pitfall to Avoid

Do not interpret minimal flamingo view asymmetry as confirmation of instability requiring surgery. The 3.3 mm finding is likely within normal variation or represents chronic adaptive changes rather than acute structural failure. Proceeding to surgical fixation without objective evidence of significant instability (>10-11 mm vertical displacement or >25 mm horizontal diastasis) would expose the patient to unnecessary operative risk without addressing the likely source of her symptoms 2, 8.

The discordance between her significant symptoms and minimal objective instability suggests either an occult fracture (requiring MRI to detect) or chronic pain syndrome from remote childbirth injury that has since healed structurally but left functional deficits.