An Analysis of the Surface Anatomical Location of the Posterior-inferior Margin of the Sacroiliac Joint

Abstract

Background: The blind sacroiliac joint (SIJ) block cannot always be performed accurately; it is commonly performed in the office based setting because intraarticular and periarticular injections are effective for SIJ pain. However, knowledge on the surface anatomy of the SIJ is lacking. The purpose of this study was to analyze the surface anatomical location of the posterior-inferior margin of the SIJ. Methods: After informed consent was obtained, fifty patients undergoing SIJ block in the prone position were examined. The oblique angles where the anterior-inferior margin and the posterior-inferior margin of the SIJ overlap on X-ray were evaluated. In addition, the surface anatomical relationships between the posterior-inferior margin of the SIJ on X-ray and the posterior superior iliac spine (PSIS) and sacral hiatus by palpation were assessed. Results: The oblique angle was 5.4 2.9. The vertical and transverse distance between the posteriorinferior margin of the SIJ and PSIS were 3.8 0.8 cm and 0.9 0.6 cm, respectively. The vertical and transverse distance between the posterior-inferior margin of the SIJ and the midpoint of the sacral hiatus were 3.4 0.7 cm and 3.9 0.6 cm, respectively. Only the vertical distance between the posterior-inferior margin of the SIJ and PSIS showed significant difference between the male and the female groups (P = 0.0016). Conclusions: The measurements in this study can be used as a reference standards for the blind SIJ block.