A retrospective radiographic study asking whether the critical shoulder angle (CSA) changes over time. The authors compared paired shoulder radiographs taken at least 10 years apart in patients without shoulder surgery or advanced arthropathy. The goal was to settle whether a large CSA is a fixed anatomical trait or an acquired change driven by rotator cuff tearing.
When you measure a large CSA on a shoulder with a cuff tear, read it as a preexisting anatomical driver of the tear, not damage the tear caused. This study is the key evidence for that reasoning: over 12 years the CSA held constant in torn, intact, and newly-torn shoulders alike. If acromial remodeling drove the large angle, the newly-torn group would have climbed, and it did not.
The biomechanical model to remember: a large CSA forces the supraspinatus to work harder to keep the joint centered, predisposing to cuff tears, while a small CSA raises glenohumeral joint reaction force and predisposes to OA.
Two practical pitfalls. First, the CSA is only trustworthy on a well-oriented AP; 5° of scapular malposition moves it more than 2°. Second, do not rely on the Bigliani-Morrison type: it flipped in a quarter of shoulders here and had poor reliability.
A retrospective radiographic study asking whether the critical shoulder angle (CSA) changes over time. The authors compared paired shoulder radiographs taken at least 10 years apart in patients without shoulder surgery or advanced arthropathy. The goal was to settle whether a large CSA is a fixed anatomical trait or an acquired change driven by rotator cuff tearing.
When you measure a large CSA on a shoulder with a cuff tear, read it as a preexisting anatomical driver of the tear, not damage the tear caused. This study is the key evidence for that reasoning: over 12 years the CSA held constant in torn, intact, and newly-torn shoulders alike. If acromial remodeling drove the large angle, the newly-torn group would have climbed, and it did not.
The biomechanical model to remember: a large CSA forces the supraspinatus to work harder to keep the joint centered, predisposing to cuff tears, while a small CSA raises glenohumeral joint reaction force and predisposes to OA.
Two practical pitfalls. First, the CSA is only trustworthy on a well-oriented AP; 5° of scapular malposition moves it more than 2°. Second, do not rely on the Bigliani-Morrison type: it flipped in a quarter of shoulders here and had poor reliability.