Placement of Posterior Column Screws for Acetabular Fractures
Joshua L. Gary
The acetabulum is a concave socket formed at the confluence of the ilium, ischium, and pubis. It has been described as an inverted “Y” formed as the anterior and posterior columns join at the dome of the acetabulum and transition into the iliac wing proximally.
The posterior column (PC) of bone includes the greater and lesser sciatic notches and the ischium and has much less surface area than the anterior column. The bone about the greater sciatic notch is normally the densest bone of the human skeleton.
The bony corridor for screw placement runs from the iliac bone of the pelvic brim just anterior and lateral to the sacroiliac joint cranially to the ischium caudally.
It is bordered medially by the quadrilateral surface and laterally by the ischial bone to the greater and lesser sciatic notches. These notches and the ischial spine define the posterior border with the articular surface of the acetabulum constraining the anterior limit of the corridor.
The undulation of the lateral border with a concavity just anterior to the lesser sciatic notch and cranial to the ischial tuberosity must be taken into account to prevent placement of an “in-out-in” screw (Fig. 14-1). This concavity (red arrow below) serves as the isthmus of the bony corridor for columnar fixation of the posterior column.
Disruption and displacement of the posterior column are represented by an interruption in the ilioischial line on the anteroposterior (AP) view of the pelvis (Fig. 14-2A).
The ilioischial line on the AP view represents the medial border of the PC corridor. The AP view also demonstrates the quality of reduction in the coronal plane, with excellent reduction denoted by restoration of a contiguous ilioischial line.
The iliac oblique view brings the greater sciatic notch, ischial spine, and lesser sciatic notch into profile and provides excellent visualization of the anterior and posterior limits of the PC corridor (Fig. 14-2B). Fracture lines involving the posterior column are usually best seen with this radiographic view. The iliac oblique view allows for judgment of reduction quality in the sagittal plane and for caudal displacement of the ischial segment.
The obturator oblique view provides excellent visualization of the lateral border of the PC corridor and its undulation; the plate contour used to buttress a posterior wall fragment provides an excellent visual representation of the lateral border (Fig. 14-2C).
The lateral sacral or lateral pelvic view is also useful, especially with retrograde screw placement. The iliac cortical density represents the pelvic brim, and screws terminating cranial to this line may protrude into the iliacus muscle (Fig. 14-2D).
The iliac and obturator oblique views, or Judet views, are generally obtained rolling the patients with wedges or bumps under each hemipelvis. An iliac oblique view of the left hemipelvis is an obturator oblique view of the right hemipelvis and vice versa.
When a fluoroscope is used, the patient usually remains stationary on the operative table, and the C-arm is rotated over and back to obtain Judet view. The fluoroscopy machine should generally enter contralateral to the operative extremity.
The iliac oblique is obtained in the supine position by rolling the C-arm approximately 30 degrees away from the acetabulum (Fig. 14-3A).