As riders we sit on our horses backs because logically it’s the best place to sit! And we ride them and expect them to do things such as lateral work and jump over jumps. But do we really know what we’re sitting on or how the back is working underneath us?
This is an area that I’m really passionate about as the horses back was always designed to carry weight…. but the weight from the organs below not the rider above!
The back is such a complex structure with the joints, ligaments, tendons and muscles all needing to be in proper alignment and functioning effectively for them to be able to carry themselves properly let alone us as well!! And then when you add in a saddle that may or may not fit, postural issues, conformation and much much more we can come across all kinds of issues.
One of the biggest problems I find with riders, coaches, judges and trainers is that they talk about movement from the perspective of the rider and what the rider may or may not be feeling, but is that what is actually happening and how can we help our horses to move more efficiently and stay strong?
Unlike the head and neck, the horse’s back is a highly inflexible structure, capable of only minor movements up and down and laterally. Smythe and Goody estimate the movement to be less then 15-20cm in a supple horse, and there are not a lot of those around. When you watch a horse move you get the impression that there is a lot of movement through the spine, but when you really analyse it, most of this movement comes from the neck and pelvis, giving the appearance of bend in the back.
So what is the anatomy of the back?
The Back is made up of 18 Thoracic vertebrae (one less in Arabs) which comprise the “true back” area. These vertebrae provide the attachments for ribs (costae) and are linked by intervertebral fibrocartilages. The fibrocartilages between the thoracic vertebrae aid weight bearing, shock absorption and the maintenance of the small amount of flexibility. The spinous processes of the thoracic vertebrae are much higher then other vertebrae, reaching their peak at T4 where the highest point of the wither would be, and becoming smallest towards the back around T16 which is called the “anticlinal” vertebrae and is the vertebrae in which the direction changes from caudal to ventral.
The middle of the back is approximately T13-T15. They are the closest together vertebrae, and they are furthest away from the support areas of the forelimbs and hindquarters. This makes them most susceptible to postural issues, and guess what. They are where we sit!
The Lumbar vertebrae are not part of the “true” back, but make up what is considered the lower back region of the horse (which, like in people has numerous issues). There are most commonly 6 lumbar vertebrae, although a number of horses only have 5. These horses also tend to have one additional thoracic vertebrae. Lumbar vertebrae have very long (7-10cm) and very wide (2cm) transverse processes. The transverse processes of the last three lumbar vertebrae have synovial articulation, and like with any other synovial joint can develop arthritic changes (ankylosis). Unfortunately this fusion is very common.
The muscles of the back can be divided into epaxial (above or dorsal to transverse processes) or hypaxial (below or ventral to transverse processes). There are many muscles that make up the back of the horse, and epaxial muscles have three layers!
Other soft tissues that are important to the back are the ligaments. The Supraspinous ligament (continuation of the nuchal ligament) sits on top of the spinous processes, the dorsal ligaments sit under each vertebrae, and the ventral longitudinal ligaments sit under each vertebral disc. These give the spine support. There are also many short ligaments that people forget! The Interspinous ligament – sits between each spinous process, Ligamentum flavuum – sits between each articular process, Costovertebral ligament – sit between the vertebrae and the ribs and Costotransverse ligament – sits between the vertebrae and the ribs.