Background Muscle quality and volume are important determinants of functional outcomes after arthroscopic rotator cuff repair (ARCR). Although fatty infiltration of rotator cuff muscles has been widely evaluated using semi-quantitative methods, comprehensive three-dimensional quantitative assessment of both intrinsic and extrinsic shoulder muscles remains limited. This study aimed to evaluate artificial intelligence (AI)-driven automated shoulder muscle segmentation on pre-operative computed tomography (CT) and to investigate the associations between quantitative muscle characteristics and post-operative shoulder function after ARCR. Methods This retrospective study included 30 patients (31 shoulders) who underwent ARCR, with a mean follow-up of 20.2 months. Pre-operative CT scans were obtained using a standardized protocol with 1-mm slice thickness. Shoulder muscles were automatically segmented using an AI-based deep learning model. Six muscles—the deltoid, trapezius, subscapularis (SSc), supraspinatus, infraspinatus and teres minor complex (ISPTm), and teres major (TM)—were analyzed. Muscle composition was quantified based on Hounsfield unit thresholds and classified into functional muscle (FM), low-attenuation muscle (LAM), and adipose tissue (AT). Muscle volumes were normalized to scapular bone volume. Associations between quantitative muscle parameters and post-operative active range of motion at the final follow-up were evaluated using Pearson correlation analysis. Results FM and AT proportions differed significantly among the 6 muscles, whereas LAM showed no significant variation. The TM demonstrated the highest FM proportion, while the supraspinatus showed the highest AT proportion. The total volumes of the SSc and TM were associated with post-operative anterior elevation (AE; r = 0.410 and 0.415, respectively), as were the FM volumes of the SSc, ISPTm, and TM (r = 0.458, 0.430, and 0.427, respectively). In contrast, neither AT nor LAM measures were significantly associated with post-operative range of motion. No muscle parameter was significantly associated with post-operative external rotation. Conclusion AI-driven automated segmentation enabled the quantitative evaluation of shoulder muscle volume and composition on pre-operative CT. Both intrinsic and extrinsic shoulder muscles, particularly the SSc, ISPTm, and TM, were associated with post-operative AE after ARCR. Greater FM volume, rather than fatty muscle composition, was associated with better post-operative AE after ARCR. AI-based quantitative muscle assessment may provide clinically relevant information to support pre-operative evaluation.
Background Deterioration of sagittal spinal alignment, particularly global kyphosis (GK), negatively impacts range of motion (ROM) after reverse total shoulder arthroplasty (rTSA). Therefore, this study aimed to investigate the clinical outcomes of rTSA performed after corrective spinal surgery, hypothesizing that this sequential approach would improve post-operative ROM. Methods We categorized 129 patients (followed >2 years) into 3 groups: those without GK (n = 72), those with untreated GK (n = 42), and those who underwent prior corrective spinal surgery (n = 15). Post-operative ROM was compared among these cohorts. For the corrective spinal surgery group, we measured the C7-hip axis (C7-HA) distance, sagittal vertical axis (SVA), and lumbar lordosis (LL) before and after spinal intervention, but prior to rTSA. Results In the corrective spinal surgery group, significant improvements were observed in LL, C7-HA, and SVA. The non-GK group demonstrated significantly greater flexion, abduction, and internal rotation than the other 2 groups and significantly greater external rotation than the GK group; external rotation did not differ significantly from the corrective spinal surgery group. Following corrective spinal surgery, patients exhibited significant improvements in LL, C7-HA, and SVA, achieving better post-operative C7-HA and SVA measurements than the untreated GK group. However, despite these partial alignment improvements, forward flexion and abduction in the corrective spinal surgery group were significantly lower at 24 months than those in the GK group. Conclusion Prior corrective spinal alignment surgery was not associated with improved post-operative ROM after rTSA.
