Fractures of the neck are mercifully rare. To understand the nature of these fractures, it helps to know a little about the basic anatomy of the equine neck.
The spinal column in the horse’s neck area is made up of 7 separate vertebrae. A tube runs down the middle of them, called the vertebral canal, which encases the spinal cord. The vertebrae are held together by facet joints, one on either side, above the spinal cord. Beneath the cord, the vertebrae are cushioned by discs.
The critical structure in all this is the spinal cord, which carries nerve impulses between the brain and the body. Damage to the spinal cord is serious, with limited chance of repair. Spinal cord damage can result in a range of findings, from mild unco-ordination of the
hindlimbs through to sudden death due to paralysis of the respiratory muscles.
Research into spinal cord injury is a huge priority in healthcare, with cutting-edge research being carried out in the veterinary field. This includes the promising use of “ensheathing cells,” a specialised stem cell which originates from the link between the brain and the nose.
The challenge for any vet called to a horse who is down is to ascertain whether there is damage to the spinal cord.
In a competition situation, it can be difficult to establish if the horse has a serious spinal injury or is simply winded. It is normal to allow a horse at least half an hour after a severe fall to get back up.
Damage to the spinal cord is not visible on an X-ray, as the cord is of the same density as muscle and ligament. However, on occasion it can be inferred from the damage to the bony column, the cervical vertebrae.
If a horse has a smashed neck, an X-ray will tell us that the outlook is hopeless. Fortunately, this situation is very unusual.
We can usually only take X-rays in one plane, from side to side, yet many fractures are only visible in the up-to-down plane. More often than not X-rays are inconclusive, so a bone scan is necessary for diagnosis.
A veterinary surgeon on duty at an event or called to a riding accident where the horse is down will assess the recumbent horse. If there are no reflexes of the hind limbs and no sign of improvement over a limited timescale, then the horse will need to be euthanased to prevent any further suffering.
Sudden death or total paralysis are much more unusual presentations with an equine neck fracture. As always, the difficulty is the grey area. There may be nothing horrendous on the X-rays, but the horse is either unable to rise or is ataxic — he appears unaware of where his legs are.
The horse has a very large vertebral canal, relative to the size of his spinal column. The diameter of the canal varies with the position along the neck or back.
While upper neck fractures can be catastrophic for a human, resulting in lifelong dependency on a ventilator to breathe, horses that survive an upper neck fracture to diagnosis will often return to ridden exercise. The fractures can be radiographically dramatic, but the large diameter of the canal allows considerable disruption before there is any pressure on the spinal cord.
The equine neck is narrowest at its base, underneath the shoulders, at the junction with the thoracic spine. Fracture here often results in severe ataxia. It is also where it is hardest to X-ray, due to the massive soft tissue musculature of the horse’s shoulder.
Time will tell
Realistically, there is no effective treatment for neck fractures other than rest. The musculature of the horse provides remarkable stability and, given time, many of these fractures will heal very well.
While displacement of the fracture can occur days or weeks after the trauma, this is not common. Pelvic fractures are much more prone to displacement.
There is a surgical procedure to stabilise 2 vertebrae, either with bone plates or a stainless steel basket. The risks of general anaesthesia in a horse with an unstable neck fracture, however, are substantial.
This surgery is usually reserved for “wobblers”, a related condition where the vertebrae are malformed either through abnormal growth or through disease such as arthritis. This malformation creates pressure on the spinal cord and results in ataxia. Fusing 2 vertebrae together reduces pressure on the spinal cord during movement.
The hardest question with neck fractures is “will the horse get better”? No one wants to go through a prolonged rest regime only to find a year later that the horse is still wobbly and is a danger to himself and to everyone around him.
Predicting the degree of improvement — or indeed if there will be any improvement at all — remains very difficult.
Within a few hours of injury, the fracture haematoma (the blood clot surrounding the break) will exert pressure on the spinal cord. Over the next week or so, this is absorbed and replaced with granulation tissue — the soft, pink tissue sometimes seen filling the defect in a skin wound.
Granulation tissue then changes into scar tissue. On occasion the scar tissue enlarges, resulting in greater pressure on the cord and a marked deterioration in the horse’s condition. Most horses improve over the first 3 months, with some further improvement over the next 9 months.
Broken necks in horses are potentially devastating but rare. A crashing fall more often results in fracture of the limbs or of the thoracic spine.
When neck fractures do occur, the outcome may be sudden death or euthanasia a short while later due to paralysis. Often, however, the horse is able to rise after a while. Provided that the spinal cord is not permanently damaged or compressed and that healing is satisfactory, the horse can return to exercise.
Case study: a dramatic fracture
Racehorse Fred (name changed) broke his neck during a fall at Newbury races. X-rays showed a moderately displaced but still incomplete fracture of his 2nd cervical vertebra. As a result of muscle contraction, his 3rd vertebra was displaced forwards into the gap left by his 2nd vertebra.
Despite this dramatic fracture, Fred’s primary clinical signs were swelling of his neck and associated pain. He was ataxic — a bit wobbly —but less than you might have guessed on seeing these X-rays.
Fred was managed conservatively with painkillers and strict box rest. He later returned to training. Sadly, hopes of a happy ending for this story were shattered when, a couple of weeks before his next race, Fred fell again and broke his pelvis.
While bone scans can be very useful in the investigation of spinal trauma, there are problems with this diagnostic method.
The horse is injected with a radioactive material, combined with an agent which binds to bone. The material is carried in the bloodstream and binds whenever it reaches a bone crystal.
The horse is then scanned with a camera that can detect radiation and highlight any “hot spots” where there is increased blood supply to the bone. Typically these are areas of inflammation associated with fractures, but could also be tumours.
Because bone scans involve radiation, they are regulated by law and can only be carried out in legally-defined “controlled areas” — which are all in veterinary practices. The procedure cannot take place in a stable at a horse’s own yard. The horse must therefore be fit for transport before a scan can be considered, which can be several weeks after the injury.
Additionally, it takes a minute or two to obtain the image. A horse that is wobbly and swaying around can be very difficult to scan.
This veterinary feature was first published in Horse & Hound (26 June, 2014)