Comparison of a Dynamic Ankle Orthosis to a Walking Boot for Preserving Ankle Joint Motion and Reducing Tibial Bone Load and Strain
Date of Award
Master of Science (MS)
Denis J. DiAngelo, PhD
Richard J. Kasser, PhD; Max R. Paquette, PhD
Offload, Tibial Bone Strain, Tibial Compressive Force, Tibial Stress Fractures, Walking Boot
Tibial stress fractures are a common overuse injury accounting for 21.9 – 69% of stress fractures among runners and 24 – 51.2% of stress fractures in military cadets. Current treatment involves wearing a walking boot for 3 – 12 weeks, which limits ankle motion and causes lower limb muscle atrophy. A Dynamic Ankle Orthosis (DAO) provided a distractive force that offloaded the ankle and retained sagittal ankle excursion during walking. It remains unclear how tibial loading is affected by a walking boot or the DAO. This thesis presents a feasibility study confirming the offloading effects of the DAO on tibial loads and Achilles tendon forces during treadmill walking, and a cadaveric study evaluating the offloading effects of the DAO on distal tibia strain. The objective of study 1 was to determine the effects of the DAO and walking boot on tibial compressive force and ankle motion during treadmill walking. Twenty healthy young adults walked on a split-belt instrumented treadmill at 1.0 m/s in two brace conditions: DAO and walking boot. A 3D motion capture system recorded kinematic data, force treadmill recorded ground reaction forces, and vertical force insoles measured in-shoe vertical reaction force. Kinetic and kinematic variable calculations were used to determine the peak tibial compressive force. Target offloading of the DAO was 10% body weight. The DAO moderately reduced peak tibial compressive force (10.9%) and Achilles tendon force (12%) compared to the walking boot. Sagittal plane ankle motion during stance phase was largely reduced by 54.9% in the walking boot compared to the DAO. The objective of study 2 was to evaluate changes in strain magnitude due to the offloading effect of the DAO on tibial bone mechanics compared to standard-of-care walking boot using fresh frozen cadaver specimens. Three fresh frozen cadaver legs were placed in a robotic testing platform and dynamically loaded to 900N at a rate of 3.2mm/s in the DAO and walking boot. Linear strain gauges were attached to the distal tibia and midshaft tibia to measure the compressive strain at specific points along the longitudinal axis of the tibia. Vertical force sensing insoles measured in-shoe vertical reaction force. Target offloading of the DAO was 10% of the applied load. Peak strain was significantly reduced at the distal tibia (23.31%) wearing the DAO compared to the walking boot. Pearson correlations showed moderate to strong negative linear relationship between the compressive strain and vertical reaction force measurements within subjects at both the distal and midshaft tibia. These findings indicate the DAO moderately reduced tibial compression force and Achilles tendon force while providing greater sagittal ankle excursion compared to a walking boot. In addition to reproducing similar strain data to previous literature, the DAO strongly reduced the peak strain primarily at the distal tibia as well as reduced vertical reaction force. Moderate to strong linear correlations occurred between the external vertical reaction force and internal strain magnitude. This body of work provides evidence that the DAO could function as an alternative rehabilitation device for treating tibial stress fractures by reducing bone strain and tibial loading during walking.
Johnson, Perri Jr. (https://orcid.org/0000-0003-4956-8687), "Comparison of a Dynamic Ankle Orthosis to a Walking Boot for Preserving Ankle Joint Motion and Reducing Tibial Bone Load and Strain" (2022). Theses and Dissertations (ETD). Paper 622. http://dx.doi.org/10.21007/etd.cghs.2022.0609.
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