Association between sagittal spinal alignment and postoperative shoulder range of motion following reverse total shoulder arthroplasty

BackgroundThe range of internal rotation sometimes deteriorates after reverse total shoulder arthroplasty; however, the underlying mechanisms remain unclear. This study aimed to investigate the association between sagittal spinal alignment and internal rotation deterioration after reverse total shoulder arthroplasty.MethodsWe retrospectively reviewed 52 patients who underwent reverse total shoulder arthroplasty by a single surgeon between October 2014 and December 2018. The sagittal spine was radiographed, and the sagittal spinal alignment was evaluated based on 10 parameters (e.g. C7-HA: the distance between the plumb line from the center of the seventh cervical vertebral body and the center of the hip axis). We divided the patients into two groups, group A (internal rotation deterioration; 23 patients) and B (without internal rotation deterioration; 29 patients). Logistic regression analysis was performed to analyze the association between sagittal spinal alignment and internal rotation deterioration after reverse total shoulder arthroplasty, and a receiver operating characteristic curve was used to analyse the cutoff value of independent variables that was correlated with IR deterioration.ResultsLogistic regression analysis demonstrated the correlation between C7-HA and internal rotation deterioration (odds ratio, 1.95; 95% confidence interval, 1.33–2.84; P < 0.001). The receiver operating characteristic curve suggested that when C7-HA was at least 2.44 cm, it was strongly correlated with deterioration of internal rotation (sensitivity, 91.3%; specificity, 93.1%; P < 0.001; area under the curve, 0.938). Group A was significantly inferior to group B in not only internal rotation but also flexion and abduction.ConclusionsThis study suggested that a remarkably positive value in C7-HA was a factor that was correlated with deterioration of internal rotation. In addition, the deformation of sagittal spinal alignment would impact on the range of motion after reverse total shoulder arthroplasty.