Introduction: Dynamization is used to improve the healing process. The optimal time for dynamization however remains unknown. In this study we proved the hypothesis that an early dynamization will improve the fracture healing.

Material and Methods: Twenty-four rats underwent a diaphyseal femoral osteotomy, with a 1mm gap. The osteotomy was stabilized by either rigid (R-group; n=8) or flexible (F-group; n=8) external fixation. The dynamized group (D-group: n=8) had a rigid fixation for 1 week, and then a flexible fixation for the remaining 4 weeks. The flexible fixation design resulted in an axial stiffness of 10N/mm and the rigid fixation in 74N/mm. After 5 weeks, healing was evaluated by biomechanical, densitometric, and histological methods.

Results: The flexural rigidity was 47% higher in the R-group than in the F-group (p< 0.01). Also, the flexural rigidity was 45% higher in the R-group than in the D-group (p< 0.01) (Table 1). Mineralized callus tissue volume was 37% lower in the R-group than the D-group (p=0.002).

Conclusion: The hypothesis could not be supported, in that early dynamization did not improve healing compared to rigid or flexible fixation. The rigid fixation had a stiffer callus with smaller callus volume, and more calcified tissue in the whole callus. The rigid fixation had bridging in the gap more often, which explains the increased flexural rigidity measured. Dynamization utilized in previous studies allowed closure of the fracture gap and thereby enhanced the rate of healing, which was not the case in the present investigation.