Paratenon effusion of the Achilles tendon: a rare finding.

We present a case of Achilles tendon swelling and pain related to paratenon effusion. Further ultrasound assessment showed no evidence of acute enthesitis, although a nonspecific degenerative enthesophyte was present. Our case study presents a rare instance of paratenonitis involving effusion into the paratenon lumen. Paratenonitis has a non-specific etiology. Recent findings suggest that paratenonitis plays a role not only in cases of mechanical injury and in patients with spondyloarthritis but also in individuals at risk of developing rheumatoid arthritis. Further studies have shown that the paratenon surrounding the extensor tendons consists of a lining layer formed by fibroblasts. However, more research is needed to characterize these fibroblasts and compare them to those found in the synovium.