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Kissing spines and their relationship with the development of the ventral and dorsal muscle lines in horses - Lessons from the Old Masters
by Dr Sabina A. Holle, VS, PhD , PGDip VA
Adams’ Lameness in Horses (1987) describes ‘kissing spines” as a condition of the vertebral column in horses caused by overlapping and/or impingement of the dorsal spinous processes (DSP) in the thoracic and/or lumbar vertebrae in horses. The condition leads to pain in the back with the associated avoidance behavior such as reluctance to be saddled and inability to perform in the intended sport of equitation or racing.
The etiology in this edition of Adam’s is mainly observed to be due to injury in the back, with some ambiguity as to other causes. As yet, it does not mention training as one of the potential causative factors. More recently, this condition has firmly been established as one of the underlying osseous changes of the vertebrae causing primary back pain in horses, together with spondylosis, degenerative joint disease (DJD) and intervertebral disc disease and is more frequently seen in show jumpers and dressage horses.
The location is frequently observed between T13 to L2 and riders report the feeling of loss of power from the hindquarters not coming through the back, lack of clarity in the flying changes, especially tempi changes, in downward transitions and during quick changes of direction. On palpation horses suffering from impinged DSP will exhibit pain over the area of the processes as well as over the para-spinal muscles which are typically very sensitive to tough.
Radiographs at times are inconclusive because some clinically normal horses can show diminished spaces between the dorsal spinous processes without the horse showing any symptoms. A large field study on a population of 805 horses failed to establish a clear causative correlation between back pain and lameness nor lameness and back pain (Landman et al 2004). However, DSP impingement is clearly seen more frequently in performance horses and should be considered in all cases of back pain, leading to changes in “rideability” and general equitation performance and questions need to be asked as to the increased occurrence of this type of pain and skeletal change when at the same time, the quality of performance horses bred fit for purpose has increased significantly.
Anatomical Considerations: The skeleton of the horse shows clearly that the horse was not made to carry a rider on its back. The construction of the vertebral column, supported by front and hind legs is that of a bridge, with sufficient stability (mainly passively via the nuchal ligament and suprspinous ligament dorsally and the white line ventrally) to support weight suspended underneath (GIT tract, fetus) and the horse during straight forward movement. (Figure 1.)
Figure 1. Diagram of the equine skeleton in a neutral stance showing the stabilizing function of the ligaments on the dorsal (nuchal ligament and supra-spinous ligament shown in pink) and ventral lines (white line shown in blue). In the neutral position the area of support is large, making this position very stable for the horse.
(from Stodulka, Weiss & Meyners 2013)
This passive stability is supported by the direction of the dorsal spinous processes along thoracic and lumbar sections of the vertebral column. The first 14. DSP of the thoracic spine are directed toward the back, effectively functioning as a lever for this area, when the neck is lowered during grazing. The 15. thoracic vertebrae is the area of a directional change (anticlinal vertebrae) after which the DSP are directed upwards and slightly forwards, before changing again in the sacral area. The latter arrangement again, aiding in the “lifting of the back” from behind, when the haunches/hind legs step under the body. (Figure 2)
(from Stodulka, Weiss & Meyners 2013)
Figure 2. Equine vertebral column: thoracic, lumbar and sacral regions, showing the direction of action of the musculature upon the bony back structures and the way the DSP are being “lifted”toward the front in the area cranially to the anticlinal vertebrae and toward the back in the area caudal to the anticlinal vertebrae. This allows the horse to keep its back “up” with correct training.
When placing weight upon this structure from above, on an untrained horse, the horse automatically will brace the top line of its body, resulting in a contraction of the musculature, followed by a sinking of the back. Due to the above described anatomical make-up of this area, this will result in a narrowing of the intervertebral spaces bringing the DSP closer together, the pelvic area tilts upward and forwards, and the hind legs are set further backwards and away from the body mass. In the front, the thorax will sink relative to the shoulders and the neck will come up contracting the area at the base of the neck, in front of the shoulder blade.
It is important in the training of the riding horse, that this passive mechanism is supported and strengthened, to counteract the downward forces of the organs suspended within the abdominal cavity and the weight of the rider.
In order to achieve this, the horse has to learn to activate two major muscle chains. The ventral muscle chain is made up of the abdominal musculature (including the psoas group, and the flexor muscles running along the underside of the neck (omohyoid & sternohyoid muscles) and their associated subcutaneous fascia on shoulder and tensor facia latae around the stifle area. This muscle chain has to be activated.
The dorsal muscle chain is formed by the neck and back extensors including the multifidi muscles and the brachiocephalic muscle on the underside of the neck. Interestingly, the functional and anatomical connection of these two muscle chains is in the area of the hyoid bone. This is important to understand because only with a relaxed and “chewing” tongue base (i.e. hyoid) the horse is able to relax its jaw and poll and coordinate supportive tension and relaxation along ventral and dorsal muscle chains. Achieving this reaction to the bit is one of the corner stones in classically correct equitation.
Figures 3- 5 show the interplay of the dorsal and ventral muscle chains in 3 situations.
Fig 3. depicts a horse at rest in a neutral position. In this position, both muscle chains are relaxed and utilizing a minimal amount of energy. The back is relaxed, the horse is resting and not carrying a rider.
(from Stodulka, Weiss & Meyners 2013)
Fig 4. shows a horse with a head and neck position that allows for the hind legs to step under, due to an engaged ventral muscle chain, which in turn causes the dorsal muscle chain to function with the rhythmical “relaxed” activity which will show a swinging, oscillating back of a well engaged and “through” horse, the aim of early dressage training. Note that the neck is relatively long, the underline of the neck and jaw are open, the nose is just in front of the vertical but with the nose at a level of the point of the shoulder. The engagement of the ventral muscle chain, and its connection via the abdominal musculature and facia, allows for a backward tiling of the pelvis and a stepping under of the hind legs. Due to the connection of the long back muscles to the dorsal aspects of the last cervical vertebrae, the “telescoping” forward of the base of the neck from in between the shoulder blades is vitally important to the correct positive tension of the dorsal muscle chain, allowing for a lifting of the back.
(from Stodulka, Weiss & Meyners 2013)
Fig 5. shows the reaction of an untrained horse having to carry a rider or that of a badly trained horse, with neither muscle chain working correctly, the back legs camped out behind, and tensed muscles and a sunken back. Horses travelling like this will show lack of rhythm and short steps. In this position the DSP will be forced closer together, laying the foundation for potential impingement and pain.
(from Stodulka, Weiss & Meyners 2013)
In addition, when looking at the skeletal development of the horse, one can see that whilst some of the long bones supporting front and hind legs are maturing from 6 months to 4 years, it is in fact the vertebrae of the back that do not mature fully until the horse reaches 7 years of age, or older in some individuals (Bennett D. 2008). Not taking any other factors into account other than skeletal
maturity, it becomes obvious, that adding a rider’s weight on the back of a young horse, puts unphysiological strain onto as yet insufficiently mature bone tissue, and further sets the horse up for premature health issues.
Furthermore, bone growth in the long bones of the limbs is directed upwards, with the boney precursor cells that later develop into solid bone, being aligned along the area of greatest stress i.e., vertically. So whilst adding a rider’s weight still is not ideal, at least the stress is directed in line with the developing bone. This is not the case with the vertebral column, where bone growth is directed more horizontally and any weight added from the top will act perpendicular to the direction of growth.
Most performance horses are backed at the age of 2/3 - 4 years old, possibly due to the pressures of their planned performance careers which forces the riders, trainers and owners into a set time frame to achieve each performance milestone in open competitions (Dyson 2000).
In order to ensure the proper development of a riding horse, it becomes apparent, that horses have to be trained and conditioned, both physically and mentally, in a knowledgable, careful and patient manner, in order to avoid musculoskeletal issues and result in a horse which is capable to excel in equitation for many years without taking undue damage to its body or mind.
It is to this end, that the understanding of the principles of dressage training as described by the Old Masters, it vitally important. Even prior to the advent of scientific study in equitation, and with possibly a limited knowledge of functional anatomy, but based on decades and possibly centuries of observational experience, a training system and philosophy was developed, which takes into account the above mentioned challenges of the horse’s skeletal maturation and the need for complete re-training of its natural way of going, having to carry a rider without taking damage. Gustav Steinbrecht said in his book “The Gymnasium of the Horse” “The training of the horse is based on gymnastic exercises according to the laws of nature, through which the whole muscular system (of the horse) is being conditioned and put into a direction, which will be useful to the rider” (my translation). If you exchange the term “laws of nature” with functional anatomy”, it becomes apparent that any horse needs to be trained with sufficient knowledge of functional anatomy and biomechanics.
To train a horse able to be ridden without suffering damage, according to the Old Masters, a period of basic training of up to 2 years consisting of lunging, in-hand work and ridden work, is scheduled. This training will teach the horse gradually to adopt and maintain a posture of “artificial equilibrium” or balance which results in its ability to carry a rider with ease. To achieve such balance, the trainer uses a system of varying amounts of pressure and pressure release with legs, hands and the rider’s weight, collectively called “the aids”. Once the horse has understood and is able to maintain this new balance, it is able to shift its centre of balance further toward its haunches, can travel relatively straight (ie its hind legs follow the track of its front legs, on straight lines as well as on a circle) and it is able to work in self-carriage whilst carrying a rider through various exercises in all three basic gaits (walk, trot and canter) (Zich & Ohms 2007). The Old Masters understood, that this process cannot be rushed, that it is different for each horse and that the training schedule has to be individualized according to the conformational and temperamental challenges given by each horse, and should not be submitted to the constraints of competition schedules. As Heuschmann writes “the back (of the horse) has been regarded as the critical centre of movement in the horse since 1896” and “The whole trunk musculature in a correctly ridden horse is designed for movement - his back was not built for direct weight-bearing.”
A recent study at UCDavis using radiographic imagine of the equine vertebral column, compared the position of the DSP the horse with its back in a neutral position with that of a horse mimicking an “engaged” core (using its dorsal and ventral muscle chain). The x-rays clearly add visual and quantifiable evidence that the spaces between the DSP are enlarging significantly along the thoracic and lumbar vertebrae and especially at mid thoracic level.
Knowing that the horse will not be able to protect itself naturally when carrying a rider, correct basic training following the above outlined principles, becomes the responsibility of each trainer and rider for any horse destined for a long and healthy ridden life.
REFERENCE LIST
1. Stashak T.S. Adams’ Lameness in Horses. 4th edition. (1987) Lea & Febiger 2. Lin Y. Lumbar disease and Lameness in the Horse. (2010) In: Yang Z, Xie H. ed. Traditional Chinese Veterinary Medicine. Reddick FL Jing Tang. 253-262. 3. Henson F. Equine Back Pathology. (2009) Oxford, UK Wiley Blackwell 4. Landman M.A.A.M. et al. Field Study of the Prvalence of lameness in horses with back problems. (2004) Veterinary Record. 155, 165-168. Racinet Jean-Claude. Falling for Fallacies. Misleading Commonplace Notions of Dressage Riding. (2009). Cadmos. Bennett D. Timing and Rate of Skeletal Maturation in Horses. With Comments on starting young horses and the state of the industry. (2008). 5. Dyson S. Lameness and Poor Performance in the Sports Horse: Dressage, Show Jumping and Horse Trials (Eventing) (2000). Proceedings of the Annual Convention of the AAEP. 308 - 315. 6. Zich A. & Ohms D. Calme, En Avant, Droit. Ruhig vorwaerts, gerade (2007). WuWei Verlag. 7. Stodulka R. et al. Medizinische Sattellehre. (2013) Olms. 8.Heuschmann G. Balancing Act. The horse in Sport - An Irreconcilable Conflict? (2011). Trafalgar Square. 9. Developing your horse’s back. The biomechanics of engagement. Equitopia.