Equine field surgery: Head and neck surgery (Proceedings)

Head & Neck Surgeries

     Lip lacerations

     • Intra-oral wire fixation of rostral mandibular and maxillary fractures

     • Tracheotomy

     • Tracheostomy

     • Staphylectomy (Partial resection of the soft palate)

     • Sternohyoideus myectomy and sternothyroideus tenectomy

     • Modified Forssell's Operation for Cribbing

Rostral Mandibular & Maxillary Fractures

     • Indications    – Fractures of the rostral mandible and premaxilla/incisive bones that can be repaired with wire or acrylic.

     • Equipment    – 16 or 18 gauge stainless steel wire

                            – needle holders or pliers

                            – wire cutters

                            – Acrylic

                            – Drill

     • Ideally, a nasotracheal tube is placed during the surgery

     Anatomy

     • The structures potentially involved are:

          – premaxilla (incisive bone)

          – incisive part of the mandible

          – Incisors

          – canine teeth

          – mental and infra-orbital nerves

          – the intermandibular synchondrosis

          – permanent tooth roots

Surgical procedure

     • Thorough debridement of the fracture site

     • Maintain loose deciduous teeth if possible

     • "freshen" the edges of exposed bone with a bone curette

     • Fractures that involve 4 or fewer incisors can generally be repaired with cerclage wire fixation techniques

     • A minimum of two loops

     • wires should engage a minimum of three teeth

     • Ideally, there should be overlap

     • A 14-16-gauge hypodermic needle or 2.0 mm drill hole used as a guide

     • wires are bent flat +/- covered with acrylic

     • When necessary, additional stabilization can be achieved by securing the corner incisor(s) to the exposed canine or second premolar

Post-operative management

     • Generally no problems eating, but a pelleted feed or gruel may be of benefit

     • Rinse mouth at least 2X/day for the first week

     • Consider antibiotic therapy

     • NSAIDs are typically administered for 1-3 days

     • No grazing for 2-4 weeks

     • Check wires regularly for breakage

     Complications • purulent drainage

     • bone sequestration

     • septic osteitis

     • difficult mastication

     • unusual incisor eruption

     • wire loosening

     • fixation failure

Tracheotomy

     Indications

     • to establish an emergency airway due to an upper airway obstruction

     • to relieve nasal or laryngeal inflammation

     • route for endotracheal intubation for general anesthesia

     • to "rest" an inflamed upper respiratory tract

     Anatomy • paired sternomandibularis and sternothyrohyoideus

     • trachea

     Surgical procedure

     • A 6-8 cm ventral midline incision

     • Incise subcutaneous tissues

     • Separate paired sternothyrohyoideus mm

     • Minimize blunt dissection to decrease subcutaneous emphysema and seroma

     • Tracheal rings identified and a transverse stab incision is made between two rings

     • The incision is extended from midline 1-2 cm in both directions (~1/3 the circumference of the lumen)

     • A tracheotomy tube is then placed.

Post-operative management

     • Tracheotomy tubes require almost continuous monitoring and management

     • Clean tubes & sites at least daily

     • Exudate and blood clots should be removed with a dry, sterile sponge and the skin surrounding the site should be cleaned

     • Extra tubes should be immediately available

     • The wound is allowed to heal by second intention with daily cleaning

     • Petroleum jelly to prevent scalding

     • Healing is generally complete in 2-3 weeks

     Complications - Subcutaneous emphysema, Hemorrhage, Inflammation

     Rare complications - Tracheal obstruction or stricture, Granulomas, Chondromas, Pneumothorax

Tracheostomy

     • Indications – any permanent disorder of the larynx and upper trachea in which airflow is impaired

     • Equipment – No special equipment is required. Self-retaining retractors are desirable

     Anatomy • paired sternomandibularis, sternothyrohyoideus, omohyoideus

     • ventral trachea.

     Surgical Procedure

     • A 10-12 cm ventral midline incision

     • Avoid previous tracheotomy site

     • The cutaneous colli and the paired sternohyoideus muscles separated on midline and retracted laterally to expose a section of 3-4 tracheal rings

     • Sections of the paired sternohyoideus muscles may be removed to minimize the tension on the tracheal mucosa/skin junction during subsequent closure.

     • A midline and 2 paramedian incisions are made in the exposed tracheal rings

     • avoid incising tracheal mucosa

     • rectangular segments dissected free of mucosa

     • mucosa incised in a double-Y pattern

     • Stay sutures are placed to align and prevent retraction of the mucosa

     • mucosa is then apposed to the skin using a simple interrupted pattern

     • close all gaps between mucosal edges or between mucosa and skin

Post-operative management

     • stall rest 2 weeks with controlled hand walking only

     • clean surgery site 1-2 times daily until the sutures are removed and once daily indefinitely

     • anti-inflammatory and antibiotic therapy recommended for 1-2 days

     • sutures are removed in 10-14 days

     Complications

     • partial dehiscence of the tracheal mucosa-skin suture line

     • excessive inflammation

     • granulation tissue formation

     • stricture

     • skin growth or apposition over the tracheostomy site

     • coughing

     • Long term complications include coughing during exercise, stridor, and exercise induced dyspnea

Staphylectomy (Partial resection of the soft palate)

     • Indications

          – intermittent or permanent dorsal displacement of the soft palate (DDSP)

          – The procedure is often used in conjunction with a sternothyrohyoideus myectomy and/or epiglottic augmentation

     Equipment   • Gelpi or Weitlaner self-retaining retractor

     • Allis tissue forceps

     • long-handled or right-angle scissors

     • curved sponge forceps

     Anatomy     • performed through a laryngotomy

     • Important landmarks

                                   – paired sternohyoideus muscles

                         – v-shaped cricothyroid membrane which lies between the thyroid and cricoid cartilages.

Surgical Procedure

     • ventral midline laryngotomy through the cricothyroid membrane

     • 8-10 cm incision is made starting at the cranial border of the thyroid cartilage and extending caudal to the first tracheal ring

     • The paired sternohyoideus muscles are identified and separated longitudinally the length of the incision

     • A self-retaining retractor is inserted between the muscle bellies to expose the fascia overlying the cricothyroid membrane

     • The caudal border of the thyroid cartilage and the cranial border of the cricoid cartilage are identified

     • self-retaining retractors are then repositioned within the larynx

     • Free edge of soft palate grasped on midline with Allis tissue forceps

     • Tissue removed is either crescent shaped; approximately 3-4 cm long, 6-10 mm wide at the center and tapered to a point on either ends, or a small equilateral triangle of tissue is removed with each side measuring ~8-10 mm.

     • Laryngotomy incision left to heal by 2nd intention

Post-operative management

     • Broad spectrum antibiotics and NSAIDS are administered for 2-5 days

     • The incision site is cleaned at least once daily with moistened sterile sponges

     • Petroleum jelly is applied around the incision to minimize scalding from the anticipated drainage

     • Stall rest with controlled hand-walking only for 2 weeks to allow the inflammation of the soft palate to subside. The horse may then return to its normal activity.

     Complications • recurrence

     • development of granulation tissue at the edge of the palate

     • dysphagia if too much of the caudal palate is removed

Sternothyrohyoideus Myectomy and Sternothyroideus Tenectomy

     • Indications    – Intermittent (DDSP) which causes temporary exercise intolerance

     • Equipment    – Rochester-Carmalt forceps, Straight Péan forceps with longitudinal serrations, an angiotribe or similar instrument

                            – Penrose drain may be used in the myectomy procedure.

                            – A spay hook may be useful for the sternothyroideus tenectomy procedure.

     Surgical Procedure

     • The section of muscle removed varies:

          – from very rostral

          – to as far caudal as the separation of the sternomandibularis mm

     Post-operative care

     • antibiotics and NSAIDs

     • towel stent or neck bandage for 2-4 days after surgery

          – protects the wound

          – provides counter pressure to reduce edema, hematoma, and seroma formation

     • stall rest for at least 1 week with controlled hand walking followed by return to normal exercise over the next 2-3 weeks

     • Penrose drain removed in 2-3 days.

     Complications • seroma or hematoma formation

     • incisional infections

     • incisional dehiscence

     • reuniting of the severed ends of the muscles through scar formation

Modified Forssell's Operation for Cribbing

     • Indications – The primary indication for this procedure is modification of cribbing behavior when non-surgical methods fail

     • Special Equipment   – Large Rochester-Carmalt, Straight Péan or angiotribe forceps

                                      – Penrose drain

     Anatomy

     • The ventral branch of the spinal accessory nerve is located on the dorsomedial aspect of the sternomandibularis and enters the muscle about 5 cm from the muscle tendon junction

     Surgical Procedure

     • A 30 cm ventral midline incision is made starting 2 cm rostral to the larynx at the basihyoid bone and extending caudally.

     • Dissect between the omohyoideus and the sternomandibularis to expose the medial aspect of the sternomandibularis 5 cm caudal to the musculotendinous junction.

     • Contraction of the sternomandibularis muscle and flexion of the head is observed when the nerve is pinched with hemostats

     • A 5-10 cm section of nerve is exposed using blunt dissection and removed

     • A sternothyroideus tenectomy and sternohyoideus myectomy is performed as previously described

     • Penrose drain +/- towel stent may inhibit post-op swelling and seroma formation

Post-operative management

     • stall rest with controlled hand walking for at least 1 week

     • return to normal exercise over the next 2-3 weeks

     • Antibiotic therapy for 24 hours after drain removal

     • Phenylbutazone - 2-3 days

     • Stent removed ? 2 days

     • Penrose drain removed 2-5 days

     Complications • failure to resolve the behavioral abnormality

     • seroma or hematoma formation

     • incisional infections

     • incisional dehiscence

References

Adams SB, Fessler JF, editors: Atlas of Equine Surgery, Philadelphia, 2000, WB Saunders Co.

Auer JA, Stick JA, editors: Equine Surgery, 3rd ed. Philadelphia, 2006, WB Saunders Co.

McIlwraith CW, Robertson JT, Turner AS, editors: Equine Surgery: Advanced Techniques, 2nd ed. Ames, IA, 1998, Blackwell Publishing.

McIlwraith CW, Robertson JT, Turner AS, editors: Equine Surgery, 2nd ed. Philadelphia, 1998, Lippincott Williams & Wilkins.

Wilson DA, Kramer J, Constantinescu GM, Branson KR, editors. Manual of Equine Field Surgery, St Louis, 2006, Elsevier.