Assessing the validity of inertial measurement units for shoulder kinematics using a commercial sensor-software system: A validation study

Abstract

Background and  aims: Wearable inertial sensors may offer additional kinematic parameters of the shoulder compared to traditional instruments such as goniometers when elaborate and time-consuming data processing procedures are undertaken. However, in clinical practice simple-real time motion analysis is required to improve clinical reasoning. Therefore, the aim was to assess the criterion validity between a portable "off-the-shelf" sensor-software system (IMU) and optical motion (Mocap) for measuring kinematic parameters during active shoulder movements.

Methods: 24 healthy participants (9 female, 15 male, age 29 ± 4 years, height 177 ± 11 cm, weight 73 ± 14 kg) were included. Range of motion (ROM), total range of motion (TROM), peak and mean angular velocity of both systems were assessed during simple (abduction/adduction, horizontal flexion/horizontal extension, vertical flexion/extension, and external/internal rotation) and complex shoulder movements. Criterion validity was determined using intraclass-correlation coefficients (ICC), root mean square error (RMSE) and Bland and Altmann analysis (bias; upper and lower limits of agreement).

Results: ROM and TROM analysis revealed inconsistent validity during simple (ICC: 0.040-0.733, RMSE: 9.7°-20.3°, bias: 1.2°-50.7°) and insufficient agreement during complex shoulder movements (ICC: 0.104-0.453, RMSE: 10.1°-23.3°, bias: 1.0°-55.9°). Peak angular velocity (ICC: 0.202-0.865, RMSE: 14.6°/s-26.7°/s, bias: 10.2°/s-29.9°/s) and mean angular velocity (ICC: 0.019-0.786, RMSE:6.1°/s-34.2°/s, bias: 1.6°/s-27.8°/s) were inconsistent.

Conclusions: The "off-the-shelf" sensor-software system showed overall insufficient agreement with the gold standard. Further development of commercial IMU-software-solutions may increase measurement accuracy and permit their integration into everyday clinical practice.

Keywords: diagnostic techniques and procedures; kinematics; shoulder joint; validation study; wearable devices.

Figure 1

Calibration (“T‐pose”) position of the participant. (A) dorsal view, (B) frontal view. Reflective markers and two portable IMU sensors were attached on the torso. IMU sensor calibration pose. IMU, inertial measurement units.

Figure 2

Left: Participant performing Vertical flexion (A) and vertical extension (B). Right: angle‐time plots for Mocap (top: the red arrow indicates the calculation of a maximum) and IMU (bottom: the red arrow indicates the calculation of minimum) movement fragmentation (blue arrows indicate beginning/end of movement) before angle offset removal. Vertical flexion and vertical extension with corresponding time‐angle plots. IMU, inertial measurement units.