Complete resection of the deltoid insertion is associated with post-operative dislocation of reverse total shoulder arthroplasty following proximal humerus oncological resection

Reconstruction of an oncologically resected proximal humerus poses a challenge to surgeons, and reverse total shoulder arthroplasty (rTSA) may provide greater functional improvement. However, the characteristics of patients suitable for rTSA remain unknown, owing to the lack of data in the literature regarding post-operative functional outcomes and complications. In this retrospective cohort study of patients who underwent rTSA for tumor-related proximal humerus resection, we aimed to identify the features related to improved outcomes and decreased complications. We hypothesized that complete deltoid insertion resection would be associated with an increased risk of instability in patients treated with rTSA for oncological proximal humeral resection. We conducted a retrospective cohort study to assess the post-operative mid-term complications and functional outcomes. The range of motion, Musculoskeletal Tumor Society (MSTS), Toronto Extremity Salvage Score (TESS), and Constant-Murley score were used to evaluate functional outcomes. The patients were divided into 3 groups dependent on the resection of the deltoid insertion. Furthermore, 24 patients whose deltoid insertions were completely resected and who underwent anatomic shoulder arthroplasty (aTSA) were matched according to the demographic information of those who underwent rTSA. Fifty-eight patients who underwent rTSA in our department were included in the study based on the inclusion and exclusion criteria. The MSTS, TESS, and Constant-Murley scores were 26, 136, and 76, respectively, and the average forward flexion, abduction, external rotation, and internal rotation angles were 125&#xb0;, 121&#xb0;, 51&#xb0;, 54&#xb0;, respectively. Complications were reported in 17 patients, with instability accounting for 13. Multiple regression analysis revealed that complete resection of the deltoid insertion was an independent risk factor for post-operative dislocation (odds ratio: 16.67; P < .01). Although resection length showed a significant positive association with dislocation in all patients, no association was found in the subgroups. We following matched 24 patients with the complete resection of deltoid insertion and aTSA and found poorer functional outcomes compared to those of patients undergoing rTSA (MSTS: 21, P < .01; Constant-Murley: 50, P < .01; TESS: 101, P < .01). Our findings demonstrate that rTSA provides satisfactory functional outcomes for treating proximal humeral tumors but that complete deltoid insertion resection is an independent risk factor for post-operative dislocation. In patients whose deltoid insertions are completely resected, functional improvements make them worth attempting in those with high activity demands.