141. Preoperative Paraspinal Fat Atrophy of the Upper Instrumented Vertebrae Musculature in Spine Deformity Surgery is a Risk Factor for Proximal Junctional Kyphosis and Sagittal Malalignment

BACKGROUND CONTEXT Proximal junctional kyphosis (PJK) after spine deformity surgery is a frequent complication with multiple etiologies ranging from patient factors to surgical techniques. The paraspinal musculature at the upper instrumented vertebrae (UIV) is an understudied potential risk factor for PJK. This study classifies the paraspinal fat atrophy at the UIV into 3 different grades and correlates with postoperative sagittal alignment and PJK. PURPOSE The paraspinal musculature quality at the UIV is an understudied risk factor for PJK. We propose an easily distinguishable classification to categorize the different grades of preoperative paraspinal fat atrophy and correlate that with postoperative radiographic outcomes. STUDY DESIGN/SETTING Prospectively collected cohort. PATIENT SAMPLE A radiographic review was performed on 116 deformity patients from 2015-2018. OUTCOME MEASURES Logistic regression and Chi-square analyses were performed to study the relationship between the different UIV paraspinal muscle fat atrophy grades and postoperative sagittal balance. Methods A radiographic review was performed on 116 deformity patients from 2015-2018. The paraspinal muscle at the UIV was assessed using the preoperative axial MRI. Grade 1 was defined as fatty infiltrate between 0-10%, grade 2 between 10%-50%, and grade 3 over 50%. Preop, immediate postop and 2-year postop spine films were assessed. PJK was defined as PJA >15°. Logistic regression and Chi-square analyses were performed to study the relationship between the different UIV paraspinal muscle fat atrophy grades and postoperative sagittal balance. Results Of the 116 patients, 74 had grade 1, 34 had grade 2, and 8 had grade 3 paraspinal fat atrophy. The immediate postop T1PA for grade 1, 2, and 3 were 11.85, 14.8, and 17.7°. The 2-year postop T1PA for grade 1, 2, and 3 were 9.5, 16.9, and 19.6°. The immediate postop PJA for grade 1, 2, and 3 were 8.1, 8.7, and 15.0°. The 2-year postop PJA for grade 1, 2, and 3 were 7.7, 16.9, and 25.2°. For patients in the grade 1 cohort, 7 had PJK immediate postop and 14 had PJK at 2-year postop. Grade 2 cohort had 7 immediate postop PJK patients and 20 at 2-year postop. Grade 3 cohort had 4 immediate postop PJK patients and 7 at 2-year postop. The odds ratio of developing PJK for grade 2 fat atrophy was 6.1 and for grade 3 was 30.0. Conclusions Higher grades of preoperative paraspinal fat atrophy in the UIV musculature in spine deformity cases is a risk factor for PJK, with the odds ratio of developing PJK for grade 2 fat atrophy at 6.1 and for grade 3 an astounding 30.0. Also, there is greater progression of sagittal malalignment with higher paraspinal fat atrophy grades. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs. Proximal junctional kyphosis (PJK) after spine deformity surgery is a frequent complication with multiple etiologies ranging from patient factors to surgical techniques. The paraspinal musculature at the upper instrumented vertebrae (UIV) is an understudied potential risk factor for PJK. This study classifies the paraspinal fat atrophy at the UIV into 3 different grades and correlates with postoperative sagittal alignment and PJK. The paraspinal musculature quality at the UIV is an understudied risk factor for PJK. We propose an easily distinguishable classification to categorize the different grades of preoperative paraspinal fat atrophy and correlate that with postoperative radiographic outcomes. Prospectively collected cohort. A radiographic review was performed on 116 deformity patients from 2015-2018. Logistic regression and Chi-square analyses were performed to study the relationship between the different UIV paraspinal muscle fat atrophy grades and postoperative sagittal balance. A radiographic review was performed on 116 deformity patients from 2015-2018. The paraspinal muscle at the UIV was assessed using the preoperative axial MRI. Grade 1 was defined as fatty infiltrate between 0-10%, grade 2 between 10%-50%, and grade 3 over 50%. Preop, immediate postop and 2-year postop spine films were assessed. PJK was defined as PJA >15°. Logistic regression and Chi-square analyses were performed to study the relationship between the different UIV paraspinal muscle fat atrophy grades and postoperative sagittal balance. Of the 116 patients, 74 had grade 1, 34 had grade 2, and 8 had grade 3 paraspinal fat atrophy. The immediate postop T1PA for grade 1, 2, and 3 were 11.85, 14.8, and 17.7°. The 2-year postop T1PA for grade 1, 2, and 3 were 9.5, 16.9, and 19.6°. The immediate postop PJA for grade 1, 2, and 3 were 8.1, 8.7, and 15.0°. The 2-year postop PJA for grade 1, 2, and 3 were 7.7, 16.9, and 25.2°. For patients in the grade 1 cohort, 7 had PJK immediate postop and 14 had PJK at 2-year postop. Grade 2 cohort had 7 immediate postop PJK patients and 20 at 2-year postop. Grade 3 cohort had 4 immediate postop PJK patients and 7 at 2-year postop. The odds ratio of developing PJK for grade 2 fat atrophy was 6.1 and for grade 3 was 30.0. Higher grades of preoperative paraspinal fat atrophy in the UIV musculature in spine deformity cases is a risk factor for PJK, with the odds ratio of developing PJK for grade 2 fat atrophy at 6.1 and for grade 3 an astounding 30.0. Also, there is greater progression of sagittal malalignment with higher paraspinal fat atrophy grades.