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

This narrative review comprehensively examines the evolution and current state of the interbody cage technology for lumbar interbody fusion (LIF). This review highlights the biomechanical and clinical implications of 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 advancing LIF techniques. It discusses the strengths and limitations of these materials, leading to innovations in surface modifications and the introduction of novel materials, such as tantalum, as an alternative material. 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. This review also explores the rise of 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 in this review, including their respective clinical and radiological outcomes. While static cages have been a mainstay of LIF, expandable cages are noted for their ability to adapt to the patient's anatomy, potentially 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 development of patient-specific implants. These advancements aim to further enhance the efficacy, safety, and personalized approach of spinal fusion surgeries. This review offers a nuanced understanding of the evolving landscape of cage technology in LIF and provides insights into the current practices and future possibilities in spinal surgery.