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Diagnostic Imaging · Musculoskeletal System

Diagnostic imaging of pelvic and acetabular injuries

Diagnostic imaging of pelvic injuries is key to determining the biomechanics of trauma and surgical tactics. Radiography allows the identification of basic compression patterns and apophyseal avulsions, but computed tomography (CT) remains the gold standard for classifying intra-articular acetabular fractures.

Test your knowledge on this topicAsk the AI
Most common injuryLateral compression (LC) accounts for 57% of all pelvic ring fractures.
Gold standardCT is strictly mandatory to assess displacement and impaction in acetabular fractures.
Spur signA radiographic sign of the disruption of the ischial pillar in bicolumn fractures.
Stress fracturesT1-weighted MRI (T1-SE) is the best method for detecting bone marrow edema in the pelvis.
4 min readFor medical studentsUpdated Sep 25, 2026
Material prepared by WhiteCoat Pro editorial team based on platform study guidesReviewed by medical editor: Aulov A. A., general practitioner · 09/24/2026

Mechanisms of pelvic ring injury

Pelvic ring injuries are classified according to the vector of the applied force. The injury pattern directly determines pelvic stability.

  • Anteroposterior compression (AP Compression). In type 1, the pelvic ring is stable. Type 2 (the "open book" pattern) is characterized by pubic symphysis diastasis (>2.5 cm) and rupture of the anterior sacroiliac ligaments; the posterior ligaments are intact. Plate fixation is required. In type 3, the posterior sacroiliac ligaments (ligg. sacroiliaca posteriora) are additionally ruptured, leading to complete multidirectional biomechanical instability.
  • Lateral compression (Lateral Compression, LC). The most frequent type. With a side impact, the hip bone (os coxae) rotates internally. Type 1 LC consists of stable impacted or oblique fractures of the pubic rami. Type 3 LC occurs during a rollover (e.g., by a car tire): on the side of the impact, the pelvis is crushed inward, while on the contralateral side, it is externally rotated (as in AP compression).
  • Vertical Shear (VS). Results from a fall from a height onto one leg. The ligamentous apparatus is completely disrupted, and the affected hemipelvis is displaced cranially (upward). This is always a multiplanar instability.

Acetabulum: anatomy and classification

The acetabulum (acetabulum) structurally resembles an upside-down letter "Y". It consists of two weight-bearing columns visualized on radiographs along specific lines:

  1. Anterior column: runs from the pubic ramus to the iliac wing. Marker: the iliopectineal line (iliopectineal line).
  2. Posterior column: runs from the ischial tuberosity. Marker: the ilioischial line (ilioischial line).

To select the surgical approach, the international Judet and Letournel classification is used. It identifies 5 elementary fracture types:

  • Posterior wall fracture. The most common variant (typical for traffic accidents involving a knee strike in a seated position). If more than 40% of the wall depth is fractured or impacted fragments are present, surgery is indicated.
  • Anterior wall fracture. A rare isolated injury that does not disrupt the main weight-bearing surface.
  • Column fractures. Fracture lines run in the coronal plane through the obturator ring. In an anterior column fracture, the line exits superiorly above the acetabulum; in a posterior column fracture, it runs posteriorly.
  • Transverse fracture. Divides the acetabulum into superior (iliac) and inferior (ischiopubic) halves, crossing both columns.
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Avulsion and stress fractures

Avulsion Injuries Are typical for children and adolescents in sports due to the immaturity of apophyseal growth zones. A sudden isometric muscle contraction avulses a bone fragment along the line of preliminary mineralization.

  • The sartorius muscle avulses from the anterior superior iliac spine.
  • The rectus femoris avulses from the anterior inferior iliac spine.
  • The hamstring tendons avulse from the ischial tuberosity (surgery is required in case of severe displacement).

Stress Fractures Occur due to cyclic overloads (e.g., in runners). Preferred localizations include the sacrum and the posterior column of the acetabulum. Conventional radiography has low diagnostic value here. MRI is the method of choice: it provides excellent visualization of bone marrow edema. The optimal sequence for detecting occult fracture lines in the sacrum is T1 spin-echo (T1-SE), as on STIR sequences the fracture line may be obscured by pronounced edema.

Briefly: answers to topical questions

What are the three types of lateral compression (LC) of the pelvic ring distinguished in the Young-Burgess classification?

The classification distinguishes three types of lateral compression of the pelvic ring, differing in severity and biomechanics.

  • Type 1 (LC type 1) is the least severe type, including oblique or comminuted fractures of the pubic rami, or less commonly, symphysis disruption with overlapping margins.
  • Type 2 (LC type 2) — the hip bone (os coxae) rotates internally. Includes subtypes 2a (rupture of the posterior sacroiliac ligament) and 2b (fracture of the iliac wing).
  • Type 3 (LC type 3) is the most severe type ("rollover" injury). A type 2 pattern occurs on the side of the impact, while the pelvic bone is externally rotated on the contralateral side.

What associated (complex) types of acetabular fractures are distinguished according to the Judet and Letournel classification?

According to the Judet and Letournel classification, complex types of acetabular fractures are distinguished, representing combinations of elementary injuries:

  • Bicolumn fractures (bicolumn) — the fracture line runs through the acetabular roof, therefore there is no continuity between the ischial pillar and the acetabulum.
  • T-shaped fractures (T-shaped) — the acetabular roof and the ischial pillar maintain continuity and remain intact.
  • Column injuries associated with posterior wall fractures.

Class and exam questions

How to differentiate anteroposterior compression type 2 from type 3?

In type 2, only the anterior pelvic ligaments are ruptured ("open book" sign), while the posterior ligaments remain intact, and the pelvis is stable to lateral compression. In type 3, the posterior sacroiliac ligaments are also ruptured, leading to complete instability.

Why is radiography insufficient in acetabular trauma?

On a radiograph, it is impossible to accurately assess the percentage of articular surface involvement (e.g., of the posterior wall) or to detect small intra-articular impacted fragments. A CT scan is strictly necessary for this.

How to differentiate a T-shaped fracture from a bicolumn fracture?

The distinction is based on assessing the continuity between the acetabular roof and the ischial pillar. In a T-shaped fracture, this continuity is preserved. In a bicolumn fracture, it is disrupted, which may produce the "spur sign" on radiography.

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What else to study on this topic

  • Pelvic ring biomechanics in hybrid injuries (complex injuries with a predominance of the LC pattern).
  • Detailed analysis of complex acetabular fracture types according to Judet and Letournel (T-shaped, Bicolumn).
  • Radiographic positioning: Judet views (obturator oblique and iliac oblique views) for detecting the "spur sign".
  • Indications for surgical treatment of hamstring avulsions from the ischial tuberosity.

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