Background: Ossification of the anterior longitudinal ligament and the anulus adjacent to an anterior cervical arthrodesis has been termed adjacent-level ossification development. Initial studies suggested an association with the placement of plates <5 mm from an adjacent disc space. A follow-up study demonstrated that this ossification rarely occurs in association with arthrodeses without plate fixation. In the present study, our goal was to determine the incidence of adjacent-level ossification in patients who underwent cervical arthrodesis with plate fixation as compared with that in patients who underwent cervical arthroplasty.
Methods: We performed a post hoc analysis of prospectively collected data. Radiographic data for all patients from a single site were used. All postoperative, two-year, and four-year follow-up lateral cervical spine radiographs were collected and formatted to occlude the surgical level, blinding the readers as to the procedure performed. Three independent blinded surgeons graded the cephalad adjacent level for the degree of ossification at each time point. The data were statistically analyzed for significant ossification grade differences between arthrodesis and arthroplasty.
Results: A total of forty-six patients (twenty-one with a Bryan total disc arthroplasty and twenty-five with an arthrodesis) were included. Both cohorts were derived from previous participation in a Level-I multicenter prospective randomized controlled trial stratified by site. Ossification scores based on independent assessment by three readers at multiple follow-up times were used. The arthrodesis group had significantly higher ossification scores than the arthroplasty group at both the two-year (p = 0.003) and the four-year follow-up interval (p = 0.004). Both cohorts showed significant increases in ossification from the two-year follow-up to the latest follow-up (p = 0.001 for the anterior cervical arthrodesis group and p = 0.008 for the arthroplasty group).
Conclusions: Our data conclusively demonstrate that cervical intervertebral arthroplasty is associated with a significantly lower incidence of adjacent-level ossification than arthrodesis with plate fixation at both the two-year and the four-year follow-up. Arthroplasty has the advantage of not being associated with adjacent-level ossification, which may decrease cervical spine motion above and below the surgical level.
Level of Evidence: Therapeutic Level III. See Instructions to Authors for a complete description of levels of evidence.
1Lake Norman Orthopedic Spine Center, 170 Medical Park Road, Suite 102, Mooresville, NC 28117. E-mail address for B.J. Garrido: email@example.com
2Suite 11300 West Pavilion, One Barnes-Jewish Hospital Plaza, St. Louis, MO 63110
3Indiana Spine Group, 8402 Harcourt Road, Suite 400, Indianapolis, IN 46260