Posterior wall fractures (Fig. 2) often associated with hip dislocation involve varying extents of the posterior articular surface. The fragment size, degree of wall displacement, and impaction can be seen on the AP and obturator oblique view; the ilioischial line will, however, remain intact. The Gull-Wing sign (4) has been described where the posterior wall fragment hinges supero-medially, giving the appearance of a wing on the AP view. The stability of the hip following these injuries is dependent on the size of
Figure 1 Letournel and Judet's classification of acetabular fractures. Elementary fractures; (A) posterior wall fracture, (B) posterior column fracture, (C) anterior wall fracture, (D) anterior column fracture, (E) transverse fracture. Associated fractures; (F) posterior wall with posterior column fracture, (G) transverse with posterior wall fracture, (H) T-shaped fracture, (I) anterior column with posterior hemitransverse fracture, (J) both column fracture.
the fragments as well as their position relative to the weight-bearing area. The fragments can be described as pure posterior—the most common in Letournel's series—posterosuperior, or postero-inferior. Posterosuperior fragments are particularly important due to the involvement of the weight-bearing acetabular roof. Fragment size, comminution, and extent of marginal impaction have an influence on hip stability and degree of potential degenerative arthritis and will therefore have an impact on operative decision-making. The greater the involvement of the weight-bearing area and higher degree of marginal impaction or comminution, the more guarded the prognosis.
Posterior column fractures involve a breach of the ilioischial line on the AP and iliac oblique views. Posterior column fractures are rare—just over 3% of acetabular fractures in Letournel's series. They are important to recognize, however, since the typical fracture pattern detaches the entire posterior column, extending from the greater sciatic notch, through the acetabulum, and into the inferior pubic rami. Varieties of this pattern include extended posterior column fractures, in which the pelvic tear drop (corresponding to the floor of the cotyloid fossa) is attached to the column piece, producing a large joint fragment, and minimally displaced fractures with varying degrees of articular involvement.
Anterior wall injuries demonstrate a break in the iliopectineal line and anterior wall but do not extend into the superior pubic ramus, and therefore only involve the central portion of the anterior column. These rare injuries are usually associated with an anterior dislocation of the hip caused by abduction and external rotation.
Anterior column (Fig. 3) injuries involve variable extents of the segment of bone running from the midpoint of the iliac crest through the anterior acetabulum to the superior and inferior pubic rami. Four main categories have been described; (i) very low or distal fractures involve just the anterior horn of the articular surface and may be considered a high ramus pelvic ring injury, (ii) low fractures exit superiorly at the psoas gutter; the femoral head tends to remain subluxed anteriorly with the detached fragment, (iii) intermediate types exit superiorly between the anterior iliac spines, and femoral head positioning is similar to the low variety, and (iv) the fracture may extend though the iliac crest, resulting in a massive anterior segment. This large column piece is often minimally displaced because of extensive soft tissue attachments along its length and breadth.
Transverse fractures (Fig. 4) split the acetabulum horizontally and therefore break the anterior rim, iliopectineal, and ilioischial lines and often the posterior wall. Though these fractures involve both columns, there is a single fracture line and the columns themselves are not separated from each other. Therefore transverse fractures are not classified as acetabular both-column fractures and belong in the elementary fracture group. The fracture line can cross the acetabulum at various levels; transtectal, at the level of the roof; juxtatectal, at the junction of the roof and cotyloid fossa; and infratec-tal, below the weight-bearing dome. The obturator foramen is intact in transverse fractures. Not only can the fracture obliquity vary from horizontal through to almost vertical, but the fracture line may run from the postero-inferior aspect of the acetabulum exiting superiorly in the anterior column or vice versa. The degree of displacement of the femoral head can differ considerably from minimal to complete central dislocation. In osteoporotic bone transverse fractures often involve central dislocations because of
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Figure 4 (A) Anteroposterior radiograph of a transverse fracture, (B) obturator oblique view radiograph of a transverse fracture, (C) iliac oblique view radiograph of a transverse fracture, (D) CT of a transverse fracture. Abbreviation: CT, computed tomography.
comminution of the quadrilateral plate. The extent of the displacement has considerable prognostic significance, particularly in high-energy injuries.
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