Sharp contact between a horse’s hind hoof and foreleg can cause a significant injury, as Dr David Stack MRCVS explains
OVERREACH and strike wounds – known as interference injuries – are often self-inflicted. An overreach typically occurs when a horse steps on the heels of a forelimb with a hind foot, while a strike wound can result from the edge of the hoof or shoe making sharp contact with the fetlock or pastern region.
Similar incidents can occur when there is contact between the limbs of two horses moving in close proximity. Injuries can range from minor grazes and bruises that can be managed with routine first aid, to issues requiring veterinary attention. Some can be severe, leading to referral, hospitalisation and even surgery.
Injury can happen at any time in any horse moving actively – often at moments when the gait becomes uncoordinated, due to a lapse of concentration or a loss of fine motor control due to fatigue. Fatigue-related interference injuries can also occur in heavy ground, where horses tire quickly.
We often see interference issues with wobbler syndrome, where a horse loses the ability to know where his limbs are in space (a sense known as proprioception). This can cause an irregular and uncoordinated stride, leading to frequent overreach injuries.
Strikes or sharp, glancing blows from any other limb tend to result in lacerations, often in a horizontal plane, on the sides or back of the pastern or fetlock. Overreach injuries typically cause irregular skin tears that can penetrate other tissues of the heel, even ripping the coronary band.
Either type of injury can have serious consequences, irrespective of the size of the wound. Like other prey species, horses have very little muscle, fat or loose, connective tissue below the carpus (knee) or tarsus (hock). This evolutionary characteristic improves the speed and efficiency with which a horse moves, by reducing the weight of the lower limb, but leaves vital tissues vulnerable to trauma.
The joints and bones are relatively unprotected, as are the ligaments and cartilage and the cushioning, fluid-filled bursae. Nerves, blood vessels, tendons and tendon sheaths are also at risk.
What’s the damage
IF your horse sustains a strike or overreach injury, contact your vet. Even seemingly innocuous injuries can have serious consequences, including infection of the synovial (joint) fluid.
Wounds that are bleeding profusely should be bandaged carefully but snugly, with direct pressure over the wound. A pressure bandage should not be left in place for more than two to three hours, but can be replaced if blood flow continues.
All other wounds should be rinsed liberally with fresh tap water for five to 10 minutes, and then a clean, dry bandage applied. Avoid touching the site with ungloved fingers and remember that a poultice is not a suitable dressing for a wound.
If the skin is lacerated completely, but nothing deeper, the wound requires cleaning and suturing (stitching). Fresh wounds in the pastern and fetlock regions should be sutured wherever possible, as they are prone to the development of pink granulation tissue known as proud flesh.
The horse is likely to be sedated, and will be nerve-blocked and given pain relief, before suturing. He may then need stable rest for two to three weeks, with bandaging, to minimise movement at the wound site.
Your vet will check that your horse’s vaccination status against tetanus is current and will probably prescribe some pain medications such as phenylbutazone (known as bute). Antimicrobials are administered on a case-by-case basis and may not be necessary.
Surgical solutions
DEEPER wounds require careful veterinary assessment to establish whether any underlying structures have been involved. Investigation may include techniques such as X-rays, ultrasound scanning and synovial fluid sampling, ideally performed in a clinic setting.
Injuries to joints, tendons and synovial structures such as the digital flexor tendon sheath are the most serious and, unfortunately, are common. Those involving the cartilages of the foot and the coronary band are next in terms of severity, while other significant injuries, such as pedal and navicular bone fracture, are seen less often. In extreme cases, the whole heel including the hoof wall can be torn off or avulsed (pulled away). Thankfully, such catastrophic injuries are rare.
Wounds that involve synovial structures are potentially life-threatening, requiring hospitalisation and often surgery. Endoscopic (keyhole) surgery is performed under general anaesthesia to flush the joint or sheath, remove debris and address tendon or cartilage damage, before the wound is cleaned and closed.
Rehabilitation may be lengthy, depending on the severity of the injury and the resulting damage. Injuries of the deeper structures of the foot may need antimicrobials and anti-inflammatories.
Overreaches often result in ragged wounds with deeper ripping and bruising of the tissues. As the tissues are crushed by the weight of the hindquarters and hindlimb bearing down on the heel, these wounds are more prone to infection and potential “breakdown” of any surgical repair.
Infections of the cartilages of the foot can be slow to resolve and frustrating to treat. Overreach injuries that involve the heel bulbs and extend to the coronary band may benefit from a rigid foot cast following wound debridement and suturing, to limit movement.
Injuries to the coronary band can create ongoing issues as the new hoof wall grows from the damaged site, requiring careful farriery.
Reducing the risk
PREVENTION may be impossible, but certain measures will mitigate the risk of interference injuries or reduce their severity if they do occur.
Overreach boots will absorb some of the traumatic energy involved and may offer a degree of protection, as will tendon boots – especially those that extend below the fetlock. Consider the difference between getting stepped on by your horse while wearing sturdy leather boots, compared to flip-flops.
However, the force involved in an interference injury means that a hind hoof may slice right through the boot material. There is also the potential for boots to slip, rub or interfere with a horse’s action, so choose and use them with care.
Good farriery can address gait issues, to minimise interference risk. Hind shoes set further back on the foot and bevelled leading edges of the shoe can also help lessen the damage should an overreach occur.
About the author
Dr David Stack MRCVS is a European board specialist in equine surgery and senior lecturer in the University of Liverpool’s Philip Leverhulme Equine Hospital in Leahurst, where he leads the equine orthopaedic surgery and sports medicine service. Contact: 0151 794 6041, liverpool.ac.uk/equine
Also published in H&H magazine, on sale Thursday 18 March
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