Korean J Pain.  2021 Jun;34(3):339-345. 10.3344/kjp.2021.34.3.339.

Prediction of successful caudal epidural injection using color Doppler ultrasonography in the paramedian sagittal oblique view of the lumbosacral spine

  • 1Department of Anesthesiology and Pain Medicine, Jeonbuk National University Medical School and Hospital, Jeonju, Korea
  • 2Research Institute of Clinical Medicine of Jeonbuk National University, Jeonju, Korea
  • 3Biomedical Research Institute of Jeonbuk National University Hospital, Jeonju, Korea


Ultrasound-guided caudal epidural injection (CEI) is limited in that it cannot confirm drug distribution at the target site without fluoroscopy. We hypothesized that visualization of solution flow through the inter-laminar space of the lumbosacral spine using color Doppler ultrasound alone would allow for confirmation of drug distribution. Therefore, we aimed to prospectively evaluate the usefulness of this method by comparing the color Doppler image in the paramedian sagittal oblique view of the lumbosacral spine (LS-PSOV) with the distribution of the contrast medium observed during fluoroscopy.
Sixty-five patients received a 10-mL CEI of solution containing contrast medium under ultrasound guidance. During injection, flow was observed in the LSPSOV using color Doppler ultrasonography, following which it was confirmed using fluoroscopy. The presence of contrast image at L5-S1 on fluoroscopy was defined as “successful CEI.” We then calculated prediction accuracy for successful CEI using color Doppler ultrasonography in the LS-PSOV. We also investigated the correlation between the distribution levels measured via color Doppler and fluoroscopy.
Prediction accuracy with color Doppler ultrasonography was 96.9%. The sensitivity, specificity, positive predictive value, and negative predictive value were 96.7%, 100%, 100%, and 60.0%, respectively. In 52 of 65 patients (80%), the highest level at which contrast image was observed was the same for both color Doppler ultrasonography and fluoroscopy.
Our findings demonstrate that color Doppler ultrasonography in the LS-PSOV is a new method for determining whether a drug solution reaches the lumbosacral region (i.e., the main target level) without the need for fluoroscopy.


Anesthesia; Caudal; Contrast Media; Equivalence Trial; Fluoroscopy; Injections; Epidural; Low Back Pain; Lumbar Vertebrae; Sensitivity and Specificity; Ultrasonography; Doppler; Color; Ultrasonography; Interventional


  • Fig. 1 Ultrasound paramedian sagittal oblique view (PSOV) of the lumbosacral level (A). The patient was in the prone position, and the convex ultrasound probe was placed on the patient’s back aligned to the sagittal plane (median sagittal view). The sacrum can be recognized as a horizontal high-echo curve structure, and the L5 layer has a typical “serrated” shape. After checking the sacrum, the sacrum is placed on the right side of the ultrasound window through the cephalad shift of the probe, and the L3 spinous process is visible on the left side. The probe was then shifted by 1-2 fingers in the left lateral direction to ensure that the lamina was visible (paramedian sagittal view). The probe was then tilted slightly toward the midline of the spine (PSOV). In the image presented here, a serrated laminar shape is visible, and hyperechoic shadows of the anterior complex and posterior complex including the dura mater can be observed between the lamina of each level. The color Doppler in (A) shows that the injection flow has reached L5-S1. (B) is a color Doppler image of another patient performed in the same way. The drug solution rises from the caudal region to the cephalad, and Doppler flow can be observed between each lamina. Doppler flow can be observed at L5-S1, L4-L5, and L3-L4, and the anteroposterior and lateral fluoroscopy images show that the contrast medium is distributed at the corresponding levels.

  • Fig. 2 Consolidated Standards of Reporting Trials (CONSORT) flow diagram.

  • Fig. 3 The figure shows the correlation between the highest level of injection flow measured using color Doppler ultrasonography in the paramedian sagittal oblique view at the lumbosacral level (LS-PSOV) and the highest level at which contrast image was identified using fluoroscopy. In 52 of 65 patients (80%), the highest level at which image (Doppler flow or contrast medium) was observed was the same for both color Doppler ultrasonography and fluoroscopy: not detected (n = 3), L5-S1 (n = 22), L4-L5 (n = 24), L3-L4 (n = 3). The difference in the level measured by the two modalities was one level in 11 patients and two levels in two patients (16.9% and 3.0%, respectively). ND: not detected.


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