Expanded Spinal Fusion Cage With Synchronous Two-Way Expansion

The patent applies nesting by placing the middle sliding block inside the outer frame, and the outer sliding blocks inside the outer frame as well. The curved surface elements are nested within the structure before deployment. This nested configuration allows the implant to occupy minimal volume during storage and transport while enabling significant expansion during surgery, directly resolving the contradiction between adaptability and pre-expansion volume.

The patent transitions from one-dimensional telescopic expansion (conventional rod mechanism) to two-dimensional expansion by introducing the middle sliding block that simultaneously moves two outer sliding blocks in opposite directions along the outer frame. This dimensional change enables greater adjustable elongation without proportionally increasing the pre-expansion volume, as the expansion occurs along multiple axes rather than a single linear path.

The patent segments the expansion mechanism into three comparable-sized components: the outer frame, the middle sliding block, and the two outer sliding blocks. Each component has a similar diameter and occupies a comparable spatial footprint, eliminating the large size difference between the rod and main body in conventional designs. This segmentation maintains structural support through the distributed framework while enabling effective bone fusion by providing uniform surfaces for bone contact across all components.

The patent applies local quality by designing each sliding block and frame section with specific functional surfaces optimized for their local role. The outer frame provides structural support with its rigid framework, while the sliding blocks provide smooth expansion surfaces. The curved surface elements provide localized contact areas for vertebral body engagement. This distribution of specialized qualities across comparably-sized components maintains overall strength while enabling effective bone fusion at each local interface.

The patent introduces asymmetry in the expansion mechanism by having the middle sliding block differentially engage the two outer sliding blocks. The middle sliding block has asymmetric features that allow it to push the outer sliding blocks apart while maintaining differential adjustment capability. This asymmetric design enables length adjustment while the curved surface elements and vertebral arch screws provide symmetric stabilization, achieving both adaptability and support stability through complementary asymmetric and symmetric features.

The patent applies preliminary action by pre-configuring the outer frame with guide rails and the sliding blocks with matching engagement features before the expansion operation. The curved surface elements are pre-positioned to engage the vertebral bodies, and the vertebral arch screws are pre-configured for stabilization. This preliminary preparation ensures that when expansion occurs, the components immediately provide stable support rather than requiring post-expansion adjustment, thus maintaining both adaptability and stability.