Cerclage Wire for Rostral Mandibular Instability

Four things to know.

Originally published in the April 2015 issue of Veterinary Practice News

Last month we discussed iatrogenic mandibular fractures of the rostral mandible, specifically the iatrogenic parasymphyseal fracture. One of the repair techniques for this fracture, and for traumatic symphyseal separation, is use of a cerclage wire placed behind the canine teeth.

Though most practitioners are familiar with this seemingly basic procedure, there are subtle nuances of placement that will help your patients thrive following placement of the cerclage.

No. 1. Not every patient with instability requires placement of a cerclage wire

Some animals, especially brachycephalic small-breed dogs and some cats, may have significant symphyseal laxity as an incidental finding on anesthetized oral examination. If the patient is not showing signs of discomfort or jaw locking, symphyseal laxity is not likely causing any problems.

In cases with no recent history of trauma, placement of a cerclage wire will likely not allow for a long-term decrease in laxity without a more invasive procedure such as symphysiodesis (cutting into the fibrous joint of the symphysis and encouraging scar tissue formation), and this is often not necessary.

No. 2. Step-by-step: placement

Before placing a cerclage wire, the intraoral soft tissues dorsal to the bony separation are sutured in a simple interrupted pattern with absorbable suture, being careful to not cause damage to the sublingual caruncles (the openings of the mandibular and sublingual salivary glands). The hair of the chin is clipped and the skin is prepared with surgical scrub.

A 1-cm skin incision is made on midline, with the rostral edge of the incision being at the level of the distal aspect of the canine teeth. An 18-gauge needle is inserted into the incision lateral to the left or right mandible, being careful not to entrap the soft tissue lateral to the bone. The tip of the needle emerges through the oral mucosa rostral to the triangle-shaped soft tissue structure called the labial frenulum.

For cats, I like to use 22-gauge wire, which is introduced through the 18-gauge needle. The needle is removed and reintroduced lateral to the opposite mandible, emerging just rostral to the labial frenulum on the opposite side. The intraoral portion of the wire is fed through the tip of the needle so that the two ends of the wire emerge from the ventral skin incision with an intraoral loop of wire that sits just caudal to the canine teeth.

When tightening the wire, care should be taken to avoid overtightening it, since inevitably some soft tissue gets entrapped within the wire. Excessive tightening will cause the wire to cut into the soft tissue and may cause necrosis of the underlying bone.

Especially for symphyseal separations, err on the side of the wire being too loose rather than too tight, since in these cases we are hoping to achieve a fibrous union rather than a bony union.

Though bending twisted wire may weaken or loosen the wire if not done properly, I prefer bending the wire so it sits parallel to the incision and closure of skin over the twisted wire prevents the wire from getting caught on anything. Closure of the skin with a few sutures allows for only the intraoral portion of the wire to be exposed.

Patient sustained an iatrogenic rostral mandibular fracture during attempted extraction of the left mandibular canine tooth. The excessively tightened cerclage wire used for repair may have been the cause of necrosis of the soft tissue lateral to the fracture site and rostral to the wire.

Photo © 2014 John R. Lewis, NorthStar VETS

Patient sustained an iatrogenic rostral mandibular fracture during attempted extraction of the left mandibular canine tooth. The excessively tightened cerclage wire used for repair may have been the cause of necrosis of the soft tissue lateral to the fracture site and rostral to the wire.

No. 3. Don’t leave the wire in for too long

Symphyseal separations require four weeks to fully heal, and parasymphyseal fractures may take slightly longer. However, keeping the wire in place for more than four to five weeks carries with it the possibility of pressure necrosis and/or resorption of bone lateral to the mandibular canine teeth, which sometimes extends deep enough to involve the periodontium of the teeth.

The clinical consequences of a fibrous union of a parasymphyseal fracture are generally negligible provided occlusion is normal. Therefore, I try to remove rostral mandibular cerclage wires between four and five weeks after placement regardless of whether I am dealing with a symphyseal separation or parasymphyseal fracture.

No. 4.  Alternate techniques to the traditional approach

Alternative techniques for symphyseal cerclage have been described.1, 2 An 18-gauge needle is advanced as previously described into the oral cavity along the buccal aspect of mandible just rostral to the labial frenulum. The wire is threaded into the needle and the needle withdrawn.

The needle is redirected along the buccal surface of the opposite mandible and, in this alternate technique, the needle is directed from intraorally to extraorally through the ventral chin incision. The orthopedic wire exiting the skin incision is threaded into the bevel tip and guided into the mouth by withdrawing the needle.

Wire is twisted and tightened on the buccal side of the canine tooth and the twisted ends are cut and bent back toward the mucosa. A small bead of composite can be placed over the wire twists to prevent trauma from the sharp ends of the wire. The potential benefit of this technique is seen at time of wire removal since a skin incision is not required for removal.

A figure-of-eight wire wrapped intraorally between the mandibular canine teeth is not generally recommended for treatment of symphyseal separation/parasymphyseal fracture, as it may cause linguoversion (inward tipping) of the canines and may leave a gap in the symphysis ventrally if used as a sole form of fixation.

Instead, placement of a twisted wire between the canines can be accomplished by securing it around the crowns of the mandibular canine teeth. Composite will give additional stabilization and prevent lingual misalignment of the mandibular canine teeth.

References

  1. Mulherin BL, Snyder CJ, Soukup JW. An alternative symphyseal wiring technique. J Vet Dent. 2012; 29: 176-84.
  2. Matis U, Kostlin R. Symphyseal separation and fractures involving the incisive region. In: Verstraete FJM, Lommer MJ. Oral And Maxillofacial Surgery in Dogs and Cats. London: Saunders Elsevier; 2012. P. 265-274.
Leave a Comment

Comments

Your email address will not be published. Required fields are marked *