An Extended Dynamometer Setup to Improve the Accuracy of Knee Joint Moment Assessment

Abstract

This paper analyzes an extended dynamometry setup that aims at obtaining accurate knee joint moments. The main problem of the standard setup is the misalignment of the joint and the dynamometer axes of rotation due to nonrigid fixation, and the determination of the joint axis of rotation by palpation. The proposed approach 1) combines 6-D registration of the contact forces with 3-D motion capturing (which is a contribution to the design of the setup); 2) includes a functional axis of rotation in the model to describe the knee joint (which is a contribution to the modeling); and 3) calculates joint moments by a model-based 3-D inverse dynamic analysis. Through a sensitivity analysis, the influence of the accuracy of all model parameters is evaluated. Dynamics resulting from the extended setup are quantified, and are compared to those provided by the dynamometer. Maximal differences between the 3-D joint moment resulting from the inverse dynamics and measured by the dynamometer were 16.4 N ·m (16.9%) isokinetically and 18.3 N ·m (21.6%) isometrically. The calculated moment is most sensitive to the orientation and location of the axis of rotation. In conclusion, more accurate experimental joint moments are obtained using a model-based 3-D inverse dynamic approach that includes a good estimate of the pose of the joint axis.

Analysis of Knee Strength Measurements Performed by a Hand-Held Multicomponent Dynamometer and Optoelectronic System

“…The isokinetic dynamometer showed high interrater and intrarater reliability and reproducibility for the measurement of joint forces and moments when it was applied to subjects of different ages, both on lower and upper limbs [3], [12], [16]. The isokinetic dynamometer was also used in combination with 3-D motion capture to obtain accurate joint moment measurements [17]. The main drawbacks are that the system is expensive and cumbersome, not portable, and it requires long time to prepare the subject.…”

Muscle-Tendon Unit Parameter Estimation of a Hill-Type Musculoskeletal Model Based on Experimentally Obtained Subject-Specific Torque Profiles

“…The second (dyn-opt) concerns the forcevelocity relation and the related parameters and builds on top of the isom_opt results ( Figure 2). The optimisation was divided into these two consecutive stages based on the nature of the experimental data, where isovelocity measurements are prone to more noise and motion artefacts than isometric measurements, and hence the isometric measurements were prioritised [34]. Furthermore, due to the experimental and computational time-consumption associated with the isovelocity part of the process, it seems relevant to compare the quality of results obtained solely from isometric data and isom-opt with results requiring isovelocity data and dyn-opt as well.…”

Robot-aided assessment of lower extremity functions: a review

“…The most known device for muscle strength measures is the isokinetic dynamometer. This machine allows the measurement of joint torques in controlled conditions: isometric at selected joint angles or isokinetic at selected angular velocities [ 79 , 89 ]. A servo-controlled lever arm provides resistance to the subject’s joint when it reaches a defined angular velocity (≥0 deg/s).…”

“…Different mechanical configurations allow testing of hip flexion-extension and ab-adduction, knee flexion-extension, ankle plantar-dorsiflexion and eversion-inversion. The patient’s trunk and the segments proximal to the joint tested must be stabilized with straps and the axis of the dynamometer must be carefully aligned with the axis of the joint to test to avoid measurement inaccuracy [ 89 ]. In isokinetic tests the subject is asked to push “as hard and as fast as possible” while the device provides resistance to the movement of the limb so that it cannot accelerate beyond the machine’s preset angular speed [ 90 ].…”

“…A large body of research on this device have unraveled the possible shortcomings and studied different applications and measurement protocols. In particular, factors such as gravity compensation, damping of the system, human-machine interface and alignment of the human and robot axes of rotation have been considered in many publications [ 85 , 89 , 99 ]. This knowledge can be applied to the development of future robot-aided muscle strength assessments, despite the fact that the differences in hardware prevent the complete reproducibility of the results.…”