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The authors investigate underlying causes for pelvic retroversion in patients with flexible sagittal imbalance.<\/jats:p><\/jats:sec><jats:sec><jats:title>METHODS<\/jats:title><jats:p>One hundred thirty-eight patients with sagittal imbalance who underwent a total of 148 fusion procedures of the thoracolumbar spine were identified from a prospective clinical database. Radiographic parameters were obtained from images preoperatively, intraoperatively, and at 6-month and 2-year follow-up. A cohort of 24 patients with flexible sagittal imbalance was identified and individually matched with a control cohort of 23 patients with fixed deformities. Flexible deformities were defined as a 10\u00b0 change in lumbar lordosis between weight-bearing and non\u2013weight-bearing images. Pelvic retroversion was quantified as the ratio of pelvic tilt (PT) to pelvic incidence (PI).<\/jats:p><\/jats:sec><jats:sec><jats:title>RESULTS<\/jats:title><jats:p>The average difference between lumbar lordosis on supine MR images and standing radiographs was 15\u00b0 in the flexible cohort. Sixty-eight percent of the patients in the flexible cohort were diagnosed preoperatively with lumbar stenosis compared with only 22% in the fixed sagittal imbalance cohort (p = 0.0032). There was no difference between the flexible and fixed cohorts with regard to C-2 sagittal vertical axis (SVA) (p = 0.95) or C-7 SVA (p = 0.43). When assessing for postural compensation by pelvic retroversion in the stenotic patients and nonstenotic patients, the PT\/PI ratio was found to be significantly greater in the patients with stenosis (p = 0.019).<\/jats:p><\/jats:sec><jats:sec><jats:title>CONCLUSIONS<\/jats:title><jats:p>For flexible sagittal imbalance, preoperative attention should be given to the root cause of the sagittal misalignment, which could be compensation for lumbar stenosis. Pelvic retroversion can be compensatory for both the lumbar stenosis as well as for sagittal imbalance.<\/jats:p><\/jats:sec>","DOI":"10.3171\/2017.2.spine16963","type":"journal-article","created":{"date-parts":[[2017,6,9]],"date-time":"2017-06-09T14:02:18Z","timestamp":1497016938000},"page":"137-144","source":"Crossref","is-referenced-by-count":27,"title":["Pelvic retroversion: a compensatory mechanism for lumbar stenosis"],"prefix":"10.3171","volume":"27","author":[{"given":"Sina","family":"Pourtaheri","sequence":"first","affiliation":[{"name":"Department of Orthopedic Surgery, UCLA Health, Los Angeles, California;"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Akshay","family":"Sharma","sequence":"additional","affiliation":[{"name":"Case Western Reserve University School of Medicine, Cleveland; and"},{"name":"Center for Spine Health, Neurological Institute, and"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jason","family":"Savage","sequence":"additional","affiliation":[{"name":"Center for Spine Health, Neurological Institute, and"},{"name":"Departments of Orthopedic Surgery and"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Iain","family":"Kalfas","sequence":"additional","affiliation":[{"name":"Center for Spine Health, Neurological Institute, and"},{"name":"Neurosurgery, Cleveland Clinic, Cleveland, Ohio"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Thomas E.","family":"Mroz","sequence":"additional","affiliation":[{"name":"Center for Spine Health, Neurological Institute, and"},{"name":"Departments of Orthopedic Surgery and"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Edward","family":"Benzel","sequence":"additional","affiliation":[{"name":"Center for Spine Health, Neurological Institute, and"},{"name":"Neurosurgery, Cleveland Clinic, Cleveland, Ohio"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Michael P.","family":"Steinmetz","sequence":"additional","affiliation":[{"name":"Center for Spine Health, Neurological Institute, and"},{"name":"Neurosurgery, Cleveland Clinic, Cleveland, Ohio"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1754","reference":[{"key":"b1","series-title":"Eur Spine J","doi-asserted-by":"publisher","first-page":"1865","DOI":"10.1007\/s00586-010-1516-5","article-title":"Degenerative lumbar spinal stenosis and lumbar spine configuration","volume":"19","author":"Abbas J","year":"2010","unstructured":"Abbas J, Hamoud K, May H, Hay O, Medlej B, Masharawi Y, : Degenerative lumbar spinal stenosis and lumbar spine configuration. 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