Maxillofacial and Mandibular Fractures

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Maxillofacial and Mandibular Fractures

Boaz Arzi and Frank J.M. Verstraete

18.1 Anatomical Considerations

The mandibular and maxillofacial region is a complex area that poses challenges when planning the placement of internal fixation devices. In the mandibular, maxillary, and incisive bones, the teeth occupy a large portion of the bone preventing placement of screws without causing dental damage. Furthermore, the maxillary and the mandibular bones also contain important blood vessels and nerves, further limiting placement of internal fixation [1]. For example, the infraorbital foramen of the maxilla, through which the infraorbital neurovascular bundle emerges, lies dorsal to the third premolar tooth. The mandibular canal contains the inferior alveolar neurovascular bundle and rostrally the buccal surface of the mandible has the middle and caudal mental foramina through which the corresponding mental nerves and blood vessels emerge [1]. In addition, the relative position of the mandibular canal and the infraorbital foramen may differ, based on the size of the dog and skull configuration. These important aspects are the cornerstones of planning where to place plates and screws in order to avoid iatrogenic damage while still maintaining effective and biomechanically stable internal fixation. In the mandibular and maxillofacial region, plate exposure through the oral mucosa and endodontal damage to teeth and the mandibular canal, are potential complications when a plate is positioned near the alveolar margins [2, 3]. Furthermore, collateral damage to important anatomic structures such as major neurovascular bundles should also be avoided.

18.2 Biomechanics

Internal fixation failure is an important complication that can occur when the mechanical load is excessive in proportion to the implant, wrong implant selection and when bone quality is poor [2, 3]. Historically, for mandibular fracture fixation and reconstruction, miniplate systems were applied near the alveolar margin in an attempt to counter mandibular bone stresses in accordance with the tension band principle [3, 13]. Application of the tension band principle is based on the assumption that anatomic reconstructions are strongest when fixation devices are loaded in tension. Placement of a small plate along the lines of tensile stress (i.e. Champy lines) would be used to neutralize applied functional forces [3, 13]. However, recent biomechanical studies have demonstrated that a plate near the alveolar margin is not needed, as adequate internal fixation can be achieved using a single mandibular locking reconstruction plate placed at mid‐mandibular height [2]. Furthermore, miniplates applied on the alveolar margin are associated with unavoidable damage to the roots of the teeth and tend to become exposed to the oral cavity [2, 3].

Our clinical experience and research over the past several years using locking reconstruction plates for mandibular fracture and critical‐sized defects repair has revealed that a single plate placed in a buccal position (just ventral to the tooth roots and dorsal to the mandibular canal) can adequately resist mechanical load without clinical or radiographic evidence of collateral damage to blood vessels, nerves, or tooth roots or plate exposure through the mucosa [4, 5].

The thin bones of the maxillofacial complex provide a lightweight but strong frame filled with the air spaces of the nasal cavity and paranasal sinuses [6, 7]. The maxillofacial frame is strengthened by the support of the buttresses that maintain the appropriate position of the maxilla in relation to the base of the skull and the mandibles [6, 7]. Implant selection should take these biomechanical factors into consideration. We use nonlocking miniplates for the maxillofacial region as they are easier to contour to match the complex tridimensional morphology and are not subjected to the sustained loads that mandibles are.

18.3 Materials

18.3.1 Locking Reconstruction Plates for the Mandible

The authors use 2.4–3.0 mm titanium locking plates (Synthes® Maxillofacial, Paoli, PA) for mandibular fracture fixation or reconstruction of critical‐size defects in medium to large breed dogs [2, 4, 8]. Veterinary adaptation plates are available and can be cut as needed. A single plate is secured on each side of the fracture or defect with at least three 3 mm bicortical, locking screws of appropriate length in which two screw‐threads are exposed on the lingual aspect. For small‐breed dogs and cats, the authors use a single locking titanium 2.0 mm miniplate (Synthes Maxillofacial, Paoli, PA) that is adapted to the desired anatomical contour of the mandible and, at a minimum, two bicortical 2.0 mm locking screws are used on each side of the fracture or defect [5].

18.3.2 Nonlocking Titanium Miniplates for the Maxillofacial Bones

For the maxillofacial bones, the authors use a variety of low‐profile titanium 2.0 mm nonlocking miniplates (Synthes Maxillofacial 2.0 mm Mandible Trauma, Paoli, PA) [6]. These plates can also be cut and contoured, using specially designed miniplate bending cutters and pliers. For controlled drilling, a 4 or 6 mm self‐stopping drill bit or regular‐length drill bit can be used to create a 1.5 mm core hole for the 2.0 mm screw thread diameter. The length of the screws placed can be determined by using computed tomography measurements of the bone thickness or a depth‐gauge. At least two nonlocking, self‐tapping 2.0 mm titanium screws should be placed on either side of the fracture.

18.4 Surgical Approach

The surgical approach for placing internal fixation into the mandibular and maxillofacial bones should be done in the least traumatic, yet effective, method of exposure [1]. As the region is very rich in major blood vessels, nerves, and salivary glands and ducts, care must be taken to avoid damaging these structures. However, if the region underwent trauma, the normal anatomy may be distorted. Exposure of the mandibular and maxillofacial bones frequently requires subperiosteal elevation of the muscles that adhere to the underlying bone.

There are three options to approach the mandibular and the maxillofacial bones: intraoral approach, extraoral approach, and a combination of the two. A step‐by‐step description of extra‐ and intraoral approaches for the bones of the region is not within the scope of this chapter; it has been described elsewhere [1]

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Jun 13, 2021 | Posted by in SUGERY, ORTHOPEDICS & ANESTHESIA | Comments Off on Maxillofacial and Mandibular Fractures

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