Thermomechanical effects of spine surgery rods composed of different metals and alloys.
METHODS
A basic science study monitoring changes in the curvature of hand contoured commercially pure titanium (CPTi), titanium-aluminum-vanadium alloy (Ti-6Al-4V), and stainless steel (SS) rods maintained at different temperature conditions.


OBJECTIVE
To quantify changes in rod-shape at temperatures representative of those used in clinical practice.


BACKGROUND
The shape of implanted rods can be displaced due to thermo-mechanical properties of the materials. Warmer temperatures likely initiate this effect. A study of shape loss characteristics of various rod implants may help eliminate undesirable outcomes caused by shape displacement.


METHODS
Three different types of rods (CPTi, SS, and Ti-6Al-4V) were hand contoured and then maintained in one of following temperature conditions for 35 days: (1) room temperature (20 °C-25 °C) without autoclaving before contouring; (2) preliminary autoclaving (1, 5, 10, 20 cycles) at 135.0 °C ± 2 °C before contouring followed by body temperature (37.2 °C ± 2 °C). Each rod was 5 mm in diameter and 200 mm long. The rods were mounted over graph paper in fixed positions and photographed to measure displacement of the tip as a function of the curvature. RESULTS.: Statistically significant shape loss of the rods manufactured from all the tested materials was found. The hand contoured CPTi rods displayed considerably higher loss of curvature over time than Ti-6Al-4V and SS rods at all tested temperature conditions. Preliminary autoclaving at 135 °C before contouring tended to amplify this effect, in particular 1 cycle of autoclaving. If the number of preliminary autoclaving cycles was higher (5-10), a tendency of decrease of shape loss effect was observed in Ti-6Al-4V and CPTi rods.


CONCLUSIONS
The shape of the hand contoured CPTi rods was the least stable of the rods across all applied temperature conditions. The SS and Ti-6Al-4V rods were more stable than CPTi rods. Autoclaving before handcontouring tended to increase rods' shape loss.
Noshchenko
Andriy
A
The Spine Center, University of Colorado, Denver, CO 80045, USA.
Patel
Vikas V
VV
Baldini
Todd
T
Yun
Lu
L
Lindley
Emily M
EM
Burger
Evalina L
EL
D000497:Alloys / Q000737:chemistry* / Q000627:therapeutic use; D019544:Equipment Failure Analysis / Q000379:methods*; D006358:Hot Temperature / Q000009:adverse effects; D006801:Humans; D016268:Internal Fixators / Q000592:standards; D008422:Materials Testing / Q000379:methods; D008669:Metallurgy / Q000379:methods*; D008670:Metals / Q000737:chemistry* / Q000627:therapeutic use; D010865:Pilot Projects; D011474:Prosthesis Design / Q000379:methods; D011475:Prosthesis Failure / Q000009:adverse effects; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods; D013314:Stress, Mechanical
D000497:Alloys; D008670:Metals