Développement d'une orthèse de genou pour la modulation des efforts articulaires lors du squat : optimisation, évaluation et interactions avec la peau

Léa Boillereaux

doi:10.70675/30d5712ez6a97z44ebzb69fze1e5fd07e99d

This thesis, is conducted at both the Laboratory of Mechanics and Civil Engineering (LMGC) and the Montpellier Laboratory of Computer Science, Robotics, and Microelectronics (LIRMM). It concerns biomechanics applied to joint rehabilitation. It aims at developing an innovative knee orthosis capable of mechanically modulating loads on the joint to support rehabilitation following the implantation of cartilage neo-tissues. These implants require a carefully controlled mechanical environment to promote integration into native cartilage while avoiding early overload that could hinder development. The chosen approach involves designing a passive, non-invasive, customized for each patient, and adjustable orthosis to modulate tibiofemoral load during squatting, a movement that heavily stresses the knee. The mechanical principle of the device relies on custom shaped cams, coupled with pneumatic actuators, generating variable joint distraction throughout the movement. The shape of each cam is optimized to match the patient's biomechanical characteristics, ensuring targeted and progressive assistance. To validate this approach, a robotic test bench (7-axis robotic arm and instrumented pseudo-leg) reproducing the squat motion was developed. It enables reproducible assessment of the orthosis’s ability to generate the desired distraction forces. Experiments show that the orthosis can reduce joint load by up to 100%, depending on the assistance setting. This performance is strongly influenced by the cam geometry and the actuator generated pressure. While the bench provides a first validation, it uses a rigid 3D-printed pseudo-leg on which the orthosis is screwed: hence, not accounting for interactions with skin and soft tissues - a key aspect in evaluating the device. Indeed, force transmission from the orthosis to the joint strongly depends on parameters such as device tightening. It is therefore necessary to assess force transmission from skin to joint based on assistance and tightening levels, ensuring user comfort and avoiding tissue damage. The final part of the project involves analysis of the interface between the orthosis and the skin, via an experimental study on a healthy participant, validated by the University of Montpellier's Research Ethics Committee (CER). This is preparing a larger study involving eight participants, as validated by the CER.The volunteer performed multiple squat sets wearing a slightly modified orthosis, instrumented with 40 tactile sensors and additional ones (encoders, IMUs...). One goal is to identify an optimal sensor layout to reconstruct pressure and shear maps on the skin without critical data loss, while minimizing bulk and cost. The study also initiates an understanding of load distributions on the thigh during flexion, without, and then with varying assistance levels and controlled tightening. It enables extrapolated assessment of the device’s viability at higher assistance levels. An adaptive attachment design could then be considered to improve load distribution. This research opens concrete perspectives for the development of personalized medical devices tailored to the modulation needs of joint mechanical environments for post-implantation cartilage regeneration.

Développement d'une orthèse de genou pour la modulation des efforts articulaires lors du squat : optimisation, évaluation et interactions avec la peau

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