The structure of the withers makes this bony ridge vulnerable to bruising or fracture, especially if a horse rears and falls over backwards. Graham Hunter MRCVS explains
The withers are formed by dorsal extensions between the horse’s shoulder blades, from around the third to the 11th thoracic vertebrae.
At their highest point, approximately midway, these spinous processes can be up to 30cm long.
The height of these bony projections provides significant attachment for the nuchal ligament (which runs from the occipital bone to the withers, and is essential for any horse to lift and lower his head) and the substantial muscle mass required to support the weight of the horse’s head, neck and shoulders.
The fact that the top of the withers is always above the shoulder blades makes the area prone to injury. A horse’s natural survival instinct leads him to evade threat.
As a result of this response, a frightened horse may rear up and flip over backwards, leading to fracture of the spinous processes.
Fractures can also result from traumatic incidents such as getting stuck in a fence, falling into a ditch or becoming wedged under the breast bar in a trailer, or perhaps during a colic episode or a seizure. Injury has even been known to occur when a horse falls because of other neurological problems which have left him weak or uncoordinated.
A traumatic incident may not always be witnessed, and sometimes an owner will report finding their horse in the stable or paddock with pain and swelling over the withers.
Wither fractures can also cause neck stiffness, with the horse unable to extend his neck to the ground or to either side. Forelimb lameness may be seen, with a very short, stiff gait. Where significant neurological signs are present, an extensive neurological examination of the whole horse with appropriate imaging should be performed.
Fracture of the withers tends to be easy to spot on radiographs (X-rays) as there are generally a number of spinous processes involved, typically between two and seven. The most common of the spinous processes to be injured is the sixth — the tallest and therefore the first to hit the ground when a horse falls over backwards.
On a lateral (side) X-ray, there is often what looks like a separate piece of bone at the top of each spinous process. These should not be mistaken for fractures — they are what we call “separate centres of ossification” and appear in a horse of any age.
Nearly all fractures are complete across each process and the fracture piece is generally displaced deeper into the horse and off to one side.
As long as there is no open wound, initial treatment will generally involve anti-inflammatory drugs such as bute. The injury should be iced and the horse put on box rest for four to eight weeks, depending on the number and severity of the fractures.
The horse should be fed from chest height so he doesn’t have to stretch to the floor to eat. Unlike fractures in some areas of the body, which might require immobilisation, this is not generally needed with injury to the withers.
If an open wound is present, it should be cleaned and flushed out, and any contamination or bone fragments removed. In some cases antibiotics may be required. A secure dressing may be needed if the wound is severe.
Healing of these fractures is generally uneventful and horses can be returned to work in four to six months. Complications can occasionally occur, however, particularly if the injury was associated with an open wound. Infection can result and if it persists could affect the bone and result in delayed healing and a chronic discharging tract.
If this occurs, surgery is best performed — under standing sedation — to remove the infected tissue and bone, including the damaged top of the affected spinous processes.
In some horses, fractures can be associated with persistent wither pain. Surgery may be necessary to remove the fractured pieces of bone.
The long-term prognosis for these injuries is extremely good, with nearly all horses regaining their full athletic ability after six months. Most end up with chronic thickening and flatter, lower withers, and so the greatest long-term issues relate to saddle fit.
If the withers end up low and asymmetric, the saddler has a tough job. Solutions may involve croup, point or balance straps. Adjustments to the flocking or altering the pressure in air-filled panels can help prevent saddle drift.
Other injuries to the withers can include bites and rug or tack rubs, which can lead to local skin infections or abscesses.
There is a fluid bursa that sits just under the nuchal ligament at the withers. If infection of this bursa occurs, chronic recurrent infection — called “fistulous withers” — can result. A few years ago this condition was often caused by the bacteria brucella, which also caused brucellosis in cattle. Thankfully, both conditions have now almost been eradicated.
Ref: Horse & Hound; 30 July 2015