Portable AP radiographs of the chest and pelvis are the first studies obtained in setting of high impact trauma to assess for potential life threatening injury. Pelvic radiography is especially helpful to identify fractures and signs of pelvic instability-potential sources of massive internal hemorrhage.
These are the key contour lines and joint spaces for evaluating the pelvis. Trace each cortex and joint space to assess for fracture, asymmetry, or joint space widening.
- Iliopectineal line
- Ilioischial line
- Anterior acetabular rim
- Posterior acetabular rim
- Shenton line
- Pelvic teardrop
- Obturator foramen
- Sacral arcuate lines
- Sacroiliac joint
- Pubic symphysis
The Young-Burgess Classification system describes the 3 patterns of pelvic ring injury.
- Anterior Posterior compression
- Lateral compression
- Vertical shear
Features of instability include widening or vertical offset of sacroiliac joints and severe widening of the pubic symphysis suggesting ligamentous disruption.
AP compression injury
- Common in head-on MVA, motorcycle accident, and crush injuries
- Look for widening of pubic symphysis with or without fractures of bilateral superior and inferior pubic rami and sacrum.
- Signs of instability, include ipsilateral or bilateral sacroiliac joint widening, severe pubic diastasis (>2.5 cm) and sacrospinous or sacrotuberous avulsion fractures.
FINDINGS: Diastasis of the pubic symphysis measuring 3 cm with 1 cm vertical offset. Probable mild diastasis of the anterior bilateral sacroiliac joints, suggesting unstable pelvic ring injury.
Lateral compression injury
- Common in falls and side-impact MVC
- Look for fractures of ipsilateral or bilateral superior and inferior pubic rami, sacrum and iliac crest.
- Signs of instability, include ipsilateral or bilateral sacroiliac joint widening.
FINDINGS: Displaced fractures of the left third sacral arch, left inferior and superior pubic rami and right pubic body and superior pubic ramus with extension to pubic symphysis. Widening of the left sacroiliac joint, suggesting unstable pelvic ring injury.
Vertical shear injury
- Common in high energy axial loading injuries such as fall from height.
- Unilateral vertical displacement of hemipelvis with resultant offset and widening of pubic symphysis and SI joint with or without associated pelvic fractures.
- Vertical shear injuries are inherently unstable.
FINDINGS: Widening and offset of the pubic symphysis and left sacroiliac joint with superior translation of the left hemipelvis, consistent with unstable vertical shear injury. Moderately displaced fractures of left iliac wing and right superior pubic ramus and body.
Comminuted acetabular fracture involving anterior and posterior columns as well as anterior and posterior walls
Acetabular fractures
- Difficult to assess with radiography. Usually require CT for accurate characterization.
- Look for disruption of the contours of the acetabulum which represent the following relevant components of acetabular anatomy:
- liopectineal line= anterior column
- Ilioischial line= posterior column
- Anterior acetabular rim= anterior wall
- Posterior acetabular rim= posterior wall
- Pelvic teardrop= acetabular floor
Trace key contour lines and compare joint spaces to assess for asymmetry and fracture, which often appears as subtle cortical disruption or impaction. Use you knowledge of pelvic ring facture patterns know where there might be additional subtle factures.
Because the pelvis is a ring, when you find one fracture, you should be able to find another fracture or ligamentous injury. (You can't break a pretzel in just one place.) Report signs of instability including widening or vertical offset of sacroiliac joints and/or pubic symphysis.
Example report negative for traumatic injury.
FINDINGS:
- No acute fracture. The pubic symphysis is normal. The sacroiliac joints are normal.
IMPRESSION:
- No acute fracture or traumatic malalignment.
Pelvic Ring Fractures: What the Orthopedic Surgeon Wants to Know
Acetabular Fractures: What Radiologists Should Know and How 3D CT Can Aid Classification