An overview of serious lower limb wounds

By Chris O’Sullivan BVSc, Dipl VCS, MS, MACVSc, Dip ACVS

Horses are anatomically susceptible to limb wounds that involve bone, ligaments, joints, tendons or tendons sheaths. This is because there is little subcutaneous tissue and no muscle coverage in the horse’s lower limb, making these structures susceptible to being damaged with any full thickness wounds of the skin. Injuries to these structures can be potentially life threatening, particularly if not treated early and appropriately.

Hind limb laceration.

Wound assessment

The age of the wound and its level of contamination will determine the likelihood that an infection will become established. Most wounds that have been present for longer than approximately 6 hours are considered to likely be infected. If the wound has had access to soil, dirty water, faeces or if it involves the gastrointestinal, urinary or respiratory systems it will have been inoculated with a sufficient bacterial load to become infected.

Based on the age, level of contamination and after clinical examination of the wound your veterinarian will assess the infection risk of the wound and also choose the most appropriate treatment, including the choice of appropriate antibiotics for the likely bacteria involved.

Evaluating the wound for involvement of structures

The goal of wound evaluation is to first determine the structures that are involved directly with the wound, something your veterinarian is trained to do. In the meantime the wound should be cleaned and wrapped with a sterile bandage to minimise further contamination. Placing ungloved hands into wounds carries a high risk of introducing a human Staphlococcus. Many of these bacteria will be resistant to multiple antibiotics and are known as the golden Staph approximately 30% of people carry this bacteria on their skin.

Figure 1
The synovial structures of the forelimb with the joints demonstrated in red
and the tendon sheaths in yellow. Wounds that penetrate the skin in these
areas should be suspected to involve a joint or tendon sheath until proven otherwise.

A good working knowledge of anatomy allows assessment of the likely structures involved. The major principal structures that may be involved in lower limb wounds include synovial structures (joints and tendon sheaths), tendons, ligaments or bone.

A variety of diagnostics are available to determine if these structures are involved, including radiography, ultrasonography and arthrocentesis/tenocentesis (sampling and distention of joints or tendon sheaths).

In some cases multiple structures can be involved.

Joint or tendon sheath involvement

Joints or tendon sheaths are filled with synovial fluid that lubricates movement of the joint or tendon. The synovial fluid is ideal for bacteria to grow in and the body is poor at fighting infection in these structures. Once joints are infected the inflammation causes ongoing damage to the cartilage and thickening of the joint capsule and lining. Infections of joints and tendon sheaths are life threatening to the horse and expensive to resolve. The quicker that any joint or tendon sheath involvement with a wound is diagnosed and treated the better the outcome will be. Treating most joint infections with antibiotics alone is insufficient, and horses with wounds involving joints are best treated in a referral hospital setting. Typical treatment includes surgical debridement and flushing combined with appropriate broad spectrum antibiotics and ongoing wound care.

Tendon or ligament involvement

The major tendons and ligaments supporting the fetlock and foot include the deep digital flexor tendon, superficial digital flexor tendon and the suspensory apparatus. These structures are on the back side of the limb. Severe damage or complete laceration of any of these or a combination of these will result in either loss of fetlock or foot support. The extensor tendons are on the front half of the limb and they help bring the foot and fetlock forward while walking. Severe damage or complete laceration results in an inability to bring the foot forward. These horses will tend to walk on the front of the fetlock.

Similar to joints, lacerations of tendons should be assessed as quickly as possible. Often the horses may require referral to a hospital setting since treatment can include; surgical debridement/repair, casting or splinting combined with broad spectrum antibiotics, bandaging and wound care.

Bone involvement

Your veterinarian will typically assess injuries that involve the bone with radiographs of the area. Foreign bodies should ideally be left in place for the veterinarian to assess and remove. The only case where a foreign body should be removed is when it cannot be stabilised and is likely to be driven deeper into the wound by movement.

With the foreign body in place a more accurate assessment can be made regarding what structures are involved before the object is removed.

Figure 2 A and B
A horse with a metal foreign body left in place which allowed a radiograph providing an accurate assessment of structures
that could be damaged. In this case the horse was lucky and managed to miss all the vital synovial structures in the
area including; navicular bursa, coffin joint and digital tendon sheath.

Many wounds that involve bone may go on and form an infected piece of bone 2–3 weeks after the injury. This is known as bone sequestrum formation. These cases typically require surgical debridement and broadspectrum antibiotics.

FIRST AID OF LIMB WOUNDS FOR HORSE OWNERS

Step1. Consider the wound assessment based on the above information and describe the wound including (position, duration and contamination) accurately to your veterinarian.

Step 2. Clean the wound and remove contamination.

The best option to clean a wound is sterile saline. Avoid most topical wound treatment or disinfectants since these typically will damage tissues (including iodine, peroxide, yellow lotion, ointments etc). Until the wound has been assessed by your veterinarian particularly if the wound is able to be sutured applying any of the above will damage the exposed tissues and increase the likelihood of any wound repair failing. They may be indicated in infected wounds or for cleaning contaminated wounds but this is a judgement call best left to the veterinarian.

In extremely contamintated wounds the garden hose and tap water could be used to remove dirt and debris from the wound. Saline is a better choice if available.

Step 3. Bandage the wound.

Wear gloves when cleaning or applying bandages to the wound. Ideally a sterile bandage pack with sterile gauze swabs soaked in saline to make a ‘wet to dry’ bandage. This is a cheap and effective bandage when bandaging any fresh or contaminated limb wounds. This bandage acts to preserve the exposed tissue and also removes dirt or contaminants from the wound. Cotton wool should be avoided directly over the wound but can be used as the support layer provided the wound is not directly covered. Combine bandage is often an easier to manage option.

 Figure 3
Basic first aid kit for cuts to the lower limb. Including sterile
saline, gloves, gauze swabs and combine bandage.

Chris O’Sullivan BVSc, Dipl VCS, MS, MACVSc, Dip ACVS

Chris is a registered specialist equine surgeon at Randwick Equine Centre in Sydney. His interests include: performance horse lameness evaluation, diagnostic imaging (Digital radiography, ultrasonography and scintigraphy), orthopaedic and soft tissue surgery. Chris has written numerous journal articles, proceedings and book chapters.