US20040127908A1 - Cranial clamp with torque-limiting feature - Google Patents

Abstract

A clamp assembly according to the invention can be fixed through an opening between adjacent members. The clamp assembly includes a base, a cap opposing the base, and a post connecting the cap and the base in a fastening position on the adjacent members. The post includes a torque-limiting feature to prevent over tightening of the cap and base. The clamp assembly may further include an applier interacting with the post to position the cap and base in the fastening position. A method according to the invention includes placing the base and cap on opposing internal and external surfaces of the adjacent members. The post is rotated to bring the base and cap to the fastening position, and a torque-limiting feature prevents over tightening. The method may further include removing a distal portion of the post projecting from the cap and leaving a proximal portion of the post projecting from the cap and which can be deformed to secure the base and cap in the fastening position.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This case is a continuation of U.S. patent application Ser. No. 10/255,146, filed Sep. 25, 2002, which claims priority on U.S. provisional patent application Serial No. 60/324,658, filed Sep. 25, 2001.[0001]
FIELD OF THE INVENTION
• This invention relates to a fastener for quickly and securely fastening a bone plate to surrounding bone. In one embodiment, the fastener contains a torque-limiting feature to prevent over tightening when in the fastening position. In another embodiment, the invention relates to an instrument for applying the fastener to a bone plate and surrounding bone.[0002]
BACKGROUND AND SUMMARY OF THE INVENTION
• When performing surgery on the brain, it is often necessary to perform a craniotomy to provide access to portions of the brain. A craniotomy is a surgical procedure in which a portion of the cranium is removed to permit access to the brain. To perform the craniotomy, one or more holes are initially drilled through the skull. These holes, known as “burr holes,” may be located, for example, at the corners of a triangular region of bone that is to be temporarily removed. A saw, i.e., a craniotome, is then used to cut the skull along the line of separation connecting the adjoining burr holes. The resulting bone cover or bone plug is subsequently lifted from the underlying dura matter to expose the brain. The bone cover may either be completely removed from the cranium, or folded back in a flap along an uncut edge of the flap.[0003]
• After completion of the procedure on the brain, the bone cover must be re-attached to the skull. Several devices have been developed that are used to facilitate securing the bone cover to the skull. These devices suffer from the disadvantage that they are cumbersome or inefficient to apply to the bone flap and surrounding bone. Further, prior designs are relatively rigid, thus decreasing conformance to the curvature of the skull. Moreover, prior designs often required significant instrumentation to apply and/or adjust the device used to secure the bone cover to the skull. Finally, prior designs may require removal of the fastening device after sufficient healing along the line of separation.[0004]
• The Cranial Clamp And Method For Fixating A Bone Plate according to the invention generally includes a cap and base adjustably joined by a post for threadably bringing the opposing cap and base closer together, thereby tightening them against the internal and external surfaces of the bone plate and surrounding cranium. The base and cap securely fix the bone plate to the surrounding bone. In one embodiment, at least one of the base, cap and post include resorbable material.[0005]
• The clamp according to the invention may further include an applier interacting with the post to position the cap and base to securely fix the bone plate to the surrounding bone. Once appropriately secured, the applier is removed from the post while leaving the cap and base interconnected. In one embodiment, the applier includes a keyed bore and the post includes a key for engaging the keyed bore of the applier.[0006]
• The clamp according to the invention may also include a torque-limiting feature on the post. The torque-limiting feature prevents stripping of the threaded interconnection between the post and cap or overtightening of the cap relative the base. In one embodiment, the torque-limiting feature is disposed at a junction between an elongated body portion and a keyed portion of the post.[0007]
• The method for fixating a bone plate in a bony defect according to the invention allows a bone plate to be fixed in apposition against a transverse face of surrounding bone along the border of junction between the bone plate and surrounding bone. A base connected to an elongated externally threaded post projecting from the base, and a cap with an internally threaded collar for mating and threaded engagement with the threaded post connected to the base, is provided. In one embodiment, at least one of the base, cap, and post include resorbable material. The base and cap are placed on opposing internal and external surfaces of the bone plate, with a portion of each of the base and cap overlapping the border of junction. The post is rotated into the collar to bring the base and cap to a fastening position having the base and cap in tight engagement against the opposing internal and external surfaces of the bone plate. At least one of the base, cap, and post include resorbable material, which is resorbed by the body.[0008]
• The method according to the invention may further include providing an applier, wherein the applier rotates the post through inter-engagement of the applier with the post. The method according to the invention may also include removing a distal portion of the post projecting from the cap and leaving a proximal portion of the post projecting from the cap. Moreover, the proximal portion of the post projecting from the cap may be deformed to secure the base and cap in the fastening position.[0009]
• Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.[0010]
BRIEF DESCRIPTION OF THE DRAWINGS
• The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:[0011]
• FIG. 1 is a partial perspective view of a clamp and applier according to the invention securing a bone plate to surrounding cranium;[0012]
• FIG. 2 is a partial sectional view of a clamp and applier cut along line[0013]2-2 of FIG. 1;
• FIG. 3 is a partially sectioned side view of an assembled clamp and applier according to the invention;[0014]
• FIG. 4 is a top view of a base of a clamp according to the invention;[0015]
• FIG. 5 is a sectional view cut along line[0016]5-5 of FIG. 4;
• FIG. 6 is a side view of a post of the clamp according to the invention;[0017]
• FIG. 7 is an end view of the post of FIG. 6;[0018]
• FIG. 8 is a top view of a cap of the clamp according to the invention;[0019]
• FIG. 9 is a side view of the cap of FIG. 8;[0020]
• FIG. 10 is a bottom view of the cap of FIG. 8;[0021]
• FIG. 11 is a sectional view cut along line[0022]11-11 of FIG. 8;
• FIG. 12 is a sectional view of an applier according to the invention cut along line[0023]12-12 of FIG. 3;
• FIG. 13 is an end view of the applier of FIG. 12;[0024]
• FIG. 14 is a top view of an alternative embodiment of the clamp according to the invention;[0025]
• FIG. 15 is an exploded perspective view with an alternative embodiment of the clamp according to the invention;[0026]
• FIG. 16 is a sectional side view of the assembled clamp of FIG. 15; and[0027]
• FIG. 17 is a sectional side view of an assembled clamp according to another embodiment of the invention.[0028]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. While the present invention is shown securing a bone plate to a surrounding cranium, the fastener of the present invention may be used in other surgical and non-surgical applications as well.[0029]
• The present invention includes fasteners for securing flat or curved plate structures to each other. The invention also includes a positioning and applying instrument that is particularly useful for positioning and applying the fasteners in a surgical wound and for securing the fasteners to each other.[0030]
• As shown in the drawings, the fastener according to the invention is a[0031]clamp10 for closing a craniotomy. A craniotomy is performed by incising pericranium and muscle with cutting diathermy in the line of an intended bone flap. An incision is not made interiorly where a pedicle of pericranium or temporalis muscle is often left uncut to allow some blood supply to the bone and overlying tissue to remain intact. Alternatively, the pericranium and muscle may be detached completely from the intended bone flap.
• As illustrated in FIGS. 1 and 2, the craniotomy is performed by making a series of burr holes[0032]12 through thecranium28 about six or seven centimeters apart with a cranial perforator. Alternatively, a trephine can be used. The underlying dura matter is separated from the bone covering the osteotomy site (“the bone cover”) using a periosteal elevator.Osteotomies14 between the burr holes12 are then made using a craniotome that is passed between adjacent burr holes12 and moved back and forth to make theosteotomies14 from the internal to the external surfaces of thecranium28. Alternatively, a Gigli flexible saw can be used to make theosteotomies14. Abase16 is not cut with the saw. A bone forceps (such as a deVilbis forceps) is used to ply a bone plate18 until the bridge breaks at the base16 when the bone plate18 is elevated.
• The bone plate[0033]18 is separated from the surroundingcranium12 and28 along a line of separation formed byosteotomies14. Eachburr hole12 has a plate portion12(a) and a complimentary cranial portion12(b), which together form the completedburr hole12. Trephines come in graduated sizes, for example, between 0.5 and 2 inches (13-51 millimeters) diameter for drilling burr holes12 of sizes varying across this usual range.
• The bone plate[0034]18 may be completely removed if osteotomies connect all of the burr holes12. It is often preferred, however, to leave an intact edge of the craniotomy (such as base16) to preserve the blood supplied to the bone. In either case, the bone plate18 is typically referred to as the cranial cover.
• After the neurosurgical procedure is performed, the bone defect must be repaired by placing the bone plate[0035]18 back in the defect with opposinginternal surface20 and external surface22 substantially coplanar or aligned with theinternal surface24 andexternal surface26 of surroundingcranium28. Atransverse face30 of bone plate18 must also be fixed in opposition with atransverse face32 ofcranium28 along a border of junction defined by theosteotomy14 between bone plate18 and surroundingcranium28.
• In an embodiment shown in FIG. 3, the[0036]clamp10 includes a first member orbase100 selectively connected to a second member orcap150 via apost120. Thecap150 andbase120 are brought toward one another by an instrument orapplier170. In one embodiment, thebase100,post120,cap150 andapplier170 are assembled prior to use in securing the bone plate18. In another embodiment, thebase100,post120 andcap150 are assembled prior to use in securing the bone plate18. Yet another embodiment include an assembledbase100 and post120, and thecap150 andapplier170 are assembled after positioning thebase100 and post120 to secure the bone plate18.
• As shown in FIGS. 4 and 5, the[0037]base100 is formed by a generally solid disk having acentral aperture102, an annularinner face104 surrounding theaperture102, and anouter face108 except for acentral recess106 disposed coaxial with theaperture102. Theouter face108 surrounds thecentral recess106 and generally accommodates the annularinner face104. Theinner face104 andouter face108 circumscribe acollar110 projecting inwardly from theinner face104 coaxially aboutcentral aperture102. In this embodiment,aperture102 extends throughbase100 and is adapted to receive thepost120, whereby thepost120 is able to rotate relative thebase100. In other embodiments,aperture102 may only have an opening at the inner side ofcollar110 and not extend through thebase100.
• As shown in FIGS. 6 and 7, the[0038]post120 includes ahead122 at a first end and a key124 at a second end. A substantially cylindrical,elongated body126 extends between thehead122 and key124, and generally includes ribs orthreads128 along its length.Threads128 will be used in the following description, but ribs are within the scope of the invention. At the head Attorney Docket No.5490-000259/COB end of thepost120, thethreads128 taper or run out from a minor to major diameter of thebody126 over360 to720 degree revolutions. In one embodiment, the junction of thebody126 and key124 provides a torque-limitingfeature130 to allow the key124 to break from thebody126 to prevent stripping the threaded interface between thepost120 andcap150 or over-tightening theclamp10. In one embodiment, the ribs orthreads128 alongpost120 are pliable and resilient due to material elasticity. Such pliable, resilient ribs orthreads128 allow thecap150 to be quickly secured by ratchetingcap150 along thethreads128 on thepost150 to quickly position thecap150 relative thebase100 alongpost120. Due to the elasticity in engagement of the ribs or threads, however, once thecap150 is ratcheted in position alongpost120, it can be further adjusted towardbase100 by threaded rotation or further ratcheting. Further, in one embodiment,threads128 can extend partially along theelongated body126 of thepost120. In this manner, thecap150 can be slid along a portion of theelongated body126, which may include ribs, prior to engaging thethreads128.
• The[0039]head122 is preferably a rounded disk shape disposed coaxially with theelongated body126, which flares outwardly at the junction with thehead122. In one embodiment, the key124 is a generally D-shaped cross section formed at the second end of thepost120. In other embodiments, the shape or cross section of the key124 may differ. Whenclamp10 is assembled for use, thepost126 is received coaxially through theaperture102 of the base100 such thathead122 seats in thecentral recess106, as best shown in FIG. 3.
• The[0040]cap150 fastens to the base100 to secure the bone plate18 in place and occlude the burr holes12. As shown in FIGS.6-9, thecap150 is a generally solid disk with anouter face152 except for acentral recess154 disposed coaxially about acentral aperture156 extending therethrough. Thecap150 has an annularinner face160 including acollar158 surrounding theaperture156. Theinner face160 comprises an arcuate channel coaxially surrounding thecollar158 andaperture156. Further, theinner face160 includes a series ofradial teeth162 radiating circumferentially toward the outer diameter of theinner face160. Theteeth162 form aserrated edge164 about the periphery ofcap150. Theteeth162 are disposed at an angle I and height H along theserrated edge164. For example, in an approximately14millimeter cap150, theteeth162 are separated by an angle I approximating 53 degrees at a height H approximating 0.047 inches. In the embodiment shown, theaperture156 ofcollar158 includesinternal threads166. For this embodiment, the threads are left-handed, but should compliment thethreads128 of thepost120 in other embodiments.
• As shown in FIGS. 1, 3,[0041]12 and13, theapplier170 is used to position and fasten theclamp10. Theapplier170 includes a generally hexagonalelongated body172 including abore174 extending generally coaxially therethrough along its length. At a first end, thebore174 extends to anopening176. At an opposite end, thebore174 extends to akeyed bore178. In one embodiment, keyed bore178 has a generally D-shaped cross section to compliment the cross section ofkey124. When key124 is inserted into keyedbore178, rotation ofbody172 rotates thepost120. In one embodiment, theapplier170 is secured to thepost120 prior to use in securing a bone plate18 by deforming a portion of thepost120 extending through thekeyed bore178 and into thebore174. This deformation, indicated as132 in the drawings, secures thepost120 andapplier170 to one another. As shown, thebody172 of the applier has a generally hexagonal cross section, but in other embodiments can have other shapes and cross sections. Further, bore174 tapers tokeyed bore178 at an angle θ. In this embodiment, angle θ approximates 118 degrees. Also in this embodiment, bore174 extends approximately 90 percent of the length ofapplier170, while keyed bore178 extends approximately ten percent thereof.
• In one embodiment, clamp[0042]10 includes resorbable materials. In one variation of this embodiment, thebase100,post120, and cap150 are all comprised of resorbable materials. In another variation, thebase100 andcap150 are comprised of resorbable material, while thepost120 is comprised of a suitable biocompatible material. In yet another variation, either the base100 orcap150 is comprised of resorbable material, and thepost120 may be comprised of resorbable and/or biocompatible material. Alternatively, only thepost120 comprises resorbable material. The main benefit of using resorbable material is that theclamp10, or components thereof, will resorb into the body over a generally predictable time period once a sufficient level of healing has occurred, for example, at the junction of a bone fracture, thus negating need for subsequent removal of theclamp10.
• One resorbable material is used in products marketed by Biomet, Inc. (Warsaw, Ind.) under the trademark LACTOSORB®. LACTOSORB® is an absorbable co-polymer synthesized from all natural ingredients: 82 percent L-lactic acid and 18 percent glycolic acid. Unlike the homopolymers in common use, such as 100 percent poly-L-lactic acid (PLLA) or 100 percent poly-glycolic acid (PGA), LACTOSORB® co-polymer is substantially amorphous (i.e., without crystallinity), meaning that its degradation is uniform, precluding the crystalline release most often associated with degrading homopolymers that have been associated with inflammatory reactions. Furthermore, the LACTOSORB® co-polymer ratio permits the polymer to retain most of its strength for six to eight weeks, which is appropriate for healing, but not so long as to raise concerns about long-term stress shielding. It should also be understood that any other type of resorbable material may also be used herein.[0043]
• In an alternate embodiment, the[0044]clamp10 includes of non-resorbable, biocompatible materials. In one variation of this embodiment, thebase100,post120 andcap150 are all comprised of non-resorbable, biocompatible materials. In another variation, thebase100 andcap150 are comprised of resorbable material, while thepost120 is comprised of a suitable non-resorbable, biocompatible material. In yet another embodiment, either the base100 orcap150 is comprised of resorbable material, while the other of thebase100 andcap150 and thepost120 may be comprised of a suitable non-resorbable, biocompatible material. Alternatively, both thebase100 andcap150 comprise non-resorbable, biocompatible material and thepost120 comprises resorbable material.
• One non-resorbable, biocompatible material is titanium. Titanium and its alloys are high strength, durable and corrosion resistant materials. A titanium containing alloy such as, for example, Ti[0045]₆Al₄V is commonly used in surgical applications. Ti₆Al₄V is inert to human body fluids thus its resistance in bodies is very high. Furthermore, Ti₆Al₄V has been shown to have a high resistance to abrasion and also has a high fatigue resistance. It should be understood that any other suitable type of non-resorbable, biocompatible material may also be used herein and should be considered within the scope of the present invention, including other metals having a layer of biocompatible cement to line the metal in order to prevent the body's immune system from rejecting the implanted material.
• The[0046]clamp10 according to the invention can be assembled in various ways for use in replacing the bone plate18 following a craniotomy. For example, theclamp10 can be provided unassembled for use in securing the bone plate18, in which case a user would begin assembly ofclamp10 by inserting thepost120 into thebase10. In another embodiment, theclamp10 may be provided to the user at least partially assembled, for example with thepost120 assembled to thebase100, or otherwise affixed thereto. In another embodiment, theclamp10 would be assembled further by not only assembling thepost120 andbase100 to one another, but also connecting thepost120 to thecap150. In this way, once theclamp10 is in position to secure a bone plate18, theapplier170 is connected to thepost120 for securing the bone plate18 to the surroundingcranium28. In yet another embodiment, theclamp10 includes assembling thepost120 to thebase100 andcap150, as well as securing theapplier170 to thepost120. Thepost120 may be secured to theapplier170 in various ways; as shown, an end portion of thepost120 extending through the key shapedbore178 and into thebore174 is deformed after assembly of thepost120 to both thebase100 andcap150, whereby the entire assembly of thebase100,post120,cap150, andapplier170 is provided assembled for use in replacing the bone plate18 following the craniotomy.
• The[0047]clamp10 is used to replace the bone plate18 following a craniotomy, as shown in FIG. 1. The craniotomy is performed by providing at least one craniotomy hole or multiple holes, such as burr holes12, through the skull. The burr holes12 are subsequently connected byosteotomies14 to create a separation border for the bone plate18, which may be a plate that is removed or a flap that is folded back along one edge. Alternatively, a circular bone plate18 can be formed by providing oneburr hole12 and a circular osteotomy beginning and ending at the oneburr hole12. In each case, the craniotomy opening includes aportion12a of at least oneburr hole12 formed in the bone plate18 and acomplimentary portion12b of the hole formed in the surroundingcranium28. The subsequent description employs the example of multiple burr holes12 andosteotomies14 connecting theholes12, as shown in FIG. 1.
• As shown in FIG. 2, the bone plate[0048]18 has theinternal surface20 and external surface22 respectively placed in substantially coplanar relationship with theinternal surface24 andexternal surface26 of the surroundingcranium28 when a craniotomy is closed. Opposing transverse faces30,32 of the bone plate18 and surroundingcranium28 appose along the separation border when the bone plate18 is replaced. Faces30,32 are generally parallel to each other when in apposition.
• In a method of the present invention, the bone plate[0049]18 is folded back along a base16 or completely removed to expose the underlying dura matter and brain. In one embodiment, following the intracranial procedure, and prior to replacing the bone plate18 into its original orientation within the craniotomy opening, the assembledbase100 and post120 is placed below eachburr hole12 with theinner face104 of the base100 against theinternal surface24 of thecranium28 and thepost120 extending through thehole12. The base100 overlaps the margins ofhole12 and the separation border between the bone plate18 and surroundingcranium28. Thecollar110 projects upwardly toward thehole12 and thepost120 extends upwardly and through thehole12. In another embodiment, the assembledbase100,post120, and cap150 are positioned with theinner face104 and the base100 against theinternal surface24 of thecranium28, thepost120 extending through thehole12, and thecap150 positioned above thehole12 with theinner face160 of thecap150 facing theexternal surface26 of thecranium28. In yet another embodiment, theapplier170 is connected to thekeyed end124 of thepost120 such that the assembledbase100,post120,cap150, andapplier170 are positioned relative each borehole12 with theinner face104 of the base100 against theinternal surface24 of thecranium28, thepost120 extending through thehole12, and theinner face160 of thecap150 facing theexternal surface26 of thecranium28. The bone plate18 is then replaced into the craniotomy opening, for example, by folding the bone plate18 alongbase16 back down into the craniotomy opening.
• After the bone plate[0050]18 is restored to its original position in the craniotomy opening,complimentary portions12a,12bnowreform hole12. Thepost120 is positioned withinhole12 with theinner face104 of the base100 engaging theinternal surfaces20 and24 of bone plate18 andcranium28, respectively. If not already assembled to thepost120, thecap150 is positioned over the reformedhole12 to engage thepost120 above thehole12. Thepost120 is introduced into thecollar158 ofcap150 through theaperture156. In one variation of this embodiment, wherein thethreads128 extend generally along the length of theelongated body126 of thepost120, the threads of internally threadedcollar158 engage thethreads128 of externally threadedelongated body126 and thecap150 is threaded into engagement with bone plate18 and surroundingcranium28. In another variation of this embodiment, wherein a portion of theelongated body126 is externally threaded, thecap150 is slid along an unthreaded leading portion of theelongated body126 until it engages an externally threaded portion of theelongated body126. In any embodiment, the ribs orthreads128 may be pliable and resilient, whereby thecap150 is ratcheted along the externally ribbed or threadedelongated body126 into contact with the external surface of thecranium28 and bone plate18.
• In one embodiment, once the[0051]cap150 is in position to be threadably driven, theapplier170 is attached to thepost120 by inserting the key124 of thepost120 into the keyed bore178 of theapplier170. In another embodiment, theapplier170 is connected to thepost120 prior to positioning thepost120 on theburr hole12. In each embodiment, thecap150 is held in place with one hand while theapplier170 is rotated with the other hand, causing thepost120 to rotate relative thebase100 and threadedly engage thecap150 to diminish the distance between the base100 and thecap150 and tighten respectiveinner faces104,160 of thebase100 andcap150 against the respective internal and external surfaces of thecranium28 and bone plate18. Thecap150 andbase100 are brought together in frictional engagement against opposing faces of the bone plate18 and surroundingcranium28, thereby clamping the bone plate18 and surroundingcranium28 to each other. Theteeth162 of thecap150 anchor thecap150 to both the bone plate18 and surroundingcranium28, thereby preventing rotation of thecap150 while thebase100 is secured thereto. Thecap150 is attached to the bone of the bone plate18 andcranium28 as theteeth162 become progressively advanced into the bone by rotating theclamp10.
• The torque-limiting[0052]feature130 disposed at the junction of thebody126 andkey124 of thepost120 allows the key124 to break from thebody126 to prevent stripping the threaded interface of thepost120 andcap150 or overtightening thecap150 relative thebase100. The key124 will separate from thebody126 of thepost120 before the threaded interface between thecap150 and post120 strips. In this manner, the time and expense of replacing a strippedclamp10 is avoided, and a proper amount of frictional engagement of thecap150 andbase100 against opposing faces of the bone plate18 and surroundingcranium28 is provided. The torque-limitingfeature130 of thepost120 could be provided in other ways within the scope of this invention, such as by notching thepost120 at a portion other than the junction of the key124 andbody126, or narrowing the diameter of thepost120 at any point along thebody126 and key124, among other ways.
• After the[0053]cap150 andbase100 are suitably brought together against the opposing faces of the bone plate18 and surroundingcranium28 to clamp the bone plate18 and surroundingcranium28 to each other, a distal portion of thepost120 is cut a distance D above thecap150, as best shown in FIG. 2. The distance D is a distance suitable to provide aproximal portion140 of thepost120 with enough material to secure thecap150 to thepost120 upon deformation of theproximal portion140 ofpost120. In one embodiment, the distance D is approximately two millimeters for a14millimeter diameter cap150. The remaining distance D of thepost120 is flattened or otherwise deformed to prevent thecap150 from backing off thepost120 and away from thebase100. Preferably, opthalmic cautery or a heat pen is used to cut the post a distance D above thecap150, and further used to deform the remaining distance D of thepost120 to secure thecap150 relative thebase100, as best shown in FIG. 1. A heat pen, such as the LACTOSORB® Heat/Contouring Pen, is available from W. Lorenz Surgical of Jacksonville, Fla.
• The[0054]clamp10 is used to clamp the bone plate18 to the surroundingcranium28 at one or more of the burr holes12, and preferably all of the burr holes12 as shown in FIG. 1. Theclamp10 can also clamp the bone plate18 to the surrounding cranium along anosteotomy14. That is, use of theclamp10 is not limited to occluding burr holes12, but is useful for supporting a bone plate18 in a circular orcurved osteotomy14 as well. Abase100 and post120 is therefore positioned below eachburr hole12 or at discrete points along an osteotomy with thepost120 projecting up into and through thehole12 on the line of separation prior to replacement of the bone plate18. Acap150 is then threaded along each externally threadedpost120 until thecap150 andbase100 clamp the bone plate18 and surroundingcranium28 securely to each other. Thecap150 andbase100 are in a fixed relationship determined by the degree of advancement of the externally threadedpost120 into the internally threadedcollar158 of thecap150, so that the movement of the bone plate18 is substantially prevented. The bone plate18 and surroundingcranium28 are held firmly in place with respect to each other, which avoids inadvertent depression of the bone plate18 and attendant catastrophic neurological consequences.
• The outer face of the[0055]cap150 diminishes the aesthetic problem of visible indentations on the skull or face overlying the craniotomy burr holes12. Further, by employing a malleable material with high ductility for thecap150, aesthetic problems are further reduced. Theclosed base100 tightly engages the internal surfaces of the bone plate18 and surrounding cranium providing ideal occlusion of thehole12 to held avoid infection or trauma. Theclamp10 also clamps the bone plate18 in place quickly, thereby diminishing the period of time the brain must be exposed and also reduces medical expenses associated with prolonged time in the operating room. In one embodiment, as explained previously, theclamp10 is made partially or wholly of resorbable material so that the body can resorb the clamp after suitable bone growth across the osteotomies. Beside the biocompatibility of such materials, such aclamp10 need not be removed by a follow-up neurosurgical procedure.
• The[0056]clamp10 may be made in many different sizes. For purposes of illustration, the diameter of thepost120 can be 1.8 millimeters (the same diameter as theapertures156 and102), the diameter ofbase100 can be 14 millimeters, and the diameter of thecap150 may be 14 millimeters. In one embodiment, thepost120 is 35.6 millimeters long, withkey124 extending approximately 5 millimeters from a leading end of thepost120.
• The[0057]clamp10 is adjustable for use in repairing craniotomies through bone of varying thickness. The pterion (in the temporal-parietal region), for example, is quite thin and would conventionally require a shorter fastener. Because the unused portion of thepost120 is simply removed once the base100 andcap150 are appropriately positioned, different-sized fasteners are not necessary. For example, the parietal or frontal bone may be 10 to 20 millimeters thick, wherein the present invention would work properly with both bone thicknesses, as well as smaller or larger thicknesses.
• Other variations of the disclosed fastener are possible. The relative positions of the cap and base can be reversed, for example, by disposing the[0058]cap150 on the interior surface of the cranium and bone plate18 while thebase100 is disposed along the external surfaces thereof by simply threading thecollar110 of thebase100 and leaving thecollar158 of thecap150 unthreaded. Thecap150 andbase100 may assume many shapes other than circular, and may, for example, be square or triangular. Bone plates other than in the skull may be secured to surrounding bone, for example, a relatively flat top bone such as the trapezium, mandible, maxilla or bones of the orbit. The outer face of thecap150 may also be flat, particularly in areas of the skull, such as the temporal bone, with relatively flat external surfaces. The fastener may also be used to fix adjacent members together, even where the members are curved. A malleable material may be used to accommodate differing surface shapes. Such materials include LACTOSORB® copolymer, VHMN polyethylene, polyethyl ketone, silicone, nylon, etc.
• In one embodiment, the base and cap may include[0059]flexible struts200 to provide more flexibility than a solid member, as shown in FIG. 14 forexemplary base100′. Thestruts200 are preferably made of a high-density polyethylene. In the disclosed embodiment, eachstrut200 does not occupy more than about a 20 to 30 degree sector of the base or cap. Thestruts200 radiate from the center of the cap or base to a peripheral ring, but they can alternatively taper, flair, or assume other shapes that sufficiently reduce the solid areas of the base and cap to increase the flexibility such that it conforms to the curvature of the skull when the clamp is tightened to such an extent that the bone in the skull is not fractured or damages. For example, the modulus of flexibility of the cap or base, or each individual strut, is 300,000 to 700,000 PSI.
• In yet another embodiment shown in FIGS.[0060]15-17, theclamp10 includes a first member orbase100″ selectively connected to a second member orcap150″ via apost120″. As before, thecap150″ andbase100″ are brought toward one another by an instrument orapplier170. The base100″ is formed by a generally solid disk having acentral aperture102″ for rotatably receiving thepost120″. Similar reference numbers are used in this description to note features similar to those described for the prior embodiments.
• The[0061]post120″ includes ahead122″ at a first end and a key124 at a second end. A substantially cylindricalelongated body126 extends between thehead122″ and the key124, and generally includes ribs orthreads128 along its length. As before,threads128 are used in the description, but ribs are within the scope of the invention. Thehead122″ of thepost120″ includes achannel121 for receiving aperiphery103 of theaperture102″ in order to rotatably secure the base100″ to thepost120″.Slots105 allow deflection of the base100″ at theperiphery103 to facilitate insertion of thehead122″ in theaperture102″, whereby theperiphery103 is received in thechannel121. In this manner, as described in prior embodiments, thepost120″ is able to rotate relative the base100″.
• The[0062]cap150″ is a generally solid disk having a central aperture disposed coaxially therethrough for receiving thecollar110″. Thecollar110″ includes acentral aperture156″ extending therethrough and includinginternal threads166 that mate with thethreads128 on thepost120″. Thecollar110″ includes aflange157 to prevent pulling thecollar110″ through thecap150″ during assembly or use. Thecollar110″ is press fit into the aperture159 of thecap150″, whereby thecollar110″ andcap150″ rotate together. Alternatively, thecollar110″ andcap150″ could be threaded together where the threaded engagement between thecollar110″ andcap150″ is an opposite thread to that of the engagement between theinternal thread166 of thecollar110″ and thethread128 of thepost120″.
• In a variation of this latter embodiment, the[0063]collar110″ can be acollar110″ that is formed integral with acap150″, as shown in FIG. 17. The operation and use of this variation of the invention is similar to that described for the previous embodiment of the invention, and the inventions shown in FIGS.15-17 are used and assembled in manners similar to that described above for the prior embodiments.
• As used in this specification, conformance to a curved member does not require identical curvature of the conforming member at the surface to which it conforms. Substantial conformity of the members is all that is required, and that includes surfaces between flat planes and curves that precisely conforms to the curved member against which the conforming member seats.[0064]
• The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.[0065]

Claims (27)

What is claimed is:

1. A clamp assembly for repairing a bone defect in a cranium and operable to fix a bone plate relative the surrounding cranium, each of the bone plate and surrounding cranium having a near face and a far face, the clamp assembly comprising:

a cap;

a base opposing the cap;

a post having an elongate body rotatably attached to the base and the cap and including a torque-limiting feature, the post engaging the cap and base to fasten the cap and base relative one another.

2. The clamp assembly ofclaim 1, further comprising an applier operable to rotate the post to position the cap relative to the base in a fastening position.

3. The clamp assembly ofclaim 2, wherein the applier is removable from the post while leaving the cap and base interconnected.

4. The clamp assembly ofclaim 2, wherein the applier includes a body having a keyed bore.

5. The clamp assembly ofclaim 4, wherein the post includes a key for engaging the keyed bore of the applier.

6. The clamp assembly ofclaim 1, wherein the post includes external threads.

7. The clamp assembly ofclaim 6, wherein the cap includes an internally threaded collar for mating engagement with the threads of the post.

8. The clamp assembly ofclaim 1, wherein the post includes external ribs.

9. The clamp assembly ofclaim 8, wherein the cap includes a collar for ratcheting the cap along the threads on the post.

10. The clamp assembly ofclaim 1, wherein the cap and base have opposing inner faces that face each other when assembled in use.

11. The clamp assembly ofclaim 10, wherein the cap includes teeth extending from the inner face to inhibit rotation of the cap relative to the adjacent members.

12. The clamp assembly ofclaim 1, wherein the torque-limiting feature prevents over tightening of the cap relative to the base.

13. The clamp assembly ofclaim 1, wherein the post further includes a key disposed at a distal end of the elongate body.

14. The clamp assembly ofclaim 13, wherein the key is operable to matingly engage the applier.

15. The clamp assembly ofclaim 13, wherein the torque-limiting feature is disposed at a junction between the elongate body and the key.

16. The clamp assembly ofclaim 1, wherein at least one of the cap, base and post includes resorbable material.

17. The clamp assembly ofclaim 16, wherein the cap, base and post include resorbable material.

18. The clamp assembly ofclaim 1, wherein at least one of the cap, base and post includes non-resorbable, biocompatible material.

19. The clamp assembly ofclaim 18, wherein the cap, base and post include non-resorbable, biocompatible material.

20. The clamp assembly ofclaim 18, wherein the non-resorbable, biocompatible material is titanium.

21. A method of fixing a bone plate in a bony defect, wherein the bone plate has opposing internal and external surfaces that are to be held in position with internal and external surfaces of surrounding bone, and a transverse face of the bone plate is to be fixed in apposition against a transverse face of the surrounding bone along a border of junction between the bone plate and surrounding bone, the method comprising:

rotatably connecting an elongated externally threaded post to a base;

extending the post through a cap to engage the threaded post with the cap;

positioning the base and cap on opposing internal and external surfaces of the bone plate, with a portion of each of the base and cap overlapping the border of junction;

rotating the post to position the cap and base in a fastening position; and

limiting the torque applied by the post in the fastening position.

22. The method ofclaim 21, further comprising removing a distal end of the post projecting from the cap.

23. The method ofclaim 22, further comprising leaving a proximal portion of the post projecting from the cap.

24. The method ofclaim 23, further comprising deforming the proximal portion of the post projecting from the cap to secure the base and cap in the fastening positioning.

25. The method ofclaim 21, further comprising rotating an applier to cause the post to rotate in the base and position the cap and base in a fastening position.

26. The method ofclaim 21, wherein limiting the torque prevents over tightening of the cap and base.

27. The method ofclaim 21, wherein limiting the torque includes severing the post.

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