Condylar fractures are the most common long bone fractures in horses. They occur at the bottom of cannon bone where it meets the fetlock joint. They most typically occur in thoroughbred racehorses but are also prevalent in endurance horses and occasionally occur in three-day event horses.

These fractures occur via two distinct mechanisms:

Fracture at Supraphysiological Loads/Single Traumatic Event

In this instance the bone breaks when it is suddenly loaded beyond its normal failure point. Examples include getting the lower limb trapped in a hole or beneath a fixed object or being kicked by another horse. This is an uncommon presentation.

Fracture at Normal Physiological Loads/Repetitive Strain Injury

This is by far the most common mechanism by which condylar fractures occur. They usually occur at high speeds when the bone is subjected to the greatest load. Repetitive strain results in the bone becoming stiffer and more brittle, compromising its structural integrity. With continued stress, microfractures form in the bone. Under normal circumstances, the rate of microfracture formation equals the rate of bone healing and repair. However, when the balance is shifted in favour of microfracture, they may coalesce and result in a fracture that we can see on a radiograph known as a condylar fracture.

Lateral Condylar Fractures

Lateral condylar fractures occur on the outside of the lower cannon bone and account for approximately 85% of all condylar fractures. They typically travel a short distance vertically up the cannon bone from the fetlock joint before they begin to course towards the outside surface of the bone. If the fracture line is not continuous from the joint surface of the fetlock to the outside of the cannon bone, it is regarded as an incomplete condylar fracture (Figure 1A). Conversely, if the fracture extends the entire way from the joint surface to the outside of the bone, it is regarded as a complete condylar fracture. In some circumstances, complete lateral condylar fractures may become detached from the main body of the cannon bone resulting in a step defect at the joint surface of the fetlock. These are displaced lateral condylar fractures (Figure 1B).

Medial Condylar Fractures

Medial condylar fractures occur on the inside of the cannon bone. This type of condylar fracture has a distinctly different and much more life-threatening configuration. The fracture line initiates at the fetlock joint and spirals vertically towards the knee in the forelimb or hock in the hindlimb, and frequently has smaller fissure lines that are not visible on radiographs (Figure 2A). These fractures may result in the cannon bone breaking into numerous pieces with minimal additional stress.

Diagnosis

Diagnosis is not difficult. Horses display varying degrees of lameness either immediately or soon after the inciting event and usually become more comfortable over the ensuing days. It is therefore vital that the injury is not just brushed off as a sprain, with the horse placed back in work. Medial condylar fractures tend to be the most painful due to the longer fracture lines. Swelling occurs around the fracture and in the fetlock joint and horses resent flexion of the fetlock. Radiographs provide a definitive diagnosis.

Treatment and Prognosis

Non-displaced lateral condylar fractures may be treated conservatively with a prolonged period of box rest. However, I have encountered numerous cases that were treated conservatively for up to 18 months and still failed to heal. For this reason it is my opinion that a short surgical procedure using screws to compress the fracture is a superior treatment option (Figure 1C). This option often ends up being more economical as the fracture heals faster and the horse can return to training sooner (three-four months) than if box rest alone is elected. Additionally, the presence of a screw prevents the horse from re-fracturing the bone at that location in the future. Surgery may be performed under general anesthesia or standing with the horse sedated. Non-displaced lateral condylar fractures carry an excellent prognosis of 80-90% return to previous performance.

Repair

Displaced lateral condylar fractures should be repaired using screws. The displaced fragment must be realigned with the articular surface at the fetlock removing any step defect in the cartilage allowing the fetlock to articulate freely. I place a small camera into the joint to visualise the cartilage coming back into alignment and then place screws through 5mm skin incisions as normal. Due to the more severe damage to the cartilage with this type of fracture, the prognosis is approximately 50%. Conservative treatment of displaced lateral condylar fractures offers little chance of the horse returning to racing due to the severe debilitating arthritis. Most can however become paddock sound.

Medial condylar fractures are an emergency. They can be successfully treated conservatively using a cast with an extended period of box rest, however this does carry the risk of the bone breaking into many pieces up to eight weeks after the initial incident. If this occurs these cases are rarely salvageable.

For this reason, I prefer to treat medial condylar fractures using a bone plate and screws. The plate can easily be removed standing after 60 days. Some medial condylar fractures can be repaired standing using screws alone, however, this technique is not considered as effective at reducing the risk of catastrophic fracture as a bone plate. Surgical treatment of medial condylar fractures offers a 70% prognosis.

Recently there has been a drive to identify “at risk” horses before a fracture occurs. Once identified these horses can be treated with rest alone or, if recurrent, by drilling one-two small holes in the end of the cannon bone. For the unlucky few that do sustain a fracture, advances in modern veterinary surgery have allowed the majority of horses to return to their intended function.

Turlough McNally MVB Dip ACVS Dip ECVS MRCVS is a member of Veterinary Ireland Equine Group and a specialist in equine surgery at Anglesey Lodge Equine Hospital, The Curragh, Co Kildare

Email: hq@vetireland.ie

Telephone: 01-4577976