强直性脊柱炎胸腰段后凸畸形矫形前后影像学参数分析

Analysis of radiologic parameters of thoracolumbar kyphotic deformity in ankylosing spondylitis patients before and after pedicle subtraction osteotomy

目的通过对强直性脊柱炎(ankylosing spondylitis,AS)僵硬性胸腰段后凸畸形矫形前后影像学参数对比分析及相关性研究,探讨经椎弓根椎体截骨(pedicle subtraction osteotomy,PSO)矫形对矢状面脊柱骨盆序列的影响,进而探究AS后凸患者脊柱骨盆序列的代偿机制。方法 2004年1月～2010年3月,38例AS僵硬性胸腰段后凸畸形患者行后路单节段或双节段截骨矫形椎弓根螺钉内固定术。矫形前后拍摄全脊柱侧位X线片,测量AS患者全脊柱后凸角(Cobb T1～S1)、矢状面平衡距离(sagittal vertical axis,SVA)、骨盆入射角(pelvic incidence,PI)、骨盆倾斜角(pelvictilt,PT)、骶骨倾斜角(sacral slope,SS)及截骨角度(PSO angle)。观察矫形前后影像学参数变化,控制影响患者个体差异的因素,将影像学参数做偏相关分析。结果矫形前,Cobb T1～S1=56°±28°,PI=45°±9°,PT=38°±13°,SS=7°±12°,SVA=21 cm±9 cm;矫形后,Cobb T1～S1=11°±22°,PI=46°±9°,PT=21°±10°,SS=24°±9°,SVA=9 cm±5 cm。矫形前,PT、SVA与Cobb T1～S1偏相关系数分别为r=0.81(P<0.01)、0.64(P<0.01);矫形后,PT、SVA与Cobb T1-S1偏相关系数分别为r=0.58(P<0.05)、0.72(P<0.01)。PSO angle与Cobb T1～S1、PT偏相关系数分别为r=-0.82(P<0.01)、-0.56(P<0.05),PSO angle与SVA无相关性。结论矫形前后,AS患者通过后旋骨盆代偿全脊柱后凸所致的矢状面失平衡;骨盆后旋程度、矢状面平衡距离与全脊柱后凸程度呈正相关;人体自身代偿机制优先恢复骨盆的中立状态而非改善矢状面平衡距离。

Objective To compare the preoperative and postoperative radiological parameters of fixed thoracolumbar kyphotic deformity caused by ankylosing spondylitis(AS),and to explore the effect of pedicle subtraction osteotomy(PSO) on sagittal spine-pelvic sequence and the compensatory mechanism of the body.Methods From January 2004 to March 2010,38 AS patients with fixed thoracolumbar kyphotic deformity underwent posterior one or two-segment PSO.Preoperative and postoperative radiographic parameters,such as global kyphosis(Cobb T1-S1),sagittal vertical axis(SVA),pelvic incidence(PI),pelvic tilt(PT),sacral slope(SS) and PSO angle were measured.Changes of preoperative and postoperative radiographic parameters were evaluated.The factors resulting in individual difference were avoided.Correlation was determined by partial correlation analysis in these radiographic parameters.Results Preoperative Cobb T1-S1,PI,PT,SS and SVA were 56°±28°,45°±9°,38°±13°,7°±12° and 21 cm±9 cm,respectively.The postoperative were 11°±22°,46°±9°,21°±10°,24°±9° and 9 cm±5 cm,respectively.Preoperative PT and SVA had partial correlation with Cobb T1-S1(r=0.81,P<0.01;r=0.64,P<0.01),while the postoperative coefficients were 0.58(P<0.05) and 0.72(P<0.01).PSO angle had partial correlation with Cobb T1-S1 and PT(r=-0.82,P<0.01;r=-0.56,P<0.05).There was no correlation between PSO angle and SVA.Conclusion Pelvic backward rotation compensates for sagittal imbalance caused by global kyphosis in ankylosing spondylitis patients.Pelvic backward angle and SVA depend on the degree of kyphosis.The compensatory mechanism of the body is to restore pelvic neutral position rather than to change SVA.