Friday, September 28, 2018 10:30 AM–12:00 PM abstracts: deformity: technical factors: 164. Incidence, risk factors and the natural history of proximal junctional kyphosis: review of long term surgical outcomes using hybrid fusion constructs for adolescent idiopathic scoliosis

Abstract

BACKGROUND CONTEXT Proximal junctional kyphosis (PJK) is an unsolved radiographic phenomenon after corrective spinal deformity surgery with a high, but variable reported incidence. While known to influence outcomes in adults, the long-term clinical significance and natural history in children has not been well defined.Identifying incidence, risk-factors and natural course of PJK based on several proposed definitions in the literature using a large cohort may aid in enhancing our understanding of the disease entity. PURPOSE In a single-surgeon series of AIS patients undergoing deformity correction using hybrid hooks or screw constructs, the study attempted to identify potential risk-factors associated with the long-term development of PJK. Additionally, the study also defines PJK incidence and highlights the natural course of PJK development in children based on commonly proposed definitions in the literature. STUDY DESIGN/SETTING Retrospective, single-surgeon series with a minimum 2-year follow-up. PATIENT SAMPLE Overall, 253 eligible AIS patients with complete information on the proximal junctional angle (PJA) that underwent spinal deformity fusion (PSF) surgery by a single surgeon (SLW) at the University of Iowa between 2006 and 2015 that met the minimal criteria of 2-year follow-up were included. OUTCOME MEASURES The primary outcome was to assess incidence of PJK development form preoperative to postoperative measurements based on two commonly utilized definitions: Glattes et al. that defines PJK as PJA> 10°, and Bridwell et al. classification that defines the disease entity based on the critical PJA above 20°. Secondary outcome was to investigate factors associated with PJK development based on patient demographics, radiological indices and outcomes, and describe the natural course of PJK development in AIS patients undergoing deformity correction. METHODS AIS patients aged between 9 and 18 years undergoing primary long-construct PSF (UIV T2-4) between 2006 and 2015 with a minimum 2 years follow-up were included. Proximal junctional kyphosis was defined as a change in the PJA, according to Glattes et al. and Bridwell et al. classification from preop to postop. The incidence of PJK was defined at 6-week and last follow-up. Multivariable regression models were used to assess risk factors (patient characteristics, disease severity, radiographic parameters) associated with long-term PJK development. RESULTS A total of 253 eligible patients (mean age: 13.7 years; 82% female) with an average follow-up of 3.7 years (range: 24-123 months). Proximal junctional kyphosis (10°) occurred in 10.3% at 6 weeks (PJK 20: 0.4%) and 25.7% at final FU (PJK 20: 4.3%). Based on Glattes definition, a high proportion of patients developing PJK had Risser grade 3(19 vs. 6%; p=.003) and Lenke 5(13% vs. 5%; p=.028) at baseline. In an unadjusted analysis, Risser grade 3(OR:3.6; p=.01), Lenke 5(OR:3.0; p=.03) and those with UIV as T4 (vs. T2) were associated with higher odds of PJK development. In multivariable model, we noted Risser grade 3(OR:4.6; p=.045) as a factor for PJK development. Low reoperation rate (0.04%;1/253) was noted. CONCLUSIONS PJK after AIS deformity surgery varies according to follow up time and definition. In contrast to adults, there does not appear to be any clear risk factors for PJK in an AIS population. Long-term reoperation for PJK appears to be exceedingly low at 0.4%. Radiographic PJK should be followed but generally thought of a benign condition in pediatric deformity surgery. Likely risk factors for PJK include short instrumentation (upto T4 compared to T2), Risser grade 3 and Lenke 5. Consensus on PJK definition is warranted to better define the pathological entity.