Cervical spinal stenosis (CSS) is often a result of degenerative cervical spondylosis that may cause chronic compression of the cervical spinal cord, eventually leading to dysfunction 13,14. These age-related degenerative changes including intervertebral disc disease, vertebral remodeling, hypertrophy and/or ossification of spinal ligaments, and spondylolisthesis15. Although it was reported that sagittal orientation of the facet joints is a risk factor of cervical degenerative spondylolisthesis1–3, 16, to our knowledge, the direct relationship between sagittal orientation of the facet joints and CSS not yet been explored.
The present study demonstrated that the cervical facet orientations changed from level to level. The facet joint angles were more vertically oriented in the lower region of the subaxial spine, especially at the C6/C7 level, which is in agreement with some previous studies17,18. Rong et al 17 and Pal et al 18 also reported the increasing facet joint angles from C2-C3 to C6- C7 in horizontal plane. In contrast, Ebraheim et al19 evaluated the cervical facet joints using 41 cervical spines from C3 to C7, and they found that facet joint angles was decreased from 51.7° at C2/3 level to 44.2° at C6/7 level. This difference may be due to factors such as different measurement means, patients positions, differences between reference planes, and ethnic differences. Different to previous studies, in this study we also found that the facet angle of female patients was significantly smaller than that of male patients at C2-C3 in the CSS group.
The facet joints play a prominent role in stabilizing the motion segment in flexion, extension, and axial rotating restriction20. A biomechanical study reported that the facet joint bears 33% of the dynamic load and 35% of the static load of the spine21. In recent years, facet tropism become a research hotspot in those studies that related to cervical facet joints. In order to analyze the relationship between facet orientation and CSS more accurately, we excluded the patients who has a more than 7 difference in bilateral angles with respect to the axial plane22, 23.
The anteroposterior diameter of cervical spinal canal (A–P diameter) in MRI has been demonstrated that is a effective method to reflect cervical spinal stenosis11,24,25. The standard of CSS using A–P diameter shows marked ethnic differences in previous studies. Different to western countries, which suggested that cut-off value of cervical spinal canal diameter was 13 mm 24,26, it was reported A–P diameter < 11 mm is more advisable to indicate cervical spinal stenosis in our region11. In their study, A–P diameters on transverse image were 11.11 mm–12.43 mm and 6.68mm–10.76mm in the healthy group and spinal stenosis group respectively. In our study, the average A-P diameter at all levels are between 11-12mm in the control group and 7-9mm in CSS group. The etiology of variation of facet orientation is remains unclear. Some scholars theorize that facet orientation results from cervical spine degeneration2,3,27, while some believe that it is caused by developmental alterations 28–30.
The most significant limitation of this study is that we analyzed the facet orientation only in the transverse plane. If facet orientation in sagittal and coronal plane can also be analyzed, a more comprehensive and accurate relationship between facet orientation and CSS could be obtained. Besides, although imaging parameters were measured by two individuals, there also exists the possibility of a measurement error. As this was a retrospective study, we are unable to ascertain the cause-effect relationship between facet orientation and CSS.