Influence of Hoof Balance on Vertebral Joint Dysfunction

Roobarbs Mum · Influence of Hoof Balance on Vertebral Joint Dysfunction

Apologies if this has already been posted but I found this whilst looking for something else on an on-line veterinary library site and thought it might make interesting reading - I've not managed to read it all, just scanned it as I'm meant to be working Embarassed

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Influence of Hoof Balance on Vertebral Joint Dysfunction
K.J. Ridgway

Equine Therapeutic Options, Aiken, SC, USA.

INTRODUCTION
Whether due to conformation, improper trimming of the feet or improper shoeing, imbalances that alter the normal foot biomechanics will result in alterations in vertebral biomechanics and function. Foot imbalance creates postural compensations and imbalance. In the front limbs, for example, differences in heel height will cause a functional difference in leg length. A shorter heel will have the effect of placing the joints of that limb in a more extended position. Notably, it will alter the symmetry between the right and left scapulae and place the position of the scapulo-humeral joint more caudally. Many times in a horse with a difference in heel symmetry, one heel (most commonly the left) will be significantly lower (typically two or three degrees), while the other foot will have a very acceptable heel height. If critically examined, one will also commonly note that that the diagonal hind limb will have a slightly lower heel than the opposite heel (usually to a lesser degree). This diagonal asymmetry is also found in horse having a "club" foot.

Occasionally one also sees significant heel height differences in the hind feet as well. Such asymmetry of height creates compensatory use of muscles and an imbalance between the muscles of the left hind limb side as compared to the right hind limb. Asymmetry produces torque forces to the pelvis that lead to dysfunction of the lower lumbar vertebrae, the intertransverse joints and the sacro-iliac joints. Remember, joints only can do what muscles tell them to do.

Similarly, in a front limb, a club foot or an anatomically short leg will have a dramatic effect on balance of the shoulders. This is true with regard to scapular symmetry and to muscular development and symmetry.

Whether a high heel/low heel imbalance or club foot, it is certainly commonly recognized in the front feet (and often present to a lesser degree in the hind feet). The important fact is that the ramifications extend well beyond the effects on the foot itself.

POSTURAL DEVIATION AND EFFECT ON JOINT ANGLES
A lower heel creates obvious changes in the joint angles at the pastern, fetlock, elbow and scapulohumeral joint (shoulder joint). Compared to the limb with the higher heel the angles on the low-heeled limb will open (get larger), and the limb will become more vertical than its counterpart throughout its length. The pastern joints and fetlock will be placed in more extension (and possible subluxation of the P2-P3 joint). The elbow angle will be more open. As the scapulo/humeral joint (shoulder joint) opens, the "point" of the shoulder will be moved caudally so its position is farther back than on the higher heeled limb. The position of the scapula becomes altered so that it rotates to a more vertical position. This verticality creates a bulging appearance to the shoulder and is accompanied by over-development of the associated muscles on the lower heeled limb. This asymmetry in the shoulder will cause the saddle to sit diagonally across the horse’s spine. The pressure that a "crooked" saddle places on one side of the thoracic spinous processes leads to pain and primary chiropractic issues of the upper thoracic vertebrae.

BIOMECHANICS
Observe that an affected horse typically has a tendency to lean on the shoulder of the limb with the lower heel. This may lead an observer to conclude that postural symmetry is lost only because the horse is leaning on that shoulder and that if one pushes the horse to an equal limb weight bearing that the measurements tend to even up., we must, however, answer why, given a choice, does the horse choose to lean on that shoulder? This is similar to the human whose hips are not level. They choose to lean and weight the functionally shorter limb. Similarly, it is because of the difference in heel height that the horse, when allowed to do so, returns to leaning on the shoulder of the low-heeled side. This is the compensatory posture that the horse seeks and utilizes.

When one limb is shortened, either functionally or anatomically, the thorax is placed in torque and the biomechanics of the lower cervical and upper to mid thoracic vertebrae are modified. The result is a malalignment of forces on the vertebrae and on the vertebral-costal articulations. A high incidence of pain when the girth or cinch is secured is often observed. Pain in the Trapezium muscles and the Intercostal muscles often results. The involved lower cervicals and the thoracics exhibit hypomobility and fixation as a response. The muscles of the shoulder then are used more strongly on the side with the lower heel. The horse is often deemed to be right handed or left handed based on preference for one lead. I think this is not a valid conclusion and is rather an indication that an imbalance exists and needs to be addressed.

It is recognized and documented in the human that the intervertebral disk, the zygopophyseal articulations, the costo-vertebral articulation as well as spinal nerves, ligaments and the paraspinal muscles are sources of pain and neuro-muscular dysfunction. Abnormal motion of vertebrae or costo-vertebral articulations is the most common defining feature and successful treatment is often provided by mobilization of the involved vertebrae and the involved costo-vertebral articulations. According to Bidstrup,1 as in the human, intense pain associated with similar dysfunctions is mimicked in horses when they are subjected to tensioning of the girth. Such pain is often accompanied and exacerbated by, anxiety and fear. In severe cases, reactions can be violent, ranging from bolting, running backwards, severe bucking, flipping over backwards, or collapse/fainting. His findings parallel the observations of this author. As with Bidstrup, I find that most show good to excellent response to chiropractic or osteopathic intervention.

CAUSES FOR THE OCCURRENCE OF IMBALANCED HEEL SYNDROME
It is likely that there exist a number of causes. It needs to be stated that without adequate research, the etiologic sources are largely speculative.

One of the more fascinating sources that explains the significant effects on the upper thoracics and the ribs is work by D. Jean et al.2 This study investigated thoracic trauma in neonates. The study evaluated the incidence of rib fractures and costo-chondral separation. It was their purpose to identify factors that might contribute to the problem and to document the consequences. They utilized thoracic palpation and radiographic evidence on 263 foals of costo-chondral displacement and evidence of thoracic cage asymmetry; 20.1% showed thoracic cage asymmetry and 10% of the 55 foals had rib fractures. There was a higher preponderance when the parturition was difficult and when the mares were primiparous. The Livestock Disease Diagnostic Center in Kentucky reported that rib fractures were the most common fractures in foals necropsied at age one day and the second most common fracture in foals age 2 days old to 6 months old [3]. In a study of newborn calves with thoracic trauma and rib fractures, [4] it was noted that a much higher incidence of calving deaths occurred when calved in a calving box (53.5 %) or a calving stall (41.7%) versus 4.8% in calves born outside of a calving facility. This would suggest that confinement and assistance in foaling may be a key factor in inducing trauma. It is also possible that the incidence trauma could be much higher since in their study, using field radiography and choice of radiographic positioning, that the ribs of newborn may not have demonstrated some existing fractures, much less luxations, and other subtle damage. Birth trauma affecting the rib articulations with the vertebrae may well alter the neuromuscular reflexes and set up cases where extreme pain is experienced when the girth is tightened.

It is noteworthy that the widest structure in the foal is in the region of the fourth to sixth thoracic vertebrae. During the birthing process, the thorax forms a wedge to dilate the birth canal and thus is more subject to trauma. In keeping with Mee’s findings indicating a much higher incidence with neonates calved in a calving facility with valuable horses there tends to be much more human observation and intervention performed early on in the birthing. Such assistance in many instances may be contributory to trauma.

Another theory takes note of the observation that foals initially have difficulty reaching the ground to graze because of their long limbs and short necks. They may spread the front legs or they may place one forefoot well ahead of the other. It is well recognized that the hoof capsule is readily distensible according to where weight is concentrated. A foot placed well forward will receive weight on the heel area causing the balance of the foot to shift caudally, the heel of the capsule will change angle and run under. The toe will flare forward. In this scenario, the opposite foot is bearing weight more centrally will remain more upright and may even shift the balance point forward.

There is merit in this hypothesis, especially, if through the normal life experiences of a foal, it has had falls and perhaps minor injuries to the neck. Discomfort makes it likely that the foal will find the grazing foot pattern that is most comfortable and habituate that posture. Habituated patterns may last the lifetime of the horse.

There are some mares that will only allow a foal to nurse from one side. This could, in theory, cause a foot pattern and a habituation that is much like the grazing pattern theory.

Other unproven hypotheses include genetic causes or that the asymmetry is related to the way is carried in the uterus. Another hypothesis suggests that nearly all cases of shoulder and foot imbalance are created by imbalanced riders. This is belied by the observation that these foot asymmetries and muscular asymmetries are found in yearling and young horses that have not been started under saddle. However, correct riding can help many cases.

An inattentive farrier can certainly also create differences in heel height or other imbalances in the feet. As a group, farriers are not used to looking at the effects on the shoulder and back when high-low heel problems exist. Therefore, there is resistance to using any "orthotic" type of shoeing to equalize the heel heights.

THE SADDLE AS A RELATED FACTOR
Foot balance in heel height symmetry alters the balance of shoulder muscles. Altering the musculature, thus changing the posture and shape of the shoulder and wither area creates problems with saddle fit. The resulting stance of the horse affects not only saddle placement but also alters the rider’s posture and balance and ultimately the soundness of both the rider and the horse.

Most "crooked riders" from whatever causes have slowly allowed their bodies to compensate and are usually quite unaware of their compensation until it is brought to their attention. Additionally, the rider may end up with chronic back, hip or knee pain. The crooked and /or slipping saddle causes the rider to place more weight in one stirrup than the other. This also contributes to creating a "crooked" traveling horse and, therefore, becomes a cause of subclinical (and eventually) clinical lameness. Crooked riders create postural imbalances that lead to chiropractic/osteopathic problems in their mount.

With heel height asymmetry, the musculature becomes more developed on the shoulder of the low heel side. Muscle hypertrophy develops especially in the Trapezius muscle and Serratus thoracis muscles. Other involved muscles may include the Rhomboids, Deltoid, and Subscapularis muscles. The Trapezius muscle and the Longissimus muscle support the fork or gullet bar in the fork, or head of the saddle. These muscles support the forward part of the bars or panels as well.

Saddles are for obvious reasons built symmetrically, so when placed on a horse with muscle asymmetry, ie, hypertrophy on one side, the tree rotates diagonally in order to establish similar contact pressure on both sides of the "wither pocket". This torque of the saddletree, may cause it to make contact with and place excessive pressure on one side of the lightly covered thoracic spines while leaving more open space on the opposing side. Pressure exerted in areas close to bone (with little muscle covering) result in a significant magnification of the pressure. The result of this unilateral pressure is pain, and loss of ability to perform bending and lateral movements as well as making it difficult to pick up the lead on the side with the higher heel. Pressure can also create chiropractic joint issues in the thoracic vertebrae of the withers. The shoulder that is "bulged" laterally may strike the edge of the panel or bar as the scapula moves through its range of motion. This can create significant muscle bruising and serve to further twist the saddle. The rider must then twist her or his body to compensate.

Because the opposite shoulder typically has more slope in this syndrome, the saddle may tend to fall or slip to the sloping shoulder side of the horse. This is a second reason for pressure on the thoracic spinous processes. The problem of slipping to the side is particularly troubling if the pelvis and croup muscles are also involved. This can occur when a high/low condition exists in the hind feet. When the horse is observed in motion, it is commonly observed that the croup raises more on one side than the other. This relates to, muscle balance, and chiropractic or joint issues in the hind limbs. This feature can also occur when there is a significant muscle imbalance in the croup for other reasons. Regardless of cause, it creates an even worse scenario for slippage of the saddle when combined with shoulder asymmetry. The resulting hypertonicity in croup muscles can and does lead to vertebral dysfunction and lameness, subclinical or overt.

A COMPREHENSIVE APPROACH
Whether vertebral dysfunction occurs as a result of hoof imbalance, or whether the hoof imbalance is set up by the vertebral dysfunction, a comprehensive approach is needed to establish normal biomechanics. This approach requires team work between the owner/rider/trainer, the farrier and the veterinary chiropractor/osteopath. I have seen the problems resolved by orthotic/podiatric shoeing alone, by frequent and persistent orthopedic manipulation, and some cases by corrective riding. The percentage of cases returned to normal biomechanics is much smaller than when a team approach is used.

It is not within the scope of this paper to delineate the shoeing options or the training exercises and modifications. A more in-depth manuscript on high/low heel covering effects on saddle fit and shoeing corrections is available from the author and can be found on the website www.ultimatesaddlesolutions.com.

References
1. Bidstrup I. The influence of Chiropractic Intervention on Girth Pain of Horses. Thesis for Master of Animal Chiropractic Sciences, RMIT University, Melbourne, Victoria, Australia, 2002, pp 18-22.
2. Jean D, et al., Thoracic Trauma In Newborn Foals. Equine Vet J 1999;31(2):149-152.
3. Harrison L. Equine fracture cases. Equine Disease Quarterly, Univ of Kentucky, 1995, 3: 5.
4. Mee JF. Bovine perinatal trauma. Veterinary Record 1993;133:555.
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