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Purpose <p>This study investigated the formation of fracture repair tissue in response to 2.5–25% strain magnitudes under immediate and delayed loading in a large animal model with monotonically increasing interfragmentary strain.</p> Methods <p>Experimental osteotomies were created in ten sheep and were instrumented with an active fixator that generated a gradient (2.5–25%) of interfragmentary strain across the osteotomy. Sheep were randomly assigned to an immediate-loading (from day 1 post-surgery) group or a delayed-loading (from day 22 post-surgery) group. Five&#xa0;weeks post-surgery, the tibiae were scanned using high-resolution computed tomography (CT). CT images were subsequently sliced at different strain levels. For each two-dimensional slice, we evaluated the area and density of fracture repair tissue within the osteotomy and the radial span of the periosteal tissue. Repeated-measures ANOVA tested the effects of strain magnitude and loading protocol on these parameters.</p> Results <p>The area and density of osteotomy repair tissue were highest at 2.5% of strain for both groups and significantly decreased when strain increased (<i>p</i> ≤ 0.015). In contrast, periosteal tissue span increased with strain (<i>p</i> &lt; 0.001) and was significantly larger in the immediate-loading group (<i>p</i> &lt; 0.01).</p> Conclusion <p>Our study demonstrates the combined effect of strain (2.5–25%) and the timing of loading on bone healing. We observed two strain-related healing responses: up to ~ 7.5% strain, callus formed between the cortices, while higher strain shifted calcified repair tissue toward external callus. In this experimental model, strains below 25% provided a potent healing environment when stimulation was applied during the early healing stage.</p>

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Bone Formation Between 2.5 and 25% Interfragmentary Strain Induced by Immediate and Delayed Loading in a Bone Healing Model with a Monotonic Strain Gradient

  • 期刊论文

  • 发表日期：

    2025年12月19日

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  • Jan Barcik,
  • Manuela Ernst,
  • Tim Buchholz,
  • Caroline Constant,
  • Karen Mys,
  • Devakara Epari,
  • Stephan Zeiter,
  • Boyko Gueorguiev,
  • Markus Windolf

摘要

Purpose

This study investigated the formation of fracture repair tissue in response to 2.5–25% strain magnitudes under immediate and delayed loading in a large animal model with monotonically increasing interfragmentary strain.

Methods

Experimental osteotomies were created in ten sheep and were instrumented with an active fixator that generated a gradient (2.5–25%) of interfragmentary strain across the osteotomy. Sheep were randomly assigned to an immediate-loading (from day 1 post-surgery) group or a delayed-loading (from day 22 post-surgery) group. Five weeks post-surgery, the tibiae were scanned using high-resolution computed tomography (CT). CT images were subsequently sliced at different strain levels. For each two-dimensional slice, we evaluated the area and density of fracture repair tissue within the osteotomy and the radial span of the periosteal tissue. Repeated-measures ANOVA tested the effects of strain magnitude and loading protocol on these parameters.

Results

The area and density of osteotomy repair tissue were highest at 2.5% of strain for both groups and significantly decreased when strain increased (p ≤ 0.015). In contrast, periosteal tissue span increased with strain (p < 0.001) and was significantly larger in the immediate-loading group (p < 0.01).

Conclusion

Our study demonstrates the combined effect of strain (2.5–25%) and the timing of loading on bone healing. We observed two strain-related healing responses: up to ~ 7.5% strain, callus formed between the cortices, while higher strain shifted calcified repair tissue toward external callus. In this experimental model, strains below 25% provided a potent healing environment when stimulation was applied during the early healing stage.