WO1998051241A1

WO1998051241A1 - Implantable re-bar devices

Info

Publication number: WO1998051241A1
Application number: PCT/US1998/009528
Authority: WO
Inventors: Brent Constantz; Claude Pering; Morton Grosser
Original assignee: Norian Corporation
Priority date: 1997-05-16
Filing date: 1998-05-14
Publication date: 1998-11-19
Also published as: AU7377498A

Abstract

Implanting re-bar devices (30) and methods for their use are provided. The subject re-bar devices (30) are characterized by comprising a planar surface (32) having at least one protuberance (34) that has a cross-sectional profile that is substantially continuous. The radius of curvature at any point on the cross-sectional profile is between about 0.1 mm and 10 mm. The subject implanting devices (30) are particularly suited for use in conjunction with bone structural augmentation materials, such as calcium phosphate cements. The subject re-bar devices (30) find use in a variety of orthopaedic and related applications, including inter-fragmentary fixation, fastening soft tissue to bone, or holding plates or nails to bone and the like.

Description

IMPLANTABLE REBARDEVICES

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of application serial no. 60/046,668 filed on May 16, 1997, the disclosure of which is herein incorporated by reference.

INTRODUCTION Technical Field

The field of this invention is implantable medical devices.

Background of the Invention

Implantable medical devices such as bone screws play a prominent role in orthopaedics. Orthopaedic surgeons use screws for interfragmentary fixation, fastening soft tissue to bone, holding plates or nails to bone, and the like. As such, screw devices find use in a variety of orthopaedic procedures.

The most common function of screws in orthopaedic applications is to fix bone to bone. Screws also find use in applications where one wishes to hold soft tissue, such as tendons or ligaments, to bone. Yet another application in which screws find use is the fixation of plates or rods to bone, where one such instance is spinal fixation. In such instances, the bone screws, known as pedicle screws, are used in conjunction with other medical devices, such as rods or plates, that hold vertebrae in place until bone fusion occurs. In such applications, the pedicle screw is inserted through the pedicle bone of the vertebra into the cancellous region of the vertebral body.

A number of different design parameters have significant influences on the properties of screws and their suitability for use in particular applications. Important parameters include head shape, shank diameter, core (minor) diameter, thread (external, major) diameter, thread shape, thread pitch, cannulation and the like.

Specific classes of screws have been developed for use in particular applications. For example, cortical screws are designed to bite in cortical bone, are characterized by being threaded for the full length of the shaft of the screw, and are often used in lagging fragments of bone together or to hold implants, such as side plates, to bone. Cancellous screws are characterized by having a larger thread diameter and greater pitch than cortical screws, and a long shank portion which is free of threading. Herbert screws differ from cancellous or cortical screws in that the screw head is threaded. Figs. 1 A and IB provide representations of typical cortical and cancellous bone screws. A typical cortical bone screw is depicted in Fig. 1 A, where 2 indicates the pitch, 4 indicates the root diameter, 6 indicates the thread depth and 8 indicates the hexagonal drive head. A typical cannulated cancellous bone screw is depicted in Fig. IB, where 5 indicates the cannulation.

Common to all bone screws currently in use today is the presence of a cutting feature, usually the thread, which serves to cut through the bone during introduction of the screw into the particular bone site. While such cutting features are necessary to introduce the screw securely into bone, these features can be initiators of stress concentration, resulting in a variety of subsequent complications, such as stress fracture, screw pullout and the like.

Accordingly, there is a continued interest in the development of alternative fixation devices which can be used in applications such as interfragmentary fixation, fastening soft tissue to bone, or holding plates or nails to bone. Ideally, such alternative devices would be suitable for use in conjunction with structural augmentation materials, such as calcium phosphate cements, where such adjunct materials are introduced as a paste-like material that subsequently sets into a hardened product.

Relevant Literature

Perry & Gilula, Orthop. Rev. (1992) 21: 709-713 provides a review of design parameters of types of screws employed in orthopaedic surgery. See also Wentz, "Rebar Screws Provide Cost-Effective Alternative to Wedges for Revision TKA," Orthopedics Today, March 1998, pp 36-37. U.S. Pat. Nos. 5,207,678; 4,946,458; 4,653,481; 5,611,800 and 5,209,753 describe different spinal fixation systems, and aspects thereof, including bone screws for insertion into pedicles, i.e. pedicle screws.

SUMMARY OF THE INVENTION

Implantable rebar devices and methods for their use are provided. The subject devices include at least one element having a planar surface with at least one protuberance, where the protuberance has a cross-sectional profile that is substantially continuous. The cross-sectional profile is further characterized in that the radius of curvature at any point along the profile ranges from about 0J mm to 10 mm. The subject implantable devices are particularly suited for use in conjunction with bone structural augmentation materials, such as calcium phosphate cements. The subject rebar devices find use in a variety of applications, including interfragmentary fixation, fastening soft tissue to bone, or holding plates or nails to bone, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1A and IB provide a representation of a prior art cortical bone and cancellous bone screw, respectively, where each screw configuration comprises a bone cutting functionality, i.e. a thread with a sharp cutting edge. Fig. 2 provides a representation of a cross-sectional profile of an implantable device according to the subject invention.

Figs. 3 to 11 are depictions of various implantable rebar devices according to the subject invention.

Figs. 12 to 18 are depictions of alternative implantable rebar devices according to the subject invention.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS Implantable rebar devices and methods for their use are provided. Common to the rebar devices of the subject invention is the presence of a planar surface having a protuberance, where the protuberance has a cross-sectional profile which is substantially continuous. The radius of curvature at any point along the cross-sectional profile ranges from about 0J mm to 10 mm. The subject devices find use in a variety of applications, including interfragmentary fixation, fastening soft tissue to bone, or holding plates or nails to bone, and are particularly designed for use in conjunction with a structural augmentation material, such as a calcium phosphate cement.

Before the subject invention is further described, it is to be understood that the invention is not limited to the particular embodiments of the invention described below, as variations of the particular embodiments may be made and still fall within the scope of the appended claims. It is also to be understood that the terminology employed is for the purpose of describing particular embodiments, and is not intended to be limiting. Instead, the scope of the present invention will be established by the appended claims.

It must be noted that as used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural reference unless the context clearly dictates otherwise. Unless defined otherwise all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs.

The devices of the subject invention are implantable, by which is meant that they are dimensioned so as to be capable of being introduced into a living organism. Organisms into which the subject devices are capable of being introduced are generally mammals, including: domestic animals, e.g. horses, goats, pigs, cows, etc.; rare or exotic animals, e.g. zoo animals such as lions, tigers, elephants, bears, etc.; pets, e.g. cats, dogs; and humans. Of particular interest are devices suitable for implantation in humans. For devices intended for human implantation, the device dimensions may vary widely within the following ranges, depending on the intended usage of the device. Generally, the width ranges from about 0.5 mm to 50 mm, usually from about 1 mm to 20 mm and more usually from about 2 mm to 15 mm. The length ranges from about 5 mm to 250 mm, usually from about 10 to 200 mm and more usually from about 10 to 75 mm. The height ranges from about 1 to 10 mm, usually from about 1 to 5 mm and more usually from about 1 to 3 mm. The subject devices have at least one element which is characterized by the presence of a planar surface, flat or curved, with at least one protuberance emerging or arising therefrom. By at least one element is meant that the entire outer surface of the device may be the planar surface or only a portion of the outer surface of the device may be the planar surface characterized by the presence of at least one protuberance. The planar surface from which the protuberance arises may be the planar surface of a plate-like object such that it extends in two dimensions. Alternatively, the planar surface may be the surface of an object having a curvilinear cross-sectional shape, e.g. as found on the outer surface of a cylinder or cone, such that it extends through three dimensions. The planar surface will appear to be substantially smooth to the naked eye in that there will be no apparent abnormalities, irregular depressions, cracks, etc.

The protuberance is characterized by having a cross-sectional profile that is substantially continuous. The cross-sectional profile is the border or edge line of the protuberance that is produced by cutting through the protuberance along its shortest axis, i.e. the width of a ridge-like protuberance or the diameter of a hemispherical protuberance. A representative cross-sectional profile is shown in Fig. 2. As can be seen in the figure, the cross-sectional profile 20 arises or emerges from the plane 22 as a continuous reentrant curve 26 which extends through a convex protuberance 24 and returns to the plane as a second continuous reentrant curve 28, where the inception and termination of the cross-sectional profile is tangential and parallel to the planar surface 22. By substantially continuous is meant that there are no discontinuities along the cross-sectional profile. In other words, the cross-sectional profile line is a curvilinear smooth line. The cross-sectional profile is further characterized in that the radius of curvature at any point on the profile is from about 0J mm to 10 mm, usually from about 0.5 mm to 5 mm and more usually from about 1 mm to 3 mm, where by radius of curvature is meant the radius of the circle which has the same curvature as the curve at that particular point along the profile. Thus, in Fig. 2, R,, R₂ and R₃ are all between about 0J mm and 10 mm. In most embodiments, the cross-sectional profile will have three distinct inflection points, i.e. three points at which the curve of the profile changes from convex to concave or concave to convex, where there will be two flank inflection points and one crest inflection point. The crest angle of the protuberance, i.e. that angle at the intersection of the tangents of the two flanking inflection points, will range from about 179° to 10°, usually from about 90° to 30° and more usually from about 60° to 45°. The height of the protuberance, i.e. the distance between the crest and the planar surface from which the protuberance emerges, will be at least about 0.5 mm, and usually at least about 1 mm, where the height may be 10 mm or higher, but will usually not exceed about 5 mm and more usually will not exceed about 3 mm.

The protuberance may be a compact, isolated structure covering only a small portion of the surface of the plane, e.g. a hemispherical structure, or the protuberance may be extended across substantially the entire planar surface, e.g. a thread. Where the protuberance is a structure that extends across substantially the entire planar surface, such as a thread, the thread may be one continuous thread or be discontinuous, where there are gaps between portions of the thread. In some embodiments, substantially all of the planar surface may be covered by one or more distinct protuberances, such that there is no visible portion of the planar surface, e.g. where the at least one protuberance is a plurality of threads positioned adjacent to each other and spread across the planar surface.

In many embodiments, the implantable device of the subject invention is an elongate member which has a base configuration of a cylinder or cone as found in conventional screw devices. In such embodiments, the outer surface of the cylinder or cone is the planar surface from which the protuberance arises. Typically, the protuberance will be a thread which extends the length of the cone. As mentioned above, the thread may be a continuous thread or a discontinuous thread, where in a discontinuous thread there are one or more gaps or spaces positioned along the helix of the thread. The thread will typically wind around the base cylinder or cone structure of the device in a helical fashion, where the thread pitch will range from about 0.1mm to 50 mm, usually from about 0.5 mm to 30 mm and more usually from about 2 mm to 15 mm. In certain embodiments, the thread pitch will be such that there is substantially no visible planar surface of the base cone or cylinder structure. In many such embodiments, there may be more than one distinct thread on the surface of the cylinder or cone. In the above screw-type embodiments of the subject devices, the thread height will typically range from about 0J mm to 15 mm, usually from about 0.5 mm to 10 mm and more usually from about 1 mm to 5 mm. The inner diameter of the base structure, e.g. screw or cone, will range from about 1 mm to 7 mm, usually from about 2 mm to 6 mm and more usually from about 3 mm to 5 mm. As such, the ratio of the outer to inner diameter of the device will be at least about 0J , usually at least about 0.3 and more usually at least about 0.6, where the ratio may be as high as 0.9, but will usually not exceed about 0.7. The rebar implantable devices of the subject invention may be fabricated to provide for ease of insertion or removal from a physiological site. As such, the subject rebar devices may be configured to include one or more screw head features at either or both ends of the device, where such features serve a variety of purposes such as in the introduction and/or retrieval of the rebar from the bone site; in securing the rebar device to an implant device such as a plate or rod, and the like. Furthermore, the rebar devices may be cannulated, where cannulation provides for use of the subject devices in conjunction with guide wires, as is known in the art. Hollow passageways in the subject devices may also serve as conduits for cement-like materials during implantation of the device, as described in greater detail below. Turning now to the Figures, Figure 3 A provides a representation of a first embodiment of the subject invention. In Fig. 3A, device 30 comprises a core or shaft portion of circular cross-section. Extending from the otherwise smooth surface 32 are a plurality of protrusions or bumps or ridges 34 symmetrically positioned over the entire surface of the device. The bumps 34 are characterized by being free of any sharp corners or angles and having a cross-sectional profile as shown in Fig. 2. At the ends of the device 36 are hexagonal indentations 38. Fig. 3B provides a representation of a related embodiment, in which the ridges are positioned differently across the surface of the device. In both of these embodiments and many others of the subject invention, the ridges are perpendicular to the axis of the device, represented by the dashed arrow. Fig. 4 provides a representation of another embodiment of the subject device. In Fig.

4, device 40 comprises a shaft portion 42 having a circular cross-section. On the surface of shaft 42 are a plurality of symmetrically positioned hemispherically-shaped bumps 44, which have a cross-sectional profile as shown in Fig. 2.

Figs. 5 A to 5C provide three additional embodiments of rebar devices of the subject invention. In Fig. 5A, the planar surface 52 of the device 50 is characterized by the presence of a continuous thread 54 that has a cross-sectional profile as shown in Fig. 2. The device of Fig. 5B is analogous to that shown in Fig. 5A except that the 54 is discontinuous. The device in Fig. 5C is a variation of that shown in Fig. 5B.

Fig. 6 provides a representation of yet another embodiment of the subject invention, where device shown in Fig. 6 finds particular use as a fixation device in vertebral bodies, especially for placement through the pedicle of a vertebral body. In the device 60 shown in Fig. 6, the cross-sectional profile of ridge 64 extending from planar surface 62 is as shown in Fig. 2.

Fig. 7 provides a representation of a sliding hip screw according to the subject invention, in which a single helical protuberance having a cross section as shown in Fig. 2 extends across the surface of one end of the shaft.

Figs 8A and 8B show rebar cancellous bone screws according to the subject invention, where the thread is continuous in Fig. 8A and discontinuous in Fig. 8B.

Fig. 9 provides a representation of a rebar shaft screw according to the subject invention, where a single helical protuberance having a cross section as shown in Fig. 2 extends across the surface of one end of the shaft.

Fig. 10 depicts a rebar spondylolysis screw according to the subject invention.

Fig. 11 provides a representation of a cannulated, vented rebar screw according to the subject invention.

The subject rebar devices may be fabricated from a variety of different materials, where the particular material chosen may depend on a number of distinct parameters, including: the level of support required; the particular application in which the device is to be used, e.g. whether the device is to be used in conjunction with additional implant devices, such as plates or rods; the length of time the device is to remain in the patient; the desire for resorption or removal, and the like. Materials from which the subject rebar devices may be fabricated include: biocompatible, medical grade metals such as 316L stainless steel and titanium (commercially pure or alloys thereof); polymeric compounds, both standard and reinforced composites, as well as bioresorbable compounds, such as PLA, PLG and the like. The subject devices may be fabricated according to any one of a number of methods known to those of skill in the art, where the particular method chosen for fabrication of a particular rebar device will generally depend on the particular characteristics of the device, such as the material from which it is to be made, the dimensions it is to have, and the like. Methods that may be employed include tooling, molding, and the like.

In using the rebar devices of the subject invention in orthopaedic applications, the devices will usually (though not necessarily) be used in conjunction with a structural augmentation material which is capable of setting into a solid structural product from an initial flowable paste-like consistency. A variety of structural augmentation materials are known and may be employed.

The structural augmentation material used in the subject methods will typically be a flowable, paste-like material that is capable of setting up into a solid structural material in a physiological environment, such as that found in the cancellous region of a bone. Of interest are materials that are capable of non-exothermic setting, are biocompatible and bioresorbable. Of particular interest are calcium phosphate cement materials.

Calcium phosphate cements suitable for use in the subject methods will be flowable for an initial period of time following preparation and be capable of setting in an in vivo fluid environment into a solid apatitic product. The subject cements will comprise dry components and a liquid component which, upon combination, form a paste-like flowable composition capable of setting into a calcium phosphate apatitic material, preferably hydroxyapatite, and more preferably a carbonated hydroxyapatite, i.e. dahllite, having a carbonate substitution of from 2 to 10 %, usually 2 to 8 % by weight of the final product. Calcium phosphate cements which are suitable for use in the subject methods include those cements described in U.S. Patent Nos. 4,880,610; 5,047,031; 5,129,905; 5,336,264; 5,053,212; 5,178,845; 5,580,623; 5,569,442; 5,571,493 and 5,496,399, the disclosures of which are herein incorporated by reference.

The dry components of the cements suitable for use in the subject methods will comprise at least a calcium source and a phosphate source. Preferably, the dry components of the cements employed in the subject methods comprise a homogeneous storage-stable mixture of calcium carbonate, tricalcium phosphate, preferably α-tricalcium phosphate, more preferably reactive α-tricalcium phosphate, as described in U.S. Pat. No. 5,569,442 the disclosure of which is herein incorporated by reference, and monocalcium phosphate monohydrate. Generally, calcium carbonate will be present in the cement in an amount ranging from about 5 to 25 wt. %, usually from about 5 to 20 wt. %, and more usually 10 to 20 wt. % of the entire weight of the dry components. The α-tricalcium phosphate component will be present in an amount ranging from about 60 to 95 wt. %, usually from about 65 to 90 wt. % and more usually from about 70 to 90 wt. % of the entire weight of the dry components. Of particular interest for the α-tricalcium phosphate is the reactive α-tricalcium phosphate described in U.S. Pat. No. 5,569,442, the disclosure of which is herein incorporated by reference. The monocalcium phosphate monohydrate component will be present in an amount ranging from about 1 to 20 wt.%, usually from about 1 to 15 wt. % and more usually from about 2 to 15 wt. % of the entire weight of the dry components.

As described above, the cement will comprise a liquid component, e.g. setting solution or lubricant, in addition to the dry components described above. Preferably the setting solution will be a carbonate or phosphate containing solution at a pH in the range of 6 to 11 , preferably 7 to 9, wherein the concentration of carbonate or phosphate in the solution will preferably range from 0.05 to 0.5 molal (m), with a 0.05 to 0J molal (m) sodium phosphate solution being particularly preferred.

In preparing the subject calcium phosphate cements for use in the subject methods, the dry components and the liquid components will be combined using any suitable means to produce a homogeneous, flowable paste-like material. One suitable means of combining the dry and liquid components is a mortar and pestle, with which the liquid and solid components are mixed manually to produce the flowable paste. Alternatively, one may employ an automated mixing device, as described in PCT/US97/23094 entitled Methods and Devices for the Preparation, Storage and Administration of Calcium Phosphate Cements, the disclosure of which is herein incorporated by reference.

The flowable paste prepared from the dry and liquid components, as described above, will be sufficiently flowable to be introduced through a suitable delivery means, such as a needle, cannula or other introduction means, such as through hollow passageways built into the implantable device of the subject invention.

The cements employed in the subject methods are characterized by their ability to remain flowable for a limited period of time after which they set up into a solid apatitic product, where the cements are capable of setting up into the solid apatitic product in vivo, despite the presence of physiologic fluids, such as blood. Following mixing, the cements generally remain flowable for a period of time ranging from about 2 to 30 min, usually from about 5 to 15 min, and more usually from about 5 to 10 min, where preferred cements are those cements which set within a clinically relevant period of time, where clinically relevant period of time means a period of time usually less than about 15 min, more usually less than 12 min. In using the subject rebar devices in conjunction with structural augmentation materials, such as the calcium phosphate cements described above, a physiological site will be prepared first as desired, e.g. a fracture will be reduced, loose tissue will be removed, etc., and then the implantable device and the augmentation material will be introduced. The implantable device may be introduced prior to, after or at substantially the same time as the augmentation material is introduced, depending on the particular procedure being performed. In certain embodiments where the device comprises hollow passageways, the implantable device will be introduced first, and the augmentation material will then be introduced through the implantable device.

Also provided by the subject invention are kits for use in orthopaedic, dental, craniomaxillofacial and related applications. The kits of the present invention at least include the subject implantable devices in combination with instructional material on how to use the devices, where the instructional material may be present on one or more of: packaging, labeling or a package insert of the kit. The kits may further comprise one or more components of an augmentation structural material with which the device is to be used, where the components may be one or more of the components of a calcium phosphate cement, such as the dry and liquid components of such a cement, as described above, where the components may be present in the same or different containers as is practicable, e.g. dry reactants in one container and liquid components in a second container. The kits may further comprise devices which aid in the delivery of the structural material to a physiological site of interest, e.g. needles, cannulas and the like, as well as devices for preparing the physiological site, such as spatulas, probes, etc.

ADDITIONAL DEVICE EMBODIMENTS

Also provided by the subject invention are rebar bone fixation devices that are characterized by the lack of a bone cutting functionality, such as a sharp angled or sharp cornered thread component as is found in prior art bone screw devices. These rebar devices of the subject invention may or may not comprise a thread feature. However, where the subject devices comprise one or more thread features, the thread will not be configured to have a sharp cutting edge. Although the edge may be smooth or cornered, where the thread feature does comprise a corner, where the term corner is used to refer to the intersection of two planar surfaces, the corner will in many embodiments typically form an angle which is greater than 90 °, so that the thread feature does not serve as a bone cutting functionality of the device. The rebar devices of the subject invention may be fabricated in a variety of configurations. Usually, the rebars will have a cylindrical type configuration, whereby the term "cylindrical" is used broadly to refer to any type configuration which is characterized by having an overall cylindrical shape. All of the different embodiments of the subject rebar devices featured in Figs. 12 to 19 have a cylindrical configuration, as that term is used herein. Although broadly falling within the cylindrical configuration category, in addition to those embodiments in which the core has a circular cross-section, the subject devices may have, for example, hexagonal, star, square internal and/or external drive configuration, where the configuration may be the same along the entire length or core of the device or differ from one end to the other.

The surface of the rebar core may be smooth or modified in a variety of different ways. Thus, the rebar may comprise surface indentations, recessions or impressions, protrusions, ridges, bumps, threads, one or more passageways extending through the device, and the like, where such features will typically be present to provide purchase within the hardened structural augmentation material with which the subject devices are often employed and to maintain fracture proximity and alignment.

The dimensions of the rebar devices will vary greatly depending on the particular application in which they are to be employed. The dimensions of a particular rebar device according to the subject invention will be chosen primarily on their intended use, and may be readily determined by those of skill in the art. Where the rebar devices are used in the place of conventional bone screws, the rebars may have dimensions that are roughly analogous to those dimensions of the corresponding bone screws.

In Fig. 12, rebar device 120 comprises a circular cross-sectioned core component or drive 122. On the surface of core 122 is a single thread 124 which runs the entire length of the core 122. The thread is characterized by having a gradual pitch and a shape that is devoid of any bone cutting edges, since the angles formed at the planar intersections of the surfaces of the threads, i.e. 126 & 128, are greater than 90 °. Hexagonal indentations 129 are provided at either end of the device.

In Fig. 13, device 130 is a single, cylindrical wire which is shaped as a single helix. In Fig. 14 is depicted a rebar device 140 having a core component 141 with two gradual threads or fins, 142 and 143, which form paddle shape cross -sections at either end of the device, 144 and 145. At one end of the device is a hexagonal indentation 146. The basic configuration of device 140 may be modified in a number of ways. One way the device may be modified is to have an undefined transition between the core and fin components, so than the surface of the fin components gradually transition into the core component, such the core component loses its circular cross-section as shown in Fig. 14. Another modification that may be made is to modify the shapes of paddle sections 144 and 145, so that they are the same or reversed to that shown in Fig. 14, such that the cross-sectional shape of paddle 144 is rectangular as shown for paddle 145.

Device 140, and modified versions thereof as described above, is particularly suited for use in spinal fusion as a substitute for traditional pedicle screws. In spinal fusions, pedicle screws are inserted through the pedicle portion of the vertebra into the cancellous region of the vertebral body. The screw serves as an attachment point for a rod or plate. In using device 140 or modified versions thereof in place of traditional pedicle screws in spinal fusion applications, the body portion of the device, i.e. that comprising paddle 144, will first be inserted through the pedicle. During insertion, the device will slowly be turned to one side, such that following insertion, paddle portion 144 in its final position in the vertebral body is horizontal to its initial position prior to insertion, and paddle 145 fits snugly in the oblong pedicle. In such applications, the device may be used in conjunction with structural augmentation materials, as described in greater detail below.

Fig. 15 depicts yet another alternative embodiment of the subject rebar devices. In Fig. 15, device 150 has a core 152 with a star shaped cross-section. Extending from the core is a plurality of symmetrically positioned fins 154 which have sharp angle or corners 156. However, since the fins are not configured as threads, these sharp corners do not surface as bone cutting functionalities in device 150. Device 150 is further characterized by having a hexagonal indentation 158. In Fig. 16, device 160 comprises core 162 of circular cross-section. The surface of core 162 is characterized by a plurality of hemispherical indentations or depressions 164 symmetrically positioned over the entire surface of core 162.

In Fig. 17, device 170 comprises core 172 of circular cross-sectional shape. End 176 is tapered while end 178 has a head configuration with a hexagonal indentation 179. The entire length of core 172 is characterized by the presence of a single thread 174 of gradual pitch, where the thread is configured to have a shape that is devoid of any bone cutting edges, since the angles formed at the planar intersections of the surfaces of the threads, i.e. 173 and 175, are greater than 90 °.

In Fig. 18, device 180 is similar to device 170. Core component 182 comprises a single thread 184 running its entire length, where thread 184 has a shape that is devoid of any bone cutting edges, since the angles formed at the planar intersections of the surfaces of the threads, i.e. 186J88, are greater than 90 °. Device 180 differs significantly from device 90 by having blunt ends without any additional features, such as heads, indentations or tapered regions.

The implantable devices of this embodiment characterized by the lack of a cutting edge may be fabricated and used as described above in connection with the primary embodiment of the subject invention in which the devices have at least one protuberance having a substantially continuous cross-sectional profile.

It is apparent from the above description that implantable devices which provide for significant improvements over currently employed fixation instruments, such as bone screws, are provided. The subject devices are capable of being used to reinforce structural materials, e.g. enhancing tensile and/or compressive strength of such materials, without giving rise to stress fractures or other complications experienced with bone screws or other traditional fixation instruments. The subject devices also provide for superior purchase with the bone and/or augmentation material, as well as ease of insertion and removal.

All publications and patent applications cited in this specification are herein incorporated by reference as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. The citation of any publication is for its disclosure prior to the filing date and should not be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention.

Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it is readily apparent to those of ordinary skill in the art in light of the teachings of this invention that certain changes and modifications may be made thereto without departing from the spirit or scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. An implantable device comprising a planar surface having at least one protuberance, wherein said protuberance has a cross-sectional profile that is substantially continuous, and further wherein the radius of curvature at each point on said profile is between about OJ mm and 10 mm.

2. The implantable device according to Claim 1, wherein said cross-sectional profile has three inflection points.

3. The implantable device according to Claim 1, wherein said planar surface is the surface of a plate-like device.

4. The implantable device according to Claim 1 , wherein said planar surface is the outer surface of a device having a curvilinear cross-sectional shape.

5. The implantable device according to Claim 1, wherein the height of said protuberance ranges from about 0.5 mm to 10 mm.

6. An implantable device comprising at least one element with a curvilinear cross- sectional shape comprising a planar surface having at least one protuberance, wherein said protuberance has a cross-sectional profile that is substantially continuous with three inflection points, and further wherein the radius of curvature at each point on said profile is between about 0.1 mm and 10 mm.

7. The implantable device according to Claim 6, wherein said at least one element has a configuration selected from the group consisting of a cone or cylinder.

8. The implantable device according to Claim 6, wherein the radius of curvature at any point on said cross-sectional profile ranges from about 0.5 to 5 mm.

9. The implantable device according to Claim 6, wherein the radius of curvature at any point on said cross-sectional profile ranges from about 1 to 3 mm.

10. The implantable device according to Claim 6, wherein said protuberance has a height ranging from about 0.5 to 10 mm.

11. The implantable device according to Claim 6, wherein said protuberance is an isolated hemispherical structure.

12. The implantable device according to Claim 6, wherein said protuberance is a thread.

13. The implantable device according to Claim 12, wherein said thread is continuous.

14. The implantable device according to Claim 12, wherein said thread is discontinuous.

15. The implantable device according to Claim 12, wherein said thread has a pitch ranging from about OJ to 50 mm.

16. The implantable device according to Claim 6, wherein the crest angle of said protuberance ranges from about 179┬░ to 10┬░.

17. An implantable device comprising at least one element with a circular cross-sectional shape and having a planar surface with at least one thread, wherein said thread has a cross- sectional profile that is substantially continuous and has three inflection points, and further wherein the radius of curvature at each point on said cross-sectional profile is between about 0J mm and 10 mm.

18. The implantable device according to Claim 17, wherein said thread is continuous.

19. The implantable device according to Claim 17, wherein said thread is discontinuous.

20. The implantable device according to Claim 17, wherein said thread has a pitch of from about OJ to 50 mm.

21. The implantable device according to Claim 17, wherein the radius of curvature at any point on said cross-sectional profile ranges from about 0.5 to 5 mm.

22. The implantable device according to Claim 17, wherein the radius of curvature at any point on said cross-sectional profile ranges from about 1 to 3 mm.

23. A kit for use in surgical procedure, said kit comprising: an implantable device according to Claim 1 ; and components for producing a flowable structural material capable of hardening to produce a solid product.

24. The kit according to Claim 23, wherein said solid product is a calcium phosphate material.

25. The kit according to Claim 23, wherein said components comprise at least one calcium source and at least one phosphate source as dry components.

26. The kit according to Claim 25, wherein said dry components comprise: tricalcium phosphate; a partially neutralized phosphoric acid source free of uncombined water; and a carbonate source.

27. The kit according to Claim 23, wherein said components further comprise at least one aqueous medium.

28. The kit according to Claim 27, wherein said aqueous medium is a sodium phosphate or sodium carbonate solution.

29. In a method of introducing a flowable structural material capable of setting into a solid product to a physiological site, the improvement comprising: introducing an implantable device according to Claim 1 to said physiological site.

30. The method according to Claim 29, wherein said introducing of said implantable device is prior to said introducing of said flowable material.

31. The method according to Claim 29, wherein said introducing of said implantable device is after said introducing of said flowable material.

32. The method according to Claim 29, wherein said introducing of said implantable device is at substantially the same time as said introducing of said flowable material.