First and second year — the floor first, then every step
The pelvis is a ring: find the anterior and the posterior injury, name the force pattern (lateral compression, anteroposterior compression, vertical shear), and look for the arterial bleeding and the bladder and urethral injury that travel with it.
Orient first
A ring rarely breaks in one place. An obvious pubic ramus fracture means there is a posterior injury (sacrum, sacroiliac joint or iliac wing) until you have looked for it.
The FORCE decides the pattern and the bleeding risk: lateral compression crushes the ring (sacral buckle fractures, horizontal rami fractures); anteroposterior compression opens it like a book (symphyseal diastasis, widened sacroiliac joints); vertical shear displaces a hemipelvis upwards.
Pelvic bleeding is mostly venous and from fracture surfaces; ARTERIAL bleeding (seen as active extravasation) is what angioembolisation treats.
Acquire the study
The trauma CT with an ARTERIAL phase through the pelvis, thin bone-algorithm slices, coronal and sagittal reformats, and inlet/outlet-oblique or 3D reconstructions for the surgeon.
A pelvic binder, if applied, reduces an open-book injury and can hide the diastasis — note its presence and position.
The manoeuvre
Anterior ring on axial and coronal: symphysis width, pubic rami fractures (horizontal/coronal plane lines suggest lateral compression; vertical lines suggest APC or vertical shear).
Posterior ring: each sacroiliac joint (anterior and posterior widening), sacral fractures — buckle/impaction of the anterior sacral cortex (lateral compression), and the zone relative to the neural foramina (Denis I lateral, II through, III medial).
Iliac wing and the crescent fracture (an iliac fracture exiting through the sacroiliac joint).
L5 transverse process fracture — a marker of posterior ring and vertical instability.
Vertical displacement of a hemipelvis on coronal reformats (compare the heights of the iliac crests or the sacroiliac joints).
Arterial phase: active extravasation in the pelvis, its source vessel territory (superior gluteal, internal pudendal, obturator), and pelvic and retroperitoneal haematoma size.
Bladder: perivesical haematoma, bladder displacement, and whether retrograde CT cystography is needed.
What confirms it
A named pattern needs both halves: the anterior and the posterior injury, with the direction of displacement.
What licenses you to exclude it
A normal AP radiograph does not exclude a sacral fracture or a posterior ring injury — CT does.
The classic misread
Calling the ring "intact" in a binder — a reduced open-book injury can look normal.
Missing the anterior sacral buckle fracture of lateral compression by not using the sagittal reformat.
Reporting the injury
Classification to use
Young–Burgess (mechanism): LC I–III, APC I–III, VS, CM — or Tile A (stable), B (rotationally unstable, vertically stable), C (rotationally and vertically unstable); AO/OTA 61. State which.
Sacral fractures: Denis zones I–III.
Measurements — and how to take them
Symphysis width in mm on axial or coronal (normal adult under about 5 mm; > 25 mm implies sacrospinous and anterior SI ligament disruption — APC II or worse).
SI joint width anteriorly and posteriorly compared with the other side, in mm.
Vertical displacement of the hemipelvis in mm on coronal.
Sacral fracture displacement and the narrowest residual neural foramen.
What to report
Anterior and posterior injuries with the direction of displacement; the pattern name.
Symphysis width, SI joint widening, vertical displacement.
Active arterial extravasation and its likely source; haematoma size.
Bladder and urethral injury signs; acetabular extension; binder position.
How to report it
CT: "Anteroposterior compression injury (Young–Burgess APC II): symphyseal diastasis of 32 mm with widening of the anterior right sacroiliac joint and intact posterior sacroiliac ligamentous alignment. Active arterial extravasation in the right pelvis in the territory of the superior gluteal artery. Large extraperitoneal pelvic haematoma displacing the bladder; CT cystography recommended."
What not to report
Do not call the pelvis stable or unstable as a single word — describe the injured structures and displacement.
Do not call a pelvis without an anterior injury "normal" when a posterior injury is present, and vice versa.
Associated injuries to look for
Bladder rupture and urethral injury (APC, straddle), rectal and vaginal injury (open fracture), acetabular fracture, lumbosacral plexus injury with Denis II/III, L5 transverse process fracture, and haemorrhagic shock.
What changes management
Active arterial extravasation — angioembolisation or preperitoneal packing.
Rotational or vertical instability (APC II/III, LC III, VS) — external or internal fixation.
Urethral injury — no urethral catheter.
Reference values
Each value carries the caveat that keeps it from being misused. Normal limits and diagnostic criteria are kept apart on purpose: a disease cut-off read as a normal range is the more dangerous mistake.
Normal limits
Pubic symphysis · Symphyseal width
up to approximately 5 mm in the adult; over 10 mm indicates diastasis
Widening beyond about 2.5 cm in trauma implies anterior ring disruption WITH posterior ring injury — go looking at the sacroiliac joints. Peripartum widening is physiological and resolves; athletic osteitis pubis narrows and irregularises the joint instead.
X-ray · CT
See it on real cases
Direct links to Radiopaedia — the reference article and worked cases with their images. Each opens on Radiopaedia.