A shoulder that locks up is almost always caused by one of a few specific problems: the joint capsule has tightened and scarred (frozen shoulder), a torn piece of cartilage is catching inside the joint, or bone spurs or calcium deposits are physically blocking movement. The type of locking you experience, whether it’s a gradual loss of motion over weeks or a sudden catch during certain movements, points toward different causes and different solutions.
Frozen Shoulder: The Most Common Cause
Frozen shoulder, known clinically as adhesive capsulitis, is the most frequent reason a shoulder progressively locks up. What happens inside the joint is straightforward: the flexible capsule surrounding your shoulder becomes inflamed, then gradually fills with scar tissue. New collagen fibers deposit throughout the capsule, particularly in the front and bottom of the joint, making it physically thicker and stiffer. Imaging studies show the capsule wall visibly thickened compared to a healthy shoulder. The result is a joint that feels “stuck” in every direction, not just one.
The condition moves through three distinct phases. The first, called the freezing phase, lasts roughly 2 to 9 months. Pain is the dominant symptom here, often worse at night, and you’ll notice your range of motion shrinking week by week. The second phase is the frozen phase, lasting 4 to 12 months. Pain actually decreases during this stage, but stiffness becomes severe. Reaching overhead, behind your back, or out to the side all feel physically blocked. The final thawing phase brings gradual return of movement, though full recovery can take a year or more on its own.
People with diabetes, thyroid disease, or high cholesterol face a significantly higher risk of developing frozen shoulder. Low body mass index is also a notable risk factor. If you have any of these conditions and notice your shoulder progressively tightening, that combination of factors makes frozen shoulder a strong possibility.
How to Tell Frozen Shoulder From a Rotator Cuff Tear
Both conditions limit your ability to move your arm, but there’s a simple way to distinguish them. Have someone else try to lift your arm for you while you relax completely. With a rotator cuff tear, another person can usually move your arm through its full range without resistance. The limitation comes from pain and weakness in the torn tendon, not a physical block. With frozen shoulder, your arm won’t move even with help. The joint itself is locked by the scarred capsule, and no amount of external force (within reason) will push it past a certain point.
This distinction matters because treatment paths are completely different. A rotator cuff tear involves a damaged tendon that may need repair. Frozen shoulder involves a capsule that needs to be loosened, either through therapy, injection, or a procedure to stretch or release it.
Catching and Clicking During Movement
If your shoulder doesn’t feel constantly stiff but instead catches or locks at certain angles, a labral tear is a likely cause. The labrum is a ring of cartilage lining the rim of your shoulder socket, acting like a gasket to keep the ball of your upper arm bone seated properly. When a portion of the labrum tears, the loose flap can fold into the joint space. As the ball rolls over that displaced tissue, you feel a distinct catch or click, sometimes with a brief sensation of the joint locking in place before releasing.
Labral tears commonly result from falls onto an outstretched hand, repetitive overhead motions (swimming, throwing, painting ceilings), or shoulder dislocations. The locking tends to happen at specific positions rather than across all movements, which is a key difference from frozen shoulder.
Bone Spurs and Arthritis
Osteoarthritis of the shoulder joint creates bony growths called osteophytes that develop along the edges of the joint surfaces. These growths physically collide with surrounding structures when you try to move your arm, creating a mechanical block. The restriction tends to worsen at the extremes of motion: reaching all the way overhead, rotating your arm fully outward, or extending it behind you. Research using 3D modeling shows that removing these bony growths significantly increases impingement-free range of motion in multiple directions, confirming that the spurs themselves are a direct cause of restricted movement.
Unlike frozen shoulder, arthritis-related locking typically develops over years rather than months, and you’ll often hear or feel grinding (crepitus) when you move the joint. Morning stiffness that loosens somewhat with activity is another hallmark.
Calcium Deposits and Sudden Locking
Calcific tendinitis can cause a dramatic, rapid onset of shoulder locking that feels entirely different from the slow progression of frozen shoulder or arthritis. Calcium deposits form within the rotator cuff tendons, and during what’s called the resorptive phase, the body attempts to break down these deposits. This triggers intense chemical inflammation, causing the surrounding bursa to swell and thicken. The swollen tissue collides within the tight subacromial space beneath your shoulder blade, severely restricting movement.
The pain from this condition often arrives suddenly, is severe enough to prevent sleep on the affected side, and worsens at night. If your shoulder went from normal to barely movable within a day or two with extreme pain, calcium deposits are a strong possibility. An X-ray can usually confirm them quickly, since the calcium shows up clearly on imaging.
Impingement Syndrome
Shoulder impingement happens when the tendons and bursa in the narrow space beneath your shoulder blade get pinched during overhead movements. In its later stages, impingement can progress to the point where the shoulder locks up, particularly when raising your arm above shoulder height. The narrowing of this space, whether from swollen tendons, a thickened bursa, or subtle bone spur formation, creates a physical barrier that the arm cannot move past without significant pain or restriction.
Two common physical exam tests help identify impingement. One involves your arm being raised while internally rotated, and the other involves moving a bent arm into internal rotation at shoulder height. Both compress the subacromial space and reproduce the pinching sensation. These tests have moderate accuracy on their own, so doctors typically combine them with imaging to confirm the diagnosis.
What Happens at a Doctor’s Visit
A physical exam for a locked shoulder focuses heavily on comparing your active range of motion (what you can do yourself) with passive range (what the examiner can do for you). This single test narrows down the possibilities significantly. The examiner will also look for visible changes: muscle wasting around the shoulder, asymmetry compared to the other side, or swelling around the joint.
Imaging typically starts with X-rays to check for arthritis, bone spurs, or calcium deposits. If those are unremarkable, an MRI can reveal capsule thickening (pointing to frozen shoulder), labral tears, or rotator cuff damage. MRI with contrast injected into the joint is particularly useful for showing capsule changes and labral tears that standard MRI might miss.
Treatment Options by Cause
For frozen shoulder, the initial approach is physical therapy focused on gentle, progressive stretching of the capsule. Corticosteroid injections into the joint can reduce inflammation and pain enough to make therapy more effective. A procedure called hydrodilatation, where fluid is injected into the joint capsule to stretch it, shows effectiveness comparable to corticosteroid injections for pain and disability. Some studies suggest its benefits can last up to two years. For stubborn cases, manipulation under anesthesia (where a doctor moves the joint through its full range while you’re sedated) can break up adhesions.
Labral tears that cause mechanical catching often respond to arthroscopic surgery, where the torn flap is either trimmed or reattached. Smaller tears without significant locking may be managed with strengthening exercises to improve joint stability. Calcific tendinitis frequently resolves on its own as the body reabsorbs the calcium, though the acute phase can be managed with anti-inflammatory treatment or, in persistent cases, a procedure to break up the deposits. Arthritis-related locking is managed with activity modification, anti-inflammatory approaches, and therapy. Advanced cases may require joint replacement.
Warning Signs That Need Urgent Attention
Most causes of shoulder locking are not emergencies, but a few combinations of symptoms warrant prompt evaluation. Pain and loss of motion accompanied by redness, warmth, swelling, and fever could indicate a joint infection. Shoulder restriction paired with unexplained weight loss and pain out of proportion to what imaging shows raises concern for a bone tumor. Visible muscle wasting around the shoulder, where one side looks noticeably smaller or flatter than the other, suggests nerve involvement or a longstanding untreated problem that is progressing.