The horse is prone to traumatic injury of its head. Environmental conditions, a heightened flight response, and equipment
and tack used for the horse all contribute to injury occurrence. Despite the impressive bleeding and often very concerned
owner that accompanies initial head injury there are few incidents that are life threatening to the horse; depression fractures
of the cranium resulting in cerebral trauma would be one exception. However, an injury can have a significant impact on the
horse's athletic performance or appearance, and consequent value to its owner. Wounds that are left to heal by second intention
may appear cosmetically unacceptable due to scar contracture or tissue loss resulting in misshapen anatomy. This paper will
provide an overview of common facial injuries amendable to surgical repair, with the exception of eyelid lacerations. Lip
trauma is covered in the "Managing oral trauma and foreign bodies" proceeding.
General Principles
Successful surgery of the head is facilitated by a rigorous blood supply and close attention to surgical technique. There
is often limited soft tissue to work with and wounds are contaminated at initial injury and when paranasal sinuses or nasal
passages are penetrated.
Many surgical procedures of the head can be performed in the standing, sedated horse with complementary use of regional anesthesia.
The horse can be sedated with detomidine (0.01 – 0.02 mg/kg IV, or 0.02-0.04 mg/kg IM, or 0.06 mg/kg PO) and butorphanol tartrate
(0.01 – 0.03 mg/kg, IV) and re-sedated during surgery, if necessary, with additional, smaller amounts of the drugs. Constant-rate
infusions (CRI) of detomidine and butorphanol can be administered to provide a prolonged, constant state of sedation, after
first sedating the horse with a bolus dose of detomidine and butorphanol. Numerous published concentrations and flow rates
of drugs in terms of micrograms of drug per kilogram per minute or drops of a mixture per kilogram per second are available
and the reader is encouraged to review that material (eg Goodrich et al, AAEP Proceedings, 2004). A typical practical protocol
might be 10 mg of detomidine and 5-10 mg of butorphanol mixed into a 250 ml bag of sterile saline. Once the horse is sedate
from its initial bolus doses, the CRI mixture is administered to effect via a standard IV administration set (15 drops/ml)
to maintain the initial sedation and adjusted as necessary. One to two bags of this mixture may be used over 1-3 hours, depending
on the degree of sedation desired. Facial (maxillary) structures can be desensitized by administering an infraorbital or maxillary
nerve block, and the lower jaw can be desensitized by administering a mental or mandibular nerve block (these nerve blocks
are covered in detail in the "Regional anesthesia of the equine head" proceeding). Topical infusion of local anesthetic subcutaneously
around the wound is often still required for complete analgesia. More complicated, extensive trauma repairs, or particularly
head shy, fractious horses are best placed under general anesthesia for meticulous surgery.
Surgical preparation of wounds of the head should be confined to the use of povidine-iodine based solutions or scrub, especially
when working around or at the eye, and lavage or rinsing with physiologic sterile saline solution. The use of antimicrobial
and nonsteroidal anti-inflammatory drugs follows normal principles for wound management. Antimicrobials are unlikely necessary
for successful healing of clean sutured lacerations without deeper structure involvement. Assurance of adequate tetanus prophylaxis
is routine. Many facial lacerations are amenable to a pressure bandage applied around the head for compression and protection.
Nostrils
Nostril laceration repair is typically facilitated by minimal contamination and primary closure without excessive tension.
Motion at the repair site is a concern, but perhaps less so than for lip lacerations. Debridement should be meticulous and
spare all viable tissue. Undermining of the freshened wound margins 5-10 mm reduces motion on the skin layers. A three layer
closure is recommended. The internal nostril skin is closed with simple continuous absorbable 3-0 monofilament suture. Vertical
mattress size 0 non-absorbable sutures are then placed through the nostril musculature and may be tied over stents (a Penrose
drain works well as a soft stent). The external skin is apposed with simple interrupted 2-0 monofilament non-absorbable sutures.
Protection of the surgery site by muzzling or cross tying the horse should be considered.
