US 7309340 B2
A bone plating system invention is shown comprising a bone plate and bone fasteners. The bone plate has a top portion, a bottom portion, and an interior middle portion. The fastener-retaining passageway extends through the plate. The fastener-retaining passageway comprises an upper portion having an inwardly projecting capture lip. The capture lip has a first diameter. The fastener-retaining passageway also has a middle undercut portion that has a second diameter. The second diameter is larger than the first diameter. The plate also has at least one access channel extending through the capture lip so as to communicate with the interior middle portion of the plate. The fastener comprises a shaft, a fastener engager means extending from, disposed on or coupled with the shaft for engaging bone and a head mounted on the shaft having a radially elastic member.
1. A bone plating system comprising:
a bone plate having a top portion, a bottom portion, and an interior middle portion extending therebetween, the interior middle portion bounding a fastener-retaining passageway extending between the top portion and the bottom portion, the fastener-retaining passageway comprising:
an upper portion having an inwardly projecting capture lip formed thereat, the capture lip having a first diameter;
a lower undercut portion with a cross sectional shape perpendicular to an axis of the passageway, the cross sectional shape having a second diameter at a circular periphery thereof that is larger than the first diameter; and
at least one access channel extending through the capture lip, said at least one access channel intersecting a circular periphery of the capture lip so as to communicate with the lower portion; and
a fastener comprising:
a fastener engager extending from, disposed on or coupled with the shaft for engaging bone; and
a head mounted on the shaft, the head having a radially elastic member.
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a peripheral groove at least partially encircling the head or the shaft; and
wherein the radially elastic member comprises a retention ring at least partially disposed within the peripheral groove, the retention ring being resiliently movable between a constricted state and a free state.
5. A bone plating system as in
a fastener head fabricated from a highly elastic material allowing the fastener head to be resiliently movable between a radially constricted state and a free state.
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8. A bone plating system as in
a plurality of radially elastic wedge shaped slices spaced radially about the head, the wedge shaped slices being resiliently movable between a constricted state and a free state.
9. A bone plating system as in
10. A bone plating system comprising:
a bone plate having a top, a bottom, and an interior portion bounding a retaining passageway extending therebetween, the retaining passageway comprising:
an upper portion having an inwardly projecting capture lip formed thereat, the capture lip having a first diameter;
a middle portion having a second diameter that is larger than the first diameter; and
a plurality of spaced apart access channels extending through the capture lip so as to communicate with the middle portion;
a fastener having peripheral groove at least partially encircling the fastener;
a retention ring at least partially disposed within the peripheral groove, the retention ring being resiliently movable between a constricted state and a free state, the fastener being configured to pass through the passageway of the bone plate so that the retention ring is disposed within the passageway;
a removal tool comprising a plurality of spaced apart prongs, the prongs being configured to be selectively received within the plurality of spaced apart access channels so as to radially inwardly constrict the retention ring when the retention ring is disposed within the passageway of the bone plate.
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1. The Field of the Invention
The present invention relates to the design and method of use of a bone plate and fastener implant and instrumentation system for stabilizing multiple bone segments. In one embodiment of this invention the system aligns and maintains adjacent human cervical vertebrae in a selected spatial relationship during spinal fusion of the cervical spine from the anterior aspect of the vertebrae.
2. Related Technology
The use of fixation plates and fastener systems for the treatment of spinal disorders for fusion of vertebrae has progressed considerably over the past twenty years. These systems usually include bone fasteners and plate systems that stabilize bone segments. The fasteners typically have a head, a shaft and threads that engage with the bone. The bone fasteners are placed by delivery mechanisms into corresponding openings in the plates and then into the bone itself. The fasteners are then firmly tightened to secure the plate to the bone.
A common problem associated with the use of such fixation plates is the tendency of the bone fasteners to back out of the plate under the dynamics of human movement. As a result of backout, bone fasteners may loosen and eventually disengage from the bone plate resulting in poor fixation. Potentially, this loosening of the bone fastener at the bone plate interface may cause the fastener to ultimately work itself out of both the plate and the bone from which it was implanted. This problem is particularly of concern in areas such as the spine where a loose fastener may impinge or interfere with sensitive tissues and bone structures.
Designers of such bone fixation systems have employed various techniques and developed different backout-preventing mechanism in an attempt to overcome the problem of fastener backout. These systems include secondary backout-preventing mechanisms and passive backout-preventing mechanisms. In secondary backout-preventing mechanisms, the bone fastener is first affixed into the bone through an opening in a bone plate. Once the fastener is in place, the secondary backout-preventing mechanism is then activated to secure the fastener to the plate. These secondary backout-preventing mechanisms comprise devices that are activated independently from the mechanism used to place the fastener. These mechanisms include secondary locking screws, locking collars, deformable tabs or other secondary locking devices that hold the bone fasteners in place after deployment within the plate and bone. The secondary backout-preventing mechanisms are typically independently activated in such ways that the mechanism limits the movement of the head of the bone fastener with the plate. This results in the fasteners being restrained by both the plate and the bone, thus lessening the likelihood of fastener backout.
For example, some designs found in the related art disclose an anterior cervical plating system incorporating an independent locking screw that engages the head of a bone fastener to secure the cervical plate to the vertebra. The locking screw, positioned above the bone fastener after the bone fastener is placed, provides a rigid fixation of the fasteners to the plate.
Other examples of designs found in the related art of secondary backout-preventing mechanisms include a threaded screw nut for use with a bone fixation system wherein the screw nut is partially insertable into an opening of the fixation plate, from the plate underside, and engages a portion of the bone fastener to thereby secure the bone fastener to the fixation plate after the fastener has been independently placed.
Further examples of designs for secondary backout-preventing mechanisms found in the related art disclose a bone fixation system wherein the head of the bone fastener is hollow and expandable. After the fixation plate is secured to the underlying bone by the hollow head bone fastener, a setscrew is then advanced into the hollow head of the fastener to radially expand the head and thereby secure the head to the fixation plate.
The successful use of such secondary backout-preventing mechanisms in the anterior cervical spine is particularly difficult because of the limited operating space available to the surgeon due to anatomic constraints. The above discussed secondary backout-preventing mechanisms require instrumentation to enter the surgical site and activate the backout-preventing mechanism. The instrumentation needed to activate these secondary backout-preventing mechanisms occupies space in the surgical site. In addition, the implementation of these mechanisms can be technically demanding and time consuming. To address the issues related to the limited space available for tools to activate secondary backout-preventing mechanisms and ease of use of the system, fastener and plate systems have been developed that incorporate passive backout-preventing mechanisms. These passive backout-preventing mechanisms are easier to activate since they typically deploy automatically while the surgeon drives the fastener into the opening in the plate and into the bone segment. Usually, no additional steps are required to fix the fastener to the plate. These systems include designs that lock the fastener to the plate by-either passively overcoming interference between the fastener and the plate or activating a passive spring like mechanism in the plate that locks the fastener to the plate.
For example, a bone fixation system wherein the head of the bone fastener is frustoconical in shape and has a directionally corrugated outer surface, is found in the related art. Wherein each opening in the fixation plate has a complementarily corrugated inner surface and is similarly frustoconical in shape. As the fastener is advanced through the corrugated openings and into the underlying bone, the direction of corrugation in the head and in the plate opening permits the head to be received within the corresponding opening, while inhibiting rotation of the fastener in an opposite direction.
Other passive mechanisms that are designed to prevent backout include a system in which a split ring is pre-mounted and attached to the plate. The split ring in the plate that retains the fastener to the plate by engaging the split ring with a groove in the fastener head, or the top of the fastener head. As the groove or the top of the fastener head aligns with the split ring, the split ring expands then snaps into the groove or over the top of the fastener, preventing the fastener from backing out.
Due to the potentially high loads between the plates and the fasteners, the backout-preventing mechanism retaining force need be maximized. While the above described passive backout-preventing mechanisms found in the related art can restrain the fastener to the plate and limit backout, the force required to overcome these mechanisms is typically small, within the magnitude similar to the force needed to drive the fastener into the backout-preventing mechanism. This is because the backout-preventing mechanisms are deformed by the fasteners as the fasteners are driven into the openings in the plate and deformed again in the reverse direction when the fasteners are removed from the openings in the plate. Thus, the force required to remove the fastener from the plate is similar to the force initially used to insert the fastener. Unfortunately, the backout force that the passive backout-preventing mechanisms are capable of restraining may be less than is clinically required for specific high load conditions.
It is desirable to have bone plating systems that accomplish one or more or a combination of the following features: a system allowing for easy fastener deployment while eliminating backout, retaining structural integrity, allowing fastener angulations, and improving the surgeon feedback when the fastener is deployed in the plate.
One embodiment of the invention is an assembly comprised of a plate and fasteners sized to secure bone fragments. The plate has retaining passageways into which the fasteners pass. The assembly has a passive backout-preventing mechanism incorporated into the fastener that engages with the retaining passageway in the plate. This causes the fastener to be restrained by the retaining passageway. A secondary unloading mechanism is used to deactivate the backout-preventing mechanism allowing removal of the fastener from the plate.
The fastener has a radially elastic compressible member on its head. This radially elastic compressible member becomes smaller in diameter as it is compressed radially, and larger in diameter as its radial compression is relaxed. The plate has a chamfer on the top surface of the retaining passageway to facilitate compression of the radially elastic compressible member as the fastener enters the plate.
Retaining passageways are positioned through the plate in orientations that address specific orthopedic disorders. The functional diameter of the retaining passageway changes from the top of the plate to the bottom of the plate. Near the top of the plate, the functional diameter of the retianing opening is smaller than the uncompressed or relaxed diameter of the fastener head. In the middle portion of the plate, the functional diameter of the retaining passageway transitions to an undercut that is larger than the functional diameter of the retaining passageway near the top of the plate. This provides an area for the head to expand into. Near the bottom of the plate, the functional diameter of the retaining passageway is smaller than that of the functional diameter of the undercut in the middle portion of the plate. This prevents the head of the fastener from passing through the bottom of the plate.
As the radially elastic compressible fastener head is driven into the opening, it is radially compressed by the chamfer on the top portion of the retaining passageway to a diameter small enough to clear the top of the opening. Because the fastener head is radially elastic- and compressible, it is designed to elastically decompress and expand radially once it is placed in the undercut. When the fastener head is positioned in the undercut portion of the retaining passageway, it expands and its movement is restricted by the geometry of the undercut.
In a second embodiment, the fastener head has an incorporated retaining ring on its periphery that acts as the radially elastic compressible member. The retaining ring is incorporated into the fastener head and is positioned on the fastener in a circumferential groove that is also incorporated into the fastener head. The retaining ring is radially compressed as the fastener is driven into the opening in the plate. Once the retaining ring enters the undercut of the opening in the plate, it partially relaxes expanding and catching the underside of the undercut. This restrains the fastener from backing out of the plate.
To remove the fastener from the plate, the retaining ring is radially compressed, by an independent, secondary removal tool, to a smaller diameter size that allows the fastener head to clear the functional diameter of the retaining passageway near the top of the plate. As the retaining ring is compressed, the fastener is removed from the retaining passageway in the plate. The plate has access channels positioned around the periphery of the retaining passageways to facilitate the use of a tool used to remove the restrained fasteners and to facilitate visualization of the locked retaining ring so that the surgeon has visual feedback indicating that the mechanism is activated. These access channels allow space for prongs on the distal end of the removal tool to enter through the top of the plate and engage with the fastener head and radially compress the retaining member while the retaining ring is still positioned in the undercut of the middle portion of the plate.
In one alternate embodiment of the plate and fastener system, the circumferential groove on the periphery of the fastener head is substantially greater in height than the height of the retaining ring. This allows for a variable angle fastener in which the fastener head is retained from backout by the undercut in the retaining passageway, but is still able to toggle due to the clearance between the retaining ring height and height of the groove on the fastener head. This is to facilitate fastener angulation or toggle relative to the plate for variable angle fasteners. The variable angle fasteners also have variable angular position by having a shaft outside diameter that is smaller than functional diameter of the opening near the bottom of the plate. However to limit the load on the retaining ring, the shaft impinges the opening near the bottom of the plate before the retaining ring contacts the top of the undercut in the plate.
In a further embodiment of the plate and fastener system, the circumferential groove on the periphery of the fastener head is closer to the height of the retaining ring than it is in the previously described first fastener embodiment. This allows for fasteners that are more fixed in angulation. The fastener toggles less due to the lessened clearance between the retaining ring height and height of the circumferential groove on the fastener head. The fixed fasteners also maintain angular position by having a shaft outside diameter that closely matches the functional diameter of the opening near the bottom of the plate.
Thus, the type of fastener fixation, fixed or variable angled, can be determined by differences in the diameter of the shaft and the groove in the fastener head, and not differences in the diameters of the plate passageway design. All of the retaining passageways in the plate are similar and can potentially facilitate either a fixed fastener or a variable angle fastener with the only functional difference between the two types of fasteners being the geometry of the head and the shaft. Depending on the clinical situation, the surgeon can determine if a fixed or a variable fastener is required after the plate has been placed, and use the design of fastener that is most clinically appropriate.
As shown by example in
As also shown in the embodiment in
The plate 100 has a plate bottom 160 that is configured to approximate the surface of the bone that is being stabilized. The plate bottom 160 is typically concave in both its long axis and short axis. However, for bone fixation applications involving complex bone morphology, such as stabilization of pelvis fractures or skull bone fractures, the plate bottom 160 may be concave in one axis and convex in the other, or convex in both the long axis and the short axis, or twisted in either axis, or formed into any complex surface required for a specific procedure. For the embodiment shown in
The embodiment of the plate holding feature 190 shown in
As shown in
As shown in
As shown in
The amount that the fastener head 250 elastically recovers relative to the functional undercut diameter 144 is one factor that determines the fit between the plate 100 and the fastener 200. The greater the elastic recovery, the tighter the fit between the fastener head 250 and the fastener-retaining passageway undercut 140. To maintain a tight fit between the fastener head 250 and the fastener-retaining passageway undercut 140, the fastener head 250 is dimensioned to partially elastically decompress. This assures constant contact and friction between the fastener head 250 and the fastener-retaining passageway undercut 140.
Other factors that affect the fit between the fastener 200 and the plate 100 include the relative difference between the functional bottom restrainer diameter 147 of the plate 100 and a fastener shaft diameter 275. The closer that the dimension of the functional bottom restrainer diameter 147 is to the dimension of the fastener shaft diameter 275, the less toggle between the plate 100 and the fastener 200.
The radial elastic compression and recovery of the fastener head 250 is a function of both the material properties of the fastener head 250 and the structural design of the fastener head 250. The structural design and material properties of the fastener head 250 are variable depending on the radial elastic compression and recovery desired for the fastener head 250. If the elastic deformation is more a function of the material properties of the fastener head 250, the fastener head 250 can be fabricated from a biocompatible elastomeric polymer material such as polyurethane, delrin, polypropylene, PEEK or a biocompatible superelastic metallic alloy such as Nitinol. These highly elastic materials allow the fastener head 250 to elastically radially compress past the fastener-retaining passageway capture lip 142 and elastically recover to lock into place in the fastener-retaining passageway undercut 140.
If the fastener 200 is fabricated from a material that is not as highly elastic as those previously discussed, then the fastener head 250 geometry can be altered such that the required elastic radial deformation is still achieved. For example, the fastener head 250 can be designed to allow elastic radial deformation of the fastener head 250 by removing material to increase the bending displacement of the fastener head 250. Examples of materials that the plate 100 or the fastener 200 are made from include titanium, titanium alloys, cobalt-chrome alloys, stainless steel alloys, zirconium alloys, other biocompatible metal materials, biocompatible ceramics, biocompatible composites, and biocompatible polymers. For example, the fastener head 250 can be manufactured in a helical spring or spiral spring fabrication that allows the radial-compression and radial recovery of the fastener head 250. Or as shown in the embodiment of
In addition to fabricating the fastener head 250 from a highly elastic material or designing the shape of the fastener head 250 such that it allows for radial compression and decompression, the fastener head elastic deformation member 254 can be a combination of both a radially elastic fastener structural design and the fastener head 250 partially or fully fabricated from a highly elastic material. Different portions of the fastener can be fabricated from different materials with elastic properties tailored to the function of a particular fastener feature. For example, the fastener head elastic deformation member 254 can be fabricated from highly elastic materials, while the fastener engager 270 is fabricated from less elastic materials.
In a second embodiment of the plate 100 and fastener 200 system, a retaining ring 230 is formed on the fastener head 250. As shown in
The fastener 200 has a fastener engager 270 that is adapted for fixation with the bone tissue by gripping onto and engaging the bone sections to be secured by the fastener 200 and plate 100 system. Although a screw type bone engaging member such as that of a engager thread 271 shown in
Referring to the embodiment of the fastener 200 shown in
The embodiments of the fastener 200 shown in
As shown in
The configuration of the fastener-retaining passageway 110 in the plate 100 and the fastener head 250 allows for an angular play of β between the fastener 200 and the plate 100. Once the fastener head 250 is engaged with the plate 100, the fastener 200 can be oriented in a rotational position independently to any angle included in the angle β. The angular play β between the plate 100 and the fastener 200 is dependent upon the relative difference between the functional bottom retainer diameter 147 and the fastener shaft diameter 275. The amount of angulation between the long axis of the fastener 200 and an axis through the center of the fastener-retaining passageway 110 is between 0° and 15°. Generally, the more play between the plate 100 and the fastener 200, the more angular displacement.
In the first embodiment of the fastener 200 and plate variable angle system shown in
Similarly, in the second embodiment of the fastener 200 and plate 100 variable angle system shown in
Protruding from the driver shaft 530 is a driver drive feature 540. The driver drive feature 540 mates with the fastener drive member 221 in the fastener head 250 of the fastener 200. Hence, the shapes of the fastener drive member 221 and the driver drive feature 540 are similar and sized such that the male portion fits into the female portion. In the embodiments shown in
The removal tool 400 shown in the embodiment depicted in
As shown in
A prong lead in chamfer 441 is adjacent to the distal end of the internal surface 442. The prong lead-in chamfer 441 slopes outwardly from the internal surface 442 to the distal tip 445.
The prongs 440 shown in
While the present invention has been disclosed in its preferred form, the specific embodiments thereof as disclosed and illustrated herein are not to be considered in a limiting sense, as numerous variations are possible. The invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments of the plate and fastener system are to be considered in all respects only as illustrative and not restrictive. No single feature, function, element or property of the disclosed embodiments is essential. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. The following claims define certain combinations and subcombinations that are regarded as novel and non-obvious. Other combinations and subcombinations of features, functions, elements and/or properties may be claimed through amendment of the present claims or presentation of new claims in this or related applications. Such claims, whether they are broader, narrower or equal in scope to the original claims, are also regarded as included within the subject matter of applicant's invention. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.