This basic-science study used a validated virtual shoulder model to test how RSA component choices affect impingement-free glenohumeral motion. It simulated 216 combinations of humeral and glenosphere variables across abduction, flexion/extension, and rotation. The goal was to rank which component and placement choices most improve motion in each plane.
The practical takeaway is a component-selection framework you can match to a patient's functional need. If a patient most needs overhead abduction, favor a valgus (150) neck-shaft angle. If they need forward flexion and extension for daily tasks, favor a varus (130) angle. If rotation matters most, place the glenosphere inferiorly.
Two choices help across the board and carry little downside in this model: lateralize the center of rotation (10-mm offset) and use a larger glenosphere. Both increase clearance from the scapular neck and cut resting impingement, which is the mechanism behind scapular notching.
Remember this is passive motion in a rigid model with no muscle, soft tissue, or scapulothoracic contribution. Chasing motion by displacing the humerus too far inferiorly risks brachial plexus traction and acromial stress fracture, so the numbers guide but do not replace intraoperative soft-tissue balancing.
This basic-science study used a validated virtual shoulder model to test how RSA component choices affect impingement-free glenohumeral motion. It simulated 216 combinations of humeral and glenosphere variables across abduction, flexion/extension, and rotation. The goal was to rank which component and placement choices most improve motion in each plane.
The practical takeaway is a component-selection framework you can match to a patient's functional need. If a patient most needs overhead abduction, favor a valgus (150) neck-shaft angle. If they need forward flexion and extension for daily tasks, favor a varus (130) angle. If rotation matters most, place the glenosphere inferiorly.
Two choices help across the board and carry little downside in this model: lateralize the center of rotation (10-mm offset) and use a larger glenosphere. Both increase clearance from the scapular neck and cut resting impingement, which is the mechanism behind scapular notching.
Remember this is passive motion in a rigid model with no muscle, soft tissue, or scapulothoracic contribution. Chasing motion by displacing the humerus too far inferiorly risks brachial plexus traction and acromial stress fracture, so the numbers guide but do not replace intraoperative soft-tissue balancing.