In-vitro and in-vivo investigation of Nitinol corrosion behavior for pedicle screw constructs

Wednesday, May 20, 2015: 11:00 AM
Conference Theater (Crowne Plaza)
Ms. Elena Lukina , Kingston University London, Thames ditton, United Kingdom
Dmitry Gusev , MATI-Russian State Technological University, Moscow, Russia
Yulia Chernyshova , MATI-Russian State Technological University, Moscow, Russia
Alla Khon , MATI-Russian State Technological University, Moscow, Russia
Arkadiy Kazmin , Central Institute of Traumatology and Orthopaedic, Moscow, Russia
Sergey Kolesov , Central Institute of Traumatology and Orthopaedic, Moscow, Russia
Paul Wagstaff , Kingston University London, Thames ditton, United Kingdom
Peter Mason , Kingston University London, Thames ditton, United Kingdom
Gordon W Blunn , UCL, London, United Kingdom
Mikhail Kollerov , MATI-Russian State Technological University, Moscow, Russia
Background.The use of Nitinol rods in spinal pedicle screw constructs provides less rigid fixation which may eliminate adjacent segment degeneration complications. However, data on the corrosion behavior of Nitinol rods used in conjunction with Ti-6Al-4V pedicle screws is contradictory.

Objectives.To evaluate the effects of microstructure and surface finish on the corrosion behavior of Nitinol tested in conjunction with Ti-6Al-4V screws compared with corrosion damage on retrieved Nitinol rods.

Methodology. 5.5mm diameter Nitinol rods (55.8 wt.%Ni) having various bulk structure and surface finish locked using Ti-6Al-4V screws were immersed in 0.9%NaCl solution at 37±1OC for 6 months. Standard cyclic potentiodynamic polarization measurements were also carried out. More than 100 surgeries using titanium screws with Nitinol rods were carried out. Two patients underwent revisions and corrosion patterns on these retrieved components were analyzed.

Results. Pitting breakdown potential (Eb) deteriorated with increasing Ti4Ni2Ox volume fraction. Mechanically polished rods had lower Eb. No corrosion damage was observed on electro-polished Nitinol rods locked into Ti6Al4V screws, whereas discoloration corrosion deposits containing Ti, Ni and Fe were observed on mechanically polished rods after immersion test. Similar damage was seen on retrieved rods.

The Ni ion content of the patient’s blood didn’t increase.

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