German Congress of Orthopaedics and Traumatology (DKOU 2025)
Formation of fracture repair tissue in relation to low to medium interfragmentary strain – an in vivo preclinical study with actively modulated interfragmentary stimulus
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Objectives and questions: Bone healing is influenced by the mechanical conditions within the fracture gap. This study aimed to examine the formation of fracture repair tissue in response to low to medium interfragmentary strain magnitudes using a large animal model with a monotonically increasing interfragmentary strain.
Material and methods: Two partial osteotomies were performed on the tibia of ten sheep, creating a mobile wedge-shaped bone fragment. The bone was then instrumented with an active fixator that tilted the bone fragment, thus creating a gradient of interfragmentary strain in the osteotomy ranging from 2.5% to 25%. The sheep were randomly assigned to two groups, receiving either immediate loading (starting on the first day post-surgery) or delayed loading (beginning on the 22nd day post-surgery). Following euthanasia five weeks post-surgery, the tibiae were scanned using high-resolution computed tomography (CT). CT scans were then sliced at different strain levels, and for each two-dimensional slice, we assessed the area and density of the fracture repair tissue within the osteotomy and the radial span of the periosteal tissue.
Results: The largest area and highest density of repair tissue within the osteotomy were found under the lowest strain conditions, and significantly decreased as strain increased (p≤0.015). In contrast, the radial span of periosteal tissue increased with strain (p<0.001) and was significantly larger in the immediate loading group (p<0.01).
Discussion and conclusions: This study highlights the role of low but clinically relevant interfragmentary strain in bone healing. As strain increases, the formation of calcified repair tissue systematically shifts from within the fracture gap to predominantly external callus. Regardless of the strain magnitude, the entire evaluated strain window appears to support fracture consolidation, provided that the strain stimulus is applied during the early healing phase. Fixation strategies designed to promote low-strain stimulation may offer a safe and effective approach to enhancing bone healing.
