The image shows an ultrasound along the normal axis of the supraspinatus tendon. With ultrasound the normal tendon appears as a predominantly reflective fibrous structure bordered by a reflective sheath [3].

The damaged tendon loses this normal reflectivity and appears dark, a phenomenon known as anisotropy. This makes it an ideal means of imaging in sub acromial impingement (SAI).

However, the normal appearance of the tendon depends upon the incident ultrasound beam being perpendicular to the tendon. A change of the incident beam angle produces a reduction in tendon echogenicity relative to that of muscle and may mimic tendinitis/tendinosis, hence a certain amount of expertise is required [4].

Learning bite

Following plain radiographs, ultrasound is an excellent means of imaging the shoulder.