When loaded through regular cycles of activity these cellular micro-factories switch on genes that make collagen and other matrix stuff. That’s a key realisation to keep our joints healthy.
Point number 1 if you like…
1. Our cartilage needs regular load to stay healthy.Like the fibres in a carbon-fibre bicycle frame or aeroplane, fibre arrangement within the cartilage matrix matters. Cartilage has a function-specific layered microstructure.
- A hard, calcified deep layer anchors directly into bone
- A random middle layer of meshed fibres support the multi-directional forces of everyday life, and
- A superficial layer of collagen fibres run parallel to the joint surface to slide sideways the forces of one joint surface moving over the other.
Cartilage cells needs direct load to maintain the matrix…
BUT(and it's a big 'but')
…excess side-to-side forces switch on genes for enzymes that degrade cartilage.
That’s point 2.
2. Cartilage needs load, but not too much.The surface is where cartilage really excels, arguably like no other material on the planet.
In their excellent 2018 article, Sabrina Jahn and Jacob Klein invite us to:
‘Imagine supporting a 1-ton weight on your hand and then sliding it along the palm with a slight push of a finger’.That’s how slippery our joint cartilage is. Think some 10x times more slippery than an ice skate sliding over ice.
Quite surprising then that up until recently, we had no idea how cartilage did this.
How is it so slippy?
The latest evidence points to the life-giving polar water molecule.
Hydration shells or wheels of water molecules bind to positively charged phospholipid at the cartilage surface.
Firmly bonded water on one side of the joint washes over bonded water on other side of the joint. Well, that makes sense… water washing over tightly bonded water would be slippery. Wonderfully slippery!
The structure of joint cartilage at the molecular and cellular level is therefore wholly focussed on supporting and moving load.
And to do this most effectively, cartilage has done away with the usual supply and communication lines that other tissues rely on.
Cartilage is avascular, aneural and alymphatic. Complicated structure, yet…
Joint cartilage has no blood, nerve or lymph supply.That creates a problem
Cartilage still contains cells that are very much alive. And they need oxygen and nutrition or they’ll die. So… how do they stay alive?
In short... synovial joint fluid.
Synovial fluid, rich in fresh surface components, nutrition and oxygen, diffuses into the deeper layers to cartilage. But, this diffusion needs a push.
So, as well as switching on the genes that maintain our cartilage…
3. Cycles of load gives diffusion a push.Like a child on a swing. Point number 3.
The large forces loading and unloading our joints keep alive our joint cartilage. Each and every living cell is nourished.
So, the 3-point punchline is that our biological wonder material not only likes to be loaded… cartilage needs to be loaded.
(but not too much, and in the right way).
The materials we use in artificial joints are manufactured using high temperature and pressure applied to the outside of the whole material. Â The manufacturing process is exacting and precise.
However, the material is formed ‘en masse’. That produces one homogenous block. Artificial materials are the same throughout.
Cartilage on the other hand forms one building block at a time from amino acids transcribed from our DNA code.
Collagen fibres self-assemble into a microstructure that is specific to its function at different levels. The surface structure provides an astounding level of frictionless lubrication. Form follows function.
No artificial material makes for an equivalent replacement.Given the choice between highly cross-linked polyethylene, engineered cobalt chrome or fine grain ceramic, I choose to keep the living and breathing biological wonder material that is articular cartilage.
I’ll hang on to my joint cartilage for as long as possible thank you very much.
