Clinical relevance, classification, and risk factors for stress shielding in total shoulder arthroplasty: a systematic review and meta-analysis of clinical outcomes.

Background: Stress shielding of the proximal humerus represents an increasing challenge for the implantation of total shoulder arthroplasty (TSA). The literature on this topic is heterogeneous, and many studies analysing its clinical impact are underpowered, justifying a systematic review of current evidence. Materials and methods: On 1 September 2024, the Cochrane Library, PubMed, and Web of Science were searched for studies on stress shielding in shoulder arthroplasty. All studies meeting inclusion criteria were included in the qualitative review. Clinical significance was assessed through a meta-analysis of studies comparing patients with and without stress shielding using Constant-Murley score (CS) and American Shoulder and Elbow Surgeons (ASES) score. Results: Of 299 identified studies, 58 studies were included in the qualitative review and 13 studies were included in the meta-analysis. Key risk factors consistently associated with stress shielding were press-fit or long stems and high stem-to-humerus filling ratios (FRs), with threshold values of <0.7 or <0.8. Other potential risk factors include older age, poor bone quality, fracture arthroplasty, and stem length. The meta-analysis showed a statistically significant 5.6-point improvement in Constant scores for the non-stress shielding group at two years, although this fell below the minimal clinically important difference threshold and did not affect revision rates at mid-term follow-up. Conclusion: Stress shielding is a frequent radiographic finding in TSA and RTSA. Although statistically significant, its clinical impact appears limited, and revision rates remain unaffected in the mid-term. Avoiding high FRs and careful implant selection may help reduce its occurrence and preserve bone stock.