The equine back
Suzannah Povey White looks at the similarities between human and horse and, explains how it is possible for the horse to carry a rider
I’m sure we’ve all seen those graphics where they liken the equine spine and associated structures to the human spine, enabling us to draw comparisons between the two. But how similar are they? How does a horse adapt to carrying weight on its back? And how can we ensure its health and strength?
As a horse owner, rider and competitor, it’s helpful to understand the structures at work beneath you, enabling you to appreciate how to correctly train your horse’s back and potentially spot problems as they arise.
The equine spine, referred to as the ‘axial skeleton’ by professionals, starts at the poll, or occiput and continues to the sacrum, or tail bone. The vertebrae fit together like Lego bricks, much like our own. The first vertebrae, called the Atlas articulates (joins) with the skull on one side and with the ‘axis’ on the other. These are the first two cervical vertebrae and have a reasonable amount of movement both laterally (side to side) and up and down. This enables the horse to turn and twist its head to either look behind itself or scratch its sides.
The rest of the cervical vertebrae continue down the neck and disappear under the shoulder blade at the cervical-thoracic junction. You can’t feel this, as it’s under the scapula, but it’s where the spinous processes begin, which form the wither and the bony prominences that we can feel along the horse’s back. The reason the withers are so prominent on a horse, is they act as attachments for the big ligaments and muscles that support the head and neck.
The spinous processes are an upside-down T shape with the spines on the top being the longest. The ‘fingers’ of bone are what touch in kissing spines. They are supported by a very strong ligament called the supraspinous ligament, which is much like a rope running along the top of the processes, and a series of muscles called the ‘epaxial’ muscles. This muscle group consists of the multifidous, the longissimus and the iliocostalis, and is used to stabilise the back, it works in conjunction with the wider muscle groups of the core and lumbar.
The thoracic spine progresses to the lumbar spine at the thoracolumbar junction, which sits just behind the cantle of the saddle. Anatomically they look and behave very similarly to the thoracic vertebrae but, they point in a slightly different direction because they don’t anchor the ribs, that is the job of the thoracic vertebrae. There’s more lateral movement here due to the lack of ribs or pelvis, but it also means this area can be less stable.
The spine then progresses to the sacrum, which are 5 fused vertebrae sitting directly above the pelvis acting as an attachment for the big muscles of the hindquarters. They provide a lot of stability for the hindlimbs to pivot underneath the horse. The spine finally ends with the coccygeal vertebrae, that are essentially the tail bones.
Join us for the next instalment where we’ll be looking at pathology and spinal injuries of the horse and how to bullet-proof your horse’s spine.