椎体CT值在腰椎短节段内固定术后螺钉松动预测中的应用

Application of CT attenuation value in prediction of screw loosening after short-segment lumbar pedicle screw fixation

中文关键词:  螺钉松动  CT值  骨质疏松

英文关键词:Screw loosening  CT attenuation value  Osteoporosis

中文摘要:

  【摘要】 目的：探讨椎体CT值与腰椎短节段内固定术后螺钉松动的关系，选取用于预测螺钉松动的CT临界值。方法：回顾性分析2006年7月~2015年6月在我院行腰椎短节段（≤2个椎间隙）内固定术且术前1个月内行腰椎三维重建CT检查，随访≥24个月的患者资料。共297例，男104例，女193例，年龄54.3±12.5岁（21~80岁），随访36.1±16.5个月（24~110个月）。以末次随访X线评估螺钉松动和融合情况，根据螺钉是否松动及螺钉松动的位置，分为上端椎螺钉松动组、上端椎螺钉对照组和下端椎螺钉松动组、下端椎螺钉对照组，另将下端椎螺钉按是否固定到S1分为两个亚组，并分别分析各亚组内松动组和非松动组的差异。测量L1、上端固定椎、下端固定椎和S1椎体的CT值，收集年龄、性别、体重指数（body mass index，BMI）、糖尿病史、手术节段数、两端融合方式、是否固定到S1等资料。以组内相关系数评估CT值测量的一致性，以Logistic回归分析判断CT值与螺钉松动的关系，以受试者工作特征（receiver operating characteristic，ROC）曲线分析评估CT值对螺钉松动的预测价值，由于松动组例数较少，组内CT值非正态分布，因此以中位数而非均值作为松动高危者预测的界值。结果：共53例患者出现螺钉松动，松动率17.8%（53/297）。上端椎螺钉松动组21例，对照组276例；下端椎螺钉松动48例，对照组249例。共有24例患者出现不融合，总体融合率91.9%（273/297），其中上端节段融合率93.6%（278/297），下端节段融合率93.3%（277/297）。椎体CT值测量具有可靠的测量者内一致性和测量者间一致性（ICC>0.8，P<0.001）。与上端椎对照组相比，上端椎松动组的上端椎体CT值更低（87.3±41.9HU vs 140.5±55.9HU，P<0.05）；当下端固定至腰椎时，下端椎松动组的下端椎体CT值低于对照组（121.9±39.9HU vs 152.2±54.5HU，P<0.05）；当下端固定至S1时，下端椎松动组的S1椎体CT值低于对照组（216.4±61.1HU vs 254.8±81.7HU，P<0.05）。上端椎、下端腰椎和S1的松动组椎体CT值中位数分别为75HU、110HU、220HU。椎体CT值是端椎螺钉松动的独立影响因素（上端椎：OR，0.979；95%CI，0.967-0.992下端椎：OR，0.990；95%CI，0.983~0.998）。端椎CT值可用于松动预测（AUC>0.6，P<0.05）。结论：椎体CT值是腰椎短节段内固定术后端椎螺钉松动的独立影响因素，CT值越低，发生螺钉松动风险越高。

英文摘要:

  【Abstract】 Objectives: To explore the relationship between vertebral CT attenuation value and screw loosening after short-segment lumbar pedicle screw fixation, and to identify thresholds of bone density in HU for predicting screw loosening. Methods: The clinical data of patients who underwent short-segment lumbar pedicle screw fixation in our spinal center from July 2006 to June 2015 were retrospectively analyzed. The inclusion criteria included: (1)no more than 2 segments; (2)at least 2-year follow-up; (3)three dimensional reconstructive CT was done within 30 days before operation. 297 patients(104 males, 193 females) with a mean age of 54.3±12.5 years(21-80 years) and a mean follow-up of 36.1±16.5 months(24-110 months) were reviewed. Screw loosening and bone fusion with lumbar X-ray of final follow-up were assessed. According to the occurrence of screw loosening at UIV(upper instrumented vertebra) or LIV(lowest instrumented vertebra), patients were divided into screw loosening groups (screw loosening at UIV; screw loosening at LIV) and corresponding control groups. Moreover, the LIVs were divided on whether or not the LIV was at S1. The CT attenuation values of L1, UIV, LIV and S1 were measured. Patient data included age, gender, body mass index(BMI), history of diabetes, number of instrumented vertebrae, fusion methods at marginal segments, LIV at S1. According to the occurrence of screw loosening at UIV or LIV, patients were divided into screw loosening groups (screw loosening at UIV; screw loosening at LIV) and corresponding control groups. Inter-examination and inter-observer reliability were assessed by using the intraclass correlation coefficient(ICC). The role of CT attenuation values in screw loosening was explored with Logistic regression analysis. Receiver-operating characteristic curve analysis was used to evaluate the value of CT attenuation values in predicting screw loosening. Because of the relatively small sample size and non-normal distribution of CT attenuation value in screw loosening group, the median rather than the average of the CT attenuation value in screw loosening group was chosen to be the threshold forpredicting screw loosening. Results: Fifty-three patients suffered from postoperative screw loosening(17.8%, 53/297). 21 patients suffered from screw loosening at UIV, 276 patients were in the corresponding control group. 48 patients suffered from screw loosening at LIV, 249 patients were in the corresponding control group. 24 patients suffered from nonunion, the rate of union at upper interbody was 93.6%(278/297), and the rate of union at lowest interbody was 93.3%(273/297). Inter-examination and inter-observer reliability were excellent(ICC>0.8, P<0.001). There were statistically significant differences of CT attenuation values between screw loosening groups and control groups: the mean CT attenuation value of UIV was 87.3±41.9HU in the UIV-screw loosening group and 140.5±55.9HU in corresponding control group, P<0.05; the mean CT attenuation value of LIV at lumbar vertebrae was 121.9±39.9HU in the LIV screw loosening group and 152.2±54.5HU in corresponding control group, P<0.05; the mean CT attenuation value of LIV at S1 was 216.4±61.1HU in the LIV screw loosening group and 254.8±81.7HU in corresponding control group, P<0.05. The CT attenuation value was the independent risk factor of screw loosening. The CT attenuation value of marginal vertebrae was the independent risk factor of screw loosening at marginal vertebrae(UIV-CT attenuation value: OR, 0.979; 95%CI, 0.967-0.992; LIV-CT attenuation value: OR, 0.990; 95%CI, 0.983-0.998). The application of CT attenuation value in prediction of screw loosening was acceptable(AUC>0.6, P<0.05), the median CT attenuation value in UIV-screw loosening group, LIV-lumbar-screw loosening group and LIV-S1-screw loosening group was 75HU, 110HU, 220HU respectively. Conclusions: The CT attenuation value of marginal vertebrae is the independent influencing factor of screw loosening at marginal vertebrae, the lower the CT attenuation value, the higher the risk of screw loosening.