Ultrasound Block of the Medial Branch: Learning the Technique Using CUSUM Curves

Blocking the medial branch of the lumbar facet joints plays a fundamental diagnostic and therapeutic role in the treatment of lumbar pain. Attempts to replace the typical guided X-ray techniques with ultrasound-guided techniques have also involved treating the lumbar medial branches. By applying the cumulative sum control chart (CUSUM method), we sought to evaluate the learning curve associated with ultrasound-guided block of the lumbar medial branches in operators experienced in locoregional anesthesia but without expertise in pain therapy.

This study aimed to use a repeatable method to identify the learning curve of the ultrasound-guided medial branch block.

This study was a prospective application of over forty consecutive procedures of ultrasound lumbar medial branch block.

The ultrasound medial branch blocks were performed under ultrasound guidance with confirmation of correct positioning using fluoroscopy on a population of patients with low back pain with any body mass index (BMI).

The operator's performance was assessed using the learning curve cumulative summation test (LS-CUSUM).

The correct target was reached in 29 procedures out of a total of 40 (72.5%) and in 29 out of 36 procedures performed on patients with BMI <30 (80.5%). According to the CUSUM algorithm, 11 further consecutive successes would have been necessary (47 procedures in total) to achieve a proven learning of the technique in the group with only patients with a BMI <30, with a further 22 consecutive successes (62 procedures in total) in the general group. Ultrasound-guided block of the lumbar medial branch appears not to be optimal for training beginner/intermediate operators seeking to replace guided X-ray procedures with guided ultrasound.