Incomplete disruption of posterior arch, bilateral injury
Definition
Bilateral partial poster arch disruptions are classified as AO/OTA 61B3 unjuries.
Bilateral incomplete external rotation injury (open book, APC2)
Posterior injury
Both sides of the posterior arch are involved. The posterior ring injury on each side involves either an:
- Anterior SI joint disruption
- Sacral fracture
This is classified as an AO/OTA 61B3.3 injury.
Anterior injury
The typical anterior arch injury produced by these injuries is disruption of the pubic symphysis. Less frequently, fractures of the pubis or rami may occur. Anterior widening of the pelvis is evident as increased space between the two pubic bones, or fracture surfaces. Fractures are vertically oriented.
Bilateral posterior arch injuries, one externally rotated, the other internally rotated (LC III)
This is an LC3 injury, with significant, but partial, instability bilaterally. Deformity is only rotational. There is no proximal or posterior displacement at the posterior arch injuries.
This is classified as an AO/OTA 61B3.1 injury.
The pattern reflects a high-energy mechanism. The identifying feature of the LC3 pelvic ring injury is the “wind-swept” deformity, with one hemipelvis rotated externally and the other internally.
Posterior external rotation injury
External rotation injury will be either:
- Anterior sacroiliac joint disruption (partial)
- Incomplete sacral fracture
The externally rotated (APC) side is often the site of significant pelvic venous disruption and hemorrhage.
Posterior internal rotation injury
External rotation injury will be either:
- Anterior sacral compression fracture (partial)
- Partial sacroiliac joint subluxation or fracture subluxation
- Incomplete posterior iliac ring fracture
Anterior injury
Anterior arch injuries are frequently multiple, involving both symphysis and rami.
Bilateral lateral compression injury
Both hemi-pelves are internally rotated, and the pelvic ring is narrowed anteriorly.
This is classified as an AO/OTA 61B3.2 injury.
Posterior injury
Each posterior arch injury will be either:
- Anterior sacral compression fracture (partial)
- Partial sacroiliac joint subluxation or fracture subluxation
- Incomplete posterior iliac ring fracture
Anterior injury
The pelvic ring is narrowed anteriorly. The anterior arch injury, which may be unilateral on either side, or bilateral, always includes a set of horizontally oriented fractures. Impaction or overlapping of the anterior injuries is evident, and variable in degree.
Infrequently, marked internal rotation displacement through the pubic symphysis can produce a locked symphysis, with gross narrowing of the pelvic ring.
Another unusual anterior arch injury produced by internal rotation (lateral compression) is the Tilt Fracture. This involves dislocation anteriorly of one pubic bone with symphyseal disruption and anteriorly angulated ramus fractures.
