In-vivo kinematics of the cervical spine in frontal sled tests

Biomechanical analysis of cervical spine (C2-C7) at different flexed postures

Musculoskeletal diseases are often related with postural changes in the neck region that can be caused by prolonged cervical flexion. This is one of the contributing factors. When determining the prevalence, causes, and related risks of neck discomfort, having a solid understanding of the biomechanics of the cervical spine (C1-C7) is absolutely necessary. The objective of this study is to make predictions regarding the intervertebral disc (IVD) stress values across C2-C7 IVD, the ligament stress, and the variation at 0°, 15°, 30°, 45°, and 60° of cervical neck angle using finite element analysis (FEA). In order to evaluate the mechanical properties of the cervical spine (particularly, C2-C7), this investigation makes use of computed tomography (CT) scans to develop a three-dimensional FEA model of the cervical spine. A preload of 50 N compression force was applied at the apex of the C2 vertebra, and all degrees of freedom below the C7 level were constrained. The primary objective of this investigation is to assess the distribution of von Mises stress within the IVDs and ligaments spanning C2-C7 at various flexion angles: 0°, 15°, 30°, 45°, and 60°, utilizing FEA. The outcomes derived from this analysis were subsequently compared to previously published experimental and FEA data to validate the model's ability to replicate the physiological motion of the cervical spine across different flexion angles.

Société de Biomécanique Young Investigator Award 2019: Upper body behaviour of seated humans in vivo under controlled lateral accelerations

BACKGROUND

A deep understanding of human reactions and stabilization strategies is required to predict their kinematics under external dynamic loadings, such as those that occur in vehicle passengers. Low-level frontal accelerations have been thoroughly investigated; however, the human response to different lateral accelerations is not well understood. The objective of this study is to gain insight regarding the responses of seated humans to lateral perturbations from volunteer experiments in different configurations.

METHODS

Five volunteers anthropometrically comparable to the 50th-percentile American male, were seated on a sled and submitted to 21 lateral pulses. Seven configurations, each repeated three times, were investigated in this study: a relaxed muscular condition with four pulses, namely, sine and plateau pulses of 0.1 and 0.3 g in a straight spinal posture; a relaxed muscular condition with a plateau pulse of 0.3 g in a sagging spinal posture; and a braced condition with both plateau pulses in a straight spinal posture. Upper body segment kinematics were assessed using inertial measurement units.

FINDINGS

The maximum lateral bending of the head was found to differ significantly among the four acceleration pulses (p < 0.001). Braced muscles significantly reduced lateral bending compared to relaxed muscles (p < 0.001). However, no significant difference was found in lateral bending between straight and sagging spinal postures (p = 0.23).

INTERPRETATION

The study shows that not only pulse amplitude but also pulse shape influences human responses to low accelerations, while spinal posture does not influence lateral head bending. These data can be used to evaluate numerical active human body models.

Influence of a Passenger Position Seating on Recline Seat on a Head Injury during a Frontal Crash

Presently, most passive safety tests are performed with a precisely specified seat position and carefully seated ATD (anthropomorphic test device) dummies. Facing the development of autonomous vehicles, as well as the need for safety verification during crashes with various seat positions such research is even more urgently needed. Apart from the numerical environment, the existing testing equipment is not validated to perform such an investigation. For example, ATDs are not validated for nonstandard seatback positions, and the most accurate method of such research is volunteer tests. The study presented here was performed on a sled test rig utilizing a 50cc Hybrid III dummy according to a full factorial experiment. In addition, input factors were selected in order to verify a safe test condition for surrogate testing. The measured value was head acceleration, which was used for calculation of a head injury criterion. What was found was an optimal seat angle −117°—at which the head injury criteria had the lowest represented value. Moreover, preliminary body dynamics showed a danger of whiplash occurrence for occupants in a fully-reclined seat.

The biomechanical study of cervical spine: A Finite Element Analysis

The biomechanical study helps us to understand the mechanics of the human cervical spine. A three dimensional Finite Element (FE) model for C3 to C6 level was developed using computed tomography (CT) scan data to study the mechanical behaviour of the cervical spine. A moment of 1 Nm was applied at the top of C3 vertebral end plate and all degrees of freedom of bottom end plate of C6 were constrained. The physiological motion of the cervical spine was validated using published experimental and FE analysis results. The von Mises stress distribution across the intervertebral disc was calculated along with range of motion. It was observed that the predicted results of functional spine units using FE analysis replicate the real behaviour of the cervical spine.

Development and validation of a geometrically personalized finite element model of the lower ligamentous cervical spine for clinical applications

Epidemiological and clinical studies show that the magnitude and scope of cervical disease are on the rise, along with the world's rising aging population. From a biomechanical perspective, the cervical spine presents a wide inter-individual variability, where its motion patterns and load sharing strongly depend on the anatomy. This study aimed to first develop and validate a geometrically patient-specific model of the lower cervical spine for clinical applications, and secondly to use the model to investigate the spinal biomechanics associated with typical cervical disorders. Based on measurements of 30 parameters from X-ray radiographs, the 3D geometry of the vertebrae and intervertebral discs (IVDs) were developed, and detailed finite element models (FEMs) of the lower ligamentous cervical spine for 6 subjects were constructed and simulated. The models were then used for the investigation of different grades of IVD alteration. The multi directional range of motion (ROM) results were in alignment with the in-vitro and in-Silico studies confirming the validity of the model. Severe disc alteration (Grade 3) presented a significant decrease in the ROM and intradiscal pressure (flexion, extension, and axial rotation) on the C5-C6 and slightly increase on the adjacent levels. Maximum stress in Annulus Fibrosus (AF) and facet joint forces increased for Grade 3 for both altered and adjacent levels. The novel validated geometrically-personalized FEM presented in this study potentially offers the clinical community a valuable quantitative tool for the noninvasive analyses of the biomechanical alterations associated with cervical spine disease towards improved surgical planning and enhanced clinical outcomes.

Vascular geometry as a risk factor for non-penetrating traumatic injuries of the aortic arch

PURPOSE

To assess biomechanical factors in aortic arch geometry contributing to the development of non-penetrating aortic arch injury (NAAI) in multiply injured patients with an Injury Severity Score (ISS) ≥ 16.

MATERIAL AND METHODS

230 consecutive multiply injured trauma patients with an ISS ≥ 16 admitted to our Level-I trauma center during a consecutive 24-month period were prospectively included of whom 13 presented with NAAI (5.7%). Standardized whole-body CT in a 2x128-detector-row scanner included a head-and-neck CTA. Aortic arch diameters, width, height, angles and thoracic width and height were measured in individuals with NAAI and ISS-, sex-, age-, and trauma mechanism-matched controls.

RESULTS

There was no difference between groups regarding sex, age, ISS, and aortic diameters. The aortic arch angle in individuals with NAAI (71.3° ± 14.9°) was larger than in healthy control (60.7° ± 8.6°; p*<0.05). In patients with NAAI, the distance between ascendent and descendent aorta was larger (5.2 cm ± 1.9 cm) than in control (2.8 ± 0.5 cm; ***p<0.001). The aortic arch is higher above tracheal bifurcation in NAAI (3.6 cm ± 0.6 cm) than in matched control (2.4 cm ± 0.3 cm; ***p<0.001). Accordingly, the area under the aortic arch, calculated as half of an eliptic shape, is significantly larger in patients with NAAI (15.0 cm2 ± 6.5 cm2) when compared to age- and sex-matched controls without NAAI (5.5 cm2 ± 1.3 cm2; ***p<0.001).

CONCLUSION

Besides the magnitude of deceleration and direction of impact, width and height of the aortic arch are the 3rd and 4th factor directly contributing to the risk of developing traumatic NAAI in severely injured patients.