FIELD

The present disclosure relates generally to the field of medical devices, and more specifically to expandable intervertebral implants.

BACKGROUND

The disc space or intervertebral space needs to be stabilized after the core of the disc is removed in a spinal fusion procedure. The emptied disc space is often larger than the size of the access corridor, and thus the fusion implants that are typically used are too small to fill the entire disc space. This may result in long-term instability. Ideally, the fusion implant is large enough in width to fill the disc space and as wide as possible to distribute the high compressive in vivo load over a larger area to avoid subsidence which leads to instability. Furthermore, spinal fusion implants sometimes back out of the disc over time after surgery and this can cause harm to the patient. Therefore it is desired that there is an implant that can collapse to a small size to be inserted through a small access opening in the patient, and then expand both vertically and horizontally to fill up the disc space as much as possible and in effect render a more stable fusion implant long-term as well as one that does not back out because it is expanded larger than the access corridor. Oftentimes, the opening in the disc (called an annulotomy) has the height of the space between the vertebra but has a width that is much smaller than the width of the space inside the disc. The ability to expand horizontally helps to make it more difficult for the implant to back out of the disc. During the horizontal expansion step, the inserter that holds the implant can be pushed towards sensitive anatomical structures such as nerves. There are no implants on the market that can expand horizontally and vertically while maintaining good strength and stability long-term while avoiding instrument shifting during expansion that may impinge on sensitive anatomy like nerves.

Furthermore, because so many different widths and heights are needed for a conventional implant, it is not cost effective to mold because of need develop so many expensive molds. Machining is there for used but is less consistent, reliable and expensive.

Existing spinal fusion implants are either made of a polymer such as Polyether Ether Ketone (PEEK), metal such as titanium, or ceramic such as silicon nitride. Some are made by a combination thereof. Some implants are made of PEEK coated with metal particles such as titanium or silver based due to the belief that the metal coatings are more osteogenic. However, the coatings can slough off from shear during implantation or in vivo and can cause adverse reactions. Also the implant is mostly radiolucent so it is hard to visualize on x-ray the full extent of the implant profile. Some implants are made of all metal or ceramics. These implants have shown improvement in surface fusion but they are both more stiff than bony endplate and can cause stress shielding. The all-metal implants are radiopaque for the most part and makes it hard to visualize bony fusion through the center of cage on post-operative follow up scans. There are implants made of PEEK in the middle with endplates that are slabs of porous metal. These are machined and assembled. Due to the aforementioned problems presented, there is a need for an implant that is expandable in 2 or more directions and with bone like stiffness and highly osteogenic surface interfacing with the endplate. It should also be designed to enable highly repeatable and cost effective fabrication methods.

