Chanbour Hani, Steinle Anthony M, Chen Jeffrey W, Waddell William Hunter, Vickery Justin, LaBarge Matthew E, Longo Michael, Gardocki Raymond J, Abtahi Amir M, Stephens Byron F, Zuckerman Scott L
Department of Neurological Surgery, Vanderbilt University Medical Center, Nashville, TN, USA.
Department of Orthopedic Surgery, Vanderbilt University Medical Center, Nashville, TN, USA.
J Spine Surg. 2023 Jun 30;9(2):149-158. doi: 10.21037/jss-22-102. Epub 2023 Jun 14.
Low bone mineral density (BMD) is a well-established risk factor for mechanical complications following adult spinal deformity (ASD) surgery. Hounsfield units (HU) measured on computed tomography (CT) scans are a proxy of BMD. In ASD surgery, we sought to: (I) evaluate the association of HU with mechanical complications and reoperation, and (II) identify optimal HU threshold to predict the occurrence of mechanical complications.
A single-institution retrospective cohort study was undertaken for patients undergoing ASD surgery from 2013-2017. Inclusion criteria were: ≥5-level fusion, sagittal/coronal deformity, and 2-year follow-up. HU were measured on 3 axial slices of one vertebra, either at the upper instrumented vertebra (UIV) itself or UIV ±4 from CT scans. Multivariable regression controlled for age, body mass index (BMI), postoperative sagittal vertical axis (SVA), and postoperative pelvic-incidence lumbar-lordosis mismatch.
Of 145 patients undergoing ASD surgery, 121 (83.4%) had a preoperative CT from which HU were measured. Mean age was 64.4±10.7 years, mean total instrumented levels was 9.8±2.6, and mean HU was 153.5±52.8. Mean preoperative SVA and T1PA were 95.5±71.1 mm and 28.8°±12.8°, respectively. Postoperative SVA and T1PA significantly improved to 61.2±61.6 mm (P<0.001) and 23.0°±11.0° (P<0.001). Mechanical complications occurred in 74 (61.2%) patients, including 42 (34.7%) proximal junctional kyphosis (PJK), 3 (2.5%) distal junctional kyphosis (DJK), 9 (7.4%) implant failure, 48 (39.7%) rod fracture/pseudarthrosis, and 61 (52.2%) reoperations within 2 years. Univariate logistic regression showed a significant association between low HU and PJK [odds ratio (OR) =0.99; 95% confidence interval (CI): 0.98-0.99; P=0.023], but not on multivariable analysis. No association was found regarding other mechanical complications, overall reoperations, and reoperations due to PJK. HU below 163 were associated with increased PJK on receiver operating characteristic (ROC) curve analysis [area under the curve (AUC) =0.63; 95% CI: 0.53-0.73; P<0.001].
Though several factors contribute to PJK, it appears that 163 HU may serve as a preliminary threshold when planning ASD surgery to mitigate the risk of PJK.
低骨密度（BMD）是成人脊柱畸形（ASD）手术后发生机械性并发症的一个公认危险因素。计算机断层扫描（CT）扫描测量的亨氏单位（HU）是骨密度的一个替代指标。在ASD手术中，我们试图：（I）评估HU与机械性并发症和再次手术的关联，以及（II）确定预测机械性并发症发生的最佳HU阈值。
对2013年至2017年接受ASD手术的患者进行了一项单机构回顾性队列研究。纳入标准为：≥5节段融合、矢状面/冠状面畸形以及2年随访。在CT扫描中，于一个椎体的3个轴位切片上测量HU，测量部位为上位固定椎体（UIV）本身或UIV上下4个椎体处。多变量回归分析对年龄、体重指数（BMI）、术后矢状垂直轴（SVA）和术后骨盆入射角与腰椎前凸不匹配进行了校正。
145例接受ASD手术的患者中，121例（83.4%）有术前CT扫描可供测量HU。平均年龄为64.4±10.7岁，平均固定节段总数为9.8±2.6个，平均HU为153.5±52.8。术前平均SVA和T1PA分别为95.5±71.1mm和28.8°±12.8°。术后SVA和T1PA显著改善至61.2±61.6mm（P<0.001）和23.0°±11.0°（P<0.001）。74例（61.2%）患者发生了机械性并发症，包括42例（34.7%）近端交界性后凸畸形（PJK）、3例（2.5%）远端交界性后凸畸形（DJK）、9例（7.4%）内植物失败、48例（39.7%）棒体骨折/假关节形成以及61例（52.2%）在2年内进行了再次手术。单因素逻辑回归显示低HU与PJK之间存在显著关联[比值比（OR）=0.99；95%置信区间（CI）：0.98 - 0.99；P = 0.023]，但在多变量分析中无此关联。未发现与其他机械性并发症、总体再次手术以及因PJK进行的再次手术之间存在关联。在接受者操作特征（ROC）曲线分析中，HU低于163与PJK增加相关[曲线下面积（AUC）=0.63；95% CI：0.53 - 0.73；P<0.001]。
尽管有几个因素促成了PJK的发生，但在计划ASD手术时，163 HU似乎可作为一个初步阈值，以降低PJK的风险。
