Posterior second sacral alar iliac screw insertion: anatomic study in a Chinese population

Abstract

Objective To provide radiographic parameters for optimal placement of posterior second sacral alar iliac (S2AI) screw for instrumentation and fusion of scoliosis to the second sacral level in a Chinese population. Methods S2AI screw trajectories were mapped on threedimensional computed tomography (3DCT) reconstructions of 60 normal adult pelvises. 1 mm inferior and 1 mm lateral to the S1 dorsal foramen were chosen as the entry point, and ideal S2AI screw trajectories were explored by rotating and cutting the 3D pelvis, ensuring that the trajectories were of maximum length and width. The directions and depth of these determined trajectories were then measured. Results The ideal S2AI screw trajectories could be found in each pelvis. The left and right screw trajectory parameters for males were shown as follows: angulation was L 29.15 ± 8.60°vs. R 29.96 ± 8.28°(p = 0.286) caudally in the sagittal plane and L 36.49 ± 3.14°vs. R 37.16 ± 3.14°(p = 0.165) laterally in the transverse plane. The maximal and intrasacral lengths of trajectory were L 121.25 ± 8.33 vs. R 120.63 ± 7.54 mm (p = 0.460) and L 26.20 ± 3.31 vs. R 26.92 ± 4.76 mm (p = 0.268). The entry point was L 28.87 ± 3.33 vs. R 29.79 ± 3.55 mm (p = 0.186) lateral to the second sacral midline, and L 44.14 ± 11.87 vs. R 43.89 ± 12.53 mm (p = 0.687) underneath the skin. The trajectories for females were more caudal (L: 34.50 ± 6.56°vs. 29.15 ± 8.60°, p = 0.009; R: 35.72 ± 7.53°vs. 29.96 ± 8.28°, p = 0.007) in the sagittal plane, but the lateral angulation in the transverse plane showed no difference between genders (p [ 0.05). The female iliac medullar cavities were obviously narrower than those of males (L: 14.76 ± 2.46 vs. 16.98 ± 3.52, p = 0.006; R: 14.94 ± 2.60 vs. 17.00 ± 2.81, p = 0.005). Although the average maximal length of trajectories for females were about 5 mm shorter than those of males, intrasacral length were equal to those of males. Furthermore, both the distance from entry point to the S2 midline and skin in the transverse plane showed no difference between genders. Conclusion The feasibility to insert S2AI screws to the sacrum and ilium in an Asian population along with the ideal entry angle and length of trajectory were identified for clinical practice.

The three-dimensional printed template guided technique for S2AI screw placement and a comparison with freehand technique

“…CA presented signi cant differences between males and females. This result is consistent with a previous study from Zhu et al, a radiographic study assessing optimal S2AI screw placement and presented that CA in females have 4 to 5 degrees more caudal trajectory compared with males [15]. But a study from Shillingford showed there is no signi cant differences in the CA or MA between females and males [2].…”

“…The average max-length of trajectory in females was approximately 8 mm shorter than that in males. Compared with previous study from Zhu et al [15], ML is different from their investigation in which the average max-length of trajectory in females was approximately 5 mm shorter than that in males. In clinical practice, the optional S2AI trajectory exceeds more the length of usually-used screw.…”

Comparative tomographic study of the S2-alar-iliac screw versus the iliac screw

“…The use of screws in the iliac bone reduces the incidence of these complications compared with the Galveston technique. However, the use of iliac screws may also present problems, the most common of which are screw prominence and surgical wound infection [5][6][7]. The S2AI fixation technique, originally described by Kebaish and Sponseller, reduces the incidence of these problems due to minimal dissection of soft tissues and an insertion point that is far from the skin, which facilitates the construction of the system since the entry point is aligned with the lumbar and S1 pedicular screws [8,9].…”

Tomographic Study of the S2-Alar-Iliac Screw Technique in Brazilian Men

“…The studies describe a population comprised of 50% males and 50% females and demonstrate little difference between the sexes. [11][12][13] However, others showed that there are indeed anatomical differences between the sexes and between populations, [14][15][16][17] which justifies the development of studies in different populations in order to analyze the average anatomical parameters of each population group.…”