Object: Bone grafts used in anterior cervical fusion (ACF) may subside postoperatively. The authors reviewed a recent series in which instrument-assisted ACF was performed to determine the degree of subsidence with respect to fusion length, use of segmental screws, and patient smoking status, age, and sex.
Methods: Charts and implant records were reviewed for all 70 patients who underwent instrument-assisted ACF during a 2-year period. The procedures, grafting materials, plate types/lengths, and patient smoking status were recorded. The immediate postoperative and follow-up lateral radiographs were analyzed. The plate lengths and lengths of the fused segments were measured in a standardized fashion. The mean intraoperative and follow-up fusion segment lengths were 54.3 and 51.9 mm, respectively. Greater subsidence occurred in multilevel fusions than in single-level fusions. There were noticeable changes in the position of plates or screws on 14 of 70 follow-up x-ray films. No new neurological deficits related to graft subsidence occurred, and the reoperation rate was 3%. There was no statistical relation between subsidence and the following variables: segmental fixation, smoking status, sex, age, or dowel size when corrected for length of the plate. Hardware migration correlated significantly with plate length in cases of two- and three-level fusions.
Conclusions: The length of a fusion segment decreases in the immediate weeks following instrument-assisted ACF. Construct length is the most important determinant of subsidence. When designing multilevel cervical constructs, consideration of the effects of graft subsidence may help to avoid hardware-related complications.