| IntroductionScoliosis is a three dimensional deformity of the spine,which usually involves the coronal and sagittal planes.The goals of surgical treatment for AIS are to correct coronal deformity and restore sagittal profile.The use of pedicle screw constructs provided a satisfactory correction of spine deformity,especially in the correction of the coronal plane.However,the pedicle screw technique failed to restore the thoracic sagittal profile and creates a significant amount of thoracic hypokyphosis.Flattening or kyphosis in cervical region have been reported in AIS patients with thoracic hypokyphosis after surgery.Postoperative change of cervical sagittal alignment has an impact on health-related quality of life in AIS patients who underwent deformity correction.Kyphotic malalignment of cervical spine was associated with axial neck pain,degenerative changes in cervical disc and facet joint.Although the spinopelvic sagittal alignment has become an increasingly important consideration in AIS patients,the relevance of cervical sagittal balance was easily ignored.Thus,the purpose of the present study was to analyze the changes in cervical sagittal alignment of patients with AIS treated by posterior instrumentation and fusion with pedicle screw constructs.Materials and methodsWe retrospectively analyzed the data of the AIS patients who were corrected through posterior spinal fusion and instrumentation using pedicle screws between August 2009 and September 2015.Patients were included in the study as following:AIS treated by posterior spinal fusion and instrumention and minimum 1 year of follow-up.We excluded the patients with a diagnosis other than AIS,age over 20 years,a prior spine surgery and unclear radiographs.Radiographic measurements were taken on full-length standing anteroposterior and lateral radiographs of the spine before surgery,at the immediate postoperative period and at the latest follow-up.A positive value for C2-C7 Cobb angle(>0°)indicated a cervical kyphosis,whereas a negative value(?0°)corresponded to cervical lordosis or straight.C2-C7 SVA was defined as the distance between the plumb line of the center of C2 vertebrae and the posterior superior corner of the C7 vertebrae.In addition,we also measured the spinopelvic alignment parameters including thoracic kyphosis(TK),lumbar lordosis(LL),pelvic incidence(PI),sacral slope(SS),pelvic tilt(PT)and sagittal vertical axis(SVA).The definitions of these spinopelvic alignment parameters were described in the literatures.Statistical analyses were performed using SPSS for windows,Version 22.0(IBM,Corp.,Armonk,NY).Preoperative,postoperative and the final follow-up radiographic parameters were tested using paired t-tests.A correlational analysis was performed using a Spearman test.Binary logistic regression analysis was conducted to identify independent risk factors for a postoperative cervical kyphosis.P value<0.05 was considered to be statistically significant.ResultsA total of 46 AIS patients were included in this study.There were 35 girls and 11 boys(average age 15 years).The average follow-up time was 34.5 months(range 12 to 72 months).According to the Lenke classification,11 of 46 patients had Lenke 1,8 had Lenke 2,8 had Lenke 3,3 had Lenke 4,11 had Lenke 5 and 5 had Lenke 6.Five of 46 patients had the Ponte osteotomy and 2 had pedicle subtraction osteotomy.Mean main curve Cobb angle was 59.5°±14.7° at preoperative period,15.8° ± 8.9°at immediate postoperative period and 16.8°± 9.7°at the latest follow-up.Cervical kyphosis was observed in 31 of 46(67.4%)patients before surgery,but 40 patients(87%)postoperatively and 32 patients(69.5%)at the final follow up.The average preoperative C2-C7 Cobb angle of 1.5° was increased to 5.4° postoperatively and 2.9° at the final follow up.The average C2-C7 SVA was 18.1mm before surgery,17.0mm at the postoperative period and 18.5 at the final follow-up,respectively.TK was significantly decreased from preoperative 17.7° ±14.40 to postoperative 14.2° ±7.6°,and spontaneously improved to 16.9° ±8.2° at the latest follow up.TK showed a significant negative correlation with C2-C7 Cobb angle before surgery(r=-0.709,P<0.01),at the immediate postoperative period(r=-0.472,P<0.01)and at the latest follow up(r=-0.505,P<0.01),but not with C2-C7 SVA.Other parameters including LL,PI,SS,PT and SVA were not significantly changed after surgery.These spinopelvic sagittal parameters did not correlate with C2-C7 Cobb angle or C2-C7 SVA.Preoperatively,30 of 46 AIS patients had a hypokyphotic thoracic spine((TK<40°),14 had a normal TK(20°? TK ?40°)and 2 had a hyperkyphosis(TK>40°).In the patients with preoperative thoracic hypokyphosis,C2-C7 Cobb angle,C2-C7 SVA and TK were not significantly changes at the immediate postoperative period,but significantly improved at the latest follow up.In the patients with normal thoracic kyphosis,TK was significantly decreased from preoperative 25.6°±5.7° to postoperative 16.3°±5°,which were associated with increasing C2-C7 Cobb angle from preoperative lordotic 2.3°±13° to postoperative kyphotic 8.1°±5.4°;But decreased TK did not significantly cause the change of C2-C7 SVA.In the patients with preoperative thoracic hyperkyphosis,deformity correction procedures didn't significantly change the parameters of C2-C7 Cobb angle,C2-C7 SVA and TK.Binary logistic regression analysis revealed that the odds ratio of preoperative TK was 0.908(95%confidence interval(CI)= 0.831-0.994,P = 0.036),indicating a 0.9-times higher risk for developing postoperative cervical kyphosis in patients with 1° of increase in preoperative TK.ConclusionThe cervical sagittal malalignment is commonly observed in AIS patients.C2-C7 Cobb angle was significant increased after surgery,but C2-C7 SVA was not significant modified.Decrease in thoracic kyphosis after surgery is associated with significant increase in cervical kyphosis.The change of cervical sagittal profile may be a compensatory mechanism in response to loss of thoracic kyphosis. |
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