How can we change the palmar/plantar angle with the trim?
We know that hoof growth during an average shoeing cycle reduces the palmar/plantar angle by 3-4 degrees.
As such, hoof growth has detrimental effects on the biomechanical workings of the hoof, both statically and dynamically. Although the horse has some compensation devices these are not sufficient to negate the negative predispositions (Moleman et al 2006, Van Heel 2005). These studies have shown that hoof growth changed digit conformation by increasing the dorsal wall length leading to a decrease in hoof angle. Therefore, hoof growth primarily effects the DIPJ and loading on the DDFT (Moleman et al 2006).
Very often the toe growth far exceeds heel growth. Whether it’s due to the heels wearing due to their expansion and contraction, whether they collapse relative to the toe due to the negation of the hoof’s intrinsic biomechanics and haemodynamic mechanisms. Or just the fact that the hoof is a truncated oblique cone and heel angle being more acute than the toe angle affects heel to toe height ratios for every increment of growth. Or a combination.
Fig.1 The effects of hoof growth. Hoof growth affects hoof proportions, reduces hoof angle and palmar angle.
When we trim, we must consider the changes in proportions that have occurred and assess hoof Pastern axis and alignment as part of our trimming plan.
Very often this will mean changing the “trim plane” to establish better heel to toe height ratios.
Floyd (2010) and Clements (2021), (of which the author contributed to the manuscript) discussed negative palmar/plantar angles and their grades. Grade 1 is a result of this hoof growth, where a trim can restore a positive palmar/plantar angle. Grade 2 and above are often a combination of hoof growth and crushing/prolapse of the caudal hoof structures.
Very often I am asked to do some “remedial work” on feet with grade 1 negative palmar/plantar angles. In reality all that needs doing is a change to the trim plane and a shorter shoeing cycle, in the absence of crushed heels or digital cushion.
This goes hand in hand with another trimming issue. Always trimming to the widest part of the frog. In my experience, left to it’s own devices, the hoof NEVER puts the heels at the widest part of the frog, as most often this would mean the heels being on a lower plane. In fact if you trim the heels below the frog height and leave it barefoot for a couple of days. You will come back to them being on the same plane again. A phenomenon you can actually utilise with collapse/prolapse.
Fig.2 Trimming to the widest part of the frog, without consideration for the hoof pastern axis is a misnomer. The barefoot will always have the heels at the same height as the highest part of the frog.
Trimming out collapsed heels is important for creating positive hoof morphology, but after that point, my protocol is that the heels should be at least the same height as the height of the frog, and then dictated by the creation of a near straight hoof pastern axis.
Therefore, very often my trim to create better palmar/plantar angles starts at the quarters, goes down into the toe and back out the other side. In mirror fashion to the changes through the cycle. This creates a wedge like trim.
Fig.3 This trimming method creates a wedge like trim that re-orientates the capsule and establishes a better heel to toe height ratio and palmar/plantar angle. The caudal hoof was deemed healthy enough to facilitate continued positive morphology over the next few cycles.
Sometimes some bravery is required, and X-rays can hugely help in deciding how much toe depth there is.
This change in trim plane can create huge improvements in hoof proportions and phalangeal alignment and stop the downward spiral of worsening dorso-palmar/plantar balance.
Fig. 4-5 Examples of grade 1 NPA/NPLA bought back into a positive angle through a wedge trim. Red dotted line indicates inappropriate trim plane, green dotted line indicates re-alignment trim.
As discussed by Floyd (2010) This trim becomes a basic of maintaining alignment in the shod foot. In the higher grades of negative palmar/plantar angles this trim method becomes paramount and was used in the authors research on the treatment of negative plantar angles (to be published). Often in higher grades two planes can be formed with a high spot at the quarters (Floyd 2010), essentially either a banana shoe can be fitted, or the heels can be floated. If excess heel crushing exists then prosthetics can be added to create elevation but should be added to compliment an appropriate trim. Leaving the foot bare for a few days can be extremely useful in the higher grades to bring the heels and frog onto one plane.
References
Caldwell, M.N., et al (2010) Quantitative Horse Hoof Trimming Protocol for Research Purposes. Forge Magazine, p4-10.
Clements P. Therapeutic farriery of the hind feet for horses with hindlimb orthopaedic injuries. UK-Vet Equine. 2021;5(1):6–11.
Floyd AE. Use of a grading system to facilitate treatment and prognosis in horses with negative palmar angle syndrome (heel collapse): 107 cases. J Equine Vet Sci. 2010;30(11):666–75.
van HEEL, M, et al (2004) ‘Dynamic pressure measurements for the detailed study of hoof balance: the effect of trimming” Equine Veterinary Journal, volume 36, No.8, pp. 778-782
van HEEL, M, et al (2005) ‘Changes in location of centre of pressure and hoof-unrollment pattern in relation to an 8-week shoeing interval in the horse.’ Equine Veterinary journal, volume 37, No.6, pp. 536-540
Moleman, M, et al (2006) ‘Hoof growth between two shoeing sessions leads to a substantial increase in the moment about the distal, but not the proximal, interphalangeal joint.’ Equine Veterinary journal, volume 38, No. 2, pp. 170-174