Normal Acromiohumeral Distance Size on Radiography
The acromiohumeral distance (AHD) is the vertical space between the superior margin of the humeral head and the inferior surface of the acromion, measured on anteroposterior (AP) shoulder radiographs. This interval accommodates the rotator cuff tendons and subacromial bursa, making its measurement a key indicator of cuff integrity. Routine quantification of the AHD helps clinicians detect early or advanced rotator cuff disease before advanced cross-sectional imaging is obtained.
Normal Reference Values
| Orientation | Measurement |
|---|---|
| Anteroposterior | 7-11 mm |
Clinical Significance
A normal AHD of 7–11 mm reflects an intact supraspinatus tendon maintaining the humeral head in its proper position relative to the acromion. Narrowing below 7 mm is widely regarded as a threshold indicating significant rotator cuff tear or dysfunction, as loss of the tendon’s depressor function allows superior migration of the humeral head. Chronic narrowing can lead to secondary degenerative changes at the acromioclavicular joint and greater tuberosity sclerosis.
Conversely, an AHD exceeding 11 mm may occasionally be observed in patients with inferior humeral head subluxation, such as in glenohumeral joint effusion or neurological conditions causing deltoid paralysis. It is important to ensure true AP positioning, as rotational variation can artificially alter the measured interval.
- Massive rotator cuff tear — most common cause of AHD < 7 mm
- Rotator cuff arthropathy — chronic narrowing with glenohumeral joint destruction
- Subacromial impingement syndrome — borderline reduction with dynamic narrowing
- Inferior glenohumeral subluxation — AHD widening; seen with effusion or neuropathy
- Acromioclavicular osteoarthritis — inferior osteophytes may reduce functional space
Reference: Yochum TR, Rowe LJ. Essentials of Skeletal Radiology. (2005).
Imaging Notes
The AHD is measured on a true AP radiograph of the shoulder taken with the arm in neutral rotation and the patient erect or supine. The measurement is drawn as the shortest perpendicular distance between the inferior cortex of the acromion and the superior cortex of the humeral head. Proper beam centering on the glenohumeral joint and avoidance of internal or external rotation are critical, as malpositioning can spuriously widen or narrow the apparent interval.
When borderline values are obtained, comparison with the contralateral shoulder and correlation with clinical findings is recommended. Ultrasound or MRI should be considered for direct tendon evaluation when the AHD approaches or falls below the 7 mm threshold.