RT Journal Article SR Electronic T1 Ultrasound-Guided Retroclavicular Block (aka Posterior Approach Infraclavicular Block): Anatomical Variation of the Clavicle Limits Block Feasibility JF Regional Anesthesia & Pain Medicine JO Reg Anesth Pain Med FD BMJ Publishing Group Ltd SP 658 OP 659 DO 10.1097/AAP.0000000000000456 VO 41 IS 5 A1 Beh, Zhi Yuen A1 Hasan, Mohd Shahnaz A1 Lai, Hou Yee YR 2016 UL http://rapm.bmj.com/content/41/5/658.2.abstract AB