Using Radiology images to characterize an angle of insertion for S1/S2 and SI joint injections: A retrospective...

Sacroiliac (SI) joint, S1 and S2 nerve root pathology are well documented in literature as common etiologies for low back pain. Evidence demonstrating starting angle of needle insertion during S1/S2 transforaminal and SI joint injections are lacking. Using computerized tomography (CT) radiography of the lumbosacral spine, this retrospective observational study seeks to characterize a starting angle of needle insertion at the sacral spine.

This was a single-centered, retrospective observational study performed on adult cancer patients who had CT radiography of their lumbosacral spine, without significant sacral pathology, at our hospital from January 2016 and May 2021. For each patient, we determined the anatomical location of where the S1/S2 neural foramen and SI joint widens up. Using the annotation tools available in EIM image viewer, a maximum level and minimum level of insertion was recorded in order to calculate the average angle of insertion needed for procedural performance.

Through the analysis of 64 patients, average angle of insertion was 25° ​± ​1.36 for S1, 34° ​± ​1.93 for S2, and 33° ​± ​1.95 for SI injections. There were no statistically significant differences in angles when stratified based on laterality, gender, age, and BMI.

Average angle of insertion to target the S1, S2 neural foramen and SI joint are 25° ipsilateral oblique, 34° ipsilateral oblique, and 33° contralateral oblique respectively starting with a squared sacral endplate. To our knowledge, there are no studies in the current literature that have attempted to identify an entry angle to target these anatomical structures.

Chronic Pain, SI Joint Pain, Steroid Injection, S1 Transforaminal, S2 Transforaminal, Needle Placement.