Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
2000-12-04
2002-09-03
Isabella, David J. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C606S064000
Reexamination Certificate
active
06443989
ABSTRACT:
BACKGROUND OF THE INVENTION
The present application is directed to an expandable interbody device which is inserted from a posterior approach between adjacent vertebrae in the spine of a patient and which is also selectively anteriorly expandable.
Fusion cages, as well as other related interbody devices, are frequently utilized in spinal surgery between vertebrae of a patient. In particular, one or a pair of interbody devices are placed between the vertebrae to provide support and promote fusion between vertebrae where such is necessary due to disease, injury, general deterioration or a congenital problem.
Frequently, the anterior sides or fronts of the vertebrae also require additional spacing in comparison to posterior sides to correct curvature of the spine. Therefore, it is often desirable to use an anteriorly expandable interbody device so that the vertebrae are spread or spaced more on the anterior sides thereof than on the posterior sides thereof. It is seldom if ever desirable to space the posterior sides of the vertebrae more than the anterior sides thereof. Interbody devices which provide for anterior greater expansion are generally referred to as interbody expansion devices or expansion fusion cages. They are specifically expandable on the anterior end thereof such that the fronts of the adjacent vertebrae are more greatly spaced than the rears.
It is noted that interbody devices, such as fusion cages, may be inserted into the intervertebral space anteriorly or posteriorly. That is, in some instances the surgery is performed from the front and sometimes from the rear of the patient. The present application is directed to types of devices that are inserted posteriorly or from the rear of the patient and are generally referred to as posterior interbody devices or posterior fusion cages.
Interbody devices typically must be very strong along the entire length of the top and bottom walls of the device that engage the vertebrae. In particular, in the turning and twisting of everyday life, substantial forces can be exerted against the interbody devices and, in particular, against the anterior end thereof. This is even more so when the devices are subjected to unusual forces during an accident or the like. Some types of interbody devices in the prior art have provided for anterior expansion, but have not well supported the anterior end of the upper and lower walls. Such prior art devices have provided some kind of a wedge or rod that is urged rearward along a ramp of the device in such a way as to expand the anterior portion subsequent to it being placed between the vertebrae. Because the wedge moves rearwardly or posteriorly toward the back wall of the device in order to spread the walls, a lever arm of unsupported wall is formed between the front edge of each wall and the position where the wedge engages the walls. Substantial forces can act on this lever arm. The interbody devices poorly supported along the unsupported wall can fail due to forces exerted along the lever arm in the region.
Secondly, it is desirable for the interbody devices to not expand sideways, while the devices are expanding vertically. This need arises because it is often necessary to put interbody devices in close proximity to one another in side by side relationship. Sideways expansion may prevent desirable positioning of the interbody devices and may also interfere with positioning of bone chips for grafting between the interbody devices. Some prior art devices expand radially which expands the devices vertically, but also sideways.
When installing interbody devices, such as fusion cages, a surgeon may also find that it is necessary to have more anterior expansion than was initially anticipated in order to correct spinal curvature. Consequently, it is often desirable to be able to increase the expansion in increments that allow the surgeon to determine whether expansion is sufficient after each incremental advance in expansion and then further increase the expansion, if necessary. Therefore, it is desirable to have a kit that provides for alternative expansion devices, especially where such modular expansion devices can each be screwed into and secured in place in the cage so as to resist inadvertent removal during use.
Interbody devices, such as fusion cages, are quite expensive to produce in general. This is because the body of the devices must be made to very high tolerances in order to provide reproducible results and to provide the strength necessary to support the spine of the person. Because the surgeon is not always certain exactly which expansion size interbody device will be required until the surgery site is opened, it has been necessary for the surgeon to have on hand many different sizes of fusion cages and, in some cases, different types of fusion cages, such as expandable and non-expandable, so as to insure that the necessary item will be present when the surgery is performed.
Consequently, it is also desirable to be able to provide an interbody device that is modular in nature and easily adjusted to many degrees of expansion and that it may be used as efficiently with no expansion as with expansion, so that the same body can be used with different degrees of expansion. Many of the expandable types of prior art fusion cages cannot be used as non-expandable type cages.
Further, it is desirable for a single fusion cage body to be utilized for virtually any degree of expansion desired or foreseeable by simply providing a set of comparatively much less expensive expansion members in a kit, any of which expansion members may be used in conjunction with the body to provide for various and different degrees of expansion and each of which may be removed after insertion into a fusion cage body and replaced with a different expansion member without removing the cage body from between vertebrae.
SUMMARY OF THE INVENTION
A posterior interbody device or fusion cage for use between a pair of adjacent vertebrae in order to provide support and/or promote growth between the vertebrae that have been destabilized due to injury, illness or the like. The interbody device includes a body which may be rectangular in shape in which case the device is slid or driven between the vertebrae or generally cylindrical in shape and often threaded, in which case the device is screwed between the vertebrae. The body has an upper wall and a lower wall that are connected by a rear or posterior wall in a somewhat U-shaped configuration. The body is hinged about the rear wall by utilization of a material of construction that is flexible, such as stainless steel or titanium, so that the rear wall functions like a spring in conjunction with the upper and lower walls, so that the upper and lower walls are able to pivot relative to each other at the rear, when a spreading force is applied to the walls, which causes the anterior ends of the upper and lower walls rotate from an initial non-expanded configuration anteriorly to an expanded configuration anteriorly. In particular, the upper and lower walls are initially in a non-expanded state wherein the upper and lower walls are generally parallel and subsequently may be expanded by a plurality of expansion members to various expanded states wherein the upper and lower walls are at angles relative to each other which angles increase with expansion.
The upper and lower walls also have legs on either side of the anterior end thereof that face toward similarly positioned legs on the other wall and which abut against each other when the device is in the non-expanded configuration thereof, so the cage can be utilized operably in a non-expanded configuration. An aperture is formed between the legs and preferably extends through the body in such a manner as to form an interior chamber suitable for receiving bone chips or other growth promoting media. The body also preferably has upper and lower windows which communicate with the chamber and open onto the surface of the vertebrae, when in use, so as to promote growth of bone through the interbody device. The rear wall of the body inc
Chattopadhyay Urmi
Isabella David J.
McMahon John C.
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