Failure investigation of a tibiotalocalcaneal arthrodesis system

• Failure investigation of prematurely failed Intramedullary device (IM nail), involving both clinical and mechanical factors
• Pre-crack due to interference between the IM nail components
• Failure due to conjoint action of axial, bending and torsion forces
• FEA and numerical analysis were performed for better understanding the failure scenario and to validate the obtained results.

Ankle disorders such as arthritis and trauma are treated with Arthrodesis where an intramedullary (IM) nail is inserted in the ankle to fuse the joints. Fusion reduces pain and has been proposed as gold standard. Nailing is used in a variety of situations, particularly to treat fractures in long bones. This paper describes failure analysis of an ankle intramedullary nailing system implanted in a 49-year old male patient. The failure location was proximal of the two distal interlocking screw holes laterally. The medical devices are regulated in the United States, the material of the nail conformed to the ISO specification requirements. Optical and scanning electron microscopes were used to identify the fracture origin. Finite element analysis (FEA) was performed to determine maximum Von Mises stresses from torsion and translation movements. Axial load to failure of the implant was determined by conducting numerical analysis. The implant failed due to multiple factors involving clinical and biomechanical parameters exceeding the nail strength. Lack of proper bone purchase while inserting the screw and interference with the IM nail wall initiated the crack. The force and torque developed during the gait propagated the crack to a length of 0.4–0.6 mm, upon subsequent use the cracked device was unable to load-bear resulting in premature failure.

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