Back to Basics: What Causes Osteoarthritis?

Dolors & Sense

by Sanford Rose

KISSIMMEE Florida—(Weekly Hubris)—5/23/11—There seems to be an innate drive in humans to unearth fundamental causes—or at least causes as near to fundamental as a particular view of the world allows.

I like to look into the cause of disease. Consider osteoarthritis.

Living, as I am fond of saying, at the junction of Laminectomy Lane and Arthroplasty Avenue, it is impossible for me not to consider osteoarthritis.

Scores of orthopedists have funded an opulent, indeed sardanapalian, lifestyle with the proceeds from carving the knees and hips of the residents at or near this stereotypical junction.

Nationwide, 27 million suffer from the disease, and they spend nearly $190 billion annually to palliate it.

What causes osteoarthritis, a malady that involves the deterioration of cartilage in key joints to the ultimate and highly painful point where the patient experiences bone rubbing against bone?

We move into the area of proximate versus ultimate causes. A popular and entirely mechanical explanation is that, with advancing age, pressure on the cartilage separating femur from tibia or femur from pelvic bones and acetabulum builds ups. In consequence, cartilage erodes and evaporates.

Sound as a useful approximation, this explanation has one crucial drawback: it is wrong.

Or, at least, it is accurate, but not truthful.

A somewhat deeper and more useful explanation is to be found in the core functioning of the body

People who suffer from osteoarthritis of the knee, for example, tend to be somewhat corpulent and, in consequence, have an excess supply of a cytokine named leptin wafting about in their knee joint fluid.

Leptin is an inflammatory cytokine; its presence causes the body, which tends towards homeostasis, to compensate by sending in an anti-inflammatory cytokine called TGF-beta (transforming growth factor).

TGF-beta does the job. It damps down the inflammation. Unfortunately, it also promotes extra bone growth.

It is this growth that crushes the cartilage and elicits the intractable pain of bone grinding against bone.

So, while the proximate cause of osteoarthritis is undeniably mechanical, a deeper cause is the chemical warfare between two small bits of protein summoned to battle automatically by a suffering body.

But that body would probably not be suffering if excess weight had not bathed the joints in leptin to begin with.

And what causes adiposity?

Here, perhaps, we must dive into the mysteries of the human mind, our evolutionary legacy and, ultimately, our penchant for self-destruction.