Compression forces of internal and external ankle fixation devices with simulated bone resorption

Area of Science:

• Orthopedic Surgery
• Biomedical Engineering
• Bone Healing Mechanics

Background:

• Tibiotalocalcaneal (TTC) arthrodesis requires stable fixation for bone healing.
• Compression is crucial for fusion site healing, but compressive forces of ankle fixation devices are not well-quantified.
• Both internal and external fixation methods aim to provide rigidity and stability.

Purpose of the Study:

• To quantify and compare the compressive forces generated by internal intramedullary (IM) nails and external fixators used in TTC arthrodesis.
• To evaluate the ability of these devices to sustain compression under simulated bone resorption.

Main Methods:

• Tested two IM nails (PantaNail, VersaNail) and two external fixators (True/Lok, Ace-Fischer frame) using synthetic and cadaveric bone models.
• Measured compressive loads during device installation and after simulated bone resorption.
• Utilized a constitutive model to verify experimental data.

Main Results:

• IM nails generated initial compressive loads but significantly decreased (90% reduction) with minimal bone resorption (<1 mm).
• External fixators sustained approximately 50% of their initial load even with substantial bone resorption (>4 mm).
• IM nails showed reduced compressive loads after guide and instrumentation removal.

Conclusions:

• Intramedullary nails can generate compression but lack sustained force with bone resorption.
• External fixators are inherently superior in applying and maintaining compression, particularly under resorptive conditions.
• Surgeons performing TTC arthrodesis must consider device-specific compression capabilities and bone resorption when choosing fixation.