Adjustable corpectomy apparatus

A spinal fixation apparatus comprising an upper and lower endplate. Depending distally in a longitudinal direction from the upper endplate is an inner sleeve that fits inside an outer sleeve that depends distally in a longitudinal direction from the lower endplate. The inner sleeve includes grooves located on its outer surface. A finger cage including resilient fingers fits around the outer sleeve. The fingers have ends that include male grooves. The ends of the fingers fit into apertures located in the outer sleeve. The apparatus further includes a locking mechanism that pushes the tips of the fingers through the apertures of the outer sleeve such that they mesh with the grooves of the inner sleeve. When the locking mechanism is unlocked the tips of the fingers disengage from the grooves of the inner sleeve, and the inner sleeve slide axially within the outer cage, adjusting the height of the device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to the field of orthopaedic implants. Specifically, the present invention provides a prosthetic implant to replace spinal vertebra and adjacent intervertebral discs.

The vertebral column serves as the main structural support of the human skeleton. The vertebral column consists of a number of vertebrae separated by intervertebral discs. A vertebra approximates a cylindrical shape, with wing-like projections and a bony arch. The arches create a passageway through which the spinal cord runs. The vertebral column is held upright by fibrous bands of muscle and ligament. There are seven vertebrae in the cervical region, twelve in the thoracic region, five in the lumbar region, and five in the sacral region that are usually fused together. The integrity of the vertebral column is critical to protecting the fragile spinal cord, in addition to its duties in supporting the skeleton.

When a vertebra or intervertebral disc becomes damaged, either through trauma or disease, the spinal cord or nerve roots may be impinged, causing a great deal of pain. This pain can occur almost anywhere in a person's body, from the back or neck to the extremities. In such a case, patients often receive drug treatment in an initial attempt to relieve the pain, but if that is unsuccessful, it may be necessary to remove all or a portion of one or more vertebrae, including the anterior cylindrical body, which is the load-bearing portion of intervertebral discs. When this procedure is undertaken, it necessarily weakens the support structure of the spinal column, and the excised material must be replaced with some load-bearing material. Given the high propensity of spinal discs to degenerate in human beings, the need for an efficient and stable method of spinal fixation is tremendous.

It is possible to replace the excised vertebral bone with a bone graft. The bone graft may be an autograft, normally harvested from the patient's iliac crest, or, alternatively, may be an allograft—tissue obtained from a human donor. Once the bone graft is in place spanning the bony defect, it fuses over time with the remaining healthy vertebrae. Generally, a metal plate and screws are used to secure the bone graft to the natural vertebrae, providing support until the fusion process is complete. However, given that it generally takes between three and six months for bony fusion to occur, a more substantive prosthetic implant is often used to stabilize the spine, often in combination with bone graft that can grow out of the prosthesis and fuse with the adjacent bone over time.

A prosthetic spinal fixation device should accurately replace the height of the excised material, result in acceptable tension levels in the spine, maintain proper curvature of the spine, obtain balance through the spinal segments, and restore normal load-bearing characteristics throughout the spine.

Moreover, a prosthetic spinal fixation device should be easily adjustable to allow the surgeon to quickly select the height of the device during surgery to fit the needs of the patient. The desired height of the device will depend on the amount of bone that is removed from the patient, the size of the patient, as well as the location of the removed bone (i.e. cervical region or lumbar region). In addition, a one-size-fits-all device may reduce manufacturing costs because fewer different parts and/or models will be required to meet the needs of the marketplace.

While prosthetic corpectomy implants are known in the art, a need exists for improved implants that are more easily adjusted to achieve the necessary height to replace the excised bone during the implantation process, while also possessing the biomechanical properties necessary for long-term implantation in the human body and the immediate fixation ability to provide stability to the spinal column.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to an artificial corpectomy prosthesis for replacement of one or more spinal vertebrae. The apparatus is adjustable in height through use of a lockable telescoping finger mechanism that allows a surgeon to choose the appropriate height for the prosthesis when performing the corpectomy procedure. The prosthesis comprises a first endplate and a second endplate; a substantially hollow outer member; a substantially hollow inner member; a fixation device; and a locking mechanism. The sleeves are also referred to herein as cages or substantially open cylinders. Either endplate can accommodate the outer sleeve. All that is required is that one sleeve fits inside the other sleeve in a cylindrical enveloping relationship and that the sleeves are moveable with respect to each other. For the sake of brevity and ease of description herein, the outer sleeve will be described as attaching to the second, or lower endplate. Once implanted, bone graft can be packed within slots inside the components of the device, and inside the inner member such that the bone graft can grow into the body and fuse with healthy bone adjacent the prosthesis.

The first and second endplates serve as the respective ends of the prosthesis, and fit against the healthy vertebrae adjacent to the removed vertebrae and vertebral discs. Each of the first and second endplates includes a first and a second surface.

The first surfaces of each endplate interact with the healthy bone adjacent each end of the prosthesis. One or both endplates may include a feature located on its first surface that encourages and/or facilitates fusion of the prosthesis and the healthy bone. This feature can be in the form of physical protuberances (such as spikes, ridges, keels, knurling, and the like) or chemical or biological treatments such as hydroxyapatite and the like. This improves the fixation characteristics of the prosthesis and lengthens the overall life of the prosthesis. The footprint and angle of the first surface of both the first and second endplates can be varied depending on the location of placement in the spine.

Depending distally in a longitudinal direction from the first endplate is an inner member. The inner member has an outer surface that comprises a number of circumferential grooves. The inner member can also include a number of holes or slots spaced longitudinally or radially along its outer surface.

Depending distally in a longitudinal direction from the second endplate is a substantially hollow outer member. The inside perimeter of the outer member is large enough that the inner member can fit within the hollow defined by the perimeter of the outer member. The outer member includes one or more locking apertures and preferably also includes one or more ingrowth apertures. When the inner member is inserted into the hollow of the outer member, the locking apertures provide access to the grooves present on the outer surface of the inner member.

A finger cage is a hollow body that fits over the outer member. The finger cage includes one or more resilient fingers that are free to bend inwardly or outwardly. The free end of each finger includes one or more tabs. When the finger cage is fitted in place over the outer member, the fingers of the finger cage align with the locking apertures of the outer member such that the tabs of the fingers are inserted through the locking apertures of the outer member and into engagement in the circumferential grooves of the inner member.

A locking mechanism comprises a ring that fits around the fingers of the finger cage. The locking mechanism preferably has two positions—locked and unlocked. When in the locked position, the tabs of the fingers are forced through the locking apertures of the finger cage and mesh with the grooves of the inner member. Which grooves of the inner member the tabs of the fingers engage depends upon how far the inner sleeve is inserted into the outer sleeve. Therefore, when the locking mechanism is in the locked position, the inner member is prevented from sliding axially with respect to the outer member, and the height of the apparatus is thus fixed.

When the locking mechanism is in the unlocked position, the tabs of the fingers are not forced to mesh with the grooves of the inner member, and the inner member is free to slide axially with respect to the outer member. Therefore, when the locking mechanism is in the unlocked position, the height of the apparatus may be adjusted by the surgeon to fit the needs of the individual patient by sliding the inner sleeve axially with respect to outer sleeve. Preferably, the fingers of the finger cage are resiliently biased in an outward direction. In this manner, the apparatus is adjustable at all times until the locking mechanism is moved into a locked position. Therefore, the grooves, the finger cage, and the locking ring comprise a means for selectively altering and fixing the height of the prosthesis.

If it is desired to prevent rotation of the inner member relative to the outer member, it is possible to incorporate a security mechanism between them to be activated after the desired height of the apparatus has been selected. The security mechanism could, as but one example, consist of a key inserted through a slot on the outer mechanism that is aligned with one of the slots or openings of the inner sleeve such that when the key is inserted, the inner sleeve is not free to rotate within the outer sleeve.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

While the present invention will be described more fully hereinafter with reference to the accompanying drawings in which particular embodiments and methods are shown, it is to be understood from the outset that persons of ordinary skill in the art may modify the invention herein described while achieving the functions and results of this invention. Accordingly, the description that follows is to be understood as illustrative and exemplary of specific embodiments within the broad scope of the present invention and not as limiting the scope of the invention. In the following descriptions, like numbers refer to similar features or like elements throughout.

Ideally, an artificial corpectomy prosthetic provides the surgeon with an easy adjustment mechanism that allows the length of the prosthetic to be modified during surgery with a minimum of time and effort to fit the needs of the patient. The prosthetic must allow a significant range of adjustment because the size and number of vertebrae removed will vary from patient to patient.

Referring now toFIG. 1, one embodiment of a prosthetic is shown which includes an adjustable telescoping mechanism that allows the height100of the prosthetic to be expanded or contracted during surgery, and also prevents both accidental compression or expansion of the device once implanted in the patient.

FIG. 1shows an embodiment with a short outer cage30.FIGS. 2 and 7show a second embodiment with a longer outer cage30. Referring now toFIGS. 4,4A, and4B, the apparatus10comprises an inner member20; an outer cage30; a finger cage40; and a lock ring50. In the embodiment shown, the inner member20includes a first endplate21that serves as the uppermost surface of the prosthesis and fits against the healthy vertebra adjacent to the uppermost removed bone. The first endplate21includes an upper surface21aand a lower surface21b. The upper surface21aof the first endplate21may include spikes21c, ridges, or some other protrusion or surface treatment in order to facilitate fusion between the prosthesis and the adjacent bone, thus providing better fixation of the prosthesis and increasing the life of the implant. In other embodiments, the first endplate21also can include an aperture21d, preferably located at or near the center of the first endplate21. In one embodiment, a cupped insert (not shown) is placed in the aperture21d. The purpose of the aperture21d, and the cupped insert, will be explained below.

Referring now toFIG. 7, the outer cage30includes a second endplate31that serves as the lowermost surface of the prosthesis and fits against the healthy vertebra adjacent to the lowermost removed bone. The second endplate31includes a lower surface31aand an upper surface31b. The lower surface31aof the second endplate31may include spikes31c, ridges, or some other protrusion or surface treatment in order to facilitate fusion between the prosthesis and the adjacent bone, thus providing better fixation of the prosthesis and increasing the life of the implant. The second endplate31also can include an aperture (not shown), preferably located at or near the center of the second endplate31.

As can be seen inFIG. 4, the inner member20further comprises a hollow inner sleeve22that depends distally in the longitudinal direction from the lower surface21bof first endplate21. The inner sleeve22has an outer surface22athat includes a number of circumferential grooves23. Preferably, the grooves are separated by thin ridges and are approximately one (1) millimeter wide, though many spacings and numbers are possible. The inner sleeve22further comprises a number of slots24that are spaced longitudinally along the outer surface22aof the inner sleeve22.

Referring again toFIG. 7, the outer cage30further comprises a hollow outer sleeve32depending distally in the longitudinal direction from the upper surface31bof second endplate endplate31. The outer sleeve has an outer surface32aand an inner surface32b. The perimeter of the inner surface32bof outer sleeve32is designed such that the inner sleeve22can fit within the outer sleeve32. When the inner sleeve22is in place within the outer sleeve32, it is free to slide axially relative to the outer sleeve32. The outer sleeve32also includes locking apertures33that allow access to grooves of inner sleeve22when inner sleeve22is in place within the outer sleeve32.

As shown inFIG. 3, the finger cage40includes a ring41that fits over the outer sleeve32and rests on a ledge31fthat is formed at the intersection of the outer sleeve32and the second endplate31. Depending distally in a longitudinal direction from the ring41are one or more fingers42. Preferably, there are a plurality of fingers42. Each of the fingers42has a first end42aand a second end42b. The first end42ais the point of attachment with the ring41. The fingers42are preferably resilient, allowing the second end42bto bend inward under force toward the center of the ring41while maintaining the capability to return to their original position after the force is removed from the finger42. Preferably, the fingers42are resiliently biased outwardly.

Each of the fingers42has a tab43at its second end42b. Each tab43has an interior side43aand an exterior side43b. The interior side43aof each tab43has incrementally spaced male nubs44. Each of the exterior sides43bof tabs43have locking grooves45.

When the ring41of the finger cage40is in place on the ledge31fof the outer cage, the tabs43of the fingers42align with locking apertures33of the outer sleeve32. In resting position, with no force applied to the fingers42, the tabs43are located within the apertures33, but are not forced to engage the circumferential grooves23of the inner sleeve22. However, when inwardly-directed force is applied to the tabs43of fingers42, the tabs43push through the locking apertures33of the outer sleeve32and the male nubs44of tabs43meshingly engage with the grooves23of the inner sleeve22. When the male nubs44of finger cage40engage the grooves23of the inner sleeve22, the inner sleeve22is locked in place within the outer sleeve32, and the height100of the apparatus10is fixed.

To effectuate the locking action, the apparatus10includes a locking ring50(seeFIGS. 5 and 6). The locking ring50fits over the second end42bof fingers42such that it fits within the locking grooves45located on the exterior side43bof tabs43. The locking ring50rotates about the grooves45about the longitudinal axis of the apparatus10. Preferably, the locking ring50is rotatable between two positions—locked and unlocked.

The locking ring50has an interior surface51and an exterior surface52. The interior surface51is in contact with the locking groove45of the tabs43. The interior surface51of locking ring50is cammed such that the thickness of the locking ring50varies over the course of its circumference in a manner allowing the locking ring to be rotated relative to the finger cage40between a first locked position and a second unlocked position. Referring toFIG. 6, when the locking ring is in a first position within the locking groove45of the finger cage40, a thinner portion51aof the locking ring50is in contact with each of the locking grooves45of the exterior side43bof tabs43. In this position, the locking ring does not apply inwardly-directed force to the fingers42. Therefore, the male nubs44of tabs43do not mesh with the grooves23of the inner sleeve22. Conversely, when the locking ring is rotated to a second position, a thicker portion51bof the locking ring50is in contact with each of the locking grooves45of the exterior side43bof tabs43. In the second position, the locking ring50squeezes the resilient fingers42inward, bringing the male nubs44of tabs43into contact with the grooves23of the inner sleeve22. When the locking ring50is in the second, or locked, position, the inner sleeve22cannot slide axially relative to the outer sleeve32. Therefore, the height100of the apparatus10is fixed.

It is also possible to include a secondary locking mechanism, such as a locking screw (not shown), that prevents rotation of the inner sleeve22within the outer sleeve32after the desired height100of the apparatus10is determined and the locking ring50is rotated to the second, or locked, position. In one embodiment, the outer sleeve32may include one or more locking apertures34. Once the locking ring50is rotated to the locked position, the inner sleeve22is rotated within the outer sleeve32such that the locking aperture34of the outer sleeve30is aligned with one of the slots24and can receive a screw in one of the holes therein. In another embodiment, the slots24of the inner sleeve22can align with one or more appurtenances in the inner surface32bso that the appurtenances ride in the slots24and prevent rotation.

In another embodiment, shown inFIG. 2, the ring41of the finger cage40does not rest on a ledge31fformed at the intersection of the second endplate31and the outer sleeve32, but instead on a plateau32cthat is located on the outer surface32aof outer sleeve32(seeFIG. 7). Below the plateau32c, the outer sleeve32extends distally in the longitudinal direction to second endplate31. The same finger cage40and inner member20are used in this embodiment. This embodiment is preferred when it is necessary for the apparatus10to replace a large amount of bone because the elongated outer sleeve32allows for a significantly taller prosthesis with which the components of the shorter apparatus10other than the outer sleeve32, such as the finger cage40and the inner member20, are still compatible.

Preferably, the first and second endplates20,30include bone openings5, allowing bone graft to be packed inside. This allows the bone graft to fuse to the prosthesis, then grow outward into the body after implantation and connect with the healthy bone adjacent to the prosthesis, improving fixation of the device within the body. The outer sleeve40and the inner sleeve50also preferably include openings39to allow more bone graft to be packed inside the hollow of the inner sleeve50such that it can grow out of the slots and fuse with adjacent bone. Further, as mentioned above, the first endplate21includes an aperture21d, while the second endplate31can include an aperture. The aperture21dof the first endplate21and the aperture of the second endplate31, respectively, align with the hollow sections of the inner and outer sleeves22,32, respectively. This allows bone graft to be packed inside the hollow sections of the inner and outer sleeves22,32and grow out of the apertures21d, to fuse with the healthy bone adjacent the apparatus10. Further, cupped inserts (not shown) can be placed within the aperture21dof the first endplate21and the aperture of the second endplate31, respectively. Bone graft can be placed in the cupped inserts, ensuring that bone graft will be in contact with the adjacent healthy bone even if the device is expanded after the bone graft is packed into the hollow sections of the inner and outer sleeves22,32. The cupped inserts are preferably slotted, thus still allowing bone graft to be packed in the hollow sections of the inner and outer sleeves22,32and grow through the cupped inserts to fuse with the healthy bone. Also, although it is not required, it is preferred that the prosthesis be made of titanium alloy, such as Ti-4Al-6Va.

The apparatus10is manufactured of materials that are suitable for implantation in the human body. Many such materials are known presently. In the preferred embodiment, the apparatus10is made of titanium alloy, such as Ti-4Al-6Va.

While there has been described and illustrated particular embodiments of an adjustable corpectomy apparatus, it will be apparent to those skilled in the art that variations and modifications may be possible without deviating from the broad spirit and principle of the present invention, which shall be limited solely by the scope of the claims appended hereto which shall be limited solely by the scope of the claims appended hereto.