To better understand adhesive capsulitis, it helps to understand the anatomy of the shoulder joint.

The shoulder joint allows motion between two major bones: the humerus and the scapula. The shoulder joint is a ball and socket joint. A depression of the scapula, known as the glenoid, provides the socket for the head of the humerus. Ligaments and muscles act to stabilize the scapular-humeral joint during range of motion and weight bearing.

The clavicle, or collar bone, connects to the scapula at the acromion, which is a bony projection off the scapula. The acromioclavicular ligaments normally surround and secure this joint.

There are four main ligaments supporting the A-C joint. One or more can be sprained (torn) during this injury. The ligaments include:

• Acromioclavicular ligament
• Coracoclavicular ligament
• Deltoid ligament
• Trapezius ligament

Anatomy examples:

• The shoulder joint viewed from the front
• The shoulder joint viewed from the back
• The shoulder joint viewed from the top showing rotator cuff
• Muscles of the shoulder
• The acromioclavicular joint