Pelvic fractures on X-ray

Written by the X-Ray Atlas editorial team from the sources listed below · Medical review pending · Updated 24 October 2026 · Level: Intermediate

Pelvic fractures range from an undisplaced pubic ramus fracture in an older person who slipped at home, to an unstable ring disruption after a high-speed collision that can bleed enough to kill. The plain AP pelvis is still a common first film, but it is a screening tool: it shows the obvious ring injuries and many low-energy fractures, and it misses a significant number of sacral and posterior ring injuries. The key principle is that the pelvis is a ring, so when you find one break, look for a second.

1. The ring and how to look

The pelvis is formed by the two innominate bones and the sacrum, held together anteriorly at the pubic symphysis and posteriorly by the very strong sacroiliac (SI) ligaments. Smaller rings sit within it: the two obturator foramina. Breaking a rigid ring in only one place is difficult, so a displaced fracture in one part almost always comes with a second injury (a fracture or a ligamentous disruption) elsewhere.

On the AP pelvis, trace each of these in turn:

1. The pelvic brim (iliopectineal line) from the sacrum round to the symphysis on each side.
2. The obturator rings: the superior and inferior pubic rami and the ischium.
3. The pubic symphysis: width, and whether the superior borders of the pubic bones are level.
4. The sacroiliac joints: width and symmetry. Compare the two sides.
5. The sacrum: trace the arcuate lines of the sacral foramina on each side. A break or asymmetry suggests a sacral fracture. These lines are often obscured by bowel gas.
6. The acetabula and hips, including Shenton's line.
7. The iliac wings and the transverse processes of L5 (an L5 transverse process fracture can accompany posterior ring injury).

2. Normal measurements

3. Low-energy fractures in older people

A fall from standing in an older person with osteoporosis commonly causes:

• Pubic rami fractures, superior and/or inferior, often on one side. These patients may present with "hip pain" and inability to walk.
• Sacral insufficiency fractures, which frequently accompany pubic rami fractures. They are often invisible on plain film, because the sacrum is obscured by bowel gas and the fracture lines run vertically along the sacral ala. They are shown well on MRI or CT.
• Acetabular fractures, increasingly recognised in older people after simple falls.

So a pubic ramus fracture is usually only half of the ring injury; the other half is often in the sacrum. A normal-looking sacrum on plain film does not exclude a fracture there. If the patient cannot mobilise as expected, or the hip films are normal, MRI (or CT) should be considered according to local policy and the occult hip fracture pathway (NICE CG124).

4. High-energy ring injuries: Young-Burgess

High-energy pelvic injuries are classified by the direction of the force. The Young-Burgess system is widely used in trauma; the Tile classification (stable, rotationally unstable, rotationally and vertically unstable) is an alternative.

Type	Mechanism	X-ray features
Anteroposterior compression (APC), "open book"	Force from front to back, as in a head-on collision or a crush	Widening of the pubic symphysis (or vertical rami fractures) and widening of one or both SI joints. Higher grades open the SI joint completely. The pelvic volume increases, so bleeding from the venous plexus can be large.
Lateral compression (LC)	Side impact, the commonest pattern	Horizontal or overlapping fractures of the pubic rami, with compression (impaction) of the sacrum on the same side, and in higher grades an iliac wing fracture or opposite SI injury
Vertical shear (VS)	Fall from height onto one leg	Vertical displacement of one hemipelvis, with fractures or disruption both anteriorly and posteriorly. Highly unstable.
Combined mechanism	More than one force	A mixture of the above

In UK major trauma practice, adults with significant blunt trauma usually go straight to CT, and the AP pelvis film may be omitted when CT is immediately available (NICE NG39, major trauma). A pelvic binder applied before imaging can reduce an open-book injury so that the film looks deceptively normal; always note whether a binder is in place.

5. Acetabular fractures

The acetabulum is assessed with reference lines on the AP pelvis, particularly the iliopectineal line (anterior column) and the ilioischial line (posterior column), along with the anterior and posterior walls, the roof and the teardrop. The Letournel classification describes the patterns, and oblique (Judet) views were traditionally used to show the columns. CT with reconstructions is now the standard for characterising these fractures. A posterior wall fracture commonly accompanies posterior hip dislocation.

6. Avulsion fractures

In adolescents, sudden muscle contraction during sport can avulse an apophysis (a growth centre for a tendon attachment) before it has fused:

Site	Muscle
Anterior superior iliac spine (ASIS)	Sartorius (and tensor fascia lata)
Anterior inferior iliac spine (AIIS)	Rectus femoris
Ischial tuberosity	Hamstrings
Lesser trochanter	Iliopsoas

The fragment is usually a curved sliver of bone displaced from its normal site. Compare with the other side. In an adult, an apparently isolated lesser trochanter avulsion should raise suspicion of a pathological fracture through a lesion such as a metastasis.

7. Pitfalls

• Stopping at one break. Always look for the second injury in the ring, especially in the sacrum and SI joints.
• Bowel gas over the sacrum hides sacral fractures. Trace the arcuate lines carefully and have a low threshold for CT or MRI.
• Rotation of the pelvis makes the obturator foramina and iliac wings asymmetrical and can mimic SI widening.
• Normal variants: unfused apophyses in young people, and the widened symphysis of pregnancy and the postpartum period.
• Pathological fractures in patients with known cancer, myeloma or Paget disease. See metabolic bone disease.
• Bladder and urethral injury accompany anterior ring disruption; these are not shown on the film.

Red flags: act now

What to focus on, by role

Role	Priorities
Medical student	The ring principle, pubic rami fractures in older people, and the open-book injury.
Nurse	Recognise that a pelvic binder must stay on, and that pelvic fractures can bleed. Mobility and analgesia for older patients with rami fractures.
Junior doctor	Look for the second break, consider sacral insufficiency fractures, and know when CT is the right test.
Radiographer	A straight, unrotated AP pelvis; note binder presence; do not move a suspected unstable pelvis unnecessarily.
Advanced / FRCR	Young-Burgess grading, acetabular lines, sacral arcuate lines and subtle SI widening.

Practise on real lower limb X-rays →

References

1. Radiopaedia. Young and Burgess classification of pelvic ring fractures. radiopaedia.org
2. Radiology Masterclass. Hip and pelvis X-ray gallery. radiologymasterclass.co.uk
3. NICE NG39. Major trauma: assessment and initial management. nice.org.uk
4. NICE CG124. Hip fracture: management. nice.org.uk
5. British Orthopaedic Association. BOAST guidelines (pelvic and acetabular fractures). boa.ac.uk

For education only. Not a substitute for a formal report, senior review or your local policy. Never use this page to make decisions about a real patient.