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Effect of Micrometer-Scale Roughness of the Surface of Ti6Al4V Pedicle Screws in Vitro and in Vivo
Zvi Schwartz, DMD, PhD1; Perry Raz, DMD, PhD2; Ge Zhao, MD, PhD1; Yael Barak, BS3; Michael Tauber, MD4; Hai Yao, PhD5; Barbara D. Boyan, PhD1
1 Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, 315 Ferst Drive N.W., Atlanta, GA 30332-0363. E-mail address for B.D. Boyan: barbara.boyan@bme.gatech.edu
2 Hebrew University Hadassah, P.O. Box 12272, Jerusalem 91120, Israel
3 Impliant, Inc., 7 Giborey Israel Street, P.O. Box 8630, Ramat Poleg 42504, Israel
4 Department of Spinal Neurosurgery, Arkade Klinik, Rathausstrasse 43, 98597 Breitungen, Germany
5 Clemson-MUSC Joint Bioengineering Program, Medical University of South Carolina, 173 Ashley Avenue, BSB 303, Charleston, SC 29425
View Disclosures and Other Information
Disclosure: In support of their research for or preparation of this work, one or more of the authors received, in any one year, outside funding or grants in excess of $10,000 from Impliant, Inc., the National Science Foundation (EEC 9731645), and the National Institutes of Health (AR052102). In addition, one or more of the authors or a member of his or her immediate family received, in any one year, payments or other benefits in excess of $10,000 or a commitment or agreement to provide such benefits from a commercial entity (Impliant, Inc.). No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.
Investigation performed at Georgia Institute of Technology, Atlanta, Georgia, and Hebrew University Hadassah, Jerusalem, Israel

The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2008 Nov 01;90(11):2485-2498. doi: 10.2106/JBJS.G.00499
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Background: Titanium implants that have been grit-blasted and acid-etched to produce a rough microtopography support more bone integration than do smooth-surfaced implants. In vitro studies have suggested that this is due to a stimulatory effect on osteoblasts. It is not known if grit-blasted and acid-etched Ti6Al4V implants also stimulate osteoblasts and increase bone formation clinically. In this study, we examined the effects of micrometer-scale-structured Ti6Al4V surfaces on cell responses in vitro and on tissue responses in vivo.

Methods: Ti6Al4V disks were either machined to produce smooth surfaces with an average roughness (Ra) of 0.2 µm or grit-blasted, resulting in an Ra of 2.0, 3.0, or 3.3 µm. Human osteoblast-like cells were cultured on the disks and on tissue culture polystyrene. The cell number, markers of osteoblast differentiation, and levels of local factors in the conditioned media were determined at confluence. In addition, Ti6Al4V pedicle screws with smooth or rough surfaces were implanted into the L4 and L5 vertebrae of fifteen two-year-old sheep. Osteointegration was evaluated at twelve weeks with histomorphometry and on the basis of removal torque.

Results: The cell numbers on the Ti6Al4V surfaces were lower than those on the tissue culture polystyrene; the effect was greatest on the roughest surface. The alkaline-phosphatase-specific activity of cell lysates was decreased in a surface-dependent manner, whereas osteocalcin, prostaglandin E2, transforming growth factor-ß1, and osteoprotegerin levels were higher on the rough surfaces. Bone-implant contact was greater around the rough-surfaced Ti6Al4V screws, and the torque needed to remove the rough screws from the bone was more than twice that required to remove the smooth screws.

Conclusions: Increased micrometer-scale surface roughness increases osteoblast differentiation and local factor production in vitro, which may contribute to increased bone formation and osteointegration in vivo. There was a correlation between in vitro and in vivo observations, indicating that the use of screws with rough surfaces will result in better bone-implant contact and implant stability.

Clinical Relevance: The osteointegration of screws with rough microtopographies is likely to be better than that of screws with smoother surfaces.

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    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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