The effect of ultraviolet photofunctionalization of titanium instrumentation in lumbar fusion: a non-randomized controlled trial

Abstract

Background: Titanium instrumentations are widely used in orthopedics; the metal bonds with bone in a process called osseointegration. Over time, hydrocarbons adhere to the instrumentation, which weakens the bone-binding ability. Ultraviolet photofunctionalization enhances the bone-binding ability of instrumentation by reducing hydrocarbons. The process has been proven effective in dentistry, but its effects in orthopedics are unverified. We aimed to determine the effect of ultraviolet photofunctionalization of titanium instrumentation used in lumbar fusion.

Methods: This was a non-randomized controlled trial. We prospectively enrolled 13 patients who underwent lumbar fusion surgery. We inserted two pure titanium cages into each intervertebral space; one cage had undergone ultraviolet photofunctionalization, while the other was untreated. The degree of osteosclerosis around both cages was then compared by measuring the densities around the cages on imaging at 2, 3, 6, and 12 months postoperatively compared with 1 month postoperatively. The carbon attachment of the titanium cages was measured using X-ray photoelectron spectroscopy.

Results: There was no significant difference between the degree of osteosclerosis (as assessed by the density) around the treated versus untreated cages at any timepoint. The ratio of carbon attachment of the titanium cages was only 20%, which was markedly less than the ratio of carbon attachment to titanium instrumentation previously reported in the dentistry field.

Conclusions: The effect of ultraviolet photofunctionalization of titanium instrumentation in spine surgery is questionable at present. The biological aging of the titanium may be affected by differences in the manufacturing process of orthopedics instrumentation versus dentistry instrumentation.

Trial registration: UMIN Clinical Trials Registry (Identifier: UMIN000014103 ; retrospectively registered on June 1, 2014).

Keywords: Instrumentation aging; Posterior lumbar interbody fusion; Titanium; Ultraviolet (UV) photofunctionalization.

Fig. 1

CT images showing the method used to measure bone sclerosis. The red lines in the left image represent the anterior, middle, and posterior regions of the intervertebral spacer on an axial CT image. We measured the mean range of image in the 2 mm above and below each of these three regions on coronal CT images (middle and right images). Density range: 0 (black)–255 (white)

Fig. 2

The effect of ultraviolet (UV) photofunctionalization. a. Photograph of an intervertebral spacer undergoing UV photofunctionalization. b. The intervertebral spacer became hydrophilic after UV photofunctionalization. Blood was absorbed into the cage that underwent UV photofunctionalization, immediately after the drop was applied. c. The intervertebral spacer remained hydrophobic without UV photofunctionalization. Absorption of the blood drop into the cage without UV photofunctionalization was delayed

Fig. 3

Changes in density over time. Postoperative duration indicates the length of time after lumbar fusion surgery performed using titanium instrumentation either without UV treatment or with UV treatment. There were no significant differences in the density of the titanium implants that were UV-treated versus those that were not UV-treated at any timepoint (Mann-Whitney U test). (2 months: P = 0.84, 3 months: P = 0.52, 6 months: P = 0.81, 12 months: P = 0.94)

Fig. 4

Composition of the surface elemental analysis by X-ray photoelectron spectroscopy. By measuring the energy distribution of photoelectrons generated after irradiation with X-rays on the sample surface, we were able to analyze the constituent elements and electronic states of our instrumentation samples. The actual titanium instrumentation used in lumbar fusion surgery 1 year after production is shown. We used PROSPACE® intervertebral cages (B-Braun Company, Melsungen, Germany) in all patients in this study. The surface of the PROSPACE® is pure titanium, which covers a Ti-6Al-4 V alloy. Actual titanium instrumentation that underwent ultraviolet photofunctionalization had a decreased amount of carbon attached to it. Vertical axis: photoelectron speed (C/S: counts / sec). Horizontal axis: binding energy (eV: electronvolt)