Nationwide trends and variations in reverse shoulder arthroplasty in Japan: national database analysis 2014-2023.

Background: Since the introduction of reverse total shoulder arthroplasty (rTSA) in Japan in 2014, the Japanese Orthopaedic Association (JOA) has mandated specialized training and registration for all rTSA procedures. There has been no comprehensive analysis of nationwide trends in shoulder arthroplasty use or the indications for rTSA, especially for proximal humerus fractures (PHF). The objective of this study was to elucidate the 10-year nationwide trends in total shoulder arthroplasty (TSA) in Japan, focusing on age distribution, regional variations, and clinical indications for rTSA. We hypothesized that rTSA utilization for PHF is expanding, particularly among the geriatric population. Methods: This study used data from Japan's National Database of Health Insurance Claims and Specific Health Checkups spanning fiscal years 2014-2023. The counts of TSA procedures, including both anatomical TSA and rTSA, humeral head replacements, and open reduction and internal fixation (ORIF) for intra-articular shoulder fractures, were identified via K codes. Actual rTSA case numbers and diagnostic details were obtained from the JOA National Registry. We examined trends over time in procedure volume, age distribution, and regional differences, calculating population-adjusted rates based on national census data. Additionally, we analyzed shifts in the diagnostic profiles of rTSA and compared trends in surgical treatment options. Results: TSA procedures rose from 1,246 in 2014 to 6,750 in 2023. The percentage of patients aged ≥85 years increased from 8.6% to 15.3%. In 2023, regional TSA rates varied from 10.4 per 100,000 people in Shikoku to 3.3 in Tokai. According to the JOA National Registry, Japan saw rTSA procedures grow from 630 in 2014 to 5,601 in 2023, making up most of the overall shoulder arthroplasty increase. The share of rTSA performed for PHF went up from 5.4% (34 cases) to 21.2% (1,188 cases). Meanwhile, ORIF for intra-articular shoulder fractures and humeral head replacements decreased. We also noted approximately a threefold regional variation in TSA use, similar to the variation seen in ORIF and other procedures. Conclusion: Over the past decade, TSA procedures in Japan increased 5.4-fold, driven by an 8.9-fold rise in rTSA, particularly among the oldest-old population and for PHF indications. Japan's strict implementation and certification criteria may have contributed to maintaining patient safety during this rapid expansion and may provide a useful reference framework for the controlled diffusion of new surgical technologies. While notable regional variations persist, continued outcome-based research is essential to ensure that this rapid adoption aligns with long-term clinical appropriateness and established best practices.