When is the Pelvic Impression Test Positive?
The pelvic impression test (also called pelvic compression or pelvic spring test) is considered positive when manual compression or distraction of the iliac crests elicits pain, crepitus, or abnormal movement, indicating potential pelvic ring instability or fracture. 1
Clinical Technique and Interpretation
The test involves applying downward compression on the iliac crests (compression test) or distraction pressure on the iliac crests (distraction test) while the patient is supine 2. A positive result occurs when:
- Pain is elicited at the fracture site or symphysis pubis
- Abnormal movement or instability is detected (crepitus, "springing" sensation)
- Asymmetry is noted compared to the contralateral side 1, 3
Diagnostic Performance
The physical examination for pelvic instability has moderate sensitivity (44%) but excellent specificity (99%) for detecting pelvic fractures 3. This means:
- A positive test strongly suggests pelvic injury and should trigger immediate action
- A negative test does NOT reliably exclude fracture, particularly in severely injured or intubated patients 3
Among specific maneuvers tested, the hip flexion test (active hip flexion with knee extension) demonstrated superior predictive value compared to compression/distraction tests, with 95% positive predictive value and 90% negative predictive value for pelvic fractures 2.
Clinical Context and Immediate Actions
When the Test is Positive:
Immediately order blood products and consider surgical intervention 3. Patients with positive pelvic examination demonstrate:
- Higher injury severity scores
- Greater incidence of hemorrhagic shock
- Lower initial systolic blood pressure and hemoglobin
- Higher transfusion requirements
- Increased need for pelvic stabilization procedures 3
Critical Pitfall to Avoid:
Do NOT perform repeated pelvic compression maneuvers 1. The Lelly maneuver (pelvic spring test) should be done cautiously as it can increase bleeding by dislocating bone margins and converting a stable fracture into an unstable one 1.
Imaging Requirements
- Pelvic X-ray is mandatory even with negative physical examination in blunt trauma patients, as clinical examination misses approximately 20% of surgically significant pelvic fractures 3
- In awake, alert patients without pain on examination, selective X-ray use is reasonable, as clinically significant missed fractures are rare 4
- CT scan with 3D reconstruction is recommended for hemodynamically stable patients to guide surgical planning 1
Alternative Bedside Tests
The patellar pubic percussion test (PPPT) offers an alternative approach with 85% sensitivity and 70% specificity for hip and pelvic fractures, including occult fractures not visible on plain radiographs 5. This test involves tapping the patella while auscultating over the pubic bone, with asymmetry indicating fracture 5.