Effect of Facet Tropism on Postoperative Cervical Range of Motion After Single-Level Cervical Disc Arthroplasty

Abstract

Study Design: Retrospective analysis. Objectives: Cervical disc arthroplasty (CDA) was designed to replace the degenerated disc with the prosthesis to preserve cervical motion. The commonly used artificial discs are designed symmetric, whereas the facet joints were reported to be asymmetric in many people. This study aimed to evaluate the effect of facet tropism on the cervical range of motion (ROM) after single-level CDA using Prestige LP. Methods: A total of 90 patients who underwent single-level CDA using Prestige LP from 2012 to 2017 were retrospectively reviewed. Radiographs were taken at each time point to measure the C2-C7 ROM and the ROM at the surgical segment. The pre-operation CT scans were utilized to reconstruct and calculate the angular direction of facet joints with respect to transverse, coronal, and sagittal reference planes. Facet tropism above 7° was defined as facet joint asymmetry. Results: No significant difference was found in flexion-extension C2-C7 ROM or ROM at the surgical segment between patients with symmetric and asymmetric fact joints regarding the sagittal plane. Patients with coronal asymmetric facet joints had lower flexion-extension ROM at the surgical level. Patients with transverse asymmetric facet joints had both lower flexion-extension C2-C7 ROM and ROM at the surgical level. After CDA surgery, patients obtained good clinical outcomes including increased Japanese Orthopedic Association (JOA) and decreased Neck Disability Index (NDI) as well as Visual Analogue Scale (VAS). Conclusion: The coronal and transverse tropism seemed to be correlated with decreased flexion-extension ROM after CDA using Prestige LP.

Tropism of Sub-Axial Cervical Facet Joints Is Not Related to Segmental Movement during Active Movement or Therapist-Perceived Symptomatic Locations

“…In relation to angular movement, these findings differ from some previous studies where tropism was found to be related to mobility, at least in flexion/extension in the lumbar [14] and cervical spines [5]. Methodological differences could account for the findings being different from other studies.…”

“…Even in those studies that measured the asymmetry from 3D images, most measured tropism from single two-dimensional slices [8,13]. A difficulty with this method is that the angles of the facets can be different depending on which slice is measured [5,8]. To overcome this difficulty, Liu et al [5] fit a single plane to each facet but still calculated asymmetry in each cardinal axis separately.…”

“…A difficulty with this method is that the angles of the facets can be different depending on which slice is measured [5,8]. To overcome this difficulty, Liu et al [5] fit a single plane to each facet but still calculated asymmetry in each cardinal axis separately. It might seem that asymmetry in a given plane would likely be related to alteration of movement around an axis perpendicular to that plane, but this does not seem to be the case [5,6].…”

“…In the lumbar spine, findings are mixed, with some studies finding no relationship between tropism and the magnitude of movement [13], while others found that increased tropism correlated with reduced segmental movement [14]. In the cervical spine, tropism in the axial and coronal planes was associated with decreased movement in flexion/extension, but not with any alterations in lateral bending [5]. In summary, although it appears that tropism in both the lumbar and cervical spines is related to increased degenerative changes and decreased mobility in the sagittal plane, it is unclear what effects tropism has on movements in other planes, particularly on rotational movements.…”

“…Even with three dimensional (3D) images, tropism was still usually considered to describe asymmetry of the facets in the sagittal plane as seen in axial images [3,4]. Currently, tropism is also used to indicate 3D asymmetry of the facets in any plane [5], which is how the term will be used in this manuscript.…”