Background:
Annually, there are approximately 300,000 fusion surgeries performed in the United States. Numerous types of spinal fusion cages exist, varying in design, material, size, and implantation method. Regardless of the type of cage used, a full or partial discectomy is performed prior to implantation. Once the necessary portion of a spinal disc is removed, the disc space is then expanded using a distracter. In order to accept a cage, the disc space must be distracted so that the intervertebral height can be reestablished. Distraction also enhances stability by tensioning the ligamentous apparatus, which increases the compressive forces that hold the cage in place. The amount of disc space distraction is a crucial aspect of the spinal fusion surgery; too little or too much distraction results in various complications that compromise the clinical outcome of the Surgery.
Summary:
The present invention provides an expandable interbody fusion cage that includes an inferior baseplate, a superior baseplate, an insert mounted rotatable between the inferior and superior baseplates, and a guide peg that facilitates the rotation of the insert. Expansion of the cage is achieved by rotating the insert 90° within the inferior and superior baseplates from its initial collapsed position to its final expanded position. Each of the inferior and superior baseplates includes an external surface adapted for interaction with a vertebral body, and an internal portion adapted to house and guide the insert during rotation.
The external surfaces of the inferior and superior baseplates incorporate geometry to match the natural shape and curvature of the vertebral endplate and gain purchase into the endplate to secure the cage in place. The external surface of the superior baseplate is also angled to account for the lordosis of the spine. The internal surfaces of the baseplates incorporate various grooves and curves so as to enclose the insert and prevent unwanted motion during its rotation. The baseplates are designed to interact with each other, being in constant contact once assembled to further guide the expansion and prevent unwanted motion. The guide peg includes a solid axle from which the insert rotates about, interacting with the insert as well as the inferior and superior baseplates. The guide peg fits into a slot formed within the inferior and superior baseplates when the cage is assembled. When the insert is placed into the assembly, it engages the guide peg, ensuring that the insert is centered within the baseplates and stabilized during rotation. The insert drives the expansion of the cage. In an embodiment, the insert is oval in shape and includes dog-eared, angled, flat edges. Such a size and shape allow for the insert's rotation to cause expansion of the cage, as the inserts major axis is longer than its minor axis. The insert is initially placed into the cage with its minor axis vertical, and is then rotated 90° so that its major axis becomes vertical. This rotation forces the two baseplates apart, thus expanding the cage. The insert is guided during the rotation by the guide peg and grooves within the internal surfaces of the inferior and superior baseplates. The insert is secured into its final confirmation by pushing it posteriorly into another groove within the interior surfaces of the baseplates. In its locked position, the insert is prevented from dis-rotating and, thus avoids a col lapse of the cage. In an embodiment, each of the four main components described above are interchangeable, as they may consist of different sizes, shapes, etc., so as to allow for enhanced adjustability of the cage. The superior baseplate is selected to match the lordosis angle of the operated segment, and an insert is selected to achieve the desired final height once the cage is expanded. This adjustability enhances the fit and positioning of the cage.
Benefits:
- The endplate needn’t be vascularized which may delay or impede fusion (Non-threaded cages)
- The strong subchondral bone of the cortical endplate is partially removed, which compromises the endplate's integrity (Threaded cages)
Applications:
- Expandable interbody fusion cages used in spinal fusion procedures.
Full Patent: Expandable Interbody Fusion Cage With Rotational Insert
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