Ultrasound-guided PNS system implantation. The Tuohy needle (arrow-head) was inserted with a conventional infraclavicular approach, and the needle tip was placed between the axillary artery and the medial cord. After a 10-ml normal saline injection, the lead (arrow) was inserted until resistance was felt. The lead’s proper position was settled with repeated electrical stimulation during lead withdrawal. PM: pectoralis major muscle, Pm: pectoralis minor muscle, MC: medial cord, LC: lateral cord, A: axillary artery, V: axillary vein, PC: posterior cord, PNS: peripheral nerve stimulation.