Comparing Titanium and PEEK in spinal cages

Selecting optimal materials for interbody fusion cages is a key challenge in spinal surgery since implant performance depends on both mechanical integrity and biological compatibility [۱]. Among the most widely adopted materials, titanium (Ti) alloys and polyetheretherketone (PEEK) dominate clinical use due to their favorable mechanical and biocompatible properties [۲]. Titanium, especially Ti-۶Al-۴V, offers high strength, corrosion resistance, and osseointegration potential [۳], yet its elastic modulus (۱۰۰-۱۱۰ GPa) far exceeds that of cortical bone (۱۰-۴۰ GPa), leading to stress shielding and cage subsidence. In contrast, PEEK exhibits an elastic modulus (۳-۴ GPa) that closely matches that of native bone, thereby improving load sharing and minimizing subsidence risk [۴]. However, its hydrophobic, bioinert surface limits bone bonding, often resulting in fibrous encapsulation or pseudarthrosis [۵]. Titanium's strong osseointegration is attributed to the spontaneous formation of a TiO۲ surface layer that mimics hydroxyapatite, enhancing osteoblast attachment and bone anchorage [۶]. Additionally, roughened or micro-textured surfaces increase frictional stability and cell adhesion, promoting mechanical interlocking and osteogenic differentiation [۷]. Despite these benefits, titanium's radiopacity interferes with postoperative imaging and hinders accurate fusion assessment [۸]. PEEK, introduced in spinal fusion in the early ۱۹۹۰s, rapidly gained favor due to its radiolucency and biomechanical compatibility. Its elastic modulus approximates that of cortical bone [۹], reducing stress shielding and providing stable load transmission during spinal motion. Furthermore, its radiolucency enables precise postoperative evaluation of fusion, eliminating CT and MRI artifacts typical of metallic implants. Yet PEEK's biological limitations remain significant; its smooth, hydrophobic surface discourages osteointegration and encourages fibrous tissue formation at the implant-bone interface [۵]. To overcome these drawbacks, titanium- or hydroxyapatite-coated PEEK designs have been explored, though coating delamination and limited osteointegration persist. Comparative studies have shown that titanium cages achieve superior bone-implant integration and fusion rates, while PEEK offers better elastic compatibility with vertebral bone [۱۰]. Histological findings confirm that titanium surfaces support bone ingrowth, whereas PEEK typically develops fibrous layers that reduce intervertebral height under compressive loads. Although titanium's stiffness mismatch remains a mechanical drawback, the advent of surface-optimized and porous designs has helped mitigate stress shielding and subsidence [۱۱]. In conclusion, titanium remains the benchmark material for mechanical durability and osseointegration, while PEEK is preferred for its radiolucency and closer elastic compatibility with bone. Neither material, independently, meets the ideal criteria for spinal fusion cages. The next generation of implants is expected to integrate titanium's bioactive surface with PEEK's imaging and mechanical advantages, creating hybrid devices that achieve a superior balance of mechanical strength, biological fixation, and radiological clarity [۱۲].

کلیدواژه ها:

Additive Manufacturing ، Osseointegration ، Polyetheretherketone (PEEK) ، Titanium Alloys