Strain-Dependent Effects of Controlled Micromotion on Fracture Healing: Rethinking the Strain Threshold
Weichen Qi1, Jiaxin Lv1, Xiaoreng Feng1,2
1Department of Orthopaedics and Traumatology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China.
JB & JS Open Access
|June 4, 2026
Summary
Controlled micromotion up to 20% strain optimizes fracture healing in rats, exceeding the traditional 10% threshold. This finding suggests new possibilities for managing fractures with callus formation.
Area of Science:
- Biomedical Engineering
- Orthopedic Research
- Regenerative Medicine
Background:
- The optimal strain for indirect fracture healing is debated, with traditional ranges (2%-10%) challenged by studies showing healing at higher levels.
- Understanding the strain-healing relationship is crucial for optimizing fracture repair strategies.
Purpose of the Study:
- To evaluate the strain-healing relationship in a controlled micromotion model of fracture healing.
- To determine if the strain threshold for optimal indirect fracture healing exceeds 10%.
Main Methods:
- A standardized osteotomy in Sprague-Dawley rats was stabilized with an external fixator.
- Controlled micromotion at 0%, 10%, 20%, 30%, and 40% strain was applied daily for two weeks.
- Healing was assessed using radiography, micro-CT, mechanical testing, histology, and immunohistochemistry.
Main Results:
- A 20% strain level demonstrated the most favorable healing profile, with no nonunions observed.
- Lower strains resulted in limited callus formation, while higher strains led to delayed bone conversion and mineralization.
- Moderate strain (20%) showed balanced inflammatory marker expression (IL-6, IL-1β, RANKL/OPG), unlike excessive strain, which indicated impaired remodeling.
Conclusions:
- The functional upper limit for beneficial strain in stable fixation, before cartilaginous tissue stiffens, exceeds the 10% threshold.
- Approximately 20% compressive strain applied between days 14-21 post-osteotomy provided the optimal balance of early repair and remodeling in this rat model.
- Controlled micromotion at 20% interfragmentary strain may be relevant for fractures managed with relative stability and callus formation.
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