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It can develop after an injury or out of the blue: One day you wake up with intense pain in your shoulder, and over the next few weeks the joint grows so stiff that your range of motion becomes severely compromised.
Known as frozen shoulder (aka, adhesive capsulitis), this mysterious condition usually occurs between the ages of 40 and 65 and affects more women than men. “It’s an interesting process, and it only happens to shoulders; we don’t see frozen knees or frozen elbows,” says Brian Feeley, M.D., a professor of orthopedic surgery at the University of California, San Francisco.
The problem arises where the head of the humerus, or upper arm bone, fits into a shallow socket in the shoulder blade — more specifically, in the shoulder capsule, which is the strong connective tissue surrounding the joint. “The name adhesive capsulitis says a lot because the [shoulder] capsule is the problem — there’s inflammation of the sac the shoulder lives in, and adhesive means it gets stuck after a while,” explains Beth Shubin Stein, M.D., an associate attending orthopedic surgeon and codirector of the Women’s Sports Medicine Center at the Hospital for Special Surgery in New York City.
The three stages of a frozen shoulder
In the early phase, the shoulder simply hurts and the pain gradually worsens. The second stage is the frozen stage, when the shoulder loses range of motion and “the capsule becomes thicker from inflammation,” notes Shubin Stein. The third stage, called the thawing phase, brings a gradual improvement to the shoulder’s range of motion. How long someone will spend in each stage is unpredictable and varies significantly from one person to the next, but the condition can take six months to two years or longer to resolve.
The exact causes of frozen shoulder remain a mystery, which is why it’s often referred to as idiopathic (meaning, of unknown cause). What is known is that it likely involves an element of inflammation, which triggers the release of chemicals that irritate the joint, causing pain, explains Jon J.P. Warner, M.D., cochief of the MGH Shoulder Service in Boston. “That, in turn, causes the release of other chemicals that cause stiffness or freezing and scarring.” More often than not, frozen shoulder affects the non-dominant arm, and if someone develops idiopathic frozen shoulder in one shoulder, she’s at higher risk for getting it on the other side later, Warner says.
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