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The back feet - negative plantar angles.



Everybody knows the phrase ‘no hoof, no horse’. We normally associate it with the front feet. Rightly so. The majority of forelimb lameness is due to pain within the hoof. However, we often forget that the front feet only make up half of the ‘no hoof, no horse’ phrase.

In this blog, I am going to look into a particular aspect of hind foot balance - dorsoplantar balance. To assess this balance, you need to look at the foot from the side.


In my experience, horses with poor dorsoplantar balance often have long toes and low heels. They sometimes rest their hind feet, intermittently shifting weight from one foot to the other or resting their feet on a ledge or back end on a wall when in their stable. If it has been going on for a prolonged period of time, they may struggle to lift their core, and therefore might not be able to perform sternal lifts (belly lifts) and pelvic tucks.

They are generally tight through their hamstring muscles, and may have pain through their glutes. This glute pain has been linked with poor dorsoplantar angles before (1) with correction of this imbalance resulting in a significant decrease in discomfort within a few days (1).



The hamstrings are marked blue and function to push the leg forward by extending the hock and hip and flexing the stifle.





The gluteal muscles are marked green and function to propel the leg and provide impulsion mainly through extension of the hip.




Obviously, horses with tight hamstrings and sore glutes find it difficult to work. They often shuffle as they struggle to flex their limbs due to initial hamstring tightness, showing gradual improvement as the muscles warm up. Owners often complain about their horses being unable to build up gluteal strength, having a flat bottom. This shouldn't be surprising, as if the muscles are sore, and therefore can’t be used correctly, they will not build up strength. I know that a lot of horses have hind limb lameness, but I have never heard of a horse having hind foot lameness. Does it really matter if they have bad dorsoplantar balance?

A negative S angle was linked to increased risk of bone injury in the metatarsal bone (2), hock/ suspensory pain (3) and stifle pain (2). It has also been linked with sacroiliac and lower back discomfort. We do not know whether the foot conformation predisposes lameness or vice versa, however, treating one and not the other will limit the efficacy of treatment. How can I tell if my horse has a negative plantar angle?

3 methods: photographs, coronet angle direction and radiographs.


It is worth remembering that NPA can be on one or both of the back feet. The shoeing plan may therefore be different based on each individual foot.

Photographs

Look at your horse’s feet - these horses generally have low or under run heels and long toes with decreased frog support. Examination of digital photography (4) and assessment of the external characteristics of the hoof capsule (5) can be extremely useful tools in both the tracking progress between treatments and being able to recognise a lengthening toe and the risks associated with it.


Within the digital photography study (4), the researchers (Kalka, Pollard and Dyson) found that the average dorsal hoof wall angle was 50.9° and heel angle was 36.4°. They also showed that there was a positive relationship between the S angle and both the dorsal hoof wall and heel angle. This means that hind feet which are long or have under-run heels are more likely to have negative plantar angles.


Note that the dorsal hoof wall angle (DHWA) is 44°, therefore, it is considered to be low and at an increased risk for negative plantar angle.


We can also look at the angle of the coronet (CA). The coronet is the line band which separates the hoof from the skin. 88% of horses with a CA of 28° or more had a negative plantar angle (6).

Note that the CA is 28°, therefore, there is an increased risk of a negative plantar angle.

This means that you can track your horse's feet. It is important to do this at consistent times within the shoeing cycle - either just at the beginning or half way through. The feet will obviously get longer throughout the cycle, and some horse might develop a negative plantar angle mid way through a cycle.


This is such an important point to remember because if your horse is consistently going into a negative plantar angle 3 weeks into a 6 week cycle, then they are at increased risk for injury for half of their lives.


Learning how to take as close to perfect photos as possible is key in tracking your horse's feet - remember to:

  1. Use a level surface.

  2. Get level to the ground, as perpendicular to the hoof as possible (try to line up with the heel bulbs), about two feet away.

  3. Do not tilt your phone/ camera up or down.

  4. Use apps like AngleMeter 360 or HoofMapp to track angulation.


Coronet angle direction

When standing square, your horse's coronet angle should direct towards the forelimb knee (carpus). If it directs towards the elbow, then the horse most likely has a negative plantar angle.

This is probably the easiest way to check, but, also, in my opinion, the least accurate. It is obviously still worth doing, and one of the first things that I do when I start any assessment.


Radiographs

Foot balance radiographs can show whether the foot is broken back or not, meaning that it is putting more weight through the plantar processes of the pedal and navicular bone (kind of like you lifting your toes and standing on your heels). It can also give guidance to your farrier to know whether sufficient sole is present to correct the angle solely with a trim. The sole (distance between the pedal bone and bottom of the foot) should be as thick as the hoof wall (distance between the DHWA and pedal bone).


Pre-trim radiograph showing a negative plantar angle. Note that the sole depth (red) is thicker than the hoof wall, and therefore, a more aggressive trim may be sufficient to correct the NPA.


Another benefit of radiographs is that, like photographs, they allow you to track progress and make small changes in the trim and shoeing plan.


These are the before and after radiograph of the horse pictured above, showing a negative S angle of -1.03° improving to +3.60° following a trim. This was possible due to sufficient sole thickness. Note how the sole is initially thicker than the hoof wall. This horse already had a pad in place, and this was maintained for the next cycle . The farrier planned to use the dorsal hoof wall as an indicator of when the pad could be removed going forward.

This is the radiograph of a different horse with a negative S angle of -6.68°. Although the trim will help, the sole depth is insufficient and gradually wedging the heel with a thick pad would be necessary to improve the plantar angle.

It is very important to remember that every horse is different, and that there is no fixed plan which will suite every horse. Each horse should be treated based on its individual circumstance, including the cause of any lameness, expected workload, farrier's experience in dealing with these cases, and facilities present at the yard.


Conclusion

If you think that your horse might have negative plantar angles, it is important to try to address any underlying issues through specific rehabilitation plans which improve posture depending on a thorough initial assessment. Changes can start to happen relatively quickly, and I always stress the importance in working as a team with your farrier, vet and body workers to get optimal results.


References

  1. Mansmann, R., James, S., Blikslager, A. and vom Orde, K., 2010. Long Toes in the Hind Feet and Pain in the Gluteal Region: An Observational Study of 77 Horses. Journal of Equine Veterinary Science, 30(12), pp.720-726.

  2. Walmsley, E., Jackson, M., Wells‐Smith, L. and Whitton, R., 2019. Solar angle of the distal phalanx is associated with scintigraphic evidence of subchondral bone injury in the palmar/plantar aspect of the third metacarpal/tarsal condyles in Thoroughbred racehorses. Equine Veterinary Journal, 51, pp.720-726.

  3. Pezzanite, L., Bass, L., Kawcak, C., Goodrich, L. and Moorman, V., 2019. The relationship between sagittal hoof conformation and hindlimb lameness in the horse. Equine Veterinary Journal, 51, pp.464-469.

  4. White, J., Mellor, D., Duz, M., Lischer, C. and Voute, L., 2008. Diagnostic accuracy of digital photography and image analysis for the measurement of foot conformation in the horse. Equine Veterinary Journal, 40(7), pp.623-628.

  5. Kalka, K., Pollard, D. and Dyson, S., 2020. An investigation of the shape of the hoof capsule in hindlimbs, its relationship with the orientation of the distal phalanx and comparison with forelimb hoof capsule conformation. Equine Veterinary Education, 33(8), pp.422-429.

  6. Stewart, J. (2022) “The Angles of the Horse’s Foot: Is there a consistent relationship between the coronary band and the hoof capsule and to the distal phalanx? Assessing Strasser’s Angles.,” International Farriery Research Symposium 2022. Available at: https://equineeducationhub.thinkific.com/courses/Assessing-Strassers-Angles?fbclid=IwAR361F1OGM1UN7kB0U7TTblRkIdi-C4pWxH6v0g83RnK9VsCKxfUramHQDc.





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