In-Service Exam
Mandible - 2001




A 38-year-old man has paresthesias of the lip and chin on the side of the fracture after rigid fixation is applied for management of a nondisplaced fracture of the mandibular angle. He has complete dentition with class I occlusion; sensation of the lip and chin was normal preoperatively.

The most likely cause of his current findings is injury to which of the following nerves?

(A) Buccal
(B) Facial
(C) Inferior alveolar
(D) Superior alveolar
(E) Lingual

The correct response is Option C.

This patient who has paresthesias of the lip and chin following the application of rigid fixation has most likely sustained an injury to the inferior alveolar nerve. Injury to this and other sensory nerves occurs frequently in patients with mandibular fractures. In patients with displaced fractures, the incidence of injury has been reported to range from 11% to 59%. Although most injuries involve neurapraxias that develop secondary to stretching or compression, traumatic sensory nerve damage is most likely to occur within the intrabony course of the inferior alveolar nerve. This patient's injury most likely occurred during placement of a cortical screw into the mandibular canal, which is common. Other causes include bony fracture displacement and extraction of third molars.

Because the buccal, facial, and lingual nerves are not found within the bony canal of the mandible, they are not likely to be involved with fracture. The superior alveolar nerve provides sensory innervation to the maxilla and thus would not be affected by a mandibular fracture.

References
1. Koury ME. Complications of mandibular fractures. In: Kaban LB, Pogrel MA, Perrott DH, eds. Complications in Oral and Maxillofacial Surgery. Philadelphia, Pa: WB Saunders Co; 1997:121-145.
2. Manson PN. Facial injuries. In: McCarthy JG, ed. Plastic Surgery. Philadelphia, Pa: WB Saunders Co; 1990;2:867-1141.

Which of the following mechanisms of action of the mandible occurs during the terminal 4 cm to 5 cm of jaw opening?

(A) Rotation within the lower joint space
(B) Rotation within the upper joint space
(C) Translation and rotation within the lower joint space
(D) Translation within the lower joint space
(E) Translation within the upper joint space

The correct response is Option E.
Normal opening of the mandible results from the synchronized movements of muscles surrounding the joint space. The articular disk separates the joint space into upper and lower spaces. The combination of motions of the mandibular condyle generates the motion of the temporomandibular joint. At rest and during rotation, the mandibular condyle is located in the lower joint space. During translation, the condyle moves into the upper joint space.

Most patients have a maximal incisal opening of 4 cm to 5 cm. The initial 1 cm to 2 cm of jaw opening involves rotatory, or hinge, movements. Jaw opening at 2 cm to 3 cm is a combination of rotation and translation. The terminal 3 cm to 5 cm of jaw opening involves translatory movements only.

References
1. Jacobs JS, Mendes D. Traumatic deformities and reconstruction of the temporomandibular joint. In: Ferraro JW, ed. Fundamentals of Maxillofacial Surgery. New York, NY: Springer-Verlag; 1996:307-320.
2. Mendes D, Jacobs JS. Traumatic deformities and reconstruction of the temporomandibular joint. In: Cohen M, ed. Mastery of Plastic and Reconstructive Surgery. Boston, Mass: Little, Brown & Co; 1994;2:1220-1229.
3. Zide BM. The temporomandibular joint. In: McCarthy JG, ed. Plastic Surgery. Philadelphia, Pa: WB Saunders Co; 1990;2:1475-1513.

Distraction osteogenesis of the mandible in an 8-year-old boy is optimally performed at a rate of how many millimeters daily?

(A) 0.1
(B) 0.5
(C) 1.0
(D) 2.0
(E) 5.0

The correct response is Option C.

In a patient who is undergoing distraction osteogenesis for bone lengthening to compensate for a deformity, the distraction zone forms a radial pattern, allowing for the formation of bone at different rates within the zone. Although experimentation with different rates of distraction has had positive results with rates from 0.5 mm to 2.0 mm daily, distraction at a rate of 1.0 mm has been shown to be optimal in most situations, including mandibular lengthening in an 8-year-old child. Some surgeons are performing distraction osteogenesis in infants at rates as high as 2.0 mm daily because of the greater osteogenic potential seen in infants, which allows for an acceleration of the process. However, this high rate is associated with delays in ossification, especially in areas of low metabolism, such as the diaphysis. Rates of 0.5 mm daily or less are associated with an increased risk for premature consolidation.

References
1. Aronson J. Principles of distraction osteogenesis: the orthopedic experience. In: McCarthy JG, ed. Distraction of the Craniofacial Skeleton. New York, NY: Springer-Verlag; 1999:55-56.
2. Ilizarov GA. The tension-stress effect on the genesis and growth of tissues: part 1: the influence of stability of fixation and soft-tissue preservation. Clin Orthop. 1989;238:249-281.
3. Farhadieh RD, Gianoutsos MP, Dickinson R, et al. Effect of distraction rate on biomechanical, mineralization, and histologic properties of an ovine mandible model. Plast Reconstr Surg. 2000;105:889.

A 21-year-old man sustains blunt trauma to the face while playing football. On examination, he has unilateral pain and facial swelling; he is unable to open his mouth. Radiographs show a nondisplaced coronoid fracture. Which of the following is the most appropriate initial step in management?

(A) Coronoidectomy
(B) Maxillomandibular fixation
(C) Endoscopic reduction and fixation
(D) Open reduction and rigid internal fixation
(E) Open reduction and wire fixation

The correct response is Option B.

In this 21-year-old man who has an isolated nondisplaced fracture of the coronoid process, the most appropriate management is short-term maxillomandibular fixation. The tendons of the temporalis muscle act as splints for the fracture fragments, allowing osseous union to occur spontaneously. Because ankylosis may develop between the coronoid process and the zygomatic arch if immobilization is prolonged, fixation should only be applied for one to two weeks. Following removal of fixation, physical therapy may be required to re-establish the normal vertical dimension of the face.

In rare patients who have displaced fracture fragments that obstruct normal mandibular motion, partial coronoidectomy may be performed. Endoscopic approaches to the temporomandibular joint are reserved for intra-articular injuries such as meniscal tears. Rigid or wire fixation is not required because of the expected osseous union associated with this type of fracture.

References
1. Gundlach K. Fractures of the mandible. In: Cohen M, ed. Mastery of Plastic and Reconstructive Surgery. Boston, Mass: Little, Brown & Co; 1994;2:1165-1180.
2. Manson PN. Facial injuries. In: McCarthy JG, ed. Plastic Surgery. Philadelphia, Pa: WB Saunders Co; 1990;2:867-1141.

An edentulous 65-year-old man sustains bilaterally displaced fractures of the mandibular body in a motor vehicle collision. Which of the following is most effective for determining the patient's maxillomandibular relationship prior to the application of rigid fixation?

(A) Analysis with a face-bow
(B) CT scans of the face
(C) Custom-fabricated intraoral splints
(D) Erich arch bars
(E) Plain radiographs

The correct response is Option C.

Management of maxillomandibular fractures involves determination of the anatomic relationship of the maxilla and mandible to each other, as well as to the cranial base. After the orientation of the jaws has been established, the fracture segments can be exposed and rigid fixation can be applied. Human teeth are typically used to establish maxillomandibular orientation; however, this is not possible in the edentulous patient. Custom-fabricated intraoral splints or the patient's own dentures can instead be rigidly fixed to the maxilla and mandible using wire or screws. The maxilla and mandible can then be brought into occlusion and fixed together.

A face-bow is used to determine the relationship of the maxilla and the midface to the cranial base; the mandible is not assessed. Plain radiographs and CT scans of the face are also helpful in determining the extent of the patient's injuries and in planning surgery, but not in establishing skeletal orientation. Erich arch bars can only be used in patients with functional dental occlusion.

References
1. Calloway DM, Anton AM, Jacobs JS. Changing concepts and controversies in the management of mandibular fractures: advances in craniomaxillofacial fracture management. Clin Plast Surg. 1992;19:59-69.
2. Jacobs JS, Chidyllo SA, Ferraro JW. The application of dental splints in regard to the modern techniques of rigid fixation: a basic maxillofacial technique reviewed. In: Ferraro JW, ed. Fundamentals of Maxillofacial Surgery. New York, NY: Springer-Verlag; 1996:327-333.
3. Yaremchuk MJ. Fractures of the maxilla. In: Cohen M, ed. Mastery of Plastic and Reconstructive Surgery. Boston, Mass: Little, Brown & Co; 1994;2:1156-1164.