Shoulder Anatomy 101

The deltoid muscle is the most superficial and is very essential for normal shoulder function. It covers the anterior, middle and posterior part of the shoulder.The deltoid muscle can easily be felt on your shoulder.

If we remove the deltoid muscles we get to the next layer of muscles. These include the important pectoralis muscles, biceps attachments and rotator cuff muscles. The rotator cuff muscles help rotate the arm and attach to the top of the humerus, hence the name, “rotator cuff.”

There are four rotator cuff muscles: the supraspinatus, infraspinatus, subscapularis and teres minor (not all pictured).

These are the ones that tear when you have rotator cuff problems. See section on impingement and rotator cuff tears in this web site.

As we remove more of the surrounding muscles, we are left with only the rotator cuff muscles. All four of them originate on the scapula (shoulder blade) and attach onto the humeral head (top of the humerus). They attach onto the greater and lesser tuberosities (see bony anatomy picture below).

Once the rotator cuff muscles have been removed, we are left with the shoulder capsule and glenohumeral ligaments. When these are damaged or injured one can get pathological conditions such as shoulder instability (ligaments are too loose) or frozen shoulder (ligaments are too tight).

With all of the muscles, tendons and ligaments removed we are left with the bones which make up the shoulder. These joints can get arthritic and subsequently cause pain. See section on shoulder arthritis in the website.

You are now a graduate of Shoulder Anatomy 101.