Stiff shoulder, or adhesive capsulitis, is a condition that causes restriction of motion in the shoulder joint. The cause of a frozen shoulder is not well understood, but it often occurs for no known reason. Frozen shoulder causes the capsule surrounding the shoulder joint to contract and form scar tissue.
What causes frozen shoulder?
Most often, frozen shoulder occurs with no associated injury or discernible cause. There are patients who develop a frozen shoulder after a traumatic injury to the shoulder, but this is not the usual cause. Some risk factors for developing a frozen shoulder include:
Age & Gender
Frozen shoulder most commonly affects patients between the ages of 40 to 60 years old, and it is twice as common in women than in men.
Endocrine Disorders
Patients with diabetes are at particular risk for developing a frozen shoulder. Other endocrine abnormalities, such as thyroid problems, can also lead to this condition.
Shoulder Trauma or Surgery
Patients who sustain a shoulder injury, or undergo surgery on the shoulder can develop a frozen shoulder joint. When injury or surgery is followed by prolonged joint immobilization, the risk of developing a frozen shoulder is highest.
Other Systemic Conditions
Several systemic conditions such as heart disease and Parkinson’s disease have also been associated with an increased risk for developing a frozen shoulder.
What happens with a frozen shoulder?
No one really understands why some people develop a frozen shoulder. For some reason, the shoulder joint becomes stiff and scarred. The shoulder joint is a ball and socket joint. The ball is the top of the arm bone (the humeral head), and the socket is part of the shoulder blade (the glenoid). Surrounding this ball-and-socket joint is a capsule of tissue that envelops the joint.
Normally, the shoulder joint allows more motion than any other joint in the body. When a patient develops a frozen shoulder, the capsule that surrounds the shoulder joint becomes contracted. The patients form bands of scar tissue called adhesions. The contraction of the capsule and the formation of the adhesions cause the frozen shoulder to become stiff and cause movement to become painful.