The very mention of the word, “fracture”, strikes fear into the heart of every horse owner and most of us assume that if their horse has sustained such an injury, there is only one sure outcome. That’s not necessarily the case though where the splint bones are concerned.
Splint bone injuries
The metacarpal and metatarsal bones II and IV, that’s the splint bones to you and me, are found either side of the cannon bone. The function of the splint bones is to provide support for the lower rows of hock and knee bones and they are attached to the cannon bone by a thin interosseous ligament. Fractures of the splint bones are quite a common injury (not to be confused with a splint which is a minor soft tissue injury. Fractures can occur due to trauma following a kick from another horse but can also be associated with other secondary conditions, for example suspensory ligament damage which is commonly seen in horses that race over fences.
The majority of splint injuries occur on the forelimbs; more frequently on outside splint of the left fore and the inside splint of the right. These findings are probably not entirely accurate though as the majority of the research used in compiling these statistics was carried out in the racing industry where horses are worked more in a counter clockwise direction. This results in increased loading on these areas. The distal ends of the splints attach to the sesamoid bones by fibrous bands which become stretched excessively during hyperextension when the leg is at full stretch and the fetlock joint is at its lowest point during a stride. This tug of war effect causes excessive stretching of the attachments and predisposes the splint bone to fracture, usually in the lower third of the bone.
Swelling of the suspensory ligament can create a bowstring effect which may lead to a progressive deviation of the splint away from the cannon bone. Poor knee and foot conformation will predispose a horse to splint bone fractures.
Kicks are by far the most frequent cause of splint bone fractures. They are very often accompanied by open wounds, heat and swelling and the horse will be very lame. Occasionally, the horse will appear slightly lame and there is no apparent cause other than a minor abrasion from a kick. This may in fact be masking a fracture which may not become apparent until weeks after the injury was sustained.
Diagnosis and treatment
If your vet suspects a splint bone fracture, he will want to take X-rays immediately to establish if the injury is causing instability of the surrounding structures in the horse’s leg. If the fracture does not affect stability, is non-infected and is simple in that any bone fragments are minimal and relatively unified, treatment is usually by heavy strapping and box rest for 12 to 14 weeks. Regular X-rays will be necessary during this period to make sure that healing is progressing satisfactorily. If there are multiple loose fragments of bone, your vet may decide to remove them surgically.
In cases where the fracture has caused instability of the knee or hock, fixation with steel plates and screws may be necessary. Although injuries like this will heal, the horse is likely to be affected by osteoarthritis and long term ligament damage and may never be sound enough for ridden work again.
Generally speaking the prognosis for splint bone fracture injuries is pretty good with most horses being able to return to work again once healing is complete regardless of whether treatment was surgical or not. The main problem in the long term may well be suspensory ligament damage rather than the fracture itself. This can be treated using ultrasound therapy or steroids and the horse may be able to return to some sort of work eventually.
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