Radiographic Characteristic Of Bi-planar Pelvic Alignment(BPPA) Served As Compensation Of Coronal Spinal Alignment(CSA) In Severe Spinal Deformity(SSD)

Objective:The phenomenon of pelvic asymmetry(pelvic coronal obliquity-PCO or pelvic axial rotation-PAR of the pelvic)has been noted in AIS patients.However.there is paucity study about the occurrence situation of PCO and/or PAR in severe spinal deformity-SSD(Coronal Cobb≥90°).In this study,the most commonly used method-X-ray was chosen to evaluate PCO and PAR,and we did the statistics and analysis the variation characteristics of pelvic coronal and axial plane compensating SSD.The purpose are to obtain prospective conclusions that can be used to reduce the risks of post-operative spinal coronal imbalance in such patients during orthopedic surgeries.Methods:All the patients with SSD admitted for spinal surgery were evaluated from 2003.5-2018.11 in a single medical centre.Inclusion criteria:patients who present with coronal Cobb>90°(and/or the sagittal cobb>90°);patients with standing whole spine radiographs done preoperatively.Exclusion criteria:Tuberulosis,tumors,scoliosis secondary to bone destruction,degenerative deformities in adults,ankylosing spondylitics,leg length discrepancy caused by various reasons.The 2-dimensional space coordinate system was evaluated with the International Cartesian coordinate convention and Scoliosis Research Society convention global coordinate system to classify the variation of bi-planar pelvic planar,forming a total of 9 combinations.We did statistics on the incidence of various combinations in overall patient group,characteristics of patients in coronal spinal imbalance-CSI and coronal spinal balance-CSB,the relationship between trunk deviated to the concave side or the convex side and the PCO and/or PAR,characteristics of patients with different curve types and curve numbers.The correlation between clinical and imaging features were analyzed.Statistics were calculated using SPSS v20.0 statistical software.The relationship between the variation of pelvic coronal and axial plane and CSB,relationship between the variation of pelvic coronal and axial plane and CSI were compared using chi-square test.A p-value<0.05 was considered statistically significant.The relationship between trunk deviated to the concave and convex side of the major curve in CSI was compared using chi-square test.A p-value<0.05 was considered statistically significant.The relationship between the incidence of PCO and PAR in CSB was compared using chi-square test.A p-value<0.05 was considered statistically significant.The relationships not only between major thoracic curve and thoraciclumbar curve but between major thoracic curve and lumbar curve also were compared using chi-square test.A p-value<0.05 was considered statistically significant.Results:A total of 128 patients fulfilled the criteria were included.The average age of the patients was 15±3 years and the average angle of the main curves was 105.7±20.9°.The average angle of the kyphosis was 89.8±31.1°.The ratio of the male patients and the female patients was 60:68.100 patients were detected with bi-planar pelvic compensation(BPPC)(78.1%,100/128).The most common BPPC were PCO+PAR 5(32/128,25.0%),and PAR 2(29/128,22.7%).There were few PCO 8(0%,0/128),and 4(1/128,0.8%)served individually.33 patients were detected with CSB(33/128,25.8%)with 24(24/33.72.7%)BPPC.PAR 2(33.3%,11/33).6(8/33,24.2%,)were seen in BPPC mostly.95 patients(95/128,74.2%)were detected CSI with 76(76/95,83.5%)BPPC.PCO+PAR 5(29/76,38.2%)was the most common BPPC.In CSI patients,59(59/95,62.1%)were detected with trunk deviated to the convex side with 50(50/59,84.7%)BPPC.PCO+PAR 5(20/50,40.0%)was the most common BPPC.36(36/95,37.9%)patients were detected with trunk deviated to the concave side with 33(33/95,34.7%,)BPPC.PCO+PAR 5(10/33,30.3%)was seen in BPPC mostly.The cases of the major thoracic curve were 94(94/128,73.4%).The cases of thoraciclumbar curve were 28(28/128,21.9%)and the cases of lumbar curve were only 6(6/128,4.7%)Conclusion:①The incidence of BPPC to CSB in SSD was 78.1%,100/128.Type 5 was main component.Pelvic always presents as PAR to compensate CSB firstly in SSD.Pelvic always presents as PAR to compensate CSB firstly,but rarely observed with PCO alone.②There was a high component with CSI in SSD,Whether CSI or not,the incidence of PAR was higher than PC.O in SSD.When PCO and PAR participated together,the two were mainly with reverse direction.③When PCO participated the compensation to SSD together.,pelvic elevation was the main form of compensation,and it was not much related to the direction.④The thoracic curve was the main component.PAR with the same direction of major thoracic curve was always the main component.