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Study design Biomechanical study using cadaveric cervical spines. Objective To evaluate joint mobility and stiffness at the craniovertebral junction. Summary of background data Data on the intersegmental kinematics of the craniovertebral joints are available in the literature with a widespread range of values. The effect that alar ligament injuries have on intersegmental kinematics remains unclear and requires further biomechanical investigation. Methods Ten occipito-atlanto-axial (C0-C1-C2) human specimens were articulated to flexion, extension, bilateral lateral bending, and bilateral axial rotation. The moment-rotation response was continuously tracked through the entire range of motion before and after unilateral alar ligament transection of the right side. Results The intersegmental (C0-C1/C1-C2) moment-rotation response was continuously quantified in full flexion (7.2 ± 6.6°/12.1 ± 5.8°), extension (11.1 ± 6.4°/3.0 ± 2.8°), lateral bending to the right (3.1 ± 2.2°/1.6 ± 1.2°) and left sides (3.3 ± 1.6°/2.1 ± 1.5°), and axial rotation to the right (1.2 ± 3.5°/32.3 ± 9.3°) and left sides (2.7 ± 2.6°/25.3 ± 8.3°). Unilateral alar ligament transection increased the range of motion of C0-C2 in the three planes of movement; however, intersegmental motion alterations were not always observed. Conclusion Increases in the range of extension and lateral bending at C0-C1, which had not been reported previously, were observed. Further, the range of rotation on the right and left sides increased, in conjunction with the increased ranges at C0-C1 and C1-C2.Level of Evidence: N/A.

The present study has three objectives: First, to analyze the chest deflection measured in nearside oblique tests performed with three post mortem human subjects (PMHS). Second, to assess the capability of a HBM to predict the chest deflection sustained by the PMHS. Third to evaluate the influence on chest deflection prediction of subject-specific HBM. Three dimensional chest deformation of five anterior chest landmarks was extracted from three PMHS (A-C) in three sled tests. The sled test configurations corresponded to a 30 degree nearside oblique impact at 35 km/h. Two different restraint system versions (RSv) were used. RSv1 was used for PMHS A and B while RSv2 was used for PMHS C. The capability of the SAFER HBM (called baseline model) to predict PMHS chest deflection was benchmarked by means of the PMHS test results. In a second step, the anthropometry, mass and pre-impact posture of the baseline HBM were modified to the PMHS-specific characteristics to develop a model to assess the influence of personalization techniques in the capability of the human body model to predict PMHS chest deflection. In the sled tests, the measured sternum compression relative to the eighth thoracic vertebra in the PMHS tests was 49, 54 and 55 millimeters respectively. The HBM baseline model predicted 48%, 43% and 34% of the deflections measured in the PMHS tests, while the personalized version predicted 38%, 34% and 28%. When chest deflection was analyzed in x-, y- and z-direction for the five chest landmarks it was found that neither the baseline HBM nor the personalized model predicted x, y and z axis deflections. The PMHS in situ chest deflection was found to be sensitive to the variation in restraint system and the three PMHS exhibited greater values of lower right chest deflection compared to what was found in available literature. The baseline HBM underpredicted peak chest deflection obtained in the PMHS test. The personalized model was not capable of predicting the chest deflection sustained by the PMHS. Hence, further biofidelity investigations have to be carried out on the human body thorax model for oblique loading.

Previous studies indicate that maximum upper cervical axial rotation occurs only through a combination of transverse, frontal, and sagittal plane motions. This study explores the relationship between transection of the alar ligament and combined upper cervical axial rotation movements. Ten cryopreserved upper cervical spines were manually mobilized in bilateral axial rotation and two different motion combinations with simultaneous motion in the three anatomical planes: rotation in extension (extension + axial rotation + contralateral lateral bending) and rotation in flexion (flexion + axial rotation + ipsilateral lateral bending). These three motions were performed before and after right alar ligament transection. The occiput-axis axial rotation was measured using an optical motion capture system while measuring the applied load. With intact alar ligament, the axial rotation in flexion showed the lowest range of motion (right, R: 9.81 ± 3.89°; left, L: 15.54 ± 5.89°). Similar results were found between the other two mobilizations: axial rotation (R: 33.87 ± 6.64°; L: 27.99 ± 6.90°) and rotation in extension (R: 35.15 ± 5.97°; L: 28.96 ± 6.47°). After right alar ligament transection, rotation in flexion (particularly in left rotation) showed the largest increase in motion: rotation in flexion (R: 13.78 ± 9.63°; L: 23.04 ± 5.59°), rotation in extension (R: 36.39 ± 7.10°; L: 31.71 ± 7.67°), and axial rotation (R: 38.50 ± 9.47°; L: 31.59 ± 6.55°). Different combinations of movements should be evaluated when analyzing the maximum axial rotation of the upper cervical spine, as axial rotation alone and rotation in extension showed a larger range of motion than rotation in flexion. After unilateral alar ligament injury, rotation to the non-injured side in flexion demonstrates the most movement increase. info:eu-repo/semantics/publishedVersion

Instability is a serious and life-threatening diagnosis in the upper cervical spine (occiput-atlas-axis), and a depth understanding of normal range of movement is required for clinical manual evaluation. To improve this knowledge, ten upper cervical spine specimens have been tested in flexion, extension, lateral bending, and axial rotation.

Background The side-bending stress test is a pre-manipulative screening test for assessing upper cervical instability. To our knowledge, there is no study that simulates the clinical application of side bending stress test before and after alar ligament transection with fixation of C2. Objective To simulate the effect of alar ligament transection in the side bending stress test for an in vitro validation. Design In vitro study. Methods After the dissection of the superficial structures to the alar ligament and the fixation of C2, ten cryopreserved upper cervical spines were manually mobilized in right and left lateral flexion with and without right alar ligament transection. Upper cervical lateral flexion range of motion and mobilization force were measured with the Vicon motion capture system and a load cell respectively. Results The right alar ligament transection increased the upper cervical spine (UCS) range of motion (ROM) in both side bendings (1.30°±1.54° and 1.88°±1.51° increase for right and left side bending respectively). As an average, with standardized forces of 2N, 4N and 6N, right alar ligament transection increased both right and left lateral flexion UCS ROM. Conclusion This in vitro study simulates the clinical application of the side bending stress test with intact and right transected alar ligament. Unilateral transection of the alar ligament revealed a predominantly bilateral increase in upper cervical side bending and variability in the mobilization force applied during the test.

The rotation stress test is used to evaluate stability of the craniocervical junction by assuming that it gives the maximum rotation. However, a more complex manipulation might show a higher rotation: the rotation with extension and contralateral bending. This was tested in vitro with ten upper cervical spine specimens.