LAUSR

Application of external fixators for comminuted, open, or unstable elbow injuries is not infrequent, and carries the risk of iatrogenic injury to the radial nerve via pin placement [1–4]. This cadaveric CTbased investigation reports on the placement location and angle of external fixator pins in an effort to minimize this injury risk [5]. There have been other anatomic studies of the radial nerve, but these largely focus on the location of the nerve laterally, and not in a more three-dimensional manner [6, 7]. This investigation found that the proximal anterolateral area and distal posterolateral areas of the humerus are the relatively safe quadrants for halfpin placement, and the authors recommend placement into these two areas to minimize risk to the radial nerve. As the distal humerus is not a simple cylinder, half-pin placement can be more difficult if attempting to insert into the lateral crest. Therefore, the authors recommend placing distal pins approximately 50mm from the center of rotation of the elbow with an insertion angle of 30–45 degrees aiming anterior to avoid the lateral crest and more anterior radial nerve. If the surgeon was to aim from anterior to posterior at 30 degrees, the nerve was found at a mean of 58.3mm from the elbow, and the risk of injury from the drill sleeve or even pin would be very significant; the distance from nerve to elbow was nearly doubled with a posterior to anterior insertion angle. However, the triceps tendon and injury to this is critical to avoid in order to optimize elbow motion and decrease scarring of the triceps. This is why a straight posterior elbow fixation pin placement is not recommended, and this study validates pin placement away from the tendon in a safe manner. Most of the other anatomical investigations about radial nerve locations in relation to humerus or elbow fixation constructs rely on palpable or other easy to identify structures, whereas this investigation used the wire placed for a hinged external fixator as the location from which to measure from. Clinically, this would be very helpful if placing a hinged external fixator, as this wire would be in place, but results from this study also can be extrapolated to intraoperative use by locating this wire position via C-arm and then measuring from this spot. Despite the well described location in this analysis, I would recommend avoidance of purely percutaneous insertion of the distal humeral halfpins, as anatomic locations of the radial nerve and other structures can be altered with bony and soft tissue injury, and avoidance of iatrogenic injury to the radial nerve is critical to obtain an optimal outcome.