Abstract
The estimate of a consistent and clinically meaningful joint kinematics using wearable inertial and magnetic sensors requires a sensor-to-segment coordinate system calibration. State-of-the-art calibration procedures for the upper limb are based on functional movements and/or pre-determined postures, which are difficult to implement in subjects that have impaired mobility or are bedridden in acute units. The aim of this study was to develop and validate an alternative calibration procedure based on the direct identification of palpable anatomical landmarks (ALs) for an inertial and magnetic sensor-based upper limb movement analysis protocol. The proposed calibration procedure provides an estimate of three-dimensional shoulder/elbow angular kinematics and the linear trajectory of the wrist according to the standards proposed by the International Society of Biomechanics. The validity of the method was assessed against a camera-based optoelectronic system during uniaxial joint rotations and a reach-to-grasp task. Joint angular kinematics was found as characterised by a low-biased range of motion (<−2.6°), a low root mean square deviation (RMSD) (<4.4°) and a high waveform similarity coefficient (R2 > 0.995) with respect to the gold standard. Except for the cranio–caudal direction, the linear trajectory of the wrist was characterised by a low-biased range of motion (<11 mm) together with a low RMSD (8 mm) and high waveform similarity (R2 > 0.968). The proposed method enabled the estimation of reliable joint kinematics without requiring any active involvement of the patient during the calibration procedure, complying with the metrological standards and requirements of clinical movement analysis.
Highlights
Wearable magnetic and inertial measurement units (MIMUs), consisting of a three-axial accelerometer, gyroscope and a magnetometer, represent a self-contained alternative to conventional lab-based motion capture systems for joint angular kinematics assessment[1,2]
All three approaches may be critical with bedridden acute patients as they are usually equipped with medical devices and apparatus the positioning of which might jeopardise the alignment of the MIMU with the underlying bone and limit the joint range of motion
This study proposes an innovative upper limb movement analysis protocol based on the use of wearable MIMUs, which provide anatomically and clinically consistent joint kinematics estimates
Summary
Wearable magnetic and inertial measurement units (MIMUs), consisting of a three-axial accelerometer, gyroscope and a magnetometer, represent a self-contained alternative to conventional lab-based motion capture systems for joint angular kinematics assessment[1,2] Their use is favourable when motion analysis must be performed outside the laboratory (such as clinical settings) or for a long period of time[3]. Www.nature.com/scientificreports sound joint kinematics requires knowledge of the orientation of the MIMU-embedded coordinate system with respect to the anatomical coordinate system of the body segment on which the MIMU is strapped This information is retrieved during a sensor-to-segment axes calibration procedure ( called “anatomical calibration”), which can be implemented in different ways. The aim of this study was to develop a MIMU-based anatomical calibration procedure to estimate linear and angular kinematics of an upper limb kinematic model and assess the procedure’s validity against a camera-based optoelectronic system
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