INTRODUCTION: Reverse total shoulder arthroplasty (RTSA) has become a pivotal intervention for managing rotator cuff arthropathy in the elderly, showing consistent improvements in pain relief and shoulder function. However, the broad spectrum of indications for RTSA is accompanied by a notable incidence of complications, prompting continuous advancements in technology and surgical techniques. CASE REPORT: This case report presents an uncommon complication rarely discussed in the existing literature - humeral tray-taper breakage after RTSA. The patient, a 68-year-old with a history of rotator cuff repair surgery, underwent RTSA with concurrent subscapularis repair due to rotator cuff arthropathy. Postoperatively, the patient gradually reported weakness in internal rotation (IR), leading to a subsequent secondary pectoralis major (PM) transfer. However, following an incident where the patient experienced acute pain due to a slip, a tray-taper breakage in the implant was revealed. To address the broken implant and the weakness in IR, the patient underwent revision RTSA combined with the PM transfer. With a post-operative rehabilitation program, at 1 year and 6 months postoperatively, the patient demonstrated significant pain relief and improved functional outcomes. CONCLUSION: The case report underscores the importance of recognizing and addressing rare complications associated with RTSA, providing insights into the management of humeral tray-taper breakage. Furthermore, combined PM transfer to RTSA could be a solution to weakness in IR. This case report emphasizes the need for careful consideration of potential complications and innovative solutions for optimal patient outcomes. LEVEL OF EVIDENCE IV: Case report.