Clinical And Radiographic Results After Posterior Wedge Osteotomy For Thoracolumbar Kyphosis Secondary To Ankylosing Spondylitis:Comparison Of Long And Short Segment Instrumentation

Part 1:Clinical and radiographic results after posterior wedge osteotomy for thoracolumbar kyphosis secondary to ankylosing spondylitis:comparison of long and short segment instrumentationObjective.To compare the efficacy of long and short segment instrumentation following pedicle subtraction osteotomy(PSO)for thoracolumbar kyphosis caused by ankylosing spondylitis(AS).Methods.A retrospective review of 269 consecutive AS patients who had undergone lumbar PSO for fixed thoracolumbar kyphosis between January 2001 and December 2014 were performed.64 consecutive AS patients who fulfilled the included and excluded criteria were enrolled with an average age of 34.4 years(range,17-54 years).The mean follow-up period was 4.6 years(range,2-15 years).Patients were divided into two groups according to the uppermost instrumented vertebra(UIV):Long segment instrumentation(LSI)group(n=44)(UIV at or above T10)and short segment instrumentation(SSI)group(n=20)(UIV below T10).Both groups are matched cohorts.Radiographic evaluations included global kyphosis(GK),lumbar lordosis(LL),sagittal vertical axis(SVA),angle of fused segments(AFS),osteotomized vertebra angle(OVA),proximal junctional angle(PJA),and mSASSS(modified Stoke Ankylosing Spondylitis Spinal Score).Clinical assessment involved oswestry disability index(ODI),visual analogue scale(VAS)and complications.The Pearson correlation coefficient(r)was used to assess the association between significant radiographic parameters and mSASSS for both groups.Results.LSI and SSI group consisted of 44 and 20 patients,respectively.LSI group had significantly larger deformity correction in global kyphosis(GK)and lumbar lordosis(LL)than SSI group.Correction loss in global kyphosis(GK)and lumbar lordosis(LL)of LSI group was higher than that of SSI group slightly(3.84° vs 2.63°,4.30° vs 2.89°).Also,no significant changes in osteotomized vertebral angle(OVA)and angle of fused segments(AFS)was noted.Notably,significant higher modified stoke ankylosing spondylitis spine score(mSASSS)was noticed in the SSI.The Pearson correlation analysis demonstrated that mSASSS for thoracic and lumbar spine was significantly associated with correction loss in GK and LL,respectively(r were-0.574 and-0.722,respectively).Improved ODI and VAS were found in both groups at the final follow-up.There were two proximal junctional kyphosis(PJK)and one rod fracture in LSI group.Conclusions.Both two approaches could maintain sustained surgical outcomes for thoracolumbar kyphosis secondary to AS.Short segment instrumentation is recommended for AS patients with bridging syndesmophytes.Long constructs are better indicated for patients without fully ossified anterior longitudinal ligaments.Nevertheless,extension for length of instrumentation might not prevent the complications such as PJK or rod fracture in patients without fully ossified spine.Part 2:The patterns of loss of correction after posterior wedge osteotomy in ankylosing spondylitis-related thoracolumbar kyphosis:a minimum of five-year follow-upPurpose:Short-term studies have demonstrated good surgical outcomes after pedicle subtraction osteotomy(PSO)in ankylosing spondylitis(AS)patients,but there is a paucity of literature focused on middle-term results,especially regarding patterns of loss of correction.The objective of this study is to assess the durability of surgical outcomes and the patterns of loss of correction in thoracolumbar kyphosis secondary to AS following lumbar PSO with over 5-year follow-up.Methods:We performed a retrospective review of 155 consecutive AS patients undergoing lumbar PSO from January 2001 to December 2011.Twenty-four patients were included with an average follow-up of 6.9 years(range,5-15 years).Radiographical evaluations included global kyphosis(GK),lumbar lordosis(LL),sagittal vertical axis,spinal-sacral angle,kyphosis of proximal non-fused segments(KPNS),angle of fused segments(AFS),osteotomized vertebra angle(OVA),distal intervertebral disc wedging(DIDW)and proximal junctional angle.Meanwhile,clinical outcomes were assessed by the Oswestry disability index(ODI)and Numerical rating scale(NRS).Results:The average correction per PSO segment was 34.9°.Significant improvement in sagittal parameters were found postoperatively,and no obvious deterioration was noticed during the follow-up.Mild loss of correction in GK(2.82°)and LL(3.77°)were observed at the final follow-up(P<0.05).The KPNS and DIDW increased from 26° and-5.0° postoperatively to 30° and-2.2° at the final follow-up(P<0.05),respectively.In contrast,no significant diminishment was identified in OVA and AFS(P>0.05).The ODI and NRS improved significantly from 20.6 and 6.6 preoperatively to 5.9 and 2.3 at the final follow-up(P<0.05).Conclusions:PSO is an effective procedure for treating AS-related thoracolumbar kyphosis and can maintain sustained surgical outcomes during the middle-term follow-up.The loss of correction was mainly attributable to non-instrumented segments without fully ossified bridging syndesmophyte in the thoracolumbar region instead of instrumented levels.