Fractures may involve the columns, walls, or dome of the acetabulum. They are classified by Letournel and Judet as five elementary and five associated fractures. Elementary fractures are predominantly single-plane injuries. Associated fractures are combinations of the elementary types, and are multiplane and more complex. The AP pelvis radiograph is typically the first imaging study followed by CT scanning. Some patients may have additional 45° oblique pelvis radiographs, known as Judet views. CT is more sensitive than plain radiographs for detecting acetabular fractures.
Five fracture types in the Letournel–Judet classification account for 80-90% of cases. Posterior acetabular wall fractures are the most common. A portion of the posterior articular surface and rim is sheared from the pelvis by posterior dislocation of the hip. Transverse acetabular fractures divide the hemipelvis through the acetabulum into superior and inferior portions, and do not involve the obturator ring. Radiographically, part of the superior articular surface or dome remains attached to the intact ilium. The fracture plane actually is oblique from superomedial to inferolateral. A combination of posterior wall and transverse injuries characterizes the transverse and posterior wall fracture. The T-shaped fracture combines the transverse fracture with a vertical fracture most commonly passing through the acetabular fossa and notch and the inferior ischiopubic ramus. The both-column fracture is a complex injury with no part of the articular surface of the hip socket remaining attached to the axial skeleton. The “spur” sign, representing the edge of intact ilium adjacent to the fracture, is pathognomonic of the both-column fracture.
Figure 8.1 ▪ Posterior Wall Acetabular Fracture.
A-C: AP (A) and oblique (B) conventional radiographic images and transverse CT image (C) show posterior wall acetabular fracture. A: AP image shows displaced posterior wall fragment with typical triangular or fin-shaped appearance (arrow). Femoral head is projected over the superior surface of acetabulum (arrowhead) because the hip is dislocated posteriorly. B: Oblique image demonstrates both the fracture fragment (arrow) and the posterior acetabular wall defect (arrowhead) that is its source. Femoral head is located on this image. C: Transverse CT image shows rotated and displaced fracture fragment (arrow) and typical oblique fracture plane (arrowheads) through ischium and posterior acetabulum.
Figure 8.2 ▪ Transverse Acetabular Fracture.
A, B: Oblique conventional radiographic image (A) and transverse CT image (B) illustrate transverse acetabular fracture. A: Conventional image shows the fracture plane dividing hemipelvis into superior and inferior portions through the hip socket (arrows). Superior articular surface or “dome” remains attached to superior portion (arrowhead). Note that inferior ischiopubic ramus is intact. (Skin fold artifact simulates ramus fracture.) (B) Transverse CT image ...