Area of cutaneous sensory loss following an ultrasound guided posterior antebrachial cutaneous nerve (PABCN) block via the fat-filled tunnel” (FFT) in volunteers.

Background and Objectives: The aim of the study was to investigate a novel ultrasound-guided posterior antebrachial cutaneous nerve (PABCN) block based on visualising the nerve within the fat-filled flat tunnel (FFFT) and describe the area of cutaneous sensory loss. Methods: Twelve healthy volunteers were included in the study. The PABCN was identified within the FFFT in the upper arm using high frequency ultrasound. The nerve was blocked using an in-plane needle guidance technique with 1ml 2% lignocaine. Sensory loss to pinprick was evaluated 15 minutes after performing the block and the cutaneous sensory block area (CSBA) mapped. Results: Ultrasound visualization of the PABCN in the FFFT was possible in all volunteers. The median distance of the PABCN to the lateral epicondyle of the elbow was 67.5 (range, 54-105) mm. Sensory loss to pinprick extended from the posterior aspect of the distal upper arm and posterior forearm to the wrist. The median CSBA was 103 (range, 61-341) cm2. Two volunteers had sensory block over the anterior forearm of 29 and 10 cm2 respectively. This amounted to 11% and 4.5% of the total CSBA. One volunteer had a sensory block over the dorsum of the hand of 39cm2 (15% of the total CSBA). Conclusions: The results of this study indicate that the FFFT can be a useful sono-anatomical landmark in identifying the PABCN and may serve as a target for injection. Although sensory block is predominantly confined to the posterior distal arm and forearm, inter-individual variability in the area and distribution was observed. Sensory block in the anterior forearm and dorsum of the hand can occur.