The biomechanics of facial bone fracture

Does the type of craniomaxillofacial fracture (CMF) differ between patients with intracranial hemorrhage (ICH) and those with blunt cerebrovascular injury (BCVI)? A retrospective study

The purpose of the present study was to investigate and compare craniomaxillofacial fracture (CMF) type in patients with intracranial hemorrhage (ICH) versus blunt cerebrovascular injury (BCVI). A retrospective cohort study was performed. The predictor variables were the types of CMF. The primary outcomes variables were ICH and BCVI. Secondary outcomes were death and survival with or without neurological sequelae. Descriptive, bivariate, and multiple logistic regression statistics were computed, and the significance level was set at P ≤ 0.05. The sample was composed of 1440 patients with a mean age of 46.6 years ±24 years, and 71% were men. Pure orbital wall (odds ratio [OR]), 3.62; 95% confidence interval [CI], 1.32-12.69; P < 0.022), Le Fort III (OR, 16.08; 95% CI, 5.89-43.50; P < 0.001), cranial vault (OR, 9.74; 95% CI, 3.83.24.32; P < 0.001), skull base (OR, 9.42; 95% CI, 3.86-24.02; P < 0.001) and cervical fractures (OR, 5.50; 95% CI, 1.65-15.97; P = 0.003) were significantly associated with BCVI. All of the CMFs (P < 0.001), except for Le Fort I (OR, 0.79; 95% CI, 0.18-2.63; P = 0.731), nasal (OR, 1.05; 95% CI, 0.77-1.42; P = 0.758), and mandibular (OR, 0.68; 95% CI, 0.45-1.01; P = 0.066) fractures, were significantly associated with ICH. Secondary outcomes were negatively influenced by ICH and BCVI (P < 0.001). Within the limitations of the study it seems that Le Fort I and nasal fractures could be protective of cerebrovascular injuries, by cushioning impact forces. On the other hand it seems that patients with pure orbital wall, Le Fort III and cranio-cervical fractures are more prone to having concomitant life-threatening cerebrovascular injuries. This category of patients should have an immediate and comprehensive neurological assessment and CT angiography to rule out BCVI and to determine its severity.

Comparison of characteristics of kick- and electric-scooter-related dental and maxillofacial injuries: A retrospective study

BACKGROUND/AIM

Owing to the nearly three-year-long COVID-19 pandemic, small personal transportation devices that allow for greater freedom of movement within the cities have gained attention. Therefore, the number of people using kick or electric scooters has increased. This study aimed to compare the characteristics of kick and electric scooter-related dental and maxillofacial trauma and provide helpful information for preventing scooter accidents, appropriate treatment of patients with scooter-related trauma, and policy establishment.

MATERIALS AND METHODS

This retrospective observational study analysed the medical records of 310 patients who visited the emergency room of Ajou University Dental Hospital for kick and electric scooter-related oral and maxillofacial injuries between 1 January 2017 and 31 December 2022. Sex, age, scooter type, time, and mechanism of the accident, helmet use, alcohol consumption, dental and maxillofacial injury types, and treatment were analysed.

RESULTS

The average age in the kick-scooter group (5.71 ± 4.25) was lower than that in the electric-scooter group (28.24 ± 10.02) (p < .0001). There were more males in both groups. The helmet usage rates of the two groups were 2.80% and 7.88%, respectively. In the kick-scooter group, periodontal damage was more common than pulp injury, while in the electric-scooter group, pulp injury was more common than periodontal injury. There was no significant difference in soft-tissue damage between the two groups; however, bone fractures occurred significantly more frequently in the electric-scooter group (p < .0001).

CONCLUSIONS

Electric scooters cause more crown and bone fractures than kick scooters and require more active treatment of dental and maxillofacial injuries. Riders should use protective equipment to prevent dental and maxillofacial injury. Although there are regulations related to scooters, the effectiveness of both kick- and electric-scooter related laws needs to be evaluated.

Reduction of comminuted fractures of the anterior wall of the frontal sinus using threaded Kirschner wires and a small eyebrow incision

Background: Frontal sinus fractures are relatively rare. Their surgical management significantly differs depending on whether the posterior wall is invaded and the clinical features vary. A bicoronal incision or endoscopic approach can be used. However, the minimally invasive approach has been attracting attention, leading us to introduce a simple and effective surgical method using multiple-threaded Kirschner wires.Methods: All patients had isolated anterior wall fractures without nasofrontal duct impairment. The depth from the skin to the posterior wall was measured using computed tomography to prevent injury. The edge of the bone segment on the skin was marked, a threaded Kirschner wire was inserted into the center of the bone segment, and multiple Kirschner wires were gently reduced simultaneously.Results: Surgery was performed on 11 patients. Among them, seven patients required additional support for appropriate fracture reduction. Therefore, a periosteal elevator was used as an adjunct through a small sub-brow incision because the reduction was incomplete with the Kirschner wire alone. The reduction results were confirmed using facial bone computed tomography 1 to 3 days postoperatively. The follow-up period was 3 to 12 months.Conclusion: The patients had no complications and were satisfied with the surgical results. Here we demonstrated an easy and successful procedure to reduce a pure anterior wall frontal sinus fracture via non-invasive threaded Kirschner wire reduction.

Automated 3D Analysis of Zygomaticomaxillary Fracture Rotation and Displacement

Background

The zygomaticomaxillary complex (ZMC) can experience a multitude of deforming forces. There is limited understanding on which deformities alter patient outcomes. This study utilized an automated, three-dimensional analysis to elucidate which fracture patterns and rotational deformities are most prevalent and associated with postoperative complications.

Methods

This study was a 7-year retrospective review of patients with unilateral ZMC fractures who underwent surgical intervention. Patient demographics, injury mechanisms, presenting symptoms, and postoperative outcomes were collected. Segmentation was completed using Mimics software. The lateral-medial, superior-inferior, and anterior-posterior axes were manually identified on the zygoma and then displacement, rotational direction, and rotational degrees were automatically calculated using Geomagic software. Total displacement score was generated by summation of individual displacement scores at each of the five sutures.

Results

Eighty-one patients satisfied inclusion criteria. The most prevalent rotational pattern of the zygoma was medially-superiorly-posteriorly (P < 0.001). When comparing rotation along the three axes, the zygoma had the greatest rotation along the lateral-medial axis compared with the superior-inferior (P = 0.003) and anterior-posterior (P < 0.001) axes. Within each axis, the zygoma was more likely to rotate medially than laterally (P = 0.003) and posteriorly than anteriorly (P = 0.01). Multivariate analysis identified total displacement scores and degrees rotated along the lateral-medial axis as significant predictors of facial complications and reoperation.

Conclusions

This study suggests that patients with unilateral ZMC fractures who undergo surgical intervention are at an increased risk for adverse outcomes with greater rotation along the lateral-medial axis and higher total displacement scores. Additionally, the automated analysis method described can provide objective data to better characterize ZMC fractures.

The association of Le Fort midfacial fractures with frontobasal injuries: a 17-year review of 125 cases, reflections on biomechanics, classifications and treatment

The frequency of midface and frontobasal fractures has increased over the past 40 years despite the improvement and stringent regulation implemented on modern safety equipment (belts, helmets…). This observation might be correlated with the progress of radiodiagnosis tools. Literature was reviewed according to Prisma guidelines. We searched for reviewed articles, published between January 2000 and December 2017, through Medline (Pubmed) online databases and ScienceDirect, using the following MeSH Keywords: "Le Fort classification", "Le Fort fracture", "Frontobasal fracture", "skull base fracture", "Midface Fractures". Among 652 patients with frontobasal fractures, 125 (19.1%) were associated with a Le Fort fracture. 59 (9%) were associated with Le Fort III fracture, 51 (7.8%) with Le Fort II fracture and 15 (2.3%) with Le Fort I fracture. When frontobasal fractures were associated with midfacial fractures, we found 18 cerebrospinal fluid leaks (11.8 %) and 19 cases of meningitis (12.5 %). When only the frontobasal area was involved, there were 6 cerebrospinal fluid leaks (4.3 %) and 6 meningitis (4.3 %). Our results highlight a regular association between Le Fort fractures and frontobasal fractures for stages II and stage III of Le Fort fractures and also found a higher rate of neuro-septic complication. Further research shall investigate treatment and monitoring recommendations fitting modern epidemiology of craniofacial traumatology.

An Anatomic Predisposition to Mandibular Angle Fractures

PURPOSE

To investigate a predisposition to mandibular angle fractures, a retrospective study was performed in which fractured mandibles were compared with healthy mandibles with no history of fracture. Other investigations of angle fracture risk have exclusively studied patients with existing fractures. In addition, the risk has not been comprehensively explained in conjunction with the specific features of mandibular anatomy. We sought to characterize any anatomic variations between the jaws that had fractured and those that had never fractured.

MATERIALS AND METHODS

Healthy mandibles with no history of fracture were physically measured at the William M. Bass Skeletal Collection at the University of Tennessee, Knoxville and compared with fractured mandibles from computed tomography (CT) scans at the Dartmouth Hitchcock Medical Center. A total of 52 healthy mandibles and 44 CT scans were evaluated. MATLAB machine learning algorithms (MathWorks, Natick, MA) were used to compare the study populations and isolate those anatomic features that differed between healthy and fractured mandibles.

RESULTS

Machine learning classifiers were able to differentiate between male and female jaws, with the condylion-gnathion distance the most distinguishing feature. The 6 most common anatomic features that differed between healthy and fractured mandibles were the 1) retromolar space, 2) perimeter of the cross-section just proximal to the second molar, 3) breadth of the ramal cross-section, 4) thickness of the oblique ridge, 5) transgonial angle, and 6) location of the ipsilateral mental foramen. The presence of third molars was also related to fracture risk, with third molars present in 72.7% of the fractured mandibles versus 26.9% of unfractured mandibles. Of the fractured mandibles with third molars present, 87.5% had the fracture running directly through the tooth or its socket.

CONCLUSIONS

The results from the present study have provided evidence that anatomic differences exist between mandibles that sustain angle fractures and those that do not. Although much of the morphology was found to be interdependent, the fracture risk could be accurately predicted using 6 anatomic features. Understanding these mandibular variations and identifying patients vulnerable to mandibular fracture could provide clinicians with additional objective information. Furthermore, using the methods demonstrated in our study, future research could focus on developing an algorithm that includes these unique anatomic features in the hope of assisting surgeons in providing tailored treatment for mandibular angle fractures according to patient-specific morphology.

Patterns of Facial Fractures and Protective Device Use in Motor Vehicle Collisions From 2007 to 2012

Importance

Facial fractures after motor vehicle collisions are a significant source of facial trauma in patients seen at trauma centers. With recent changes in use of seat belts and advances in airbag technology, new patterns in the incidence of facial fractures after motor vehicle collisions have yet to be quantified.

Objectives

To evaluate the incidence of facial fractures and assess the influence of protective device use in motor vehicle collisions in patients treated at trauma centers in the United States.

Design, Setting, and Participants

Using a data set from the National Trauma Data Bank, we retrospectively assessed facial fractures in motor vehicle collisions occurring from 2007 through 2012, reported by level I, II, III, and IV trauma centers. Data analysis was performed from March 13 to September 22, 2015.

Main Outcomes and Measures

We characterized the data set by subsite of facial injury using International Classification of Diseases, Ninth Revision codes including mandible, midface, and nasal fractures. We assessed the influence of variables such as age, sex, race/ethnicity, crash occupant (driver or passenger), use of protective device, and presence or suspicion of alcohol use.

Results

A total of 518 106 patients required assessment at a trauma center after a motor vehicle collision, with 56 422 (10.9%) experiencing at least 1 facial fracture. Nasal fracture was the most common facial fracture (5.6%), followed by midface (3.8%), other (3.2%), orbital (2.6%), mandible (2.2%), and panfacial fractures (0.8%). Of the subset sustaining at least 1 facial fracture, 5.8% had airbag protection only, 26.9% used a seat belt only, and 9.3% used both protective devices, while 57.6% used no protective device. Compared with no protective device, the use of an airbag alone significantly reduced the likelihood of facial fracture after a motor vehicle collision (odds ratio, 0.82; 95% CI, 0.79-0.86); use of a seat belt alone had a greater effect (odds ratio, 0.57; 95% CI, 0.56-0.58) and use of both devices provided the greatest odds reduction (odds ratio, 0.47; 95% CI, 0.45-0.48). Younger age, male sex, and alcohol use significantly increased the likelihood of facial fracture.

Conclusions and Relevance

For patients who presented to US trauma centers after motor vehicle collisions between 2007 and 2012, airbags, seat belts, and the combination of the 2 devices incrementally reduced the likelihood of facial fractures.

Level of Evidence

3.

The traumatic potential of a projectile shot from a sling

Herein, we analyze the energy parameters of stones of various weights and shapes shot from a sling and based on this data evaluate its traumatic potential. Four police officers proficient in the use of a sling participated in the trials. The following projectile types, shot using an overhead technique at a target 100m away were: round steel balls of different sizes and weights (24mm, 57g; 32mm, 135g; 38mm, 227g); different shaped stones weighing 100-150g and 150-200g and a golf ball (47g). Our data indicated that projectiles shot from unconventional weapons such as a sling, have serious traumatic potential for unprotected individuals and can cause blunt trauma of moderate to critical severity such as fractures of the trunk, limb, and facial skull bone, depending on the weight and shape of the projectile and the distance from the source of danger. Asymmetrically shaped projectiles weighing more than 100g were the most dangerous. Projectiles weighing more than 100g can cause bone fractures of the trunk and limbs at distances of up to 60m from the target and may cause serious head injuries to an unprotected person (Abbreviated Injury Scale 4-5) at distances up to 200m from the target. Due to the traumatic potential of projectiles shot from a sling, the police must wear full riot gear and keep at a distance of at least 60m from the source of danger in order to avoid serious injury. Furthermore, given the potential for serious head injuries, wearing a helmet with a visor is mandatory at distances up to 200m from the source of danger.

Surgical management of traumatic frontal sinus fractures: Case series from a single institution and literature review

BACKGROUND

Neurosurgeons are frequently involved in the management of patients with traumatic frontal sinus injury; however, management options and operative techniques can vary significantly. In this study, the authors review the current literature and retrospectively review the clinical series at a single tertiary referral center.

METHODS

After Institutional Review Board approval, the medical records and computed tomographic (CT) imaging of patients whose traumatic frontal sinus fractures were treated surgically at the University of Utah were retrospectively reviewed. Demographic information, mechanism of injury, associated injuries, operative technique, and pattern of injury on CT were analyzed.

RESULTS

Between 2000 and 2012, 33 patients underwent successful cranialization of the frontal sinus following traumatic injury. The material used to obliterate the sinus varied. No patients required immediate or delayed reoperation. Nasofrontal outflow tract obstruction, the importance of which has been emphasized in the plastic surgery literature, was apparent on either initial or retrospective review of the available CT imaging in 96%.

CONCLUSIONS

In this series, we successfully surgically treated 33 patients with frontal sinus fractures. The presence of cerebrospinal fluid leak, nasofrontal outflow tract injury, associated depressed skull fractures, and subsequent formation of communicating pathways and infection must be considered when constructing a treatment plan. The goals of treatment should be: (i) surgical repair of the defect and elimination of the conduit from the intracranial space to the outside and (ii) elimination of any cerebrospinal fluid pressure gradient that may develop across the surgical repair. We present a treatment algorithm focusing on the presence of nasofrontal outflow tract injury/obstruction, cosmetic deformity, and cerebrospinal fluid leak.

Video analysis of the biomechanics of a bicycle accident resulting in significant facial fractures

INTRODUCTION

This study aimed to use video analysis techniques to determine the velocity, impact force, angle of impact, and impulse to fracture involved in a video-recorded bicycle accident resulting in facial fractures. Computed tomographic images of the resulting facial injury are presented for correlation with data and calculations. To our knowledge, such an analysis of an actual recorded trauma has not been reported in the literature.

MATERIALS AND METHODS

A video recording of the accident was split into frames and analyzed using an image editing program. Measurements of velocity and angle of impact were obtained from this analysis, and the force of impact and impulse were calculated using the inverse dynamic method with connected rigid body segments. These results were then correlated with the actual fracture pattern found on computed tomographic imaging of the subject's face.

RESULTS

There was an impact velocity of 6.25 m/s, impact angles of 14 and 6.3 degrees of neck extension and axial rotation, respectively, an impact force of 1910.4 N, and an impulse to fracture of 47.8 Ns. These physical parameters resulted in clinically significant bilateral mid-facial Le Fort II and III pattern fractures.

DISCUSSION

These data confer further understanding of the biomechanics of bicycle-related accidents by correlating an actual clinical outcome with the kinematic and dynamic parameters involved in the accident itself and yielding a concrete evidence of the velocity, force, and impulse necessary to cause clinically significant facial trauma. These findings can aid in the design of protective equipment for bicycle riders to help avoid this type of injury.

Biomechanical investigation of the supraorbital arch - a transient FEA study on the impact of physical blows

Introduction

As fractures of the supraorbital region are far less common than midfacial or orbital fractures, a study was initiated to investigate whether fist blows could lead to fractures similar to those often seen in the midface.

Methods

A detailed skull model and an impactor resembling a fist were created and a fist blow to the supraorbital region was simulated. A transient finite element analysis was carried out to calculate von Mises stresses, peak force, and impact time.

Results

Within the contact zone of skull and impactor critical stress values could be seen which lay at the lower yield border for potential fractures. A second much lower stress zone was depicted in the anterior-medial orbital roof.

Conclusions

In this simulation a fist punch, which could generate distinct fractures in the midface and naso-ethmoid-orbital region, would only reach the limits of a small fracture in the supraorbital region. The reason is seen in the strong bony architecture. Much higher forces are needed to create severe trauma in the upper face which is supported by clinical findings. Finite element analysis is the method of choice to investigate the impact of trauma on the human skeleton.

Frontal sinus fractures

The management of frontal sinus fractures has changed over the past 20 years. Whereas the indications for an invasive procedure had been much broader in the past, it has become more common to treat these fractures conservatively, due to improved imaging modalities, the advent of endoscopic surgical treatment of the nasofrontal outflow tracts, and the improved understanding of frontal sinus physiology. A variety of algorithms have been proposed for the management of frontal sinus fractures; however, we present a simplified treatment algorithm, which uses cranialization, obliteration, reconstruction, observation, and endoscopic sinus surgery.

The influence of headform orientation and flooring systems on impact dynamics during simulated fall-related head impacts

Novel compliant flooring systems are a promising approach for reducing fall-related injuries in seniors, as they may provide up to 50% attenuation in peak force during simulated hip impacts while eliciting only minimal influences on balance. This study aimed to determine the protective capacity of novel compliant floors during simulated 'high severity' head impacts compared to common flooring systems. A headform was impacted onto a common Commercial-Carpet at 1.5, 2.5, and 3.5 m/s in front, back, and side orientations using a mechanical drop tower. Peak impact force applied to the headform (F(max)), peak linear acceleration of the headform (g(max)) and Head Injury Criterion (HIC) were determined. For the 3.5 m/s trials, backwards-oriented impacts were associated with the highest F(max) and HIC values (p<0.001); accordingly, this head orientation was used to complete additional trials on three common floors (Resilient Rubber, Residential-Loop Carpet, Berber Carpet) and six novel compliant floors at each impact velocity. ANOVAs indicated that flooring type was associated with all parameters at each impact velocity (p<0.001). Compared to impacts on the Commercial Carpet, Dunnett's post hoc indicated all variables were smaller (25-80%) for the novel compliant floors (p<0.001), but larger for Resilient Rubber (31-159%, p<0.01). This study demonstrates that during 'high severity' simulated impacts, novel compliant floors can substantially reduce the forces and accelerations applied to a headform compared to common floors including carpet and resilient rubber. In combination with reports of minimal balance impairments, these findings support the promise of novel compliant floors as a biomechanically effective strategy for reducing fall-related injuries including traumatic brain injuries and skull fractures.

The Tolerance of the Maxilla to Blunt Impact

This study reports the results of 38 infraorbital maxilla impacts performed on male cadavers. Impacts were performed using an unpadded, cylindrical impactor (3.2 kg) at velocities between 1 and 5 m/s. The peak force and acoustic emission data were used to develop a statistical relationship of fracture risk as a function of impact force. Acoustic emission sensors were used to provide a noncensored measure of the maxilla tolerance and were essential due to the increase in impactor force after fracture onset. Parametric and nonparametric techniques were used to estimate the risk of fracture tolerance. The nonparametric technique produced an estimated 50% risk of fracture between 970 and 1223 N. The results obtained from the parametric and nonparametric techniques were in good agreement. Peak force values achieved in this study were similar to those of previous work and were unaffected by impactor velocity. The results of this study suggest that an impact to the infraorbital maxilla is a load-limited event due to compromise of structural integrity.

The Tolerance of the Frontal Bone to Blunt Impact

The current understanding of the tolerance of the frontal bone to blunt impact is limited. Previous studies have utilized vastly different methods, which limits the use of statistical analyses to determine the tolerance of the frontal bone. The purpose of this study is to determine the tolerance of the frontal bone to blunt impact. Acoustic emission sensors were used to provide a noncensored measure of the frontal bone tolerance and were essential due to the increase in impactor force after fracture onset. In this study, risk functions for fracture were developed using parametric and nonparametric techniques. The results of the statistical analyses suggest that a 50% risk of frontal bone fracture occurs at a force between 1885 N and 2405 N. Subjects that were found to have a frontal sinus present within the impacted region had a significantly higher risk of sustaining a fracture. There was no association between subject age and fracture force. The results of the current study suggest that utilizing peak force as an estimate of fracture tolerance will overestimate the force necessary to create a frontal bone fracture.

Critical computed tomographic diagnostic criteria for frontal sinus fractures

PURPOSE

Diagnosis and treatment of frontal sinus fractures (FSFs) have progressed over the previous 30 years. Despite advances in computed tomography, there is no current diagnostic uniformity with regard to classification and treatment. We developed a statistically valid treatment protocol for FSFs based on injury pattern, nasofrontal outflow tract (NFOT) injury, and complication(s). These data outlined predictable injury patterns based on specific computed tomographic findings critical to the diagnosis and ultimate treatment of this potentially fatal injury.

MATERIALS AND METHODS

A retrospective review was conducted on patients with FSF from 1979 to 2005 under institutional review board approval. All computed tomographic scans were reviewed by the authors and fractures categorized by location, displacement, comminution, and degree of NFOT injury.

RESULTS

One thousand ninety-seven patients with FSF were identified, 87 expired and 153 had inadequate data, leaving a group of 857 patients. Simultaneous displacement of anterior-posterior tables constituted the largest group (38.4%). NFOT injury occurred in most patients (70.7%) and was strongly associated with anterior (92%) and posterior (88%) table involvement (comminuted 98%). Sixty-seven percent of patients with NFOT injury had obstruction. Five hundred four patients (59.6%) had surgery with 10.4% complications and 353 patients were observed with 3.1% complications. All but 1 patient with complications had NFOT injury (98.5%).

CONCLUSIONS

Predictable patterns of injury based on specific computed tomographic data play a pivotal role in classification and surgical management of potentially fatal frontal sinus injuries. Radiologic diagnosis of NFOT injury in FSFs, particularly obstruction, plays a decisive role in surgical planning.

Epistaxis as the only initial symptom in pediatric naso-orbital-ethmoid fracture complicated with meningitis

Epistaxis is a frequent finding in patients with facial trauma. Herein, we report an unusual presentation of pediatric naso-orbital-ethmoid (NOE) fracture with epistaxis as the only initial symptom. The course of the patient's condition was later complicated by meningitis, related in part to the delay in diagnosis. A 3-year-old girl with preexisting upper respiratory symptoms was involved in a traffic accident, sustaining blunt trauma to the right side of her face. During the initial examination, only right-sided epistaxis was noted. Five days later, she developed febrile convulsion and was admitted to the intensive care unit with other signs of meningitis such as mental status change and neck stiffness. Her craniofacial computed tomographic scan showed a right-sided NOE fracture with minimal displacement and without dura tear. The cerebrospinal fluid culture grew Streptococcus pneumoniae, which may be due to ascending infection as a result of cribriform plate fracture. Intravenous antibiotic therapy was initiated with good response, and she was discharged from the hospital after 2 weeks. The presence of epistaxis and periorbital bruise, together with other symptoms and signs, helps in the identification of NOE and cribriform plate fracture. A high index of suspicion with repetitive computed tomographic scans is necessary to achieve correct early diagnosis. Parental antibiotic therapy is indicated if ascending cerebrospinal fluid infection develops.

Twenty-six-year experience treating frontal sinus fractures: a novel algorithm based on anatomical fracture pattern and failure of conventional techniques

BACKGROUND

Frontal sinus fracture treatment strategies lack statistical power. The authors propose statistically valid treatment protocols for frontal sinus fracture based on injury pattern, nasofrontal outflow tract injury, and complication(s).

METHODS

An institutional review board-approved retrospective review was conducted on frontal sinus fracture patients from 1979 to 2005. Fractures were categorized by location, displacement, comminution, and nasofrontal outflow tract injury. Demographic data, treatment, and complications were compiled.

RESULTS

One thousand ninety-seven frontal sinus fracture patients were identified; 87 died and 153 were excluded because of insufficient data, leaving a cohort of 857 patients. The most common injury was simultaneous displaced anteroposterior walls (38.4 percent). Nasofrontal outflow tract injury constituted the majority (70.7 percent), with 67 percent having a diagnosis of obstruction. Of the 857 patients, 504 (58.8 percent) underwent surgery, with a 10.4 percent complication rate; and 353 were observed, with a 3.1 percent complication rate. All complications except one involved nasofrontal outflow tract injury (98.5 percent). Nasofrontal outflow tract injuries with obstruction were best managed by obliteration or cranialization (complication rates: 9 and 10 percent, respectively). Fat obliteration and osteoneogenesis had the highest complication rates (22 and 42.9 percent, respectively). The authors' treatment algorithm provides a receiver operating characteristic area under the curve of 0.8621.

CONCLUSIONS

A frontal sinus fracture treatment algorithm is proposed and statistically validated. Nasofrontal outflow tract involvement with obstruction is best managed by obliteration or cranialization. Osteoneogenesis and fat obliteration are associated with unacceptable complication rates. Observation is safe when the nasofrontal outflow tract is intact.

Measuring Pulsatile Forces on the Human Cranium

The cyclic stresses in the cranium caused by pulsation of the brain play an important role in the design of materials for cranioplasty, as well as craniofacial development. However, these stresses have never been quantified. In this study, the force in the epidural space against the cranium was measured intraoperatively in 10 patients using a miniature force probe. Heart and ventilatory rates computed from the force tracing correlated closely with the corresponding measured values in the patients, confirming that the forces measured were indeed a result of brain pulsation. The mean outward systolic normal and tangential stresses were 54.2 kilo-Pascals (kPa) and 345.4 kPa, respectively. The systolic shear stress was 199.8 kPa. Through mechanotransduction, these stresses play a role in cranial development. The calculated yield stress of a cranioplasty repair was 0.4 MPa, which is within one order of magnitude of the known strength of common calcium-phosphate cements. This indicates a possible relation of these pulsatile forces and occult failure of calcium-phosphate cement cranioplasties through material fatigue.

Ballistic Impact to the Forehead, Zygoma, and Mandible: Comparison of Human and Frangible Dummy Face Biomechanics

BACKGROUND

Currently, there is a greater use of nonlethal force in law enforcement and military operations. Because facial injuries have been observed, there is a need to understand the human response to ballistic impacts involving various regions of the face. This study aimed to establish blunt ballistic response corridors for high-speed, low-mass facial impacts to the forehead, zygoma, and mandible, and to determine how these responses compare with those of the frangible Hybrid III headform. Correlation of the human and dummy responses allows injury risk assessment for munitions used in the field.

METHODS

Facial impacts to the forehead, zygoma, and mandible of six cadavers at 42 +/- 10 m/sec were conducted using a 25- to 35-g projectile 37 mm in diameter that was instrumented with an accelerometer to determine impact force. High-speed video analysis determined penetration of the projectile, and autopsy determined the facial fractures. Force and deflection were normalized for the 50% tile response, and corridors were determined for blunt ballistic impacts. Similar tests were conducted on the frangible face of the Hybrid III dummy.

RESULTS

Peak normalized force of 3.5 +/- 0.9 kN on the forehead and 3.0 +/- 1.0 kN on the mandible did not result in fractures, whereas an impact force of 2.3 +/- 0.5 kN on the zygoma caused anterior maxilla fractures. The frangible Hybrid III face developed similar force levels, but with less penetration of the projectile. Its stiffness was 43% greater than that of the cadaver.

CONCLUSIONS

Higher impact force can be tolerated on the forehead and mandible than on the zygoma. Normalized force-deflection and force-time corridors were established for the human response. The frangible Hybrid III face is an effective surrogate for assessing ballistic injury risks, but greater compliance would make it more biofidelic. Initial human tolerance levels of 6.0 kN for the forehead, 1.6 kN for the zygoma, and 1.9 kN for the mandible have been established for ballistic impacts to the face.

Experimental trauma to the malar eminence: fracture biomechanics and injury patterns

OBJECTIVES

To document patterns of facial fractures after trauma to the malar eminence and to elucidate biomechanical factors relevant to the injury patterns.

STUDY DESIGN AND SETTING

Studies were conducted on 14 cadaver heads. Study variables included impact velocity, contact area, impact force, and zygomatic skin thickness. Bony fractures and clinical injury patterns were documented. A fracture severity rating scale was devised and statistically correlated to the study variables using regression ANOVA analysis.

RESULTS

A broad spectrum of facial fracture patterns was found. Skin thickness and surface area did not correlate with fracture severity (P = 0.67, P = 0.83, respectively). Impact force demonstrated a trend toward significance (P = 0.14). Velocity was most correlative with fracture severity (P = 0.07). A critical threshold velocity (3.5 m/s) was found to correlate with the most severe fracture patterns.

CONCLUSIONS

A broad spectrum of facial fracture patterns was demonstrated after experimental trauma to the malar eminence. Contact surface area and zygomatic skin thickness were not found to be significant factors in fracture severity. Velocity, rather than impact force, was most correlative with fracture severity. The most severe fracture patterns were elicited by velocities above 3.5 m/s.

Biomechanical properties of calvarium prosthesis

There are many materials available for the reconstruction of calvarial defects. Even though their biomaterial properties are well known, the biomechanical properties as part of the calvarium have not been investigated. In this article, calvarial implants are reviewed with their historic development into modern cranioplasty. Materials for trephined skulls are classified by their category. Individual parameters to describe their mechanical properties are collected and revealed in detail. The laboratory testing methodology for cranioplasty material is introduced to understand each parameter. At last, we discuss an engineering technique to look into the implant behavior. Since there is no standard goal for the biomechanical and biomaterial point of view for cranioplasty, this article suggests the finite element method for evaluation of the implant behavior and the degree of damage upon the impact injury.

The effect of mandibular third molar presence and position on the risk of an angle fracture

PURPOSE

This study assessed the relationship between the presence and position of mandibular third molars (M3) and angle fractures.

PATIENTS AND METHODS

A retrospective cohort study design and a sample composed of patients admitted for treatment of mandible fractures between January 1993 and April 1998 were used. Data sources were the patients' medical records and radiographs. The predictor variables were the presence and position of M3. M3 position was grouped into 9 categories based on the Pell and Gregory classification. The outcome variable was the presence of an angle fracture. Other study variables included age, sex, race, mechanism of injury, and fracture location.

RESULTS

The eligible sample was composed of 437 patients, of whom 367 had data available for analysis. Patients with M3 present had a 1.9 times (95% confidence interval = 1.2 to 2.9) greater chance of an angle fracture than patients without M3s (P = .003). There was a statistically significant variation in the risk for an angle fracture, depending on M3 position (P = .049).

CONCLUSION

The study results confirm other reports that patients with M3 present have an increased risk for angle fractures. Furthermore, it also showed that the risk for an angle fracture varied depending on M3 position.

Relationship between fractures of the mandibular angle and the presence and state of eruption of the lower third molar

OBJECTIVES

This study attempted to relate the incidence of fractures at the mandibular angle with the presence and state of eruption of lower third molars.

STUDY DESIGN

The records and radiographs of 200 patients with mandibular fractures were examined. The presence and degree of impaction of lower third molars were assessed for each patient and related to the occurrence of fractures of the mandibular angle. Data were analyzed by chi-square statistic and the Student's t test.

RESULTS

The incidence of angle fractures was found to be significantly greater when unerupted lower third molars were present (p < 0.001). Bilateral unerupted third molar teeth predisposed to a fracture at the angle significantly more than unilateral unerupted third molars (p < 0.01). Furthermore, the amount of bony space occupied by an unerupted third molar tooth directly related to the weakness of that area of bone (p < 0.001).

CONCLUSIONS

This study provides clinical evidence to suggest that unerupted third molar teeth weaken the mandibular angle both quantitatively and qualitatively.

Midfacial fractures: importance of angle of impact to horizontal craniofacial buttresses

The complex nature of midfacial fractures is a result of the interaction of impact forces and inherent resistance of the facial bones to displacement. Analysis of fractures created in cadavers shows that impact forces angled obliquely to the horizontal craniofacial buttresses cause LeFort III fractures with inferior and posterior displacement of the midface. Forces directed head-on to the buttresses cause LeFort II-I fractures with inferior rotation of the midface around the lower ends of the pterygoid plates. It appears that the point of impact is of lesser importance in creating midfacial fractures than is the angle of impact in relation to the horizontal craniofacial buttresses. This may explain why victims of equal impact forces at the same level on the face suffer widely varying injuries.

Experimental fractures of monkey mandibles

Forty vervet monkey half mandibles, 20 with unerupted third molars and 20 with erupted third molars, were partially embedded in acrylic and loaded in an Instron tensiometer. Mandibles with unerupted third molars fractured at 15.8 +/- 2.5 kg while those having erupted third molars fractured at 26.4 +/- 4.2 kg. Mandibles having unerupted third molars were shown to be significantly weaker than the mandibles with erupted third molar (t = 8.45, P less than 0.001).