Distance of the radial nerve from distal interlocking screws in long-stem reverse shoulder arthroplasty: a cadaveric analysis

Long-stem reverse total shoulder arthroplasty (rTSA) with interlocking screws is indicated for trauma and revision shoulder arthroplasty and enables fixation of the prosthesis without cement or a plate while maintaining rotational stability. We investigated the distance of the radial nerve from the distal interlocking screws of the long-stem rTSA to recommend a safe approach in placement of this prosthesis. The 3 distal 4.5-mm cortical interlocking screws of a 200-mm long-stem rTSA (FX Shoulder) were inserted with the humeral prosthesis at 0° and 20° of retroversion in 8 cadaveric specimens. A curvilinear incision from the anterolateral cubital fossa extending superolaterally along the humerus was made to expose the radial nerve between the brachialis and brachioradialis. The shortest distance from each screw to the radial nerve at 90° of elbow flexion was measured, and mean and standard deviations were calculated. At 0° of retroversion of the humeral prosthesis, the most distal 3 screws were a mean 9.5, 4.2, and 0.93 mm away from the radial nerve, respectively, whereas 20° of retroversion yielded mean screw-to-radial-nerve distances of 20, 15, and 8.7 mm, respectively. The mean distance to the radial nerve increased with increasing retroversion of the stem. We recommend using at least 20° of retroversion and making an incision anteriorly with careful retraction of soft tissues posteriorly on the humeral shaft to enable direct visualization during placement of the most distal interlocking screws to protect neurovascular structures.