Use of a curved needle to facilitate four-in-one nerve block performance after total knee arthroplasty in elderly patients: a randomized clinical trial.

Background: Peripheral nerve block is the main analgesic technique for total knee arthroplasty (TKA) in elderly patients. Accurate delivery of the needle tip to the target nerve under ultrasound-guided is a prerequisite for successful nerve block. Failed needle-tip positioning in sciatic nerve (SN) or medial femoral cutaneous nerve (MFCN) block can be due to anatomical structure shadow.