The Use of Radiolucent Technology in Spine Tumors

Instrumentation is often used to stabilize the spine after resection of a spine tumor. Titanium is the most commonly used material for spine instrumentation because of its favorable modulus of elasticity, increased ability to bond with bone compared to other implant materials, and magnetic resonance imaging (MRI) compatibility. However, there are potential negatives with using titanium implants in patients with spine tumors. Titanium can create artifact and obscure or degrade the quality of MRIs, increasing the difficulty in evaluating patients for tumor recurrence. Titanium also creates radiation shielding from adjuvant radiotherapy treatments.1 Thus, it would be beneficial to identify a material lacking such limitations while maintaining spinal stability after implantation.

Polyetheretherketone (PEEK) cages have some advantages over titanium in tumor patients. Some benefits of PEEK cages include a modulus of elasticity more similar to cortical bone, less artifact on MRI, and less radiation shielding (Figure 1).1 Some studies have shown good results with PEEK and other carbon-based implants. Potential negatives of carbon-based implants may include potential difficulty visualizing screw placement on fluoroscopy and the inability to bend the rods intraoperatively. The carbon-based pedicle screws are also more costly when compared to regular titanium pedicle screws. In a cohort study of 34 patients with operable spine tumors, Boriani et al examined the use of carbon fiber-reinforced PEEK implants. In this study, the authors noted that one intraoperative screw breakage occurred out of 232 implanted screws, and only two incidences of sacral screw loosening were found at long-term follow-up. However, 6 local recurrences were discovered, benefited by lack of implant artifact on follow-up imaging. Also, radiation oncologists reported better treatment planning on CT and lacking of scattering effect during the treatment. 2

Carbon fiber–reinforced cages have also been shown to have favorable results when used with spine tumors (Figure 2). In a separate study by Boriani et al, the authors evaluated the efficacy of carbon fiber reinforced PEEK cages in 42 patients with spine tumors. 3 At 24 months, 80% of the patients had radiographic evidence of a solid fusion and the remainder had probable fusions. There were no complications related to the carbon fiber–reinforced PEEK cages.

Biomechanical studies have been performed on PEEK and carbon fiber–reinforced implants. In a cadaveric study by Bruner et al., the authors performed biomechanical testing on titanium, PEEK, and carbon fiber– reinforced PEEK rods.4 All 3 constructs significantly limited range of motion in all planes in the destabilized cadaver spine except in axial rotation. All of the rods similarly restricted motion in all planes, except axial rotation (P < 0.05). In combined loading, rod stiffness was similar for each material. Rod strain was least in the titanium construct, intermediate in the carbon fiber reinforced PEEK construct, and maximal in the pure PEEK construct.

The radiolucency and lack of radiation shielding of PEEK and carbon fiber–reinforced implants have potentially large benefits for patients with spine tumors. More studies are needed to further evaluate the efficacy of these implants; however, initial data support the use of these implants in spine tumor patients. n

1. Ringel F, Ryang YM, Kirschke JS, et al. Radiolucent carbon fiber-reinforced pedicle screws for treatment of spinal tumors: advantages for radiation planning and follow-up imaging. World Neurosurg. 2017;105:294-301.

2. Boriani S, Tedesco G, Ming L, et al. Carbon-fiber-reinforced PEEK fixation system in the treatment of spine tumors: a preliminary report. Eur Spine J. 2018;27(4):874-881.

3. Boriani S, Bandiera S, Biagini R, De Iure F, Giunti A. The use of the carbon-fiber reinforced modular implant for the reconstruction of the anterior column of the spine. A clinical and experimental study conducted on 42 cases. Chir Organi Mov. 2000;85(4):309-335.

4. Bruner

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DJ,

Biomechanics of polyaryletherketone rod composites and titanium rods for posterior lumbosacral instrumentation. Presented at the 2010 Joint Spine Section Meeting. Laboratory investigation. J Neurosurg Spine . 2010;13(6):766-772.

From the Hospital for Special Surgery in New York, New York.