Fractured Spinous Processes in a Horse

A 10 year-old gelding arrived to a horse show and was seriously injured during the unloading from the trailer. The rear gate was lowered and the horse remained standing in the trailer with the "butt bar" in place (Figure 1). For some unknown reason, the horse panicked and attempted to unload with the butt bar in place. The horse became trapped below the butt bar and struggled for several minutes before the owner was able to release the bar. Within moments of the event, the horse's withers became swollen and very sensitive to the touch. The gelding was treated with systemic anti-inflammatory agents and returned home in the trailer WITHOUT the  butt bar!

Figure 1

Two weeks after the injury, the gelding presented to PHD veterinary services for a radiographic evaluation of the withers. In Figure 2, the green line outlines the withers of the horse. The bone-like fingers projecting upward below the green line are the spinous processes which make up the withers. On physical exam there was minimal swelling over the withers however the horse was very sensitive to any pressure and there appeared to be a "dip" in the very bottom of the withers (yellow arrows).

Figure 2

Radiographic evaluation of the "dip" in the withers confirmed multiple fractures of 3 spinous processes (yellow arrows in Figure 3). The first spinous process that is fractured appears to be in several fragments and displaced from its normal position. The second spinous process appears fractured but not displaced and the third process appears to have an avulsion of the most proximal aspect of the spinous process. Although it is likely that these fractures will heal in time and be some what stable, the current concern is the development of a frustrating condition known as fistulated withers. This  occurs when a piece of fractured bone becomes devitalized of blood supply and subsequently "dies" becoming a sequestrum. The body's natural response is to rid itself of the sequestrum and will develop a draining wound that originates from the sequestrum. These wounds do NOT resolve until the sequestrum has been removed and this can be extremely challenging from a surgical stand point. Currently there is not evidence of a sequestrum however it will take several weeks/months to determine if one will develop. Prognosis for return to riding will depend the development of fistulated withers and how comfortable the horse is once the fractures have stabilized.

Figure 3

Kissing Spines!

The radiographs below are of the dorsal spinous processes of  the vertebral bodies in the top-line of a horse. Essentially, these bones are directly below the saddle and directly below the rider's center of gravity. As such, they represent some of the most stressed areas during riding under saddle. The first two radiographs are of the same horse and the yellow circles correspond to where the spinous processes are in contact with the each other. This is also know as "Kissing spines". This horse presented for a chronic history of a tender back and unwillingness to move forward at the trot and/or canter. The 3rd radiograph is that of a normal horse. There is significant space between the spinous processes. These spinous processes are slightly cranial to the ones depicted in the previous 2 radiographs.  Unfortunately, the diagnosis of kissing spines is not favorable for the horse to have a performance career without chronic back pain. There are therapies aimed at reducing the pain and muscle spasm associated with this condition which include; saddle fitting, shockwave therapy, mesotherapy, acupuncture, chiropractic adjustment, deep message, and cortisone injections. I strongly recommend having radiographs taken of any horse with a chronic history of back pain to determine if this might be the cause!!