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Effect of cervical alignment change after anterior cervical fusion on radiological adjacent segment pathology.

Background
Adjacent segment pathology (ASP) is one of the primary complications affecting the long-term efficacy of anterior cervical fusion (ACF). At present, the cause and mechanism of adjacent segmental lesions are still controversial.


Methods
We performed a retrospective analysis on 88 patients with cervical spondylotic myelopathy (CSM) who had been followed up for at least 1 year after ACF. The patients were divided into radiological adjacent segment pathology (RASP) and non-RASP groups according to the presence of postoperative RASP. On the lateral radiographs of the cervical spine of all patients taken before and after surgery at the short-term and final follow-ups, the following parameters were measured: C2-7 Cobb angle of the cervical vertebrae; Cobb angle of the operated segments; and the anterior and posterior height of the fused segments [i.e., the anterior fusion segment height (AFH) and the posterior fusion segment height (PFH)]. The intra- and inter-group differences of the patients before and after surgery were calculated, as well as correlation of ACF with the occurrence of RASP.


Results
There were 42 cases in the RASP group and 46 cases in the non-RASP group. In the RASP group, the C2-7 Cobb angle was significantly reduced in the short term after surgery (20.42±9.92° vs. 13.81±8.52°, P<0.01), while in non-RASP group the C2-7 Cobb angle was significantly increased in the short term after surgery (12.65±11.91° vs. 15.35±10.05°, P<0.05). The heights of both the anterior and posterior fused segments in the 2 groups were significantly higher after surgery, and they were significantly lower at the final follow-up than at the short-term follow-up. Post-operative AFH change was significantly correlated with C2-7 Cobb angle (r=0.274, P=0.010) and fused segment Cobb angle change (r=0.333, P=0.002). However, Cox regression analysis showed that only the postoperative C2-7 Cobb angle change was associated with RASP, with a hazard ratio of 0.336.


Conclusions
Decreased cervical lordosis after ACF may be related to postoperative RASP. Maintaining good cervical curvature after surgery may reduce the incidence of RASP after ACF.