rotator cuff

ROTATOR CUFF
Muscles on the dorsum of the scapula, and the Triceps brachii.
The scapular and circumflex arteries.
Gray's	subject #123

In anatomy, the rotator cuff (rotator cuff) is the group of muscles and their tendons that act to stabilize the shoulder. The four muscles of the rotator cuff, along with the teres major and the deltoid, make up the six scapulohumeral (those that connect to the humerus and scapula and act on the glenohumeral joint) muscles of the human body.

Function

The rotator cuff muscles are important in shoulder movements and in maintaining glenohumeral joint (shoulder joint) stability.^[1] These muscles arise from the scapula and connect to the head of the humerus forming a cuff at the shoulder joint. They hold the head of the humerus in the small and shallow glenoid fossa of the scapula. The glenohumeral joint is often likened to a golf ball(head of the humerus) sitting on a golf tee (glenoid fossa). During abduction of the arm, the rotator cuff compresses the glenohumeral joint, a term known as concavity compression, in order to allow the large deltoid muscle to further elevate the arm. In other words, without the rotator cuff, the humeral head would ride up partially out of the glenoid fossa, lessening the efficiency of the deltoid muscle. The anterior and posterior directions of the glenoid fossa are more susceptible to shear force perturbations as the glenoid fossa is not as deep relative to the superior and inferior directions. The rotator cuff's contributions to concavity compression and stability vary according to their stiffness and the direction of the force they apply upon the joint.

Muscles composing rotator cuff

The mnemonic 'SITS', sometimes written 'SItS' as an additional hint that the teres minor is a member, is often used to remember the four muscles of the rotator cuff.^[2]

Injuries

Rotator cuff tear

The tendons at the ends of the rotator cuff muscles can become torn, leading to pain and restricted movement of the arm. A torn rotator cuff can occur following a trauma to the shoulder or it can occur through the "wear and tear" of tendons, most commonly that of the supraspinatus under the acromion. It is an injury frequently sustained by athletes whose duties involve making repetitive throws, such as baseball pitchers, American football quarterbacks, volleyball (due to their swinging motions), water polo players, shotput throwers (due to using poor technique), swimmers, boxers, kayaking, fast bowlers in cricket, and tennis players (due to their service motion). This type of injury also commonly affects conductors (music), choral conductor, orchestral conductor, due to the swinging motions and other movements used to lead their ensemble. It is commonly associated with motions that require repeated overhead motions or forceful pulling motions.

Rotator cuff impingement

A systematic review of relevant research found that the accuracy of the physical examination is low.^[3] The Hawkins-Kennedy test^[4][5] has a sensitivity of approximately 80% to 90% for detecting impingement. The infraspinatus and supraspinatus^[6] tests have a specificity of 80% to 90%.^[3]

Treatment

Reduce pain and swelling

As with all muscle injuries, R.I.C.E. is the modality recommended by physicians (MDs and DOs), physical therapists, athletic trainers, and chiropractors.^{[citation needed]}

• Rest means ceasing movement of the affected area.

• Icing uses ice to reduce inflammation.

• Compression limits the swelling.

• Elevation involves placing the area higher to reduce inflammation and swelling.

Cold compression therapy is very useful for all muscle tears and strains as it reduces pain and swelling. Using a cold compression therapy wrap for 15 minutes before sleeping can aid in reducing the pain that causes restless sleep.^{[citation needed]}

Strengthening

The rotator cuff can be strengthened to rehabilitate shoulder injuries, and prevent future ones. There are different exercises to target the individual rotator cuff muscles.

Description	Beginning	End
The most effective is the side-lying external rotation, which activates the supraspinatus, subscapularis, infraspinatus and teres minor. The side-lying external rotation involves the person selecting a dumbbell of low weight initially when first training - no more than 3 kilograms. The lifter lies on a bench sideways, with the arm next to his side and flexed about 90 degrees at the elbow. Rotate the upper arm, raising the dumbbell towards the ceiling to a 45 degree angle, with the elbow still flexed and the upper arm close to the body, at a pace of two seconds up and four seconds down. This is an excellent all-around shoulder exercise.
Another exercise is the propped external rotator, which targets the infraspinatus and teres minor. The lifter should sit perpendicular to the barbell, with his arm flexed at 90 degrees at the elbow and the forearm resting parallel on the barbell. Again, selecting a dumbbell of modest weight if just beginning, raise the dumbbell up until the forearm points up. Slowly lower the dumbbell and repeat, exercising both arms.
The final exercise is the lateral raise with internal rotation (LRIR). Grasping a dumbbell in each hand, the lifter should internally rotate his arm so that his extended thumbs point towards the floor - as if the lifter is emptying a drink into a bin. The lifter should then raise his arms sideways, with the thumbs still pointing downwards, until the dumbbells are just below the shoulders. The LRIR primarily targets the supraspinatus.

Strengthening the rotator cuff allows for increased loads in a variety of exercises. When weightlifters are unable to increase the weight they can lift on a pushing exercise (such as the bench press or military press) for an extended period of time, strengthening the rotator cuff can often allow them to begin making gains again. It also prevents future injuries to the glenohumeral joint, balancing the often-dominant internal rotators with stronger external rotators. Finally, exercising the rotator cuff can lead to improved posture, as without exercise to the external rotator, the internal rotators can see a shortening, leading to tightness. This often manifests itself as rounded shoulders in the population.

Surgery

Even for full thickness rotator cuff tears, conservative care outcomes are usually reasonable.^[7] However, many patients still suffer disability and pain despite non-surgical therapies. For massive tears of the rotator cuff, surgery has shown durable outcomes on 10 year follow-up.^[8] However, the same study demonstrated ongoing and progressive fatty atrophy and re-tears of the rotator cuff. Shen has shown that MRI evidence of fatty atrophy in the rotator cuff prior to surgery is predicative of a poor surgical outcome.^[9] To address this issue of failure of surgical repair and poor conservative care outcomes caused by muscular atrophy, bioengineering may be the answer. Mesenchymal stem cells have been shown to differentiate into skeletal muscle.^[10] If the rotator cuff is completely torn, surgery is usually required to reattach the tendon to the bone.^[11]

Additional images

Diagram of the human shoulder joint

Suprascapular and axillary nerves of right side, seen from behind.

The suprascapular, axillary, and radial nerves.

References

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