Effects of axial dynamization on bone healing

Area of Science:

• Orthopedic surgery
• Biomechanical engineering
• Veterinary medicine

Background:

• Fracture healing is a complex biological process.
• Early controlled loading (dynamization) may influence healing outcomes.
• External fixation is a common method for fracture stabilization.

Purpose of the Study:

• To investigate the effects of early dynamization on canine tibial fracture healing.
• To compare dynamized fractures with rigidly fixed controls at six weeks.
• To assess radiographic, mechanical, and microscopic healing parameters.

Main Methods:

• Bilateral transverse mid-tibial osteotomies created in dogs.
• Initial stabilization with a 2-mm gap using rigid external fixators.
• One fixator per dog was dynamized after seven days, allowing physiologic loading.
• Contralateral fixator remained locked as a rigid control.

Main Results:

• Dynamized osteotomies showed gap closure and increased functional weight bearing from week three.
• No significant difference in callus size between dynamized and control groups radiographically.
• Dynamized osteotomies were significantly stiffer and tolerated higher maximum torque.
• Microscopic evaluation revealed no difference in callus volume but a greater proportion of the gap filled with new bone in dynamized fractures.

Conclusions:

• Early dynamization improved fracture healing in a delayed union model.
• Improvements were attributed to reduced fracture gap size and increased weight bearing.
• Dynamization did not alter the fundamental pathway of fracture healing.
• Findings suggest dynamization is a beneficial adjunct to external fixation for specific fracture types.