Etiology
In primary (idiopathic) adhesive capsulitis, no underlying etiology or cause can be identified. Little is known about what precipitates the loss of motion and pain in these patients. Certain characteristics of the shoulder capsule may predispose to a fibrotic response; however, these have not yet been fully elucidated.[1][2]
On occasion, a contributing factor may be identified, such as diabetes mellitus, trauma, previous shoulder surgery, or thyroid dysfunction.[6][9][10][11][12] This is then referred to as secondary adhesive capsulitis.[10][13] Although these conditions may lead to the development of adhesive capsulitis, the mechanism behind this is not yet fully understood.
Pathophysiology
The exact pathophysiology of adhesive capsulitis is unknown. Many authors argue that adhesive capsulitis is a chronic fibrosing condition, whereas others contend that it is inflammatory in nature.[14] One histologic and immunocytochemical study found that the pathologic process is due to active fibroblastic proliferation, accompanied by some transformation to a smooth muscle phenotype such as myofibroblasts. These fibroblasts lay down collagen in thick bands that appear very similar to those in Dupuytren contracture of the hand.[15]
Work with cytokines and metalloproteinases suggests that adhesive capsulitis is both an inflammatory and a fibrosing condition.[16][17] Transforming growth factor beta, platelet-derived growth factor, and hepatocyte growth factor have been implicated in adhesive capsulitis.[16] However, their exact roles in the inflammatory and fibrotic signaling cascade have yet to be determined.
Classification
Types of adhesive capsulitis
Primary (idiopathic)
No underlying cause or precipitating event.
Secondary
Attributable to an underlying cause (e.g., diabetes mellitus, thyroid dysfunction) or precipitating event (trauma, prior surgery to affected shoulder).
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