Thinking About Knee Design

Why were knees “designed” the way they were? Why does articular cartilage lack a blood supply and nerve endings -- the former, if present, would facilitate healing and the latter would warn us away from activities that are causing further damage?

I often pondered such questions during the year I spent in Hong Kong without a job, when I was concentrating full time on healing my bad knees. My focus had turned completely to all things knee.

At first when your knees hurt, and they prove stubbornly resistant to getting better, your inclination is to think, “Stupid knees! These dumb joints always wear out. Why couldn’t they be better designed?” But then, as I took a closer look at the inner workings of the human knee, I was surprised at how ingenious the design actually is.

Some of this I captured in Saving My Knees, in a chapter I’m sure half of readers skipped over, eyes glazed. It was the chapter that took a sort of Fantastic Journey through knee cartilage and introduced proteoglycans, chondrocytes and glycosaminoglycans. While writing it, I tried to keep a sense of wonder at how well all of articular cartilage’s adaptations actually worked.

But no nerves, no blood vessels -- how could this be a good thing? As I thought this over, an answer began to take shape: Of course it could be.

Imagine you’re designing a very tough cushion, to insert in a joint, that can withstand big impacts. Would you want to lace this tissue with delicate blood vessels and sensitive nerves? Or would that make a simple stroll across the room feel like walking on broken glass -- a refrain of “ouch, ouch, ouch” with each step?

I don’t know, but it’s something interesting to ponder.

To me, the real fatal design flaw in knees would have been if they had no capacity to self-repair, considering all the abuse they take. Happily, as I found out during my recovery from chronic knee pain, this is not the case.