Influence of glenosphere diameter and lateralization on instability of reverse shoulder arthroplasty
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Original Contribution Obere Extremität 2020 · 15:199–206 https://doi.org/10.1007/s11678-020-00593-x Received: 8 May 2020 Accepted: 23 July 2020 Published online: 25 August 2020 © The Author(s) 2020
K. Wegmann · A. Alikhah · T. Leschinger · A. Harbrecht · L. P. Müller · M. Hackl · N. Ott Center for Orthopedic and Trauma Surgery, Faculty of Medicine and University Hospital, University of Cologne, Cologne, Germany
Influence of glenosphere diameter and lateralization on instability of reverse shoulder arthroplasty A biomechanical investigation
Reverse shoulder arthroplasty (RSA) has gained a prominent role in the treatment of unreconstructable fractures of the proximal humerus as well as of other pathologies such as cuff tear arthropathy and failure of anatomical shoulder prostheses [4, 5, 9, 10, 29]. By shifting the center of rotation (COR), the Grammont design and the more recent reverse shoulder prosthesis designs achieve an improvement of the abductor lever arm of the deltoid muscle, therefore compensating for deficiencies of the cuff or loss of the tuberosities [5, 9, 10]. Although reverse prostheses are used in growing numbers, they are accompanied by high rates of complications of up to 60% [2, 3, 11]. Besides infections, periprosthetic fractures, and loosening, a common cause of failure of reverse prostheses is instability [5, 13, 15]. Soft tissue balancing is known to play a major role in shoulder replacement, especially for stability. Furthermore, bone loss is common in many indications for reverse prostheses and is a known contributor to instability [13, 15]. As RSA does not replicate normal joint anatomy, implant selection is a key factor in gaining joint stability by tensioning the deltoid muscle and the remaining soft tissues. Glenosphere diameter has been investigated for its role in range of motion in reverse joint reconstruction [1, 14, 28] and for decreasing scapular notching [26], but also for its role in joint tensioning and stability [20,
24]. A further tool to influence soft tissue tensioning is lateralization of the glenosphere and the COR compared to the implant designed by Grammont, which has been investigated in recent biomechanical papers such as that of Ferle et al. in 2019 [12]. The present study aimed to investigate the influence of glenosphere diameter and metaglene lateralization on stability using a dynamic test setup with preloading of the rotator cuff and the deltoid. It was hypothesized that a larger glenosphere diameter and increased lateralization will add to stability, while excess lateralization might lead to dislocation of the prosthesis due to over-tensioning of the deltoid.
Materials and methods Specimens All procedures involving human cadavers were performed in accordance with the ethical standards of the institutional research committee (Ethical Committee of the Medical Faculty of the University of Cologne, VT 19-1540). For the present study, seven freshfrozen cadaveric shoulder specimens were available. Four left and three right shoulder specimens were used. Mean age of body d
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