Innovative Developments in Lumbar Interbody Cage Materials and Design: A Comprehensive Narrative Review

Abstract

This review comprehensively examines the evolution and current state of interbody cage technology for lumbar interbody fusion (LIF). This review highlights the biomechanical and clinical implications of the transition from traditional static cage designs to advanced expandable variants for spinal surgery. The review begins by exploring the early developments in cage materials, highlighting the roles of titanium and polyetheretherketone in the advancement of LIF techniques. This review also discusses the strengths and limitations of these materials, leading to innovations in surface modifications and the introduction of novel materials, such as tantalum, as alternative materials. Advancements in three-dimensional printing and surface modification technologies form a significant part of this review, emphasizing the role of these technologies in enhancing the biomechanical compatibility and osseointegration of interbody cages. In addition, this review explores the increase in biodegradable and composite materials such as polylactic acid and polycaprolactone, addressing their potential to mitigate long-term implant-related complications. A critical evaluation of static and expandable cages is presented, including their respective clinical and radiological outcomes. While static cages have been a mainstay of LIF, expandable cages are noted for their adaptability to the patient's anatomy, reducing complications such as cage subsidence. However, this review highlights the ongoing debate and the lack of conclusive evidence regarding the superiority of either cage type in terms of clinical outcomes. Finally, this review proposes future directions for cage technology, focusing on the integration of bioactive substances and multifunctional coatings and the development of patient-specific implants. These advancements aim to further enhance the efficacy, safety, and personalized approach of spinal fusion surgeries. Moreover, this review offers a nuanced understanding of the evolving landscape of cage technology in LIF and provides insights into current practices and future possibilities in spinal surgery.

Keywords: 3D printing; Biodegradable cage; Expandable cage; Lumbar interbody fusion; Surface modification.

Fig. 1

(A–D) Examples of tantalum cages. Representative cases illustrate the application of tantalum cages, such as in a 68-year-old male patient where a tantalum cage was placed in the L1–2 intervertebral space, resulting in artifact generation on postoperative computed tomography and magnetic resonance imaging.

Fig. 2

The lumbar interbody cages vary in design and size. (A) A titanium cage suitable for transforaminal lumbar interbody fusion (LIF) and posterior LIF. (B) A larger polyetheretherketone cage designed for oblique LIF, lateral LIF, or anterior LIF. Views (C, D) present lateral and axial perspectives of two distinct cages. The larger cage measures 15 mm in width and 40 mm in length, making it suitable for endoscopic transforaminal lumbar interbody fusion, while the smaller cage’s dimensions are 10 mm by 32 mm. From Kim JE, et al. World Neurosurg 2023;178:e666–72 [116], with permission from the authors.

Fig. 3

(A) A 71-year-old female patient underwent L4–5 oblique lumbar interbody fusion (OLIF) with a static polyetheretherketone cage and exhibited cage subsidence in the 3-month postoperative follow-up X-ray. (B) A 75-year-old female patient received L4–5 OLIF with an expandable cage and has sustained proper alignment without any signs of cage subsidence for 3 months.