166. A Hounsfield unit value below 125 on preoperative CT at upper instrumented vertebrae is predictive of proximal junctional kyphosis after adult spinal deformity surgery

Abstract

<h3>BACKGROUND CONTEXT</h3> As adult spinal deformity (ASD) prevalence increases in our ever-aging population there is a concomitant increase in poor bone quality. ASD surgery is expensive and carries a high complication profile. It is important to optimize modifiable preoperative risk factors, such as osteopenia or osteoporosis. Additional diagnostic modalities such as a DEXA can add cost, delay diagnosis, and can be an additional insurance hurdle. Some studies suggest HU's can be utilized as a proxy for frailty, but it is unclear if this is useful in risk stratification. <h3>PURPOSE</h3> Our goal was to evaluate the relationship between bone health as measured by HU's and PJK and identify a HU threshold in which PJK risk is increased. We hypothesize that HU will correlate with occurrence of PJK after ASD surgery. <h3>STUDY DESIGN/SETTING</h3> Retrospective review of a prospective, multicenter ASD database. <h3>PATIENT SAMPLE</h3> Of 1,330 pts eligible, 997 (74.9%) had complete 2Y follow-up. Of these, 605 meet inclusion criteria with 110 (18.18%) patients having a PJK. <h3>OUTCOME MEASURES</h3> Development of PJK within 2 years of surgery. <h3>METHODS</h3> Operative ASD patients (scoliosis >20, SVA>5cm, PT>25, or TK>60) with available baseline (BL) and 2-year (2Y) radiographic and HRQL data were included if they had a preop CT. HU were measured from axial views within the cancellous body (x3) at both L1 and UIV with the mean value calculated for each. Threshold linear regression with Bayesian information criteria was utilized to identify optimal cut-offs of risk factors for PJK. Multivariable analysis (MVA) controlled for PJK prophylaxis and surgeon. Additionally, risk factors identified were controlled against each other. <h3>RESULTS</h3> Threshold regression identified that cut-offs of <125 HU for UIV, >63 years for age, >0.31 for ASD-FI, and >47° for preoperative T4-12 thoracic kyphosis, and <10 levels fused were predictive of PJK on bivariate analysis (P<0.05 for all). On MVA, age > 63 years old (OR 4.7; P = 0.003), female gender (OR 3.33; P=0.035), HU at UIV vertebrae <125 (2.83; P=0.008), ASD-FI >0.31 (OR 4.02; P=0.011), TK > 46° (OR 3.75; P=0.003), and < 10 levels fused (OR 3.31; P=0.0310) were associated with increased odds of PJK. <h3>CONCLUSIONS</h3> Bone health as measured by HU appears to be an independent predictor of PJK after ASD surgery, specifically values <125 at the UIV. It also parallels frailty in prediction of PJK and can potentially be used as a proxy for frailty assessment. This can be easily measured and could help with risk stratification in the future. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.