Equine Conditions - "Kissing Spines"

Kissing spines refers to a common condition in the horse, otherwise known as overriding dorsal spinous processes. 

To understand this condition, let's first look at the anatomy of the horse's spine.

The horse's spine is divided into five regions - the cervical, thoracic, lumbar, sacral and coccygeal vertebrae. There are 7 cervical, 18 thoracic and 6 lumbar vertebrae. The sacrum is comprised of 5 fused vertebrae and the coccygeal (tail) vertebrae can number anywhere from 15-25, with the average number being 18. 

In the thoracic, lumbar and sacral regions the vertebrae each have a dorsal spinous process. Their purpose is to form a point of attachment for the muscles running along the top of the spine (the 'topline' muscles). 

 skeleton of the horse, showing the 5 spinal regions & the spinous processes

skeleton of the horse, showing the 5 spinal regions & the spinous processes

In a normal spine there is a gap between each of these spinous processes. In horses suffering from kissing spines, there is a loss of this spacing, ranging from the spinous process touching the adjacent spinous process, to completely fusing with it. 

 GRADE 0 -  A NORMAL SPACING BETWEEN THE SPINOUS PROCESSES, GRADES 1-5 - THE VARYING DEGREES OF KISSING SPINES

GRADE 0 -  A NORMAL SPACING BETWEEN THE SPINOUS PROCESSES, GRADES 1-5 - THE VARYING DEGREES OF KISSING SPINES

 THIS IMAGE SHOWS VARYING DEGREES OF THE CONDITION AFFECTING A NUMBER OF VERTEBRAE. IN THE 2ND - 4TH VERTEBRAE CIRCLED WE CAN SEE THAT THERE IS STILL A GAP BETWEEN THE SPINOUS PROCESSES BUT THERE IS NEW BONY GROWTH ON EACH SPINOUS PROCESS WHICH IS STARTING TO ENCROACH INTO THE INTERSPINOUS SPACE. ACCORDING TO HAUSSLER (199) THE RANGE OF VERTEBRAE AFFECTED CAN BE FROM 0 - 9 LEVELS, WITH 4 BEING THE AVERAGE.

THIS IMAGE SHOWS VARYING DEGREES OF THE CONDITION AFFECTING A NUMBER OF VERTEBRAE. IN THE 2ND - 4TH VERTEBRAE CIRCLED WE CAN SEE THAT THERE IS STILL A GAP BETWEEN THE SPINOUS PROCESSES BUT THERE IS NEW BONY GROWTH ON EACH SPINOUS PROCESS WHICH IS STARTING TO ENCROACH INTO THE INTERSPINOUS SPACE. ACCORDING TO HAUSSLER (199) THE RANGE OF VERTEBRAE AFFECTED CAN BE FROM 0 - 9 LEVELS, WITH 4 BEING THE AVERAGE.

The area most commonly affected is the thoracic region, in particular over the area that the saddle sits (T11-18). Research by Leo Jeffcott (1980) suggests that this condition is present in 39% of horses presenting with back pain and most prevalent in young adult to middle aged horses used for jumping or dressage and in Thoroughbreds with short backs. 

Symptoms

Symptoms can vary from horse to horse, with some horses showing no signs or symptoms at all. Symptoms will often depend on the degree of impingement of the spinous processes and the amount of inflammation, bony reaction and soft tissue compensation that is associated with the condition. Symptoms will depend largely on the occupation of the horse and the amount of work they are currently doing. Most often owners or riders notice behavioural changes in the horse. These can include a reluctance to being saddled up - either by way of not standing still when the saddle is brought out and/or placed on the back, biting or 'girthy' behaviour as the girth is tightened or hollowing through the back as the saddle is placed on the back or the girth is tightened.

Under saddle the horse may show reluctance to round or bend through the spine and show difficulty in transitions. The horse may show signs of anxiety, with the rider sensing they feel ready to 'explode'. If the horse is experiencing considerable pain they may display behaviours such as bucking, pig-rooting or rearing - basically anything they can do to try and get the rider's weight off their back.

Diagnosis

On assessment the horse may have limited range of motion into flexion and lateral bend of the spine. They may have local tenderness to palpation over the affected spinous processes. Diagnosis by a veterinarian is commonly done via x-ray.

Treatment

Depending on the owner's goals and plan for the horse, treatment for this condition will typically involve input from a number of different sources. First and foremost your veterinarian will be called upon to diagnosis the condition and provide a treatment plan for the horse. Medical management may include medication for pain and inflammation and injections into the interspinous spaces. Referral to physiotherapy will be commonly made. 

Saddle fit is a must if the horse is to continue to be ridden, ideally with the saddle fitter provided with as much information as possible about the level of the affected spinous processes. In much the same way our bodies change shape as we lose or gain weight, bulk up or trim down, so too does a horse's. Therefore it is imperative to get your horse's saddle fitted by a qualified saddle fitter regularly, especially in times where they may have had a notable change in weight or muscle bulk. Recent literature suggests that saddle fit should be done at a minimum of every 12 months.

In the cases that don't respond to conservative management, surgery may be considered by the veterinarian.

Physiotherapy treatment

Physiotherapy may include a number of different modalities. Massage to release surrounding muscles may help reduce pain and spasm. Thermotherapy - the use of heat packs or ice, can be beneficial to reduce pain, inflammation and muscle spasm. Often a combination of the two will work well, your physio can advise on which will be the best option for your horse. The use of electrotherapy devices, such as TENS and neuromuscular electrical stimulaton, can be very effective in both the management of pain and helping to stimulate muscle activation.

Mobility exercises to help increase range of motion of the spine and core stability exercises to help train the back and abdominal muscles are of the outmost importance in the rehabilitation of this condition, particularly in the performance or race horse. These include specific baited carrot stretches and rounding/lifting reflexes performed off the horse (see Activate Your Horse's Core, by Narelle Stubbs & Hilary Clayton), the use of training systems such as the equiband or pessoa and specific riding drills under saddle, specifically encouraging the horse to engage the hindquarters and round through the back. Trot poles and cavaletti can be vey effective for this. Your physiotherapist will be able to tailor a specific rehabilitation program for your horse.

While a change in occupation might be necessary for some horses diagnosed with kissing spines, for others a well managed rehabilitation plan may mean a continued (and possibly progressive) career in their current discipline. 

References:

  • Haussler K.K., Stover S.M. and Willits N.H (1999) Pathologic changes in the lumbosacral vertebrae and pelvis in Thoroughbred racehorses. Am. J. Vet. Res. 60(2): 143-53. 
  • Jeffcott, L.B (1980) Disorders of the thoracolumbar spine of the horse – a survey of 443 cases. Equine Vet. J. 12(4): 197-210. 
  • McGowan C, Stubbs N, Hodges P and Jeffcott L (2007) Back Pain in Horses - Epaxial Musculature. RIRDC 07/118.