• Jean-Luc Clément, Sebastien Pesenti, Brice Ilharreborde, Christian Morin, Yann-Philippe Charles, Henri-François Parent, Philippe Violas, Marc Szadkowski, Louis Boissière, and Federico Solla.
• Department of Pediatric Orthopedics and Scoliosis Surgery, Hôpitaux Pédiatriques de Nice Chu Lenval, 57 Avenue de la Californie, 06200, Nice, France. clement.jluc@wanadoo.fr.
• Eur Spine J. 2021 Jul 1; 30 (7): 1988-1997.

PurposeMany authors tried to explain proximal junctional kyphosis (PJK) after adolescent idiopathic scoliosis (AIS) surgery by looking for risk factors. Latest publications focus on sagittal alignment. Each healthy adolescent has a specific thoracic kyphosis (TK) depending on their pelvic parameters and lumbar lordosis (LL). The objective of this work is to determine if the difference between TK at follow-up (TKFU) and the patient-specific TK (PSTK) plays a role in PJK occurrence after AIS surgery. The secondary objective was to find other risk factors.MethodsWe analyzed retrospectively 570 thoracic AIS who underwent a posterior thoracic fusion from nine centers. The series was separated in two groups: with and without PJK. PSTK was calculated with the formula PSTK = 2(PT + LL-PI). TK Gap was the difference between TKFU and PSTK. Logistic regression was utilized to test the impact of TK Gap and other known risk factors on PJK occurrence.ResultsUnivariate analysis showed 15 factors significantly different between the groups. In a multivariate analysis, three factors had a strong significant influence on PJK: TKFU, TK Gain and TK Gap. Four additional factors affected the rate of PJK: Posterior translation on two rods, preoperative TK, preoperative LL and number of instrumented vertebrae.ConclusionPJK is related to the insufficient TK at follow-up, compared to the specific TK that every patient should have according to their pelvic parameters. PJK incidence is significantly reduced by a strong gain in TK and a thoracic selective fusion which leaves the proximal lumbar vertebrae free.Level Of Evidence IDiagnostic: individual cross-sectional studies with consistently applied reference standard and blinding.© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.

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