[Long-term effect of excessive length of bone graft via anterior cervical approach on cervical curvature and axial symptom].

OBJECTIVE

To evaluate the long-term effect of excessive length of bone graft via anterior cervical approach and over distraction of intervertebral space on cervical curvature and postoperative neck axial symptom (AS).

METHODS

From June 2001 to June 2004, 30 patients with nerve root cervical spondylosis at the C5,6 level underwent anterior cervical decompression, autogenous iliac bone graft and internal fixation with titanium plate. There were 14 males and 16 females aged 32-73 years old (average 54.7 years old), and the course of disease was 1-31 months (average 7 months). No instability of cervical vertebrae was noted on the cervical dynamic position x-ray films. Intervertebral height was measured immediately after operation, and accordingly the patients were divided into two groups: the over distraction group (n = 11), in which the length of bone graft was excessive, the intervertebral space was over distracted, and the intervertebral height was increased by more than 3 mm compared with the preoperative value; the proper distraction group (n = 19), in which the length of bone graft was proper, no over distraction of the intervertebral space occurred, and the intervertebral height was increased by less than 3 mm compared with the preoperative value. Regular X-ray exams were performed 1 week and 3, 24, and 48 months after operation to analyze bone fusion condition of the grafted bone, changes of the intervertebral height of the fused segments, and variation of physiological curvature of the cervical vertebra. The postoperative neck AS was evaluated according to the the neck AS evaluation criteria set by ZENG Yan and co-workers.

RESULTS

All patients were followed up for 48-66 months (average 54.5 months). Clinical symptoms were eliminated in all cases. No complications occurred in the proper distraction group; 1 patient of the over distraction group had postoperative nerve root paralysis at C5 level, and recovered 3 months after proactive treatment. Bone fusion was achieved in all patients 3-6 months after operation, except for 1 case in the proper distraction group suffering from non-fusion 12 months after operation. There was no occurrence of loosening or breakage of steel plate and screw, and no displacement of the grafted bone. At 48 months after operation, the intervertebral height of the proper distraction group and the over distraction group was increased by (1.9 +/- 1.8) mm and (3.5 +/- 2.7) mm, respectively, when compared with the preoperative value (P > 0.05). The physiological curvature of the operated cervical segment was well maintained. The curvature of the proper distraction group and the over distraction group at the final follow-up visit was increased by (2.17 +/- 1.83) degrees and (3.32 +/- 2.71) degrees, respectively, when compared with the preoperative value (P > 0.05). The physiological curvature of the whole cervical vertebra at the final follow-up visit was increased by (4.57 +/- 3.71) degrees in the proper distraction group and decreased by (2.43 +/- 2.13) degrees in the over distraction group, when compared with the preoperative value (P < 0.05). The incidence rate of postoperative neck AS at 48 months after operation was 15.79% in the proper distraction group (11 cases excellent, 5 cases good, 3 cases fair) and 54.55% in the over distraction group (3 cases excellent, 2 cases good, 5 cases fair, 1 case poor), showing a significant difference between two groups (P < 0.05).

CONCLUSION

Excessive length of bone graft via anterior cervical approach and over distraction of intervertebral space are bad for maintaining the physiological curvature of the whole cervical vertebra, and increase the incidence of postoperative neck AS. Selection of bone graft at the proper height is essential in anterior cervical operation.