Operator-dependent and position-dependent — anisotropy is the artefact that manufactures tears, and dynamic assessment is what ultrasound adds.
Orient first
- ANISOTROPY is the dominant artefact and the commonest cause of a false-positive tear: a tendon looks artificially DARK when the beam is not perpendicular to its fibres. Correcting the angle and watching the hypoechoic area disappear is the test.
- A full-thickness tear is a defect extending from the bursal to the articular surface, usually with fluid filling it and often with the overlying bursa and deltoid sagging into the gap.
- The CRITICAL ZONE of supraspinatus, just posterior to the biceps and near its footprint, is where most tears begin — it is where to look hardest.
- DYNAMIC assessment is what ultrasound offers over MRI: impingement on abduction, and subluxation of the biceps tendon on rotation, are seen in real time.
- Fluid in the subacromial-subdeltoid bursa alone is non-specific; it accompanies tears but also bursitis.
Acquire the study
- High-frequency linear probe, 10–15 MHz. Patient seated on a rotating stool so the shoulder can be positioned freely.
- Use the standard positions: modified Crass or Crass for supraspinatus, arm in neutral external rotation for subscapularis, and internal rotation for infraspinatus.
- Scan every tendon in TWO orthogonal planes — long and short axis — and never call a tear from one plane.
- Set the focal zone at the tendon and keep the probe PERPENDICULAR to the fibres, heel-toeing to correct anisotropy.
The manoeuvre
- Start with the biceps long head in short axis in the bicipital groove, then follow it in long axis; assess for subluxation, tenosynovitis and rupture.
- Assess subscapularis in external rotation, in both planes.
- Assess supraspinatus in the Crass or modified Crass position, in both planes, covering the critical zone and the footprint.
- Assess infraspinatus and teres minor posteriorly.
- When a hypoechoic area is seen, TOE the probe to change the angle and confirm it persists — anisotropy disappears, a tear does not.
- For any tear, state whether it is partial (and which surface) or full-thickness, and measure it in the anteroposterior and mediolateral dimensions.
- Assess the subacromial-subdeltoid bursa for fluid and thickening.
- Perform DYNAMIC assessment: abduct the arm and watch for impingement, and rotate to test biceps stability.
- Assess the acromioclavicular joint and the greater tuberosity cortex for irregularity.
What confirms it
- A full-thickness tear is a defect through the entire tendon in BOTH orthogonal planes, usually fluid-filled, with sagging of the overlying bursa.
What licenses you to exclude it
- A tendon of uniform fibrillar echotexture in both planes, with the angle corrected, excludes a significant tear.
- ⚠️ Ultrasound cannot assess the labrum, and assesses the intra-articular structures and the glenohumeral joint poorly. It does not exclude labral or intra-articular pathology — name MR arthrography where that is the question.
- A massive retracted tear can be missed because the empty footprint is mistaken for a normal-looking area — check that the tendon is actually present, not just that the area looks uniform.
The classic misread
- Calling anisotropy a tear.
- Assessing in one plane only.
- Missing a retracted tear by not confirming the tendon reaches its footprint.
- Reporting bursal fluid as though it were a tear.