The concept of the critical shoulder angle (CSA) was introduced in 2013 with studies showing larger CSA is associated with rotator cuff tears (RCT) and smaller CSA with glenohumeral osteoarthritis. However, there is limited data on the impact of CSA, if any, on total shoulder arthroplasty (TSA) outcomes.
We conducted a matched case-control study using a shoulder arthroplasty registry from a US integrated healthcare system to identify patients who underwent primary elective anatomic TSA for the diagnosis of osteoarthritis from 2009-2018. 78 adult patients who underwent revision following the primary TSA due to glenoid component failure or rotator cuff tear comprised the case group. A control group of non-revised patients were identified from the same source population. Two controls were matched to each case by age, gender, body mass index, American Society of Anesthesiologists classification, surgeon who performed the index TSA, and post-TSA follow-up time. The relationships between revision and CSA as measured on radiographs were analyzed as a 1:2 matched-pairs case-control study with use of multiple conditional multivariable logistic regression.
Revised cases had a higher likelihood of a CSA ≥35° (odds ratio [OR]=2.41, 95% confidence interval [CI]=1.27-4.59). A higher likelihood of CSA ≥35° was observed for those revised for glenoid loosening (OR=4.58, 95% CI=1.20-17.50) and revised for rotator cuff tear (OR= 2.41, 95% CI=1.18-4.92) compared to non-revised controls. Every 5° increase in CSA had higher odds of overall revision (OR=1.62, 95% CI=1.18-2.21), glenoid loosening (OR=2.50, 95% CI=1.27-4.92), and rotator cuff tear (OR=1.51, 95% CI=1.07-2.14).
In a matched case-control study of primary anatomic TSA, individuals who were revised for aseptic glenoid loosening and superior cuff failure had a higher CSA compared to non-revised individuals. These data suggest that surgeons may consider utilizing reverse arthroplasty in cases of primary shoulder arthritis with a CSA of 35° or greater.

Copyright © 2021. Published by Elsevier Inc.
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