Background: 

Preoperative planning of lower-limb realignment surgical procedures necessitates the quantification of alignment parameters by using landmarks placed on medical scans. Conventionally, alignment measurements are performed on 2-dimensional (2D) standing radiographs. To enable fast and accurate 3-dimensional (3D) planning of orthopaedic surgery, automatic calculation of the lower-limb alignment from 3D bone models is required. The goal of this study was to develop, validate, and apply a method that automatically quantifies the parameters defining lower-limb alignment from computed tomographic (CT) scans.

Methods: 

CT scans of the lower extremities of 50 subjects were both manually and automatically segmented. Thirty-two manual landmarks were positioned twice on the bone segmentations to assess intraobserver reliability in a subset of 20 subjects. The landmarks were also positioned automatically using a shape-fitting algorithm. The landmarks were then used to calculate 25 angles describing the lower-limb alignment for all 50 subjects.

Results: 

The mean absolute difference (and standard deviation) between repeat measurements using the manual method was 2.01 ± 1.64 mm for the landmark positions and 1.05° ± 1.48° for the landmark angles, whereas the mean absolute difference between the manual and fully automatic methods was 2.17 ± 1.37 mm for the landmark positions and 1.10° ± 1.16° for the landmark angles. The manual method required approximately 60 minutes of manual interaction, compared with 12 minutes of computation time for the fully automatic method. The intraclass correlation coefficient showed good to excellent reliability between the manual and automatic assessments for 23 of 25 angles, and the same was true for the intraobserver reliability in the manual method. The mean for the 50 subjects was within the expected range for 18 of the 25 automatically calculated angles.

Conclusions: 

We developed a method that automatically calculated a comprehensive range of 25 measurements that defined lower-limb alignment in considerably less time, and with differences relative to the manual method that were comparable to the differences between repeated manual assessments. This method could thus be used as an efficient alternative to manual assessment of alignment.

Level of Evidence: 

Diagnostic Level III. See Instructions for Authors for a complete description of levels of evidence.

中文翻译：

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计算机断层扫描下肢对齐的自动评估

背景： 

下肢矫正外科手术的术前规划需要通过使用放置在医学扫描上的地标来量化对齐参数。通常，对准测量是在二维 (2D) 站立射线照片上执行的。为了能够快速准确地进行骨科手术的 3 维 (3D) 规划，需要根据 3D 骨骼模型自动计算下肢对齐。本研究的目的是开发、验证和应用一种方法，该方法可以自动量化定义计算机断层扫描 (CT) 扫描的下肢对齐的参数。

方法： 

对 50 名受试者的下肢 CT 扫描进行了手动和自动分割。将 32 个手动地标两次定位在骨骼分割上，以评估 20 名受试者子集中观察者内的可靠性。地标也使用形状拟合算法自动定位。然后使用这些地标计算 25 个角度，描述所有 50 名受试者的下肢对齐。

结果： 

使用手动方法重复测量的平均绝对差（和标准差）对于地标位置为 2.01 ± 1.64 mm，对于地标角度为 1.05° ± 1.48°，而手动和全自动方法之间的平均绝对差为 2.17地标位置为 ± 1.37 mm，地标角度为 1.10° ± 1.16°。手动方法需要大约 60 分钟的手动交互，而全自动方法需要 12 分钟的计算时间。对于 25 个角度中的 23 个，组内相关系数在手动和自动评估之间显示出良好到极好的可靠性，手动方法中的观察者内部可靠性也是如此。50 名受试者的平均值在 25 个自动计算的角度中的 18 个的预期范围内。

结论： 

我们开发了一种方法，可以自动计算 25 个测量值的综合范围，这些测量值在相当短的时间内定义了下肢对齐，并且与手动方法的差异与重复手动评估之间的差异相当。因此，该方法可以用作手动对齐评估的有效替代方法。

证据等级： 

诊断三级。有关证据等级的完整描述，请参阅作者须知。