Biomechanical Study of a Novel, Expandable, Non-Metallic and Radiolucent CF/PEEK Vertebral Body Replacement (VBR)

Abstract

Vertebral body replacement is well-established to stabilize vertebral injuries due to trauma or cancer. Spinal implants are mainly manufactured by metallic alloys; which leads to artifacts in radiological diagnostics; as well as in radiotherapy. The purpose of this study was to evaluate the biomechanical data of a novel carbon fiber reinforced polyetheretherketone (CF/PEEK) vertebral body replacement (VBR). Six thoracolumbar specimens were tested in a six degrees of freedom spine tester. In all tested specimens CF/PEEK pedicle screws were used. Two different rods (CF/PEEK versus titanium) with/without cross connectors and two different VBRs (CF/PEEK prototype versus titanium) were tested. In lateral bending and flexion/extension; range of motion (ROM) was significantly reduced in all instrumented states. In axial rotation; the CF/PEEK combination (rods and VBR) resulted in the highest ROM; whereas titanium rods with titanium VBR resulted in the lowest ROM. Two cross connectors reduced ROM in axial rotation for all instrumentations independently of VBR or rod material. All instrumented states in all planes of motion showed a significantly reduced ROM. No significant differences were detected between the VBR materials in all planes of motion. Less rigid CF/PEEK rods in combination with the CF/PEEK VBR without cross connectors showed the smallest reduction in ROM. Independently of VBR and rod material; two cross connectors significantly reduced ROM in axial rotation. Compared to titanium rods; the use of CF/PEEK rods results in higher ROM. The stiffness of rod material has more influence on the ROM than the stiffness of VBR material.

Keywords: CF/PEEK; Vertebral body replacement (VBR); biomechanics; non metallic; radiolucent; spine; tumor; vertebral fracture.

Figure 1

Non-metallic X-ray-translucent carbon fiber reinforced polyetheretherketone (CF/PEEK) pedicle screws (icotec: VADER^®, Altstätten, Switzerland).

Figure 2

Spine tester (Schunk FT Delta SI 660-60, Lauffen/Neckar, Germany) with six degrees of freedom; three in translation (green) and three in rotation (orange). Specimen embedded in PMMA.

Figure 3

Prototype of the non-metallic, X-ray-translucent CF/PEEK expandable VBR. icotec, Altstätten, Switzerland.

Figure 4

Lateral view native radiographs documenting correct positioning of the (a) prototype non-metallic, X-ray-translucent CF/PEEK expandable vertebral body replacement (VBR) and the expandable titanium VBR (b).

Figure 5

Boxplot showing the median and quartiles of the index segment for all tested states in the three motion directions normalized in percentage of the native state.