Anatomy of the shoulder
Find out more about the anatomy of the shoulder
The human shoulder is the most mobile joint in the body. This mobility provides the upper extremity with tremendous range of motion such as adduction, abduction, flexion, extension, internal rotation, external rotation, and 360° circumduction in the sagittal plane. Furthermore, the shoulder allows for scapular protraction, retraction, elevation, and depression. This wide range of motion also makes the shoulder joint unstable. This instability is compensated for by rotator cuff muscles, tendons, ligaments, and the glenoid labrum.
The shoulder joint is formed where the humerus (upper arm bone) fits into the scapula (shoulder blade), like a ball and socket. Other important bones in the shoulder include:
- The acromion is a bony projection off the scapula. The acromion of the scapula is a large bony projection on the superior end of the scapula. It is an important landmark of the skeletal system and a muscle attachment point essential to the function of the shoulder joint. The acromion also forms the acromioclavicular (AC) joint with the clavicle.
- The clavicle (collarbone) meets the acromion in the acromioclavicular joint. The collabone is very delicate and fragile. And any trauma hides about 65% of breakage with required long-lasting treatment. A broken collarbone is usually pretty obvious. You might feel a crack when it happens. Afterward, you will probably have: Pain and swelling Difficulty moving your arm and shoulder A grinding feeling when you try to raise your arm Sagging in your shoulder A bump around the area of the break
- The coracoid process is a hook-like bony projection from the scapula. It is small structure on the lateral edge of the superior anterior portion of the scapula. Pointing laterally forward, it, together with the acromion, serves to stabilize the shoulder joint. It is palpable in the deltopectoral groove between the deltoid and pectoralis major muscles. "Coracoid" in itself means "like a raven's beak", with reference to its shape. (Greek "Korax" = Raven)
The shoulder has several other important structures:
- The rotator cuff is a collection of muscles and tendons that surround the shoulder, giving it support and allowing a wide range of motion. The rotator cuff is a group of tendons and muscles in the shoulder, connecting the upper arm (humerus) to the shoulder blade (scapula). The rotator cuff tendons provide stability to the shoulder; the muscles allow the shoulder to rotate. It has four types of muscles and each of them inserts at the scapula, and has a tendon that attaches to the humerus. Together, the tendons and other tissues form a cuff around the humerus.
- The bursa is a small sac of fluid that cushions and protects the tendons of the rotator cuff. Sandwiched between the rotator cuff muscles and the outer layer of large bulky muscles is a structure known as the subacromial bursa. Bursae are everywhere in the body. They are found wherever two body parts move against one another and there is no joint to reduce the friction. A bursa is simply a sac between two moving surfaces that contains a small amount of lubricating fluid.
- A cuff of cartilage called the labrum forms a cup for the ball-like head of the humerus to fit into. The labrum is similar to the meniscus of the knee. It is a fibro-cartilaginous rubbery structure which encircles the glenoid cavity deepening the socket providing static stability to the glenohumeral joint. It acts and looks almost like a washer, sealing the two sides of the joint together.
The humerus fits relatively loosely into the shoulder joint. This gives the shoulder a wide range of motion, but also makes it vulnerable to injury. Depending on the type of the trauma, shoulder injury treatment can vary from a serious and long-lasting surgery to steroid injection or only pain killer consumption. Afterwards, though, rehabilitation will be needed and having a specialist in the field by your side is always a great idea. Never underestimate the expert opinion for any anomaly you observe in your shoulder or its motion performance. Contact your GP as soon as possible! And when it comes to keeping your shoulder flexible and healthy, eating Ca-rich food and staying in shape is always a great and 100% risk-free approach.