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The rotator cuff muscles are a group of muscles that make up the major muscles that rotate the arm and act to stabilize the shoulder joint. There are four muscles that make up the group: supraspinatus muscle, infraspinatus muscle, teres minor muscle, and the subscapularis muscle.  Injury to the rotator cuff muscles are very common with 9.7% in people 20 years old or younger, and 62% in people over the age of 80. The most common muscle to injure in the group is called the supraspinatus muscle. 

The supraspinatus originates from the superior (upper) portion of the scapula (shoulder blade) and inserts into the superior humerus bone (arm). It is innervated by the suprascapular nerve which stems from the cervical 5th and 6th nerve roots. Its main action is to abduct the arm (move arm out to the side) and it also helps to keep the head of the humerus bone attached when lifting the arm overhead. 

Any type of overhead or throwing motions put the supraspinatus at a high risk of injury. Baseball players, swimmers, and tennis players are at a higher risk of injuring this muscle due to the high forces being applied while the arm is overhead. 

The supraspinatus may be injured in a few different ways. The tendon can become inflamed which causes tendonitis. It can be pinched when it travels underneath the acromion bone (part of your collar bone) causing impingement syndrome. The muscle or tendon can tear either partially or fully. Typically, the supraspinatus can be treated through rehabilitation exercises unless it is a severe tear or it is being pinched due to a misshaped bone. If one of these are present typically surgical intervention is needed, then rehabilitation will happen after to help the recovery.

Rehabilitation of an injured supraspinatus depends on the severity but typically follows certain guidelines. Returning normal range of motion to the shoulder in abduction is an initial goal. Strengthen up the muscles that stabilize the shoulder blade by doing exercises like scapular retractions, rows, and modified push-ups. Then exercises that will specifically strengthen the supraspinatus like lateral raises, shoulder presses, internal and external rotations with resistance. All these exercises should be done with the guidance of your health practitioner to progress in a safe way.

References:

May T, Garmel GM. Rotator Cuff Injury. [Updated 2020 Jul 2]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK547664/

https://emedicine.medscape.com/article/93095-overview