This retrospective case-control study introduces the critical shoulder angle (CSA) — a single true AP radiograph measurement combining glenoid inclination and lateral acromial extension. It tests whether CSA can distinguish shoulders predisposed to rotator cuff tears from those predisposed to glenohumeral osteoarthritis. The study included 298 shoulders across three groups: asymptomatic controls, MRI-confirmed full-thickness rotator cuff tears, and primary glenohumeral osteoarthritis confirmed at total shoulder replacement.
When you look at a shoulder radiograph, the CSA tells you what disease the patient is likely to have before you ever order an MRI.
Measure the angle from the inferior glenoid margin to the superior glenoid margin, then from the inferior glenoid margin to the lateral acromion tip on a true AP view. A result above 35° should raise immediate concern for rotator cuff pathology. A result below 30° points strongly toward glenohumeral osteoarthritis as the primary diagnosis.
Before this paper, the acromion index was the standard acromial measure — but it is unreliable in OA because humeral head flattening artificially inflates it. The CSA solves this by anchoring the measurement to the glenoid, which is unaffected by humeral degeneration.
The practical takeaway: in a patient with vague shoulder pain and a CSA of 37°, push for MRI to characterize the cuff. In a patient with a CSA of 27°, direct your workup toward articular cartilage and prepare the patient for the likelihood of arthroplasty down the road.
This retrospective case-control study introduces the critical shoulder angle (CSA) — a single true AP radiograph measurement combining glenoid inclination and lateral acromial extension. It tests whether CSA can distinguish shoulders predisposed to rotator cuff tears from those predisposed to glenohumeral osteoarthritis. The study included 298 shoulders across three groups: asymptomatic controls, MRI-confirmed full-thickness rotator cuff tears, and primary glenohumeral osteoarthritis confirmed at total shoulder replacement.
When you look at a shoulder radiograph, the CSA tells you what disease the patient is likely to have before you ever order an MRI.
Measure the angle from the inferior glenoid margin to the superior glenoid margin, then from the inferior glenoid margin to the lateral acromion tip on a true AP view. A result above 35° should raise immediate concern for rotator cuff pathology. A result below 30° points strongly toward glenohumeral osteoarthritis as the primary diagnosis.
Before this paper, the acromion index was the standard acromial measure — but it is unreliable in OA because humeral head flattening artificially inflates it. The CSA solves this by anchoring the measurement to the glenoid, which is unaffected by humeral degeneration.
The practical takeaway: in a patient with vague shoulder pain and a CSA of 37°, push for MRI to characterize the cuff. In a patient with a CSA of 27°, direct your workup toward articular cartilage and prepare the patient for the likelihood of arthroplasty down the road.