A three-dimensional femoral head necrosis classification system based on biplanar (frontal and frog-leg lateral) X-ray images: Biomechanics Laboratory of Guangzhou University of Chinese Medicine Classification system

doi:10.3969/j.issn.2095-4344.1330

Abstract

Abstract:

BACKGROUND: Three-dimensional information of osteonecrosis of the femoral head is critical for the treatment planning. The geometry and loading condition of the anterolateral of the femoral head can influence the progression of collapse. However, current assessment using radiography cannot reveal the relevant information and thus may hinder understanding for accurate treatment planning.

OBJECTIVE: To visualize the three-dimensional necrotic site and area based on a biplanar X-ray, to advance the three-dimensional division of femoral head and make new classification method, so as to guide clinical practice.

METHODS: We established a three-dimensional five-column classification system for osteonecrosis of the femoral head according to the load/stress transfer profile of the femoral head during daily activities, and the abnormal stress boundaries and threshold values during the onset and collapse progression of osteonecrosis of the femoral head. The classification system is further optimized as “anterolateral column classification system” by the geometry information of the anterolateral columns acquired from the frog-leg lateral and frontal images. The classification is named as the “Biomechanics Laboratory of Guangzhou University of Chinese Medicine Classification system”.

RESULTS AND CONCLUSION: This study describes the classification principle, method and standard of “Biomechanics Laboratory of Guangzhou University of Chinese Medicine Classification system” in detail. Through a case study, the advantages of the new system are highlighted. The new system can easily and accurately assess the condition and prognosis of osteonecrosis of the femoral head that provides effective guidelines for treatment planning.

Key words:

osteonecrosis of the femoral head, anterolateral column, division of five columns, biomechanics, Biomechanics Laboratory of Guangzhou University of Chinese Medicine Classification, the National Natural Science Foundation of China

CLC Number:

R445.2

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R445.2

Cai Miaoxin, Yang Bin, Deng Peng, Ge Yingjie, Guo Fuming, Liang Zhenghui, Zhai Pei, Pang Zhihui, Fan Yueguang.

A three-dimensional femoral head necrosis classification system based on biplanar (frontal and frog-leg lateral) X-ray images: Biomechanics Laboratory of Guangzhou University of Chinese Medicine Classification system

[J]. Chinese Journal of Tissue Engineering Research, 2019, 23(24): 3786-3791.

Figures/Tables 1

2 股骨头颈部三柱划分法的局限性 Limitations of femoral head neck division of three columns 在现行的三柱划分法中，所选取的划分层面是股骨头T1WI冠状位正中层面，但是股骨头坏死是一个立体的范围，现存的三柱划分法在二维层面上划分，难免对病情的判断具有一定的局限性。若要更加准确的反映坏死的部位和范围，如何选择划分的平面也需要更多的考虑。该选择哪一个层面呢？冠状位还是股骨颈中轴矢状位？坏死病灶累及面积最大、最小还是中位数值的层面？最近有相关的研究认为，选取正中层面进行分型比选取坏死最大层面进行分型对病情的估计不足，前者比实际病情偏低[12]。从理论上来说任何一个二维平面都无法准确评估坏死病灶的三维定位和范围的|从临床实践上来说二维划分法存在较大的观察者个体差异，即不同观察者选用不同的划分平面所引起的差异，因而其评估的一致性和可重复性是受到影响的，也无法有效预测坏死股骨头的塌陷风险及保髋预后，其临床应用价值是有待观察的。 3 股骨头颈部形态学分区的再认识和前外侧柱的再划分 Re-recognization of femoral head neck division and re-division of anterolateral column 如上所述，基于股骨头颈部二维三柱划分法存在的准确性、一致性、可重复性有待提高等问题，有必要引入三维指标对二维划分法做出改良，改良的目的是明确坏死病灶的三维定位和便于坏死容积百分比的估算，提高观察者的一致性和可重复性，从而提高塌陷风险和保髋预后预测的准确率，为临床保髋实践提供更准确的影像学依据。 3.1 改良的依据 3.1.1 股骨头与股骨颈的一体化关系股骨头并不是一个孤立的球体，它与股骨颈连为一体，股骨颈的颈干角、前倾角和中轴线等几何形态数据对股骨头的载荷承载和传递具有决定性的影响，单纯的对股骨头进行形态学划分，难以体现其生物力学特性。因此在划分股骨头的几何和承载功能分区时必须要考虑到与股骨颈相关的因素，要将头颈部作为一个整体来考虑，尤其要重视股骨颈中轴线的特殊地位和作用。因此，五柱分区及新分型方法的正蛙位平片中，股骨颈中轴线都是重要的参考标志。 3.1.2 日常活动时髋臼的负重区主要集中在眉弓 2003年Kumagai等[13]根据髋臼软骨的接触应力分布特点将髋臼分为前柱、后柱、中央顶部和外侧顶部4部分，见图2。2006年Yoshida等[1]根据髋臼的动态接触应力分布特征将髋臼分为前柱、后柱、髋臼中央顶部以及外侧顶部4个解剖分区，见图3。并运用三维有限元模型分析了人类日常生活活动中髋关节接触与相对应的压力。 3.1.3 站立时与活动时股骨头的负重区 1997年Langlais等[14]定义了站立时股骨头的负重区[15]，在此基础上2001年Genda等[16]定义了行走时股骨头的负重区[15]，在简化的股骨头模型上前者是一个圆锥体，圆锥体的顶点是股骨头几何中心，圆锥体的顶角是围绕股骨颈轴线的40°角；后者是前者的延伸，前屈增加40°、后伸增加5°、外展和内收各增加5°，见图4。 3.1.4 临床实践揭示股骨头的顶部和前外侧部的是坏死的主要受累区域根据上述髋臼及股骨头的应力分布来看，人类日常活动各种常用的站立、下蹲及行走等姿势，其应力多分布在股骨头的顶部、前部及外侧部。大量的临床资料同样表明，该部位也是股骨头坏死最容易塌陷的部位[1，15]。在临床实践中发现，这也常是股骨头坏死MRI影像的最大坏死层面。若仅仅采取MRI影像的冠状位正中层面的二维图像，难以准确的反应股骨头坏死的立体范围，见图5。因此如何把股骨头承载功能的顶部和前外侧部准确有效地、简便一致地描述出来也是改良的应有之义。 3.2 改良五柱分区如上所述，基于对股骨颈中轴线的特殊地位和作用、股骨头和髋臼在日常活动中的核心负重区、股骨头坏死病灶主要集中股骨头的顶部和前外侧部这3方面的再认识，此研究小组对股骨头颈部的前外侧柱进行再划分，其核心要素是1条中轴线、1个核心负重区、2条旋转45°的分区线[15]，将股骨头颈部划分为五柱五区[17]。根据上述研究中髋臼和股骨头对应的应力分布特点，该课题组将股骨头的应力区划分为5个应力柱，示意图见图6，7。顶柱为站立位时股骨头的负重区，即以股骨头几何中心为顶点，围绕股骨颈轴线40°角圆锥体的底面(a)以顶柱中心为轴心，将原有的水平轴和矢状轴在水平面上旋转45°，这2条轴线就将顶柱以外的球面分成4个部分，顶柱的外侧为外侧柱(c)；顶柱前侧为前柱(b)；顶柱后方为后柱(d)；顶柱内侧的为内侧柱(e)；外侧柱(c)和前柱(b)合称前外侧柱[13]。 3.3 股骨头颈部五柱五区划分法的先进性及其局限性改良的股骨头颈部五柱五区划分法需要对患者进行平片、CT和MR检查，然后采用专门的三维重建软件和数字图像融合技术进行处理，从而三维可视化地显示坏死病灶的部位、容积、容积百分比等指标，能够较好的提高二维三柱划分法的准确性、一致性和可重复性，从而提高塌陷风险和保髋预后预测的准确率，为临床保髋实践提供更准确的影像学依据。有利就有弊，需要指出的是改良的股骨头颈部五柱五区划分法的临床应用存在门槛高、成本大、周期长、便利性欠佳的局限性，并不适宜在临床推广使用，尤其不适用于基层医院，因此能否在二维划分法和三维划分法之间折衷，平衡两者的优势与局限性，开发出一个相对低门槛、低成本、简便实用，但是准确性、一致性和可重复性得到提升的股骨头颈部分区方法呢？答案是肯定的。 "

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