Korean J Pain.  2023 Jan;36(1):98-105. 10.3344/kjp.22227.

Measurement of S1 foramen depth for ultrasound-guided S1 transforaminal epidural injection

• Kim YS
• Park S
• Lee C
• Lee SK
• Doo AR
• Son JS

• KMID: 2537616
• DOI: http://doi.org/10.3344/kjp.22227

Abstract

Background
Ultrasound-guided first sacral transforaminal epidural steroid injection (S1 TFESI) is a useful and easily applicable alternative to fluoroscopy or computed tomography (CT) in lumbosacral radiculopathy. When a needle approach is used, poor visualization of the needle tip reduces the accuracy of the procedure, increasing its difficulty. This study aimed to improve ultrasound-guided S1 TFESI by evaluating radiological S1 posterior foramen data obtained using three-dimensional CT (3D-CT).
Methods
Axial 3D-CT images of the pelvis were retrospectively analyzed. The radiological measurements obtained from the images included 1st posterior sacral foramen depth (S1D, mm), 1st posterior sacral foramen width (S1W, mm), the angle of the 1st posterior sacral foramen (S1A, °), and 1st posterior sacral foramen distance (S1ds, mm). The relationship between the demographic factors and measured values were then analyzed.
Results
A total of 632 patients (287 male and 345 female) were examined. The mean S1D values for males and females were 11.9 ± 1.9 mm and 10.6 ± 1.8 mm, respectively (P < 0.001); the mean S1A 28.2 ± 4.8° and 30.1 ± 4.9°, respectively (P < 0.001); and the mean S1ds, 24.1 ± 2.9 mm and 22.9 ± 2.6 mm, respectively (P < 0.001); however, the mean S1W values were not significantly different. Height was the only significant predictor of S1D (β = 0.318, P = 0.004).
Conclusions
Ultrasound-guided S1 TFESI performance and safety may be improved with adjustment of needle insertion depth congruent with the patient’s height.

Keyword

Epidural Space; Fluoroscopy; Injections; Epidural; Low Back Pain; Pain Management; Radiculopathy; Sacrum; Steroids; Tomography; X-ray Computed; Ultrasonography; Interventional

Figure

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  Fig. 1 A flowchart depicting patient enrollment.

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  Fig. 2 Measured parameters using axial computed tomography at the level of the 1st posterior sacral foramen. S1D: 1st posterior sacral foramen depth defined as the length from the posterior surface of the sacrum to the margin of the sacral canal, S1W: 1st posterior sacral foramen width defined as the largest diameter of the S1 posterior foramen, S1A: angle of the 1st posterior sacral foramen defined as the angle between the S1 posterior foramen and the midsagittal line of the sacrum, S1ds: 1st posterior sacral foramen distance defined as the distance between the midsagittal line of the sacrum and the parallel line passing through the center of the S1 posterior foramen.

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  Fig. 3 Relationships between S1D and the patients’ height. (A) Male. (B) Female. S1D: 1st posterior sacral foramen depth.

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  Fig. 4 Bland–Altman plot comparing predicted and measured values of S1D. (A) Male. (B) Female. S1D: 1st posterior sacral foramen depth, SD: standard deviation.

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