Application of back-forward Bending CT localization image in the prediction of proximal junctional kyphosis after spinal deformity surgery in adults

May 16, 2023

Objective:

To investigate the feasibility of predicting proximal junctional kyphosis (PJK) in adults after spinal deformity surgery based on back-forward Bending CT localization images and related predictive indicators.

Methods:

A retrospective analysis was performed for 31 adult patients with spinal deformity who underwent posterior osteotomy and long-segment fusion fixation between March 2017 and March 2020. There were 5 males and 26 females with an average age of 62.5 years (range, 30-77 years). The upper instrumented vertebrae (UIV) located at T ₅ in 1 case, T ₆ in 1 case, T ₉ in 13 cases, T ₁₀ in 12 cases, and T ₁₁ in 4 cases. The lowest instrumented vertebrae (LIV) located at L ₁ in 3 cases, L ₂ in 3 cases, L ₃ in 10 cases, L ₄ in 7 cases, L ₅ in 5 cases, and S ₁ in 3 cases. Based on the full-length lateral X-ray film of the spine in the standing position before and after operation and back-forward Bending CT localization images before operation, the sagittal sequence of the spine was obtained, and the relevant indexes were measured, including thoracic kyphosis (TK), lumbar lordosis (LL), local kyphosis Cobb angle (LKCA) [the difference between the different positions before operation (recovery value) was calculated], kyphosis flexibility, hyperextension sagittal vertical axis (hSVA), T ₂-L ₅ hyperextension C ₇-vertebral sagittal offset (hC ₇-VSO), and pre- and post-operative proximal junctional angle (PJA). At last follow-up, the patients were divided into PJK and non-PJK groups based on PJA to determine whether they had PJK. The gender, age, body mass index (BMI), number of fusion segments, number of cases with coronal plane deformity, bone mineral density (T value), UIV position, LIV position, operation time, intraoperative blood loss, osteotomy grading, and related imaging indicators were compared between the two groups. The hC ₇-VSO of the vertebral body with significant differences between groups was taken, and the receiver operating characteristic curve (ROC) was used to evaluate its accuracy in predicting the occurrence of PJK.

Results:

All 31 patients were followed up 13-52 months, with an average of 30.0 months. The patient’s PJA was 1.4°-29.0° at last follow-up, with an average of 10.4°; PJK occurred in 8 cases (25.8%). There was no significant difference in gender, age, BMI, number of fusion segments, number of cases with coronal plane deformity, bone mineral density (T value), UIV position, LIV position, operation time, intraoperative blood loss, and osteotomy grading between the two groups ( P>0.05). Imaging measurements showed that the LL recovery value and T ₈-L ₃ vertebral hC ₇-VSO in the PJK group were significantly higher than those in the non-PJK group ( P>0.05). There was no significant difference in hyperextension TK, hyperextension LL, hyperextension LKCA, TK recovery value, LL recovery value, kyphosis flexibility, hSVA, and T ₂-T ₇, L ₄, L ₅ vertebral hC ₇-VSO ( P>0.05). T ₈-L ₃ vertebral hC ₇-VSO was analyzed for ROC curve, and combined with the area under curve and the comprehensive evaluation of sensitivity and specificity, the best predictive index was hC ₇-L ₂, the cut-off value was 2.54 cm, the sensitivity was 100%, and the specificity was 60.9%.

Conclusion:

Preoperative back-forward Bending CT localization image can be used to predict the occurrence of PJK after posterior osteotomy and long-segment fusion fixation in adult spinal deformity. If the patient’s T ₈-L ₂ vertebral hC ₇-VSO is too large, it indicates a higher risk of postoperative PJK. The best predictive index is hC ₇-L ₂, and the cut-off value is 2.54 cm.

目的:

探讨基于过伸位CT定位像预测成人脊柱畸形矫形术后近端交界性后凸（proximal junctional kyphosis，PJK）的可行性以及相关预测指标。.

方法:

以2017年3月—2020年3月符合选择标准的31例成人脊柱畸形患者作为研究对象。其中男5例，女26例；年龄30～77岁，平均62.5岁。均接受后路截骨长节段融合固定矫形术治疗；最上端固定椎（upper instrumented vertebrae，UIV）位置：T ₅ 1例，T ₆ 1例，T ₉ 13例，T ₁₀ 12例，T ₁₁ 4例；最下端固定椎（lowest instrumented vertebrae，LIV）位置：L ₁ 3例，L ₂ 3例，L ₃ 10例，L ₄ 7例，L ₅ 5例，S ₁ 3例。基于手术前后站立位脊柱全长侧位X线片、术前过伸位CT定位像，获得脊柱矢状面序列，分别测算以下指标。① 胸椎后凸角（thoracic kyphosis，TK）、腰椎前凸角（lumbar lordosis，LL）、局部后凸Cobb角（local kyphosis Cobb angle，LKCA），计算上述指标术前不同体位差值（回复值）；② 脊柱后凸柔韧度；③ 过伸位矢状面垂直轴（hyperextension sagittal vertical axis，hSVA）；④ T ₂～L ₅过伸位C ₇-椎体矢状位偏移（hyperextension C ₇-vertebral sagittal offset，hC ₇-VSO），记为hC ₇-节段；⑤ 术前及术后1周、6个月、末次随访时近端交界性后凸角（proximal junctional angle，PJA）。末次随访时根据PJA判断患者是否发生PJK，分为PJK组和非PJK组。比较两组患者性别、年龄、身体质量指数（body mass index，BMI）、融合节段数量、合并冠状面畸形例数、骨密度T值、UIV位置、LIV位置、手术时间、术中出血量、脊柱矫形截骨分级以及相关影像学测量指标差异。取组间差异有统计学意义节段椎体的hC ₇-VSO，采用受试者工作特征曲线（receiver operating characteristic curve，ROC）评价其预测PJK发生的准确性。.

结果:

31例患者术后均获随访，随访时间13～52个月，平均30.0个月。末次随访时患者PJA为1.4°～29.0°，平均10.4°；其中8例（25.8%）发生PJK。两组患者性别、年龄、BMI、融合节段数量、合并冠状面畸形例数、骨密度T值、UIV位置、LIV位置以及手术时间、术中出血量、脊柱截骨矫形分级比较，差异均无统计学意义（ P>0.05）。影像学测量示，PJK组LL回复值以及T ₈～L ₃椎体hC ₇-VSO高于非PJK组，差异有统计学意义（ P>0.05）。两组患者过伸位TK、过伸位LL、过伸位LKCA、TK回复值、LL回复值、脊柱后凸柔韧度、hSVA以及T ₂～T ₇、L ₄、L ₅椎体hC ₇-VSO比较，差异均无统计学意义（ P>0.05）。取T ₈～L ₃椎体hC ₇-VSO进行ROC曲线分析，结合ROC曲线下面积与敏感度、特异度综合评估得出最佳预测指标为hC ₇-L ₂，阈值为2.54 cm，敏感度为100%，特异度为60.9%。.