How The Anatomy Books (Unintentionally) Fail Us Over The Nuchal Ligament

nuchal-ligament-header-1

The nuchal ligament is a soft tissue structure that is widely discussed in dressage circles. Unsurprisingly, given its deep location, relatively few of us get to cast eyes on it or feel it directly under our hands.

It’s equally unsurprising, then, that most of us don’t realize that the image we hold in our heads is somewhat different to the reality of the ligament inside our horse.

 © All text copyright of the author, Jane Clothier, www.thehorsesback.com. No reproduction of images, partial or entire text without permission. Sharing the link back to this page is fine. Please contact me for more information. Thank you!

I have recently been fortunate enough to attend another dissection with renowned Australian gross anatomist (and she will point out repeatedly that despite this title, she is not gross – or, at least, not that often), Sharon May-Davis.

In this dissection workshop, Sharon had yet another opportunity to show us that an aspect of textbook anatomy is incorrect.

Yes, apparently there are many points where this is the case.

 

Where the nuchal ligament is and what it connects

The structure in question is the nuchal ligament, or the nuchal ligament lamellae to be exact.

George Stubbs illustration

George Stubbs, 1777, showed the NLL attaching from C2 to C7.

To quickly explain, the funicular part of the nuchal ligament is the cord-like part that runs from the withers to the occiput (back of skull). The lamellae is the fibrous sheet-like part that extends from the funicular part to the cervical (neck) vertebrae.

According to the majority of anatomy diagrams and textbooks, it extends down to attach to the cervical vertebrae, from C2 to C7.

According to Sharon, it doesn’t. And here’s why.

 

Findings on the nuchal ligament’s true location

In this study of 35 horses on the dissection table, Sharon found:

  • No cases where the attachments were from C2 to C7.
  • No horses where the attachments were from C2 to C6.
  • In all 35 horses, the attachments were from C2 to C5.
  • And in 9 of the 35, the attachments to C5 consisted of thin and feeble fibers.
  • The horses were of a mixture of identifiable breeds, aged 2 to 28 years old.

So, why do the majority of anatomical drawings of the deeper structures of the horse show something different?

When received knowledge can be a problem

Nuchal ligament, 5yo TB [click to enlarge]

Nuchal ligament, 5yo TB [click to enlarge]

Many of today’s illustrators are referring to illustrations that have themselves been amended from earlier illustrations.

(The header image for this site’s most viewed post, The Disturbing Truth About  Neck Threadworms and Your Itchy Horse, shows an inaccurate rendering of this ligament, as do most of the other illustrations I used. Dang!)

Inaccuracy is a recognized problem when it comes to received knowledge – was this anomaly due to an earlier artist’s error, or was it a characteristic of some 17th century horses that has been progressively bred out over subsequent centuries?

  • And this raises the question of which structure, exactly, is supporting the base of the neck of the horse in motion? Read more about m. Spinalis cervicis in this post, Meet Spinalis, the Forgotten Muscle in Saddle Fitting.
  • And how does this awareness inform current training approaches that require horses to raise themselves into self-carriage?

The findings from this study are in a peer-reviewed paper by Sharon May-Davis and Janeen Kleine currently in press with the Journal of Equine Veterinary Science. The paper includes a detailed review of illustrations in equine anatomy literature, an explanation of the study, and a thought-provoking discussion on the implications for our understanding of equine biomechanics.

Variations and implications of the gross anatomy in the equine nuchal ligament lamellae, Sharon May-Davis, Janeen Kleine, Journal of Equine Veterinary Science 30 June 2014 (Article in Press DOI: 10.1016/j.jevs.2014.06.018)

Have you read about Sharon’s findings on arthritis of the humeroradial (elbow) joint in all ridden or driven horses?

 


Questions, thoughts or comments? Join us at The Horse’s Back Facebook Group


 

Revealed: the Common Equine Arthritis You Won’t Read About in Textbooks

elbow-header2

Sometimes, a person from outside a profession successfully identifies something that has been unnoticed, overlooked or wrongly assessed for a long, long time. Coming from another direction, they see something that has been hidden in plain sight, simply because nobody looked there before.

Take amateur astronomers. They’re particularly well known for rocking the scientific community. In 2009, Australian Anthony Wesley discovered a visible scar left by a comet or meteoroid that had slammed into Jupiter, and we’ve all heard about Mr and Mrs Shoemaker and their neighbor Mr Levy and the comet they discovered in 1993.

Unusually, the astronomy community is able to recognize that while professionals have more technical background to analyze data, amateurs still play an important role in collecting it.

You might think that there’s no new data to be collected about equine pathologies, because every condition that can affect a horse, certainly above the level of microbiology, must already have been charted, mapped, researched and thoroughly understood. But, in the words of the song, it ain’t necessarily so.

Sometimes, all it needs is for someone else to be looking. And if that someone is looking with a rather different set of eyes or from a slightly different direction to the conventional scientific community, some rather remarkable results can come about.

 © All text copyright of the author, Jane Clothier, www.thehorsesback.com. No reproduction of partial or entire text without permission. Sharing the link back to this page is fine. Please contact me for more information. Thank you!

One lady who’s working in the field

If you’re looking for a different set of eyes for equine musculoskeletal pathologies, they don’t come much sharper than those of Sharon May-Davis. Few people have the razor sharp eye she has for a hidden pathology or condition in the horse.

She’s held in high esteem by riders in the sporting fields, because as an equine therapist, she has managed elite equine athletes at State, National and Olympic levels in 7 different disciplines including the recognized FEI ones such as eventing, dressage, showjumping and endurance. This has been accompanied by her extensive experience in the Australian and Japanese racing industries.

Teaching biomechanics, Sept 2013

Sharon, seated, teaching biomechanics, Sept 2013

Sharon is also a biomechanics expert, a university lecturer in equine therapies and anatomy, and – significantly – a practical anatomist.

She has been conducting private equine autopsies for many years – it’s not for nothing that she’s been labeled The Bone Lady and Equine CSI. She also uses these 2-3 day dissection workshops to teach equine professionals and horse owners more about how their horses move and the damage their bodies can incur as a result of breeding, illness, injury or work.

She has been dissecting for personal research for over 20 years and professionally for 14 years. In fact, she now conducts up to 15 professional dissections per year – that’s a total of around 300 dissections so far.

Sharon is the first to state that she isn’t a vet and doesn’t hold a doctorate, but as a practicing equine scientist, researcher and practitioner, she is uniquely placed to provide a source of raw data that is all but unparalleled.

Evidence from the dissection table

Some years ago, Sharon noticed an unusual action in the elbow of horses. She mentioned this to qualified practitioners and was informed that this action was quite normal. Not convinced, she began videoing horses prior to dissection and, within a short period of time, was able to match this action to a change in the elbow.

Humerus, radius and ulna, showing damage to cartilage

Humerus, radius and ulna, showing damage to cartilage

Not to beat around the bush, it’s an unusual form of degeneration in the horse’s elbow joint that involves all three bones. It’s a form of osteoarthritis that strikes the humeroradial joint and the ulna, causing deep and dramatic gouges into the cartilage, and eventually eroding bone.

When the joint is opened up, blood is frequently found in the synovial fluid (haemarthrosis). The fluid also displays decreased viscosity.

This is more than a little bit odd, as arthritis of the elbow is supposed to be rare in the horse.

Yet Sharon has found it to be present in numerous horses that have been euthanized under veterinary supervision for completely unrelated reasons.

Note: that’s not just some horses, but many.

Do you know where the nuchal ligament attaches on the cervical vertebrae? You think so? Evidence from the dissection table might prove you wrong – read more about Sharon’s findings on the nuchal ligament’s lamellar attachments…

This equine arthritis is visible in the living horse

The vital connection from video to dissection has enabled Sharon to indicate the presence of the elbow osteoarthritis in the horses she had been treating as an equine therapist.

It’s easy to spot, being a noticeable jarring in the elbow as the horse moves downhill – a kind of double action – you can see it here. Significantly, it’s what can be termed a gait anomaly, rather than lameness.

(If you can’t see the above video, you can view it here.)

Does it look familiar? It’s very likely that you’ve seen it in horses before and wondered what it was. The fact is that it’s so common, many people think it’s a normal action. It’s not. It’s a form of equine arthritis.

Sharon tells us she has seen the elbow problem in all types, breeds, sizes and ages of horses. Some affected horses have been elite dressage and eventing competitors. Interestingly, the problem is only presenting in ridden and driven horses.

If never worked, horses appear to remain forever free of this particular joint change.

Why the fuss – isn’t this just regular arthritis?

No. Arthritis of the horse’s elbow is considered to be rare in equine veterinary medicine.

How it should look: healthy radius and ulna (unridden horse)

How it should look: healthy radius and ulna (unridden horse)

The key to why it doesn’t often get diagnosed and is considered rare could be the absence of visible lameness. The arthritis identified by Sharon does not cause a distinctive lameness in the horse, although it does bring on a notable gait change, with the double step in the joint’s motion on the downhill.

Riders of such horses often just feel that their horse is a bit ‘off’, feeling a hesitation in the movement, but without being able to define the point of origin.

There are a couple more reasons why it’s not very visible: first, the action of the elbow is highly integrated with the overall shoulder action, and second, the massive triceps muscle has a further stabilizing effect on the joint.

Radius and ulna of ridden horse, showing cartilage wear and blood in joint

Radius and ulna of ridden horse, showing cartilage wear and blood in joint

And even if the elbow is explored, the relatively tight joint space means that degenerative problems are rarely seen in diagnostic imaging, although inflammation can show up in thermographic images.

When, unusually, a problem has been recognized and vets have attempted a corticosteroid injection of the joint (which happens to be the most difficult joint to access), blood has been found to be present.

A closer look at Sharon’s findings

Sharon May-Davis first presented some of her findings into elbow arthritis at a conference in Australia in February 2013: the Bowker Lectures at the Australian College of Equine Podiatherapy. Presenting alongside Prof Robert Bowker and Dr Bruce Nock amongst others, she discussed the club foot in the horse, and noted how the elbow degeneration she observes on the dissection table is always worse in the forelimb with the more upright hoof.

 

If the condition is bilaterally present, it unfortunately appears worse on the side with the slightly upright or higher hoof. What’s more, and according to Sharon, this also applies to the limb where an inferior check ligament desmotomy (surgery undertaken with the aim of correcting an upright hoof) has taken place and the ligament has later reconnected.

She has, as already mentioned, since established that it can occur in any ridden or driven horse. Here, she describes the problem in her own words.

“The action looks like a slip and or clunk into the shoulder or a shudder or a sliding / slipping action. It depends upon your perspective. The actual change in the action begins when the foreleg is in the ‘Stance Phase’ during the stride as the limb goes into the posterior phase of the stride. It is more obvious going down a hill.

“So far, 100% of ridden horses exhibit this condition to a varying degree (under dissection). Horses not ridden and with no abnormalities do not exhibit this condition (under dissection). Horses in harness also exhibit this condition.

“What does the joint look like? There appears under dissection to be substantial degradation in the cartilage of the humerus, radius and ulna.

“Most horses appear to handle this condition and continue with a normal life if not pushed to extremes. Although this sounds career-ending, in fact it is not. Once the horse gets through the worst of the wear pattern they re-settle in the joint and continue on with work.

“High level competitors require joint support to help sustain the elbow and other joints that may compensate for the change in action.

“Horses that jump are more inclined to land with straighter forelimbs. Be mindful that jumping and downhill work could possibly make the condition worse.

“Riders often feel instability in the horse’s forelimbs when traveling downhill and some even question the horse’s proprioception.

“Bodyworkers massaging the triceps (particularly the lateral triceps) actually exacerbate the condition as the massage releases the cast-like formation that this muscle provides.”

 

More research is needed, but so is support

Humerus and radial bones of ex-racehorse, showing arthritic wear

Humerus and radial bones showing arthritic wear

Despite finding and documenting a huge number of dissection cases involving this particular issue, all unaided and unfunded by outside bodies, Sharon has consistently met with brick walls and skeptical responses when she has put the information forward to relevant authorities.

Why? It’s not as if she’s new to this. She has previously identified congenital malformations in the caudal cervical vertebrae of thoroughbreds, and in the atlas of Spanish Mustangs, as well as asymmetries in the femur structures of racehorses due to racing (published in the Australian Veterinary Journal).

She isn’t looking for funding (although she obviously wouldn’t say no), but would like to have this research taken up for the benefit of all ridden and driven horses. The sooner the problem is recognized and investigated, the sooner that episodic pain in the horse can be recognized, with appropriate joint support or rest given where appropriate.

And the sooner we can all learn more in our great drive towards improved equine health, the better. As Sharon says,

“In truth, we are still in the dark. Seeing it is one thing, analyzing it and providing a preventative program is something totally different.”

 


Questions, thoughts or comments? Join us at The Horse’s Back Facebook group. 


 

Two more cases (added January 2014)

Case 1: Thoroughbred gelding

Raced, then showjumped to ‘B’ grade, before being ridden as a trail horse. Euthanized at 14 years due to ongoing colic issues. Here is a video of this TB, filmed in 2011:

 

Here are images from the dissection table:

TB gelding radius and ulna, showing wear and blood spot.

TB gelding radius and ulna, showing wear and blood spot.

 

TB distal humerus, showing significant wear to cartilage.

TB distal humerus, showing significant wear to cartilage.

 

Read more about ex-racehorses and their prevailing physical problems here.

 

Case 2: Warmblood gelding

Showjumped up to 10 years. Competed in dressage from 11 years. Retired from riding at around 20 years due to unresolved lameness.

Here is a video of this horse, showing severe elbow degeneration (as well as other pathologies):

 

 

And here are images from the dissection table. Note the bruised and bloody cartilage of the radius, ulna and humerus. Also, the droplets of synovial fluid are discolored, being a very unhealthy reddish brown.

 

WB: cartilage wear evident in the radius and ulna.

WB: cartilage wear evident in the radius and ulna.

 

WB humerus showing significant wear.

WB humerus showing significant wear.

 

WB humerus showing wear - note spots of synovial fluid showing brown discoloration.

WB humerus showing wear – note spots of synovial fluid showing brown discoloration.

More Information

Shop for the Best Discounted Pet, Equine, & Livestock Supplies!
Sharon May-Davis, B. App. Sc. (Equine), M. App. Sc. (Ag and Rural), ACHM, EBW, EMR was the Equine Therapist for the Modern Pentathlon Horses and the Australian Reining Team at the Sydney 2000 Olympics. She has worked with the Australian Champion from seven differing disciplines and has a particular interest in researching the musculoskeletal system. She also conducts clinics and seminars in relation to her work and regularly presents in the Northern and Southern hemisphere.

You can learn about Sharon’s work and approach in this interview: Skeletons from the Bone Lady’s Closet.

Meanwhile, Sharon is answering questions in the comments section, below. Discussion is positively welcomed, so please feel free to ask questions or share experiences. Sharon will drop in to answer them if you do.

 

 © All text copyright of the author, Jane Clothier, www.thehorsesback.com. No reproduction of partial or entire text without permission. Sharing the link back to this page is fine. Please contact jane@thehorsesback.com for more information. Thank you!

 

 

Social media & sharing icons powered by UltimatelySocial