A thorough knowledge of the anatomy of the terminal branch of the posterior interosseous nerve (PIN) and its relationship to the anterior interosseous nerve (AIN) is essential in facilitating regional anesthetic blocks as well as in planning surgical exposures for wrist surgery. Division of the PIN has been recommended in patients with persistent wrist pain who have not responded to conservative treatment and whose physical demands are low. 1 Denervation of the PIN is undertaken as an adjunct to salvage procedures for arthritis of the wrist, such as four-corner fusion and proximal row carpectomy. In addition, the last motor branch of the PIN has been a source of nerve grafts.The wrist joint capsule is supplied by the terminal branches of the AIN, PIN, lateral cutaneous nerve of the forearm, median nerve, and dorsal branch of the ulnar nerve. Total wrist denervation may provide pain relief, but multiple incisions and the possible loss of proprioception are potential problems. 2-5 Partial denervation of the terminal branches of the AIN and PIN can be achieved with a single incision on the dorsum of the wrist. 2 The current study focuses on the terminal branches of the PIN, particularly in the forearm, and analyzes the consistency of its anatomic location, its dimensions, its last motor branch, and its relationship to the most proximal part of ulnar head and the AIN, as these parameters may have clinical relevance for diagnostic and therapeutic procedures in and around the wrist. MethodsThirty embalmed forearms, 15 right and 15 left, 18 males and 12 females, with a mean age of 81 (range 37 to 96 years) were dissected. Demographic data were obtained from the records maintained in the anatomy department. These selected Keywords ► cadaveric wirst study ► terminal posterior interosseous nerve ► denervation wrist surgery AbstractA thorough knowledge of the anatomy of the terminal branch of the posterior interosseous nerve (PIN) and its relationship to the anterior interosseous nerve (AIN) is essential in facilitating regional anesthetic blocks and planning surgical exposures for wrist surgery and arthrodesis of wrist and proximal row carpectomy. This cadaveric study focused on the anatomy and course of the PIN and its anatomical relationships at the distal forearm. Thirty embalmed cadaver forearms were dissected using microsurgical techniques. A structured pro forma was used to collect data. The PIN was consistently found in the fourth extensor compartment in all specimens. The last motor branch was given off 46.9 AE 8.4 mm (mean AE standard deviation) from the most proximal part of the ulnar head. The AIN was found lying consistently on the anterior aspect of the interosseous membrane, being on average 2.8 AE 0.2 mm (mean AE standard deviation) from the PIN. This knowledge will facilitate the planning of diagnostic and therapeutic procedures associated with the wrist.