Combined anterior-posterior surgery is the most important risk factor for developing proximal junctional kyphosis in idiopathic scoliosis

Abstract

Background: Several studies have identified risk factors for proximal junctional kyphosis (PJK) after instrumentation for scoliosis, but the relative risks are unclear.

Questions/purposes: We identified risk factors for PJK in idiopathic scoliosis and determined their relative risks in a predictive model.

Methods: We retrospectively reviewed the charts of all 249 patients with idiopathic scoliosis who underwent surgery from 1996 to 2008. We compared those who developed PJK to those who did not. We identified risk factors for PJK and performed univariate and multivariate analyses to determine independent risk factors. We then used a Cox proportional-hazards model to evaluate the time to the development of PJK. The minimum followup time was 1.5 years (mean, 4 years; range, 1.5-9 years).

Results: The incidence of PJK in our series of patients with idiopathic scoliosis was 17%. There was no difference in Scoliosis Research Society-22 scores between patients without and with junctional kyphosis. Independent risk factors included proximal fusion to T1 through T3 and sagittal sacral vertical line, while in the Cox model a combined anterior-posterior approach surgery was the most important risk factor.

Conclusions: Patients with a T1 through T3 upper instrumented level, combined anterior-posterior surgery, and increased sagittal sacral vertical line difference had a higher likelihood of developing PJK. Of these risk factors, anterior-posterior surgery was the strongest risk factor.

Level of evidence: Level III, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.

Figures

Fig. 1

The graph shows a cumulative hazard plot for the development of PJK with stratification based on UIV. According to this model, those with proximal fusion levels ending at T1-T3 have a higher risk at all time points for developing PJK than those with fusions ending more distally in the T4-T12 region.

Fig. 2

The graph shows a cumulative hazard plot for development of PJK with stratification based on surgical approach. In this model, those with anterior-posterior combined surgery are approximately three times more likely to develop PJK at 2 years after surgery than those who received only posterior surgery.