Rachid Aissaoui

Ambulatory measurement of 3D knee joint angle

Three-dimensional measurement of joint motion is a promising tool for clinical evaluation and therapeutic treatment comparisons. Although many devices exist for joints kinematics assessment, there is a need for a system that could be used in routine practice. Such a system should be accurate, ambulatory, and easy to use. The combination of gyroscopes and accelerometers (i.e., inertial measurement unit) has proven to be suitable for unrestrained measurement of orientation during a short period of time (i.e., few minutes). However, due to their inability to detect horizontal reference, inertial-based systems generally fail to measure differential orientation, a prerequisite for computing the three-dimentional knee joint angle recommended by the Internal Society of Biomechanics (ISB). A simple method based on a leg movement is proposed here to align two inertial measurement units fixed on the thigh and shank segments. Based on the combination of the former alignment and a fusion algorithm, the three-dimensional knee joint angle is measured and compared with a magnetic motion capture system during walking. The proposed system is suitable to measure the absolute knee flexion/extension and abduction/adduction angles with mean (SD) offset errors of -1 degree (1 degree ) and 0 degrees (0.6 degrees ) and mean (SD) root mean square (RMS) errors of 1.5 degrees (0.4 degrees ) and 1.7 degrees (0.5 degrees ). The system is also suitable for the relative measurement of knee internal/external rotation (mean (SD) offset error of 3.4 degrees (2.7 degrees )) with a mean (SD) RMS error of 1.6 degrees (0.5 degrees ). The method described in this paper can be easily adapted in order to measure other joint angular displacements such as elbow or ankle.

Functional calibration procedure for 3D knee joint angle description using inertial sensors

Measurement of three-dimensional (3D) knee joint angle outside a laboratory is of benefit in clinical examination and therapeutic treatment comparison. Although several motion capture devices exist, there is a need for an ambulatory system that could be used in routine practice. Up-to-date, inertial measurement units (IMUs) have proven to be suitable for unconstrained measurement of knee joint differential orientation. Nevertheless, this differential orientation should be converted into three reliable and clinically interpretable angles. Thus, the aim of this study was to propose a new calibration procedure adapted for the joint coordinate system (JCS), which required only IMUs data. The repeatability of the calibration procedure, as well as the errors in the measurement of 3D knee angle during gait in comparison to a reference system were assessed on eight healthy subjects. The new procedure relying on active and passive movements reported a high repeatability of the mean values (offset<1 degrees) and angular patterns (SD<0.3 degrees and CMC>0.9). In comparison to the reference system, this functional procedure showed high precision (SD<2 degrees and CC>0.75) and moderate accuracy (between 4.0 degrees and 8.1 degrees) for the three knee angle. The combination of the inertial-based system with the functional calibration procedure proposed here resulted in a promising tool for the measurement of 3D knee joint angle. Moreover, this method could be adapted to measure other complex joint, such as ankle or elbow.

A 3D Generic Inverse Dynamic Method using Wrench Notation and Quaternion Algebra

In the literature, conventional 3D inverse dynamic models are limited in three aspects related to inverse dynamic notation, body segment parameters and kinematic formalism. First, conventional notation yields separate computations of the forces and moments with successive coordinate system transformations. Secondly, the way conventional body segment parameters are defined is based on the assumption that the inertia tensor is principal and the centre of mass is located between the proximal and distal ends. Thirdly, the conventional kinematic formalism uses Euler or Cardanic angles that are sequence-dependent and suffer from singularities. In order to overcome these limitations, this paper presents a new generic method for inverse dynamics. This generic method is based on wrench notation for inverse dynamics, a general definition of body segment parameters and quaternion algebra for the kinematic formalism.

Simultaneous bilateral 3-D able-bodied gait

Abstract This paper reports on the muscle powers and mechanical energies developed during gait by the lower limbs over two consecutive cycles. Nineteen male able-bodied subjects participated in this study. An 8-camera video system filmed the subjects bilaterally as they walked at their natural speed over two force plates. A 3-dimensional inverse dynamic analysis was carried out to determine joint moments, powers and mechanical energy at each joint and in all planes for a total of 57 trials. The walking speed (1.30 m/s), the cadence (106.5 steps/min) and the stance phase relative duration (60.7% of the gait cycle) of the right limb were not significantly different from those of the left limb. The limb muscle peak powers were mostly different in the sagittal plane and reflected gait adjustments rather than asymmetry in gait. Generally, these differences occurred during absorption bursts. The total positive work was similar for both limbs and was associated with maintaining a similar walking speed for each limb. The right limb developed a significantly greater total negative work than the left limb. This was associated with the control of the lower limb in locomotion.

Analysis of sliding and pressure distribution during a repositioning of persons in a simulator chair

This study was undertaken to investigate the effect of system tilt and back recline angles on sliding and pressure distribution of seated subjects. Ten able-bodied subjects adopted successively 12 postures on a multiadjustable simulator chair. The system tilt angle was varied from 0/spl deg/ to 45/spl deg/ posterior tilt, while the seat to back angle varied from 90/spl deg/ to 120/spl deg/. A maximum of 40.2% of weight shift was found when combining a system tilt angle of 45/spl deg/ to a seat to back angle of 120/spl deg/. Maximum value of 74 mm of sliding was observed for the acromion marker during repositioning. Significant weight shift at the level of the seat is obtained only when the system tilt angle exceeds 15/spl deg/ in a posterior direction. We can put forward here that a small tilt /spl les/15/spl deg/ can be used to adjust back pressure distribution, whereas large posterior tilts are used for an effective weight shift at the seat level. The peak pressure gradient remains in general in the interval of /spl plusmn/30% from the neutral posture for the able-bodied subjects and is fairly constant at 15/spl deg/ of tilt. A significant amount of displacement along the back and seat reference plane were found for the shoulder and hip markers, but this displacement does not necessarily correspond to a pure translation motion of the pelvic segment.

Personalized body segment parameters from biplanar low-dose radiography

Body segment parameters are essential data in biomechanics. They are usually computed with population-specific predictive equations from literature. Recently, medical imaging and video-based methods were also reported for personalized computation. However, these methods present limitations: some of them provide only two-dimensional measurements or external measurements, others require a lot of tomographic images for a three-dimensional (3-D) reconstruction. Therefore, an original method is proposed to compute personalized body segment parameters from biplanar radiography. Simultaneous low-dose frontal and sagittal radiographs were obtained with EOS/spl trade/ system. The upper leg segments of eight young males and eight young females were studied. The personalized parameters computed from the biplanar radiographic 3-D reconstructions were compared to literature. The biplanar radiographic method was consistent with predictive equations based on /spl gamma/-ray scan and dual energy X-ray absorptiometry.

New Accelerometric Method to Discriminate Between Asymptomatic Subjects and Patients With Medial Knee Osteoarthritis During 3-D Gait

This study presents a new method to estimate 3-D linear accelerations at tibial and femoral functional coordinate systems. The method combines the use of 3-D accelerometers, 3-D gyroscopes and reflective markers rigidly fixed on an exoskeleton and, a functional postural calibration method. Marker positions were tracked by a six-camera optoelectronic system (VICON 460, Oxford Metrics). The purpose of this study was to determine if this method could discriminate between medial osteoarthritic and asymptomatic knees during gait. Nine patients with osteoarthritic knees and nine asymptomatic control subjects were included in this study. Eighteen parameters representing maximal, minimal, and range of acceleration values were extracted during the loading and preswing to mid-swing phase periods, and were compared in both groups. Results show good discriminative capacity of the new method. Eight parameters were significantly different between both groups. The proposed method has the potential to be used in comprehending and monitoring gait strategy in patients with osteoarthritic knee.

Analysis of pressure distribution at the body-seat interface in able-bodied and paraplegic subjects using a deformable active contour algorithm

In this paper, a semi-automatic method for segmenting pressure distribution image-based data at the body-seat interface is presented. The purpose of this work was to estimate the surface and the load supported by the ischial tuberosity (IT) region. The proposed method involves three steps: (1) detecting the IT region using a pressure-distribution image gradient; (2) estimating the contour of the IT region by an iterative active contour algorithm and finally (3) estimating the percentage of the surface and the weight-bearing of the IT region in a group of able-bodied (AB) and spinal-cord injury (SCI) subjects. It was found in this study that the weight bearing on the IT for the spinal-cord injured group is distributed on half the surface in comparison with the AB group or the powered wheelchair users groups. The findings of this study provide insights concerning pressure distribution in sitting for the paraplegic and able-bodied.

Biomechanics of manual wheelchair propulsion in elderly: system tilt and back recline angles

Aissaoui R, Arabi H, Lacoste M, Zalzal V, Dansereau J: Biomechanics of manual wheelchair propulsion in elderly: System tilt and back recline angles. Am J Phys Med Rehabil 2002;81:94–100. ObjectiveTo investigate the effects of the system tilt and back recline angles on the biomechanics of wheelchair propulsion for a group of older, disabled patients. It was hypothesized that increasing both the system tilt and backrest recline angles would have a positive effect on the biomechanical efficiency of manual wheelchair propulsion. DesignThree kinetic variables were estimated during a 10-m, steady-state propulsion between 0.96 m/sec and 1.01 m/sec. The fraction of the mechanical effective force is defined by the ratio between the tangential and the total force applied to the pushrim: It expresses the directionality of force application. The mechanical use is defined as the ratio between the total force generated during wheelchair propulsion and that generated during maximal isometric contraction. The biomechanical efficiency is defined as the product of mechanical effective force and the mechanical use. ResultsOn average, the fraction of the mechanical effective force was found to be low when compared with other studies. Tilting the system by 10 degrees and reclining the back by 10 degrees increase significantly the biomechanical efficiency of the subject by 10%. The biomechanical efficiency variable was more sensitive to the system tilt than to the back recline adjustment. ConclusionsThe results of this study confirm the hypothesis that system tilt angle but not back recline significantly affects biomechanical efficiency. The findings of this study will help in designing and adjusting a wheelchair intended for self-propelled, older people.

Relationship Between Resultant Force at the Pushrim and the Net Shoulder Joint Moments During Manual Wheelchair Propulsion in Elderly Persons

OBJECTIVE To determine the relationship between the resultant force at the pushrim and the net shoulder joint moments during manual wheelchair propulsion in elderly persons. DESIGN Convenience sample. SETTING Motion analysis laboratory. PARTICIPANTS Older manual wheelchair users (N=14; age, 68.2+/-5.2y) were tested. INTERVENTIONS Kinematic and kinetic data were collected during manual wheelchair propulsion at a speed between 0.96 and 1.01m/s for 10 seconds and at a power output around 22.4W on a wheelchair ergometer. MAIN OUTCOME MEASURES Net shoulder joint moments were computed with an inverse dynamic model. The mechanical use of the forces at the pushrim and the mechanical fraction of effective force were measured during propulsion. RESULTS Mechanical use and mechanical fraction of effective force had a positive and significant correlation with the net internal (P<.05) and external (P<.001) shoulder rotation moment, the net flexion (P<.05), and extension (P<.001) moment in the sagittal plane, and the net flexion (P<.001) moment in the horizontal plane. CONCLUSIONS The results suggest that because the resultant force at the pushrim has a greater tangential component and a greater proportion of the maximal voluntary force, most of the net moments around the shoulder are higher. Thus the optimal way of propelling, from a mechanical point of view (ie, tangential), may not be advantageous for manual wheelchair users.