Neutral glenoid alignment in reverse shoulder arthroplasty does not guarantee decreased risk of impingement.

Reverse Shoulder Arthroplasty (RSA) has gained popularity over the recent years, but impingement concerns are still present. Surgeons aim to correct pre-operative glenoid deformities to reduce impingement but it can be challenging without assistance like patient specific guides. However, it is unclear how accurate glenoid correction affects the impingement. The main objective of this study was to determine whether accurate glenoid correction to neutral version and tilt can reduce the risk of impingement. Two types of virtual surgeries were performed on 22 pre-operative arthritic shoulders: (i) "Interactive," the glenoid baseplate could be placed with accuracy, and (ii) "Blind," surgeons placed the RSA baseplate while they could only visualize the glenoid. The virtual models were then used in an RSA biomechanical model which recorded impingement for (i) four Range of Motion (ROM) tasks, (ii) ten Activities of Daily Living (ADL). The "Blind" method resulted in more variable glenoid placement (version and tilt) than the "Interactive" method (p = 0.001). However, both methods showed similar ROM and impingement occurrence in ADLs. The results suggest it is challenging for surgeons to accurately correct version and tilt on arthritic glenoids when only referencing off of the face of the glenoid. However, the variable glenosphere placement observed in the "Blind" method did not result in worse impingement compared to the accurate "Interactive" method. This was because both methods had similar inferior baseplate positioning which is more important than correcting version or tilt. Implantation accuracy remains important in RSA, but pre-operative planning should not just target at correcting version and tilt. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1213-1219, 2018.