Frozen Shoulder Anatomy
Your shoulder joint involves bones, muscles, tendons, ligaments, connective tissues and synovial fluid. There are 3 main bones in your shoulder: the shoulder blade (scapula), the collarbone (clavicle) and the upper arm bone (humerus). These are attached to each other by ligaments (attach bone to bone). Muscles move your bones by pulling on your tendons (attach muscle to bone). Both tendons and ligaments provide stability and alignment to your joint to ensure easy movement in your shoulder. The main muscles involved with your shoulder joint are your rotator cuff muscles (supraspinatus, subscapularis, infraspinatus and teres minor), as well as your biceps brachii (upper arm), deltoid (top of the shoulder), and trapezius (upper back) muscles.
The shoulder is one of the most mobile and flexible joints in your body. It is a "ball and socket" joint (glenohumeral joint), in which the ball (the top, rounded part of your humerus) is held in the socket (the shallow, depressed area called your glenoid cavity, located on the outer edge of your scapula). There is a ring of fibrous cartilage (labrum) that surrounds the glenoid cavity and articular cartilage (slick, hard connective tissue) that covers the end of the humerus to help stabilize the ball in the socket and reduce friction. Your entire joint is surrounded by a tough, fibrous, flexible shoulder joint capsule and inner synovial membrane that produces synovial fluid (thick, egg-white like fluid). This helps to lubricate your shoulder joint and allows the bones to move easily within your joint. When your arm is raised over your head the joint capsule is fully stretched, when your arm is lowered to your side, the capsule rests in a small, pouch-like sac. Your bursa is a fluid-filled sac that lies beneath your acromion (bump on top, outer edge of your clavicle) and above your soft tissues to prevent rubbing when your bones are moved.
What is Frozen Shoulder?
Your shoulder has an amazing range of motion which is a blessing and a curse, as it can sometimes lack stability which makes it more prone to injury. The conditions adhesive capsulitis and frozen shoulder are often used interchangeably; however there is a slight difference between the two conditions.
Literally the word adhesive means "scarring", and capsulitis means "inflammation of the capsule". Adhesive capsulitis happens when the shoulder joint capsule and soft tissues surrounding your socket (glenoid cavity) become inflamed, swollen and contracted. This causes bands of scar tissue (adhesions) to develop in your joint; as a result your tissues become less flexible, stick together and restrict movement. You will experience pain, stiffness, a limited range and gradual loss of overall motion in your shoulder joint, because of the adherence of your shoulder capsule to the top of your humerus. Eventually your joint may become stuck to the point where you have no movement at all.
Frozen shoulder is the generalized name for gradual loss of ability to move your shoulder in all directions. A number of pre-existing conditions can cause and/or encourage adhesive capsulitis to occur in your shoulder joint. This condition is influenced by injuries to your shoulder muscles, tendons, ligaments and the associated bursa, as well as other diseases. Often before you can deal with or determine the other conditions, you must first get rid of the adhesive capsulitis and regain movement in your shoulder.
Frozen shoulder affects 2 - 5% of the population (about 1 in 50 adults will get this at some time in their life). Generally you will experience frozen shoulder in either your left or right shoulder, whichever is your non-dominant shoulder (if you are right handed it would be in your left shoulder and vice versa). About 15% of the population (1 in 5 cases) will get it on both sides at some time in their life, however rarely ever at the same time. It is very uncommon to suffer from frozen shoulder in the same shoulder twice and normally it does not affect other joints in your body. Frozen shoulder is not known to lead to major damage and/or other more serious conditions; more so, it is generally a side effect of other conditions and/or a condition in and of itself.
Since adhesive capsulitis and frozen shoulder are very similar and difficult to differentiate, they are treated in the same way. For our purpose, we will look at these injuries as one condition.
Alternate Names and Related Conditions:
Adhesive capsulitis, pitcher's arm, rotator cuff tears, calcific bursitis, arthritis, tendinitis, supraspinatus tendinitis, brachial neuritis, reflex sympathetic dystrophy, pericapsulitis, periarthritis, adherent bursitis, obliterative bursitis, dupuytren contracture.