FRACTURES of the long pastern bone, one of the bones forming the fetlock joint, are among the most common fractures affecting the racehorse.

Fractures in the pastern are most commonly sagittal fractures where the bone fractures straight down the centre. Described colloquially as a ‘split pastern’, such fractures typically range from incomplete non-displaced fractures, where the fracture line extends from the fetlock joint downwards into the pastern bone, to complete displaced fractures which extend the whole way through the bone from the fetlock joint into the pastern joint.

On the extreme end of the scale, these fractures can be comminuted or catastrophic when the pastern bone fractures into multiple pieces.

Fractures of normal equine bones are a result of either external or internal forces. External forces are single violent incidents, such as falls, kicks, collisions etc. Pastern fractures are a result of the internal forces of speed and fatigue. Microfractures in the bone structure are a common response to exercise stress. In most cases the body will repair these fractures by reinforcing and remodelling the bone matrix so it can better cope with the repeated stresses of exercise. If bone is subjected to enough force before the body has time to mend these fissures, they can multiply until the bone eventually fails, resulting in a fracture.

Horses with a fractured pastern will present acutely lame when pulling up after fast exercise.

On examination there will be swelling in the fetlock joint and resentment to passive flexion of the joint. They will also resent palpation of the front of the pastern bone.

The first consideration with these horses is to support the leg sufficiently to safely transport them back to the yard for X-rays to be taken.

A multi-layer veterinary bandage, known as a Robert Jones Bandage, is applied to the leg. Once a diagnosis has been confirmed, the horse must then be transported to a specialist surgical facility for repair. It is crucial again that the fracture is adequately supported for transport to prevent any further displacement of the bone.

Repair of the fractured pastern bone is achieved by placing screws to compress the fracture together. Before placing the screws, it is critical that the fracture is accurately realigned and that the joint surface is restored without defect. This is achieved by inserting a camera into the joint which allows the surgeon to visualise the joint surface.

Once the joint surface is aligned, the fracture fragments are held in reduction by a clamp and screws are inserted to compress the fracture.

A cast is then applied to the leg and the horse is recovered in a padded stall. Thanks to advances in expertise and modern repair techniques, the prognosis for these horses returning to training has improved dramatically in recent years and most are now back in full work in under four months.

CASE STUDIES

We recently had two interesting variations of a fractured pastern.

Case A was in a three-year-old gelding who presented with acutely lame left hindleg after routine cantering exercise. On examination, he had filling in his fetlock joint and resentment to flexion of the joint. The leg was bandaged and he was transported back to our veterinary facility for radiographs.

Due to the clinical presentation, we were strongly suspicious that this horse had fractured his pastern but the initial X-rays showed no obvious abnormalities.

Further imaging revealed a transverse fracture of the pastern bone, a very unusual variation of this injury. Fortunately the prognosis is the same as a sagittal fracture and the horse was referred to Newmarket Equine Hospital where he was operated on that night by Ian Wright and Matt Smith.

The surgery went well and he has begun his recuperation. We fully expect to see him back on the track before the end of the year.

The second interesting pastern injury, case B, involved a three-year-old colt who initially presented slightly lame right fore at the end of last year. At the time he had some increased digital pulses which drew our attention to his foot and pastern region, but apart from this there were no obvious localising signs of lameness.

We investigated further with nerve blocks and the results of this investigation confirmed the pastern was the source of lameness.

Initial X-rays of the pastern showed no abnormalities and the horse was rested until sound before we repeated the imaging of the pastern. These X-rays revealed a faint short lytic line in the pastern bone and some new callus formation on the front of the pastern bone, changes which are consistent with a stress fracture.

This horse was initially treated with box rest followed by extended periods of walker exercise and then ridden walk/trotting exercise. He resumed cantering without issue and cantered for a month before pulling out slightly lame on his right fore. He was only lame for a day and X-rays of the pastern showed an old callus on the front of the pastern bone but no distinct fracture line was present on X-ray. The horse was rested for a week and the X-rays were repeated. They again showed no fracture line but there was a very slight increase in the callus on the front of the pastern bone. The horse was referred to Ian Wright at Newmarket Equine Hospital and it was agreed a single screw should be inserted across the old fracture. When the horse was in surgery, he had a CT scan of the pastern which quite clearly shows that the fracture had not fully healed.

Stress fractures can be difficult to diagnose and in a case where there is a suspicion of a stress fracture, the horse should be rested for at least two weeks before repeating X-rays. Stress fractures can be treated successfully with rest alone but it is often safer and ultimately quicker to insert a single screw.

As with all veterinary procedures at Mark Johnston Racing, the cost of in-house diagnostics as well as the specialised surgical treatment and aftercare of the highly skilled team at Newmarket Equine Hospital is covered in the basic daily training rate.

John Martin from Stradbally, Co Laois, graduated from University College Dublin and is in practice at Mark Johnston Racing. This article first appeared in the Kinglsey Klarion, published by Mark Johnston Racing