Download Injuries of the Head

Injuries of the Head
Jim Schumacher
University of Tennessee
Wounds of the head involving only skin usually heal rapidly. They are slow to become
infected because of the excellent blood supply of the head, which causes bacteria in a head
wound to multiply slowly to the critical, infective concentration of 105 organisms per gram of
tissue. Many cutaneous wounds of the head can be sutured successfully days after injury.
Wounds of the head of horses are often more than just cutaneous, however, and are accompanied
by serious damage to deep structures. An injury to the head may be accompanied by restricted
movement of air, ocular damage, neurologic deficits, or hypovolemia from severe hemorrhage.
Fracture of the facial bones
A horse that has suffered crushing of the nasal and maxillary bones may require
temporary tracheotomy because this injury is also frequently accompanied by crushing of the
nasal septum and conchae, resulting in restriction of movement of air through the nasal cavities.
A healed fracture of one or both nasal bones is commonly accompanied by thickening of the
nasal septum, and so, the status of the nasal septum of a horse that has suffered a fracture of a
nasal bone should be evaluated after sufficient time has elapsed for the fracture to have healed.
The owner should be forewarned, at the time of injury, that the horse may later require resection
of its nasal septum.
A fracture of a facial bone can usually be identified and assessed more accurately by
visual inspection and palpation than by radiographic examination of the skull, especially if the
injury has just occurred. Fracture of a facial bone can be easily overlooked during radiographic
examination of the head, because multiple radiographic projections are often required to observe
the facture. A depression fracture that may be obvious at the time of injury may become less
obvious when a hematoma forms between the fracture fragment and the periosteum from which
the bone has separated, temporarily restoring normal contour to the damaged area. The owner
becomes aware of the fracture when the hematoma resolves to reveal the depression, by which
time the fracture may be difficult to reduce.
A depression fracture of a facial bone overlying the paranasal sinuses can often be
reduced with a bone hook or a finger after positioning the hook or finger beneath the fracture
fragment through a trephine hole created into paranasal sinuses adjacent to the fracture.
Interdigitation of the reduced fragments creates stability. The straight incision created to expose
bone for trephination is closed with staples. Another method of elevating a fracture fragment is
to drill a hole into the fragment with a drill bit or a Steinmann pin and then to insert small
Kirshner wire with a 90o angle into the hole to elevate the fragment. If the fracture cannot be
reduced using either of these methods, the fracture site should be exposed through a large
cutaneous flap. Reduced fragments that are not stable can be stabilized with sutures or one or
more reconstruction plates.
A fracture of a supraorbital process can usually be confirmed by inserting a gloved and
lubricated finger over the dorsum of the globe to palpate the ventral surface of the supraorbital
process. A depression fracture of the supraorbital process can be reduced, usually with the horse
sedated, by using a bone hook positioned in the conjunctival fornix beneath the fragment.
Anesthetizing the supraorbital and auriculopalpebral nerves may facilitate the procedure. The
reduced fracture is usually stable. Fluorescein dye placed in the conjunctival sac can be used to
evaluate the integrity of the lacrimal and nasolacrimal ducts. Discharge of dye from the nasal
opening of the nasolacrimal duct indicates that the ducts are intact.
A small, full-thickness defect into a paranasal sinus or nasal cavity caused by a
comminuted fracture may heal by contraction and epithelialization, but when the defect is large,
the skin heals to the mucosal layer of the sinus or nasal cavity, forming a completely
epithelialized surface that prevents the wound from closing. A full-thickness defect into a frontal
sinus can be closed using a temporalis muscle transposition flap, and defect into a maxillary
sinus can be repaired using a levator labii superioris muscle transposition flap. Full-thickness
defects anywhere over the paranasal sinuses or nasal cavities can be closed using periosteal flaps.
The cambium layer of the transposed periosteum forms new bone over the defect. Rotational or
free skin grafts are used to cover the transposed muscle or periosteum.
Lacerations of the lip
Full-thickness lacerations of the lip rarely become infected because of the good blood
supply to the lip and can be repaired at any time. Sutured lacerations of the lip frequently dehisce
because of tension caused by movement, however, unless they are anchored to the. After the fullthickness laceration to a lip is closed in 3 layers, it should be anchored to the mandible or
premaxilla with stainless steel wire. To anchor the lip, tunnels are drilled through the lip and the
bone at the gingival margin of the incisors with a small Steinmann pin or a 3.2 mm drill bit
mounted in a handchuck. The pin enters the oral cavity slightly caudal to the incisors. Eighteengauge wire is passed through the tunnels in the lip and bone in a horizontal mattress pattern. A
button or piece of rubber or plastic tubing is placed beneath each horizontal arm of the suture to
prevent the wire from cutting through the skin and mucosa.
Lacerations of the tongue
Lacerations of the tongue may occur during recovery from general anesthesia, but are
most are caused by the horse rearing backwards, with a bit in its mouth, while tied with the reins.
Most tongue lacerations are located in the free portion of the tongue at right angles to the
tongue’s long axis. They extend dorsal to ventral through the tongue, often leaving only the
ventral mucosa intact. If left to heal by second intention, the laceration eventually becomes
covered with mucosa, but a gap at the site of laceration persists. Regardless, the function of the
tongue is usually preserved. Partial amputation of the tongue (i.e., partial glossectomy) at or
rostral to the attachment of the frenulum seems to cause no impairment to the function of the
tongue. Acute lacerations can be sutured with the horse sedated and the tongue desensitized by
infiltrating the margin of the laceration with local anesthetic solution. The laceration is debrided
and cleansed, and the wound is closed, from ventral to dorsal, with successive rows of simple
interrupted, synthetic, absorbable sutures. The lingual mucosa is closed with absorbable, vertical
mattress sutures, and the sutured laceration is spanned with vertical or horizontal mattress
tension sutures. Some dehiscence should be expected.
Lacerations of the ear
An ear with a full-thickness laceration left unsutured tends to curl, worsening an already
obvious disfigurement. Full-thickness lacerations of the ear are usually closed in 2 layers, one
layer being the skin on the concave surface of the ear and the other layer being the skin on
convex surface. The cartilage is not penetrated with the suture. Splinting the ear with rolled
gauze or x-ray paper, placed on the concave surface of the ear, may be helpful in diminishing the
likelihood of dehiscence. The rolled gauze is maintained with elastic, adhesive tape, and x-ray
paper is maintained with sutures placed through the full-thickness of the ear.
A large, cutaneous, avulsion wound on either the concave or convex surface of the ear
that cannot be sutured should be covered with a skin graft because a wound left open to heal by
second intention may deform the ear when the wound contracts. Acceptance of the graft on a
fresh wound halts contraction, but contraction of a granulating wound may not be diminished,
even if the graft is accepted, and so, a long period of splintage may be required to prevent
deformity.
Lacerations of the eyelid
Wounds of the eyelid should be closed primary, even when contaminated, because
scaring associated with healing by secondary intention is unsightly and often results in
complications such as chronic epiphora, chronic conjunctivitis, keratitis from corneal exposure
or abrasion, and entropion or ectropion. Fortunately, lacerations of the eyelid, even contaminated
lacerations, rarely become infected because of the good blood supply to the eyelid.
Only nonviable tissue should be excised, and the edges of the laceration should not be
trimmed. The first suture should approximate the lid margin and is the most important suture in
the repair. This suture is placed in a figure-of –eight fashion (i.e., an inverted cruciate suture) or
as a mattress suture using 4-0 or 5-0 soft, absorbable or non-absorbable suture. The suture
pierces the meibomian glands on the margin of the lid and the tarsal plate. The conjunctiva need
not be sutured unless it is avulsed from the stroma of the lid. The rest of the skin sutures are
simple interrupted.
An eyelid laceration can be sutured with the horse sedated using regional blocks to
desensitize the affected lid. The nasal portion of the upper eyelid and conjunctiva can be
desensitized by injecting local anesthetic solution into the supraorbital foramen to anesthetize the
supraorbital nerve. Injecting local anesthetic solution subcutaneously over the foramen provides
some loss of motor function to the upper eyelid by anesthetizing terminal branches of the
auriculopalpebral nerve. The supraorbital foramen is located by placing the thumb at one
canthus and the middle finger at the other canthus. The index finger falls on or near the foramen.
The lateral canthus and temporal 25% of the upper lid can be desensitized by anesthetizing the
lacrimal nerve at the orbital rim just nasal to the lateral canthus. The nasal portion of the upper
and lower eyelids can be desensitized by anesthetizing the infratrochlear nerve at its location in
a notch in the upper portion of the orbital rim near the nasal canthus. Sensory innervation to the
temporal portion of the lower eyelid can be desensitized by placing the index finger on the
ventral rim of the orbit tightly against the lateral canthus and injecting local anesthetic solution
close to the orbital rim, medial to the finger to anesthetize the zygomaticofacial nerve.
Lacerations of the parotid salivary gland
The parotid salivary gland and its duct are commonly lacerated because of their
superficial position. The duct is especially vulnerable to injury at the caudal or ventral border of
the mandible. Laceration of the gland or duct should be suspected if a large volume of fluid
discharges from the wound, especially when the horse is fed. A wound to the gland is not as
serious as a wound to the duct, because leakage of fluid from a lacerated gland tends to gradually
diminish and then cease completely. If discharge from a wound over the parotid gland continues
unabated, laceration of one of the several large radicles that form the parotid salivary duct should
be suspected.
Horses with a lacerated parotid salivary duct are often presented for treatment after the
epithelium of the duct has healed to cutaneous epithelium, causing a salivary fistula. Deferring
treatment may allow continuity of the duct to spontaneously re-establish, especially if the duct
has not been completely transected, but if the fistula persists, continuity of the duct must be reestablished, or the gland must be destroyed. Excising the parotid gland is nearly impossible
because critical vessels and nerves are embedded deep within its parenchyma.
To re-establish continuity of a severed duct, one end of a catheter is inserted through the
fistula into the distal portion of the duct, and the other end of the catheter is inserted through the
fistula into the proximal portion of the duct. The ends of the duct are then anastomosed over the
catheter using fine, absorbable suture. The catheter is withdrawn through the mouth, and the
cutaneous wound is sutured or left open to heal by second intention.
Destroying the gland is far easier and more practical than reconstructing the gland’s duct,
and no complications have been associated with loss of one parotid salivary gland. The parotid
salivary gland can be destroyed by instilling a destructive chemical into the gland or by ligating
the duct to cause its physiological death. Formalin is the chemical most commonly used to
destroy the parotid salivary gland, and 35 to 40 mL of it are infused into the gland by inserting a
catheter into the proximal aspect of the duct at the fistula. The solution is maintained within the
gland for about 90 seconds before it is allowed to drain. Secretion of saliva is eliminated usually
within 3 weeks.
To cause physiological destruction of the parotid gland, the duct is ligated between the
gland and the fistula. A catheter is advanced into the proximal portion of the duct through the
fistula, and an incision is made over the catheter, which can be palpated beneath the skin. Several
sutures are placed around the catheterized duct and tied after the catheter is withdrawn. The duct
should be ligated with heavy sutures because if fine suture is used for ligation, the suture may cut
through the duct causing the duct’s lumen to be re-established. If the wound is fresh, making
locating the severed end of the duct difficult, the duct can be located and ligated where it crosses
the tendon of insertion of the sternomandibularis muscle. To locate and ligate the duct where it
crosses the tendon, an incision is made caudal to the vertical ramus of the mandible over the
longitudinal axis of the tendon. The duct can be located by palpation through this incision.
Because a radicle may occasionally exit the gland distal to the duct at this location, the duct
should also be ligated further distally. To locate the duct further distally, the lumen of the duct
distal to the ligatures is catheterized, and a second incision is made over the catheter 3 to 4 cm
distal to the first incision, and several sutures are placed around the portion of the catheterized
duct exposed in the second incision and tied after the catheter is withdrawn. The cutaneous
incisions are sutured.
Wounds of the temporomandibular joint
Wounds to the region between the base of the ear and the eye may involve the
temporomandibular joint (TMJ) and may be accompanied by fracture of the articulation, or
septic arthritis of that joint. The TMJ is difficult to image radiographically because of the
complexity of the region and because other regions of the skull are superimposed over it.
Ultrasonographic examination of the area may provide useful information. Contrast radiographic
examination of the TMJ can be performed after introducing a contrast medium into the joint,
either through the wound or, if possible, at a site remote from the wound to confirm
communication between the joint and the wound. Horses with septic arthritis of a TMJ may
respond favorably to systemic or intra-articular administration of antimicrobial drugs alone or to
administration of antimicrobial drugs coupled with surgical excision of septic tissue, even if
sepsis has extensively destroyed the articular surfaces of the affected TMJ. If conservative
treatment fails to resolve pain associated with the TMJ, removing the mandibular condyle may
bring relief from pain and restore normal mastication.
Fractures of the mandible or premaxillae
Fractures of the premaxillae or the incisive portion of the mandible are common and most
often involve just the alveolar plate or the alveolar plate and the body of the mandible or
premaxillae. These types of fracture most commonly occur when the horse’s teeth are caught on
a solid object. They can usually be evaluated without the use radiography and most can be
reduced and stabilized with interdental wiring. Unilateral fractures of the incisive portion of the
mandible and bilateral fractures of the rostral portion of the mandible or maxilla/premaxillae in
the interdental space are usually transverse and most commonly occur from kicks from other
horses. Common methods of repair of these fractures include application of an intraoral or
extraoral acrylic prosthesis, dynamic compression plating, and lag-screw fixation.
Performing surgery of the head with the horse standing
Many of the surgeries described above can be performed with the horse standing,
provided that the horse is compliant. Horses are generally more tolerant of surgery of the head
than of surgery of other parts of the body, and administering regional or local anesthesia and a
sedative aides compliance. To perform surgery of the head with the horse standing, the horse can
be sedated with detomidine (0.01 – 0.02 mg/kg IV or 0.03-0.04 mg/kg IM) and butorphanol
tartrate (0.02 – 0.05 mg/kg, IV) and re-sedated during surgery, if necessary, with xylazine (0.5
mg/kg, IV). Constant-rate infusion of detomidine (0.02 mg/kg/hour) and butorphanol (0.012
mg/kg/hour) can be administered to provide a prolonged, constant state of sedation, after first
administering a loading dose of detomidine (0.008 mg/kg, IV) and butorphanol (0.02 mg/kg, IV).
Structures of the face can be desensitized by administering an infraorbital or maxillary
nerve block, and structures of the lower jaw can be desensitized by administering a mental,
mandibular alveolar, or mandibular nerve block. Even with these nerve blocks, however, skin
surrounding the wound may need to be desensitized by subcutaneous infiltration of local
anesthetic solution.