'Innocuous' lower leg injuries can end career

Injuries of the lower leg are very common in horses. While they are often seen as innocuous, if not properly taken care of, they can become career ending. A good understanding of the anatomy of the area is very important.

Heel bulb laceration prior to slipper cast application.

Heel bulb lacerations

Heel bulb lacerations are one of the most common lacerations an equine practitioner will face. In most cases, the lacerations involve only the skin, but in some cases, the seemingly innocuous laceration can be life threatening. The only way to accurately determine the extent of an injury is to carefully clean the laceration and explore the wound. In many cases, the horse will resent the practitioner working on the injured area. While systemic sedation can cause unwanted side effects such as recumbency in cases of severe hypovolemia secondary to blood loss, local desensitization from nerve blocks generally will allow a complete examination.

The wound should be filled with some type of water-soluble gel and then clipped. The gel will trap the pieces of hair that are cut off, keeping them from falling into the wound and providing easier cleaning. The lube and hair can be washed out with water or saline. Much research has been performed on the best type of antiseptic to use, and as of this writing, it would seem that chlorhexidine (1:40 dilution) would be the antiseptic of choice. If the wound is grossly contaminated or even infected, it is most important to clean the wound and worry about the cells later. Wound cleansers are surfactants and offer very effective wound cleaning without the negative side effects that the antiseptics cause such as cell death, but will not kill bacteria.

Once the wound has been completely clipped and cleaned it should be carefully explored. Generally this requires digital palpation. Wear sterile gloves to reduce the likelihood of iatrogenic contamination. The wound should be examined in both weight bearing and non-weight bearing positions. It is at times difficult to determine what structures are involved while the horse is weight bearing.

Depending on the location of the laceration, the associated synovial structures should be examined to ascertain their involvement. The digital tendon sheath, pastern joint, and coffin joint can all be affected when a horse has a laceration in the pastern region. The digital tendon sheath lies just under the skin in the pastern region and can easily be involved in a laceration. The coffin and pastern joints are deeper structures and are less likely to be involved. Digital palpation of the synovial structures is helpful in determining the extent of involvement, but in most cases, distension of the synovial structure will be the most helpful diagnostic test. A site remote from the laceration is clipped (generally at the time of initial wound preparation in anticipation for checking the synovial structures) and aseptically prepared. It is imperative that the anatomy of the area is well understood in order to accurately determine synovial involvement. A needle is placed into the suspect synovial structure. If possible, synovial fluid is collected and set aside for analysis and culture. A large volume of sterile saline is injected into the synovial structure. If saline leaks from the laceration site, synovial involvement is confirmed. If the wound is present for a longer period of time, the synovial membrane may have healed closed, and saline will not escape.

If a synovial structure is involved, the treatment must be very aggressive to prevent a career-ending septic arthritis or tenosynovitis. Generally this will involve a thorough lavage of the structure with a large volume of sterile saline. DMSO can be added to the saline to provide antibacterial and free radical scavenging effects. Local antibiotics can be instilled after the lavage. The horse should be started on broad-spectrum systemic antibiotics until culture and sensitivity is completed. In long-standing cases, a synovectomy coupled with fibrin removal should be performed to allow more expedient clearing of the contamination or infection. Local intravenous perfusion of antibiotics after tourniquet application has been shown to greatly enhance the effectiveness of antibiotic therapy in cases of severe contamination. Once the contamination/infection has been brought under control, the wound can be treated similarly to those wounds that do not involve synovial structures.

Hoof wall avulsion before and after hoof wall removal.

If the wounds are grossly contaminated it is advisable to clean and debride the wound for three to five days prior to suturing or casting. Hypertonic saline dressings can be used in combination to stimulate autolytic debridement and provide protection from bacterial penetration respectively. (See related article on p. 7.) If the wound has minimal contamination, it can often be at least partially sutured, and a slipper cast applied. Systemic antibiotics use is determined by clinical impression. An anti-microbial dressing can be placed over the wound to prevent bacterial penetration, and will, in all likelihood, reduce bacterial numbers at the wound site. The slipper cast allows the wound exudate to remain in contact with the wound bed, providing for moist wound healing. Slipper casts have the advantage over longer casts in that they rarely lead to cast sores, and horses tend to tolerate them better. The casts are generally removed in three weeks and the wound will often be completely healed. After cast removal, the leg should be bandaged for two weeks to provide protection of the newly healed wound.

Hoof wall avulsions

Hoof wall avulsions can be very dramatic injuries, but in spite of the outward appearance can often be treated with a very positive end result. As with pastern lacerations, it is important to clean and examine the wound to determine what, if any, deeper structures are involved. Radiographs are often useful to rule out coffin bone or collateral ligament involvement. In most cases, the avulsed hoof wall is removed to allow better apposition of the coronary band. The skin can be apposed to attempt healing of the corium, but oftentimes the tissue will not heal back in place. Standard moist wound healing techniques should be used until the wound has healed.

Sub-solar abscesses

Sub-solar abscesses are a common cause of severe lameness in the horse. Horses with abscesses will often present non-weight-bearing lame on the affected foot. A thorough physical exam will differentiate between a sub-solar abscess and a fracture as the source of the lameness prior to an extensive work-up and local anesthesia. Hoof tester examination will generally isolate the lameness to the foot. Once isolated, the foot is "blocked" with local anesthetic and the hoof is pared out to allow adequate ventral drainage. The foot can be soaked in a dilute povidone iodine solution to clean the area of the abscess. The foot should be bandaged between soakings to minimize continued contamination. An anti-microbial dressing can be used to improve bacterial elimination as well as to prevent bacterial penetration through the bandage. Once the abscess has granulated in and hardened, the bandage can be left off. Long-standing cases should be radiographed to rule out coffin bone involvement. If present, extensive curettage will be necessary to eliminate infection. Systemic antibiotics are used only in cases with deep-seated infection, or involvement of the soft tissues proximal to the coronary band.

Gravel

Gravel is a condition similar to a sub-solar abscess, where the abscess "breaks out" above the coronary band. The name comes from the days of the carthorses when the streets were made of gravel. The small stones would penetrate into the sole, form an abscess, and then as the abscess "broke out" of the coronary band, small stones would be present, hence the name "gravel". These cases should be treated similarly to sub-solar abscesses, trying to provide ventral drainage and curettage of the abscess track. Systemic antibiotics are more commonly used since the infection has moved proximal to the coronary band. Bandaging, soaking, and other aftercare are the same as for sub-solar abscesses.