Forces transmission to the skull in case of mandibular impact.

BACKGROUND: Forensic investigations have been reported regarding the loss of consciousness and cardiac arrests resulting from direct mandible impact. However, the mechanisms by which the forces are transferred to the skull through direct mandible impact remain unclear. We conducted a study regarding direct mandible impact on the level of energy required to create a mandible fracture and on the energy dispersion phenomenon to the skull and to the brain. MATERIALS AND METHODS: This study combines an experimental and numerical approach. Mandible strike was studied using experimental trials performed on post-mortem human subjects. A finite element model of the head and face of a male was also developed based on tomodensitometry scans. The model was validated with literature data and experimental trials. A parametric study was then performed to study the effect of diverse variables such as the dentition integrity, cortical bone thickness, etc. RESULTS: The forces measured on our reference model were 3000 N on the chin, 1800 N at the condyles, and 970 N in the occiput. Of all the results, we observed a decrease of approximately one-third of the efforts from the chin to the base of the skull and a lower half of the still forces at the occiput, except in the edentulous and for the lateral and frontal impact where the force is transmitted directly to the skull base area. CONCLUSION: This study allowed us to create a 3D model of the mandible and face bones to better understand the force transfer mechanisms into and from the mandible. The parameters of the model may be modified to suit the individual characteristics for forensic investigations and legal matters.

Simulation of high energy vertebral fractures on complete porcine specimens.

This work presents a novel method creating high energy vertebral fractures on complete swine specimens to investigate realistic vertebral fracture mechanisms. An apparatus was developed to maintain a porcine specimen in an upright position and apply a caudal impact simulating a fall. Five mature minipigs were impacted with varying impact magnitude. Computed tomography scans were used to assess the resulting fracture type, fracture level, spinal canal encroachment and fractures of adjacent bony structures. Lumbar fractures were produced on four specimens: three inferior endplate burst fractures (L2) and one superior endplate burst fracture (L5). One trial resulted in a hyperextension fracture between L2 and L3 vertebrae. Spinal canal encroachment was important for three specimens. No fracture was created on the pelvis or hind limbs. The proposed method developed and the resulting swine model of high energy vertebral fractures could be used to instigate novel biomechanical studies, to validate finite element models or to investigate surgical strategies.

Compressive loading of the spine may affect the spinal canal encroachment of burst fractures.

STUDY DESIGN: Spinal canal encroachment of burst fractures under different compressive loading. OBJECTIVE: To assess whether the application of different compressive loads affect the spinal canal encroachment (SCE) of thoracolumbar burst fractures and to relate any significant encroachment differences to the fracture morphology. SUMMARY OF BACKGROUND DATA: The SCE is an important part of the evaluation process of thoracolumbar burst fractures. It is, however, not well understood how a variation in spinal internal loads resulting from a change in patient posture may affect the SCE after a burst fracture. The application of a compressive load on fractured vertebrae may displace bony fragments further into the canal and increase the encroachment. METHODS: Ten thoracolumbar functional spinal units harvested from mature minipigs and compressed to create burst fractures were imaged by computed tomography under 3 loading conditions: without compressive force and with 2 compressive forces analogous to the load expected in vivo. SCE were measured for all loading cases and compared with each other to identify whether they systematically changed between loading cases and to discriminate which specimens were affected by an increase in the loading. RESULTS: The application of a compressive loading did not systematically increase the SCE. However, specimens with a large bony fragment originating from the superior and posterior aspect of the vertebral body with a centrifugal orientation had a significant increase of SCE when loaded. CONCLUSIONS: An increase in spinal internal loads resulting from a change in the patient posture may increase the SCE of burst fracture. Measurement of the SCE should take into account the bony fragment distribution of burst fracture.

Effect of spinal level and loading conditions on the production of vertebral burst fractures in a porcine model.

Vertebral burst fractures are commonly studied with experimental animal models. There is however a lack of consensus as to what parameters are important to create an unstable burst fracture with a significant canal encroachment on such model. This study aims to assess the effect of the loading rate, flexion angle, spinal level, and their interactions on the production of a vertebral thoracolumbar burst fracture on a porcine model. Sixteen functional spinal units composed of three vertebrae were harvested from mature Yucatan minipigs. Two loading rates (0.01 and 500 mm/s), two flexion angles (0° and 15°), and two spinal levels (T11-T13 and T14-L2) were studied, following a full factorial experimental plan with one repetition. Compression was applied to each functional unit to create a vertebral fracture. The load-to-failure, loss of compressive stiffness, final canal encroachment, and fracture type were used as criteria to evaluate the resulting fracture. All specimens compressed without flexion resulted in burst fractures. Half of the specimens compressed with the 15° flexion angle resulted in compression fractures. Specimens positioned without flexion lost more of their compressive stiffness and had more significant canal encroachment. Fractured units compressed with a higher loading rate resulted in a greater loss of compressive stiffness. The spinal level had no significant effect on the resulting fractures. The main parameters which affect the resulting fracture are the loading rate and the flexion angle. A higher loading rate and the absence of flexion favors the production of burst fractures with a greater canal encroachment.