Matthew O’Donnell MRCVS – Cheshire Equine Clinic
How do we approach dealing with fractures at Cheshire Equine Clinic? Horses breaking their legs often provokes images of tragic scenarios with euthanasia being the only solution to alleviate the animals suffering. Questions are asked along the lines of comparative techniques to repair humans and dogs….where are the answers for horses? Why can we fix them up in small animals and not apply the same techniques in the horse?
Why are limb bone fractures challenging to manage?
Horses must weight bear on all four legs soon after the injury otherwise the other legs will be weakened by carrying too much weight. Horses can’t lie down for six weeks in a hospital bed until the leg is better! So any repair has to quickly get the horse comfortable enough to stand. Because some fractures, particularly those sustained at speed, break the bone into many small pieces, it is not possible to get the horse comfortable quickly enough. In spite of all the modern materials available, the largest implants for repairing bones are still not strong enough to withstand the weight of the horse for the time it takes for the bone to heal and become stronger than the screws. So some fractures just can’t be fixed because the screws will break afterwards, even if the horse is box rested.
In the first instance, lets start with a definition… what is a fracture?.
Actually fracture means the same as a break, but is better defined as a break in the continuity of the bone. This can happen in two general ways. Fracture on a large scale results in the two ends of the bone separated from each other. When this happens the bone can no longer provide its structural function because its shape has changed. On the other hand there are fractures that have not yet broken through into two separate pieces, in the same way the perforations in a tear-off ticket or label have not joined up, and these are described as incomplete.
How do bones break then?
To smash something up we can hit it in a direction that it is not designed to be loaded, for example when a horse falls or is kicked – representing an unusually large force applied in an unusual direction for the normal movement of the horse. These are unpredictable, often are ‘high energy’ or explosive and the broken pieces often have sharp edges and many small splinters. In this way they are as complex to put back together as a jigsaw or broken pottery with many different edges and surfaces needing to meet back up.
Other fractures occur following repetitive strain, with each individual loading event being small, but the gradual long-term effect building up to fatigue or perish the bone structure on a microscopic level. This gradually weakens the structure until a normal load applied in a normal direction can be sufficient to cause the bone to break. This group are called stress fractures, and generally occur in horses performing lots of regular fast exercise, particularly young thoroughbreds. They can be hard to spot before they happen, often with the horse appearing sound until the fracture occurs. In some cases there can be subtle warnings or prodromal signs. Severe lameness that wears off after 2-3 days rest only to recur when the horse goes fast again are classic signs of underlying ‘bone pain’, and can be recognised through regular monitoring or supervised trot-ups on the yard.
How does Cheshire Equine Clinic investigate stress fractures in the lower limb of the horse?
A clinical examination, palpating, twisting or flexing the joints of the lower limb may provoke an unusual response in a horse that otherwise had a normal leg. With experience, looking for indications in the recognised risk areas in this way may prompt the need for further investigation. X-ray examinations, looking at the physical shape and structure of the bone can indicate a short fracture line or area of hardening associated with a stress modelling response. X-rays can sometimes look normal, and in these cases bone scanning, looking at the metabolic activity of the bone, can be helpful. Bone scans reveal areas of increased calcium metabolism in risk areas and can highlight early fracture that is not visible radiographically, and is ideal for stress fracture monitoring, particularly of the upper limbs and larger bones that cannot be adequately examined with conventional X-ray studies.
Our approach repairing simple fractures in the standing horse.
A large proportion of fractures involve the lower limb, particularly the cannon bone and pastern of the fetlock. Stress fracture modelling of these bones may result in a number of different patterns of fracture, some of which follow regular shapes or configurations.
In the case of short incomplete fracture lines where the bones have not separated, it is possible to approach repair with the horse standing under sedation and local anaesthesia. These are called simple fractures because the pieces have not separated from each other and there are only a few steps required to return the bone back to its structurally sound shape so that it can heal.
Only a specific group of fractures are suitable for repair in this way, and so the selection process has to be quite careful. Here is an example that can be approached in this way. The surgery is performed in the clean standing surgery room. The leg is prepared, cleaned and local anaesthetic injected to numb the lower limb and surgery site. A small incision, sufficient to allow the drill bit to reach the bone is cut in the skin. Guide needles and staples provide markers for aligning the drill correctly so that the screws are put in the right place and go in straight. Using special tools, quite similar in fact to those used in cabinet making, the screw is inserted into the bone under radiographic guidance using a fast X-ray machine that gives an instant picture. There are lots of similarities to general carpentry, but in horses you only get one chance to drill the hole in the right place! The bone on the far side of the fracture is tapped, cutting threads to receive the flanges on the screw, effectively creating a ‘nut’ within the bone. In this way the screw is placed in lag fashion across the fracture gap, squeezing the fracture between the far side of the threads and the head of the screw. It is this compression that gives stability for the horse to weight bear and heal after surgery.
The technique relies heavily on an experienced team and careful planning to bring the horse ready to the point of repair with a minimum of sedation. In this way the actual surgery time between when the skin incision is opened to when the last sutures are in place can be reduced to less than 10 minutes per screw.
Following a course of medication and simple supportive bandaging the horse is box rested until 6 weeks after surgery. Repeat X-rays at this stage guide further management, but usually a horse will start walking, gradually increasing exercise towards fast work within approximately 6 months after injury. The screws can be left in the leg if they are not causing any reaction in the bone.
Fractures vary greatly in the way they can disrupt the function of the limb. Many fracture cases are best treated through procedures under general anaesthesia, particularly when the joint surface requires examination, or the fracture pieces are separated. Some fractures cannot be repaired because the function of the leg, even after repair, will not allow sufficient weight bearing.
Standing fracture repair is a technique applied to the treatment of simple fractures of the lower limb. Suitable cases require careful selection, examination and discussion regarding the options available for fracture repair. As part of our commitment to high standards of clinical care, an audit of recent cases confirmed our technique and method has been applied with great success with no significant complications. It is very satisfying to see a horse limp into Cheshire Equine Clinic, get repaired and then walk comfortably out of the door, but even more pleasing to follow them as they return successfully to competition!
Tel: 01829 770 999