People with diabetes may be much more likely to develop frozen shoulder, according to research that examined evidence from several earlier studies.
The condition can cause months of shoulder pain and stiffness and may make ordinary activities surprisingly difficult.
Frozen shoulder is also called adhesive capsulitis. It develops when the flexible tissue surrounding the shoulder joint becomes inflamed, thick and tight, gradually reducing how far the arm can move.
At first, pain may be the main problem, particularly when moving the arm or sleeping on the affected side. As the condition progresses, the shoulder can become so stiff that reaching overhead, getting dressed, brushing hair or reaching behind the back becomes difficult.
The condition often develops slowly and can last for a long time. Many people eventually recover, but improvement can take months or even years, and some people continue to have reduced movement.
Researchers have known for years that frozen shoulder appears more frequently in people with diabetes. Diabetes affects the way the body controls blood sugar and can also damage blood vessels, nerves and other tissues over time.
To examine the connection more closely, Brett Paul Dyer of Keele University in the UK and colleagues reviewed eight previous studies. The studies investigated whether people with type 1 or type 2 diabetes were more likely to develop frozen shoulder.
Six of the studies included a combined total of 5,388 participants. When the researchers analyzed these results, they found that people with diabetes had nearly four times the odds of developing frozen shoulder compared with people who did not have diabetes.
Two other studies followed people over time and also found evidence of an increased risk. Together, the results supported the idea that diabetes is an important risk factor for the shoulder condition.
However, the researchers warned that the evidence was not perfect. Most of the studies included in the review had weaknesses that could introduce bias, while only one was judged to have a moderate risk of bias.
This means the exact size of the increased risk remains uncertain. Better long-term studies are needed to confirm how strongly diabetes affects the chance of developing frozen shoulder and to identify which patients are most vulnerable.
Scientists are also still working to understand why the two conditions are connected. One possibility is that long-term exposure to high blood sugar changes proteins in connective tissues, making tissues around the shoulder joint thicker and less flexible.
Diabetes may also affect inflammation and blood flow, which could contribute to changes in the shoulder. These possible explanations are still being investigated and should not be considered proven causes.
The findings could nevertheless be useful for doctors and patients. Healthcare professionals may want to ask people with diabetes about new shoulder pain or stiffness during routine appointments, particularly when symptoms begin to interfere with everyday movement.
Early recognition can help people get appropriate advice and treatment. Treatment may include pain relief, gentle exercises, physical therapy or, in some cases, injections or other medical procedures depending on the severity and stage of the condition.
People with diabetes do not need to assume that shoulder pain means they have frozen shoulder. Many conditions can cause similar symptoms, so persistent pain or increasing stiffness should be assessed by a healthcare professional.
The review was published on January 4 in the peer-reviewed medical journal BMJ Open. The researchers concluded that diabetes appears to be associated with a substantially higher risk of frozen shoulder, while emphasizing that stronger studies are needed to provide more certain answers.
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