Division of Orthopaedic Surgery.
Department of Orthopaedic Surgery, Meir Medical Center, Tel Aviv University, Tel Aviv, Israel.
J Pediatr Orthop. 2020 Oct;40(9):e822-e826. doi: 10.1097/BPO.0000000000001633.
Rotation of the humerus out of the coronal plane is presumed to alter the Baumann angle (BA) value. Identifying the rotational limits of the humerus at which the BA can be accurately and reliably measured will circumvent repeated radiographs and unnecessary exposure to radiation, may improve patient comfort, and save time and medical resources.
A retrospective chart review was performed to identify patients under the age of 18 who underwent an elbow computed tomography (CT) scan without any humeral pathology and with an open distal humeral physis. For each patient, a 3-dimensional (3D) computerized model was generated with 30% transparency to mimic a plain radiograph. These models were rotated in 10-degree increments and the BA was measured on each position. In addition, the measurements were taken on an anteroposterior radiograph for each patient. Analysis of variance and the Pearson tests were performed to locate differences and define associations.
Fifteen 3D CT reconstructions were generated from 14 patients. The mean BA on the neutral position was found to be 72.2±3 degrees, which correlated with the 70.6±5.91 degrees measurement obtained on radiographs. The most extreme rotational positions on which the BA values were consistent with the neutral position values were +40 external rotation (70.97±7.01 degrees, P=1) and -70 degrees internal rotation (68.4±7.47 degrees, P=0.14). A negative correlation was found between the BA values and the extent at which the humerus was rotated from the neutral position. The variability of the BA between patients, implied by the SD of measurements on each position increased with increasing rotation from the neutral position (r=1, P<0.05).
On the basis of 3D CT images, the BA is the most accurate when the arm is positioned at an exact anteroposterior position. It is reliable to measure the BA when the humerus is rotated no more than +40 degrees external rotation to -70 degrees internal rotation. This range of rotation can act as an "accurate zone" and help avoiding multiple radiographs.
Level III.
肱骨在冠状面外旋被认为会改变肱骨头倾斜角（BA）值。确定可以准确可靠地测量 BA 的肱骨旋转极限，将避免反复拍摄 X 光片和不必要的辐射暴露，可能会提高患者舒适度并节省时间和医疗资源。
对年龄在 18 岁以下且肱骨无病理改变且肱骨远端干骺端开放的接受肘部 CT 扫描的患者进行回顾性图表审查。为每位患者生成一个 30%透明度的 3 维（3D）计算机模型，以模拟普通 X 光片。将这些模型以 10 度增量旋转，并在每个位置测量 BA。此外，还对每位患者的前后位 X 光片进行了测量。进行方差分析和 Pearson 检验以确定差异和定义关联。
从 14 名患者中生成了 15 个 3D CT 重建。在中立位置发现的平均 BA 为 72.2±3 度，与 X 光片上获得的 70.6±5.91 度测量值相关。BA 值与中立位置值一致的最极端旋转位置是外旋+40（70.97±7.01 度，P=1）和内旋-70 度（68.4±7.47 度，P=0.14）。发现 BA 值与肱骨从中立位置旋转的程度之间存在负相关。从每个位置的测量值的标准差来看，BA 的变异性随着从中立位置的旋转增加而增加（r=1，P<0.05）。
基于 3D CT 图像，当手臂处于确切的前后位置时，BA 最准确。当肱骨外旋不超过+40 度或内旋不超过-70 度时，测量 BA 是可靠的。这种旋转范围可以作为一个“准确区域”，并有助于避免多次拍摄 X 光片。
3 级。
