Polyetheretherketone vs titanium cages in oncological spine surgery: Beyond mechanics toward oncological precision

Abstract

Spinal reconstruction in oncological patients presents unique challenges that extend beyond mechanical stability to include impaired bone biology, radiotherapy considerations, and the need for accurate postoperative imaging. Implant material selection - primarily between titanium and polyetheretherketone (PEEK), including carbon fiber-reinforced PEEK - has therefore evolved into a critical component of oncological treatment strategy. To critically evaluate current evidence comparing titanium and PEEK-based cages in oncological spine surgery, with emphasis on biomechanical performance, imaging characteristics, radiotherapy implications, and clinical outcomes. Narrative review of contemporary literature focusing on implant material properties, biomechanical studies, imaging and radiotherapy data, and clinical outcomes in oncological and relevant non-oncological populations. Titanium cages provide superior mechanical strength and osteointegration, making them favorable in cases requiring immediate structural stability, such as multilevel corpectomy or extensive vertebral destruction. However, their high elastic modulus may contribute to stress shielding and increased subsidence risk, particularly in compromised bone. Additionally, titanium implants generate significant imaging artifacts and may affect radiotherapy dose distribution. PEEK and carbon fiber-reinforced PEEK implants offer radiolucency, enabling improved postoperative imaging and more accurate radiotherapy planning, with minimal radiation perturbation. Despite these advantages, PEEK-based implants demonstrate limited intrinsic osteointegration and have not shown clear superiority in fusion rates or clinical outcomes. Current evidence indicates comparable complication rates, hardware durability, and patient-reported outcomes between materials. Importantly, no high-level data demonstrate that improved imaging or dosimetric accuracy with PEEK translates into better oncological outcomes. Hybrid implants, such as titanium-coated PEEK, and patient-specific 3D-printed constructs represent promising developments but lack robust oncological validation. Implant selection in oncological spine surgery should extend beyond biomechanics to incorporate imaging requirements, radiotherapy planning, and tumor-specific factors. Titanium remains the standard for structural reliability, whereas PEEK-based implants offer advantages in imaging and radiotherapy compatibility. However, no material has demonstrated clear oncological superiority. A multidisciplinary, patient-specific approach is essential, and future prospective studies should focus on oncological endpoints, including local tumor control, recurrence, and survival.

Key Words: Spine; Polyetheretherketone; Titanium; Tumor; Cage; Stability

Core Tip: In oncological spine surgery, cage selection must balance mechanical stability, fusion biology, and postoperative tumor surveillance. Titanium cages provide superior strength and osteointegration, particularly valuable in multilevel or structurally compromised reconstructions, but may impair imaging due to artifact formation. Polyetheretherketone cages allow clearer radiographic follow-up and reduced stress shielding, though their bioinert nature may limit fusion in irradiated or bone-compromised patients. Individualized implant selection - potentially incorporating hybrid technologies - remains essential to optimize both mechanical and oncological outcomes.

INTRODUCTION

Spinal reconstruction in oncological patients represents a uniquely complex clinical scenario. Unlike degenerative or deformity surgery, reconstruction following tumor resection must address immediate structural stability, impaired bone biology, planned or prior radiotherapy, and the need for reliable postoperative imaging. Consequently, cage material selection-most commonly between titanium and polyetheretherketone (PEEK), including carbon fiber-reinforced PEEK (CFR-PEEK)-has implications that extend beyond fusion alone.

Recent literature suggests that implant choice should not be driven solely by mechanical considerations, but rather by how the material integrates into the broader oncological treatment strategy, including imaging surveillance and radiotherapy planning[1,2]. Emerging technologies further expand this paradigm. Patient-specific 3D-printed PEEK implants have been introduced as a promising solution for complex spinal tumor reconstructions, enabling anatomical customization while preserving radiolucency and potentially improving implant fit and load distribution[3]. This approach reflects a broader transition toward patient-specific and precision-based surgery in spinal oncology.

At the same time, advances in biomaterials-including porous titanium and hybrid titanium-coated PEEK implants-aim to address the long-standing trade-off between biological fixation and imaging compatibility[4-6]. However, the clinical relevance of these innovations in oncological populations remains incompletely defined. Despite increasing use of radiolucent and hybrid implants, the extent to which material selection influences not only mechanical outcomes but also oncological endpoints remains unclear. This review aims to critically evaluate current evidence and provide a clinically applicable framework for implant selection in oncological spine surgery.

BIOMECHANICAL CONSIDERATIONS

Titanium cages remain the benchmark for structural reliability. With a modulus of elasticity of approximately 110 GPa, titanium provides high compressive strength and immediate load-bearing capacity. In cases of extensive vertebral body destruction, multilevel corpectomy, or significant anterior column compromise, this rigidity offers predictable stability[4].

Modern porous and 3D-printed titanium implants enhance osteointegration and early biological fixation. Preclinical and translational studies demonstrate superior osseointegration of porous titanium cages compared with PEEK constructs, even when combined with autograft[4,7]. Biomechanical analyses further support the structural advantages of titanium cages in load-bearing scenarios, particularly under high compressive demands[8,9]. However, the stiffness mismatch between titanium (approximately 110 GPa) and cortical bone (17-21 GPa) may contribute to stress shielding and increased subsidence risk, particularly in irradiated or osteoporotic bone[6,10].

PEEK, by contrast, has a modulus of approximately 3.6 GPa, closer to cancellous bone, promoting more physiological load sharing. Nevertheless, PEEK is bioinert, and without surface modification, its intrinsic osteointegration capacity is limited[4]. Emerging material modifications, including porous PEEK structures, may improve the bone-implant interface and partially mitigate this limitation[11].

IMAGING AND RADIOTHERAPY IMPLICATIONS

In oncological spine surgery, imaging plays a central role in both postoperative assessment and long-term disease surveillance. Titanium implants produce beam-hardening artifacts on computed tomography and signal distortion on magnetic resonance imaging, which may obscure residual or recurrent tumor[1,2]. In contrast, PEEK and CFR-PEEK implants are radiolucent and generate minimal artifact, enabling improved visualization of the tumor bed and adjacent anatomical structures[12-15].

Radiotherapy planning introduces an additional layer of complexity. Metallic implants may alter dose distribution through scattering and attenuation effects[16]. Experimental and clinical data suggest that PEEK implants produce minimal radiation perturbation, thereby facilitating more accurate dose delivery to the target volume[2,17,18].

However, whether improved imaging and dosimetric accuracy translate into meaningful oncological benefit remains uncertain. Although several studies report enhanced visualization and planning with CFR-PEEK constructs, there is currently no high-level evidence demonstrating improved recurrence detection, local tumor control, or survival[14,15]. Local recurrence remains a significant challenge following surgery for spinal metastatic disease, particularly in patients with extensive tumor involvement, highlighting the importance of reliable postoperative surveillance strategies[19]. This represents a critical gap in the literature.

CLINICAL OUTCOMES AND CURRENT EVIDENCE

Available clinical evidence indicates that CFR-PEEK instrumentation demonstrates safety and effectiveness comparable to titanium constructs, with similar complication profiles and short- to mid-term outcomes[12,14,15,20]. However, direct comparative data in oncological populations remain limited and are predominantly derived from retrospective series. Recent multicenter data further support the clinical feasibility of CFR-PEEK systems in oncological populations, particularly in facilitating postoperative imaging and multidisciplinary management[21].

High-level evidence from meta-analyses in spinal fusion - primarily in non-oncologic cohorts - demonstrates no overall difference in fusion rates between titanium and PEEK cages, although a modest lumbar-specific advantage for titanium has been reported[9,22]. Despite this, titanium implants are associated with a significantly higher risk of subsidence (relative risk approximately 2.17), likely related to modulus mismatch and stress concentration, a phenomenon that may be further amplified in irradiated or osteoporotic bone[9].

With respect to mechanical durability, rates of hardware failure appear broadly comparable between titanium and CFR-PEEK constructs, although available evidence is limited and primarily short-term[12,14,20]. Some reports suggest that CFR-PEEK systems may reduce stress concentration and potentially lower rod fracture risk; however, these findings remain inconclusive and require validation in larger prospective cohorts[14,15,21].

Patient-reported outcomes, including Oswestry Disability Index and visual analogue scale scores, are consistently similar across materials, with no clinically meaningful differences demonstrated[9,22]. Importantly, while radiolucent implants such as PEEK and CFR-PEEK improve postoperative imaging quality and facilitate radiotherapy planning, there is currently no high-level evidence demonstrating that these advantages translate into improved oncological outcomes, including earlier recurrence detection, enhanced local tumor control, or increased survival[14,15]. These findings highlight a critical distinction between biomechanical and oncological endpoints, underscoring the need for implant selection strategies that integrate both domains rather than prioritizing a single outcome.

INDIVIDUALIZED MATERIAL SELECTION

Given the absence of definitive superiority of any single material, implant selection in oncological spine surgery should be individualized and guided by a multidisciplinary assessment. Representative imaging characteristics and material-related behavior are further demonstrated in Table 1.

Table 1 Integrated comparison of interbody cage materials in oncological spine surgery across biomechanical, biological, radiological, and clinical domains.

Domain	Property	Titanium (Ti)	PEEK	CFR-PEEK	Evidence type	Certainty
Biomechanics	Elastic modulus/stiffness	High (approximately 110 GPa) → increased rigidity	Low (approximately 3.6 GPa) → reduced stress shielding	Intermediate (fiber-dependent)	Mechanistic	Moderate
	Load-bearing capacity	High; excellent immediate stability	Moderate	Moderate-high	Mechanistic	Low
	Stress shielding	Increased due to stiffness mismatch	Reduced	Reduced	Mechanistic	Low
Implant-bone interaction	Osteointegration	Strong, especially porous/3D Ti[4,7]	Limited (bioinert); may require modification[4]	Limited; similar to PEEK	Mechanistic + preclinical	Moderate
	Biological fixation	Reliable early fixation	Slower; graft-dependent	Similar to PEEK	Mechanistic	Low
Radiology/oncology	Imaging artifact (computed tomography/magnetic resonance imaging)	Significant artifact limiting assessment[1,2,4]	Radiolucent; clear visualization[1,2,4]	Radiolucent; similar to PEEK[12-15,18]	Mechanistic + clinical	High
	Tumor surveillance	May obscure recurrence/margins[1,2]	Improved visualization[12-15,18]	Improved visualization[12-15,18]	Clinical + mechanistic	Moderate
	Radiotherapy compatibility	Dose perturbation possible[2,18]	Minimal interference[2,18]	Minimal interference[2,18]	Clinical + experimental	Moderate
Clinical outcomes	Fusion rate	No overall difference; lumbar advantage (OR: 2.12)[6,22]	Comparable overall; lower in lumbar subgroup[6]	No data	Clinical (meta-analysis)	Moderate
	Subsidence	Higher risk: 2.17[6]	Lower risk[6]	No data	Clinical (meta-analysis)	Moderate
	PROMs (ODI, VAS)	No meaningful difference[5]	Comparable outcomes[5]	No evidence	Clinical (RCT/meta-analysis)	High
	Complications	No difference[6,22]	Similar safety[6,22]	Comparable (limited data)[12-15,18,20]	Clinical	High
Special scenarios	Compromised bone (oncologic/irradiated)	Strong support; advantageous in instability[1,4]	Potential fixation concerns	Promising but unproven	Mechanistic + limited clinical	Low
Material innovation	Ti-coated PEEK	-	Improved osteointegration vs PEEK[5]	Emerging	Clinical	Moderate
Summary	Net clinical effect	Modest fusion benefit offset by subsidence and imaging artifact	Balanced profile with imaging and RT advantages	Insufficient evidence	Synthesis	-

PEEK: Polyetheretherketone; CFR-PEEK: Carbon fiber-reinforced polyetheretherketone; OR: Odds ratio; PROMs: Patient-reported outcomes; ODI: Oswestry Disability Index; VAS: Visual analogue scale; RCT: Randomized controlled trial; RT: Radiation therapy.

Titanium may be preferred in: (1) Extensive anterior column reconstruction; (2) Multilevel corpectomy defects; and (3) Situations requiring maximal immediate structural stability. PEEK or CFR-PEEK may be advantageous in: (1) Cases requiring meticulous postoperative imaging surveillance; (2) Anticipated complex radiotherapy planning; and (3) Tumors with high recurrence risk or close surgical margins. Hybrid solutions, such as titanium-coated PEEK devices, aim to combine osteointegration with radiolucency, although oncological-specific comparative data remain limited[4-6].

HYBRID IMPLANTS: TITANIUM-COATED PEEK

Hybrid implants, particularly titanium-coated PEEK cages, represent an emerging strategy aimed at combining the biological advantages of titanium with the radiological properties of PEEK. This approach seeks to overcome one of the principal limitations of conventional PEEK implants - namely, their bioinert surface - while preserving radiolucency.

At the cellular level, microporous titanium coatings promote osteoblast adhesion, proliferation, and extracellular matrix deposition, thereby enhancing bone-implant integration. This may improve early fixation and address the limited intrinsic osteointegration associated with unmodified PEEK[5,6]. Preclinical and non-oncological clinical studies suggest that titanium-coated PEEK implants may achieve improved fusion rates compared with standard PEEK devices[5,6]; however, these findings have not yet been validated in oncological populations.

From a biomechanical perspective, hybrid implants maintain an elastic modulus closer to bone than solid titanium constructs, potentially preserving more physiological load sharing while simultaneously improving the bone-implant interface. This dual behavior may be particularly advantageous in patients with compromised bone quality, where both mechanical stability and biological integration are critical.

In the context of oncological spine surgery, hybrid implants may offer additional theoretical advantages. The PEEK core reduces imaging artifacts compared with fully metallic implants, thereby facilitating postoperative tumor surveillance. Furthermore, reduced metal content may decrease radiation dose perturbation during radiotherapy planning, potentially improving target accuracy in stereotactic body radiotherapy. Despite these potential benefits, there is currently no high-level evidence demonstrating improved oncological outcomes associated with hybrid implants.

Several technical and biological challenges must also be considered. The durability of the titanium coating remains a concern, particularly with respect to potential delamination during implantation or under cyclic physiological loading. Additionally, the biological response to wear debris or coating degradation - especially in irradiated or immunocompromised tissues - has not been fully elucidated, raising questions about long-term implant performance.

Overall, titanium-coated PEEK implants represent a promising but still evolving technology. While early biomechanical and clinical data are encouraging, high-quality, oncology-specific studies are required to determine whether these hybrid constructs can meaningfully improve both mechanical stability and oncological outcomes.

CONCLUSION

In oncological spine surgery, implant selection extends beyond biomechanics and must incorporate imaging requirements, radiotherapy planning, and tumor biology. Implant material selection should be guided by multiple clinical factors, as summarized in Figure 1.

Figure 1 Clinical decision-making framework for implant material selection in oncological spine surgery, incorporating mechanical demand, bone quality, oncological factors, radiotherapy planning, and expected survival. PEEK: Polyetheretherketone; CFR-PEEK: Carbon fiber-reinforced polyetheretherketone. This figure was created with the help of an AI tool to summarize the main concepts of the article. This figure is illustrative and does not present original data.

Titanium provides robust mechanical stability and osteointegration but is associated with imaging artifacts and increased subsidence risk. PEEK and CFR-PEEK offer superior imaging compatibility and radiotherapy advantages, yet currently lack evidence demonstrating improved oncological outcomes.

Hybrid materials and patient-specific implants represent promising future directions but require further validation. Ultimately, a patient-specific, multidisciplinary, and evidence-informed approach remains essential to achieving both structural stability and oncological precision. Future research should focus on prospective, oncology-specific studies evaluating not only mechanical outcomes but also local tumor control, recurrence patterns, and survival.