G. Parent

A simple and rapid method for electromagnetic field distortion correction when using two Fastrak sensors for biomechanical studies

The article presents a simple and rapid method for the correction of electromagnetic distortions when using electromagnetic Fastrak (Polhemus, USA) sensors. It is based on the minimization of objective functions composed of derivative polynomial functions, hence estimating the distortion of the electromagnetic field. The polynomial functions composing the objective function each contain 35 deformation coefficients. These coefficients are then used to correct the electromagnetic measures in position and orientation. Preliminary results on the efficacy of the method are presented for two subjects who walked on a treadmill, and for whom relative movement of the lower leg with respect to the thigh was recorded using two Fastrak sensors. The corrected Fastrak measurements were compared with optoelectronic measurements (Vicon, USA), which are not affected by distortions as electromagnetic sensors are. Results showed that after 3 min of calibrating a volume of approximately 1m(3), the method proved to be efficient in correcting errors in orientation (56% (2.72-1.12 degrees ), 78% (4.4-0.89 degrees ), and 56% (2.25-0.90 degrees ) of error reduction in the respective flexion/extension, ab/adduction and tibial internal/external rotation) and position (53% (18.9-8.9 mm), 21% (6.6-4.6mm), and 48% (15.9-8.1mm) of error reduction in the respective medial/lateral, anterior/posterior and proximal/distal translations) (values are overall means for two subjects and four calibration procedures). That amount of correction compared favorably with values presented in the literature.

Automatic filtering techniques for three-dimensional kinematics data using 3D motion capture system

The purpose of this paper is to investigate the performance of three algorithms for automatic filtering of 3D displacement data. The first approach is based on power spectrum analysis of signal with auto regressive modeling approach to detect a signal bandwidth in the frequency domain. The second method uses the autocorrelation of the residual signal between filtered and unfiltered data to separate the signal bandwidth from noise. The third approach uses a singular spectrum analysis to detect the variance of the signal and reject the noise based on the eigenvalue decomposition of the signal. Overall, the highest RMS value of 0.480 m/s2 was measured in the X direction for PSA method, whereas the lowest RMS value of 0.162 m/s2 was recorded for cluster 2 for SSA method. This represents a gain of 3 in accuracy in estimating higher-order derivatives such as linear acceleration of rigid body motion. SSA method is robust and seems to behave well for different signal combinations

Three-dimensional Kinematic Assessment of Ligament Rupture and Surgery

Only a few areas of contemporary orthopedics have raised as many controversies and diverging opinions as optimal reconstruction of the cruciate ligaments of the knee. The annual incidence of ligament tears is 1/3,000 in the United States, adding up to 95,000 ruptures and 50,000 reconstructions per year. It is, therefore, not surprising that there is a large amount of literature on the subject. Over the past 20 years, more than 4,000 papers have been written, including review articles and book chapters [1].