Assessment of intra-operative impact durability of additively manufactured mock lumbar intervertebral body fusion devices.

Abstract

Spinal interbody fusion devices (IBFD) are commonly used to treat various spinal pathologies. Additive Manufacturing (AM) has been used to incorporate lattice structures into IBFD designs, intended to facilitate bony in-growth and reduce stress shielding. However, there is concern with IBFDs failing intra-operatively based on the medical device adverse event reporting to FDA, in which such failures were reported for both AM titanium as well as traditional PEEK IBFDs. This study aims to develop a bench test to simulate intra-operative impact loading and then use different AM lattice parameters to assess the sensitivity of the test method. A benchtop mechanical test setup was developed based on drop weight methodology to evaluate impact resistance of an IBFD under impact loading. A set of mock IBFDs (n = 120) were fabricated to investigate the sensitivity of the test method towards variation in IBFD design (1) lattice relative density (RD) (0.15, 0.25, 0.35, 0.45 RDs), (2) lattice pattern (Regular, Stochastic), (3) IBFD/lattice interface (Framed, Unframed), and (4) fabrication technique (EBM, LASER). Results indicate the number of impacts needed to deform the IBFD sample increased with an increase in RD of the IBFDs. The method was able to show differences in lattice design including the Stochastic lattice pattern having significantly different impact durability compared to Regular lattice, and Framed IBFDs having different impact durability compared to the Unframed. Overall, the pre-clinical test method developed for assessing intra-operative impact resistance of IBFD designs has been shown to be reasonably sensitive to differing designs.