Optimal Micromotion for Rapid Fracture Healing Using a Novel Electronic Linear Servo Motor Actuator : A Pilot Study

Abstract

Introduction: The optimal amount of micromotion that is beneficial for callus formation and fracture healing is seldom studied and remains to be debated. Our objective is to accurately define the optimal amount of micromotion that may promote fracture healing. Methods: Three groups (n=3 for each group) of 12-week-old female Sprague-Dawley rats with 2-mm segmental bone defect in the femur mid-diaphysis was bridged by a novel self-designed strain regulating external fixator. The 0% strain group (control), 10% strain group, and 20% strain group had the predefined micromotion precisely applied by an electronically controlled linear servo actuator, at a frequency of 0.6 Hz for 2 weeks after a 2-week static resting period. X-ray was taken weekly, and animals were sacrificed at 8 weeks with computed tomography (CT) scan to quantify callus volume. Results: The average diameters of callus measured by X-ray at 8 weeks after operation increased from 3.28 ± 0.36 mm (control) to 3.84 ± 0.18 mm (10%) and 3.94 ± 0.63 mm (20%). The 10% group and 20% group had larger callus volume (26.65 ± 0.07 mm3 and 22.16 ± 11.04 mm3 ) than the control group (18.12 ± 4.51 mm3 ) measured by CT. Conclusion: In all, 20% micromotion was superior in accelerating new bone formation over 10% and 0% micromotion. Increased sample size and testing for 30% and 40% micromotion are further required.