Ultrasound-guided lumbar medial branch block in obese patients: a fluoroscopically confirmed clinical feasibility study.

BACKGROUND AND OBJECTIVES Obesity is a major risk factor for lower back pain. Fluoroscope-guided medial branch block is a common diagnostic tool in these patients. Although approach to the facet joint guided by ultrasound has been demonstrated successfully in lean patients, its success in obese patients is unknown.We therefore evaluated the success rate of real-time ultrasound approach in obese patients in a clinical feasibility study. METHODS We performed a total of 84 medial branch blocks in 20 obese patients (body mass index, >30 kg/m2) using ultrasound. We studied the success rate, measured depth to the facet joint, and assessed radiation dose and pain relief. RESULTS Our success rate was 62% (52/84 blocks) when using ultrasound to guide needle placement. The average distance from skin to target point at the transverse process was 76 mm (SD, 15 mm). Skin-target depth was significantly different between L4 and L5 on both sides (P = 0.01). The needle advancement could not be tracked to the target. The verbal rating scale scores before, immediately after, and 24 hrs after the procedure were 7.1 (SD, 2.4), 4.3 (SD, 3.1), and 3.8 (SD, 2.7), respectively. The average radiation dose was 0.226 mGy/m2 (SD, 0.196 mGy/m2). CONCLUSION Medial branch blocks in obese patients cannot be performed by ultrasound guidance exclusively.