The Effects Of Cages Implantation On Surgical And Adjacent Segmental Intervertebral Foramina

Background:Since Anterior Cervical Discectomy and Fusion（ACDF）was originally reported in the 1950s,ACDF has become the gold standard for the treatment of cervical degenerative diseases,with the application of intervertebral implants and Caspar planting.However,the optimal size of the cage is still widely controversial.Furthermore,although previous studies illustrated the effects of distraction and cage implantation on the surgical segmental intervertebral foramen,little attention was paid to the adjacent segment.Objective:The purpose of this study was to compare the clinical and radiological outcomes with different sizes of cages inserted in ACDF and evaluate the effect on surgical and adjacent segment foramen.Methods:The clinical and radiographic data of 61 patients who underwent single segment ACDF in our hospital from January 2017 to June 2020 were analyzed retrospectively.The distraction degree was described by the ratio of postoperative surgical intervertebral space height（H）to the mean height（H_m=（H₁+H₂）/2）of the adjacent upper（H₁）and lower（H₂）segments（H/H_m）.Then,according to the different range of distraction,patients were divided into three groups:group A（H/H_m<1.20,n=13）,group B（1.20≤H/H_m≤1.80,n=37）and group C（H/H_m>1.80,n=11）.The radiological parameters included the area and height of the surgical and adjacent segment foramen,the surgical segmental Cobb angle（α₁）,C2-7Cobb angle（α₂）,and the intervertebral space height of surgical and adjacent segments.The clinical outcomes were evaluated by the Japanese Orthopaedic Association Scores（JOA,0-17）,the recovery rate of JOA scores and the Visual Analog Scales（VAS,0-10）.T-test,One-way analysis of variance and nonparametric tests were used to analyze the data.Results:No significant difference was found between the surgical intervertebral space height and the mean height of adjacent segments before the operation（all P>0.05）.After the operation and at the final follow-up,the area and height of the surgical segment foramen all increased in three groups,compared to preoperation（all P<0.05）.However,the adjacent segment foramen showed no significant changes in group A and B（all P>0.05）except for a decrease in group C（all P<0.05）.The area and height of the surgical segment foramen and the degree of intervertebral distraction（H/H_m）were positively correlated（0<R<1,all P<0.05）.However,the adjacent segments and H/H_m were negatively correlated.Except the postoperative area（R=-0.243,P=0.059）and height（R=-0.236,P=0.067）of the upper segment showed no statistically significant correlations with H/H_m,there were statistically significant correlations between H/H_m and the upper segment at follow-up（area:R=-0.350,P=0.006;height:R=-0.296,P=0.020）,lower segment after the operation（area:R=-0.259,P=0.044;height:R=-0.262,P=0.041）and at follow-up（area:R=-0.396,P=0.002;height:R=-0.276,P=0.031）.Additionally,theα₁ increased obviously after the surgery and at last follow-up（all P<0.05）,whereas theα₂ showed no significant change（all P>0.05）.During the postoperative and last follow-up period,the JOA scores in all three groups significantly improved（all P<0.05）,and the VAS scores decreased simultaneously（all P<0.05）.No significant difference was found for JOA scores and the recovery rate among the three groups（all P>0.05）.As for the VAS score,there was no difference among the three groups before and after the operation（all P>0.05）.However,at the last follow-up,a lower score was found in group B（P=0.034）.Conclusion:When performing ACDF,the cages insertion and intervertebral distraction could increase the area and height of the surgical segment foramen,which is beneficial to the indirect decompression of spinal cord and nerve roots.However,the oversize cage might lead to a negative impact on the adjacent intervertebral foramen.By referring to the mean height of the adjacent intervertebral space,the 1.20-1.80 fold of distraction with optimal cages would achieve a better long-term prognosis.