Effect Of Pedicle Subtraction Osteotomy And Smith-peterson Osteotomy On Sagittal Balance Restoration In Patients With Ankylosing Spondylitis Kyphosis

Objective The paper aims to compare the restoration of sagittal balance following pedicle subtraction osteotomy(PSO)and Smith-Petersen osteotomy(SPO)for ankylosing spondylitis kyphosis.Methods Data of 21 patients with ankylosing spondylitis kyphosis,who underwent PSO or SPO from June 2011 to August 2015 in our center,were retrospectively analyzed.There were 10 cases of PSO and 11 of SPO.Long-cassette standing upright postero-anterior and lateral radiographs of the spine and pelvis were taken before,two weeks after surgeries and during follow-ups.The pre-operative,post-operative and follow-up parameters including Cobb angle,sagittal vertical axis(SVA),global kyphosis(GK),thoracic kyphosis(TK),lumbarlordosis(LL),pelvic tilt(PT),pelvic incidence(PI)and sacral slope(SS)were measured and compared.Results The pre-operative parameters were matched between SPO and PSO groups except significantly larger GK in PSO group.Only SVA showed significant difference between the two groups post-operatively.No significant differences in parameters were observed between the two groups at the last follow-up.Significant differences were observed in terms of the improvement of TK,LL,PT,PI and SS.GK in PSO decreased from 75.31±17.13° pre-operatively to 31.81±15.15° post-operatively and it increased to 36.72±15.16° at last follow-up.GK in SPO decreased from 65.21±21.43° pre-operatively to 25.60±16.22° post-operatively and it increased to 40.72±20.41° at last follow-up.SVA in PSO decreased from 78.62±63.31 mm pre-operatively to-15.13±27.82 mm post-operatively and it increased to 11.02±52.54 mm at last follow-up.SVA in SPO decreased from 54.23±77.61 mm pre-operatively to 16.68±42.76 mm post-operatively and it increased to 19.26±37.04 mm at last follow-up.Conclusion sagittal balance of patients with ankylosing spondylitis kyphosis can be well restored by both SPO and PSO despite different indications.Overcorrection of SVA is often seen in PSO group while loss of correction occurred frequently in SPO group which may attribute to post-operative posture.The postoperative imbalance of sagittal plain could be corrected spontaneously during follow-ups.So,in the choice of ankylosing spondylitis kyphosis surgical approach should rigid analysis the clinical and radiographic outcomes,and make reasonable operation strategy.