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View Full Version : Question regarding Barbaro to a veterinary "knowledgeable" person



shawneeAcres
May. 23, 2006, 08:28 AM
I was curious as to why many horses with broken legs are slung, but barbaro is not. Is this becuase it is a hind leg not a front leg and horses typically put less weight on the hind end (when at rest that is) as well as have the ability to shift weight and "rest" hind limbs? Just curious about this.

Janet
May. 23, 2006, 09:00 AM
I am not a "veterinary person", but I do know that there are a lot of downside risks to using a sling. Both the internal organs and the circulation to ALL the limbs suffer if the horse is in a sling. It is only used if there really is no other alterantive.

JustJump
May. 23, 2006, 09:03 AM
I have a question too...maybe someone in the vet field will be able to answer the many questions that will arise, or maybe the COTH could eventually invite some of the NBC vets into the Tackroom Chat...

I'd like to know how (considering the thin skin and general lack of tissue surrounding the area of Barbaro's injuries) was all that hardware (screws/plate) made to fit within the leg?

DMK
May. 23, 2006, 09:23 AM
Actually, I don't think it's correct to say that "many horses with a broken leg are slung".

For the reasons noted above, the sling is the last resort not the first line of treatment. If you don't think the horse can come out of surgery with the ability to be mostly weight bearing, you know the odds of survival decrease immediately.

Ghazzu
May. 23, 2006, 10:06 AM
Actually, I don't think it's correct to say that "many horses with a broken leg are slung".

.

I don't think so, either.

ejm
May. 23, 2006, 10:20 AM
The only horse I am aware of that spent a lot of time in a sling and survived was Nureyev, who broke his leg almost completely off just below the hock and spent almost 2 years recovering at the Hagyard-Davidson-McGee clinic in Lexington. This happened about 15 years ago so forgive me if I am fuzzy on the details. He was not weight-bearing for many months and then was in and out of the sling for a long time.

Nureyev apparently kicked the paddock fence, and was found with his hind leg broken and dangling. Somehow, they got him to the clinic and managed to put it all back together. He lived (and covered mares) for about 10 years after the accident, thanks to a lot of good luck and a tremendous effort by the HDM vets and barn personnel and the Walmac Farm management. If I recall correctly, either his groom, the farm manager, or the farm vet was with the horse just about 24 hours a day while he was at the clinic, along with the regular clinic staff. They even built him his own barn at the clinic when he started recovering and was getting a bit too interested in the mares in the main barn.

I saw him at the farm a year or so before he died. He had his own barn, with a sling in the stall that apparently was used as needed. A groom stayed with him all the time, and at that point he was hand-grazed several times daily.

Angela Freda
May. 23, 2006, 10:26 AM
It may actually not all be under the skin, JJ.

shawneeAcres
May. 23, 2006, 10:38 AM
why is it I post a QUESTION and get criticized?! You guys are just WEIRD! yes, a LOT of horse ARE slung, look on the breeding forum right now there is a warmblood stallion with a broken front leg who is SLUNG. I simply would like a VETERINARY reason, I totally realize that slinign should not be done unless necessary, but what constitued "necessary" when should a leg bear some weight, and when should it bear little to no weight? Is it an effect of front vs. hind? These are jsut questions I'd like to have an answer from, not a bunch of peopel trying to second guess what I said! And I am saying "slung" for recovery, not for a more exteneded period of time

buschkn
May. 23, 2006, 10:50 AM
Actually, based on the xrays, I would say all the hardware is under the skin. None of that looks like external hardware. It is similar to a human ankle where there is not a lot of soft tissue to cover everything. Frequently you can feel the plates and screws through the skin, which stretch to accommodate all that. Also, looks like his bone were fractured so severely as to not necessarily be taking up quite as much room as before, so probably more room for hardware there.

Also, Shawnee Acres, I don't think anyone was jumping on you, just stating their experience and opinion, just as you did. Relax.

caffeinated
May. 23, 2006, 10:57 AM
why is it I post a QUESTION and get criticized?! You guys are just WEIRD!

:confused:

Who criticized you?

Ghazzu
May. 23, 2006, 10:59 AM
why is it I post a QUESTION and get criticized?! You guys are just WEIRD! yes, a LOT of horse ARE slung, look on the breeding forum right now there is a warmblood stallion with a broken front leg who is SLUNG. I simply would like a VETERINARY reason, I totally realize that slinign should not be done unless necessary, but what constitued "necessary" when should a leg bear some weight, and when should it bear little to no weight? Is it an effect of front vs. hind? These are jsut questions I'd like to have an answer from, not a bunch of peopel trying to second guess what I said! And I am saying "slung" for recovery, not for a more exteneded period of time

Telling you that your assumption is incorrect, is, IMHO, an answer.
Maybe you like the answer, maybe you don't.
You get to decide that.
You don't get to decide what answers you get, though.
Since it seems to upset you, though, I'll refrain from answereing your questions in the future.

Mega Rock
May. 23, 2006, 11:02 AM
I think people may look at the x-ray and go " wow those screws are huge!" But the x-ray may be in blown up proportion and the screws are fit to the size of bone. I have a screw in my hip and a screw in my knee but if I looked at my x-rays blown out of proportion they might look big too. I bet if you held one of those screws in your hand it may be smaller than you think.

Shawnee Acres I believe I heard on the news when they were interviewing the surgeon, they opted to not put him in the sling because his best chance of recovery was to see if he could bear full weight on the leg.

monstrpony
May. 23, 2006, 11:15 AM
If I'm not mistaken, the warmblood horse broke the bone above the knee. It seems it would be difficult to fashion a weight-supporting cast for that part of the leg, as it does have muscle around it, and is just so much higher off the ground, and above a bunch of functioning joints. That, and the fact that horses do bear more weight in front, would seem to be reasons why the WB horse is in a sling and B is not.

I think they've said that the cast on Barbaro is fiberglass and includes the fetlock joint and the entire foot, so that cast is probably more weight-supporting than what's on the WB horse.

But I'm not a vet, these are just some observations and suppositions.

RAyers
May. 23, 2006, 11:15 AM
I have a question too...maybe someone in the vet field will be able to answer the many questions that will arise, or maybe the COTH could eventually invite some of the NBC vets into the Tackroom Chat...

I'd like to know how (considering the thin skin and general lack of tissue surrounding the area of Barbaro's injuries) was all that hardware (screws/plate) made to fit within the leg?


While not a vet, I am an orthopedic/bone reconstruction researcher. Skin is very elastic. No, they did not have to make the hardware fit in the leg. The plates come form the manufacturer (Synthes in this case) in a preset size. They are then cut and shaped in the OR to fit the given need. The pate (the bar looking thing) is thin enough (4mm or A316L stainless steel) that the skin can be sutured over it.

Reed

shawneeAcres
May. 23, 2006, 11:18 AM
sorry,, i seemd like people were critiziing the question I asked in stead of an answer, I guess I misread the tone. I jsut seriously was wodnering that was all, and I realise not ALL hroses are slung, many do get slung for various reasons and wondered how the decision was made about that, thats all, again sorry

RAyers
May. 23, 2006, 11:23 AM
I think people may look at the x-ray and go " wow those screws are huge!" But the x-ray may be in blown up proportion and the screws are fit to the size of bone. I have a screw in my hip and a screw in my knee but if I looked at my x-rays blown out of proportion they might look big too. I bet if you held one of those screws in your hand it may be smaller than you think.

Shawnee Acres I believe I heard on the news when they were interviewing the surgeon, they opted to not put him in the sling because his best chance of recovery was to see if he could bear full weight on the leg.

Actually, thos screws ARE pretty big. I have a set on my desk as I write this from a couple of tibial reconstructions in people. The magnified image on your computer screen is just bout real size. The screws HAVE to be big in order to withstand the bending and tensile loads due to the horse's weight.

As for slings, I too have almost never seen a horse in a sling (worked for a large animal hospital and collaborate with veterinary orthopedics at CSU). There are too many risks and very few horses will tolerate it. On top of that given the time of recovery from a fracture (say 12 weeks), I suspect there would be significant bone loss in the rest of the skeleton due to the unloading (similar to what happens with astronauts, bed ridden people, people in wheelchairs). Thus, you would have a horse with weaker bones coming out of recovery.

Reed

caffeinated
May. 23, 2006, 11:25 AM
Wouldn't having a horse in a sling increase the possibility of hoof problems?

I know laminitis is a possible danger as it is, but since circulation in the hoof is related to bearing weight, could taking weight off the hooves completely increase chances of those types of problems?

If I'm totally mistaken on all counts, feel free to punish me as you see fit

:)

shawneeAcres
May. 23, 2006, 11:29 AM
both of those replies make sense. I'm just trying to figure out when they woudl and when they wouldn't sling a horse, I guess I jsut assumed he'd be slung and was surprised to see the photos of him standing on it. Does the plate give it enough strength then that the weight is able to be borne?

RAyers
May. 23, 2006, 11:47 AM
both of those replies make sense. I'm just trying to figure out when they woudl and when they wouldn't sling a horse, I guess I jsut assumed he'd be slung and was surprised to see the photos of him standing on it. Does the plate give it enough strength then that the weight is able to be borne?

In a word, yes. The caveat, the plate will have to removed after time due to a condition called stress shielding. Bone must have a load to grow and maintain itself. The plate changes the load path in the bone thus causing a shift in how the bones will "remodel." This is similar to why some hip implants fail in humans. Right now the plate is taking the entire load and it will fail around 2-3 million flexions (it is what is called A316L stainless steel as that is what Synthes makes). This comes out to about 1 year of walking around if the fractures fail to heal (non-union fracture). If the plate is left in, the surrounding bone will become weaker over time.

Also, the plate will fail on its own due to fatigue in its current position and its current configuration. The curve is a "stress concentrator" that will cause fatigue and micro fracturing in the plate over time. Hopefully the bones will be healed sufficiently to take the load when the plate goes.

The screws and plate will all go. Since the plate is held in place by the screws. In humans we do the same thing with intremedually nails when a person shatters their femur or tibia.

Reed

Glimmerglass
May. 23, 2006, 11:52 AM
I have to hand it to the Baltimore Sun for providing this graphic to its readers to better educate them on what the impact of a gallop represents on any horse:

Baltimore Sun 5/22 GRAPHIC: 'Powerful animal, long and light legs' (http://www.baltimoresun.com/media/graphic/2006-05/23564876.jpg)

(source:Knight-Ridder Tribune, Florida Sun-Sentinel, Equusite.com, Baltimore Sun)

DontWorryAboutIt
May. 23, 2006, 12:03 PM
Just out of curiosity - I was in Lexington last month, and we went to Overbrook farm and met Jump Start. He has a plate in his front leg, but you can see the plate very clearly under his skin. Why would his plate stay in? I don't know how long he's had it in there, but I do know that is why he was retired from racing and that he has a few babies that are racing now, so it's been a few years.

DMK
May. 23, 2006, 12:54 PM
That is a great graphic, but "1200 pounds" impact? Aone legged rear, maybe. ;) Something about physics, speed, force and a bunch of other stuff I long forgot in my physics calsses makes me think it's a heck of a lot more PSI during a gallop!

FourWands
May. 23, 2006, 01:12 PM
Since he was mentioned, I thought I would throw this out there.
Forgive me if someone already posted and I missed it.

http://tcm.bloodhorse.com/viewstory.asp?id=6788

Peggy
May. 23, 2006, 01:12 PM
DMK - it seems that way to me too since the mass of the horse is supported on one leg at a given point and that leg is moving as it hits the ground.

What I'd like to find is one of those photos that shows how the back of the ankle joint (front or hind) looks like it's hitting the ground on a galloping race horse. I was trying to describe this to a colleague yesterday.

The other vet related question I got from a colleague was what sort of tranquilizers Barbaro might be on during the recovery.

I helped to answer some of the questions that were directed at me by posting the photos and x-rays from the New Bolton Barbaro site on my office door.

shawneeAcres
May. 23, 2006, 01:13 PM
A question about the plate being removed. I have five metal plates in my back (fusion) however they did do a bone graft from my hip, and said the plates were only initially holding my spine in place but the bone actually did the fusion, yet the plates remained in my back. Is the reason they did not remove them becuase my back is not like a limb is? It doesn't ahve the same stress loading?

Slewdledo
May. 23, 2006, 01:17 PM
Jump Start broke down as a 2yo.

DMK
May. 23, 2006, 01:30 PM
Peggy, what you need to find is that famous picture of Secretariat from the Preakness where he just lunged ahead. The photo was the basis for the statue of him at the Belmont, but that doesn't begin to capture the sheer force his left hind leg was under. (the photographer was Ray Woolfe)

Years ago I watched PBS special about the TB racing and the biomechanincs of racehorses. They even had a machine that measured the force needed to shatter bone (creepy and yet still wierdly fascinating, and yes, it does sound like an explosion when it finally shatters :( ). Anyway, I can't recall the exact numbers, but I thought it was more in the area of 100 of thousands of pounds of force being transmitted to the track and back to the leg.

caffeinated
May. 23, 2006, 01:42 PM
Peggy, what you need to find is that famous picture of Secretariat from the Preakness where he just lunged ahead. The photo was the basis for the statue of him at the Belmont, but that doesn't begin to capture the sheer force his left hind leg was under. (the photographer was Ray Woolfe)

this one? (http://www.galleryofchampions.com/galleryresults.asp?Base_ID=1246)

DMK
May. 23, 2006, 01:46 PM
that one indeed, you are a goddess...

DMK
May. 23, 2006, 01:51 PM
Actually, I looked at my picture and it is taken what must be a nanosecond earlier, since his nose is not quite at the man in the beig jacket, his RF leg is higher and the LH ankle is even more flexed.

Still, that's a lot of force on one leg. They are amazing creatures, aren't they?

Janet
May. 23, 2006, 02:15 PM
both of those replies make sense. I'm just trying to figure out when they woudl and when they wouldn't sling a horse, I guess I jsut assumed he'd be slung and was surprised to see the photos of him standing on it. Does the plate give it enough strength then that the weight is able to be borne? Because of all the downside risk associated with using a sling, you would only use a sling if the downsides of NOT using a sling were even worse. E.g., if you already knew that the horse could not support enough weight on the "bad leg" to avoid major damage to the "good leg." Or if the horse could not stay upright on his own.

Janet
May. 23, 2006, 02:23 PM
To a first approximation, the horse's hoof is on the order of 30 square inches. So the static pressure on one foot supporting the entire horse is about 40 psi.

The cross section of of the pastern bone is probably less than 6 square inches, so you are talking on the order of 200psi.

To get the force (= mass times acceleration) you need to multiply in the acceleration, which is considerable.

RAyers
May. 23, 2006, 03:06 PM
That is a great graphic, but "1200 pounds" impact? Aone legged rear, maybe. ;) Something about physics, speed, force and a bunch of other stuff I long forgot in my physics calsses makes me think it's a heck of a lot more PSI during a gallop!


Ahhh, I am here.

O.K. consider that the cannon bone in a horse is perfectly straight. This is a problem with ungulates. They are the only animals with a perfectly straight bone in their body. In the rest of the animal kingdon the long bones are curved. That is a great thing becasue what the curve means is that fractures will be localized, at the same time it provides a load sensing mechanism that the cannon bone does not have.

Since the cannon bone is straight is can be modeled as a compression column. Given the bone is roughly 2.5 inches in outer diameter and about 12 inches long. The bone generally does not fail due to inelastic stability because of how it operates so we can narrow down the equations. If we say the bone is a thin cylindrical tube we can assume that the thickness is about 1/4 inch with a mean radius of 1.125 inches.

Using the formula for maximum pressure (stress) to fail a column P<(pi*2/4)(EI/L*2) (E= modulus of elasticty, I= cross sectional moment of inertia, L= length of the bone), it all works out to about 4 million pounds per square inch of pressure needed to shatter a bone similar to Barbaro's. This works out to 3,500 lbs. of load per leg.

Reed

Peggy
May. 23, 2006, 04:19 PM
Duly impressed by both caffeinated and RAyers. Thank you both.

shawneeAcres
May. 23, 2006, 04:20 PM
VEry cool calculation!! My neice needs to do a project for college involving mathematics, and she'd like to incorporate horses, this might be a good starting point for her, thanks for the idea!

SGray
May. 23, 2006, 04:21 PM
Actually, I looked at my picture and it is taken what must be a nanosecond earlier, since his nose is not quite at the man in the beig jacket, his RF leg is higher and the LH ankle is even more flexed.

Still, that's a lot of force on one leg. They are amazing creatures, aren't they?

how about this one?
http://www.galleryofchampions.com/galleryresults.asp?Base_ID=837

DMK
May. 23, 2006, 04:38 PM
Using the formula for maximum pressure (stress) to fail a column P<(pi*2/4)(EI/L*2) (E= modulus of elasticty, I= cross sectional moment of inertia, L= length of the bone),
Ow.

Keep it up Reed, I'll start talking insurance. :p

SGray, I saw that one, and it is impressive but the frame shot from the Preakness is even more amazing. Must. Resist. Temptation. To Scan.

RAyers
May. 23, 2006, 04:40 PM
If we go a step further, and using Netwon's first law, the 3,500 lbs of force is equal to an acceleration of 94 feet/second^2. That is the leg is being driven into the ground at only about 11 miles per hour. Then again, I dare ANYBODY to run directly into a wall at full speed (about 10 miles per hour) and not hurt themselves.

shawnee acres, the field of study for your neice is biomechanics. Hillary clayton at Michigan State does quite a bit of equine biomechanics. My biomechanics work focuses only of bone.

There have been a lot of studies that show as the tendons begin to heat up because of their own metabolism and retained heat form the muscles during hard work, they stretch and allow the leg to drop like is hown in those pictures. You see it in Grand Prix horses, Eventers, Barrel Racers, Race Horses and so on and so forth. Thus many times the horses do end up running on their fetlocks. That is why "legging up" is so important. It builds more tissue mass to handle the heat.

DMK, love ya!

Reed

monstrpony
May. 23, 2006, 04:41 PM
Interesting that Secretariat was running bare-legged. I've never watched the use of wraps in racing, but I did wonder if the wraps on Barbaro's legs didn't help keep the injury from breaking thru the skin.

Do most race people wrap legs? Most run bare? Does it run in trends?

ejm
May. 23, 2006, 04:42 PM
FourWands, thanks for the link to the article on Nureyev. I read it in the Blood-Horse when it first came out, but it had been quite a while and I was a bit fuzzy on the detail. Amazing horse, amazing story.

Jump Start had a major fracture, but I don't know exactly what bone or bones were involved. Once he went back to the farm the injury was not recovering as well as hoped, so they operated again to fuse the joint. I *think* that once the joint is fused, the plate is permanent. He had to miss his first scheduled season at stud while recovering from the last surgery, but apparently made a very good recovery.

DMK
May. 23, 2006, 04:50 PM
Interesting that Secretariat was running bare-legged. I've never watched the use of wraps in racing, but I did wonder if the wraps on Barbaro's legs didn't help keep the injury from breaking thru the skin.

Do most race people wrap legs? Most run bare? Does it run in trends?

I think Secretariat predated most of the high tech wrap stuff we have now - most of the horse in the field were bare legged as well. Not much stays in place on a TB in full stride, even less if the track is wet!

Ghazzu
May. 23, 2006, 04:52 PM
I have to hand it to the Baltimore Sun for providing this graphic to its readers to better educate them on what the impact of a gallop represents on any horse:

Baltimore Sun 5/22 GRAPHIC: 'Powerful animal, long and light legs' (http://www.baltimoresun.com/media/graphic/2006-05/23564876.jpg)

(source:Knight-Ridder Tribune, Florida Sun-Sentinel, Equusite.com, Baltimore Sun)

Nice graphic, but there's no carpus on the pelvic limb, sofar as I know :D

Mega Rock
May. 23, 2006, 04:55 PM
Do most race people wrap legs? Most run bare? Does it run in trends?

It all depends on the horse. Some horses "run down" others don't. Some horses run down through the bandages, then other measures and badages have to be taken, to insure the horse doesn't run down through them.

JAGold
May. 23, 2006, 04:59 PM
Reed, does the composition or elasticity of the surface that the horse is galloping on matter? Would it take more force or acceleration to break bone on a soft track than on a very hard track (or on concrete)? I suppose this is irrelevant, just something I've wondered about. --Jess, who fulfilled her college science requirement with a class called "The Oceans"

Janet
May. 23, 2006, 05:02 PM
If we go a step further, and using Netwon's first law, the 3,500 lbs of force is equal to an acceleration of 94 feet/second^2. That is the leg is being driven into the ground at only about 11 miles per hour. Then again, I dare ANYBODY to run directly into a wall at full speed (about 10 miles per hour) and not hurt themselves.

...

ReedOK, I am confused. My physics is admittedly rusty but I remember Force = Mass x Acceleration.

What is "pounds force" when it is reduced to its basic units? Presumably it is pounds ("distance metric") per second per second. But what is the "distance metric"? foot? inch?

And how can you say that a "force" is "equal to" an "acceleration"? Are you assuming a particular mass? In which case the comparison to a horse's leg "driven into the ground at only about 11 miles per hour" with a person running "directly into a wall at full speed (about 10 miles per hour)" doesn't make sense to me, since the masses are very different.

Not trying to criticize, just trying to understand.

DMK
May. 23, 2006, 05:02 PM
JAGold, the surface most definitely does play a role, although I can't scare you with a formula like Reed. :D

But the surface plays a huge role in how much force is transmitted back up the leg. Now Reed will explain in excruciating detail. :p

JAGold
May. 23, 2006, 05:05 PM
JAGold, the surface most definitely does play a role, although I can't scare you with a formula like Reed. :D

But the surface plays a huge role in how much force is transmitted back up the leg. Now Reed will explain in excruciating detail. :p

Yeah, I know somewhere there was a formula drilled into my brain that said it should...but I took AP Physics 10 years ago and promptly forgot as much of it as possible. Which means pretty much all of it :lol:

But I know it hurts my knees more to run on concrete than on dirt or grass...

mickeydoodle
May. 23, 2006, 05:12 PM
Just out of curiosity - I was in Lexington last month, and we went to Overbrook farm and met Jump Start. He has a plate in his front leg, but you can see the plate very clearly under his skin. Why would his plate stay in? I don't know how long he's had it in there, but I do know that is why he was retired from racing and that he has a few babies that are racing now, so it's been a few years.

As a human orthopaedic surgeon, I can tell you there is no need to remove hardware like plates and rods. There is no need to remove the hardware unless it bothers someone (rubs on shoe at the ankle for example). Unlike total joint implants, once the bone is healed, the implant does not stress shield. Especially this plate, as it is a locking plate and the screws are unicortical- go only through one cortex of the bone. The goal of the plate is to hold the bone in alignment until the bone heals. The plate will break if it does not heal- but it will not break if the bone heals. What worries me about the x-rays is that the vets indicated that they wanted the joint to fuse, however it looks like they left the cartilage in - a cardinal rule of joint fusion is that the cartialge has to be removed for the bone to grow together across the joint. I wonder if the vets ever talk to orthopaedic surgeons who do a lot of trauma?

Janet
May. 23, 2006, 05:14 PM
Reed, does the composition or elasticity of the surface that the horse is galloping on matter? Would it take more force or acceleration to break bone on a soft track than on a very hard track (or on concrete)? I suppose this is irrelevant, just something I've wondered about. --Jess, who fulfilled her college science requirement with a class called "The Oceans" I can answer that one- it goes into the "per second per second" part.

When the horse's leg comes down on a hard surface the leg goes from going a certain speed (say X feet per second) to going 0 feet per second in a very short time (say y) so the acceleration is (-) X/y feet per second per second.

But if the horse's leg comes down on a SOFT surface, it takes longer (say 5y) to go from X feet per second to 0 feet per second. Then the acceleration is (-) X/5y feet per second per second. So the acceleration (and thus the force, given you are dealing with the same mass) is much less on the soft surface than on the hard one.

If something went from X feet per second to 0 feet per second instantly (in 0 seconds) the acceleration would be (-) infinity, and the force would also be infinite. It ALWAYS takes time (even if we are only talking about nanoseconds) to go from moving to stationary.

mickeydoodle
May. 23, 2006, 05:17 PM
A question about the plate being removed. I have five metal plates in my back (fusion) however they did do a bone graft from my hip, and said the plates were only initially holding my spine in place but the bone actually did the fusion, yet the plates remained in my back. Is the reason they did not remove them becuase my back is not like a limb is? It doesn't ahve the same stress loading?

Stress sheilding occurs primarily in joint replacement. There is no need to remove the vast majority of hardware unless it is bothering someone. The hardware in your back was there to hold the vertebrae still while they fused together. There is no stress sheilding once it is fused together. The surgeon put the bones in the alignment they wanted, then roughed up the outer surface of the bones, cleaned the cartilage out of the facet joints, then put bone graft down to stimulate the bones to grow together. The bone graft is like fertilizer- it helps stimulate your body to do the work fusing the spine, or joint, or fracture for that matte, together.


In response to the soft versus hard surface, as described above it is indeed the deceleration rate that makes the difference in force to the limb. In humans, running is much better accomplished on athletic shoes with a soft rubbery heel than hard leather loafers- the body decelerates into the rubber much better.

JAGold
May. 23, 2006, 05:18 PM
Very cool! Thanks, Janet.

(Now I'm going back to economics, where at least I have some intuition!!) --Jess

RAyers
May. 23, 2006, 05:28 PM
Reed, does the composition or elasticity of the surface that the horse is galloping on matter? Would it take more force or acceleration to break bone on a soft track than on a very hard track (or on concrete)? I suppose this is irrelevant, just something I've wondered about. --Jess, who fulfilled her college science requirement with a class called "The Oceans"

Yes and no. The track surface would go towards what is called inelastic stablilty. What I provided was a simplified calculation. If we bring the track into play, the calculations become very complex and are dependant on some very specific conditions (such as the angle at which the limb strikes the ground and the speed of strike).

Janet you are totally correct, however you are running up on the difference between English and metric units. In english you have "pounds-mass" and "pounds -force." When we think of weight like that 1200lbs mentioned we really are thinking in pounds force. That is the number 1200 represents the MASS of the body times the acceleration of gravity (32.2ft/second^2). This is why engineers and scientists use the metric system becasue you have to always delineate between pounds-mass (lbm) and pounds force (lbf).

This is also why I can equate force and acceleration because force is simply a function of the acceleration. Now if I take the acceleratoin over time I get SPEED. Therefore, if I assume the leg strike takes around 1/2 second I get a speed of about 11 mph.

The metric system is WAY more simple. Kilogram is mass, meter is distance, period. The "weight" of the horse in metric is 540kg*9.8m/second^2 = 5292 newtons (which is the force or weight the animal exerts on the ground).

Suffice to say, I am trying to give folks an idea of the power, speed and forces involved when dealing with animals.

As for a person running into the wall, the force is REDUCED because the body mass is almost 5 time LESS than a horse. That is why we have relatively stronger bones than a horse. We are lighter but our bone size (cross sectionally) is almost the same as a horse in some points.

Reed

RAyers
May. 23, 2006, 05:34 PM
Stress sheilding occurs primarily in joint replacement. There is no need to remove the vast majority of hardware unless it is bothering someone. The hardware in your back was there to hold the vertebrae still while they fused together. There is no stress sheilding once it is fused together. The surgeon put the bones in the alignment they wanted, then roughed up the outer surface of the bones, cleaned the cartilage out of the facet joints, then put bone graft down to stimulate the bones to grow together. The bone graft is like fertilizer- it helps stimulate your body to do the work fusing the spine, or joint, or fracture for that matte, together.


In response to the soft versus hard surface, as described above it is indeed the deceleration rate that makes the difference in force to the limb. In humans, running is much better accomplished on athletic shoes with a soft rubbery heel than hard leather loafers- the body decelerates into the rubber much better.

I beg to differ. I see stress shielding in all sorts of conditions other than just joint replacement. I see it in craniofacial and dental implants as well as in spinal cages. The difference is in the bone physiology. Vertabra and craniofacial bone are genetically programmmed to grow so you won't see as much but they still have the mechanico-sensory elements that will cause remodeling as the result of artifical devices.

As for the body "deceleration" that is incorrect. Why? The laws of physics and conservation of energy. The energy whether you are in a hard sole or soft has to remain the same. The answer is that the rubber in a shoe simply heats up to dissapate the energy but does not change the acceleration, nor the actual forces imposed on the limb. A "soft" track will heat up quicker during the foot strike reducing the shock load but not the overall load. Shock load is a function of time. Overall load is not.

Still love ya, DMK
Reed

Janet
May. 23, 2006, 05:40 PM
Thanks.

Yes, I understood that "pounds force" was different from "pounds mass", but what I was missing was whether it was foot-pounds per sec^2 or inch-pounds per sec^2 or furlong-pounds per sec ^2.

I understand that for a fixed mass, you can map between force and acceleration- what got me confused was when you SEEMED to be taking the speed (11 mph) derived from the HORSE's mass, and applying the same speed to a HUMAN's mass, and implying it involved similar force. But your reply clarified that for me.

TamiTee
May. 23, 2006, 06:11 PM
Nice graphic, but there's no carpus on the pelvic limb, sofar as I know

Yep, no carpus on the pelvic limb. For those that do not understand this, the hock is the tarsal joint and is basically a human ankle. The horse "ankle" or fetlock is like a human toe joint...:lol:

Basically everything else I was going to say has been covered. I've seen three horses with severly broken bones. One was slung because she broke her rear cannon and needed to be OFF the leg. She developed severe cast sores and had nonhealing of the fracture and was humanely euthanized. The other two were not slung.

Also keep in mind that some horses react very violently to the whole 'cant put my feet on the ground' thing. Especially 3 year old, racing fit colts.

DMK
May. 23, 2006, 09:15 PM
Still love ya, DMK
Reed
You just say that because you don't want me to break out the insurance jargon. :p

But I guess I should clarify, surface plays a role in fatigue, which plays a role in whether a horse breaks down (I'm having a Dr. Rooney moment). In a perfect world the track surface would return energy equal to the amount it received, right? If a horse runs on a very deep, soft track that does not optimally return energy, the horse becomes fatigued, thus leading to bad steps. And if the track is too hard, energy can possibly rebound back and forth through the leg more than once, leading to excess wear and tear on the shock absorbing structures (the leg, which thanks to the lack of muscle tissue below the knee is not as efficient at absorbing this stress as muscle mass, right?), also leading to fatigue and excess wear. Last but not least, if the track surface doesn't have the perfect angle on turns, the inside edge of the foot can hit before the entire surface, thus throwing all Reed's equations cattywampus now all that energy is pinpointed on an area much smaller than the entire foot, and transferring energy up that cylindrical bone structure in an altogether different fashion than the gods intended.

Or am I just blowing smoke up everyone's a$$? :D :D :D

DVM2003
May. 23, 2006, 09:29 PM
Mickey-

Although this is just speculation - I'd be pretty sure that they did remove cartilage and did cancelous bone graphs in the joint. I'll see if my AAEP list serve can confirm this. With most "normal" pastern arthrodesis this is the normal course of action - as you said - to increase the speed of anklylosis.

Cathy

edit: yes...a lot of boarded vet surgeons do spend time with human orthopods - both in clinical and research settings - although some of the issues are similar - lots of our issues with horses are very species specific.

Lookout
May. 23, 2006, 10:51 PM
Bone must have a load to grow and maintain itself. The plate changes the load path in the bone thus causing a shift in how the bones will "remodel."
Is that why the xray looks like the angle of the cannon/P1 joint is straighter than normal, to redirect that force to remodel the bone? I guess it needs to shift in order to fuse?

Lookout
May. 23, 2006, 10:56 PM
And if the track is too hard, energy can possibly rebound back and forth through the leg more than once, leading to excess wear and tear on the shock absorbing structures (the leg, which thanks to the lack of muscle tissue below the knee is not as efficient at absorbing this stress as muscle mass, right?),
I don't know that muscle mass absorbs shock, but since as you say there isn't any in the lower half of the leg, the foot is designed to do so, on the order of about 80% of impact shock. Some of the mechanisms are, the spiral horn tubules which compress (because they're spiral) like a spring, and the reversible deformation of the hoof capsule which produces heat. Granted this of course doesn't take into account extra layers added between the bottom of the foot and the landing surface.

shawneeAcres
May. 24, 2006, 09:12 AM
not only the foot, but more importantly the structure of the fetlock and pastern is the main shock absorber in a galloping horse. THe tendons and ligaments being the "Absorber" in this case (At least this is how I see it, someone correct me if I am wrong). This puts tremendous stresses on teh pastern bones,t he sesamoid and if they fail, the cannon, which is exactly the scenario with Barbaro. I am of the thought that his foot came down at an angle, which more force placed along the inside of the cannon, and due to the fact his foot was angled when it hit (perhaps a "pot hole" in the track, perhaps a shoe that was a bit misplaced, perhaps a slight strain from him breaking thru the gate prior to the race start) cuased the inner portion of his leg to be overloaded. If you look at the xrays the fractures are along the inner aspect (if I am reading them correctly) of the pastern, which crumbled, probably the sesamoid failed first, and then the cannon bone had too much force on it torquing it and causing the inner portion of it to fracture. Curious as to if others feel this is a logical explaination

DMK
May. 24, 2006, 09:48 AM
yes, lookout, it's a given that the hoof, bones and ligaments receiving the immediate impact are the primary shock absorbing structures. But it has certainly been tossed out there that maybe it isn't the best shock absorbing structure on the planet, just the best one for the evolutionary speed trade off. More speed, higher chance of crash and burn. Something's got to give somewhere, otherwise how would the predators get dinner?

Lookout
May. 24, 2006, 11:00 AM
Do you have any references indicating that bones and ligaments are primary shock absorbers?

DMK
May. 24, 2006, 11:10 AM
No, just some distant memory of watching some stuff on biomechanics of the race horses and an even more distant memory of reading Rooney. But you know, logically, it ain't all the foot.

summerhorse
May. 24, 2006, 11:20 AM
Yep, no carpus on the pelvic limb. For those that do not understand this, the hock is the tarsal joint and is basically a human ankle. The horse "ankle" or fetlock is like a human toe joint...:lol:

Basically everything else I was going to say has been covered. I've seen three horses with severly broken bones. One was slung because she broke her rear cannon and needed to be OFF the leg. She developed severe cast sores and had nonhealing of the fracture and was humanely euthanized. The other two were not slung.

Also keep in mind that some horses react very violently to the whole 'cant put my feet on the ground' thing. Especially 3 year old, racing fit colts.


It isn't a knee either, that's a bit higher up in the stifle (the patella). But it IS a nice graphic if you take out the labels!

Janet
May. 24, 2006, 11:31 AM
If you look at the xrays the fractures are along the inner aspect (if I am reading them correctly) of the pastern, which crumbled, probably the sesamoid failed first, and then the cannon bone had too much force on it torquing it and causing the inner portion of it to fracture. Curious as to if others feel this is a logical explaination I spoke to my vet about this today (I think every one of his clients has been bombarding him with questions). He thinks that it is most likely that the cannon bone broke first, and then the damaged cannon bone "acted like a screwdriver" on the fetlock joint and long pastern bone, causing the other fractures.

Lookout
May. 24, 2006, 11:33 AM
No, just some distant memory of watching some stuff on biomechanics of the race horses and an even more distant memory of reading Rooney. But you know, logically, it ain't all the foot.

No, just about 80% :cool: the rest being mostly in the shoulder.

Janet
May. 24, 2006, 11:35 AM
Nice graphic, but there's no carpus on the pelvic limb, sofar as I know :D At least they are in good company!

Samuel Johnson wrote the first Dictionary of English. In a famous instance, he was approached at a dinner party by a woman who asked:
"Why did you define the 'pastern' as the 'knee of the horse'?"

To which Johnson replied:
"Ignorance woman, sheer ignorance."

Lookout
May. 24, 2006, 11:36 AM
Quore: If you look at the xrays the fractures are along the inner aspect (if I am reading them correctly) of the pastern, which crumbled, probably the sesamoid failed first, and then the cannon bone had too much force on it torquing it and causing the inner portion of it to fracture. Curious as to if others feel this is a logical explaination


I spoke to my vet about this today (I think every one of his clients has been bombarding him with questions). He thinks that it is most likely that the cannon bone broke first, and then the damaged cannon bone "acted like a screwdriver" on the fetlock joint and long pastern bone, causing the other fractures.

I think the first scenario is the logical one. It provides an explanation for the sequence and a reason why it would have started where it did, plus it seems fractured sesamoids are very common in racing (casual observation). Although it seems to be the popular theory, the cannon breaking first doesn't say why it would have done so to begin with. "Just because" doesn't count. :winkgrin:

monstrpony
May. 24, 2006, 11:54 AM
Mickey-

Although this is just speculation - I'd be pretty sure that they did remove cartilage and did cancelous bone graphs in the joint. I'll see if my AAEP list serve can confirm this. With most "normal" pastern arthrodesis this is the normal course of action - as you said - to increase the speed of anklylosis.

Cathy

edit: yes...a lot of boarded vet surgeons do spend time with human orthopods - both in clinical and research settings - although some of the issues are similar - lots of our issues with horses are very species specific.

I was wondering about this myself (I'm not a medical person, neither animal nor human, just a horse owner dealing with fusing hocks). I was assuming they would have to do something to the inside surfaces of the joints to promote fusion, and I recall Dr. Richardson saying at some point that they had the joint totally open (when he said he saw no evidence of prior dammage); my first reaction was Yikes! that would destroy the joint surfaces!, and then I realized that was probably the point ...

All of which made me wonder, how, exactly, do they prepare the joint surfaces to promote fusing?

(and you guys are scaring me about the stress shielding in joint replacements, having been there, done that :o )

DMK
May. 24, 2006, 12:07 PM
No, just about 80% :cool: the rest being mostly in the shoulder.

okay, so you are saying energy dissipates 80% in the foot and then zero energy is lost as it travels up the leg until it reaches the shoulder, then the remaining 20% just dissapears into the shoulder apparatus?

Hmmm. sneaky stuff, that energy. Almost majikal. Sort of like a gypsy vanner... :lol:

Now me, I tend to think the majority is absorbed by the foot and the remaining amount dissipates as it travels further from the point of impact, but then I already said that. :cool:

Where'sMyWhite
May. 24, 2006, 12:38 PM
I also thought I remember hearing earlier that the guess was that the cannon fracture was first, followed by the sesamoid and P1 (although I don't recall any conjecture on if P1 or the sesamoid was next).

I don't know horse boimechanics (and certainly don't play an expert on TV :) ) but it makes sense to me that the cannon going first may have helped avoid the fractures going through the skin (ie, wreck the underlying structures before coming out the skin).

Don't think they'll ever really know what order things occured in.

Lookout
May. 24, 2006, 12:42 PM
okay, so you are saying energy dissipates 80% in the foot and then zero energy is lost as it travels up the leg until it reaches the shoulder, then the remaining 20% just dissapears into the shoulder apparatus?

Hmmm. sneaky stuff, that energy. Almost majikal. Sort of like a gypsy vanner... :lol:

Now me, I tend to think the majority is absorbed by the foot and the remaining amount dissipates as it travels further from the point of impact, but then I already said that. :cool:

Well, maybe some is "dissipated" as it travels up the leg, but that is not absorption. It would continue to travel until it encountered something with absorption capabilities.

mickeydoodle
May. 24, 2006, 12:45 PM
I was wondering about this myself (I'm not a medical person, neither animal nor human, just a horse owner dealing with fusing hocks). I was assuming they would have to do something to the inside surfaces of the joints to promote fusion, and I recall Dr. Richardson saying at some point that they had the joint totally open (when he said he saw no evidence of prior dammage); my first reaction was Yikes! that would destroy the joint surfaces!, and then I realized that was probably the point ...

All of which made me wonder, how, exactly, do they prepare the joint surfaces to promote fusing?

(and you guys are scaring me about the stress shielding in joint replacements, having been there, done that :o )

To prepare the joint surfaces you use tools (a curette- like a sharp little spoon, rongeurs-biting tool like a sharp pliers, osteotomes-chisels, etc) to remove the cartilage. Then you use a burr (spinning rough bit like a Dremmel tool) to remove the hard dense bone under the cartilage and expose the more porous cancellous bone. Then I take a small osteotome (chisel) and flake the entire surface to increase the roughness and surface area to stimulate healing. Then you put the two pieces together (you have to make sure there is good contour match and good bone to bone contact) and you hold them there with screws/plates whatever you need while it is healing. I always use bone graft as fertilizer. Using this method, my non-union (bones not fusing) rate is less than 1% in 13 years.

DMK
May. 24, 2006, 01:19 PM
OK, lookout, you told me earlier that you didn't think muscle mass absorbed shock, but that energy isn't absorbed between the hoof and shoulder, because the energy has to find something absorptive and bone/ligament/tendon is not that thing, so presumably there is something else in the shoulder that does the trick (muscle?) and that while energy dissipates between the hoof and shoulder it is not absorbed, although there is less energy by the time it gets to the shoulder because it dissipates.

I'm totally down with this, but just wanted to see if I got it right?

Because I was working on the theory that while energy primarily dissipated in the hoof, because the lower leg structure was not not the most efficient thing to absorb energy (like the foot or possibly muscle tissue) even though it can, the dissipation can create fatigue and stress over enough time/poor enough footing to cause injury. But clearly this is not correct, so I need to make sure I get down with how it really is.

monstrpony
May. 24, 2006, 01:23 PM
Thanks, that's very interesting.

What do you see in the xrays that makes you wonder whether or not this (removing cartilege, preparing surfaces for fusion) was done in Barbaro's case? I just looked back at the one xray that's posted on the UPenn website, and I could be convinced that the cannon-P1 joint is pretty well mashed together, but there does appear to be a good bit of space in the P1-P2 joint, yet there appear to be screws across that joint.

Also, what do you mean by "unicortical" screws? You said earlier this meant they went through only one cortex of the bone--what defines a cortex? They look to me like they go all the way through the bone.

And, while we're at it--what is meant by a "locking compression plate"; in what sense is it "locking"? "Compressing"?

Is the "fertilizer" a single slice of bone, or is the bone ground up and spread along the prepared joint surface? I remember when I had my hip replacement, there was talk of keeping the piece of bone removed at the head in case it was needed to be ground up and somehow used in fitting the artificial joint--is this the same kind of thing?

My question about the xrays assumes I'm seeing what I think I'm seeing, but, again, I'm not any kind of expert--just very interested and curious! And I appreciate your being willing to share your knowledge.

I'm not at all questioning what was done for Barbaro, just trying to understand the what/why/how of it.

wanderlust
May. 24, 2006, 01:39 PM
Lookout, I'm curious. Are you a veterinarian? Or perhaps a physicist or equine physiologist? Or in academic/veterinary research of some type? You seem very knowledgable and very convinced of your knowledge...

mickeydoodle
May. 24, 2006, 01:53 PM
Thanks, that's very interesting.

What do you see in the xrays that makes you wonder whether or not this (removing cartilege, preparing surfaces for fusion) was done in Barbaro's case? I just looked back at the one xray that's posted on the UPenn website, and I could be convinced that the cannon-P1 joint is pretty well mashed together, but there does appear to be a good bit of space in the P1-P2 joint, yet there appear to be screws across that joint.

Also, what do you mean by "unicortical" screws? You said earlier this meant they went through only one cortex of the bone--what defines a cortex? They look to me like they go all the way through the bone.

And, while we're at it--what is meant by a "locking compression plate"; in what sense is it "locking"? "Compressing"?

Is the "fertilizer" a single slice of bone, or is the bone ground up and spread along the prepared joint surface? I remember when I had my hip replacement, there was talk of keeping the piece of bone removed at the head in case it was needed to be ground up and somehow used in fitting the artificial joint--is this the same kind of thing?

My question about the xrays assumes I'm seeing what I think I'm seeing, but, again, I'm not any kind of expert--just very interested and curious! And I appreciate your being willing to share your knowledge.

I'm not at all questioning what was done for Barbaro, just trying to understand the what/why/how of it.

What I see in the x-ray (and it is only one view that I have seen) is that the cannon-P1 joint still looks like it has some space (the black line is cartilage) in doing the surgery on humans I want my x-ray to not have the black line- or not so much of it. I am not critizing them either, just wondering as a human surgeon. The lower joint definitely has cartilage- but I do not think the plate has a screw in the lower bone, I think that screw hole in the plate is empty.

A locking plate has threads in the screw holes, and the heads of the screws thread into the hole threads- making it a rigid construct, with no toggle of the head in the hole. This makes the construct stronger. The locking screws are generally unicortical, meaning they go through one cortex. The cortex is the outer, hard bone, and remember the bones are essentially tubes, so the unicortical screw goes through the nearest side of the tube, but not out the other. Again, this makes a stronger construct with the locking plate. Plates that do not have locking threads usually get bicortical screws- screw goes through and out the other side. The compression term means that the holes are oval, and you can put the screw in at either end to push the fragments together, or pull them apart.

Bone graft in this type of case is usually ground up. Segments of bone are usually used in neck and back fusions, or unusual cases. The docs who did your him might have ground up the femoral head to use to fill in defects (voids) around the prostheses. In unusual hip/knee revision cases a femoral head may be shaped to fill in a large segment. The ground up type is much more common.

Lookout
May. 24, 2006, 02:06 PM
Lookout, I'm curious. Are you a veterinarian? Or perhaps a physicist or equine physiologist? Or in academic/veterinary research of some type? You seem very knowledgable and very convinced of your knowledge...

Reading the results of a study, and repeating them, this is not 'my' knowledge, nor does it take any special qualifications. (Having said that I do have some background in structural forces, perhaps enabling me to understand the work).