Splint Bone Injuries in the Horse

By Dr. Garret Metcalf, DVM

Splint bone issue in horses is a common problem in various ages and disciplines. These injuries can be caused by excessive work in young horses to traumatic injuries. The splint bones do play an important role in the stability of the joints that they help make up at knee or hock level. These various types of injuries will be discussed in this article as well as treatments.

The splint bones are small bones that are intimately attached to inside and outside of the cannon bone. The splint bone is divided into sections to understand which section is injured. At the top you have the head of the splint, then a mid-body section and at the bottom the button of the splint. The head of the splint bones make up part of the carpus (knee) in the forelimb and in the hind limbs the hock. There is a fair amount of research that has demonstrated the role the splint bones play in the stability of these joints. A study conducted at Colorado State College of Veterinary Medicine noted that when larger portions of the splint bone were removed rotational stability was significantly impacted within the carpus including other directional forces affected.

Diagnosing splint bone injuries are rather straight forward with radiographs, but some cases ultrasound is also helpful. Some of the bone or callus formation that occurs around these splint bone injuries can compress on the suspensory ligament leading to chronic pain and lameness issues.

Popped Splints

Splints that are popped are referring to injuries that generally occur to the younger population of horses entering training and work. Younger horses generally develop these injuries on the inside forelimb splints and they can be rather painful leading to loss of training time. The popping of a splint is the tearing of a ligament that holds the splint bone to the cannon bone called the interosseous ligament. When the ligament is torn bleeding can occur and disruption of the periosteum of the bones causing a callus or firm boney lump. These splints are more prone to injury because the medial or inside splint on the forelimb bears direct load with the second carpal bone at the head of the splint bone. This puts direct force on the splint bone where other splint bones share the load of the adjacent carpal or hock bones with the cannon bone.

Popped splint bones are often rather painful, have notable swelling associated near the splint bone and will have heat present. When palpated or squeezed a moderate amount of pain will be elicited. 

Treatments of these popped splints are often rest, systemic anti-inflammatory drugs and local anti-inflammatory treatments. Acute inflammation from a splint injury can be soothed with ice or cold therapies and bandaging. Also alternative therapies such as cold laser therapy, MagnaWave or shockwave can be incorporated to the treatment plan. In some more extreme cases surgical removal of the bone callus is necessary to prevent the callus from compressing the suspensory ligament.

Splint Bone Fractures

Fractures of a splint bone can occur at any level or in any one of the splint bones but there are some that are more commonly fractured. The lowest or distal one-third of the splint bone is commonly broken in the forelimbs. These fractures can be occasionally to forelimb suspensory related issues. The suspensory is has a small ligament attachment to the button of the splint bone and whenever the lower limb is extended heavily this can put bending forces on the lower part of the splint bones leading to fractures. In the hind limb the outside or lateral splint bone is the most commonly fractured splint bone. This splint bone is often fractured from kicking injuries. Whenever two horses don’t get along back up to each other and fire some kicks, this splint is often the one that gets broken. These injuries are particularly more problematic because of the open wounds that are heavily contaminated with manure, hair and dirt, plus injuries to flexor tendons as well.

Fractured splints near the head of the splint are also very problematic injuries that can be career ending or life threatening at times for horses. These fractures can involve the joints of the carpus or hock leading to septic arthritis, severe lameness and possibly serious instability of the corresponding joint. The rule of thumb for equine veterinaries that are familiar with surgically removing damaged or fractured splint bone is the two-thirds one –third rule. The rule is the lower two-thirds can be safely removed and try to never remove the upper one-third if at all possible. Cases of complete splint bone removal can lead to chronic lameness or worse, catastrophic joint dislocation when the horse tries to get back up from anesthesia. Instead of removal of the fractured upper one-third of the splint, the fracture can in some cases be repaired with plates and screws to maintain a stable upper part of the splint bone.

Other smaller traumatic injuries that can occur to splint bones often come from interference injuries or the horses own feet hitting the inner splint bones when working. These injuries can be avoided rather easily with splint boots placed on the lower limbs whenever working. Some lower limb boots can provide some support to the fetlock and suspensory to avoid distal splint bone fractures but overall these are not going to be very protective.

Some splint bone injuries are rather simple and common problems that a lot of horse owners are familiar with addressing. When it comes to the more serious traumatic fractures and wounds related to splint injuries it is best to contact a veterinarian and get these examined.