The Role of the External Bar in a 6-Pin Type 1 External Skeletal Fixation Device

Summary

External skeletal fixation devices are commonly used in human and veterinary orthopedics. Although external fixators have proven useful over the years, their use is still associated with complications. The most frequently encountered complication is premature pin loosening with or without pin tract infection. Occasionally, implant failure involving the transla tion pins, pin clamps or external bar is seen. Each of these complications can contribute to patient morbidity through poor limb use, pain, loss of fracture reduction, and delayed unions or nonunions. A more thorough understanding of the biomechanics of external fixation devices may reduce the incidence of complications and associated patient morbidity. The objective of this study was to determine the role of the external connecting bar in a 6-pin type 1 external skeletal fixation device with respect to the forces transmitted to the surrounding bone for an axial load on the bone.

The methods used were finite element computer analysis and in vitro experimentation using a bone analog. The results obtained in both the FEA and in the in vitro experiments was that the middle pins on each bone segment experienced axial tension while the remainder of the pins experienced axial compression. Furthermore, increasing the stiffness of the external bar decreased the axial loads on all the pins, and more evenly distributed the end shear load and end moment on the pins.

The role of the external bar in a 6-pin type 1 ESF device was investigated using finite element computer analysis and in vitro experimentation. The results show that increasing the stiffness of the external bar decreases the axial loads and more equally distributes the end shear loads on the pins. Therefore, increasing the stiffness of the external bar may reduce the chance of complications related to excessive pin loads, such as pin loosening, pin breakage, and pin tract infection.

Keywords

External skeletal fixation - biomechanics - finite element analysis

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