Significance of cervical spine computed tomography Hounsfield Units to predict change of adjacent segment height after Anterior Cervical Discectomy and Fusion postprint

Abstract: Background　Bone density, as preoperative measured in Hounsfield units (HUs) on CT, may be associated with Loss of adjacent segment height after anterior cervical discectomy and fusion（ACDF），Studies relating CT values to postoperative complications of ACDF are still rarely reported . Objective　This study evaluated the association between HUs and change of upper adjacent segment height after ACDF. Methods　A retrospective study of patients　treated with single-level ACDF at the Sixth Affiliated Hospital of Xinjiang Medical University was performed. Preoperative CT and X-ray data at least 12 months after follow-up were collected.Patients with posterior surgery, tumor, trauma,　deformity, infection or osteoporosis treatment were excluded . HU values were measured according to previously published methods.Changes in upper adjacent segmental height were measured at 1-year follow-up compared with immediate postoperative radiographs .Patients were divided into groups A and B according to the height loss of intervertebral space exceeded 20% of the original height. Result　A total of 86 patients met inclusion criteria. There was no significant difference in age,sex,the average follow-up time and BMI between two groups. Mean HU values in the A group (313.64± 19.84, n = 15) were significantly lower than B group (349.42±32.85, n = 71, p < 0.01). There was a negative correlation between the HU values and upper adjacent segmental height loss (Pearson’s coefficient −0.844，p<0.01). Using receiver operating characteristic curves, the area under the curve was0.830 , and the most appropriate threshold of HU value was 329.17(sensitivity71.8%, specificity 86.7%). A preoperative lower HU is a risk factor for postoperative loss of adjacent segment height(binary logistic regression, p < 0.05). Conclusions　Lower preoperative CT HU values are associated with loss of adjacent segment height after single-level ACDF.Preoperative measurement of HUs may be useful in predicting Adjacent segment degeneration （ASD）after ACDF.