The rotator cuff consists of four muscles: infraspinatus, supraspinatus, teres minor and subscapularis; the tendons of which blend with the capsule of the glenohumeral joint, aiding its stability. Due to its location in the subacromial arch, the supraspinatus is particularly susceptible to injury.
The supraspinatus muscle, together with the deltoid, raises the arm to initiate abduction. The weakest point of the supraspinatus tendon is the part, which forms the cuff over the joint in the area that is 1cm from the attachment of the tendon to the humerus. It is at this point that ruptures most often occur.
Mechanism of Injury
Excessive load through either overuse, poor biomechanics of the shoulder or a combination of both.
May be acute, chronic or acute on chronic injury.
In acute injury, sudden intense pain is felt over the shoulder.
On exertion, the pain may return and can increase at night causing problems with sleeping.
Pain occurs when the arm is externally rotated (thumbs turned out) and raised upwards and/or outwards. When the tendon is only partially torn, activities undertaken at 60-80° of arm elevation may cause little or no pain.
The arm can be held at an angle of more than 120° to the body when the tendon has sustained total rupture but when it is lowered further it suddenly drops, this is known as the ‘dropping arm’/ ‘dead arm’ sign.
The ‘empty can test’ is positive. The arms are held in 90° of elevation in the scapular plane and the thumbs are rotated down towards the ground. Pain is elicited when the patient resists downward pressure.
Please consult with your medical professional for a complete diagnosis and treatment plan.