Anatomical distribution of mandibular fractures from severe bicycling accidents: A 12‐year experience from a Norwegian level 1 trauma center

Abstract Background/Aim The mandible makes up a substantial part of the lower face, and is susceptible to injury. Even in helmeted cyclists, accidents may lead to fractures of the mandible because conventional helmets provide little protection to the lower part of the face. In addition, some studies indicate that helmets may lead to an increased risk of mandibular fractures. Thus, the aim of this study was to examine the anatomic distribution of mandibular fractures in injured cyclists and to assess if helmet use influenced the fracture locations. Material and Methods Data from a Norwegian Level 1 trauma center were collected in the Oslo University Hospital Trauma Registry over a 12‐year period. Of 1543 injured cyclists, the electronic patient charts of 62 cyclists with fractures of the mandible were retrospectively evaluated in detail. Demographic data, helmet use, and fracture type were assessed. Results Sixty‐two patients (4%) had fractures of the mandible, and women had an increased risk (OR 2.49, 95% CI 1.49–4.16, p < .001). The most common fracture site was the mandibular body, followed by the condyle. Isolated mandibular fractures occurred in 45% of the patients and 55% had other concomitant facial fractures. There were 42% of the patients with fractures in multiple sites of the mandible, and 42% had a concomitant dentoalveolar injury. Half of the cyclists were wearing a helmet at the time of the accident and 39% were not. There was no significant difference in fracture distribution between the helmeted and non‐helmeted groups. Conclusions Fracture of the mandibular body was the most prevalent mandibular fracture type following bicycle accidents. Women had an increased risk of mandibular fractures compared with men, whereas helmet wearing did not affect the anatomical fracture site.


| MATERIAL S AND ME THODS
Oslo University Hospital, Ullevål is a regional, Level I trauma center for approximately 3 million people. The study used prospectively collected data from the Oslo University Hospital Trauma Registry (OUH-TR), a custom built hospital based registry. Eligible for inclusion in the OUH-TR are all patients admitted with trauma team activation. Furthermore, all patients with penetrating injuries to the head, neck, torso and/or extremities proximal to the elbow or knee, all patients with Injury Severity Score (ISS) 19 ≥ 10, and patients with AIS Head severity code ≥3 are also included. 20 The study included patients admitted in the period 2005-2016, whether they were admitted to OUH-U directly or via a local hospital within 24 h after injury. All injuries were classified according to the Abbreviated Injury Scale 1990 Revision Update 98 (AIS). 21 Data from all patients admitted with bicycle-related injuries in the OUH-TR were obtained. Demographic variables and information on helmet use were acquired. AIS-codes were examined in order to identify patients with facial fractures and dentoalveolar injuries, and the electronic patient charts of cyclists with fractures of the mandible were thoroughly examined. Information regarding mandibular fracture type and treatment was obtained from a retrospective patient chart review. In addition, fractures of the frontal bone were registered, as they do not have a unique AIS code. The following fracture types were registered: angle, body, condyle, coronoid process, and ramus.
Fractures anterior to the angle of the mandible were classified as fractures of the body, and fractures of the condylar head, neck, and subcondylar region were grouped together as fractures of the condyle.
Following the review of the electronic patient charts, the patient details were anonymized, and the study was approved by the Data

| RE SULTS
A total of 1,570 patients with bicycle-related accidents were admitted during the study period, of whom 27 patients were pedestrians who had been struck by a cyclist and they were excluded accordingly. Of the remaining 1,543 patients, 66 were registered with fractures of the mandible. Among these, four patients were excluded after reviewing the electronic patient charts which revealed an incorrect diagnosis. Consequently, 62 patients (4%) with 100 mandibular fractures were included in the study.
The age-distribution of the patients is presented in Figure 1.
Half of the cyclists (n = 31) who sustained fractures of the mandible were wearing a helmet at the time of the accident while 24 (39%) were not. Helmet status was not registered in seven (11%) patients. There was no association between helmet wearing and the mandibular fracture types when analysed in isolation ( Table 2).

| DISCUSS ION
The scientific evidence of the distribution of mandibular fractures in bicycling accidents is limited. Therefore, the aim of the present study was to investigate the anatomical injury patterns of mandibular fractures in cyclists admitted to a Level 1 trauma center. Furthermore, the study sought to examine the association between mandibular fracture types and helmet use, concomitant facial fractures and dentoalveolar injuries, as well as the choice of treatment.
The body of the mandible was the most frequent fracture location in bicycle-related mandibular fractures in the present study. This is in accordance with the findings of Lin et al. in their study of bicycling injuries from a Level I trauma center in Taiwan 11 as well as a recent Japanese study on road traffic accidents. 15 In the latter, bicycling accidents accounted for around two thirds of the maxillofacial injuries. However, that study did not report the specific fracture pattern of the mandibular fractures for the eighteen cyclists included. 15 The authors did, nevertheless, report a similar percentage of single mandibular fractures as in the present study (58%), and that fractures of the condyle were the second most frequent fracture location. 15 This is in contrast to other studies where fractures of the condyle were more common. 7,8,[12][13][14] The direction and the amount of force during an injury influence the fracture site of the mandible, 22,23 and several authors have ascribed the higher risk of condylar fractures to trauma applied to the symphyseal region with consequent indirect fracture of the condyle. 11,12,14 Thus, it is possible that a greater force applied to the symphyseal region may lead to fracture at the site of the blow rather than at the condylar area. This is supported by a recent study which performed a finite element analysis of bicycling accidents and fractures of the mandible. 24 In contrast to previous studies which assessed bicycle-related fracture patterns of the mandible, the current study exclusively included patients examined by a trauma team and/or patients with either confirmed or high likelihood of serious injury. Therefore, the difference in fracture distribution could be due to more severe accidents in this study's population. This is consistent with the present study's finding of a positive association between fractures of the mandible and increasing ISS.
Another reason for the observed difference could be the heterogeneity between the study populations, such as age or gender. Although age has been identified as a risk factor for maxillofacial fractures, 24 the present study found no association between age and fractures of the had a higher mean age compared with those who only had mandibular fractures. This study also found that women had an increased risk of sustaining fractures of the mandible, which may be due to gender differences in shape or bone structure, with men having bigger, and possibly more robust mandibles. 23,[25][26][27] Furthermore, women undergo a more pronounced decline of mandibular bone quality with age compared with men. 28 The observed difference in fracture risk could also be the result of different riding styles or other fundamental physiological differences between genders. 29,30 Although helmets provide protection of the head and upper part of the face, they may increase the risk of fractures of the mandible if it leads to a second blow to the lower part of the face after the helmet has hit an object. 31 Consequently, it is possible that helmet use can alter the anatomical distribution of mandibular fractures.
However, the present study found no difference in anatomical fracture distribution of the mandible when comparing helmeted and non-helmeted cyclists. To the best of the authors' knowledge, this has only been examined in one previous study, which was limited by a small sample size of only seven patients. 11 Although the present study included more patients, it is also limited by size. Thus, larger TA B L E 1 Demographic characteristics of the patients with and without mandibular fractures studies are warranted to further examine the effect of helmet wearing on injury to the lower face.
Full-face helmets may provide better protection of the lower face compared with open helmets, and although full-face helmets are more common in motorcycling and downhill cycling, they are rarely seen in regular cyclists. The reason for this could be that they are not available through retail stores or because they are considered less fashionable or impractical due to their larger size.
However, new technology for helmet design, such as a self-inflating helmet which includes protection of the lower face is already commercially available and may become more common in the future.
Nevertheless, more research is needed to improve helmet design. This is evident by a recent meta-analysis which found no difference in the occurrence of facial fractures between full-face and open helmets in motorcyclists. 32 Yamamoto et al. 12  were considered more serious than closed fractures of the condyle, and that the former were referred to the trauma center but not the latter. The same could be true for patients with combinations of facial fractures and dentoalveolar injuries which may appear more  Abbreviations: CI, confidence interval; OR, odds ratio; SD, standard deviation. a Cyclists with unknown status for helmet use not included in the analysis.