Clinical

The supraspinatus has five layers, but mainly functions as two layers: joint surface fibres and bursal surface fibres. Overuse or misuse of any tendon leads to accelerated apoptosis and to what has been called 'degeneration'.

Changes within the tendon which do not lead to symptoms may be referred to as tendinosis. When symptoms develop, the term tendinopathy is used. Impingement plus weakness suspicious for tear.

MRI is less reliable in the diagnosis of tendinopathy. The signs described include signal alteration with loss of the normal low signal on T1 weighted images, diffuse increase signal on T2 weighted images and alterations in tendon dimension. A wide inter and intra observer variation has been described with all of these. This is particularly the case with signal alterations on T1 weighted images. Similar alteration can be seen with variation in muscle tendon interdigitation and signal changes induced by the magic angle phenomenon. The latter are particularly problematic on short TE images.

Radiography

Abnormal only in late stages. Look for acromiohumeral impaction and secondary cuff arthropathy. Normal acromiohumeral distance approximately 1 cm but depends on radiographic projection.

Also look for calcification and x-ray as symptoms can mimic rotator cuff tear.

MRI

A full thickness tear is diagnosed when high signal is seen to completely traverse the tendon on T2 weighted or fat saturated images. Look carefully at the leading edge right up to the biceps tendon. Leading edge tears are easy to miss.

Using a cross reference facility on a workstation, can help with diagnosis of small tears. Joint surface partial tears (JSPT) often begin at the medial point of the tendon attachment (footprint) and undercut in a linear fashion. This type is called a 'Rim-Rent' tear or PASTA lesion. Reverse rim rent lesions are the same but involve the bursal surface.

Ultrasound

Use both axial and coronal images for diagnosis. US gives excellent visualisation of internal tendon structure. Look for loss of normal architecture and decide if it involves one or both surfaces.

Dynamic assessment with movement can be helpful as tendons move differently to tear debris. Bone irregularity at the footprint is a good clue as often indicates an abnormal tendon.