To preface this blog, farriery and horse hooves are something that I find extremely interesting, however, also very perplexing. This is very much a “starter” article for this topic, I have done a lot of research but there are always different opinions and concepts around it (some to follow, some to ignore!). I am not a farrier, but I have observed a lot of work, a lot of hooves and my dissertation covered hoof shape analysis compared to saddle positions… so I have done some research!
Before we start, the following picture offers a brief recap of the limb’s anatomy. (Distal phalanx = P3 or coffin bone):
“No foot, no horse” I first heard echoed over 10 years ago… My trainer was discussing the shape of her horse’s hooves, and at the time I had truly minimal appreciation of the hoof’s anatomy/function and even less idea as to what shape they should be. I thought this horse’s hooves looked just fine, but I was aware that “just fine” was probably not quite enough for a Grand Prix horse! A very perplexed me took this little mantra on as gospel, with hopes to one day actually understand the message.
The last few weeks I have felt the difference that X rays and remedial farriery can have on your horse’s performance… and this little mantra took on a life of its own. Yesterday I posted a video of my mare who has had a summer of a sore back due to no riding during COVID. I decided to go back to basics because nothing really seemed to be working (Physio, veterinary treatments etc), and that niggling mantra “no foot, no horse” was ringing in my head. Gratefully, it seems to be working as she is starting to do harder work, with greater wase, developing muscle that she lost throughout the year and her body is recovering faster and faster from the increased workload. These are all great indicators of a horse that is comfortable.
If there is anything that my dissertation explained to me, it is that the hoof, and its interaction with the distal limb is a phenomenal feat of engineering. This interface is responsible for communicating between the muscles, tendons and bones of the horse’s legs which are ever moving, and the hard, immovable exterior it collides with 24/7.
The hoof capsule “holds” the skeleton by Laminae. Laminae exist as thousands upon thousands of interlocking folds of tissue, which connect the coffin bone to the hoof capsule. These folds, and the hoof wall, stretch and absorb energy as the hoof capsule hits the ground with each stride. As much as it is powerful, this structure is sensitive; which is why diseases such as laminitis (inflammation of these folds) and problems like abscesses cause so much pain. Finally, the weight of your horse is actually held almost suspended by these folds of tissue, which allow their weight to be transferred and actually supported by their fingernails/hoof wall. Furthermore, this wall is a living and growing structure which can and does adapt to the different pressures applied to it (which is one of the reasons why hooves change shape over a lifespan).
A hoof’s heel and toe angles should be parallel and should match the hoof pastern axis, which should be approximately 45-55° (Lesniak, et al., 2017) (Clements, et al., 2019!). This angle in theory represents optimal bone, tendon, ligament and joint alignment for function and comfort. CAUTION is warned: Just because the limb looks normal from the outside, does not mean serious deviations from this axis aren’t occurring… This is where X-rays are extremely useful!
A broken back HPA is associated with a lower heel, longer toe and generally coincides with a lower coffin bone angle. This broken back axis and lower coffin bone angle has been increasingly associated with greater risk of injury (Dyson, et al., 2011). An interesting description for this which I heard recently is this angle causes the tendons/limb to be “pre-pushed” … Imagine standing on the ground and lifting your weight on to your toes for several reps (flexing your calves). It is tiring, but easily manageable. Now do it with your toes on an elevated surface (for example, the edge of a step) … This becomes much harder. The step mimics a pre-pushed posture and mimics the broken back axis. This increases the distance that your muscles need to work over, to pull your heels up to the same point. Fatigue increases with this broken back posture, and again, flashback to the first blog posts, fatigue is an effective precursor to injury.
MANY sources have found different statistics and observations which highlight just how negative the effects of a broken-back HPA can have. A few of these are mentioned…
- Function and condition of the Deep digital flexor tendon (DDFT) and the navicular bone (NB) are dependent on heel angle. Low heels increase the distance over which the DDFT has to pass to reach its insertion on the coffin bone. This means greater strain on the tendon, and greater pressure on the structures underneath it, such as the navicular bone. (Eliashar, et al., 2004) (Dyson, et al., 2011) (Clements, et al., 2019!)
- Coffin bone angles:
o Optimal = 5° (wedge from the ground) (Clements, et al., 2019!)
o Raised 1° ((2) on image) = 4% DECREASE of peak pressure on NB (Eliashar, et al., 2004) (Dyson, et al., 2011)
o Dropped 1° ((3) on image) = 20% INCREASE of peak pressure through the first moments of hoof contact with the ground. (Lesniak, et al., 2017)
These are related to the heel angle, and one of the reasons low, collapsed heels are not desired!
- Length of toe:
o 1cm excess of toe, adds about 50kg strain to the tendons (Murray, 2020)
This causes additional pressure at breakover. Increased length of toe increases the distance the tendons and muscles must contract and travel over in order to rotate and lift the limb (kind of like the pre-pushed posture discussed earlier!). Again, excess strain increases risk of injury.
- The angle of the coronet band of the hindlimbs should draw a line directly to the back of the knee of the forelimb. This should indicate correct conformation!
These are all factors somewhat out of control of a veterinary physiotherapist. So, what is the relevance?
Firstly, all of the above should indicate the hoof shape can cause internal tendon and joint problems, and these certainly are applicable to a VP. These problems are likely to cause compensations and secondary problems. These CAN be addressed by Veterinary Physiotherapy and complementary services. First and foremost, Veterinary diagnostics (especially X-rays, and ultrasound if necessary), and farrier intervention will be necessary to address fixing the conformation, if there are problems.
Secondly, pain and compensation require rehabilitation and remedial exercises. This is because your horse will stop moving their bodies in an efficient and correct manner, in order to offload the painful pressures. Rehabilitation will help limit more damage to these tissues, while maintaining form and function. Your Vet Physio can help make your horse more comfortable both during and after the appropriate farrier and veterinary interventions have been made. Ice therapy, heat therapy, manual therapies and some electrotherapies could absolutely benefit your horse!
A Veterinary Physiotherapist should coordinate treatment alongside your veterinarian and farrier, so if you have any queries about what we can do to help, what you should be expecting at any stage, or any questions about anything mentioned, please do get in contact!
References
Clements, P., Handel, I., McKane, S. & Coomer, R., 2019!. An investigation into the association between plantar distal phalanx angle and hindlimb lameness in a UK population of horses. Equine Veterinary Education, Volume NEED VOLUME AND ISSUE, pp. 1-8.
Dyson, S. et al., 2011. An investigation og the relationships between angles and shapes of the hoof capsule and the distal phalanx. Equine Veterinary Journal, 43(3), pp. 295-301.
Eliashar, E., McGuigan, M. & Wilson, A., 2004. Relationship of foot conformation and force applied to the navicular bone of sound horses at the trot. Equine Veterinary Journal, 36(5), pp. 431-435.
Lesniak, K., Willians, J., Kuznik, K. & Douglas, P., 2017. Does a 4-6 week shoeing interval promote optimal foot balance in the Working Equine?. Animals, 7(29), pp. 1-14.
Murray, D. R., 2020. Risk factors for injury in sport horses. Newmarket, VetFest 2020.