The "safe zone" for infrapectineal plate-screw fixation of quadrilateral plate fractures: An anatomical study and retrospective clinical evaluation

Abstract

Extra-articular screw placement in the true pelvis for fixing quadrilateral plate fractures remains challenging. We aimed to define the "safe zone" on the quadrilateral surface to facilitate safe plate-screw placement.Twenty cadaveric hemipelves were sectioned and assembled to define the projection of the acetabular boundary on the quadrilateral surface. Three lines (X, Y, and Z) were drawn tangent to the projection, with X parallel to the iliopectineal line, Y perpendicular to the iliopectineal line, and Z parallel to the posterior border of the ischial body. Then, the distances between X and the iliopectineal line (D1), Y and the sacroiliac joint (D2), and Z and the posterior border of the ischium (D3) could be used to determine a "safe zone" on the quadrilateral surface for screw insertion. We included 15 patients whose conditions satisfied the definition of a comminuted quadrilateral plate fracture and applied two-ended buttress plates for treatment in accordance with this "safe zone."The average D1 was 50.0 mm, the average D2 was 30.6 mm, and the average D3 was 12.4 mm. For all 15 patients with comminuted quadrilateral fracture who were treated, no intraoperative or postoperative screw penetration of the acetabulum was identified, and no loss of reduction was observed during an average follow up of 17.7 months.The "safe zone" established in this study simplifies extraarticular screw placement for managing quadrilateral plate fractures in the true pelvis. As a result, two-ended buttress plate fixation in the true pelvis becomes safe, therefore, treatment with two-ended buttress plates may represent a viable alternative to single-ended elastic fixation in the management of comminuted quadrilateral fractures.

Figure 1

A reconstruction plate in one of several different configurations (A and B), a T-shaped plate (C) or a π-shaped plate (D) was used to fix quadrilateral plate fractures. The symbol ^∗ indicates the potential locations for safe screw insertion in the “safe zones” (green areas), which are located outside the projection of the acetabulum on the quadrilateral surface (red area). E = iliopectineal eminence, IL = iliopectineal line, SI = sacroiliac joint.

Figure 2

The initial cut was made at the superior border of the quadrilateral plate in line with IL and perpendicular to the quadrilateral surface. The first cut plane is indicated by the blue plane (A). Two green dotted lines tangential to the boundary of the acetabulum and perpendicular to the quadrilateral surface (as indicated by the red lines) were drawn and projected two points (red dots) on the quadrilateral surface. One blue dotted line tangential to the lowest boundary of the acetabulum and perpendicular to the quadrilateral surface (as indicated by the blue line) was drawn and projected one point (blue dot) on the quadrilateral surface (B). The sections were then assembled to form the original acetabulum and all red dots were connected to depict the exact projection of the acetabular boundary on the quadrilateral surface, as indicated by the red area (C). Next, three red lines (X, Y, Z) were drawn tangent to the projection, with X parallel to IL, Y perpendicular to IL, and Z parallel to the posterior border of the ischial body. The distance between X and IL (D1), Y and the sacroiliac joint (D2), Z and the posterior border of the ischium (D3) can be used to determine the “safe zone,” as indicated by the green area (D). E = iliopectineal eminence, IL = iliopectineal line.

Figure 3

Screws in the green “safe zone” should be inserted perpendicular to the quadrilateral surface or should point away from the red acetabular projection, as indicated by the black screws; otherwise, they will encroach upon the acetabulum, as indicated by the red screws (A). The screw angulation is further demonstrated in a section perpendicular to the quadrilateral surface and parallel to the IL (B). E = iliopectineal eminence, IL = iliopectineal line, SI = sacroiliac joint.

Figure 4

Intraoperative image showing the infrapectineal plate, which is indicated by the black arrowhead (A). Intraoperative image showing screw angulation, which is indicated by the red dotted lines (B). Postoperative pelvic radiographs in the AP view (C), the obturator oblique view (D), and the iliac oblique view (E) revealed no screw penetration of the acetabulum; the infrapectineal plate is indicated by the black arrowhead.

Figure 5

Patient number 2 was a 49-year-old male with posterior column and quadrilateral plate fractures. His fractures were reduced through the modified Stoppa approach combined with the Kocher-Langenbeck approach. Pre-operative anteroposterior pelvic radiograph (A) and CT scan (B and C) all showing a quadrilateral plate fracture on the left side, with obvious protrusion of the femoral head. Preoperative three-dimensional reconstruction CT scan providing a comprehensive image of the fracture and showing a disruption of the posterior column (D and E). The surgeon is positioned on opposite side of the fracture, and the quadrilateral plate is visualized through the Stoppa approach and fixed with a plate as indicated by the white arrowhead (F). Postoperative three-dimensional reconstruction CT scan (G and H) and anteroposterior pelvic radiograph (I) showing that the quadrilateral plate fracture has been reduced. The two-ended buttress plate for quadrilateral plate fracture fixation is indicated by the black arrowhead (G, I).

Figure 6

Patient number 1 was a 57-year-old male with anterior column and quadrilateral plate fractures, and his fractures were reduced through the modified Stoppa approach combined with the first window of the ilioinguinal approach. Pre-operative anteroposterior pelvic radiograph (A) and CT scan (B and C) all showing a comminuted quadrilateral plate fracture on the right side of the pelvis. Pre-operative three-dimensional reconstruction CT scan showing the quadrilateral plate fracture (D–F). Post-operative anteroposterior view (G) showing that the radiographic grade was anatomic. The correct position of the screws can be verified in the iliac oblique view (H) and obturator oblique view (I). The two-ended buttress plate for quadrilateral plate fracture fixation is indicated by the black arrowhead (G–I).