Abstract
The skull base is uniquely positioned to absorb force imparted to the craniofacial skeleton, thereby reducing brain injury. Less well understood is the effect of the direction of force imparted to the craniofacial skeleton on the severity of brain injury. Eighty-one patients from two UK major trauma centres who sustained a fronto-basal fracture were divided into two groups: those struck with predominantly anterior force and those by predominantly lateral force. The first recorded Glasgow Coma Score (GCS), requirement for intubation, and requirement for decompressive craniectomy were used as markers of the severity of brain injury. An average GCS of 5 was found in the lateral group and 14 in the anterior group; this difference was statistically significant ( P < 0.001). There was an increased need for both intubation and decompressive craniectomy in the lateral group compared to the anterior group (absolute risk difference 46.6% and 15.8%, respectively). These results suggest that the skeletal anatomy of the fronto-basal region influences the severity of head injury. The delicate lattice-like structure in the central anterior cranial fossa can act as a crumple zone, absorbing force. Conversely in the lateral aspect of the anterior cranial fossa, there is a lack of collapsible interface, resulting in an increased energy transfer to the brain.
Traumatic brain injury (TBI) is a major cause of morbidity and mortality to the individual, with a high social cost both to the family and the wider community. Personality change, physical and psychological dependence, and an inability to reintegrate socially or return to gainful employment are but some of the factors to consider when determining the cost burden of these injuries.
The severity and outcome of TBI for individual patients is multifactorial. Age, co-morbidity, and major extracranial injury all influence the outcome. Similarly, the direction of the impact force, i.e. antero-posterior (AP) versus lateral, and whether the impact force is linear or rotational, affects both the severity and nature of the brain injury. Directional studies using both primates and cadavers have demonstrated that lateral impacts result in more severe TBI in comparison to anteriorly directed impacts. It is believed that this is the result of torsional or rotational forces acting on the white matter tracts of the brain and brainstem. A recent human study has suggested that AP impacts are more likely to result in subdural haematomas, whereas parenchymal injuries are more likely with lateral impacts. Diffuse axonal injury is particularly associated with rotational stresses.
TBI frequently accompanies craniofacial trauma and fronto-basal fractures. The fronto-basal area consists of the upper midface and the anterior cranial fossa (ACF). In the context of this article, a fronto-basal fracture was considered a fracture of the floor of the ACF resulting from blunt trauma to the frontal bone. These fractures make up around 5% of all fractures involving the craniofacial skeleton and are the result of high-energy impacts.
The direction of the impact force has also been considered in studies examining its influence on the pattern of the fractures sustained to the skull base. These studies have involved the analysis of computed tomography (CT) scans and cadaveric dissection.
What appears to be absent in the comprehensive literature on head injuries is the possible influence, if any, of the bony architecture of the ACF on the severity of the brain injury sustained in human subjects. Neurosurgeons quite reasonably are primarily interested in the severity of the brain injury and whether or not there is a leak of cerebrospinal fluid (CSF). Maxillofacial/plastic/ENT surgeons, whilst also concerned with the presence of a leak of CSF, are primarily interested in the nature and severity of the facial injury. It could be argued that the anatomy of the base of the skull has, to an extent, been overlooked when considering brain injury severity.
This study considered the effect of direction of force applied to the craniofacial skeleton on the severity of brain injury sustained by patients with fronto-basal fractures. Furthermore the possible role of the bony anatomy of the skull base in this context was considered.
The aim of this study was to determine whether there are differences in the severity of the brain injury sustained by patients depending on the predominant direction of force striking the anterior fossa. The null hypothesis was that the direction of force does not influence the severity of brain injury sustained as a result of blunt impact to the frontal bone.
Materials and methods
Subjects
This study was based at two UK major trauma centres (MTC). All patients who sustained a fracture of the ACF at MTC 1 between 17 June 2006 and 17 July 2013 and at MTC 2 between 1 January 2012 and 28 February 2014 were included. MTC 1 data collected prospectively (2006–2013) and MTC 2 data collected retrospectively (2012–2014). Ethical approval was granted by the necessary research ethics committee.
Fronto-basal fractures were defined for the purposes of this study as a fracture of the floor of the ACF resulting from blunt trauma to the frontal bone.
Patients with penetrating skull base fractures and fractures confined to the anterior table of the frontal sinus were excluded. Patients with inadequate clinical information or CT imaging were also excluded.
Patient age and sex were recorded, as well as the mechanism of injury. The predominant direction of force was classified as anterior or lateral and was judged from the CT imaging and aided by the clinical notes. The ACF was bisected by a line 45° to the right angle formed by the midline and the sphenoid wing. The force was deemed ‘anterior’ if the predominant force struck the frontal bone anterior to this line and ‘lateral’ if behind ( Fig. 1 ). A predominantly lateral impact would therefore strike the frontal bone at an angle of 45° or greater. It is accepted that in a number of cases, due to the severity of the impact force, both anterior and lateral impacts may occur. An attempt in these cases to determine the ‘predominant’ direction of force was made, accepting that this would involve a degree of subjectivity.
Outcomes
The first recorded Glasgow Coma Score (GCS), requirement for intubation, and requirement for decompressive craniectomy were used as markers of the severity of brain injury. Given the diverse nature of presentation of a patient with a fronto-basal fracture, the ‘first recorded’ GCS was used as opposed to a fixed time point. It is accepted that there is likely to be variation in the timing of this measurement.
Statistical analysis
All data were analysed using IBM SPSS Statistics version 21.0 (IBM Corp., Armonk, NY, USA) and Confidence Interval Analysis version 2.2.0 (CIA; Southampton University, Southampton, United Kingdom). A P -value of less than 0.05 was considered to show a statistically significant difference between data. A Mann–Whitney U -test was completed to compare the effect of direction of force and the first recorded GCS. The Pearson χ 2 test was used to compare the effect of direction of force and the requirement for intubation. Fisher’s exact test was used to compare the effect of direction of force and the requirement for decompression given an expected count of less than 5.
Results
Eighty-one patients met the inclusion criteria; 36 were from MTC 1 and 45 from MTC 2. There was no statistically significant difference between the patients of these two cohorts in terms of demographics, mechanism of injury, or predominant direction of impact force ( Tables 1 and 2 ). Furthermore, there was no significant difference in the cause of trauma between the anterior and lateral groups ( Table 1 ).
| MTC 1 | MTC 2 | Anterior | Lateral | |
|---|---|---|---|---|
| Road traffic collision | 19 | 17 | 21 | 15 |
| Fall from height | 11 | 16 | 15 | 12 |
| Other | 6 | 12 | 14 | 4 |
| P -value a | 0.357 | 0.276 | ||
| Study population | MTC 1 | MTC 2 | P -value | |
|---|---|---|---|---|
| Number of patients | 81 | 36 | 45 | – |
| Age of patients, years | 30.0 (22.5, 45.0) | 27.5 (21.3, 41.5) | 32.0 (23.0, 46.0) | 0.339 b |
| Sex of patient | ||||
| Male | 69 (85.2%) | 31 (86.1%) | 38 (84.4%) | 0.834 c |
| Female | 12 (14.8%) | 5 (13.9%) | 7 (15.6%) | |
| Direction of force | ||||
| Anterior | 50 (61.7%) | 25 (69.4%) | 25 (55.6%) | 0.201 c |
| Lateral | 31 (38.3%) | 11 (30.6%) | 20 (44.4%) | |
| First recorded GCS | 13 (5, 15) | 14 (8, 15) | 10 (4, 15) | 0.233 b |
| Requirement for intubation | ||||
| Yes | 42 (51.9%) | 18 (50.0%) | 24 (53.3%) | 0.765 c |
| No | 39 (48.1%) | 18 (50.0%) | 21 (46.7%) | |
| Requirement for decompressive craniectomy | ||||
| Yes | 13 (16.0%) | 5 (13.9%) | 8 (17.8%) | 0.636 c |
| No | 68 (84.0%) | 31 (86.1%) | 37 (82.2%) | |
a Results are reported as the median (lower quartile, upper quartile), or as the number (% of patients within the centre).
b Mann–Whitney U -test (asymptomatic significance, two-tailed).
Anteriorly directed force versus laterally directed force
In total, 50 patients sustained a predominantly anteriorly directed force (anterior group) and 31 patients sustained a predominantly laterally directed force (lateral group) to their craniofacial skeleton.
GCS
The median GCS for the anterior group was 14 (lower quartile 13, upper quartile 15). This was greater than that of the lateral group of patients who had a median GCS of 5 (lower quartile 3, upper quartile 11). This difference in median GCS was statistically significant (median difference 7, 95% confidence interval 5–9; P < 0.001) ( Fig. 2 ).
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