Morphology and kinematics of the atlanto-axial joints and their interaction during manual cervical rotation mobilization

Anatomy and mobility in the adult cadaveric craniocervical junction

Genetic diseases with craniofacial malformations can be associated with anomalies of the craniocervical joint (CCJ). The functions of the CCJ are thus impaired, as mobility may be either limited by abnormal bone fusion causing headaches, or exaggerated in the case of hypermobility, which may cause irreparable damage to the spinal cord. Restoring the balance between mobility and stability requires surgical correction in children. The anatomy and biomechanics of the CCJ are quite unique, yet have been overlooked in the past decades. Pediatric evidence is so scarce, that investigating the adult CCJ is our best shot to disentangle the form-function relationships of this anatomical region. The motivation of the present study was to understand the morphological and functional basis of motion in the CCJ, in the hope to find morphological features accessible from medical imaging able to predict mobility. To do so, we have quantified the in-vitro kinematics of the CCJ in nine cadaveric asymptomatic adults, and estimated a wide range of mobility variables covering the complexity of spinal motion. We compared these variables with the shape of the occipital, the atlas and the axis, obtained using a dense geometric morphometric approach. Morphological joint congruence was also quantified. Our results suggest a strong relationship between bone shape and motion, with the overall geometry predicting best the primary movements, and the joint facets predicting best the secondary movements. We propose a functional hypothesis stating that the musculoligamental system determines movements of great amplitude, while the shape and congruence of joint facets determine the secondary and coupled movements, especially by varying the geometry of bone stops and the way ligaments are tensioned. We believe this work will provide valuable insights in understanding the biomechanics of the CCJ. Furthermore, it should help surgeons treating CCJ anomalies by enabling them to translate objectives of functional and clinical outcome into clear objectives of morphological outcome.

Association between Age, Sex and Cervical Spine Sagittal Plane Motion: A Descriptive and Correlational Study in Healthy Volunteers

Active motion examination of patients with cervical spine-related pathologies is necessary to establish baseline function, set physical therapy goals, and choose interventions. This study investigated the sagittal plane active range of motion (ROM) of the global (GCS) and upper cervical spine (UCS) in relation to age and sex in healthy volunteers. One hundred twenty-two volunteers aged 18 to 75 years participated. Volunteers were excluded if they displayed any characteristic that could affect cervical spine ROM. GCS and UCS flexion and extension were each measured three times using a CROM device. Linear regression models (LRMs) were developed to explore the relationships between age and sex and GCS and UCS ROM. The LRM for age showed a decrease in GCS flexion (-2.01°), GCS extension (-3.33°), and UCS extension (-1.87°) for every decade of increasing age. The LRM for sex showed that men displayed less ROM than women in GCS extension (-6.52°) and UCS extension (-2.43°). These results suggest an age-related loss of sagittal plane GCS ROM and UCS extension ROM, and sex-related differences in GCS and UCS extension with women having greater motion than men.

In vitro upper cervical spine kinematics: Rotation with combined movements and its variation after alar ligament transection

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.

Effects of occipital-atlas stabilization in the upper cervical spine kinematics: an in vitro study

This study compares upper cervical spine range of motion (ROM) in the three cardinal planes before and after occiput-atlas (C0–C1) stabilization. After the dissection of the superficial structures to the alar ligament and the fixation of C2, ten cryopreserved upper cervical columns were manually mobilized in the three cardinal planes of movement without and with a screw stabilization of C0–C1. Upper cervical ROM and mobilization force were measured using the Vicon motion capture system and a load cell respectively. The ROM without C0–C1 stabilization was 19.8° ± 5.2° in flexion and 14.3° ± 7.7° in extension. With stabilization, the ROM was 11.5° ± 4.3° and 6.6° ± 3.5°, respectively. The ROM without C0–C1 stabilization was 4.7° ± 2.3° in right lateral flexion and 5.6° ± 3.2° in left lateral flexion. With stabilization, the ROM was 2.3° ± 1.4° and 2.3° ± 1.2°, respectively. The ROM without C0–C1 stabilization was 33.9° ± 6.7° in right rotation and 28.0° ± 6.9° in left rotation. With stabilization, the ROM was 28.5° ± 7.0° and 23.7° ± 8.5° respectively. Stabilization of C0–C1 reduced the upper cervical ROM by 46.9% in the sagittal plane, 55.3% in the frontal plane, and 15.6% in the transverse plane. Also, the resistance to movement during upper cervical mobilization increased following C0–C1 stabilization.

The effect of alar ligament transection on the rotation stress test: A cadaveric study

BACKGROUND

The rotation stress test is a pre-manipulative screening test used to examine upper cervical instability. This in vitro study simulates the clinical application of the rotation stress test before and after alar ligament transection.

METHODS

After the dissection of the superficial structures to the alar ligament and the fixation of C2, ten cryopreserved upper cervical columns were manually mobilized in right and left rotation without and with right alar ligament transection. Upper cervical rotation range of motion (RoM) and mobilization torque were recorded using the Vicon motion capture system and a load cell.

FINDINGS

Ligament transection resulted in a larger rotation range of motion in all specimens (contralateral rotation (3.6°, 12.9%) and ipsilateral rotation (4.6°, 13.7%)). The mobilization torque recorded during rotation varied among the different specimens, with a trend towards reduced torque throughout the test in contralateral rotation.

INTERPRETATION

This study simulated the rotation stress test before and after alar ligament transection. Unilateral transection of the alar ligament revealed a bilateral increase of the upper cervical rotation. Additional in vivo studies are necessary to validate the results of this study in patients with suspicion of upper cervical instability.

Analysis of three-dimensional facet joint displacement during two passive upper cervical mobilizations

BACKGROUND

Understanding the 3D-kinematics of the upper cervical spine during manual mobilization is essential for clinical examination and therapy. Some information about rotational motion is available in literature but translational components are often ignored, complicating the understanding of the complex inter-segmental motions.

OBJECTIVES

This study aims to describe the amount, trajectories and reproducibility of atlanto-occipital facet joints' displacement during a flexion-extension mobilization and of the atlanto-axial facet joints during an axial rotation mobilization.

DESIGN

Original research using quantitative data.

METHODS

20 fresh frozen human cervical specimens were examined with a Zebris® CMS20 ultrasound-based motion tracking system. Two physiotherapists performed regionalmobilizations in flexion-extension and axial rotation. The amount of displacement and the trajectories were calculated along the XYZ axes. Difference between measurements was evaluated with the Friedman two-way ANOVA test. Intra- and inter-rater reliability were estimated through ICC scores.

RESULTS

3D-displacement (2.6-23.4 mm) was larger at C1-C2 during axial rotation, Atlanto-occipital flexion displayed the greatest variability in the C0 trajectory. During a right rotation, the left C1 facet moved mainly forward, and the right C1 facet moved backward. During a left rotation, the left C1 facet moved backward, while the right C1 facet moved forward. Intra-tester and Inter-tester ICCs varied between 0.5 and 0.90 (p < 0.005).

CONCLUSIONS

During passive spinal motion, there is an important variability in magnitude and trajectory of joints' displacement. Nevertheless, different clinicians may be able to achieve the same position at the end of the mobilization.

In vivo three-dimensional kinematics of the cervical spine during maximal axial rotation

The cervical spine exhibits considerable mobility, especially in axial rotation. Axial rotation exerts stress on anatomical structures, such as the vertebral artery which is commonly assessed during clinical examination. The literature is rather sparse concerning the in vivo three-dimensional segmental kinematics of the cervical spine. This study aimed at investigating the three-dimensional kinematics of the cervical spine during maximal passive head rotation with special emphasis on coupled motion. Twenty healthy volunteers participated in this study. Low-dose CT scans were conducted in neutral and in maximum axial rotation positions. Each separated vertebra was segmented semi automatically in these two positions. The finite helical-axis method was used to describe 3D motion between discrete positions. The mean (±SD) maximum magnitude of axial rotation between C0 and C1 was 2.5 ± 1.0° coupled with lateral flexion to the opposite side (5.0 ± 3.0°) and extension (12.0 ± 4.5°). At the C1-C2 level, the mean axial rotation was 37.5 ± 6.0° associated with lateral flexion to the opposite side (2.5 ± 6.0°) and extension (4.0 ± 6.0°). For the lower levels, axial rotation was found to be maximal at C4-C5 level (5.5 ± 1.0°) coupled with lateral flexion to the same side (-4.0 ± 2.5°). Extension was associated at levels C2-C3, C3-C4 and C4-C5, whereas flexion occurred between C5-C6 and C6-C7. Coupled lateral flexion occurred to the opposite side at the upper cervical spine and to the same side at the lower cervical spine.