Anatomical relation between S1 sacroiliac screws' entrance points and superior gluteal artery

Abstract

Background: To conduct radiologic anatomical study on the relation between S1 sacroiliac screws' entry points and the route of the pelvic outer superior gluteal artery branches with the aim to provide the anatomical basis and technical reference for the avoidance of damage to the superior gluteal artery during the horizontal sacroiliac screw placement.

Methods: Superior gluteal artery CTA (CT angiography) vascular imaging of 74 healthy adults (37 women and 37 men) was done with 128-slice spiral CT (computed tomography). The CT attendant-measuring software was used to portray the "safe bony entrance area" (hereinafter referred to as "Safe Area") of the S1 segment in the standard lateral pelvic view of three-dimensional reconstruction. The anatomical relation between S1 sacroiliac screws' Safe Area and the pelvic outer superior gluteal artery branches was observed and recorded. The number of cases in which artery branches intersected the Safe Area was counted. The cases in which superior gluteal artery branches disjointed from the Safe Area were identified, and the shortest distance between the Safe Area and the superior gluteal artery branch closest to the Safe Area was measured.

Results: Three cases out of the 74 sample cases were excluded from this study as they were found to have no bony space for horizontal screw placement in S1 segment. Among the remaining 71 sample cases, there are 32 cases (45.1%) where the deep superior branch of superior gluteal artery passes through the Safe Area of S1 entrance point. There was no distinguishing feature and rule on how the deep superior branches and the Safe Area overlapped. In the 39 cases in which superior gluteal artery branches disjointed from the Safe Area, the deep superior branches of superior gluteal artery were the branches closest to the Safe Area and the part of the branch closest to the Safe Area was located in front of the widest part of the Safe Area. The shortest distance between the deep superior branch and the Safe Area is 0.86 ± 0.84 cm.

Conclusion: There is a high risk of accidental injury of the deep superior branches of superior gluteal artery in the process of S1 sacroiliac screw placement. Even if the entry points are located in the safe bony entrance area, the absolute secure placement cannot be assured. We suggest that great attention should be paid to make thorough preoperative plans.

Keywords: Anatomy; CTA; Pelvis; Sacroiliac screw; Superior gluteal artery.

Fig. 1

Two horizontal lines were drawn through the bilateral sacroiliac joints from the right to the left in S1 segment, and they were limited in the bone substance and could not break both the front and back margins of sacrum, canales sacralis, nor sacral foramen. The two lines were defined respectively as passing through the anterior and posterior edges of the bone substance of the pelvic posterior ring. The intersection points of the two lines and the outer margins of ilium were marked and named as point As (S1 sacroiliac screw entrance points)

Fig. 2

Two horizontal lines were drawn through the bilateral sacroiliac joints from the right to the left in S1 segment, and they were limited in the bone substance and could not break both the front and back margins of sacrum, canales sacralis, nor sacral foramen. The two lines were defined respectively as passing through the anterior and posterior edges of the bone substance of the pelvic posterior ring. The intersection points of the two lines and the outer margins of ilium were marked and named as point As (S1 sacroiliac screw entrance points)

Fig. 3

The length between the two horizontal lines aforesaid in Figs. 1 and 2 (the width of safe insertion region) was named as S

Fig. 4

The point As were connected to form a region (green borders in the pictures) named as the S1 sacroiliac screw’s safe entrance bony area (Safe Area for short). The relations of the Safe Area and various branches of superior gluteal artery outside of the pelvis were observed. In Fig. 4, the deep superior branch of superior gluteal artery just passes through the Safe Area. In contrast, the branches of superior gluteal artery and the Safe Area do not intersect in Fig. 5, “D” means the shortest distance between the bony Safe Area and the deep superior branch

Fig. 5

The point As were connected to form a region (green borders in the pictures) named as the S1 sacroiliac screw’s safe entrance bony area (Safe Area for short). The relations of the Safe Area and various branches of superior gluteal artery outside of the pelvis were observed. In Fig. 4, the deep superior branch of superior gluteal artery just passes through the Safe Area. In contrast, the branches of the superior gluteal artery and the Safe Area do not intersect in Fig. 5, “D” means the shortest distance between the bony Safe Area and the deep superior branch