THE EQUINE BACK
The equine back is referred to as a quadrupedal trunk and has been more recently been described biomechanically as a “Bow and String” concept. The “bow” comprises the thoraco-lumbar spine and the epaxial musculature comprising mainly of the longissimus dorsi and the multifidus. The “string” refers to the soft tissue structures supporting the trunk. e.g. The lower abdomen.
When we refer to the back we are often referring to the saddle area, however the back is part of a “sling” that runs from the atlanto-occip
ital to the coccygeal vertebrae (head to tail).
An overview of the osseus vertebrae
The neck or cervical vertebrae are C1 to C6, the thoracic vertebrae (withers to mid back) runs from T1 to T18, the Lumbar vertebrae run from the back of the saddle to the front of the pelvis, (L1 to L6), the sacrum (S1 to S5) and finally the tail comprising 15-21 coccygeal vertebrae.
The Highest point of the withers is generally T5 and the lowest point is C7 to T1. The anticlinal vertebra is often T15 and is the most vertical dorsal spinous process.
There are certain conditions of the horse that become topical and hence a popular diagnosis. This is in part due to the mobile, high quality imaging systems that are now widely available. Some of it is due to the fact that many of these conditions are quite Subjective and open to interpretation. This author is k
een to take all factors into consideration before making a diagnosis, with particular emphasis on the clinical findings.
As a colleague used to say to me from a previous era “I am a clinician not a technician” Although he was from a very different age it is important as vets we don’t get carried away with technology and forget the basics i.e. clinical evaluation.
The back has the potential to be over diagnosed, this is because x rays can be very visually convincing, for example it is known that c80% of racing thoroughbreds have “Kissing Spines”, but radiographs are not necessarily significant without clinical information backing it up. On the other hand normal back x-rays do not mean there is not a back problem. Like humans pain thresholds differ widely from one individual to another.
It has become more routine for back x-rays to make up part of the routine vetting (pre-purchase examination) and sometimes also cervical vertebrae. Whilst severe radiographic abnormalities cannot be ignored, mild changes should be interpreted in conjunction with clinical findings.
The most commonly affected region of the back is simple physics and is the most dependent or lowest part of the back, which is often mid
to caudal thoracic vertebrae.
Causes of back pain
Saddle fit, conformation (e.g. lordosis/kyphosis), muscle development, breed, rider weight, training techniques, skin issues, hind limb lameness issues. DSP impingement (kissing spines or overriding DSP’s), articular facet pain (APJ), muscular pain, supra-spinous and inter-spinous ligaments, disc rupture
As a vet presented with a new case, one of the first things considered is the clinical history. For example, is it cold backed, does it rush off when being mounted, have a shortened hind limb gait, tension under saddle, abnormal forelimb presentation (less well documented), or resents “girthing up.” Has there been a change of saddle or change in body condition.
As has been already mentioned clinical palpation is paramount along with taking an in-depth history from the rider. Observe the horse ridden and its movement with and without the saddle. Assess the horses reaction to saddling up. After observing the horse it may be that X-rays are the next step. However any doubt would require nerve blocks to confirm or eliminate the back as an issue. Note that nerve blocking to assess back softness/tension can be unhelpful, as extension and flexion of the back will increase in range of movement and can give a false positive. However behavioural changes can be a very important marker following regional DSP nerve blocks.
Other modalities include, ultrasound, nuclear scintigraphy, thermal imaging.
Phenylbutazone (bute) trials are an option to observe changes in performance or behaviour. However even on relatively high doses some types of back pain can be unresponsive to this approach.
Dependant on the diagnosis a number of approaches can be taken with regards treatment including physiotherapy, medication, rehabilitation, saddle fit, shockwave, tildruonic acid, laser, acupuncture, surgery, Articular Process Joint (APJ) medication. From a veterinary perspective I like to work alongside physiotherapists and infiltrate or medicate the affected areas with specific anti-inflammatories as a first line approach.
Opinion varies hugely on when to intervene surgically. I believe that in most cases surgery should be withheld until all other options have been exhausted. The main surgical options are; Dorsal Spinous Process resection (removal) or inter-spinous ligament desmopathy
Other common causes of perceived back pain
Equine gastric ulcer syndrome (EGUS), behaviour, rib pain, ovarian pain (mares only), skin issues,
In summary, back pain can present itself in many different ways and be caused by a number of factors. It should also be remembered that issues in other areas e.g. concurrent or even primary lameness (mainly hind limb) can be a major factor in many back presentations. Subclinical or mild lameness is thought to play a role in the pathogenesis of back pain. This is why a complete lameness assessment is always recommended when assessing back pain as often they may be connected.