Lateral External-fixation Adjacent to Radial Nerve.

Introduction The aim of our study was to describe the injury pattern and outcomes of active-duty subjects that underwent humeral external fixation and to determine if the placement of external fixator pins outside of the radial nerve safe zones is correlated with injury to the radial nerve. Materials and methods We examined all US Service members treated with humeral external fixation at our facility from June 2005 through June 2015. The mechanism of injury, injury pattern, location of external fixation application, pre- and postoperative radial nerve function, presence or absence of radial nerve transection from injury or external fixation, anatomic location of pins in relation to the radial nerve safe zone, and final radial nerve outcomes were recorded. We defined the proximal safe zone as 5 cm distal to the acromion to 14.8 cm proximal to the lateral epicondyle, and we defined the distal safe zone as the proximal 70% of the transepicondylar width of the humerus when projected proximally from the lateral epicondyle. Results  For our study, 123 patients were identified over our date range, and 16 subjects were included with documentation regarding nerve function/injury characteristics, appropriate radiographs, and active duty status. Around 80% of injuries resulted from a blast mechanism, and 80% of injury patterns included either an intraarticular or open fracture. The radial nerve safe zone was violated in 15 of the 16 subjects (94%). The one subject with a safe construct did not sustain a nerve injury. Complete preoperative documentation on nerve function was only available for half of the subjects. Two of five subjects known to have intact function prior to external fixation had a postoperative neurologic deficit (40%). Of eight subjects with unknown radial nerve function prior to external fixation, seven subjects had full nerve function at the final follow up, and one subject had partial sensory function only. Of the three subjects with impaired preoperative radial nerve function, two made a full recovery, and the third recovered sensory function only. Around 50% of all subjects required medical retirement. Conclusion External fixation of upper extremity injuries in combat is rarely absolutely indicated, often results in the placement of pins outside of the radial nerve safe zone, and is associated with up to a 40% incidence of radial nerve injury.