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

BACKGROUND: 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. AIM: This study aimed to use a repeatable method to identify the learning curve of the ultrasound-guided medial branch block. SETTINGS AND DESIGN: This study was a prospective application of over forty consecutive procedures of ultrasound lumbar medial branch block. MATERIALS AND METHODS: 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). STATISTICAL ANALYSIS: The operator's performance was assessed using the learning curve cumulative summation test (LS-CUSUM). RESULTS AND CONCLUSIONS: 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.