The memory properties of cold-worked titanium rods in scoliosis constructs.
METHODS
Time series monitoring changes in titanium and stainless steel rod curvature kept at a constant temperature of 37 C as a function of time.


OBJECTIVE
To assess the possibility of loss of curvature in titanium rods after scoliosis surgery.


BACKGROUND
Titanium rods have gained use in scoliosis surgery due to their excellent biocompatibility, while allowing medical personnel to obtain undistorted magnetic resonance imaging scans following surgery. However, the impression of several clinicians has been that when screw pullout and/or loss of sagittal balance occurs, it may be due to the rods losing some of their curvature.


METHODS
Five 6-mm rods of differing compositions and lengths (titanium 300 and 100 mm, stainless steel 300 and 100 mm, prebent titanium 85 mm) were bent at room temperature with a 3-point rod bender, then placed in an incubator at 37 C. Digital photographs were taken every 2 weeks and analyzed to extract the radius of curvature of each rod.


RESULTS
The Ti rods had a significantly decreasing curvature with time. The prebent Ti and stainless steel rods did not exhibit significant change in curvature.


CONCLUSIONS
Titanium rods bent at room temperature and then exposed to body temperature over time tend to exhibit "metal memory"; they gradually revert to their original shape. This may result in loss of sagittal balance and/or proximal screw pullout.
Burger
Evalina L
EL
Department of Orthopedics, Bioengineering Laboratory, Louisiana State University Health Sciences Center, New Orleans, Louisiana 70112, USA. EBurge1@lsuhsc.edu
Baratta
Richard V
RV
King
Andrew G S
AG
Easton
Robert
R
Lu
Yun
Y
Solomonow
Moshe
M
Riemer
Barry L
BL
D001858:Bone Nails / Q000592:standards; D003080:Cold Temperature; D008422:Materials Testing / Q000379:methods*; D018583:Pliability; D012600:Scoliosis / Q000601:surgery*; D013193:Stainless Steel / Q000592:standards; D013997:Time Factors; D014025:Titanium / Q000592:standards*
D013193:Stainless Steel; D014025:Titanium