190. C2 pelvic angle (C2PA) is a useful radiographic parameter that correlates with clinical outcomes of symptomatic proximal junctional kyphosis

Abstract

<h3>BACKGROUND CONTEXT</h3> Proximal junctional kyphosis (PJK) after spine deformity surgery is a radiographic phenomenon defined based on the proximal junctional angle (PJA). Currently, there is minimal literature demonstrating correlation between clinical outcome scores and PJA. The lack of correlation may be due to the inadequate assessment of global spinal alignment from the PJA. The C2PA is a novel radiographic angle that portrays the mismatch between the global spinal alignment and alignment proximal to the spine that corresponds with ODI and SRS scores. <h3>PURPOSE</h3> The definition of PJK after spine deformity surgery is based on the PJA. Despite the growing amount of literature on PJK, minimal correlation exists between PJK and clinical outcome scores. PJA poorly represents, and is difficult to measure, PJK for global spinal alignment after deformity surgery. C2PA is a novel radiographic angle that demonstrates the difference between global spinal alignment and alignment proximal to the spinal construct. <h3>STUDY DESIGN/SETTING</h3> Prospectively collected cohort. <h3>PATIENT SAMPLE</h3> A radiographic review was performed on 98 deformity patients from July 2015-July 2018. <h3>OUTCOME MEASURES</h3> Logistic regression and Chi-square analyses were performed to study the relationship between the postop PJA and C2PA with ODI/SRS scores. <h3>METHODS</h3> A radiographic review was performed on 98 deformity patients from July 2015-July 2018. The angle between the posterior superior sacrum, C2 centroid and upper instrumented vertebrae (UIV) centroid in the pre- and postop setting (2-year or prior to return to OR) were measured and labeled as C2PA. The patients were divided into PJK and non-PJK groups based on (a) PJK defined as PJA >20° and (b) PJK defined as C2PA >20°. Logistic regression and Chi-square analyses were performed to study the relationship between the postop PJA and C2PA with ODI/SRS scores. <h3>RESULTS</h3> Of the 98 patients, there were 20 patients with PJK when it was defined as PJA >20°. There was no statistically significant correlation between ODI and SRS scores in the non-PJK and PJK group when it was defined as PJA. There were minimal differences between the ODI scores (8.0 vs 7.0, p=0.66) and the SRS total scores (71.3 vs 70.6, p=0.85) in the Non-PJK and PJK group when it was defined as PJA >20°. When PJK was defined as C2PA >20°, there were 31 patients with PJK. There were statistically significant differences between the non-PJK and PJK group for both ODI (8.0 vs 16.0, p=0.015) and SRS total scores (97.0 vs 88.0, p=0.010) when PJK was defined as C2PA >20° <h3>CONCLUSIONS</h3> This is the first study demonstrating that C2PA is a superior radiographic representation of PJK, and directly correlates with patient-reported outcomes. C2PA >20° is the critical angle that corresponds with clinical PJK. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.