Hollingworth Abby L, Hutchinson Jayson B, Bechtel Jocelynn R, Chapman Ryan M
University of Rhode Island, Department of Electrical, Computer, and Biomedical Engineering, Fascitelli Center for Advanced Engineering, 2 East Alumni Avenue, Kingston, RI, 02881, USA.
University of Rhode Island, Department of Kinesiology, 25 W. Independence Way, Kingston, RI, 02881, USA.
Comput Biol Med. 2025 Jul;193:110469. doi: 10.1016/j.compbiomed.2025.110469. Epub 2025 May 29.
Consumer-grade wearable inertial measurement units (IMUs) with limited degrees of freedom (DOF) are common computing knee motion before/after clinical intervention. Appropriate use requires attaching sensors per manufacturer's instructions. However, IMU misplacement error remains problematic. Thus, we assessed error computing sagittal knee angles across sensor misplacement orientations of one consumer-grade IMU system with 6DOF. We hypothesized error would increase during frontal plane misplacement. Ten young, healthy individuals (20.9 ± 0.7 years) were enrolled. IMUs were adhered/calibrated per manufacturer instructions and IMU-computed knee angles were compared to optical motion capture (MOCAP) during self-selected speed treadmill walking. Shin/thigh IMUs were then moved across sagittal, frontal, and transverse planes (±10°, ±20°). At each orientation, IMU calibration and treadmill walking was re-completed. Error was computed between MOCAP/IMU by calculating the difference and computing the absolute value (i.e. absolute value error). This was averaged across participants at each sensor position (i.e. average absolute value error). Bland Altman analyses assessed MOCAP/IMU agreement. ANOVAs assessed how plane, segment, and falsified IMU angle impacted error. MOCAP/IMUs were highly correlated with IMUs achieving clinically acceptable error (<5°) when placed correctly or with sagittal/transverse plane misalignment. Frontal plane (varus and valgus) and shin sensor misalignment caused significantly greater error (∼7°), likely due to limited IMU DOF. Limited DOF IMUs can accurately compute knee motion even with significant sagittal/transverse plane misalignment. However, frontal plane placement is critical for proper function, implying patients with frontal plane deformities should not use reduced DOF IMUs. Moreover, patient education is critical for appropriate deployment of wearable IMUs.
具有有限自由度（DOF）的消费级可穿戴惯性测量单元（IMU）常用于临床干预前后的膝关节运动计算。正确使用需要按照制造商的说明附着传感器。然而，IMU放置错误误差仍然是个问题。因此，我们评估了一个具有6自由度的消费级IMU系统在传感器放置方向错误时计算矢状面膝关节角度的误差。我们假设在额状面放置错误时误差会增加。招募了10名年轻健康个体（20.9±0.7岁）。按照制造商说明粘贴/校准IMU，并在自选速度的跑步机行走过程中将IMU计算的膝关节角度与光学运动捕捉（MOCAP）进行比较。然后将小腿/大腿IMU在矢状面、额状面和横断面（±10°，±20°）上移动。在每个方向上，重新完成IMU校准和跑步机行走。通过计算差值并取绝对值（即绝对值误差）来计算MOCAP/IMU之间的误差。在每个传感器位置对参与者进行平均（即平均绝对值误差）。Bland Altman分析评估MOCAP/IMU的一致性。方差分析评估平面、节段和伪造的IMU角度如何影响误差。当正确放置或矢状面/横断面未对准时，MOCAP/IMU高度相关，IMU达到临床可接受误差（<5°）。额状面（内翻和外翻）和小腿传感器未对准会导致明显更大的误差（约7°），可能是由于IMU自由度有限。即使存在明显的矢状面/横断面未对准，有限自由度的IMU也能准确计算膝关节运动。然而，额状面放置对于正常功能至关重要，这意味着患有额状面畸形的患者不应使用自由度降低的IMU。此外，患者教育对于可穿戴IMU的正确使用至关重要。
