Quantification of impingement-free range-of-motion in reverse shoulder arthroplasty planning

Abstract

Glenoid implant position and scapula shape affect the impingement-free range-of-motion (ROM) of a patient's glenohumeral joint. Currently, methods to evaluate the impingement-free ROM during preoperative planning do not result in one overall score, which is required for an objective optimization of the implant position. Therefore, our study aims to quantify the impingement-free ROM so that surgeons can easily compare the result for various implant positions.250 virtual shapes from a healthy scapula statistical shape model (SSM) were virtually implanted with a reverse glenoid implant in diverse positions. The impingement-free ROM was visualised on a 2D polar plot and quantified based on healthy kinematic motion data.ROM scores for a neutral implant position resulted in a mean value of 0.84 +/- 0.06. A lateral, inferior and posterior implant position and a negative shape coefficient in the first SSM mode improved the mean ROM score. The impact of implant position and scapula shape was also visible in the 2D polar plots.Hence, the defined ROM score was sensitive to implant position and scapula shape. A lateral, inferior and posterior implant position resulted in a better ROM, which agrees with many studies in literature. We conclude that the ROM score proposed in this study agrees well with what has been published in literature and is therefore considered as a suitable candidate to objectively evaluate and improve an implant plan during preoperative planning.