Department of Orthopaedic Surgery, Beth Israel Deaconess Medical Center, Harvard Combined Orthopaedic Residency Program, Boston, MA.
J Orthop Trauma. 2018 Jul;32(7):e258-e262. doi: 10.1097/BOT.0000000000001175.
To determine and test mathematical models of the relationship between hip flexion-extension, femoral rotation, and NSA. We hypothesized that hip flexion-extension and femoral rotation would result in NSA measurement error.
Two mathematical models were developed to predict NSA in varying degrees of hip flexion-extension and femoral rotation. The predictions of the equations were tested in vitro using a model that varied hip flexion-extension while keeping rotation constant, and vice versa. The NSA was measured from an anterior-posterior radiograph obtained with a C-arm. Attributable measurement error based on hip positioning was calculated from the models.
The predictions of the model correlated well with the experimental data (correlation coefficient = 0.82-0.90). A wide range of patient positioning was found to result in <5-10 degrees error in the measurement of NSA. Hip flexion-extension and femoral rotation had a synergistic effect in measurement error of the NSA. Measurement error was minimized when hip flexion-extension was within 10 degrees of neutral.
This study demonstrates that hip flexion-extension and femoral rotation significantly affect the measurement of the NSA. To avoid inadvertently fixing the proximal femur in varus or valgus, the hip should be positioned within 10 degrees of neutral flexion-extension with respect to the C-arm to minimize positional measurement error.
确定并测试髋关节屈伸、股骨旋转与 NSA 之间关系的数学模型。我们假设髋关节屈伸和股骨旋转将导致 NSA 测量误差。
开发了两种数学模型来预测在不同髋关节屈伸和股骨旋转角度下的 NSA。通过使用保持旋转不变而改变髋关节屈伸的模型和反之亦然的模型，在体外测试方程的预测。NSA 通过 C 臂获得的前后位 X 线片进行测量。从模型中计算基于髋关节定位的归因测量误差。
模型的预测与实验数据相关性良好（相关系数=0.82-0.90）。发现患者的多种定位会导致 NSA 测量误差小于 5-10 度。髋关节屈伸和股骨旋转在 NSA 的测量误差中具有协同作用。当髋关节屈伸在中立位以内 10 度时，测量误差最小。
本研究表明，髋关节屈伸和股骨旋转会显著影响 NSA 的测量。为了避免无意中将股骨近端固定在内翻或外翻，髋关节应在 C 臂上保持中立屈伸位 10 度以内，以最小化位置测量误差。
