(original graphic by marvistavet.com)

A joint consists of articulating bones, a fibrous capsule enclosing the joint, and slippery lubricating joint fluid to facilitate the gliding of the two bones across each other when the joint is flexed.

The articulating bones are capped by cushions of cartilage to facilitate this frictionless gliding. The integrity of the smooth, somewhat soft cartilage is crucial to normal range of motion and comfort. Approximately 95% of cartilage consists of material called "cartilage matrix," the other 5% being the cells that produce the matrix.  Cartilage matrix consists of collagen (the tough structural fibers that most people have heard of) and proteoglycans (the water absorbent molecules most people have not heard of). A proteoglycan’s function is to soak up water thus creating a plump soft cushion, sort of like a water bed, to absorb the pressure exerted on the joint as it works. A proteoglycan molecule looks something like a bottlebrush: it has a long “handle” (the “proteo” part) and long bristles called glycosaminoglycans (or GAG’s) which soak up the water.

Over years, either through injury or poor conformation, cartilage wears down or is damaged and arthritis results. The body must then make more matrix and will require the raw materials to do so. Polysulfated GAG’s may be injected into the body where they will be distributed to any joints currently effecting cartilage repair.

It turns out, however, that polysulfated GAG’s represent more than just building materials. They have anti-inflammatory properties of their own which helps slow down the actual damage to the cartilage. They also promote enzyme systems that facilitate other aspects of joint repair beyond simply making more matrix. They help the joint create more lubricating fluid as well.

Proteoglycan depiction: core proteins in green,
GAG "bristles" in red, hyaluronic acid in blue.
(original graphic by marvistavet.com)