Description

The rotator cuff comprises four muscles and their
tendons. The supraspinatus, infraspinatus and teres minor
muscles arise from the scapula and their tendons insert into
the greater tuberosity of the humerus. The subscapularis
muscle arises from the scapula but the tendon inserts into the
lesser tuberosity. Rotator cuff disease principally affects the
supraspinatus tendon. Tendon pathology is generally
classified as tendonosis or tendonopathy, partial thickness
tear and complete rupture. Tendonpathy correlates
histologically with microscopic disruption and
disorganisation of collagen fibres and an increase in mucoid
ground substance and fibroblasts within the tendon. Partial
thickness tears may arise on the articular or bursal surface of
the tendon. A complete tear extends through the full
thickness of the tendon. There are three principle causes of
rotator cuff tears: mechanical impingement, intrinsic
degeneration and trauma. The concept of mechanical
impingement or “primary extrinsic impingement” was
popularised by Neer who proposed that tears of the
supraspinatus tendon are related to compression of the
tendon between the humeral head and coraco-acromial arch.
The relative importance of impingement versus intrinsic
degeneration may vary between patients. There is however
general agreement that surgical decompression is appropriate
in patients with tendon damage and a narrow subacromial
space. Rotator cuff damage may also be due to “secondary
extrinsic impingement” in which there is laxity of rotator
cuff tendons and superior migration of the humeral head
causing impingement on the tendon in the presence of a
normal coraco-acromial arch. In throwing athletes “internal
impingement” can cause rotator cuff damage due to repeated
impaction between the greater tuberosity and posterosuperior
glenoid labrum resulting in damage to both structures. Sub-
coracoid impingement results in damage to the subscapularis
tendon in patients with an abnormally prominent coracoid
process. Rotator cuff tendonosis is characterised by increased
signal intensity within the tendon and best appreciated on
short TE and fat suppressed images. Discrete defects within
the bursal or articular surface of the tendon indicate partial
thickness tears. Most full thickness tears are seen as a fluid
filled defect traversing the whole tendon. Occasionally this
defect may be filled by synovial or granulation tissue and appear of intermediate signal intensity. Documentation of
the site and size of the rotator cuff tear is of value in
planning appropriate treatment.