Complex rigid foot deformity correction with hexapod external fixator system.

PURPOSE: Complex rigid foot deformities include three-plane deformities and usually presents with poor soft tissue coverage. In the last decades, gradual correction with computer-assisted fixator became an appropriate option for the treatment rigid foot deformities. This study aims to report our experience about treatment of complex foot deformities using Smart Correction fixator system®. METHODS: We retrospectively analyzed 13 complex rigid foot deformities of ten consecutive patients treated with Smart Correction fixator system® from 2016 to 2020. Primary outcomes were classified as good, fair, and poor according to previously determined criteria. The outcomes were also assessed with The Manchester-Oxford Foot Questionnaire (MOXFQ). Non-parametric analysis (Wilcoxon test) for continuous variables and the Fisher's exact test for categorical variables were used. RESULTS: Plantigrade foot was achieved in all patients after correction program. Supramalleolar osteotomy was applied in nine feet, midfoot osteotomy was applied in two feet, hindfoot osteotomy was required in one foot, and only soft tissue distraction performed in two feet. Two patients had recurrent deformity managed by further acute corrections. The mean MOXFQ scores improved from 72.7 preoperatively to 24.8 at last follow-up. CONCLUSIONS: Present study shows that SCF the reliable option for the treatment of complex foot deformities, which also facilitates three-plane correction and concomitant lengthening with gradual soft tissue balance.

Trajectory Correction and Locomotion Analysis of a Hexapod Walking Robot with Semi-Round Rigid Feet.

Aimed at solving the misplaced body trajectory problem caused by the rolling of semi-round rigid feet when a robot is walking, a legged kinematic trajectory correction methodology based on the Least Squares Support Vector Machine (LS-SVM) is proposed. The concept of ideal foothold is put forward for the three-dimensional kinematic model modification of a robot leg, and the deviation value between the ideal foothold and real foothold is analyzed. The forward/inverse kinematic solutions between the ideal foothold and joint angular vectors are formulated and the problem of direct/inverse kinematic nonlinear mapping is solved by using the LS-SVM. Compared with the previous approximation method, this correction methodology has better accuracy and faster calculation speed with regards to inverse kinematics solutions. Experiments on a leg platform and a hexapod walking robot are conducted with multi-sensors for the analysis of foot tip trajectory, base joint vibration, contact force impact, direction deviation, and power consumption, respectively. The comparative analysis shows that the trajectory correction methodology can effectively correct the joint trajectory, thus eliminating the contact force influence of semi-round rigid feet, significantly improving the locomotion of the walking robot and reducing the total power consumption of the system.

A foot/ground contact model for biomechanical inverse dynamics analysis.

The inverse dynamics simulation of the musculoskeletal system is a common method to understand and analyse human motion. The ground reaction forces can be accurately estimated by experimental measurements using force platforms. However, the number of steps is limited by the number of force platforms available in the laboratory. Several numerical methods have been proposed to estimate the ground reaction forces without force platforms, i.e., solely based on kinematic data combined with a model of the foot-ground contact. The purpose of this work is to provide a more efficient method, using a unilaterally constrained model of the foot at the center of pressure to compute the ground reaction forces. The proposed model does not require any data related with the compliance of the foot-ground contact and is kept as simple as possible. The indeterminacy in the force estimation is handled using a least square approach with filtering. The relative root mean square error (rRMSE) between the numerical estimations and experimental measurements are 4.1% for the vertical component of the ground reaction forces (GRF), 11.2% for the anterior component and 5.3% for the ground reaction moment (GRM) in the sagittal plane.