Risk of suprascapular nerve injury during glenoid baseplate fixation for reverse total shoulder arthroplasty: a cadaveric study

Background: Reverse total shoulder arthroplasty (rTSA) is an effective treatment for patients with advanced rotator cuff arthropathy. During implantation of the glenoid baseplate, screws are inserted through the glenoid face into the scapular body to achieve adequate fixation. Placement of peripheral baseplate screws in the superior and posterior glenoid may increase the risk of injury to the suprascapular nerve (SSN). The purpose of this cadaveric study was to evaluate the risk of SSN injury with placement of baseplate screws in the superior and posterior direction. Methods: Twelve cadaveric shoulders were implanted with glenoid baseplates. A bicortical 44-mm screw was placed in both the superior and posterior glenoid baseplate screw holes. Following implantation, the SSN was dissected and visualized through a posterior shoulder approach. The distance from the tip of the screws to the SSN and the distance from the screw's scapular exiting hole to the SSN was recorded. Average distances were calculated for each measurement. Results: The superior screw contacted the SSN in 8 of the 12 specimens (66%). For the superior screw, the average distance from the exiting point in the scapula to the SSN was 9.2 +/- 6.3 mm, with the shortest distance being 3.9 mm. The posterior screw contacted the SSN in 6 of 12 specimens (50%). For the posterior screw, the average distance from the exiting point to the SSN was 8.9 +/- 3.8 mm, with the shortest distance to the nerve being 2.2 mm. Conclusion: Placement of the superior and posterior screws in the glenoid baseplate during rTSA risks injury to the SSN. The safe zone for superior- and posterior-directed baseplate screw is <2 mm from its exiting point on the scapula. Therefore, precise measurements of screw lengths in this area is important in avoiding injury to the SSN. (C) 2020 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved.