A Review of Synthetic Bone Grafts in Lumbar Interbody Fusion

Lumbar interbody fusion is widely performed for degenerative, deformity-related, and instability-associated spinal conditions. Yet, reported outcomes remain variable across grafting strategies and surgical techniques. While advances in instrumentation and cage design improve immediate construct stability, successful arthrodesis depends on early graft behavior within the interbody environment. This includes positional stability, interface contact, and load transfer prior to mature bone formation. Synthetic bone graft substitutes are commonly used to supplement or replace autograft. However, the clinical literature describing these materials is heterogeneous with respect to composition, structural presentation, surgical context, and outcome reporting. This narrative review synthesizes clinical, translational, and biomechanical studies published between 2019 and 2025 that evaluate synthetic bone graft substitutes used in adult lumbar interbody fusion. Rather than comparing individual products or reported fusion rates, grafts are organized by material class and examined through early mechanical events such as graft migration, loss of graft–endplate contact, and cage subsidence. Across recent studies, variability in fusion definitions, imaging modalities, postoperative timepoints, and documentation of early mechanical events limits direct comparison and quantitative synthesis. These findings highlight the need for improved reporting consistency and greater emphasis on engineering-relevant variables in future investigations.