Frozen Shoulder (Adhesive Capsulitis)

Your shoulder is a ball-and-socket joint wrapped in a balloon-like sleeve called the joint capsule (the glenohumeral capsule) — a continuous bag of tough, fibrous tissue that anchors the ball to the socket and lets the shoulder swing through its full range. In the bottom of that capsule there's normally a small loose pouch (the axillary recess) that unfolds like a curtain to give the shoulder its overhead range. Frozen shoulder is what happens when the inside of that capsule gets inflamed, then progressively scars, thickens, and contracts. The pouch shrinks down. The joint loses room to move. And because it's the capsule itself that's stuck — not the rotator cuff, not the muscles — the motion loss happens in every direction at once and is just as bad when someone else moves your arm for you (passive motion) as when you move it yourself (active motion). That all-direction, even-when-relaxed pattern is what distinguishes frozen shoulder from a torn cuff or an impingement.

The condition runs a stereotyped three-phase course that takes one to three years to complete on its own. The freezing phase (typically 2–9 months) is dominated by deep aching pain, often worse at night, and slowly worsening motion. The frozen phase (4–12 months) is the stiff phase — the pain backs off but the shoulder is now genuinely locked, and patients describe being unable to reach for a seatbelt, hook a bra, or wash the opposite armpit. The thawing phase (5–24 months) is a gradual, spontaneous return of motion. Each phase blends into the next without sharp boundaries; the goal of treatment isn't to skip the disease but to shorten each phase and keep the pain manageable while the shoulder gets through it.

Two facts matter for who gets it: diabetes raises the risk roughly five-fold (and diabetic frozen shoulders tend to be more severe and slower to thaw), and any reason to immobilize the shoulder for a stretch — a fracture in a sling, a stroke, prolonged rotator-cuff pain that the patient was simply not moving — can trigger it. It's more common in women and in the non-dominant shoulder, more common in middle age (40s–60s), and more common in patients with thyroid disease or cardiac conditions. About 1 in 7 patients eventually develops it on the other shoulder.

The early picture is deep, aching shoulder pain that the patient can't quite localize — it's diffusely achy across the front and side of the shoulder, often radiating down toward the upper arm. Sleeping on that side becomes impossible within weeks. Reaching overhead, behind the back, or out to the side starts to hurt and progressively becomes harder, not because of weakness but because the arm physically won't go that direction anymore. Many patients describe trying to reach into the back seat for something and being shocked at how short their reach has become.

As the freezing transitions into the frozen phase, the pain quiets but the stiffness takes over. The classic functional losses are washing the opposite armpit, fastening a bra, putting on a seatbelt, or reaching into a back pocket — each of these motions requires the very ranges the capsule has shrunk down. What's not typical: weakness, numbness, or sharp pinching pain in a specific arc of motion. Those point toward the rotator cuff, the cervical spine, or impingement, where motion is usually preserved when someone else moves the arm for you. Frozen shoulder is the one where passive motion is just as restricted as active motion — that's the diagnostic giveaway.

The diagnosis is made on exam. Your provider will move your arm into external rotation (turning the forearm outward with the elbow tucked at your side) and into overhead reach — frozen shoulder typically loses external rotation first and most severely, often by 50% or more compared with the other side, even when you let the arm hang relaxed. That loss of passive external rotation is the single most reliable finding and the one that separates frozen shoulder from a rotator cuff tear, where passive motion is usually preserved. X-rays are obtained to make sure nothing else is going on (arthritis, calcium deposits, an old fracture) and are typically normal. MRI isn't routinely needed — when ordered, it shows the capsule thickening and bright contrast uptake in the inflamed lining, but the diagnosis is already made by the time the MRI is being read.

1. Hydrodilatation

   An ultrasound- or fluoroscopy-guided injection that distends the joint capsule with a larger volume of fluid (saline plus steroid) — essentially stretching the capsule from the inside. Can provide rapid improvement in motion in stubborn cases that haven't responded to a standard intra-articular injection alone.

Surgery is considered for patients with persistent severe restriction that has not responded to a sustained trial of injections and therapy.

External patient-education references and related OSI pages for additional background:

• Britannica — Shoulder (anatomy)
• AAOS OrthoInfo — patient education library
• OSI glossary — orthopedic terminology in plain language