Instability after reverse total shoulder replacement

Background: Despite advances in technique and implant design, instability after reverse total shoulder arthroplasty remains a challenging postoperative complication. Materials and methods: We examined our institutions' first 57 reverse total shoulder arthroplasties performed during a 3-year period (2004-2006). There were 9 cases of instability, all occurring within the first 6 months after surgery. Results: All 9 patients had compromise of the subscapularis tendon at the time of initial reverse total shoulder implantation. With regard to implant positioning, 2 patients had superiorly inclined metaglenes and 3 had metaglenes positioned superior to the inferior glenoid. Each patient with a dislocation had at least 1 revision surgery, and 4 patients had underlying infection. At most recent follow-up, only 3 patients had a concentrically reduced reverse total shoulder arthroplasty in place whereas 3 remained explanted, 2 chronically dislocated, and 1 chronically subluxated. Conclusions: Early instability after reverse total shoulder arthroplasty can be related to inadequate soft tissue, inadequate deltoid tension, malpositioned implants, and/or infection, and outcomes of treatment of early instability are generally poor.