Splint Bone Fracture

Introduction

Fractures of both the distal and proximal splint bones in are common. Distal splint bone fracture normally occur during exercise in performance horses and proximal fractures are normally the result of trauma.

Distal Splint Bone Fractures

Signalment

It is most commonly seen in horses between four and seven years of age. Injury most commonly occurs during high intensity exercise, therefore performance horses such as thoroughbreds are most commonly affected. It is thought to be caused by the suspensory ligament (which lies adjacent to the splint bone) placing stresses on the bone causing a fracture. Fracture of the distal splint bone occurs during hard exercise when the suspensory ligament snaps back against the comparatively fixed metacarpal or metatarsal bones.

Clinical Signs

The horse may present with a low level of lameness that may only be apparent at faster gaits. Pain or swelling may be apparent on palpation of the fracture. Normally the fracture does not heal by bony union, instead a fibrous tissue or callus forms, which may be visible on clinical exam if the injury is old. This does not tend to cause any long-term problems. Damage to the adjacent suspensory ligament may have occurred at the time of the fracture. This can cause a persistant lameness, and severe damage to the ligament can cause pain, swelling and dropping of the fetlock joint.

Diagnosis

Radiography - simple transverse fractures are most common. There may be reactive change on the adjacent cannon bone and the reactive change around the fracture presents as a soft tissue density. It has been reported that slightly underexposed radiographs produce a clearer image of the splint bone.

Ultrasound examination should also be performed to check for suspensory desmitis.

Treatment

Conservative Therapy

Advantages: no anaesthetic risk and low costs

Disadvantages: prolonged box-rest (2 months) and heavy protective bandages or plaster casting

Early return to exercise can result in excessive callus formation or a repeat fracture.

Surgical Excision

Advantages: simple procedure with shorter recover period, no risk of excessive callus affecting the function of the suspensory ligament

Disadvantages: anaesthetic risk and greater costs

This is the treatment of choice

Prognosis

Prognosis is dependant on the performance level of the horse and the presence of concurrent suspensory desmitis. Prognosis for a non-performance horse with no concurrent suspensory desmitis is good.

Proximal Splint Bone Fractures

Signalment

No breed, sex or age predilection as fracture is normally traumatic in origin. As the trauma is normally caused by a kick or collision, fracture of the lateral splint bone is more common (as it is more exposed than the medial splint bone).

Clinical Signs

The horse will often present markedly lame with both pain and swelling of the area when presented acutely. The level of lameness will decrease over time. There is often a wound overlying the fracture which often exudes a purulent discharge. A sequestrum or osteomyelitis may develop. E.coli and Strep species are the most common bacterial isolates following culture of the discharge.

Diagnosis

Presenting signs of pain, heat and swelling over the proximal splint bone are suggestive of a fracture of the proximal splint bone. Diagnosis should be confirmed with radiography. If a wound is present, then a metal probe may be inserted during radiography to ascertain the direction and extent of the draining tract. Swabs of any discharge from wound should be obtained as aseptically as possible and sent for culture and sensitivity.

Ultrasound examination should also be performed to check for suspensory desmitis.

Treatment

Treatment is dependant on which splint bone is fractured. All fractures except that of the lateral hindlimb splint bone should be treated surgically if possible, as success with conservative treatment is low. With surgical treatment it is only necessary to remove unstable fragments of bone. Additional stabilisation of the remaining bone may be necessary. All infected tissue should be debrided and the wound allowed to heal by second intention.

With fractures of the lateral splint bone of the hindlimb conservative treatment can be attempted as it has reported success in up to 50% of cases.

Concurrent infections should be treated with broad spectrum antibiotics until culture and sensitivity results can guide the treatment.

Prognosis

If infection is appropriately managed and the remaining portion of the proximal splint is stable, the prognosis is fair.

References

May, SA & McIlwraith, CW (1998) Equine Orthopaedics and Rheumatology Self-Assessment Colour Review Manson Publishing Ltd

Kidd, J (2003) Management of Splint Bone Fractures in Horses In Practice 2003 25: 388-395