Saddle fit and anatomy

Anatomy and what it means for saddles

SkeletonSaddle skeletonIf we look at the horse from the inside out then there are a few anatomical facts that we have to bear in mind when fitting a saddle. (and that's quite apart from the fact that the horse was not designed and has not evolved to have a saddle on his back in the first place).

(1) The scapula rotates as the front legs move. If the saddle restricts the scapula then the horse's movement cannot be as free as possible.

(2) The spinous processes of the vertebrae can be felt all the way along the back, any pressure on these spinous processes is going to be painful to the horse and will restrict movement.

(3) Each of 18 ribs slots into a gap made by the junction of two vertebrae. This design is strong and does not allow very much movement in the rib cage. As a consequence the rib cage is strong and is a suitable place to put a saddle

(4) The lumbar vertebrae behind the last rib are weak and weight should not be put in this area

(5) Muscles run over the top of the vertebrae and a thick layer of fascia runs over the whole back. The muscles may change shape but the fascia is strong and think, protecting the back to some extent.

The scapula

scapula1Always consider that the scapula needs to move with the horse and allow enough space in front of the saddle for there to be freedom. While a saddle may look OK on a stationary horse there may not be enough space once you get going. Make sure that you can identify the scapula.


The spinous processes

backThis diagram shows the surface features of the back, i.e. the places where bones could potentially make contact with a saddle. If they do so the horse will be uncomfortable.

The red boxes highlight the scapula and the spinous processes. The scapula can be affected by a saddle that is too far forward, too tight or moves forward as the horse is ridden. The spinous processes can be affected by lack of clearance at the withers or at any point along the gullet, too narrow a gullet or poor flocking.

The rib cage

ribs2The body of the vertebrae lie a little way below the top of the spinous processes (i.e. the bones that can be felt along the top of the back). The photo shows some of the vertebrae at the withers where the spinous process are the longest.






ribs3Where the vertebrae join there is a space for the head of the rib. This overlaps the two vertebrae and sits into a fairly deep 'pocket' as can be seen in this photo. There is very little or no range of movement of the rib. Given that there are 18 ribs on each side of the rib cage this gives a strong and solid structure. (On a deer the ribs do not sit in such deep 'pockets' and the animal has much more flexibility in the spine than a horse).

The anatomy of the vertebrae and ribs means that the rib cage is a great place to put a saddle as it is pretty strong and stable.



ribs1Its worth feeling for the junction of the vertebrae and the ribs, because of the spinous processes, its lower than you may have thought.







The lumbar vertebrae

ribs4There are no ribs to strengthen the lumbar section of the vertebrae so problems are going to arise if the weight of the saddle and rider are placed further back than the 18th rib.The red line marks the approximate position of the 18th rib. This is pretty easy to find as you can feel the last rib but remember that it curves up and forwards, it does not go straight up, that would cause you to over estimate the load bearing length of the spine. You can see the curvature of the rib on the diagram of the skeleton above.




Muscles, ligaments and fascia

The horse's bones are not going to change a huge amount once he is physically mature but the space between the ribs and the spinous processes is made up with ligaments (interspinal ligaments and supraspinous ligament), muscles (e.g. thoracic part of the trapezius, longissimus muscle, thoracic spinal muscle) and a great deal of fascia. There is also a great deal of fascia along the back.

When the template of a horse changes with the seasons, with changes in diet, health or fitness it must be the muscles or fat deposits that are changing as the bones in the spine are not going to alter.

There are some conclusions that could be drawn from the anatomy with regards to treeless saddles. It the rib cage is a strong area which is capable of bearing weight from the withers to the 18th rib then there is no problem, in principle, with a correctly fitting tree to spread the weight. As treeless saddles don't have a tree to spread the weight of the rider and the pressure from the stirrup bars then there is a risk that this weight is going to get concentrated in the area of the rider's seat bones and underneath the bars. This may not be a problem if the saddle is only used for short periods and not every day but I have had significant problems with several brands of treeless saddle for exactly this reason. I even still have some white hairs in the shape of two seat bones and a pair of stirrup bars on one of my horses backs to show for it.