This case-control study used MR arthrography to identify objective imaging criteria for frozen shoulder. 22 patients with surgically confirmed frozen shoulder were compared to 22 matched controls. The study defines specific thickness thresholds for the coracohumeral ligament and rotator cuff interval capsule that distinguish frozen shoulder from normal.
Prior MRI literature (Emig et al, 1995) taught that axillary recess capsular thickening >4 mm was the hallmark of frozen shoulder on MRI. This paper challenges that teaching directly: on MR arthrography with a distended joint, axillary recess thickness is identical between frozen shoulder patients and controls.
When you read a shoulder MRI arthrogram and suspect frozen shoulder, look at the rotator cuff interval and the CHL. A CHL ≥4 mm is 95% specific. Rotator cuff interval capsule ≥7 mm is 86% specific. If you see complete obliteration of the fat triangle under the coracoid (subcoracoid triangle sign), the diagnosis is confirmed — it has never been seen in a normal shoulder in this series.
The practical takeaway for residents: do not diagnose frozen shoulder based on axillary recess capsular thickness on standard MRI. That measurement is unreliable without joint distension. The rotator cuff interval is where the disease lives.
This paper also reinforces the anatomy worth knowing for boards: the rotator cuff interval is bounded superiorly by the supraspinatus and inferiorly by the subscapularis. The same interval involved in biceps pulley lesions and glenohumeral instability.
This case-control study used MR arthrography to identify objective imaging criteria for frozen shoulder. 22 patients with surgically confirmed frozen shoulder were compared to 22 matched controls. The study defines specific thickness thresholds for the coracohumeral ligament and rotator cuff interval capsule that distinguish frozen shoulder from normal.
Prior MRI literature (Emig et al, 1995) taught that axillary recess capsular thickening >4 mm was the hallmark of frozen shoulder on MRI. This paper challenges that teaching directly: on MR arthrography with a distended joint, axillary recess thickness is identical between frozen shoulder patients and controls.
When you read a shoulder MRI arthrogram and suspect frozen shoulder, look at the rotator cuff interval and the CHL. A CHL ≥4 mm is 95% specific. Rotator cuff interval capsule ≥7 mm is 86% specific. If you see complete obliteration of the fat triangle under the coracoid (subcoracoid triangle sign), the diagnosis is confirmed — it has never been seen in a normal shoulder in this series.
The practical takeaway for residents: do not diagnose frozen shoulder based on axillary recess capsular thickness on standard MRI. That measurement is unreliable without joint distension. The rotator cuff interval is where the disease lives.
This paper also reinforces the anatomy worth knowing for boards: the rotator cuff interval is bounded superiorly by the supraspinatus and inferiorly by the subscapularis. The same interval involved in biceps pulley lesions and glenohumeral instability.