Date of Award

12-2013

Document Type

Thesis

Degree Name

Master of Science (MS)

Program

Biomedical Engineering

Research Advisor

Denis J. DiAngelo, Ph.D.

Committee

Richard J. Kasser, Ph.D. Brian P. Kelly, Ph.D.

Keywords

Biomechanical Testing, Foot and Ankle, Gait Simulation, Kinematics, Robotics

Abstract

Ankle instantaneous axis of rotation (IAR) measurements represent a more complete parameter for characterizing joint motion. However, few studies have implemented this measurement to study normal, injured, or pathological foot-ankle biomechanics. Additionally, while load is suggested to play a major role in ankle biomechanics, including influences on articular surfaces, bony motion, and formation of the arches, studies concerning the effects of joint loading are limited.

A novel testing protocol was developed to simulate in vivo mechanics of the foot-ankle complex during early stance phase gait in a human cadaveric model. Two studies were conducted. The first study was to assess the repeatability and accuracy of an existing robotic testing platform (RTP) and loading protocol using force measurements and IAR data from two cadaver specimens. A lower leg was mounted in a RTP with the tibia upright and foot flat on the baseplate. Axial tibia loads (ATLs) were controlled as a function of a vertical ground reaction force (vGRF) set at half body weight (356N) and a 50% vGRF (178N) Achilles tendon (AT) load. Two specimens were repetitively loaded over 10 degrees dorsiflexion and 20 degrees plantarflexion. Platform axes were controlled within 2µm and 0.008 degrees resulting in ATL measurements within ±2N of target conditions. Mean ATLs and IAR values were not significantly different between cycles of motion, but IAR values were between dorsiflexion and plantarflexion. A linear regression analysis showed no significant differences between slopes of plantarflexion paths.

The second study aimed to determine the effects of a passive (unloaded) and active Achilles and axial tibial loads on ankle mechanics using IAR data and translational and rotational data of the calcaneus, talus, and navicular from four cadaver specimens during stance phase gait. Specimens were mounted in the RTP with the tibia upright and foot flat on the baseplate. Passive loading applied a 5N ATL with no AT. Active ATLs were controlled as a function of a vGRF set at body weight (534N) and static ATs set at 25%, 50%, 75%, 100% vGRF. Four specimens were repetitively loaded over 10 degrees dorsiflexion and 10 degrees plantarflexion. An optoelectric motion measuring system was used to track bony talus, calcaneus, and navicular translations and rotations. Kinematics in passive motion were predominantly governed by the shape of the mating articular surfaces. Once actively loaded, net joint loading had no surgically relevant effect on the kinematics data other than to suggest they were governed more by soft tissue structures.

The customized robotic platform and advanced testing protocol produced repeatable and accurate measurements of the IAR. Biomechanical properties of the foot and ankle were demonstrated, including the tibiotalar and soft tissue relationship on the axis of rotation and the effect of load on foot-ankle kinematics. The platform and protocol can be useful for assessing foot-ankle biomechanics under different loading scenarios and foot conditions, as well as studying the biomechanical effects of orthotics, footwear, and surgery or injury.

DOI

10.21007/etd.cghs.2013.0272

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