BackgroundUse of a baseplate with a smaller diameter in reverse shoulder arthroplasty is increasing, especially in patients with a small glenoid or glenoid wear. However, the effect of a smaller baseplate on stability of the glenoid component has not been evaluated. Thus, the purpose of this study was to determine whether a smaller baseplate (25 mm) is beneficial to the initial stability of the glenoid component compared to that with a baseplate of a commonly used size (29 mm).MethodsMicromotion of glenoid components attached to 14 scapulae of fresh-frozen cadavers was measured and compared between 25- and 29-mm baseplates in biomechanical testing. Impingement-free range of motion in abduction, adduction, internal rotation, and external rotation was evaluated by using a simulated computer model constructed based on the same fresh-frozen cadavers used in biomechanical testing.ResultsMicromotion at the inferior third of the glenoid-glenosphere interface was higher in the 29-mm baseplate group than in the 25-mm baseplate group during both 0.7- and 1-body weight cyclic loading in biomechanical testing. Adduction deficit was smaller, and total impingement-free range of motion from abduction to adduction and rotation were greater in the 25-mm baseplate group than in the 29-mm baseplate group in the simulated computer model.ConclusionsUse of a baseplate with a smaller diameter (25 mm) in reverse shoulder arthroplasty is suitable for improving the primary stability of the glenoid component. With a smaller baseplate, impingement-free range of motion is optimized in a smaller glenoid.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2474-15-417) contains supplementary material, which is available to authorized users.

Glenoid component fixation with inferior tilt has been suggested as one of the surgical methods to decrease scapular notching and improve stability, but its clinically beneficial effect remains a concern. We evaluated the influence of inferior tilt fixation of the glenoid component on primary stability in reverse total shoulder arthroplasty by finite element analysis. Finite element models were constructed from cadaveric scapulae of females over the age of 60 years and glenoid components from reverse total shoulder arthroplasty. The relative micromotion at the bone-glenoid component interface, distribution of bone stress under the glenoid component and around the screws, contact area between the bone and screws, and cut surface area of the cancellous bone exposed after glenoid reaming were analyzed and compared between a neutral and 10˚inferior tilt fixation of the glenoid component. The 10˚inferior tilt fixation demonstrated greater relative micromotion and higher bone stress than the neutral tilt fixation. Eccentric reaming, which is done to produce the inferior tilt fixation of the glenoid component, increased glenoid cancellous bone exposure and decreased bone-screws contact area. Inferior tilt fixation of the glenoid component may adversely affect primary stability and longevity after reverse total shoulder arthroplasty. Keywords: reverse total shoulder arthroplasty; glenoid component; inferior tilt; finite element analysis; primary stability Reverse total shoulder arthroplasty (RTSA) is an effective treatment option for cuff tear arthropathy and massive, irreparable rotator cuff tears, 1,2 and indications for its use are expanding. 3 However, compared with conventional total shoulder arthroplasty, RTSA is associated with more frequent complications; glenoid component loosening and scapular notching are major concerns that can affect RTSA longevity and functional outcome. [4][5][6] Numerous methods, such as inferior overhang, inferior tilt, and a more lateral center of rotation of the glenoid component, have been suggested to maximize initial fixation and to prevent scapular notching and glenoid component loosening for optimal glenoid component fixation. 2,[6][7][8][9] Inferior tilt fixation of the glenoid component has been proposed to improve stability and reduce the likelihood of mechanical failure because it provides uniform compressive forces and imparts low tensile forces and micromotion. 7 Glenoid component inferior tilt improves the impingement-free range of motion and reduces scapular notching. 7,8,10 However, controversy still exists regarding the ability of inferior tilt fixation to improve long-term outcomes. 6,9,11 Most previous biomechanical studies on the effect of glenoid component inferior tilt used a solid rigid polyurethane foam or sawbone blocks, instead of cadaveric scapulae, to evaluate RTSA stability. 7,12,13 Computer simulations to analyze the effect of glenoid component inferior tilt have not accounted for anatomical and morphological variations of glenoid or scapulae, and...

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