Tuesday 23 February 2010

Stress shielding - more about bones, and shoes

While I was following up research on bone regeneration that I blogged about on Monday (http://rockleyfarm.blogspot.com/2010/02/reversing-navicular-bone-damage.html), I came across an even more interesting fact from research into human biomechanics.

As with bone regeneration, its something that you could discuss with a medical doctor and they would simply say - "Duh, of course - thats nothing new"...BUT I don't think its crossed over into equine veterinary research yet. Maybe I am wrong, so if anyone can point me at any studies, PLEASE do so!

Its common ground that bone forms in response to mechanical load, so the stresses and strains which the bone receives from movement and its environment are critical to its strength.

What is mind-blowing (but when you think about it, not surprising) is that if you replace or support a bone with a stiffer material, like metal, then the stiffer material becomes the primary load-bearing structure. This reduces load to the bone and it degenerates in response.

This process is called "stress shielding" and it has received a lot of attention from researchers into human medicine, because bone degeneration is a consequent problem in patients with hip or knee replacements, and its also a factor when fractures are repaired with metal plates.

I had a lightbulb moment when I read about this, because stress shielding may well be the one of the factors affecting shod hooves.

Bob Bowker is already starting to look at pedal bone density in cadaver hooves, and is postulating a link between peripheral loading and osteoporotic bones - his article is here.

The question is whether shoes are also causing stress shielding; if so, this would be another way in which bone density could be adversely affected. Changing both the loading of the hoof and removing the stress shielding should therefore lead to bone restoration over time.

What we need, of course, is research into how seriously bone density in horses (particularly navicular and pedal bone density) is affected by shoes, and whether its possible (and how long it takes) to restore density in a correctly loaded, unshod hoof.

In humans, it used to be thought that bone loss due to stress shielding peaked 2 years after an implant, but now its thought to continue indefinitely. Its also a common cause of pain for human patients and there is no reason why this shouldn't also be true for horses.

Meanwhile, I am posting photos tomorrow which illustrate things quite nicely :-)


cptrayes said...

Aaaaaaagh. Do I need the titanium taken out of my arm???? Thankfully it's not terribly load bearing, being my arm and not my leg. But it has twinged more this winter with constant work shifting snow and moving haylage bales than it did in the previous year.


Nic Barker said...

Do a search - there is loads of stuff out there and lots of the new materials are specifically designed to shift the load over time back to the bones. Worth talking to your surgeon about though, especially if its hurting :-(

Nic Barker said...
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