Spinal implant adjustment
An adjustable spinal implant 10 is provided for use in connecting elongate members 12 as well as in vertebral spacers such as corpectomy devices, intervertebral fusion devices, and other prostheses. The implant 10 may have fittings 80 on either end comprising fixed 100 or articulating jaws 200, endplates, or other engagement structures. The implant 10 comprises a housing 40 with an internal rotor 60; an extending shaft 20; and a locking collar 70. The extending shaft 20 has an external helical groove 23 that meshes with an internal helical groove 63 on the rotor 20. Length adjustment occurs by transforming axial movement of the extending shaft 20 into a rotary movement of the rotor 60 via helical engagement. The locking collar 70 comprises protrusion 73 engaging grooves 63 of rotor 60, thus providing a simple, positive locking mechanism without requiring the surgeon to apply excessive force to lock the length.
Latest Theken Surgical, LLC Patents:
This patent application is a continuation of the currently pending application bearing Ser. No. 10/550,329, filed on Sep. 22, 2005, which is a national phase application claiming priority from PCT Application Serial No. PCT/US04/008980, filed on Mar. 24, 2004, which claims priority from U.S. Provisional Application Ser. No. 60/457,158, filed on Mar. 24, 2003.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention generally relates to a device for spinal fixation, and in particular to an adjustment device for many types of spinal implants. The device finds particularly suitable applications in spinal fusion devices such as a connector for coupling elongate members (such as spinal rods), plates, and the like, as well as in adjustable vertebral spacers for intervertebral fusion devices, corpectomy devices, and other vertebral prostheses.
2. Background
The spinal column is a complex system of bones in stacked relation held upright by fibrous bands called ligaments and contractile elements called muscles. This column is critical for protecting the delicate spinal cord and nerves and for providing structural support for the entire body. There are seven bones in the neck (cervical) region, twelve bones in the chest (thoracic) region, and five bones in the low back (lumbar) region. There are also five bones in the pelvic (sacral) region which are normally fused together and form the back part of the pelvis. Each vertebra has a roughly cylindrical body with wing-like projections and a bony arch. The arches, which are positioned next to one another, create a tunnel-like space which houses the spinal cord. The anterior cylindrical bodies of the vertebrae, which are spaced apart by intervertebral discs, bear most of the compressive load of the spinal column. The spinal column is also flexible and is capable of a high degree of curvature and twist through a wide range of motion.
It is often necessary to surgically treat spinal disorders, such as scoliosis, as well as to surgically correct spinal problems such as those that occur due to trauma, developmental irregularities, or disease. Numerous systems are known for use in spinal correction and fixation, depending on the type of problem sought to be solved.
Spinal fusion (arthrodesis) devices attempt to restore stability to the spine by fusion in the problem area. These systems generally employ spinal instrumentation having connective structures such as one or more plates or rods that are placed on portions of the spinal column near the area intended to be fused. These systems usually include attachment devices including, but not limited to, pedicle screws, transverse process hooks, sublaminar hooks, pedicle hooks, and other similar devices. Rod systems, of which there are several, are frequently used in spine stabilization. Typically, the rods are utilized in pairs longitudinally along the length of the spinal column. For the sake of simplicity, the term “rod” will be used throughout to refer to any elongate or longitudinal member.
It is known that the strength and stability of a dual rod assembly can be increased by coupling the two rods with a cross-brace or connector that extends substantially perpendicular to the longitudinal axes of the rods across the spine. The simplest situation in which a connector could be used occurs when the two rods are geometrically aligned. Specifically, the two rods are parallel to each other, that is, there is no rod convergence or divergence in the medial-lateral direction. Stated alternatively, the two rods have the same orientation with respect to the coronal plane (viewed in the anterior-posterior direction); or, the rods are coplanar from a lateral view; and the two rods are located a uniform distance from each other.
In reality, spinal rods are rarely geometrically aligned in the above-mentioned simplest situation. The actual variations of geometrical alignment must be accommodated in some fashion. One way to accommodate actual arrangement is for one or both of the rods to be bent to accommodate the connector. However, any bending in either of the rods can adversely affect the fixation to the spine and compromise clinical outcome. Furthermore, the bending can adversely affect the mechanical properties of the rods, not to mention the fact that bending is both difficult and time-consuming for the surgeon. The connector can also be bent so that the disturbance to the rod positioning is minimized. Unfortunately, this too can cause the mechanical properties of the connector to be compromised.
To remedy these concerns, connectors with some adjustability have been designed to adapt for variations from the simplest geometrical alignment. One major problem with current devices is that those that do provide some form of length adjustability utilize inferior locking designs. Some utilize a slideable member with a pin anchor. Others use a slideable member with a compression style lock. The former style is cumbersome and runs the risk of pin-removal. The latter style is cumbersome and provides inadequate locking strength. In fact, most require the surgeon to impart a large amount of force on the construct in order to engage the lock. Despite engagement of these locking devices, none of these types of locking devices has been shown to adequately positively lock the length.
Another major problem with the current devices is that the method of locking the rod to the connector is inefficient or inadequate. Many current devices utilize threaded set screws that engage an exterior surface of the rod. Threading the set screw into the set screw opening applies a compressive force on the rod, which is supposed to secure the rod. Several problems exist with these threaded connections, including cross-threading, loosening over time, and the structural deformities imposed on the surface of the rod that is contacted by the set screw. Another current device uses a clamp body having opposable arms and utilizes a cam lug to force the arms closed in a scissors-like action to compressively load the rod. Yet another device utilizes a yoke-like clamping body disposed in a through-bore having resilient sidewalls that provide a wedging effect on the rod upon tightening of a locking screw in the through-bore. None of these devices, however, provide the simple, secure locking fit desired to positively retain a rod in situ long term.
An additional problem with these types of devices is that they are typically multi-piece systems that can be difficult to assemble and use in the surgical environment. And, even those that are one-piece designs do not allow for adjustments to compensate for all three modes in which there may be variation from geometrical alignment: convergence or divergence in the medial-lateral plane, non-coplanar rods, and variability in rod separation distances. For example, U.S. Pat. No. 5,947,966 discloses a device for linking adjacent spinal rods. In one embodiment, the device includes two members that are movable with respect to one another to accommodate different rod separation distances. A pin on one member engages a groove on the other member to provisionally couple the two members, thereby preventing a surgeon from separating the two members. Because the pin is sized to exactly fit the groove, no movement of the pin transverse to the longitudinal axis of the groove is possible. As a result, the device disclosed in the '966 patent cannot accommodate non-coplanar rods or adjust for rod convergence or divergence.
In some spinal surgeries, different types of devices are used to maintain the normal spacing between vertebrae, as well as to alleviate compression of the spinal cord. These devices are known as corpectomy devices and are typically inserted into a cavity created when all or a portion of one or more vertebrae are removed. One example of corpectomy devices are hollow mesh cages filled with bone chips or marrow, or even artificial bone material. Limitations of most present-day intervertebral implants are significant and revolve largely around the marked variation in disc space shape and height that results from either biologic variability or pathologic change. For example, if a disc space is 20 mm in height, a cylindrical implant bridging this gap requires a minimum height of 20 mm just to contact the end plate of the vertebral bone. Generally, end plate disruption must occur to allow a generous bony union, meaning that an additional 2-3 mm must be added on each end, resulting in a final implant size of 24-26 mm. During implantation from an anterior approach, excessive retraction is often required on the great blood vessels which significantly enhances the risk of devastating complications such as vascular tears or thrombosis. On the other hand, during a posterior approach, large implants may require excessive traction on neural elements for adequate placement, even if all posterior bony elements are removed. In some instances, an adequate implant size cannot be inserted posteriorly, particularly if there is a significant degree of ligamentous laxity requiring higher degrees of distraction to obtain stability by tightening the annular ligamentous tension band. Compromising on implant size risks sub-optimal stability or a loose implant, which has a greater chance for migration within or expulsion from the disc space. The alternative of excessively retracting neural elements to facilitate a posterior implant application results in a neuropraxia at best and permanent neural damage at worst.
Thus the need exists for an adjustable corpectomy that is simple to use in clinical procedures and that adequately and effectively spans the distance between vertebral bodies, is easily adjustable to account for space variability, and provides a secure lock once the desired dimension is achieved. Additionally, the need exists for an improved connector for spinal rods that can allow adjustability in all geometrical arrangements; that can provide quick and secure locking of the rod; and that provides a simple, positive locking length-adjusting mechanism that does not rely on compression fit or pin locking mechanisms.
BRIEF SUMMARY OF THE INVENTIONThe present invention generally relates to devices for spinal fixation, and in particular to adjustable devices for use as connectors for coupling spinal rods or other elongate members; as well as for use as corpectomy devices and the like. Various embodiments are discussed, with the primary invention being utilized in different types of implants. As used herein, the general term “connector” shall refer to the device in its many embodiments, regardless whether the device is being used to connect elongate members (as in spinal rod systems) or to span the distance between two vertebral bodies (as in corpectomy devices). The connector generally comprises a two-piece body having an extending shaft and a housing; a rotor; and a locking collar. The terminal ends of each connector may be fitted with a fixed rod-receiving jaw, an articulating rod-receiving jaw, or simply with endplates or other structures of various designs having bone receiving surfaces thereon.
In a first embodiment the extending shaft has an external surface containing thereon a helical profile. The rotor likewise has an internal surface containing thereon one or more helical surfaces that correspond to the external surface of the extending shaft. The internal helical surface of the rotor is placed in intimate contact with the external helical surface of an extending shaft, thus providing a means for adjusting the length. This intimate contact couples the rotor to the extending shaft such that translational movement of the extending shaft results in rotation of the rotor, and vice versa. Similarly, preventing movement of either the extending shaft or the rotor automatically prevents movement of the other.
The rotor is a substantially cylindrical body that has axial grooves disposed about its circumference. The locking collar is also a substantially cylindrical member having at least one protrusion disposed radially on the internal surface thereof. When the extending shaft is translated into or out of the body, the helical surface causes the rotor to spin inside the housing. When the desired length of the connector is achieved, the locking collar is moved from its unlocked position to its locked position, wherein the at least one protrusion engages the grooves on the rotor's circumference. Once a protrusion is inside a groove, rotational movement of the rotor is prevented, which thereby prevents axial movement of the extending shaft. This provides a means to selectively provide a positive lock for the extending shaft (and therefore for the length of the connector) without the need for a compression fit and without requiring the surgeon to impart large forces onto the construct.
In another aspect of the invention, a unique locking cam is provided at each jaw to secure a rod to the connector. The locking cam generally comprises a substantially cylindrical body having an engaging end and a driving end. The engaging end has a combination concave surface having differing curvatures disposed about its circumference, or simply having curvatures disposed at different points on the surface. The driving end has a cavity to receive a driving instrument and an appurtenant stop disposed at a location along its perimeter. The jaw comprises an opening to receive the locking cam therein. The opening is preferably substantially cylindrical having a discontinuity disposed out of phase with the appurtenant stop. Upon insertion of the cam into the opening, the driving instrument turns the cam the desired amount (preferably 180 degrees). This turning rotates the engaging end about the cam's axis of rotation, which brings the cam into tighter engagement with the rod as the combination curvatures rotate into engagement with the outer surface of the rod. Once the cam is fully turned, the stop engages the discontinuity, which visually and tacitly informs the surgeon that the cam is locked.
In another aspect of the invention, an articulating jaw is provided. The articulating jaw itself comprises a jaw with a locking cam on one end and a ball-shaped protrusion on the other end. The terminal end of the connector comprises a substantially cylindrical member having an axial opening therein and comprising axial fingers for receiving the ball of an articulating jaw. The axial fingers are deflectable inwardly by a locking collar. The locking collar is disposed about the external surface of the fingers and is slideable between a first unlocked position and a second locked position. In the second position, the articulating jaw locking collar imparts a radial compressive force on the surface of the ball, thereby locking it into position. This can be achieved in various ways, including shaping the external surface of the fingers with an increasing diameter toward the distal ends thereof, such that as the articulating jaw locking collar moves distally, it rides along the increasing diameter, thus forcing the internal surface into compressive contact with the ball. Additionally the articulating locking collar itself may be fitted with an inner surface that has an increasing diameter in the locked direction. Many other structural combinations are possible to achieve this effect, the end result being to lock the ball in a given orientation. The articulating jaw can therefore assume any number of angles to better facilitate the rod.
The articulating jaw therefore forms a ball and socket joint that enables movement to allow the connector to join rods that are not parallel. Alternatively, the ball-shaped protrusion may be fitted on the body of the connector and the jaw may have the corresponding socket to provide the ball and socket union.
In another aspect of the invention, a fixed length connector is provided. The connector comprises a solid shaft with jaws on either end. The shaft is made from titanium or any material suitable for implantation. The jaws may be of the fixed or articulating variety as described.
In another embodiment of the invention the jaws comprise endplates or other structures to be used to engage vertebral bodies or other bony structures. The endplates can be fixed or variable to allow for better anatomical fit.
Alternative embodiments are also depicted utilizing pre-bent connectors; connectors utilizing multiple articulating jaws; connectors using grooved extending shafts; connectors using helical ratcheting shafts; connectors using a taper lock; and connectors utilizing a pivoting body.
BRIEF DESCRIPTION OF THE DRAWINGSThe teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which:
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. As stated before, the invention is usable in a variety of medical applications and indeed is not limited to spinal applications. The invention will be denoted as connector 10, it being understood that a variety of implant locations are possible. For ease of understanding, however, since spinal applications currently see great benefit from the invention, the following description is made with reference to spinal applications.
The second portion 42 preferably has a generally stepped cylindrical shape with a proximal end 46 having a first outer surface 48 and a distal end 47 having a second outer surface 49, wherein the second outer surface 49 has a diameter greater than that of the first outer surface 48. One or more slots 50 are formed in the first and second outer surfaces 48, 49. A ramping surface 51 provides a transition between the first outer surface 48 and the second outer surface 49. A lip 52 preferably is provided at the distal end of the ramping surface 51.
Referring to
Referring to
With continuing reference to
Referring now to
Referring to
Referring now to
While there has been described and illustrated particular embodiments of a novel adjustable implant device, 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.
Claims
1. An adjustable corpectomy implant comprising:
- a shaft having a proximal end and a distal end and having at least one helical profile on an external surface thereof;
- a housing having a proximal end with a first axial opening therein and a distal end and an inner surface and an outer surface, wherein said first axial opening receives therewithin said proximal end of said shaft;
- a first endplate attached to said distal end of said shaft for engaging a first vertebral body;
- a second endplate attached to said distal end of said housing for engaging a second vertebral body;
- a rotor disposed within said first axial opening having an inner surface and an outer surface, wherein said inner surface has a profile that matingly engages said at least one helical profile on said external surface of said shaft, wherein said rotor spins about a cylindrical axis in response to axial movement imparted to said shaft within said housing; and
- a locking collar engageable with said rotor, wherein said locking collar is moveable from a first, unlocked position wherein said rotor is free to rotate about said cylindrical axis to a second, locked position wherein said rotor is prevented from rotating about said cylindrical axis.
2. The adjustable corpectomy implant of claim 1 wherein said rotor further comprises grooves on said outer surface.
3. The adjustable corpectomy implant of claim 2 wherein said locking collar further comprises at least one protrusion directed radially inwardly for engagement with said grooves of said outer surface of said rotor.
4. The adjustable corpectomy implant of claim 3 wherein said first endplate is fixedly attached to said distal end of said shaft.
5. The adjustable corpectomy implant of claim 4 wherein said second endplate is fixedly attached to said distal end of said housing.
6. The adjustable corpectomy implant of claim 4 wherein said second endplate is articulatably attached to said distal end of said housing.
7. The adjustable corpectomy implant of claim 3 wherein said first endplate is articulatably attached to said distal end of said shaft.
8. The adjustable corpectomy implant of claim 7 wherein said second endplate is fixedly attached to said distal end of said housing.
9. The adjustable corpectomy implant of claim 7 wherein said second endplate is articulatably attached to said distal end of said housing.
10. A bi-directional adjustable corpectomy implant comprising:
- a shaft having a first end and a second end and having at least one helical profile disposed on an outer surface thereof,
- a housing having a first end for receiving said first end of said shaft in an axial relationship and also having a second end;
- a first endplate attached to said second end of said shaft for engaging a first vertebral body;
- a second endplate attached to said second end of said housing for engaging a second vertebral body;
- an annular rotor disposed within said housing having a cylindrical axis and an outer surface and an inner surface, wherein said inner surface has a profile that intimately engages said at least one helical profile of said shaft;
- a locking collar coupled to said housing and moveable from a first position wherein said rotor is free to spin about its cylindrical axis, to a second position wherein said rotor is prevented from spinning about its cylindrical axis;
- wherein when said locking collar is in said first position said at least one helical profile on said shaft and said profile of said rotor provide bi-directional adjustability for said implant, said shaft being freely extendable within said housing in response to an applied tension force on said first and second endplates, and said shaft being freely retractable within said housing in response to an applied compression force on said first and second endplates.
11. The bi-directional adjustable corpectomy implant of claim 10 wherein said outer surface of said annular rotor further comprises grooves.
12. The bi-directional adjustable corpectomy implant of claim 11 wherein said locking collar further comprises at least one protrusion directed radially inwardly for engagement with said outer surface of said rotor.
13. The bi-directional adjustable corpectomy implant of claim 12 wherein said first endplate is fixedly attached to said distal end of said shaft.
14. The bi-directional adjustable corpectomy implant of claim 13 wherein said second endplate is fixedly attached to said distal end of said housing.
15. The bi-directional adjustable corpectomy implant of claim 13 wherein said second endplate is articulatably attached to said distal end of said housing.
16. The bi-directional adjustable corpectomy implant of claim 12 wherein said first endplate is articulatably attached to said distal end of said shaft.
17. The bi-directional adjustable corpectomy implant of claim 16 wherein said second endplate is fixedly attached to said distal end of said housing.
18. The bi-directional adjustable corpectomy implant of claim 16 wherein said second endplate is articulatably attached to said distal end of said housing.
19. An adjustable length corpectomy implant comprising:
- a corpectomy cage having a first end and a second end;
- a first endplate attached to said first end of said cage;
- a second endplate attached to said second end of said cage;
- a means for providing bidirectional length adjustment responsive to tension or compression on said first and second endplates, respectively; and
- a means for selectively fixing a length of said implant.
20. The adjustable length corpectomy implant of claim 19 wherein said means for providing bi-directional length adjustment responsive to tension or compression on said first and second endplates further comprises a shaft having at least one helical profile disposed on an outer surface thereof coupled with complementary surface profile on an inner surface of said corpectomy cage.
21. The adjustable length corpectomy implant of claim 20 wherein said means for selectively fixing a length of said implant further comprises a rotor within said corpectomy cage having an internal surface that mates with said at least one helical profile, and an external surface having grooves for receiving a projection from a locking collar coupled to said corpectomy cage.
22. A bi-directionally length adjustable corpectomy implant comprising:
- a corpectomy cage having a first end and a second end;
- a first endplate attached to said first end of said cage;
- a second endplate attached to said second end of said cage;
- a means for adjusting a length of said implant responsive to tension or compression on said first and second endplates, respectively; and
- a means for selectively preventing length adjustability.
23. The bi-directionally length adjustable corpectomy implant of claim 22 wherein said means for adjusting a length of said implant responsive to tension or compression on said first and second endplates further comprises a shaft having a helical external profile and a rotor within said corpectomy cage having a mating internal helical profile.
24. The bi-directionally length adjustable corpectomy implant of claim 23 wherein said means for selectively preventing length adjustability further comprises external surface contours on said annular rotor for receiving a protrusion from a locking collar coupled to said corpectomy cage.
Type: Application
Filed: Jan 6, 2006
Publication Date: Aug 31, 2006
Applicant: Theken Surgical, LLC (Akron, OH)
Inventors: Richard Mueller (Macedonia, OH), Andrew Budd (Uniontown, OH), Marc Silski (Hartville, OH)
Application Number: 11/327,621
International Classification: A61F 2/30 (20060101); A61B 17/56 (20060101);