• Yann Philippe Charles, Bo Yu, and Jean-Paul Steib.
• Service de Chirurgie du Rachis, Hôpitaux Universitaires de Strasbourg, Fédération de Médecine Translationnelle (FMTS), Université de Strasbourg, 1, Place de l'Hôpital, B.P. 426, 67091, Strasbourg Cedex, France. yann.philippe.charles@chru-strasbourg.fr.
• Eur Spine J. 2016 May 1; 25 Suppl 1: 63-74.

BackgroundSagittal decompensation after pedicle subtraction osteotomy (PSO) is considered as late onset complication. Several mechanisms have been suggested, but little attention has been paid to the caudal end of lumbar instrumented fusion, especially sacral iliac joint (SIJ) deterioration.MethodsClinical histories and radiographic sagittal parameters of two patients with SIJ luxation after PSO are presented. The biomechanical failure mechanism and risk factors are analysed.ResultsTwo patients underwent correction of fixed anterior sagittal imbalance by PSO, followed by pseudarthrosis revision surgery. Both of them sustained persistent sacroiliac pain, progressive recurrence of anterior imbalance and progressive pelvic incidence (PI) increase around 10°. An acute bilateral SIJ luxation occurred in both patients leading to sharp increase or PI around 20°. One patient was treated by SIJ fusion and the other patient was placed on non-weight-bearing crutch ambulation for 1 year. Both patients had a high preoperative PI (95° and 78°). A theoretical match between lumbar lordosis (LL) and PI was not achieved by PSO. Osteopenia was present in both patients. Computed tomography evidenced L5-S1 pseudarthrosis and sacroiliac joint violation by pelvic or sacral ala screws.ConclusionPatients with high PI might seek for further compensation at their SIJ when lacking LL after PSO. Chronic anterior imbalance might lead to progressive weakening of sacroiliac ligaments. Initial circumferential lumbosacral fusion and accurate iliac screw fixation might reduce stress on implants, risk for pseudarthrosis, implant failure and finally SIJ deterioration. Bone mineral density should further be investigated preoperatively.

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