Normal Acromiohumeral Distance Size on Radiography
The acromiohumeral distance (AHD) is the space between the inferior surface of the acromion and the superior aspect of the humeral head, measured on anteroposterior shoulder radiographs. It serves as an indirect indicator of rotator cuff integrity, since the rotator cuff — particularly the supraspinatus — normally maintains the humeral head in a depressed position. Accurate AHD measurement is a rapid, accessible screening tool in the evaluation of shoulder pain and suspected cuff pathology.
Normal Reference Values
| Orientation | Measurement |
|---|---|
| Anteroposterior | <7 mm |
Clinical Significance
A reduced AHD, defined as less than 7 mm on an AP radiograph, is associated with significant rotator cuff abnormalities. As the cuff degenerates or tears, the dynamic stabilizing force depressing the humeral head is lost, allowing superior migration and consequent narrowing of the subacromial space.
Chronic superior migration leads to secondary changes including subacromial enthesophytes, acromial remodeling, and eventually glenohumeral arthrosis — a pattern termed cuff tear arthropathy. Clinicians should note that AHD alone cannot distinguish partial from full-thickness tears; MRI or ultrasound is required for definitive characterization.
- Full-thickness supraspinatus tear (most common cause)
- Massive rotator cuff tear involving multiple tendons
- Cuff tear arthropathy (advanced glenohumeral arthritis)
- Superior labrum pathology with secondary instability
- Paralytic shoulder (deltoid or cuff denervation)
Reference: Saupe N, Pfirrmann CW, Schmid MR et al. Association between rotator cuff abnormalities and reduced acromiohumeral distance. AJR Am J Roentgenol. 2006;187(2):376-82.
Imaging Notes
AHD is measured on a true anteroposterior (Grashey) radiograph of the shoulder obtained with the patient upright and the arm in neutral rotation at the side. The measurement is taken as the shortest perpendicular distance between the inferior cortex of the acromion and the superior cortex of the humeral head. Patient positioning is critical — internal or external rotation, arm abduction, or beam angulation can artifactually alter the apparent distance and lead to misinterpretation.
Dynamic assessment (radiographs with arm elevation) may further reveal functional narrowing not apparent at rest. When AHD is borderline or clinical suspicion is high despite a normal static measurement, ultrasound or MRI provides direct visualization of rotator cuff tissue and is the recommended next step.