Info on sidebone's etc

[Super_Kat]

I really read up on this alot a while ago, side bone = ossification of the lateral/or collateral (I forget which it is) cartilage.
Can be caused by wear and tear (being hammered/direst trauma), can be part of the natural aging process, poor limb conformation, poor conformation of the hoof...........am I right saying this? Is there anything I've missed?

My 13yo mare has them (on what feels like all 4 limbs), she's a bit cow hocked, was a broodmare/field ornament until she was 8 1/2, I've had her 5 years and I think she's been lame once for a few days in the time that I've had her, she's never done excessive work on the roads (the usual walk and trot), been hunted a few times........What could have caused them? is she too young for them to have been caused by aging? (I noticed them about a year ago)

Any help appreaciated

x

 

[puddicat]

To excited to sleep because its Xmas so this is a way over the top reply that I hope at least someone finds interesting!!!

I think your synopsis of sidebone is really good. Bear with me, this is relevant... Cartilage is a precursor of bone, as a tissue it existed before before bone and so early vertebrates, fish basically, were made of cartilage rather than bone. Sharks are a moden day example of cartilagenous fishes, they have no bone in their skeleton. Somewhere in fishy evolution bone evolved/was created by God and it proved to be such a good idea that from then on vertebrates were built around a skeleton of bone. There is a principle in biology that goes like this "ontogeny replicates phylogeny". Ontogeny means development from conception onwards, phylogeny refers to the development over many generations, ie evolution. So the idea is that each developing embryo echoes stages of evolution. The relevant point here is that mammals form a cartilagenous skeleton first then it changes to bone through ossification. What is really interesting is that not all the cartilage changes to bone. The lateral cartlages in the horse's foot are attached to the distal phalanx (the last of three bones in the digit counting down the leg) the distal phalanx becomes bone but the lateral cartilages don't. Similarly the scapula or shoulder blade becomes bone except for a section at the end towards the horse's spine which remains cartilagenous. The reason why some parts of the skeleton ossify and some remain cartilagenous is not completely understood but the differing material properties of bone and cartilage may be a clue:

The notable advantage of bone over cartilage is that it is stiff, ie it doesn't bend unless you apply a lot of force to it. This allows nature/God to make larger animals that move faster and are more resistant to injury than would otherwise be possible. The stiffness of bone is however a disadvantage in situations where deformation is useful. Its possible that the muscles that insert on the cartilagenous region of the scapula would cause larger stresses in the bone if the whole bone was ossified. Similarly the lateral cartilages allow the hoof to expand during weight bearing wheras if they were ossified with the rest of the distal phalanx they would not (this raises an interesting question which I'll address later). So it makes sense to have cartilage in places where strength and support is required in combination with some movement or deformation, and bone where strength and virtually no deformation is required.

So why does cartilage that is suppoesed to be cartilage ossify? That isn't completely understood either but there is enough known to have a pretty good guess, there are just gaps in the detail. First of all there is a trend for cartilage to ossify in old age which seems to be simply a slowed down version of the ossification that occurs in the cartilage that forms the skeleton in early development. This doesn't explain why it occurs in some structures and not others and in some animals and not others. Second, one of the stimuli for cartilage to ossify is mechanical loading. It may be mechanical loading in the womb as muscles develop and the foetus becomes mobile that triggers and modulates ossification of the skeleton. So the formation of sidebones following trauma such as extended periods of road work may be simply the result of triggering a process that was always retained by the cartilage although not normally invoked. This is similar to the formation of splints.

So if the purpose of the lateral cartilages is to allow movement in the foot, what is the consequence of them ossifying? Well, lameness in some cases, in others, apparently nothing. At the risk of being repetative, the cause of lameness due to sidebone is not completely understood, if it was it would be easy(er) to explain why some horses go lame and others don't. The uppermost edge of the lateral cartilages can be felt by palpating the foot just above the top of the hoof wall. If you can deform them they aren't ossified. If you can't then the 10% of them that you can feel are ossified. So, conclusion, there is no rhyme or reason why your mare would develop sidebone in the situation you describe, or at least none that is known at the moment. having said that, its not particularly suprising because "it happens" Statistically "it happens" is a euphonism for "I haven't a clue about the cause" which is probably about right. If its not lame, don't worry about it.

 

[S_N]

Puddicat, I have SO missed reading your posts!!! just brilliant!!! In lay terms and so informative - thank you!!

 

[Super_Kat]

You really need to post more often, that was really good!

And I'm quite pleased that I understood everything. Thats made my general understanding of the technical bits of sidebone and was very helpful, thankyou

x

 

[puddicat]

gee thanks, will try to be about more in 2007!

x x x