How do you diagnose rotator cuff tendinitis?
By carefully examining the shoulder and by knowing the function of the four rotator cuff muscles (i.e.,
abduction, external rotation, and internal rotation).
The supraspinatus is the most important and most commonly damaged of the four. It links the top of the
scapula to the humerus, inserting into its greater tuberosity. It is partially responsible for arm
abduction (the initial 15–30 degrees are actually produced by the deltoid, the next 60 degrees by the
supraspinatus, and the final 90 degrees by the deltoid again). Hence, inflammation of the supraspinatus tendon leads to pain at 30–90 degrees of abduction, as the humerus impinges the tendon against the acromion. It can be easily tested through the empty can test.
The infraspinatus produces external rotation of the humerus, a function assisted by the teres minor. The
two also cooperate to maintain glenohumeral stability. To test external rotators (infraspinatus and
teres minor): (1) have the patient abduct both shoulders to 20–30 degrees, while keeping the elbows flexed at 90 degrees; (2) instruct the patient to push the arms outward (externally rotate) against resistance. External rotation elicits pain in tendinitis and weakness in tears.
The subscapularis is the only of the four rotator muscles to originate from the anterior surface of the scapula (the others arise instead in the back). It connects the scapula to the humerus, serving as humeral head depressor and, in certain shoulder positions (adduction), as internal rotator. Function is evaluated through the “Gerber’s lift-off test”: (1) have patients place the hand behind the back, with palm facing out, and (2) instruct them to lift the hand away from the back and against resistance. Internal rotation elicits pain in tendinitis and weakness in tears.
Note that given the anatomic closeness of the long head tendon of the biceps (which passes down the
bicipital groove in a fibrous sheath between the subscapularis and supraspinatus tendons), patients with
rotator cuff disease also may have biceps tendinitis
By carefully examining the shoulder and by knowing the function of the four rotator cuff muscles (i.e.,
abduction, external rotation, and internal rotation).
The supraspinatus is the most important and most commonly damaged of the four. It links the top of the
scapula to the humerus, inserting into its greater tuberosity. It is partially responsible for arm
abduction (the initial 15–30 degrees are actually produced by the deltoid, the next 60 degrees by the
supraspinatus, and the final 90 degrees by the deltoid again). Hence, inflammation of the supraspinatus tendon leads to pain at 30–90 degrees of abduction, as the humerus impinges the tendon against the acromion. It can be easily tested through the empty can test.
The infraspinatus produces external rotation of the humerus, a function assisted by the teres minor. The
two also cooperate to maintain glenohumeral stability. To test external rotators (infraspinatus and
teres minor): (1) have the patient abduct both shoulders to 20–30 degrees, while keeping the elbows flexed at 90 degrees; (2) instruct the patient to push the arms outward (externally rotate) against resistance. External rotation elicits pain in tendinitis and weakness in tears.
The subscapularis is the only of the four rotator muscles to originate from the anterior surface of the scapula (the others arise instead in the back). It connects the scapula to the humerus, serving as humeral head depressor and, in certain shoulder positions (adduction), as internal rotator. Function is evaluated through the “Gerber’s lift-off test”: (1) have patients place the hand behind the back, with palm facing out, and (2) instruct them to lift the hand away from the back and against resistance. Internal rotation elicits pain in tendinitis and weakness in tears.
Note that given the anatomic closeness of the long head tendon of the biceps (which passes down the
bicipital groove in a fibrous sheath between the subscapularis and supraspinatus tendons), patients with
rotator cuff disease also may have biceps tendinitis