Extra-articular screw placement strategy in Stoppa approach based on three-dimensional reconstruction model

Abstract

The study aimed to explore an extra-articular screw placement strategy in Stoppa approach. Radiographic data of patients who underwent pelvic computed tomography from January 2016 to June 2017 were imported into Materiaise's interactive medical image control system software for three-dimensional reconstruction. Superior and lower margins of acetabulum and ipsilateral pelvic brim could be observed simultaneously through inlet-obturator view. A horizontal line from superior acetabular margin intersected pelvic brim at point "A" and another vertical line from lower margin intersected pelvic brim at point "B" were drawn, respectively. Lengths form sacroiliac joint to "A" (a), "A" to "B" (b), and "B" to pubic symphysis (c) were measured. Patients were divided into four groups depending on gender and side difference of measured hemi-pelvis: male left, male right, female left, and female right. Lengths of adjacent holes (d) and spanning different holes (e) of different plates were also measured. Mean lengths of a, b, c in four groups were 40.94 ± 1.85 mm, 40.09 ± 1.93 mm, 41.78 ± 3.62 mm, and 39.77 ± 2.23 mm (P = 0.078); 40.65 ± 1.58 mm, 41.48 ± 1.64 mm, 40.40 ± 1.96 mm, and 40.66 ± 1.70 mm (P = 0.265); 57.03 ± 3.41 mm, 57.51 ± 3.71 mm, 57.84 ± 4.40 mm, and 59.84 ± 4.35 mm (P = 0.165), respectively. Mean d length of different plates was 12.23 mm. Average lengths spanning 1, 2, 3 and 4 holes were 19.33 mm, 31.58 mm, 43.80 mm, and 55.93 mm. Our data showed that zones a and c could be safely inserted three and four screws. Penetration into hip joint could be avoided when vacant 3-hole drilling was conducted in zone b. Fracture line in zone b could serve as a landmark for screw placement.

Figure 1

Three-dimensional reconstruction model of pelvis was obtained by MIMICS software. (A) Uninjured hemi-pelvis and other parts of pelvis were marked with red and blue colors, respectively; (B) three-dimension reconstruction inlet-obturator view of uninjured hemi-pelvis.

Figure 2

Lengths of three zones were measured successively by surface distance measurement function of MIMICS software. (A) Length measurement of b; (B) length measurement of a; (C) length measurement of c.

Figure 3

Distances of adjacent holes (d) and lengths spanning one, two, three, and four holes (e₁, e₂, e₃, and e₄) of different plates were measured.

Figure 4

Zone b was further divided equally into three parts to accomplish extra-articular screw placement for patients of acetabular fractures. (A) Schematic diagram of three parts in zone b and plating technique in Stoppa approach; (B) fracture line in superior 1/3 of zone b; (C) fracture line in middle 1/3 of zone b; (D) fracture line in inferior 1/3 of zone b.

Figure 5

Preliminary clinical application of the technique proposed in this study. (A) Preoperative anteroposterior radiograph of a male patient with bilateral acetabular fractures; (B) extra-articular screw placement was accomplished based on the results obtained in this study.