Biomechanical effects of glenoid retroversion in total shoulder arthroplasty.

The purpose of this study was to evaluate the effects of glenoid retroversion after total shoulder arthroplasty on glenohumeral joint contact pressures, contact areas, and forces. We studied 8 cadaveric shoulders with a custom shoulder testing system that permits anatomic loading of the rotator cuff and the humerothoracic muscles. Each shoulder was tested intact and after total shoulder arthroplasty with the glenoid component in a neutral position and with the glenoid component retroverted 15 degrees . Glenohumeral contact pressures and areas were measured with Fuji pressure-sensitive film, and the glenohumeral forces were measured with a 6-df load cell. Glenohumeral contact areas decreased significantly, and contact pressures increased after total shoulder arthroplasty with both neutral glenoid components and retroverted glenoid components (P < .0002 to .04). Inferior forces decreased significantly after total shoulder arthroplasty with the retroverted glenoid components when compared with the intact, native shoulder (P < .02). Posterior forces also decreased significantly with the retroverted glenoid when compared with the neutral glenoid (P < .03). Placement of the glenoid in 15 degrees of retroversion significantly decreased glenohumeral contact area, increased contact pressure, and decreased inferior and posterior glenohumeral forces. Glenoid component retroversion may result in eccentric loading of the glenoid component and possibly lead to wear and loosening, signifying the importance of correct anatomic placement during total shoulder arthroplasty.