A Novel Method to Estimate the Full Knee Joint Kinematics Using Low Cost IMU Sensors for Easy to Implement Low Cost Diagnostics

Abstract

Traditional motion capture systems are the current standard in the assessment of knee joint kinematics. These systems are, however, very costly, complex to handle, and, in some conditions, fail to estimate the varus/valgus and internal/external rotation accurately due to the camera setup. This paper presents a novel and comprehensive method to infer the full relative motion of the knee joint, including the flexion/extension, varus/valgus, and internal/external rotation, using only low cost inertial measurement units (IMU) connected to the upper and lower leg. Furthermore, sensors can be placed arbitrarily and only require a short calibration, making it an easy-to-use and portable clinical analysis tool. The presented method yields both adequate results and displays the uncertainty band on those results to the user. The proposed method is based on an fixed interval smoother relying on a simple dynamic model of the legs and judicially chosen constraints to estimate the rigid body motion of the leg segments in a world reference frame. In this pilot study, benchmarking of the method on a calibrated robotic manipulator, serving as leg analogue, and comparison with camera-based techniques confirm the method's accurateness as an easy-to-implement, low-cost clinical tool.

Accuracy of Measuring Knee Flexion after TKA through Wearable IMU Sensors

“…Previous studies focusing on the accuracy of IMU-based knee flexion measurement systems are often limited to the relative range of motion or based on assumptions around the patient’s ability to fully extend their leg or position sensors accurately. These studies often overlook the offset or systematic bias that could be introduced during the sensor-to-leg registration process studied in this paper and associated misalignment of the sensors relative to the patient’s anatomy [ 22 , 23 ]. This issue has important clinical limitations, particularly in a patient population recovering from knee replacement surgery or anterior cruciate reconstruction surgery [ 24 ] where a lack of full extension during recovery often leads to re-operation [ 25 , 26 ].…”

Development of a Low-Cost Open-Source Measurement System for Joint Angle Estimation

“…The biggest limitation in using JAMA is the non-validation of two measurements. Most of the works that develop hardware using IMU use gold standard devices as a reference during development and for measurement validation [ 2 , 3 , 24 ]. Although it is not the best technique for device validation, the use of robots is a form of validation, and here we use Lokomat to carry out the proof of concept of the JAMA measurements [ 20 , 24 , 25 , 26 ].…”

“…Most of the works that develop hardware using IMU use gold standard devices as a reference during development and for measurement validation [ 2 , 3 , 24 ]. Although it is not the best technique for device validation, the use of robots is a form of validation, and here we use Lokomat to carry out the proof of concept of the JAMA measurements [ 20 , 24 , 25 , 26 ]. In this context, the signals extracted by JAMA present an expected pattern, which can be observed based on the results of the performed experiments but also on the shape of the extracted signal (data presented on GitHub).…”

Acquisition of Lower-Limb Motion Characteristics with a Single Inertial Measurement Unit—Validation for Use in Physiotherapy

“…In between, there are many other different approaches, for example, in [ 7 ], an application for gait classification in patients with different neurological disorders, and in [ 8 ], a project with the development goal of a wearable feedback system, both with seven IMU sensors placed on the lower extremities only. Some systems specialize in measuring the movement of only one joint [ 9 ]. Using modelling is a bit risky when examining patients, since their motion patterns deviate from the norm, at least at the beginning of therapy.…”