Contrary to what might be expected, people who sustain a jaw fracture and lose consciousness actually tend to have milder bone injuries than those who do not black out from a trauma to the jaw, according to a study published in the Journal of Oral and Maxillofacial Surgery.
A retrospective review of hospital charts for 225 mandible (lower jaw) fracture patients found that individuals with more severe fractures or multiple fracture sites were significantly less likely to lose consciousness with their injuries than patients with fewer fracture sites or less severe injuries.
The phenomenon may be explained by the distribution of force in response to a traumatic blow, the authors suggest.
"Multiple fracture patterns probably serve a neuroprotective function, allowing greater dissipation of forces and resulting in the transmission of less residual energy to the cranial vault," states principal author Yuan Cathy Hung, D.D.S., chief resident at Lincoln Medical and Mental Health Center in Bronx, New York.
"When the jaw sustains fewer or less severe fractures, more force from the blow travels to the cranial vault because less energy has been absorbed by the jaw," she says.
Few studies have looked at the incidence of closed head injury, including loss of consciousness, associated with facial injury, Dr. Hung notes. "The information from this study may help surgeons evaluate whether a patient should have a CT scan of the head and decide which patients need closer observation and monitoring," she says.
Patients with multiple mandible fracture sites were significantly less likely to sustain LOC, the study found. Twice as many patients who did not experience LOC sustained multiple fractures (54%) compared with the positive LOC group (27%). In the negative LOC group, 46% of subjects sustained a single mandible fracture, an additional 46% sustained two fractures, and 8% sustained three fractures. By comparison, in the positive LOC group, 73% of subjects sustained a single fracture and 27% of subjects sustained two fractures. None of the subjects from this group sustained three or more fractures.
"The greater the number of fracture sites, the more dissipation of force occurred with less transmissible energy," Dr. Hung reports.
Significantly more negative LOC patients than positive LOC patients experienced fractures of the mandibular condyles, the rounded bumps at the ends of the mandible on each side of the face that connect the lower jaw to the maxilla (upper jaw). "This implies that the condyles fractured off to prevent the force from reaching the skull," Dr. Hung notes.
This 'safety device' worked in instances when a relatively low force of impact, such as interpersonal violence, was involved, she adds. A higher force of impact, such as a car accident, might still produce enough energy to result in LOC even with fractures of the condyles.
Fracture severity was higher in the negative LOC group than the positive LOC group as well. The positive LOC group had only one fracture (5%) with severe displacement, while the negative LOC group had 20 (19%). The positive LOC group had seven fractures (37%) with moderate displacement and 11 (58%) with minimal displacement. The negative LOC group had 53 (51%) fractures with moderate displacement and 31 (30%) with minimal displacement.
The overall incidence of LOC in patients sustaining mandible fractures in this study was 17.6%, a finding consistent with other studies. Patients consisted primarily of males, with a male/female ratio of 5.6:1. The relatively high male/female ratio in this study compared to other studies is due to demographic and geographic factors, Dr. Hung says. "In this study, interpersonal violence was the leading cause of mandible fractures. This finding reflects the location of Lincoln Hospital in the South Bronx, a level I trauma center with a mid-to-lower socioeconomic status where violence among males is common," she says.
Interpersonal violence accounted for 70% and 73% of injuries in the negative LOC and positive LOC groups, respectively. The fist was most commonly used in interpersonal violence and contributed to 57% of the cases without LOC and 33% of cases with LOC. The second most common cause of mandible fracture was motor vehicle accident (7.6% of negative LOC patients and 20% of positive LOC patients). Other causes included a fall (9%, 7%), a gunshot wound (3.8%, 0%) and being hit by an unknown object (1.3%, 0%).