World Congress of Biomechanics edition:7 location:Boston, USA date:6-12 July 2014
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.
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.
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).
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.