In vivo 3D kinematic analysis of cervical facet joints under physiological loading in healthy individuals

As cervical total disc arthroplasty progresses, the biomechanics and physiology of cervical facet joints are gaining more attention. Yet, knowledge of their in vivo kinematics and synergistic functions remains limited.

Approved by the ethics committee of a tertiary hospital, 20 asymptomatic adults (10 males, 10 females; mean age 34.4 years (SD 9.2)) were recruited with informed consent. Participants underwent cone-beam CT (CBCT) scans in seven functional cervical positions. 3D vertebral models were reconstructed, and local coordinate systems were established for each facet joint. Using 3D-3D registration, segmental motions and displacements were calculated in six degrees of freedom relative to the neutral position. Rotations were described as Cardan angles, and displacements as left-right, anteroposterior, and superoinferior components. Range of motion (ROM) was defined as the absolute difference between end positions and averaged across left and right facet joints.

In vivo analysis revealed distinct kinematic characteristics of the cervical facet joints. During flexion-extension, C0-C1 exhibited the greatest ROM (mean 25.6° (SD 5.9°)), whereas C2-C3 and C6-C7 showed relatively restricted motion. The mean total craniocervical (C0-C7) primary ROM was 62.9° (SD 7.6°), with segmental displacements mainly occurring in the anteroposterior direction, particularly at C0-C1. During axial rotation, the C1-C2 joint accounted for approximately 85% of the total motion (mean 51.4° (SD 5.1°)) and demonstrated the largest LR displacement (mean 5.2 mm (SD 4.4)). In lateral bending, the overall ROM was 35.2° (SD 7.7°), with C1-C2 again contributing the most and showing the largest LR displacement (mean 8.7 mm (SD 2.2)). These findings highlight the dominant role of C0-C1 in flexion-extension and C1-C2 in axial rotation and lateral bending, as well as the segment-specific displacement patterns of cervical facet joints.

CBCT-based 3D-3D registration enabled precise in vivo assessment of cervical facet joint kinematics. These findings could offer valuable insights into the rehabilitation of facet joint manipulation and provide meaningful prospects for future research.