• Jeremiah T Lowe, Sarah M Lawler, Edward J Testa, and Andrew Jawa.
• New England Baptist Hospital, Boston, MA, USA; Boston Sports and Shoulder Center, Waltham, MA, USA.
• J Shoulder Elbow Surg. 2018 Oct 1; 27 (10): 1845-1851.

HypothesisGrammont-style reverse shoulder arthroplasty (RSA) has an increased risk of nerve injury compared with anatomic total shoulder arthroplasty (TSA) due to arm lengthening. We hypothesized that an RSA with a lateralized glenosphere and 135° neck-shaft angle would reduce humeral lengthening and decrease the risk of nerve injury to the level of a TSA.MethodsThe study prospectively enrolled 50 consecutive patients undergoing RSA (n = 30) or TSA (n = 20) as determined by a power analysis based on previous research for our institution. Intraoperative neuromonitoring was used to detect nerve alerts during 4 distinct stages of the procedure. Preoperative and postoperative arm lengths were measured on scaled radiographs. Patients were examined immediately postoperatively and at follow-up visits for neurologic complications.ResultsMean motor and sensory nerve alerts per case were similar for TSA and RSA (motor: TSA, 1.5 ± 2; RSA, 1.5 ± 2; P = .96; sensory: TSA, 0.6 ± 0.9; RSA, 0.2 ± 0.6; P = .06). The mean change in arm length was 3 ± 7 mm in the TSA cohort vs. 14 ± 7 mm in the RSA cohort (P = .0001). Temporary neurologic changes postoperatively were noted in 1 TSA and 1 RSA patient, amounting to a 4% incidence of nerve injury.ConclusionsAn RSA design with a lateralized glenosphere and a lower neck-shaft angle decreases arm lengthening compared with the Grammont design. The reduction in lengthening appears to eliminate the historically increased risk of neurologic injury associated with RSA relative to TSA.Copyright © 2018 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.

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