|Beitragstitel||What is the Best Glenoid Configuration in Reverse Shoulder Arthroplasty?|
The impacts of glenoid offset and the combination between glenoid and humeral design after reverse shoulder arthroplasty (RSA) have not been well-studied, particularly with regard to flexion/extension and to internal/external rotation which have been demonstrated to be the cause for scapular notching. The purpose of this study was to analyze the effect of different glenoid designs, and then of combination of glenoid and humeral designs on arm position and range of motion (ROM) following RSA.
Using a three-dimensional computer model of RSA, a short curved onlay stem with a 145° inclination was combined to five different glenoid design varying by glenoid sphere diameter and glenoid sphere center of rotation location. Glenoid offset, acromiohumeral distance (AHD), ROM and muscle length were evaluated for each configuration.
Altering glenoid design led to a nearly 6 mm change in glenoid offset and 3 mm in the AHD. There was a 7° improvement in abduction and flexion between the different glenoid design. Only 2 of them, the 36mm centered and the Bio-RSA, did not reach native adduction. In extension and external rotation arm at side, the eccentric 36 mm sphere was the best configuration. The 42 mm sphere present a limited external rotation at 90° of abduction. When combining glenoid and humeral design, a threshold of 1.8 on the Humeral Offset/AHD discriminated between configuration with external rotation limitation or deficit.
With varying glenoid prostheses, dramatic change could be observed on extension, external rotation arm at side and external rotation at 90° of abduction. Taking particular attention to a low placement of the glenoid implant, which could be increase by using eccentric sphere, is important as this directly improvement ROM.