Posterior Lumbar plexus block (PLPB) combined with an ipsilateral sacral plexus block is a valuable anaesthetic technique in patients undergoing hip fracture surgery. PLPB is performed through the acoustic window of the lumbar ultrasound trident and the position of the needle tip, before injection of LA, was confirmed by observing quadriceps femoris muscle contraction to peripheral nerve stimulation (i.e., dual guidance). We report an uncommon cause of nerve stimulator malfunction that might impair block performance and promote complications. We add an algorithm to limit the risk of complications.