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Mandibular Symphyseal Separation Repair in Cats

erin-dentistryErin Abrahams, DVM
617-522-7282
www.angell.org/dentistry
dentistry@angell.org

The mandibular symphysis is a fibrocartilaginous joint that is the most common site of mandibular fractures in feline patients1. Fortunately, uncomplicated mandibular symphyseal separations are also the most amenable to surgical repair with inexpensive and readily available materials, and they are easily performed in general practice.

Fig 1. Incisor-step and fractured left mandibular canine

Fig 1. Incisor-step and fractured left mandibular canine

Patients present with a history of known or suspected trauma – most commonly falls2 and vehicular accidents1 – and may have concomitant ocular involvement, fractured teeth, additional jaw fractures, temporomandibular joint (TMJ) involvement, or neurologic symptoms. To identify a symphyseal separation, assess the mandibular incisors for an “incisor-step,” resulting from separation at the joint and loss of alignment across the incisors.

Fig 2. Significant soft tissue trauma

Fig 2. Significant soft tissue trauma

The severity of the separation can range from minor soft tissue involvement and minimal displacement of the incisor line, to dramatic soft tissue tearing and marked incisor-step that is readily apparent. With more advanced separations, the two mandibles will freely move and slide back and forth when manipulated; other times, movement is only appreciated once the patient is under sedation or general anesthesia.

Fig 3. Repair materials

Fig 3. Repair materials

As with any oral fracture repair, the most important consideration when repairing a mandibular symphyseal separation is the return to a functional and comfortable occlusion. This is achieved by reducing the separation to achieve a level row of mandibular incisors, and ensuring that when downward pressure is placed on the one of the mandibular canines to open the jaw, that both mandibles move in unison. If there are additional jaw fractures, or TMJ involvement, these will need to be considered in fracture repair planning, and may be better suited for referral. A simple mandibular symphyseal separation, however, can easily be repaired in general practice with the following materials:

  • 5-0 Monocryl Suture
  • 19 gauge needle
  • 24 gauge orthopedic wire
  • Needle drivers
  • Dental radiographs

Step 1: Obtain full-mouth intraoral radiographs to determine the extent of the symphyseal separation and determine if there are any additional fractures that must be addressed. Before placing the orthopedic wire, use 5-0 Monocryl suture to place 2-3 simple interrupted sutures to close any soft tissue tear on the lingual aspect of the mandibular incisors. Apposing the soft tissues will aid in reducing the symphyseal separation and will facilitate alignment of the bony repair.

Fig 4. Pre-operative radiograph

Fig 4. Pre-operative radiograph

Step 2: Use a scalpel blade to make a stab skin incision between the mandibular halves at the level of the canine apices, just caudal to the symphysis. This will be the exit point for the orthopedic wire. Place the 19 g. needle on the buccal aspect along the mandibular body at the level of the diastema between the canine and the 3rd premolar, working the needle through the soft tissue to exit through the skin incision. Use the needle to guide the 24 gauge orthopedic wire to exit the skin incision.

Fig 5. Placement of sutures aids reduction

Fig 5. Placement of sutures aids reduction

Fig 6. Needle guide for wire placement

Fig 6. Needle guide for wire placement

Fig 7. Ensure proper needle position that allows the needle to be removed after final wire placement

Fig 7. Ensure proper needle position that allows the needle to be removed after final wire placement

Step 3. Reposition the needle to the other side of the mandible and insert it along the buccal aspect in the opposite direction, so that the needle hub is on the outside of the patient’s mouth and can be removed once the wire is in place.

Fig 8. Note alignment of incisors in a straight line

Fig 8. Note alignment of incisors in a straight line

Step 4. Once the wire has been placed on the buccal aspect of each mandible, with the free ends exiting through the skin incision, manually reduce the separation while twisting the wires together with needle drivers. It is helpful to have an assistant bring the canines and incisors into proper alignment while the wire is tightened.

Fig 9. The wire is cut and bent to blunt the edge and prevent a sharp edge

Fig 9. The wire is cut and bent to blunt the edge and prevent a sharp edge

Step 5: Continue to tighten the wire until adequate reduction is achieved, using radiographs to check the alignment. Remember that the goal is to achieve a functional and comfortable occlusion, using this as the primary criteria for assessing the final outcome of the repair. While the radiograph in Figure 4 demonstrates residual incongruence between the two mandibles, the patient’s occlusion was functional and the repair was considered a success.

Fig 10. Post-operative radiograph

Fig 10. Post-operative radiograph

Average healing for mandibular symphyseal  fracture is 6 weeks (range 3-12 weeks)1. It is recommended that fractured teeth be left in place to facilitate bone healing when not compromised by periodontal disease, with extraction occurring at the time of wire removal. The author does not bury or cover the end of the orthopedic wire. Once bent, it is left exposed, which facilitates easy removal. Removal of the wire is achieved by cutting the wire under the tongue, and pulling the cut ends outward by the twisted portion of the wire through the skin incision. A modified version of this repair technique has been proposed, which negates the need for a ventral skin incision, which places the wire twist distal and buccal to one of the mandibular canine teeth; this has not yet been attempted by the author3.

Fig 11. Final radiograph 4 weeks after initial repair. The left mandibular canine was extracted at wire removal

Fig 11. Final radiograph 4 weeks after initial repair. The left mandibular canine was extracted at wire removal

For more information, please contact Dr. Erin Abrahams at dentistry@angell.org or 617-522-7282.

 

References:

  1. Umphlet RC and Johnson AL. Mandibular fractures in the cat. A retrospective study. Vet Surg 1988; 17:333-337
  2. Bonner SE, Reiter AM and Lewis JR. Orofacial manifestations of high-rise syndrome in cats: a retrospective study of 84 cases. J Vet Dent 2012; 29: 10-18
  3. Mulherin BL, Snyder CL and Soukup JW. An alternative symphyseal wiring technique. J Vet Dent 2009; 26: 176-184.
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