As an industry, we are mostly influenced by the mechanical leverage theory; however, after considering the information in my last two blogs, we can see that the theory provides an incomplete picture or a simplified appreciation of the locomotion throughout the equine body. Yes, the muscular system activates the movement throughout the body with individual muscles attached to the skeletal system. The skeletal system is united by a seamless integration of connective tissue, which forms an overall regulatory system for the complex biomechanical processes in the animal. Therefore, we have to consider and incorporate the nerve cells that convey information about mechanical pressure from the peripheral nervous system to the central nervous system and into the animal's brain so it can be analysed and sent back to the different bodily systems to affect change in the biology of the animal.
It is these different individual animals' responses that change the locomotion of their breathing, the limbs and their stance, changing the flight and movement of a series of joints and the responding neurological systems that govern variation in direction, speed, weight and limb placement and results in reactionary forces in the loading of the distal Interphalangeal joint and the associated soft tissue encapsulating the joint and distal limb. Hence, we have a change in the orthopaedic balance and stance of the equine, affecting their hoof capsule, upper body and performance in completing everyday life tasks.
After studying these neurological and biological issues the horse deals with daily, I now consider the effects on the architecture of the distal limb in each horse I see in my everyday work environment by studying and acknowledging that the commonly found issue in most equines is the reduction in size and shape of their digital cushions and how that significantly contributes to the variabilities in limb movement and loading on the upper body during the flight phase, and again changing the loading characteristics when coming into contact with the ground or when stationary.
The internal broadcast of neurological information about a digital cushion's dysfunctional state causes a change in ligament and tendon tension in the limb. It affects the speed at which the limb moves, as well as the descending arc of the proximal-distal joints of the limb, and the overloading of the palmar aspect of the distal interphalangeal joint, all of which affects the break-over timing of the limb and foot resulting in a dysfunctional loading of the hoof capsule and it's proceeding shape. Because the precise articulation of the distal interphalangeal joint is essential for the functional integrity of the entire equine body, and therefore, any issue throughout the body will affect the animal's upper body and have an influence on their gravitational loading aspect, we need to ensure appropriate break-over ensuring longevity and soundness of the entire animal's biological systems.
Appropriated articulation of the Distal Interphalangeal Joint depends mainly on the palmar aspect of the solar surface of the distal phalanx. That forms the attachment position of the Deep Digital Flexor Tendon (DDFT) and the Distal Sesamoidean Impar Ligament (DSIL) of the distal Sesamoidean bone (DSB or navicular bone). This structural alignment of the Deep Digital Flexor Tendon with the distal Sesamoidean bone has a direct mechanical and neurological response to the articulation within the joint (DIP), triggering a neuro-muscular tension response in the corresponding Passive Stay Apparatus (PSA) in the upper body of the equine.
With either precise or imprecise neuro-muscular tension response in the upper body, different limb regions, such as the shoulder, elbow, fetlock, and pastern joint, must all be unified in their movement and rotate concurrently. Initiating movement requires a chain reaction of all the muscles involved, transforming a neural impulse into action; the animal's body has locomotion. Here lies the science of orthopaedic balance, for when we understand the characteristics of a functional or dysfunctional loading of the distal interphalangeal joint, we can utilise the structures involved that can be palpated externally, such as the deep digital flexor tendon, the superficial deep flexor tendon, the collateral cartilages that all relate to the functional integrity of the interphalangeal joint and therefore, the break-over of the limb and the so-called break-over of the foot that as farriers we are always working with. It is not only the structures named above that you should be concerned with, as they are the main structures of the related palmar foot issues and the higher you move up the limb away from the distal joint you will find other structures that relate to the loading of the distal joints being ascending or descending thought the limb and upper body of the animal.
In my next blog, part 4, we will find out what causes a change in the balance of the palmar section of the equine foot.
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