Radiopaque polymeric spinal cages: a prototype study

Abstract

Back pain, originating from degeneration of intervertebral discs, is often alleviated by the insertion of one or more interbody fusion cages. The function of the cage is to restore the height between two adjacent vertebrae and to mediate osseous fusion. Most commercial cages consist of titanium or a titanium alloy, while polymeric cages, mostly consisting of polyether-etherketone (PEEK), are also in use. Titanium is known for its excellent biocompatibility. Titanium cages can be located easily with imaging techniques based on X-ray absorption (e.g. CT scans). However, they introduce artefacts in magnetic resonance (MR images). PEEK cages, on the other hand, do not show up in CT images. For this reason, small metallic markers are usually incorporated. The markers reveal the position of the cage, albeit indirectly. PEEK cages are clearly and integrally seen on MR images, as they are essential free of water. There are no artefacts or disturbances; this feature, as well as its strength, makes PEEK particularly attractive for the construction of cages. Here, we introduce new all-polymeric cages on the basis of an iodine-containing methacrylic copolymer (I-copolymer). This material has been prepared from methylmethacrylate and 2-[4-iodobenzoyl]-oxo-ethylmethacrylate. Copolymerisation of both monomers results in a high molecular weight material. Cytocompatibility experiments reveal that the material contains no toxic leachables and that cells can well adhere to and proliferate on the I-copolymer. Compression experiments at physiologically relevant strains disclose mechanical characteristics comparable to PEEK. The advantage of cages prepared from this I-copolymer over commercially available cages is that the present cage contains no metallic components, implying that it is compatible with MR imaging, and the presence of the iodine atoms ensures X-ray visibility.