The case history of the horse highlighted that the horse had not been trimmed but not shod for years. The hoof conformation was long in the toe and very low in the heel with the frog touching the ground. Calculations show that 1 centimetre of toe length in an average Thoroughbred comes to 50 kilos of force acting on the tendons (Kane et al 1998). With such a long, forward toe, more tension is placed through the digital flexor tendon whilst in an exaggerated stretched state in order to break over the long fulcrum (Anderson, G.F., 1992). During palpation of the digital flexor tendons some swelling was noted bilaterally, but there were no obvious signs of bowing. The horse has unhappy to fully protract the legs which indicates the deep and superficial digital flexor sprain may have painful, another indicator of ligament sprain (Cks.nice.org.uk, 2017). Also Also venograms have revealed that horses with 10mm or less heel do not have a healthy vascular supply with severe compression of the circumflex vessels and solar papillae. Solar papillae, if present, are very short relative to the foot with 15+mm of sole, and the medial quarter will usually have stark loss of solar perfusion in the palmar zone. The horse observed did display signs of vascular deficit with quarter cracks and information during the history taken of frog bruising and larger cracks that took a long time to heel.
The horse also had hoof an incorrect hoof conformation when the heel begun further forward than the widest part of the frog, this is a condition known as underrun heels. Because of the angle of underrun heels, the total length of the hoof is shorter causing parallel or even negative angle of the pedal bone to the ground to the extend where the pressure of the heel landing is very close to the palmer process of the pedal bone (Hunt 2012). Concussive forces placed unnaturally onto the pedal bone will result in damage to the bone itself.
A long toe, low heel hoof conformation forces the centre of the weight forward past the point of the frog (Clayton 1990). This means the frog is no longer able to act as an efficient shock absorber and extra concussion is places through the leg. The lateral cartilages, which normally also act as shock absorbers are now having to absorb a higher impact of shock which no longer first been partially absorbed by the frog first. The lateral cartilages are unable to cope and become damaged (Floyd and Mansmann 2007).
Chondrocytes possess receptors that detect damage to the cartilage matrix and and can encourage intrinsic and extrinsic growth factors, cytokines and other inflammatory mediators. Several integrins, which serve as receptors for fibronectin (FN) and type II collagen (COL2) fragments, on activation can stimulate the production of matrix-degrading proteinases and inflammatory cytokines and chemokines in chondrocytes. Chronic presentation of these results in the stimulation of osteogenic cells which form osteoid and develops into mature heterotopic ossification (Bossche and Vanderstraeten 2005). During palpation of the lateral cartilages some thickening and hardening of the cartilage was found.
With the frog and lateral cartilages unable to soften most of the concussive forces the strain of places on the joints, muscles and ligaments of the leg. There is a correlation between ossification of the lateral cartilages and distal interphalangeal joint or distal phalanx injury (Dyson et al 2010). The horse will tense its muscles in response to the concussion and brace up against movement. On observation of gait the horse had a short stride and did not track up bilaterally. On passive analysis the horse was stiff into all movements of the shoulder and hip including protraction and retraction of the fore and hind limbs. Observation of posture noted the horse lent backwards, this may be to take the strain off the digital flexor tendons. As a result, the stay mechanism was not able to work efficiently and more tension is places on the triceps having to contract in a stretched state and biceps having to remain contracted and shortened (McGowan 2007). As the horse has been unable to retract his legs, other muscles attaching from the forelimb to the cranial aspect of the horse are likely to have been under stretch and also become shortened. One such muscle is the brachiocephalic. On observation the horse held its head low and lowered its head during retraction of the forelimb which supports brachiocephalic shortening. This shifting of the body weight backwards and subsequent shortening of muscles has places incorrect loading onto the hoof lamina and exacerbated the underrun heels condition.
Treatment
With such chronically shortened and tight shoulder flexor muscles, the horse is unable to reposition its weight forwards. Therefore, muscular lengthening exercises, alongside the rocker shoes would be beneficial treatment to encourage a more correct angle of body weight placed on the hoof lamina and thus aiding a faster rate of recovery. A Bicep brachialis’ attached from the supraglenoid tubercle of the scapula and Insertions Medial head into the Medial tuberosity on the proximal radius and Lateral head into the Proximal radius (Riegel and Hakola 1999). Therefore, to stretch this muscle via retraction of the forelimb, should be beneficial. As the brachial cephalic muscle attaches from the Mastoid process of temporal bone, nuchal crest, wing of atlas and the transverse processes of the 2nd-4th cervical vertebrae and inserts onto the Deltoid tuberosity and crest of the humerus (Riegel and Hakola 1999). Side bend of the head, towards the contralateral side to the muscle being stretched, can be added to the retraction of the forelimb to include a stretch into the brachiocephalic (McGowan et al 2007).
Soft tissue massage has also been included as treatment to release tension in chronically tight muscles. Effleurage and cross fibre techniques were used before the muscle stretches to act as proprioceptive pain inhibition as explained in the pain gate theory (Melzack1990). This reduction in pain allowed the muscle to be stretch further than the horse would otherwise have allowed, resulting in a more efficient treatment of the horse in each session adding to a faster recovery.
Long term treatment
Continued treatment to the compensating muscles will speed up the rage of motion of the shoulder and hip and encourage different stresses on the hoof lamina, reducing exacerbation of the condition.
The angle of the lamina in the condition of underrun heels the direction of the force from the horse landing and even just from weight bearing from the horse standing, is angles approximately 90 degrees to the angle of the lamina, thus the hoof is forced forward even further and becomes more underrun. Therefore, correct hoof trimming and support is essential for the recovery of the hoof angle. The severity of the condition would have to be assessed by a professional in equine hooves. However, if the severity was a grade one and there was sufficient heel depth under p3 then treatment would include trimming of the running forward toe. If the severity was marked a grade two and there is insufficient depth under the tip of p3 then the hoof is trimmed to achieve a pastern angle of at least zero, then a full rocker shoe added to achieve a positive pastern and digit angle (Hunt 2012).
A rocker shoe covers the entire underside of the hoof and is domed on the underside. This allows the hoof to roll forward or to the side without necessary bending and horse to break over easier. Moving the break-over can easily have the effect of shortening the hoof length, relieving stretch and strain on the digital flexors tendons. The rocker shoe has a sloping front to allow it to tip forward from a point desirably located below a point near the front of the P3. This places a more corrective force on the lamina, reducing the forward angulation of the hoof. The rocker shoe is also shorter than the average shoe reducing surface area of the hoof contacting the ground. Therefore, lateral break-over eases turning and helps eliminate the rotational torque on the compromised lamina. The rocker shoe contains of a softer section that helps to cushion the hoof and leg and reduces the extreme concussive force on the legs that exist with metal and hard bottom shoes. The shoe may be rounded in the rear or both. This double sloped structure is less stable and requires the equine to adjust to the “rocking†effect thus providing more exercise and stimulation to the leg and hoof (Ruetenik 2016).
Self-reflection
This was a challenging case study as the horse was a companion pony who was infrequently ridden. He had not been trained to stand still and have his hooves picked up and held, he years. As a result, he was did not allow me to assess his hoof for the first couple of visits. I coped with this difficulty by going down a few times and training the horse to have his hoof picked up. I made sure the training was performed positively and not not push the horse and end on a negative note. Because of this, the horse progressed quickly and it only took to session before the horse would hold his hoof up for me calmly. From this I learnt that before I go out to assess an animal I would first ask the owner how often the horse is handles and how he/she is with their feet. If the horse was not well handled I would ask the owner to practise handling their horse’s feet in the lead up to my visit to save time. I would explain to the owner that this should not be done with negative reinforcement.
The owner believed that leaving the horses hooves alone with no trimming or shoeing was the most natural and therefore best for the horse. She was not keen to pay for hoof trimming and defiantly not shoeing. I explained to the owner that this may not be the case as the horse may have already have had muscle imbalances, perhaps from when he was previously ridden and this could have encouraged this unusual hoof posture in the first place. From this I learnt that explanation to the owner is beneficial. Next time I would encourage smaller steps first such as encouraging the owner to have a farrier come out and see the horse’s hooves and ask the owner to contact me if they do chose to do this. I would then ask the farrier to contact me with their option. This would be beneficial for the future as the farrier can then give their own professional advice and the owner may be more willing to listen. Also by increasing my communication with the farrier I can then ask for his opinion and expand my learning.