Scapular notching in reverse shoulder arthroplasty: validation of a computer impingement model

Area of Science:

• Orthopedic surgery
• Biomechanical engineering
• Medical imaging analysis

Background:

• Scapular notching is a common complication following reverse shoulder arthroplasty.
• Implant positioning is a critical factor influencing the occurrence of scapular notching.
• Accurate prediction of impingement is essential for surgical planning and complication avoidance.

Purpose of the Study:

• To validate a novel computer model for predicting scapular impingement in reverse shoulder arthroplasty.
• To quantify the effect of glenoid implant positioning on impingement.
• To compare computer model predictions with radiographic findings in a clinical cohort.

Main Methods:

• A geometric computer model simulated impingement by varying humeral rotation and glenoid implant positions.
• The model analyzed anterior and posterior scapular impingement relative to a fixed scapula.
• Results were compared to radiographic analysis of 256 patients, assessing notching, baseplate position, and glenosphere overhang.

Main Results:

• The computer model accurately predicted impingement-free positions based on specific glenoid baseplate and glenosphere overhang measurements.
• The model correctly identified the cause of impingement in 18 of 26 patients with notching based on baseplate position.
• The model predicted impingement in 15 of 26 patients with notching based on glenosphere overhang.

Conclusions:

• Reverse shoulder implant positioning significantly impacts the incidence of scapular notching.
• The validated computer model effectively predicts impingement related to implant position.
• This tool offers valuable guidance to surgeons for optimizing implant placement and minimizing scapular notching.