Danish and British researchers have learned that injecting polyacrylamide hydrogel (PAAG) into a joint can offer long-lasting pain relief, possibly via a cushioning effect. | Anne M. Eberhardt/The Horse

A transparent gel injected into arthritic joints’ synovial lining seems to be offering new hope for owners of horses with joint pain. But what exactly happens to that gel in the weeks and months after it’s injected, and is it staying put?

In a recent study Danish and British researchers have learned that injecting polyacrylamide hydrogel (PAAG) into a joint can offer a long-lasting cushioning effect. Results indicate that the horse’s body reacts to the gel by building new layers of natural synovial cells over the synthetic gel, said Lise Christensen, PhD, of the University of Copenhagen Herlev Hospital Department of Pathology, in Denmark.

The team examined 13 joints from seven horses treated with PAAG seven days to two years prior to euthanasia for unrelated reasons. They found that the gel integrates within the synovial lining gradually, creating a sort of “sublayer” under a new generation of synovial tissue, Christensen said