Background: It has been our experience that ossification occurs
adjacent to anterior cervical plates. Our hypothesis was that the closer the
plate is to the adjacent disc space, the greater the ossification.
Methods: We retrospectively reviewed the lateral radiographs of the
cervical spine of 118 patients who had a solid fusion following an anterior
cervical arthrodesis with a plate for the treatment of a degenerative cervical
condition; none of the patients had had cervical spine surgery prior to the
index arthrodesis. The plate-to-disc distance was measured on the
postoperative lateral radiograph and was used to divide the patients into two
groups for each of the two adjacent disc spaces. In group A the plate-to-disc
distance was <5 mm, and in group B it was =5 mm. The mean duration of
follow-up was 25.7 months. The severity of the ossification at the two
adjacent disc spaces was classified on a scale ranging from grade 0 (no
ossification) to grade 3 (complete bridging). Eighteen patients were excluded
from the measurement of the severity of the caudal ossification because
overlapping by the bone of the shoulder precluded adequate visualization of
the caudal level.
Results: Ossification developed in seventy (59%) of the 118 cephalad
adjacent disc spaces and twenty-nine (29%) of the 100 caudal adjacent disc
spaces (p < 0.001). The mean cephalad plate-to-disc distance was shorter
than the mean caudal plate-to-disc distance (p < 0.001). The rate of
ossification was higher in group A than in group B, both at the cephalad
adjacent disc spaces (67% compared with 24%) and at the caudal adjacent disc
spaces (45% compared with 5%) (both p < 0.001). In addition, 93%
(twenty-six) of the twenty-eight cases of moderate-to-severe ossification
developed in group A.
Conclusions: We found a positive association between adjacent-level
ossification following anterior cervical plate procedures and the
plate-to-disc distance. We now strive to place anterior cervical plates at
least 5 mm away from the adjacent disc spaces in order to decrease the
likelihood of moderate-to-severe adjacent-level ossification.
Level of Evidence: Therapeutic Level III. See
Instructions to Authors for a complete description of levels of evidence.