In-Service Exam
Mandible - 2003





A 31-year-old man sustains a fracture of the condylar neck of the mandible. On physical examination, the condylar fragment is displaced medially. This finding is most likely caused by the action of which of the following muscles?

(A) Buccinator
(B) Lateral pterygoid
(C) Masseter
(D) Medial pterygoid
(E) Temporalis

The correct response is Option B.

Fragments of fractures of the condylar neck are displaced by the action of the lateral pterygoid muscle. This muscle has two heads. The inferior head arises from the lateral pterygoid plate and inserts into the pterygoid fovea on the neck of the mandible; in patients with subcondylar fractures, the inferior head will pull the condylar fragment medially, resulting in the displacement seen in this patient. In contrast, the superior head of the lateral pterygoid arises from the greater wing of the sphenoid and inserts into the articular surface and disk of the temporomandibular joint.

The buccinator muscle is one of a group of muscles of facial expression. It is innervated by the buccal branches of the facial (VII) nerve and arises from the pterygomandibular raphae to insert into the orbicularis oris muscle and the mucosa and skin of the lips. It acts to flatten the cheek against the teeth. Because it does not arise within the condylar region, it does not exert any forces on the condyle or mandible.

The masseter, medial pterygoid, and temporalis muscles all insert below the fracture line within the condyle. Therefore, these muscles do not exert any pull on the condylar segment. The masseter muscle arises from the zygomatic arch and inserts into the lateral and inferior portion of the mandibular ramus. The medial pterygoid arises from the medial surface of the lateral pterygoid plate and inserts into the medial and inferior borders of the mandibular ramus. The temporalis muscle originates within the temporal fossa and inserts into the coronoid process of the mandible and the medial side of the mandibular ramus.

References
1. Manson PN. Facial fractures. In: Aston SJ, Beasley RW, Thorne CH, eds. Grabb & Smith's Plastic Surgery. 5th ed. Philadelphia, Pa: Lippincott-Raven; 1997:383-412.
2. Wexler A. Anatomy of the head and neck. In: Ferraro JW, ed. Fundamentals of Maxillofacial Surgery. New York, NY: Springer-Verlag; 1997:53-113.

A patient has an infection at the surgical site one week after undergoing open reduction and internal fixation of a fracture of the mandibular body using an inferior border reconstruction plate and a tension band. Occlusion is normal. The infection site is surgically drained; intraoperative exploration shows that the plates and screws are stable with no evidence of loosening.

Which of the following is the most appropriate management of the hardware?

(A) Maintenance of current stabilization without removal of the hardware
(B) Removal of all plates and immediate application of intermaxillary fixation
(C) Removal of all plates and immediate application of two miniplates
(D) Removal of all plates and immediate placement of an external fixator
(E) Removal of all plates and placement of new plates when the infection has subsided

The correct response is Option A.

Infections following open reduction and internal fixation of mandibular fractures typically result from failure of fixation devices, for example, loosening of the screws. In addition to operative drainage of the infection and antibiotic therapy, appropriate management in the majority of these situations includes removal and replacement of the hardware with intermaxillary or external fixation for stabilization of the fracture.

In this patient, the plates continue to provide stable fixation of the fracture. Because of this, the current stabilization should be maintained without removal of the hardware, and the patient should undergo operative drainage of the infection and administration of antibiotics.

References
1. Jaques B, Richter M, Arza A. Treatment of mandibular fractures with rigid osteosynthesis: using the AO system. J Oral Maxillofac Surg. 1997;55:1402-1406.
2. Koury ME, Perrott DH, Kaban LB. The use of rigid internal fixation in mandibular fractures complicated by osteomyelitis. J Oral Maxillofac Surg. 1994;52:1114-1119.

A 36-year-old woman has pain in the right side of the mandible after falling and striking her face on a sidewalk. Physical examination shows numbness of the right lower lip. The most likely cause of these findings is a fracture of which of the following regions of the mandible?

(A) Ascending ramus
(B) Body
(C) Condyle
(D) Coronoid process
(E) Symphysis

The correct response is Option B.

These findings are most consistent with a fracture of the body of the mandible. The mandibular angle and body are fractured most commonly. Fractures of the mandibular body are most likely to cause impingement or transection of the inferior alveolar nerve, resulting in numbness of the right lower lip. This nerve enters the mandible at a point proximal to the mandibular angle, travels through the angle and body to the mental foramen opposite the first bicuspid tooth, then emerges as the mental nerve, supplying sensation to the soft tissues of the lip and chin. Physical examination and radiographs are most likely to confirm the location of the fracture.

Fractures of the ascending ramus, condyle, coronoid process, and symphysis are less common than fractures of the mandibular angle and body and would not result in numbness of the lower lip.

References
1. Manson PN. Facial fractures. In: Aston SJ, Beasley RW, Thorne CH, eds. Grabb & Smith's Plastic Surgery. 5th ed. Philadelphia, Pa: Lippincott-Raven; 1997:383-412.
2. Oikarinen KS. Clinical management of injuries of the maxilla, mandible, and alveolus. Dent Clin N Am. 1995;39:113-130.