Intra-articular pressure distribution in the native and prosthetic ankle joint

status: publishe

Muscle forces affects topology and magnitude of contact joint forces in the ankle

status: publishe

Minimal influence of sensor array in hind foot joint kinematics during in-vitro gait simulations

status: publishe

Cartilage Loading in the Native Ankle & the Effect of Extrinsic Muscle Forces

status: publishe

In-vitro intra-articular pressure distribution in the ankle: can it be used for model validation?

Background Several modelling attempts to predict intra-articular pressure distribution in the ankle joint have been made. Input kinematics for such models can be measured with a variety of techiniques, for validating with intra-articular pressure though, we are limited to in-vitro experimentation. The aim of this study was to investigate the influence of the insertion of a pressure sensor on joint kinematics during in-vitro gait simulations. Methods 10 freshly frozen human cadaveric feet, amputated mid-tibially, were used to simulate gait in a robotic gait simulator (stance phase of 1sec). The activation of 6 muscle groups, was simulated based on in-vivo measurements of 10 subjects. A Tekscan sensor (5033) with dimensions approximating the articular surface of the ankle joint (38.4 x 26.7 x 0.1mm) was inserted by an experienced foot surgeon, from an anterior incision through the skin, inferior extensor retinaculum and joint capsule. The sensor was fixated posterioly on the tibia using a metallic screw. For each specimen, two tests were made: 1) prior to the incision 2) after the sensor insertion. For each test 15 repetitions were performed. The motion of 5 bones of the hindfoot (tibia, talus, calcaneus, naviculair, cuboid) was captured using a Krypton camera system at 100hz. The joint rotations and translations over stance phase were calculated for each bone combination, using anatomically defined landmarks. The range of motion (ROM) before and after the sensor insertion was compared for significant differences. Results Statistically significant differences (Wilcoxon rank sum test) between the two tests for each foot were found for several bone combinations, mainly those involving the talus bone (tibiotalar, subtalar and talonavicular joints). The effect of the sensor insertion was greater in the rotation on the sagittal plane (plantar/dorsiflexion), though minimal (~5 degrees) (Figure 1). Conclusion We are able to demonstrate that the effect of sensor insertion on the behaviour of joints varies between feet and bone combination. Even though the influence in most cases is limited, individual cases indicate that it is difficult to rely only on post-incision kinematics for accurate model validation and development.status: publishe

Insertion of a pressure sensing arrayminimally affects hindfoot bone kinematics

Background Understanding the development of ankle osteoarthritis (OA) is of high importance and interest; however its causality is poorly understood and several links to joint loading conditions have been made. One way of quantifying joint loading conditions is by measuring the intra-articular pressure distribution during gait simulations performed by in-vitro experimental set-ups. However the effect of inserting a pressure sensing array in the ankle joint could potentially disturb the proper kinematics and therefore the loading conditions. Methods In this study, we performed in-vitro gait simulations in 7 cadaveric feet, before and after inserting a pressure sensing array and quantified the effect on the joints range of motion (ROM). The gait was simulated with a stance phase duration of one second using a custom build cadaveric gait simulator (CGS). Results The results show a limited effect in the ROM for all the joints of the hind foot, not exceeding the variability observed in specimens without a sensor. However, no consistent direction (increase/decrease) can be observed. Conclusion The results suggest that even though the effect of inserting a pressure sensing array is minimal, it needs to be evaluated against the demands/requirements of the application.status: publishe

Intergrating a multi-segment foot model in simulation of gait to better understand plantar pressure distribution

status: publishe

Quality assurance in in vitro testing: pitfalls and tricks

status: publishe