Introduction: Ti-6Al-4V-ELI (Ti-ELI) and Cobalt Chromium (CoCr), alloys used for spinal implants, have limited strength and fatigue resistance therefore requiring a larger implant size. Our aim is to develop a rod construct alternative made of MoRe® that can leverage its superior mechanical properties to reduce rod size and incorporate dynamic sensor technology.
Methods: Experiments conducted: ASTM-1717 test methods for spinal implant constructs in a vertebrectomy model to evaluate mechanical performance of 4.0mm diameter MoRe® alloy vs. 5.5mm diameter Ti-ELI and CoCr rods; bone implantation study to evaluate the local tissue and bone response of MoRe® vs. Ti-ELI when implanted in the femoral bone of rabbits for 4, 13 and 26 weeks; in-vivo experiment to evaluate mechanical stabilization of a tibial defect with a novel sensor incorporated implant measuring micro-strain correlated with imaging evidence of bone growth in a sheep over 6 weeks.
Results: Reduced diameter MoRe® (4.0mm), demonstrated superior mechanical performance versus 5.5mm diameter Ti-ELI and CoCr:
Yield Strength (ksi): MoRe® 280 ksi; Ti-ELI 115 ksi; CoCr 110 ksi
Ultimate Tensile Strength (ksi): MoRe® 300 ksi; Ti-ELI 125 ksi; CoCr 170 ksi
Recoil (%): MoRe® <2%; Ti-ELI 6%; CoCr 9%
Hardness Range (HV): MoRe® 280-800 HV; Ti-ELI 350-400 HV; CoCr 255-331 HV
Max Run-Out Load Bent Rod (N): MoRe® 350 N; Ti-ELI 150 N; CoCr 200 N
Decrease in Max Run-Out Load-
Bent-Unbent-Re-bent Rod (%): MoRe® 9%; Ti-ELI -17%; CoCr -13%
MoRe® and Ti-ELI implant sites demonstrated similar osteoconduction and bone remodeling histology of cortical and medullary bone at all time points.
Implant micro-strain of 901µe at time of surgery decreased to 132.5µe at 4 weeks and 31.8µe at 6 weeks post-implant correlating (p<0.05) with radiographic appearance of partial and complete fracture healing, respectively, Figure 1.
Conclusions: MoRe® implants, with embedded novel sensor technology allow for a new generation of smaller, more fatigue resistant, bio-friendly SMART™ implants that may be able to detect evolving pseudoarthrosis prior to clinical presentation.
Patient Care: This abstract contains basic science data on a novel alloy- Molybdenum-Rhenium (MoRe® ) that will change the landscape of materials used in the spine and orthopaedic markets in addition to in-vivo data regarding novel sensor implant incorporated technology that can improve the care of patients.
Learning Objectives: By the conclusion of this session, participants should be able to: 1)Describe the mechanical properties of the Molybdenum-Rhenium alloy (MoRe®) 2)Discuss the clinical importance of dynamic sensor technology embedded in spine implants in detecting bone growth.