Splints and Fractures of the Splint Bone in Horses
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The horseman and stockman are familiar with the cannon bone of the horse limb. On each side of the cannon bone is a long narrow bone known as the splint bone. The splint bones start at the knee and taper as they descend on either side of the cannon bone, each ending in a small knob about two-thirds of the way to the ankle (Figure 1).
Figure 1. Caudal view of the bones of the leg.
There are two main conditions which affect the splint bones. The term "splints" commonly refers to an inflammatory condition and a calcium lump on the bone, while the term "broken splint bone" refers to a fracture of the splint bone and a calcium lump where it is trying to heal. When lameness in this area occurs, the above conditions may be confused and need to be differentiated.
The ligament (interosseous ligament), tying the splint bones to the cannon bone, is quite elastic in young horses; however, as the horse ages, the ligament ossifies and is replaced by bone and the three bones fuse (Figure 2).
Figure 2. Lateral view of the leg, in both young and old horses.
"Splints" are the direct result of an injury to the periostium (tissue covering the bone) or an injury to the interosseous ligament (tissue tying the splint bone to the cannon bone). These injuries to the horse may be the result of direct trauma, such as a kick or a concussion type trauma resulting from jumping, running or working. As the horse matures, the interosseous ligament slowly calcifies, fusing the splint bones to the cannon bone, allowing it to better withstand the concussion type trauma of working and the horse is therefore less likely to develop "splints". Most often, the forelimbs are affected; rarely do "splints" occur in the hindlimbs.
The majority of splint problems occur in the medial side (inside) of the forelimbs. The medial splint bone is the one usually affected, because it has a flat surface next to the knee. The lateral (outer) splint bone has a more slanted surface. When the weight is transmitted to these bones, the medial splint bone probably bears more weight than the lateral splint bone; therefore, the ligament between the medial splint bone and the cannon bone is subjected to more stress than the outer ligament.
Lameness due to "splints" is most common in two-year-old horses undergoing training. The lameness is most obvious while the horse is trotting, working or soon thereafter. Lameness may come and go or be present continuously for as lone as a year.
If one palpates the leg along the side of the cannon bone and splint bone, the horse will exhibit a pain response when pressure is applied to an inflamed area. This might be a large swelling where ossification (calcium deposition) is already taking place or a very small swelling where ossification is just starting. It is important to note that there may be more than one splint forming on a horse at the same time. After the inflammation has totally subsided and the ossification is completed, the soreness usually disappears.
Veterinarians use many different methods to treat "splints", but most would agree, that the horse should be rested and placed on soft ground for at least 30 days. Veterinarians may use medications to help reduce inflammation and help prevent excessive bone growth, but splints" may also heal without medication and treatment.
The outlook is good for most horses except those in which the bony growth is large and interferes with the knee joint or the suspensory ligament. Sometimes surgery may be helpful in these difficult conditions.
Fractures of the splint bones must be differentiated from the inflammatory condition known as "splints". Fractures of the splint bones can occur anywhere along their length, but are most commonly located at the lower third. Heat, pain and swelling will occur over the fracture site. The more acute the fracture, the more severe the swelling.
Fractures of the splint bones can occur as a result of external trauma, such as a kick from another horse or from the horse interfering with itself. During racing, excessive forces may also cause fractures.
Radiographs are necessary for a positive diagnosis of a fractured splint bone and to differentiate it from "splints". Your veterinarian will decide on the course of treatment. Often the surgical removal of the distal fragment of the fractured splint is necessary; however, this may be unnecessary in cases in which good healing is progressing and minimal callous formation and lameness is present.
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