Anatomic Structures at Risk With Antegrade Intramedullary Fixation of the First Metacarpal Using Three Start Points: Is There A Safe Zone?

Purpose: Intramedullary fixation of extraarticular first metacarpal fractures using a percutaneous technique may risk injury to important anatomic structures. The purpose of this study is to evaluate potential safe zones for antegrade implant entry of the first metacarpal and describe the anatomical structures at risk. Methods: Ten cadaveric hands were used to evaluate three start points located at the first metacarpal base: volar-radial, dorsal-radial, and dorsal-ulnar. A fluoroscopic imaging system was used to guide percutaneous placement of 0.8 mm × 100 mm guidewires and 2.0 mm diameter screws. After screw placement the guidewires were left in place and soft tissues were dissected to identify at risk anatomic structures. Results: The identified structures at risk were the radial artery, superficial branch of the radial nerve (SBRN), extensor pollicis longus (EPL) tendon, abductor pollicis longus (APL) tendon, and extensor pollicis brevis (EPB) tendon. A volar-radial start point risks injury to the APL tendon (8.3 ± 5.4 mm). A dorsal-radial start point risks injury to the SBRN (2.2 ± 3.4 mm), APL (1.4 ± 1.8 mm), and EPB (1.2 ± 2.1 mm) tendons. A dorsal-ulnar start point risks injury to the SBRN (5 ± 4.2 mm), radial artery (3.5 ± 3.1 mm), and EPL tendon (3.5 ± 2.4 mm). Conclusions: Dorsal-radial and dorsal-ulnar start points risk injuring critical anatomic structures: radial artery, SBRN, EPL, APL, and EPB. A volar-radial start point may risk injury to the APL tendon but presents the lowest risk of injury to neurovascular structures. Clinical relevance: This study identifies key anatomic structures at risk associated with three common percutaneous entry points. The volar-radial start point demonstrated the lowest risk to neurovascular structures and may represent a safe approach for percutaneous intramedullary fixation.