Saturday, January 21, 2012

Transverse Acetabular Fractures

Transverse fractures of the acetabulum involve both the anterior and posterior aspects of the acetabulum, without involvement of the obturator ring or superior extension into the iliac wing. They comprise between 5% and 20% of acetabular fractures.

The fracture plane is not purely transverse in the anatomic sense, but is transverse relative to the acetabulum. The fracture plane courses superiorly and medially in an oblique plane from the acetabulum and separates the innominate bone into an upper iliac fragment and a lower ischiopubic fragment. The ischiopubic fragment can rotate about the pubic symphysis, and the femoral head moves with the iliac fragment medially and superiorly.

Transverse fractures can be classified as transtectal, juxtatectal, and infratectal based on where the fracture plane crosses the articular surface. Transtectal fractures cross the weight-bearing dome of the acetabulum. Juxtatectal fractures cross the articular surface just superior to the cotyloid fossa. Infratectal fractures cross the cotyloid fossa.

The more superior fracture planes are more vertical in orientation and associated with a smaller intact remaining articular surface, which has implications for treatment.

Radiographs reveal disruption of both the iliopectineal (pink arrow) and ilioischial (blue arrow) lines, as well as interrupted anterior and posterior rim lines. Transtectal fractures will also involve the acetabular roof line without disrupting the relationship of the ilioischial line with the teardrop.

When scrolling down (superior to inferior) on axial CT images, the fracture plane moves medially to laterally. Coronal images reveal involvement of both anterior and posterior aspects of the acetabulum. No superior extension to the iliac wing is seen.

Differential considerations include T-shaped and transverse with posterior wall fractures, both of which have transverse components with added features. The T-shaped acetabular fracture is a transverse fracture with inferior extension into the obturator ring, but no superior extension into the iliac wing. The transverse with posterior wall fracture is a transverse fracture with a comminuted (often displaced) posterior wall fracture and an intact obturator ring.


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