Parameterization of Proximal Humerus Locking Plate Impingement with In Vitro, In Silico, and In Vivo Techniques

Abstract

BackgroundLocked plating of displaced proximal humerus fractures is common, but rates of subacromial impingement remain high. Computational predictions of implant impingement have yet to be sufficiently explored in proximal humerus fixation. The goal of this study was to utilize a multidisciplinary approach to elucidate the relationships between common surgical parameters, anatomical variability, and the likelihood of plate impingement.\n\nMethodsThe experiment was completed in three phases. First, a controlled in vitro experiment was conducted to simulate impingement. Second, a dynamic in silico musculoskeletal model was developed to simulate changes to implant geometry, surgical techniques, and acromial anatomy, where a collision detection algorithm was used to simulate contact between the plate and acromion. Finally, in vivo shoulder kinematics were recorded for nine activities of daily living and motions that created a high likelihood of impingement were identified.\n\nResultsImpingement was measured at 73.3{+/-}14.5{degrees} abduction in the cadaveric model and 92.0{degrees}{+/-}34.0{degrees} with computational simulations. Impingement events were limited to ranges of motion between 10-40{degrees} of cross-body adduction. Activities of daily living, such as combing ones hair, lifting and object overhead, and reaching behind ones head are likely to cause impingement.\n\nDiscussion and ConclusionThis multidisciplinary experiment quantified key preoperative factors to assist with implantation decisions. Results demonstrated that proximal implant placement, superior translation of the humeral center of rotation, increases in plate thickness, and increases in acromial tilt all increase the likelihood of impingement. Careful preoperative planning that includes these factors could help guide operative decision making and improve clinical outcomes.\n\nLevel of Evidence: V