Three-dimensional load measurements in an external fixator.

Area of Science:

• Orthopedic surgery
• Biomedical engineering
• Biomechanics

Background:

• External fixators are crucial for fracture management.
• Accurate in vivo load monitoring is essential for optimizing fracture healing.
• Current methods for assessing fracture healing can be limited.

Purpose of the Study:

• To develop and evaluate a six-degree-of-freedom hexapod external fixator system for in vivo measurement of axial and shear forces, torsion, and bending moments.
• To assess the system's ability to determine fracture type and monitor the healing process.
• To explore the potential for automatic adjustments and patient guidance in external fixation.

Main Methods:

• Development of a hexapod external fixator with integrated sensors for measuring all six degrees of freedom.
• Pilot study involving 9 patients with tibia fractures or osteotomies.
• In vivo load measurements taken at 2, 4, 8, 12 weeks, and at fixator removal.

Main Results:

• The system successfully measured forces and moments, differentiating between fracture types (e.g., A3, A2, B2, C3).
• Axial forces decreased over healing as bone load transfer increased.
• Bending moments correlated well with clinical healing, except in C3 fractures.
• A combination of bending moment and axial force effectively assessed fracture healing.
• Bone resorption in transverse fractures was detected at approximately 4 weeks.

Conclusions:

• The hexapod system enables separate measurement of all forces and moments with a simple mechanical setup.
• This system can control fracture healing, potentially reducing radiographic exposure.
• It represents a step towards "automatic dynamization" and "intelligent fixators" for optimized patient outcomes.