Risk of proximal junctional kyphosis after revision of growing rod constructs

IntroductionFor early-onset scoliosis (EOS) patients with growth-friendly implants, posterior distraction is a known contributor to proximal junctional kyphosis (PJK). Rib-based proximal fixation is thought to potentially reduce the risk of PJK compared to spine-based anchors. However, the effect of revising proximal rib-based implants to rib vs. spine-based implants on PJK has not yet been investigated.Hypotheses(1) Patients converted from rib-based to spine-based proximal anchors (RTS) have a higher risk of PJK two years post-revision compared to those revised to rib-based anchors (RTR). (2) Revising the upper instrumented vertebra (UIV) to a lower level increases the risk of PJK at two years post-revision compared to revising to a higher or same level.MethodsIn this retrospective cohort study of EOS patients with rib-based growing constructs undergoing revision surgery with a minimum 2-year follow-up, we assessed pre-revision, post-revision, and 2-year follow-up radiographs. We excluded patients lacking lateral radiographs and attachment data and conducted descriptive analyses.Results280 subjects were included, with an average age of 7.2 years at revision; RTS patients were slightly older (8.6y vs 7.2y), and 51% female. At 2 years, 32% of all patients developed PJK. This risk was higher in RTS patients compared to RTR patients (42.8% vs 30.2%, p = 0.17). RTS patients had a greater pre-revision total spine height (p = 0.02), a more negative sagittal balance at 2 years (p = 0.01) and were predominantly male (p = 0.08) compared to RTR. Of the factors associated with a greater risk of PJK, proximal anchor conversion from rib-to-spine had the highest predictive value of PJK development (OR 2.23, p = 0.04). While statistically significant, there was no clinical difference in risk at 2 years of developing PJK among patients revised to a lower level compared to those revised to a higher or same level (32.1% vs 32.5% vs 30.9%, respectively; p = 0.05).Conclusion32% of all subjects developed PJK at a 2-year follow-up. The risk of PJK in RTS patients was 40% higher than in RTR patients. While this did not reach statistical significance to the 0.05 level, due to the associations of risk established by literature and replicated in this study, and the magnitude of this difference, we believe these results to be clinically significant. We intend to re-evaluate this population in the future as more data becomes available. With no demonstrated risk in revision levels, these results should guide providers in revision decision-making in growing rods.