Can PEEK Dethrone Titanium as the Choice Implant Material for Metastatic Spine Tumor Surgery

Abstract Instrumentation during metastatic spine tumor surgery (MSTS) provides stability to the spinal column in cases of pathological fracture or iatrogenic instability produced while performing extensive decompression. Titanium is the current implant material of choice in MSTS. However, it hinders radiotherapy (RT) planning and generates artifacts with magnetic resonance imaging (MRI) and computed tomography (CT) scans used for postoperative evaluation of tumor recurrence and/or complications. The high modulus-of-elasticity of titanium (110GPa) results in stress shielding, which may lead to construct failure at bone-implant interface. Polyether-ether-ketone (PEEK), a thermoplastic polymer is an emerging alternative to titanium for use in MSTS. The modulus of elasticity of PEEK (3.6GPa) is close to that of cortical bone (17–21GPa), resulting in minimal stress shielding. Its radiolucent and non-metallic properties cause minimal interference with MRI and CT scans. PEEK also causes low dose perturbation for RT-planning. However, PEEK has reduced bioactivity with bone and lacks sufficient rigidity to be used as rods in MSTS. The reduced bioactivity of PEEK may be addressed by: (1) surface modification [introducing porosity or bioactive coating with hydroxyapatite (HA) or titanium], and (2) forming composites with HA/titanium. The mechanical properties of PEEK may be improved by forming composites with HA or carbon fiber. Despite these modifications, all PEEK and PEEK-based implants are difficult to handle and contour intraoperatively. Our review provides a comprehensive overview of PEEK and modified PEEK implants with description of their properties and limitations, potentially serving as a basis for their future development and use in MSTS.