Q: What's the difference between a frozen shoulder and adhesive capsulitis?

A:  The term frozen shoulder has been around since the early 1930s. But recent research has been able to show that every stiff, painful shoulder isn't necessarily a true "frozen shoulder."

You've heard the alternate term for this problem: adhesive capsulitis. According to the authors of a recent review, frozen shoulder and adhesive capsulitis are not the same things. What's the difference?

Frozen shoulder is a vague term similar to saying something like you have a limp when you walk. That doesn't tell you very much about the problem, the cause of the problem, or how to treat it.

At best, a frozen shoulder describes spasming of the short rotator muscles of the shoulder or tiny adhesions around the joint or bursae. That's the actual physical condition behind the shoulder pain and stiffness. Many conditions (not just one) can actually lead to this state of affairs.

On the other hand, adhesive capsulitis is a single problem of chronic inflammation of the joint capsule. The shoulder capsule is a covering of connective tissue interconnected with shoulder ligaments and tendons. They all help hold the head of the humerus (upper arm bone) in the shoulder socket.

The inflammatory process causes the capsule to thicken and tighten to the point that the extra fold of capsular tissue gets stuck to itself. There is a loss of normal synovial fluid in the joint.

When this happens, the shoulder can no longer slide and glide smoothly through its full range-of-motion. The capsule looses its ability to stretch. The result is the shoulder gets stuck and becomes stiff and painful just like a frozen shoulder. In chronic cases, inflammation is gone but it was the first step that got the process started. Treatment is still directed at the joint capsule.

Capsular restriction is the one factor that defines adhesive capsulitis separately from other conditions that can cause shoulder stiffness. Other problems like rotator cuff tears, tendinitis, shoulder arthritis, or nerve impingement can also cause loss of motion that looks just like adhesive capsulitis.

But in each of those other conditions, the motion loss is the result of multiple factors (not just one factor). Treatment focuses on the specific cause of the stiffness and that often has nothing to do with the shoulder joint capsule.

But if both conditions (frozen shoulder and adhesive capsulitis) look the same on the outside (stiff, painful shoulder), then how can the physician tell what's causing the problem or how to treat it effectively?

A careful history and review of what has happened over the course of time helps. Patient characteristics can also point to the correct diagnosis. For example, adhesive capsulitis is seen most often in women between the ages of 40 and 60 who are sedentary (not manual laborers or actively engaged in exercise). And there is often a history of some other serious health problem (e.g., heart attack, stroke, diabetes, breast cancer, thyroid disease).

X-rays aren't usually very helpful in distinguishing a frozen shoulder from adhesive capsulitis. They do help rule out fractures, arthritis, bone spurs, and osteopenia (decreased bone density). MRIs with dye injected into the joint (called magnetic resonance arthrography or MRA) will show changes in the joint capsule typical of adhesive capsulitis.

There is one clinical test the physician can perform that is very diagnostic. And that's moving the arm passively without the patient's help. If the shoulder resists movement into external (outward) rotation with the arm down at the side, it's likely adhesive capsulitis. There's no pain involved keeping the arm from moving (as there would be with a frozen shoulder). It's more of a mechanical hold from a sticky/stuck capsule that's keeping the joint from moving.

Reference: Andrew S. Neviaser, MD, and Robert J. Neviaser, MD. Adhesive Capsulitis of the Shoulder. In Journal of the American Academy of Orthopaedic Surgeons. September 2011. Vol. 19. No. 9. Pp. 536-543.