Study design: Retrospective analysis of adjacent disc degeneration (ADD) after anterior cervical decompression and fusion (ADF).
Objectives: To elucidate the influence of the number of levels fused in ADF on the incidence of ADD.
Summary of background data: ADD is known as a complication associated with ADF. However, how the number of levels fused affects the incidence of ADD is not well understood.
Methods: One hundred and two patients with cervical degenerative disease, who underwent ADF and were followed for more than 24 months, were retrospectively analyzed. They were classified into 2 groups, a long group (L group) consisting of 50 cases with ADF of 4 or more disc levels, and a short group (S group) consisting of 52 cases with ADF of 3 or fewer disc levels. Furthermore, the patients were also divided into 2 groups according to inclusion or exclusion of C5-6 and C6-7 (C group: including both, NC group: not including both). The incidence of ADD, and that of symptomatic ADD (sADD), was compared between the 2 classifications.
Results: In the L group, there were 13 cases of ADD (26.0%), including 1 case of sADD (2.0%), whereas in the S group, there were 22 cases of ADD (42.3%), including 11 cases of sADD (21.2%). The incidence of sADD was significantly lesser in the L group (P=0.024). Three cases with sADD in the S group required revision surgery, whereas no additional surgery related to ADD was performed on patients in the L group. In addition, in the C group, ADD occurred in 20 of 71 cases (28.2%) and sADD occurred in 4 of 71 cases (5.6%), whereas in the NC group, ADD occurred in 15 of 31 cases (48.4%) and sADD occurred in 8 of 31 cases (25.8%). The incidence of ADD and sADD were significantly lesser in the C group (P=0.048).
Conclusions: ADD occurs less frequently among patients in whom C5-6 and C6-7 are fused than among those in whom C5-6 or C6-7 is left at an adjacent level, irrespective of the length of the fusion.