Unstable Reverse Total Shoulder Arthroplasty: How to Avoid and Manage

Although the implementation of reverse total shoulder arthroplasty (RTSA) is more common today, the complication rates in the literature still reach as high as 68%. The instability following the RTSA is the most frequent reason for revision surgery and the most difficult problem to fix. Moreover, this complication has a very high recurrence rate. The factors affecting the stability of the RTSA are compressive forces, humerosocket depth, and glenosphere dimensions. The risk factors for instability are the component malposition, insufficient soft tissue tension and soft tissue coverage, choice of deltopectoral approach, subscapularis deficiency, body mass index over 30 kg/m2, male gender, any previous history of surgery performed on the affected shoulder, impingement of the components, heterotopic ossification, axillary nerve palsy, and asymmetrical polyethylene wear. Following the development of the instability, deltoid muscle and axillary nerve integrity, glenoid and humeral component position, and bone pathologies and defects should be evaluated. If these are normal, close reduction can be considered as the initial intervention in these patients. Open reduction is the second option if the close reduction fails. In these patients, glenoid and humeral components, polyethylene insert wear, bone pathologies and defects, and soft tissue tension should be evaluated. Appropriate soft tissue tension can be restored by increasing the humeral length or lateralization of the joint center of rotation offset in patients with instability due to soft tissue laxity. Humeral shortening and excessive glenoid medialization are the main problems in recurrence. In patients with humeral shortening without excessive glenoid medialization, the stability is ensured by one or more of the following: implementing a higher sized insert, metal heightener (spacer), longer cemented humeral stem, and a structural humeral bone graft. If a longer humeral stem comes up short, the stability is reexamined following changing the glenosphere with a higher sized or eccentric one. The glenoid offset is enhanced in patients with excessive glenoid medialization by lateralization or increasing the size of glenosphere and in those with glenoid defect by using bone grafts. The instability risk can be kept to minimum by choosing the most appropriate technique considering the implant design, placement of the components in anatomical position (height and version), avoiding any potential impingement, and adjusting the soft tissue tension by minimal damage. © Springer Nature Switzerland AG 2020.