Department Seminar of Elisheva Berkowicz - Stress Fractures in the Tibia Bone: A New Approach
SCHOOL OF MECHANICAL ENGINEERING SEMINAR
Wednesday December 20.12.2023 at 14:00
ZOOM SEMINAR
Stress Fractures in the Tibia Bone: A New Approach
Elisheva Berkowicz
M.Sc. student under the supervision of Prof. Dov Sherman
School of Mechanical Engineering, Tel Aviv University, Israel
Abstract - A stress fracture is an injury occurring mostly in the cortical tibia bone, in the third lower part of it. It is characterized by growing damage to the bone and hence increasing pain to the patient. Stress fractures occur in newly recruited soldiers- men and women, sportsmen and women, and the elderly, primarily due to overuse.
It is commonly accepted that stress fractures are generated by muscles’ off-axis tensile force acting parallel to the bone’s longitudinal axis to reduce the compressive loads acting on the bone during physical activity, but at the same time, it causes bending deformation, hence creating high tensile stresses on the auxiliary part of the bone. It is argued, that these tensile stresses are the direct cause of stress fracture. Microstructural treatment of the damage mechanisms is not considered.
Practically, stress fracture is not detectable by X-Ray diffraction at the early stages of the injury, and appears as a thin line thereafter (no crack opening). It is assumed subjected to load control conditions (muscles’ activity) that is not in line with the first findings above and with the principles of fracture mechanics. Hence, we integrate fracture mechanics principles by conceptualizing the bone material as a composite structure resembling fiber-reinforced plastic. In this analogy, the osteons represent the fibers, and the interstitial lamella is the cohesive matrix binding the osteons together.
These have led us to suggest different mechanisms for stress fractures. First and foremost, since the stress fracture (the crack) is stably propagated, it is caused by displacement control conditions. Additionally, stress fractures emerge due to repetitive compressive loads that lead to the deterioration of the bone's matrix material, thereby substantially diminishing the constraint force acting on the osteons. This degradation facilitates the failure of osteons through localized collapse under buckling. Crucially, we propose that the accumulation of bone edema, or damage in the matrix, is a prerequisite for stress fractures. This model was studied using Finite Element Analysis of fibrous material under compression and local buckling.
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