Influence of the deviated center of rotation on facet joint degeneration after cervical disc replacement - an in vivo study with a minimum of 10-year follow-up.

Abstract

Background: Short term results of the change of center of rotation (COR) after Bryan cervical disc replacement (CDR) have been reported. However, there is a lack of long-term studies focusing on the COR and its influences on facet joint degeneration.

Objective: To evaluate the long-term clinical and radiographic results of Bryan CDR, and to explore the influence of deviated COR on facet joint degeneration at index level.

Methods: It is a retrospective follow up study conducted in China. Eighty-three consecutive patients who received single-level Bryan CDR were retrospectively reviewed. Clinical evaluation included Japanese Orthopaedic Association (JOA) score, Neck Disability Index (NDI), and Odom's scale. Radiographic evaluation underwent before surgery, at early follow-up (3 months) and last follow-up (10 years). The radiographic parameters included range of motion (ROM), location of COR presented by the coordinates (COR-x, COR-y), and facet joint degeneration score. Correlation analysis was conducted between changes of COR and facet joint degeneration score.

Results: Fifty-nine patients were included, with an average age of 44.6 ± 7.4 years. The mean follow-up time was 135.7 ± 12.4 (120-155) months. JOA score, NDI and Odom's scale showed significant improvements at last follow-up. The ROM was well preserved through follow-up. 33 patients (55.9%) showed deterioration of facet joint degeneration at index level. The increment of facet joint degeneration score at index level was strongly correlated with the change of COR-x (r = 0.758, P < 0.001), and weakly correlated with the change of COR-y (r=-0.473, P < 0.001). The deviation of COR was significantly greater in Group Degeneration than that in Group Non-degeneration (14.8 ± 10.5% vs. -2.6 ± 8.1% for COR-x, and - 6.4 ± 7.5% vs. 0.8 ± 8.3% for COR-y).

Conclusions: Bryan CDR with minimum of 10-year follow-up achieved favorable clinical outcome and good maintenance of ROM. Deviated COR could be an important risk factor for facet joint degeneration.