Letter: Arthrodesis With Titanium Implants: A Different Picture.

ABBREVIATION: DECT Dual-energy computed tomography. To the Editor: Psuedoarthrosis is a commonly known complication of trying to achieve solid body spinal fusion (arthrodesis) in the setting of spine surgery. Although recent advances in spinal surgery instrumentation, imaging, biologics, and management have occurred, it is still a prominent complication with significant morbidity and high cost burden.1 Deciding when to operate on these patients is variable and is primarily dependent on clinician gestalt regarding degree of intervention, physical examination findings, and the presence or lack of boney bridge formation across interbody implantation. Complicating this matter even further is the presence of psuedoarthrosis in the setting of no clinical symptoms. As it stands, computed tomography (CT) is the gold standard for detecting the presence of psuedoarthrosis. When evaluating multiple modalities of imaging for effectiveness in evaluating psuedoarthrosis, Peters et al found the pooled CT odds ratio to be highest in comparison with other modalities such as flexion/extension radiography, magnetic resonance, and scintigraphy. Furthermore, the authors went on to cite several instances in the literature where psuedoarthrosis was not detected through radiographic means but was detected by unveiling motion between adjacent segments.2 Although CT imaging may be a useful tool in imaging operated vertebrae with polyetheretherketone, carbon fiber, metal alloy, or other radiolucent implants, it can be less than reliable in titanium implants which often display significant artifact. Similar artifacts are seen on magnetic resonance imaging, posing an obstacle for thorough postoperative evaluation. Altogether, these findings illustrate the necessity of alternative modalities to better evaluate arthrodesis in the setting of spine surgery using titanium implants. Dual-energy CT (DECT) may prove a step in the right direction for evaluating psuedoarthrosis. In opposition to conventional CT imaging which uses a single image set, DECT uses 2 separate x-ray photon energy spectra; thus, allowing the interrogation of different attenuation properties at different energies.3 Artifact secondary to metal prosthesis (ie, titanium spinal interbody implants) typically occurs when low-energy photons within a polychromatic x-ray beam scatter radiation and abut image quality. Using DECT, these low-energy photons are removed; thus, limiting artifact. As of now, artifact in conventional CT is a major limitation in the evaluation of arthrodesis because initial boney bridge formation can be subtle or absent. To date, several articles have investigated the use of DECT in the setting of spinal fusion. Zeng et al4 in a retrospective review of 40 patients who underwent DECT after lumbar internal fixation found superior image quality with metal artifact reduction compared with conventional methods. Srinivasan et al5 in a retrospective review analyzing transpedicular screw interfacing noted the beneficial effects of metallic streak artifact reduction alongside better visualization of the hardware-bone interface. To our knowledge, there have been no prospective studies that study the differences between DECT and non-DECT images of the same patients. Several radiological fusion scales exist for the grading and measurement of fusion including a quantitative scale such as CT-Hounsfield Unit and qualitative scales such as the Lenke, Bridwell, and Brantigan, Steffe, Fraser scales.6,7 However, these are limited in that they are significantly dependent on subjective interpretation by an individual clinician and limited in their utility in assessment of titanium implants that present with significant artifact. Taken together, these findings highlight the need for a novel, quantized scale for assessing fusion with titanium implants using DECT.