{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,22]],"date-time":"2026-09-22T12:11:46Z","timestamp":1790079106937,"version":"4.0.1"},"reference-count":17,"publisher":"MDPI AG","issue":"18","license":[{"start":{"date-parts":[[2026,9,20]],"date-time":"2026-09-20T00:00:00Z","timestamp":1789862400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["J. Clin. Med.","JCM"],"abstract":"<jats:p>Background\/Objectives: Dysplastic spondylolisthesis is associated with developmental abnormalities of the lumbosacral junction, but the contribution of extremely sagittal L5-S1 facet orientation in an adolescent with an intact pars interarticularis remains incompletely characterized. We aimed to describe this unusual quantitative morphologic phenotype and discuss its possible biomechanical implications. Methods: Clinical records and serial imaging of a 14-year-old girl with symptomatic low-grade L5-S1 dysplastic spondylolisthesis were reviewed. Standing radiographs, flexion-extension radiographs, computed tomography (CT), magnetic resonance imaging (MRI), quantitative spinopelvic parameters, intraoperative findings, treatment, and 12-month follow-up were assessed. Results: The patient had approximately one year of progressively worsening low back pain and occasional transient right-leg numbness despite more than 8 months of lumbosacral bracing and more than 6 months of supervised physical therapy. Standing radiographs showed Meyerding grade I L5-S1 anterolisthesis and mild thoracolumbar scoliosis. Quantitative spinopelvic assessment showed a pelvic incidence (PI) of 76.63\u00b0, pelvic tilt of 22.21\u00b0, sacral slope of 54.42\u00b0, lumbar lordosis of 59.5\u00b0, sagittal vertical axis of 2.67 cm, and a Dubousset lumbosacral angle of 109\u00b0. CT demonstrated an intact pars interarticularis, bilateral facet subluxation, and L5-S1 facet angles of 6\u00b0 on the left and 3\u00b0 on the right relative to the sagittal plane. Flexion-extension radiographs showed measurable L5-S1 angular motion from \u22126.7\u00b0 to +3.5\u00b0, while MRI showed no major central canal stenosis, focal disc herniation, or definite neural compression. Posterior reduction and L5-S1 fusion were performed after individualized counseling, and facet subluxation was confirmed intraoperatively. At 6 and 12 months, the patient remained free of recurrent pain or numbness and radiographs showed maintained lumbosacral alignment. Conclusions: Quantitatively extreme L5-S1 facet sagittalization accompanied by bilateral facet subluxation, an intact pars, and high-PI low-grade spondylolisthesis represents a distinctive morphologic phenotype. This configuration is biomechanically compatible with reduced resistance to anterior shear, although a single case cannot establish independent causality or justify a general indication for early surgery. Comparative quantitative imaging and longitudinal studies are required.<\/jats:p>","DOI":"10.3390\/jcm15187311","type":"journal-article","created":{"date-parts":[[2026,9,22]],"date-time":"2026-09-22T11:09:35Z","timestamp":1790075375000},"page":"7311","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Quantitatively Extreme Sagittal Orientation of the L5-S1 Facet Joints in Adolescent Dysplastic Spondylolisthesis: A Case Report and Mechanistic Considerations"],"prefix":"10.3390","volume":"15","author":[{"ORCID":"https:\/\/orcid.org\/0009-0003-1994-5186","authenticated-orcid":false,"given":"Yong-Xi","family":"Fan","sequence":"first","affiliation":[{"name":"Department of Orthopaedics, West China Hospital, Sichuan University, Chengdu 610041, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0000-0668-3859","authenticated-orcid":false,"given":"Jia-Yu","family":"Fu","sequence":"additional","affiliation":[{"name":"Department of Orthopaedics, West China Hospital, Sichuan University, Chengdu 610041, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0005-5088-5710","authenticated-orcid":false,"given":"Xiao-Ling","family":"Luo","sequence":"additional","affiliation":[{"name":"Department of Orthopaedics, West China Hospital, Sichuan University, Chengdu 610041, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Chang-Sheng","family":"Liao","sequence":"additional","affiliation":[{"name":"Department of Orthopaedics, West China Hospital, Sichuan University, Chengdu 610041, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Zhong-Jie","family":"Zhou","sequence":"additional","affiliation":[{"name":"Department of Orthopaedics, West China Hospital, Sichuan University, Chengdu 610041, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,9,20]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"80","DOI":"10.2340\/17453674.2024.42450","article-title":"Treatment of pediatric spondylolysis and spondylolisthesis","volume":"96","author":"Helenius","year":"2025","journal-title":"Acta Orthop."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"23","DOI":"10.1097\/00003086-197606000-00003","article-title":"Classification of spondylolysis and spondylolisthesis","volume":"117","author":"Wiltse","year":"1976","journal-title":"Clin. 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