The relationship between plain radiograph soft tissue thickness and perioperative outcomes following anatomic total shoulder arthroplasty: a preliminary study

Background: Computerized tomography-based assessment of local adiposity has been demonstrated to provide more accurate prediction of perioperative orthopedic outcomes when compared with body mass index (BMI). The use of plain radiographs to assess these soft tissue ratios may offer lower costs and decreased radiation exposure. Methods: A retrospective review of consecutive primary stemless anatomic total shoulder arthroplasty at a single academic institution was undertaken. Patient demographics and surgical data, including age, BMI, modified 5-item fragility index, operative time and both 90-day emergency department return and readmission were collected. Local adipose and muscle thickness, in addition to humeral head diameter were measured on standard preoperative radiographs using 2 novel measurement techniques. Gamma regression analysis determined the correlation between BMI, adipose-to-muscle ratio (AMR), and soft tissue-to-bone ratio (SBR) with postoperative outcomes. Results: There were 139 total cases included in this study. The median age of the cohort was 62 years (interquartile range 55,69). The median BMI was 33.4 kg/m² (interquartile range 27.5,37.2). BMI significantly correlated with AMR (r = 0.462, P < .001) and SBR (r = 0.433, P < .001) using the circle method and with AMR (r = 0.447, P < .001) and SBR (r = 0.452, P < .001) using the linear method. Following regression analysis, only SBR using the circle method (relative rate ratio 1.14, 95% confidence interval 1.01-1.28, P = .035) and linear method (relative rate ratio 2.03, 95% confidence interval 1.39-2.97, P < .001) was significantly correlated with increased operative time. Conclusions: Soft tissue ratios about the shoulder measured from plain radiographs provide a more accurate assessment of operative time, blood loss, and potential 90-day readmission than BMI and should be included in preoperative planning.