The Effect Of Selecting Lower Instrumented Vertebra On Sagittal Balance Of The Spine In Adolescent Idiopathic Scoliosis Patients

BackgroundScoliosis is a deformity that affects the three-dimensional structure of the spine.It can occur in various segments of the spine,but the most common scoliosis occurs in the thoracic region,followed by the lumbar region.AIS(Adolescent Idiopathic Scoliosis),the most common form of Scoliosis,affects at-risk adolescents between the age from 10 to 16,The prevalence of AIS in the adolescent population is 2%to 4%.AIS Patients with untreated scoliosis may experience limited cardiopulmonary development,lumbar back pain,and changes in appearance and overall spinal mobility as scoliosis progresses.Measurement of the Cobb Angle on an upright radiographs of the whole spine is a common method for the diagnosis of scoliosis,and it is generally considered that a Cobb Angle of more than 10°can be diagnosed as scoliosis.For AIS patients with Cobb Angle of 25° to 45°,the main treatment is to wear an appropriate brace.When Cobb Angle exceeds 45°,surgical treatment is considered.The main surgical objectives of AIS patients are to limit the progression of scoliosis,maintain the balance between coronal and sagittal planes,and preserve as many spinal motion segments as possible while achieving surgical correction of the deformity.Currently,the use of pedicle screw fixation devices for correction of scoliosis deformity is clinically approved.It is generally believed that the selection of appropriate fixed and fused vertebrae is crucial for the effect of surgical correction in AIS patients and the recovery of postoperative spinal function.ObjectiveThe purpose of this study was to investigate the effects of T12 or L1 as LIV(Lower instrumented vertebra)on sagittal balance in patients with Lenkel AIS treated with posterior pedicle screw internal fixation and fusion.MethodsA total of 42 patients with Lenkel AIS who received posterior pedicle screw internal fixation and fusion in our hospital from January 2014 to December 2019 were retrospectively analyzed,including 9 males and 33 females,aged 10-18 years(14.4±0.3 years).Patients were assigned to the TV group(LIV at T12)and LV group(LIV at LI)based on LIV levels.There were 16 patients in TV group,including 4 males and 12 females,aged 11-18 years(14.7±2.1 years),with an average fusion level of 9.6.In LV group,there were 26 patients,including 5 males and 21 females,aged 10-17 years(14.2±1.9 years),with an average fusion level of 9.4.Follow up at least 2 years after surgery.Age,sex,Risser sign,operation time,blood loss,transfusion volume and fusion level were recorded.All patients underwent standing posteroanterior spine Radiographs before and during follow-up.Cobb Angle,thoracic kyphosis Angle(TK),lumbar lordosis Angle(LL),pelvic incidence Angle(PI),sacral inclination Angle(SS),pelvic inclination Angle(PT),and sagittal axis of spine(SVA)were measured before and during postoperative follow-up.Independent sample T test was used to determine the statistical differences in general data and imaging parameters between the TV group and LV group.Pearson correlation analysis coefficient was used to explore the correlation between the changes of imaging parameters.Result:There were no significant differences in age,gender,Risser sign,operation time,blood loss,transfusion volume and fusion level between two groups(P>0.05).Preoperative Cobb Angle,TK,LL,PI,SS,PT,SVA;Cobb Angle,TK,LL,PI,SS,PT,SVA were followed up.There were no significant differences in LL,PI,SS,PT,SVA,LL,PI,SS,PT and SVA between the two groups before and during follow-up(P>0.05).The TK values of TV group and LV group were 24.1°±6.3° and 24.2°±7.3°before surgery.The TK values in TV group and LV group were 19.4°±5.8°and 17.2°±7.4°,postoperatively.There was no significant difference in TK values between the two groups before surgery and during follow-up(P>0.05).The coronal Cobb Angle correction rates of TV group and LV group were(62.6±8.4)%and(68.8±8.6)%,respectively,and the difference was statistically significant(P=0.028).The change of TK value in TV group and LV group was 4.7°±3.0°and 6.9°±1.7°,showing statistical difference(P=0.013).Pearson correlation analysis showed that there was a significant correlation between TK and LL(r=0.603,P<0.001).Conclusion:Either T12 or L1 as LIV,no significant sagittal imbalance was observed in the follow-up of Lenkel AIS patients who underwent posterior pedicle screw fixation and fusion.However,patients with distal fusion to L1 were more likely to have more reduced TK values at follow-up than patients with distal fusion to T12.