Spinal fusion remains a common surgical treatment for degenerative cervical spine pathology. By eliminating segmental motion, fusion alters spinal biomechanics and redistributes mechanical loads to adjacent levels. These changes contribute to adjacent segment degeneration (ASD). Motion-preserving spinal implants have been developed to address these limitations. Cervical disc arthroplasty (CDA) is the most widely used example. Such devices aim to maintain physiologic kinematics while preserving segmental stability. Their biomechanical behavior varies with implant design, material properties, and constraint characteristics. Previous research does not holistically compare fusion with motion-preserving treatments on the spine, resulting in an incomplete understanding of when motion-preserving devices should be considered in treatment over fusion constructs and which specific motion-preserving implants are most appropriate. This narrative review synthesizes experimental, computational, and clinical studies comparing rigid fusion constructs to motion-preserving technologies in the cervical spine. Emphasis is placed on segmental range of motion, load transmission, intradiscal pressure, facet joint forces, and adjacent-segment mechanics. By comparing effectiveness across motion-preserving treatments, alongside their effectiveness to fusion constructs, we found that CDA more closely preserves near-physiologic motion compared to fusion. Taken together, this review underscores the importance of biomechanics-informed implant design for guiding future innovation in spinal implant technologies.

Finite element analysis is widely used to study spinal biomechanics and to compare surgical strategies under controlled loading conditions. By allowing variation in alignment, fixation, and implant design, these models provide insight into stress redistribution and motion changes that are difficult to isolate experimentally. This review examines spine surgery-focused finite element studies published between 2018 and 2024, with emphasis on interbody fusion techniques, adjacent segment mechanics, and implant-related stress behavior. Across lumbar fusion models, constructs incorporating anterior column support demonstrate lower posterior instrumentation stress than posterior-only approaches, with lateral lumbar interbody techniques showing reduced rod and screw stresses across multiple loading conditions compared with posterior lumbar interbody or posterolateral fusion constructs. In the cervical spine, comparisons of plated and zero-profile anterior cervical discectomy and fusion devices show smaller increases in adjacent-level motion and intradiscal pressure with zero-profile constructs, alongside higher localized stress at fixation interfaces. More recent studies apply finite element methods to implant optimization, alignment planning, and patient-specific modeling. Together, these findings suggest that finite element analysis is increasingly used to support surgical planning and implant design, with continued advances in validation and patient-specific simulation likely to strengthen its clinical relevance.

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.