Case study of Ti6Al4V pedicle screw failures due to geometric and microstructural aspects

Pedicle screws are widely used alternatives to improve the spine fusion in the treatment of several spine diseases. However, the screw fracture rates are still high nowadays. Efforts to provide design and material selection should be encouraged. This paper deals with the analysis of design issues related to failure event of 10 Ti6Al4V pedicle screws explanted from five patients who had rupture before 5 years in use. The objective of this study was to correlate the mechanical failure with the geometric and microstructural concerns. Bending fatigue was the main mechanism responsible for the failures. Fractures occurred near the thread end or at intermediate thread level. In some cases environmental assisted cracking (EAC) was associated with failure initiation. The formation of lamellar or platelike microstructure, the small thread root radius and surface roughness were factors related to failures.

► Pedicle screws are critical elements for fracture due to geometry of the pedicles.
► We analyzed 10 pedicle screws fractured in five patients explanted before 5 years.
► Screws should be preferably machined with a smooth surface finish and fillet radius.
► Screw should be made from Ti6Al4V alloy with alpha + beta finely dispersed particles.