CORR Insights(®): implant design variations in reverse total shoulder arthroplasty influence the required deltoid force and resultant joint load.

Abstract

R everse shoulder arthroplasty has become an important and powerful tool in the treatment of a variety of severe shoulder pathologies, including rotator cuff arthropathy, complex proximal humeral fractures, and failed anatomic arthroplasties. With increased widespread use, numerous studies have been performed on how changes in its basic components affect the biomechanics and function of the implant. It is clear from several biomechanical studies [2–6] that placement of a reverse total shoulder arthroplasty lowers and medializes the center of rotation of the glenohumeral joint in comparision to the normal anatomic center of rotation. This effectively improves the deltoid moment arm reducing the overall loads to abduct the arm. It also reduces the rotator cuff moment arms, placing the posterior rotator cuff at a disadvantage and subsequently limiting some of the ability for external rotation. With any new technology, however, there exists complications, and the reverse shoulder arthroplasty is not free from this issue. Complications of particular concern include scapular notching, limited ROM, acromial stress fractures, deltoid overtensioning, and dislocation. Several techniques that have been used to reduce common complications associated with reverse shoulder arthroplasty (instability, scapular notching and reduced external rotation motion and strength) include glenosphere lateralization, humeral lateralization, and humeral lengthening. It is currently unclear which of these options is the best strategy to limit these problems without incurring further negative consequences like increased deltoid force for abduction. Excessive deltoid loads can lead to deltoid related pain, acromial stress fractures, and potentially early functional decline due to deltoid senescence. The current study by Giles and colleagues further defines the overall effects of changes in implant variables This CORR Insights is a commentary on the article ‘‘Implant Design Variations in Reverse Total Shoulder Arthroplasty Influence the Required Deltoid Force and Resultant Joint Load’’ by Giles and colleagues available at: DOI: 10.1007/ s11999-015-4526-0. The author certifies that he, or any member of his immediate family, has no funding or commercial associations (eg, consultancies, stock ownership, equity interest, patent/ licensing arrangements, etc.) that might pose a conflict of interest in connection with the submitted article. All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research editors and board members are on file with the publication and can be viewed on request. The opinions expressed are those of the writers, and do not reflect the opinion or policy of CORR or The Association of Bone and Joint Surgeons. This CORR Insights comment refers to the article available at DOI: 10.1007/s11999015-4526-0.