Retrieval and analysis of intramedullary rods

Area of Science:

• Orthopaedic Surgery
• Biomaterials Science
• Metallurgical Engineering

Background:

• Intramedullary rods are critical implants in orthopaedic surgery for fracture fixation.
• Implant failure, such as cracking, can lead to adverse patient outcomes and revision surgeries.
• Understanding the causes of implant failure is essential for improving patient safety and treatment efficacy.

Purpose of the Study:

• To investigate the causes of cracking observed in retrieved intramedullary rods.
• To identify the specific factors contributing to implant failure in retrieved intramedullary rods.
• To propose potential modifications to mitigate the risk of intramedullary rod cracking.

Main Methods:

• Examination of ten retrieved intramedullary rods of similar design.
• Analysis of retrieved rods for evidence of cracking, particularly in the proximal third.
• Correlation of observed cracking with surgical techniques, duration of implantation (in vivo), metal alloy composition, and manufacturing methods.

Main Results:

• Four out of ten retrieved intramedullary rods exhibited cracking in their proximal third.
• The observed cracking could not be attributed to surgical techniques or the time the rods were implanted.
• Cracking was determined to be a result of the specific metal alloy used and the manufacturing process, which sometimes placed weld zones at points of maximum stress.

Conclusions:

• Metallurgical and fabrication factors can significantly contribute to intramedullary implant failure.
• The location of weld zones during manufacturing, relative to points of maximum stress, is a critical factor in rod cracking.
• Modifying the alloy composition to a low-carbon form of 316 stainless steel is suggested as a means to reduce the risk of cracking and improve implant reliability.