The Hoof - The Beginning and End of the Kinetic Chain
Often horses and their teams of professionals struggle with perpetuating cycles. Vets, and physios in particular struggle with re-occurring, higher, musculoskeletal pathologies, caused by poor hoof conformation and yet often farriers are struggling with perpetuating negative hoof morphology no matter how much balancing they do at intervention because the hoof is responding to the forces from above. Links between the hoof and higher pathologies have been documented but the initiation process remains unknown, in practice the relationship may be fluid, regardless, the cycle needs to be broken and this comes from the professionals at each end of the kinetic chain working together.
Kinetic chains are found in every moving biological entity, they are systems of structures that are functionally connected, each system can be broken down from the entire organism to a body section, a limb, a digit and so on and further down to a molecular level. Each part of a kinetic chain directly effects all the other parts and often helps to create efficient locomotion by amplifying muscular effort. Levin et al (2017) expressed how the position and orientation of every anatomical point within a kinetic chain is a direct result of all the other points and each point responds to load placed upon it, this relationship can become negative when there is dysfunction or poor conformation within a section. Closed kinetic chains are formed when there is resistance that prohibits free movement (Karandikar and Vargas 2011), for instance feet on the ground, the point of resistance becomes part of the chain.
For horses to move they must use their feet, in a closed kinetic chain, to press off the ground, creating a ground reaction force as the ground pushes back, that ground reaction force can be manipulated by the animals kinetic chain to create different velocities. The hoof is the deformable structure in between the weight of the animal and the ground, this interaction with the ground both statically and dynamically results in positive or negative hoof morphology and farriery intervention can hinder or help.
Our understanding of hoof balance is constantly evolving and being questioned, but it remains without a doubt the most important aspect of the hoofs interaction with the ground and therefore has effect on the kinetic chain, as our understanding of biomechanics and kinetics evolves, so too does our ability to further manipulate the posture of the horse and the ground reaction forces, at rest and through each stage of locomotion. Using mechanics, physics and maths we can break down the functional anatomy of the horse and view it as a series of weighted levers and pullies that are subject to the forces of nature, the hoof absorbs these forces and is morphed by them, subtle changes in any section of the kinetic chain can create different morphological outcomes and conversely morphological changes to the hoof will effect every point back along the kinetic chain.
Kinetic chains in the horse have only recently begun to be studied but can be extrapolated from the many biomechanical studies. Hobbs et al (2018) is a good example of a full body kinetic chain and the effects of dysfunction in a single link, it studied high-low hoof conformation, stating that the difference in propulsive forces created the need for spinal stiffening and compensatory hind limb engagement to keep the horse going straight, this shows how far away the influences on a given structure can be, the fore hoof, by its links along the kinetic chain, effects the forces and therefore probably the morphology of the hind hoof and every part of the chain in between.
Authors illustration of Hobbs et al (2018) expressing the presence of a full body closed kinetic chain.
This principle helps to explain the links established between negative plantar angles (NPA), a hoof morphology where the heels are crushed resulting in a negative angle of the pedal bone, and higher pathologies, proximal suspensory desmopathy (Dyson 2007), gluteal pain (Mannsman et al 2010), hock pathology (Pezzanite et al 2018), stifle pathology (Clements et al 2019) and subchondral bone injury of metacarpal/tarsal (Walmsley et al 2019). Although each of these studies looked at pathologies in isolation, perhaps there is evidence of a kinetic chain emerging that could extend further along the chain to the pelvis and spine with further research. It is this kinetic chain relationship that the author believes could be the issue in the perpetuating cycles in back and hind end issues.
As well as bone and muscle chains a new theory of kinetic relationship is evolving, study of the myofascial tissue in the horse extends further the complexities of the interconnection of the entire musculoskeletal system. Elbrond and Shultz (2015) discussed the interconnective functionality of the locomotory system and highlighted the necessity for holistic consideration. Myofascial tissue envelops the entire musculoskeletal system creating a connection between every muscle, the force acting through this tissue therefore mechanically effects every muscle along its chain. As a result it can have direct effect on biomechanics and posture both positively and negatively when pathology is considered, the myofascial tissue can essentially be considered as another muscle and its tension and elasticity plays a role in both locomotion and resting posture. Denoix and Pailloix (2009) described the dorsal and ventral muscle chains as creating “functional unity” and as discussed earlier in this article, disorder in any part of the chain created predisposition for dysfunction in every other part. When you see the extension of these lines it is easy to understand the transference of load onto higher structures as in the studies on NPA, Elbrond and Shultz also concluded that both static and dynamic posture can be greatly affected by this tissue perhaps expressing why a camped under posture is beginning to be linked to NPA. Understanding the importance of holistic treatment is highlighted as although primary sources of pain may be treated secondary issues could re-ignite kinetic chain pathology.
This image shows some of the myofascial lines extending all the way into the hoof showing how the hoof is the beginning and end of a complexed system of kinetic chains. Elbrond and Shultz (2015).
The myofascial tissue as stated affects posture, NPA and higher pathologies often present with a camped under stance as eluded to by Mannsman et al (2010). Whether the cause of the posture is the hoof or higher pathology it strains the kinetic chain starting at the hoof, the hoof suffers excess heel load causing crushing, creating a cycle leading to NPA, this posture then has adverse affects on a now sub-optimally loaded chain of musculoskeletal structures and so we can see how cycles perpetuate until every part of the chain are holistically treated.
This image shows the positive progression of a horse from having a stood under posture resulting in poor hoof morphology and higher pathologies. Holistic treatment addressing hoof geometry and treatment of the higher pathologies together resulted in the kinetic chain being treated at both ends, ending the pathological perpetuation.
The title image of this article expresses the relationship between the hooves and the rest of the musculoskeletal system. The kinetic chain enables the transfer of energy and creates reproducible efficient motor patterns, until there is pathology in one or more segments which can create dysfunction along the entire chain. Hoof morphology can create pathology along the chain and pathology along the chain can cause hoof morphology and they can perpetuate one another.
This intricate relationship expresses the necessity for farriers to appreciate not only dynamic but postural effect on hoof morphology and vets and physios to understand that farriery intervention is vital in treating higher pathologies! The horse is a single entity and must be treated holistically, only addressing one end of a dysfunctional kinetic chain leads to perpetuation as each functional component of that chain effects its entirety. The compartmentalising of treatment has to be questioned and more emphasis in the veterinary, physio and farriery industries must be placed on inter-professional communication and the understanding of each respective role, even in cases that may seem abstractly connected. Farriery must be considered in every vet or physio case and remote physiology must be considered in farriery intervention, we must treat the horse and not a symptom.
École Nationale Vétérinaire, Alfort, France.
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