Human shoulder anatomy


The shoulder joint is the joint between the rib cage and the upper limb. There are two joints in the shoulder.

  1. The shoulder joint is the spherical junction of the upper arm bone and the socket of the scapula.
  2. The second shoulder joint is the junction of the clavicle with the scapula, called the acromioclavicular joint.

Most of the shoulder movement occurs at the shoulder joint, but the acromioclavicular joint must also function normally for full shoulder movement.


The three bones of the shoulder are:

  1. Arm bone ( humerus )
  2. Scapula ( scapula )
  3. Clavicle (clavicle)

The scapula has a part that forms a depression for the shoulder joint in the shape of a ball; this is called glenoids. The glenoid is covered with smooth cartilage. The place where the rounded top of the arm bone (humerus) contacts the shoulder blade is called the shoulder joint.

The second joint at the top of the shoulder is where the other part of the scapula, the acromion, connects to the clavicle. This is called an acromioclavicular joint.

Rotator cuff

The rotator cuff is a group of four muscles and tendons that surround the shoulder joint. The muscle contracts to move the bones; Tendons are where the muscle joins the bone. The rotator cuff muscles play an important role in the movement of the ball of the shoulder joint.

The rotator cuff plays an important role in many daily activities and can cause severe pain if injured. Rotator cuff inflammation or irritation is called rotator cuff tendonitis or shoulder bursitis. When the rotator cuff tendons tear, it is called a rotator cuff tear.

Get Medical Information / Alexandra Gordon

Shoulder capsule

The humeral capsule surrounds the globular portion of the shoulder joint. The capsule separates the joint from the rest of the body and contains joint fluid.

Several ligaments make up parts of the joint capsule and these ligaments are important in keeping the shoulder joint in the correct position. If the shoulder is dislocated, the ligaments of the shoulder capsule can tear.

Humeral capsule tension is important. If the capsule is too loose, the condition is called multidirectional instability . When the shoulder capsule is too tight, the condition is called frozen shoulder (adhesive capsulitis) .

Upper lip of shoulder

The upper lip is the cartilaginous border that surrounds the socket of the shoulder joint. The nest of the shoulder joint is shallow and the upper lip gives the nest more depth and therefore more stability. The upper lip also serves as the insertion site for the main tendon of the shoulder, the biceps tendon.

A broken upper lip in the shoulder can cause pain, joint instability, or both. Tears of the upper lip are generally classified based on their location. The most common lip tears are associated with shoulder dislocations, called Bankart tears , and tears associated with biceps tendon problems, called SLAP tears .

Shoulder muscles

While most people think of the rotator cuff when they think of the muscles that surround the shoulder joint, these are just four of the 17 muscles that cross the shoulder joint. Some of these muscles are also critical to normal shoulder function.

One of the muscle groups that commonly affects people with shoulder problems are the periscapular muscles. These muscles help control the movement of the scapula (scapula) and this movement is essential for normal shoulder function.

The socket of the shoulder joint is part of the scapula, and if the movement of the scapula is not normal, the function of the shoulder may not be normal. Many people with shoulder pain, weakness, and instability often need to focus on improving scapular function to improve shoulder mechanics.

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