The relationship between conformation and hoof morphology has been studied, Curtis (2002) outlined the effect of limb deformities on hoof growth and Kilmartin (2014) expressed the biomechanical effect of hoof balance, showing a fluid relationship between the two, but how do these forces get transferred around the body? Hoof growth itself has shown to affect the biomechanical forces on the hoof, Van heel et al (2004,2005) discussed the movement of the centre of pressure caudally onto the heels due to hoof growth, echoed by Moleman et al (2006). We can see from these studies that poor farriery can lead to perpetual poor hoof morphology and subsequently create the genesis of higher pathologies, for instance Floyd (2010) expressed that grade 1 Negative plantar angles (NPA) could be addressed with appropriate trimming, it can therefore be assumed that incorrect trimming could exacerbate the morphology and lead to more severe grades of NPA which has been linked to higher pathologies by Dyson (2007), Mansmann et al (2010), Pezzanite et al (2018), Clements et al (2019) and Walmsley et al (2019). Floyd (2010) explains that with more severe cases of NPA, dorso-plantar/palmer balance remains unachievable with trimming alone, in the absence of prolonged poor farriery this raises the question of outside forces acting on the hoof to create the perpetuating negative morphology.
Fig.1 Shows the authors representation of the current links between NPA and the studies mentioned above. The pathologies follow the kinetic chain and myofascial connections eluded to by Mannsman et al (2010) and have recently begun to be studied in the horse. Elbrond and Schultz (2015) studied the myofascial connections within the horse and compared it to humans via 26 dissections, it concluded that understanding the myofascial lines would aid in unravelling the cause of locomotory issues.
Fig.2 Adapted and simplified from Mannsman et al (2010) and Elbrond and Shultz (2015). This study extrapolated mechanical function of the myofascial system in locomotion and posture in the horse from human studies (Myers 2009), expressing that dysfunction within a segment could cause biomechanical disorder elsewhere. A myofascial line possibly most relevant to the studies in fig.1 described by Elbrond and Shultz (2015) is the “superficial dorsal line” which starts in the hind hoof and extends up the hind limb, along the spine and into head. This is the line expressed by Mannsman et al (2010) as “the most relevant myofascial line in the equine hind limb.”
The posture mentioned by Mannsman et al (2010) and pictured in Fig.1 has recently been described as an abnormal compensatory posture (ACP) in which the horse presents with non-vertical cannon/Shannon bones, in an unpublished paper (Gellman et al 2014) which expanded on the experiential work of J. Shoemaker, outlining that ACP perpetuated after treatment when podiatry issues where not addressed.
Fig.3 The authors similar findings to Gellman et al (2014) which expressed an improvement in hoof morphology with the relief of ACP, attributed to improved balance, this correlates with Curtis (2002) which talked about the morphology of the hoof in response to limb conformation, however, the farriery interventions where not outlined or quantified and as these morphological changes occurred during improvement of posture, causation remains unclear, but what can be taken from it is confirmation of the fluid relationship between posture and hoof morphology.
Gellman et al (2014) expressed camped under as ACP, resulting from “poor integration, anatomic distortions, or injury/misuse in critical reporting regions (spine, feet, teeth) commonly seen in domesticated horses.” Gellman et al (2019) expanded on this explaining the theoretical biomechanical inefficiencies of ACP, both statically and dynamically, again mentioning kinetic chain implications. ACP can also be described as antalgic posture (AP) which means “away from pain” and dynamically with the rise of objective gait analysis, studies into antalgic gait in the horse have become widespread, not only to observe more obvious lameness but more subtle asymmetries associated with perhaps abstract variables such as tack (Mackechnie-Guire et al 2018). Knowing that the hoof morphs according to the forces above it (Curtis 2002, Caldwell 2018), these findings may, through further research, show morphological effects on the hoof. AP, although widely recognised as far back as Steindler (1954) who correlated postures with pathologies in humans, has been far less researched in the equine, considering the performance horse is stabled and/or stands for the majority of the day this warrants further research to outline its physiological effects on not just the hoof but the entire musculoskeletal system. In humans Montenegro et al (2009) showed musculoskeletal changes in woman with postural adaption to chronic pelvic pain and Filho et al (2014) showed a link between postural habits and lower back pain to name only two studies showing the relationship between pain, posture and morphology. In the equine, Caldwell (1987) expressed the posture of horses with fore limb pain, highlighting their camping under of the hind limbs in order to take more weight from the fore feet, perhaps showing the chain extending even further then the trunk and all the way from hind hoof to fore hoof, further reading on this subject
Research into equine posture is limited and is just beginning to be researched, Gellman (2010) expressed the interaction of all the systems within the body, it stated that a change to any individual component will have an effect on the interactions across the remaining systems a statement that is used both in myofascial and kinetic chain research. Gellman (2010) went on to discuss neutral posture and the importance of recognition of posture as a picture of neuro-muscular system state. Neutral stance was outlined as four legs square and a horizontal metatarcarpal/tarsal, this stance allows effective use of the stay apparatus and most efficiently counteracts the forces of gravity while allowing the horse to rapidly initiate locomotion, the paper stated any diversion from this posture pointed toward pathology not only in the feet but it discussed the teeth and stomatognathic systems link to foot proprioception.
Fig.4 Expresses ACP or AP vs “neutral” stance outlined by Gellman (2010) although not perfect it shows vast improvement from AP with correction of the orientation of the hoof, showing the effects of manipulating a single anatomical point along a kinetic chain. The author uses postural assessment as an important factor in producing shoeing plans as part of a team. Further reading
Gellman (2010) also highlights how the forces acting on the hoof can be abstract, it highlighted the effect of posture on higher structures in the hind limb which creates the link to the studies in Fig.1 and again with the knowledge of higher forces effecting hoof morphology we can extrapolate that this will also effect hoof morphology. Ruina and Gellman (2019) expands on this paper exploring the physics of ideal posture versus camped under and camped out, hinting at musculoskeletal effort associated with non-vertical cannon/Shannon bones, horses that are camped under are “holding” themselves in that position, overusing muscles and inevitably creating soreness and possibly pathological changes. Logie (2017) echoed this in the fore feet, stating that a change in stance caused further overloading of heel structures in a perpetual cycle created in negative hoof pastern angles. Gellman (2010) and Ruina and Gellman (2019) along with Mannsman et al (2010) question camped under as a conformation, pointing towards the authors hypothesis of it being an AP creating the ubiquitous hoof conformation NPA. Ruina and Gellman (2019) eluded to the link between fore limb, back and hind limb creating a kinetic chain which have been widely studied in human medicine. Sciascia et al (2012) described kinetic chains as the segmented activation of the bodies links, the different segments of the body transfer energy and create reproducible efficient motor patterns, until there is pathology in one or more segments! Sciascia et al (2012) studied overhead activity in humans and connected overuse shoulder injury’s to biomechanical influences from leg tightness or a weak core. An earlier study, Jeffrey et al (1996) highlighted the importance of the spine in kinetic chains, acting as a link between the lower and upper body creating and dampening forces needed to create power in throwing while protecting the shoulder structures. Fuglkjaer et al (2018) studied the relationship between lower extremity pain and spinal pain in children, finding that there was a direct but fluid relationship where each could cause the other, this relationship was attributed to possible changes in the kinetic chain. Levin et al (2017) expressed that kinetic chains are ubiquitous across species, a statement most relevant to this article highlighted that the position and orientation of each anatomical part is a result of the loadings and functional demands of the wider system, the author extrapolates from this a hypothesis that the position and orientation of the equine hind limb for instance, camped under, is resultant from the physiological state of the horses entirety and the hind hoof is the most distal anatomical part of this kinetic chain and therefore subject to forces arising from this orientation. The fluidity of this relationship means this works backwards too as the position, orientation and physiological state of the hoof can affect the entire kinetic chain system, therefore creating the ideal orientation of the hoof has positive effects on the resultant kinetic chain. Further reading
This article only talks of one myofascial line and its possible farriery influence, as further studies take place we will uncover even more complexities in the relationship between the hoof and the rest of the horse.
So what does this mean in practice? Farriers are constantly fighting poor hoof morphology and are often scape goated as the cause of lameness, but with the understanding that the relationship between hoof morphology and pathology, associated with the rest of the horses entirety, is not linear, but fluid, poor hoof morphology could sometimes rather be seen as an indication of the influence from higher pathologies, of course assuming the absence of poor farriery. Farriers therefore have an obligation to understand their effect on the entire musculoskeletal system and its effect on the hoof, as well as vets/physios etc must recognise that hoof morphology could well be a sign that something is wrong somewhere else. Every practitioner involved in the care of the horse has their part to play in achieving balance, something the author defines as “A state where there is biomechanical efficiency and correct orientation and load share of the entire kinetic chain.”
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