Molybdenum Rhenium Alloy provides Superior Biomechanical and Wear Properties for a New Generation of Spine Implants

Presented at SMISS Annual Forum 2018
By Kornelis Poelstra MD, PhD
With

Disclosures: Kornelis Poelstra MD, PhD B; MiRus, LLC, K2M, Mazor Robotics, ISD, DePuy Synthes Spine, Ascension Health, Medtronic Spine, Integrity Spine. D; MiRus, LLC.

Introduction:

Spine surgery has improved dramatically over the past decades primarily due to the development of better techniques but little progress has been made in the development of new materials for spine implants. Titanium, the most commonly used alloy for spinal implants, has limited strength and is notch-sensitive so repetitive stress leads to fatigue failure of implants and generation of wear debris. Wear generation of 50 µg may serve as the impetus for late-onset inflammatory response and post-operative pain1. Wear generation as low as 25 µg/g has been reported to significantly increase the incidence of pseudoarthrosis2. Better materials with optimized biomechanical and wear properties could result in the development of superior spinal implants.

Aims/Objectives:

To evaluate the mechanical and wear properties of Molybdenum-Rhenium (MoRe) for spinal implants.

Methods:

Standard test methods (ASTM 1717) were performed to evaluate the mechanical properties of Molybdenum Rhenium (MoRe) alloy compared to Titanium (Ti-6Al-4V, ASTM F136-13 annealed bar, Ti-ELI).

Results:

Reduced diameter MoRe (4.0mm), demonstrated superior mechanical performance versus 5.5mm diameter Ti-ELI: Yield Strength (ksi): MoRe 280 ksi; Ti-ELI 115 ksi Ultimate Tensile Strength (ksi): MoRe 300 ksi; Ti-ELI 125 ksi Elongation: MoRe 13%; Ti-ELI 10% Reduction in Area: MoRe 50%; Ti-ELI 25% Recoil (%): MoRe <2%; Ti-ELI 6% Hardness Range (HV): MoRe 280-800 HV; Ti-ELI 350-400 HV Max Run-Out Load Bent Rod (N): MoRe 350 N; Ti-ELI 150 N Decrease in Max Run-Out Load-Bent-Unbent-Re-bent Rod (%): MoRe 9%; Ti-ELI ¬17% Wear Debris Generation (µg): [MoRe/Ti-ELI construct vs. standard Ti-ELI construct] (µg): MoRe/Ti-ELI construct 0.7 - 0.8 MoRe/ 7-9 ug Ti; Ti-ELI construct 800-1000 µg

Conclusions:

The MoRe alloy, with its advantageous mechanical and wear debris properties, offers great promise for the design of a new generation of smaller, more fatigue resistant and bio-friendly spine implants, resulting in less soft tissue disruption, quicker recovery and better outcomes for patients. 1Hee-Dong Kim, Ki-Soo Kim, Sung-Chan Ki and Yong-Soo Choi. Electron Microprobe Analysis and Tissue Reaction around Titanium Alloy Spinal Implants. Asian Spine J. 2007 Jun;1(1):1-7. 2Wang JC, Yu WD, Sandhu HS, Betts F, Bhuta S, Delamarter RB. Metal Debris from Titanium Spinal Implants. Spine. 1999 May 1;24(9):899-903