Elsevier

Biomaterials

Volume 27, Issue 27, September 2006, Pages 4671-4681
Biomaterials

Leading Opinion
Experimental and clinical performance of porous tantalum in orthopedic surgery

https://doi.org/10.1016/j.biomaterials.2006.04.041Get rights and content

Abstract

Porous tantalum, a new low modulus metal with a characteristic appearance similar to cancellous bone, is currently available for use in several orthopedic applications (hip and knee arthroplasty, spine surgery, and bone graft substitute). The open-cell structure of repeating dodecahedrons is produced via carbon vapor deposition/infiltration of commercially pure tantalum onto a vitreous carbon scaffolding. This transition metal maintains several interesting biomaterial properties, including: a high volumetric porosity (70–80%), low modulus of elasticity (3 MPa), and high frictional characteristics. Tantalum has excellent biocompatibility and is safe to use in vivo as evidenced by its historical and current use in pacemaker electrodes, cranioplasty plates and as radiopaque markers. The bioactivity and biocompatibility of porous tantalum stems from its ability to form a self-passivating surface oxide layer. This surface layer leads to the formation of a bone-like apatite coating in vivo and affords excellent bone and fibrous in-growth properties allowing for rapid and substantial bone and soft tissue attachment. Tantalum-chondrocyte composites have yielded successful early results in vitro and may afford an option for joint resurfacing in the future. The development of porous tantalum is in its early stages of evolution and the following represents a review of its biomaterial properties and applications in orthopedic surgery.

Introduction

Conventional orthopedic implants have typically been fashioned from stainless steel, cobalt–chromium (CoCr), or titanium alloys. Numerous surface coatings and porous designs have been developed to enhance biological fixation of these implants to bone for use in orthopedic procedures [1]. Although excellent clinical results have been shown with these materials, they have several inherent limitations (low volumetric porosity, relatively high modulus of elasticity and low frictional characteristics). To address the limitations of these solid metals, a new porous tantalum biomaterial has been developed (Zimmer, Trabecular Metal Technology, Inc., Parsippany, NJ).

Porous tantalum is an open-cell tantalum structure of repeating dodecahedrons with an appearance similar to cancellous bone. The ability to alter the vitreous carbon skeleton of the metal allows for a near limitless scope in design, as evidenced by the wide variety of available orthopedic implants [2]. Tantalum is a transition metal (atomic number 73; atomic weight 180.05) that remains relatively inert in vivo. Dating back to the mid-1900s multiple medical devices have been fabricated that utilize this material, including: pacemaker electrodes, foil and mesh for nerve repair, radiopaque markers, and cranioplasty plates [3]. Tantalum-based implants have displayed an exceptional biocompatibility and safety record in orthopedic, cranio-facial, and dentistry literature [4]. The basic structure of this porous tantalum metal yields a high volumetric porosity, a low modulus of elasticity, and relatively high frictional characteristics. Bermudez et al. have shown excellent corrosion–erosion resistance of tantalum (secondary to stable surface oxidation layer) in a highly acidic environment, with no significant weight or roughness changes in comparison to titanium and stainless steel implants [5].

Overall porous tantalum is corrosion resistant, may be associated with less peri-implant stress shielding, and has the potential to allow for immediate weight bearing (given its high frictional characteristics). These inherent properties and proven biocompatibility make porous tantalum an intriguing metal for the design and manufacture of: press-fit or cementless components for total joint arthroplasty, bone graft substitute, or a scaffold for potential cartilage resurfacing. We present here a review of the biomaterial properties of porous tantalum and its use in orthopedic surgery, today.

Section snippets

Basic science and development

Porous tantalum implants are fabricated from the pyrolysis of a thermosetting polymer foam which in turn creates a low-density vitreous carbon skeleton (98% porosity) with a repeating dodecahedron array of regular pores. Commercially pure tantalum is then deposited onto this interconnected vitreous carbon scaffold using chemical vapor deposition/infiltration [1], [6], [7]. The initial carbon skeleton can be made into many different shape and sizes affording engineers a near limitless arena for

Total hip arthroplasty(THA)

Porous tantalum components and augments are currently available for use in both primary and revision THA [71]. A wide variety of implants are offered ranging from a monoblock acetabular component for primary THA to custom augments for use in reconstituting bone stock in complex revision cases. These components offer a low modulus of elasticity, high surface frictional characteristics, and excellent osseointegration properties (i.e. bioactivity, biocompatibility, and in-growth properties) [1],

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    Editor's Note: Leading Opinions: This paper is one of a newly instituted series of scientific articles that provide evidence-based scientific opinions on topical and important issues in biomaterials science. They have some features of an invited editorial but are based on scientific facts, and some features of a review paper, without attempting to be comprehensive. These papers have been commissioned by the Editor-in-Chief and reviewed for factual, scientific content by referees.

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