Orthopaedic Surgery Spine


A Review of the Status of Ceramics in Spine Applications Mark R Foster, PhD, MD, FACS


President and Orthopaedic Surgeon, Orthopaedic Spine Specialists of Western Pennsylvania


Abstract


This review of the current literature is presented as an update on the status of ceramic applications in spinal surgery. I discuss first the structural use of ceramics, as hydroxyapatite is strong and provides bone with its rigidity, and then the use of ceramics in an osteoconductive role as a fusion or bone graft alternative and/or extender for the clinical stabilization of the spine. Within these functional uses, I consider separately the cervical and lumbar applications. Finally, I review some future applications in which ceramics might have a developing role, such as for vertebroplasty or kyphoplasty in place of poly(methyl methacrylate), as well in various applications of bone graft extenders, including bioactive molecules and other modalities to enhance bone formation.


Keywords Ceramics, spinal surgery, bone fusion, hydroxyapatite, β tricalcium phosphate


Disclosure: The author has no conflicts of interest to declare. Received: April 18, 2011 Accepted: May 20, 2011 Citation: US Musculoskeletal Review, 2011;6(1):35–8 Correspondence: Mark R Foster, PhD, MD, FACS, Orthopedic Spine Specialists of Western Pennsylvania, P.C., 425 First Ave., Pittsburgh, PA 15219. E: cherryway@pol.net


Ceramics are widely used not only in orthopedic surgery, often to coat screws or implants to enhance fixation,1


but also in trauma for fractures


or bony reconstruction where they can act as a bone graft alternative or bone graft extender. They are generally only US Food and Drug Administration (FDA) approved in non-weight-bearing applications. In spinal uses, where surgery generally involves decompressing neural structures and/or stabilizing the spine, bone grafts have been routinely used successfully to cause a fusion, or to stabilize the spine, as clinical stability has been defined as the ability to handle physiologic loads without intractable pain.2


Unfortunately, bone harvest carries with it an incidence of significant pain and other morbidity in the unrelated graft site.3


Hydroxyapatite is


into both β tricalcium phosphate and hydroxyapatite, as well as silicate-substituted calcium phosphate ceramics,6 considered for use in orthopaedic surgery.


the principal mineral that imparts strength to bone, so it could also function as an alternative to autografts as a structural member, with well-established compatibility, as it is native to bone. Furthermore, it might contribute as a bone graft extender, and porous forms of hydroxyapatite can be used. Although β tricalcium phosphate is more biologically active,4 grows5


it is not as strong as hydroxyapatite. However, bone which have also been


Hydroxyapatite and β tricalcium phosphate are referred to as being osteoconductive in that they can act as the scaffold or lattice upon which cells can form bone, partially or entirely resorbing7


the ceramic, forming


new bone (osteogenesis), which then potentially permanently replaces and adopts the architecture of the ceramic. Bone requires the combination of three factors: first, a favorable milieu, in terms of shape or structure, as


© TOUCH BRIEFINGS 2011


I reviewed the literature as an update on the current status of ceramics and suggest some areas of future research, such as biologically active molecules (BMPs), and the development of alternatives to poly(methyl methacrylate) (PMMA) for applications such as kyphoplasty and vertebroplasty.15


Bone marrow mesenchymal stem cells and calcium phosphate ceramic have together achieved bony fusion,10 hydroxyapatite with a local (laminectomy) bone graft.11


as have coralline


Porosity has commonly been introduced in hydroxyapatite by sintering the appropriate calcium phosphate powder with hydrogen peroxide, which elutes out, leaving voids of the desired size. As the ceramic is not bone, one cannot refer to ‘fusion’ (bone to bone healing or union), although bonding does occur.12


Studies with experimental animals have


demonstrated the feasibility of use in orthopaedics of several ceramics.13,14


which I briefly summarize here. As a result, these have been extended to clinical trials,


bone can even grow into metallic porous orthopaedic implants, and in terms of support in the form of nutrition or a circulation; second, it requires cells, so-called osteoctyes in mature bone, or osteoblasts in bone that is forming or being remodeled; and third, factors or morphogens to induce the cells that are settling into this favorable milieu to differentiate and make bone (i.e. osteogenesis). The scaffold is crucial because, although bone marrow aspirate can add cells for osteoinduction, without a scaffold, bone growth is inhibited.8 no bone.9


By contrast, stand-alone ceramics form


The discussion is organized around these two primary functions, using ceramics first as a structural member and then as an osteoconductive component for bone formation, but considering cervical and lumbar applications in order.


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