Anatomic Differences in the Sacral Hiatus During Caudal Epidural Injection Using Ultrasound Guidance

Abstract

audal epidural steroid injection can be helpful for treatment of symptomatic low back pain caused by lumbar disk herniation or spinal canal stenosis. [1][2][3][4][5][6] The caudal epidural steroid injection technique involves injection of a steroid into the epidural space via the sacral hiatus and is often preferred by nonanesthetists because it carries a lower risk of inadvertent thecal sac puncture or intrathecal injection. 7,8 The sacral hiatus is a triangular aperture located at the caudal end of the sacrum and bordered laterally by 2 sacral cornua. The skin, subcutaneous fat, and sacrococcygeal ligament cover the hiatus. When the needle passes through the sacrococcygeal ligament, the steroid is injected in the epidural space, as the hiatus directly communicates with the epidural space. Therefore, successful caudal epidural steroid injection relies on proper placement of the needle in the epidural space. However, anatomic variations of the sacrum pose a challenge during injection. 9 In the event of blind -young Park, MD, PhD, Dong Rak Kwon, MD, PhD, Hee Kyung Cho, MD, PhD Received December 16, 2014, Gi ORIGINAL RESEARCHObjectives-The aim of this study was to clarify differences in the anatomic structure of the sacral hiatus and angle of needle insertion during caudal epidural steroid injection using ultrasound guidance in patients according to sex and age.Methods-A total of 237 patients with low back pain with or without sciatica were included. Sonograms of the sacral hiatus were obtained, and caudal epidural steroid injection using ultrasound guidance was performed in all patients. The intercornual distance, diameter of the sacral canal, thickness of the sacrococcygeal ligament, optimal angle for needle insertion, and actual angle of needle insertion were measured.Results-Between men and women, significant differences were observed for the intercornual distance (17.7 versus 16.5 mm; P < .01) and thickness of the sacrococcygeal ligament (4.3 versus 3.9 mm; P = .02). In all patients, the thickness of the sacrococcygeal ligament (r = 0.28) and diameter of the sacral canal (r = 0.40) were positively correlated with the optimal angle for needle insertion (P < .01). In women, the thickness of the sacrococcygeal ligament (r = -0.24), diameter of the sacral canal (r = -0.27), optimal angle for needle insertion (r = -0.29), and actual angle of needle insertion (r = -0.18) were negatively correlated with age. In men, only the diameter of the sacral canal was negatively correlated with age (r = -0.30).Conclusions-We found that the sacral hiatus has anatomic differences between patients of different sexes and ages. Understanding these differences, especially in women, may improve the safety and reliability of caudal epidural steroid injection.

Caudal Epidural Block: An Updated Review of Anatomy and Techniques

“…The mean anterior-posterior (AP) diameter of sacral hiatus at its apex ranges from 4.6 ± 2 mm to 6.1 ± 2.1 mm [6, 7, 9–14] and decreased with age [14]. In clinical settings, an AP diameter of sacral hiatus at the apex of less than 3.7 mm was associated with difficulty in inserting a needle into the caudal epidural space by blind technique [13].…”

Imaging anatomy of the vertebral canal for trans‐sacral hiatus puncture of the lumbar cistern

“…Kao and Lin (2017) reviewed values for the mean depth of the sacral hiatus (i.e., the anteroposterior diameter of the midsagittal vertebral canal) at the level of its apex. This was reported to be 6.0 mm by Sekiguchi et al (2004), 4.5 mm by Crighton et al (1997), or 4.5 mm by Senoglu et al (2005), and this value decreases with age (Park, Kwon, & Cho, 2015). However, the hiatus depth may be as little as 2 mm or less in 1–6.3% of cases (Senoglu et al, 2005).…”

Anatomy and Clinical Significance of Sacral Hiatus

“…The length of the sacral hiatus has been linked to complications in procedures involving entry into the sacral canal 24,25 . It has been found that the longer length of the sacral hiatus is directly related to increase in the incidence of dural puncture.…”