HK1118186B - Osteosynthetic implants and methods of use and manufacture - Google Patents

Description

Osteosynthesis implant and methods of use and manufacture

Cross Reference to Related Applications

This application is a continuation of U.S. patent application No.11/112865 filed on 21/4/2005 and relates to U.S. provisional application No.60/563952 filed on 21/4/2004, the entire contents of which are hereby incorporated by reference in their entirety.

Technical Field

The present application relates generally to fracture repair, and more particularly to osteosynthesis implants for fracture repair and methods of their use and manufacture.

In 1959, a group of Swiss plastic surgery and general surgeons formed an Arbeitsgememefaft fur Osteosynylthesefregen (AO), also known as the International Association for internal fixation research (ASIF). The AO/ASIF is now a multinational organization of physicians and scientists with the goal of studying bone healing and the continuing development of fracture fixation techniques for patient care. In the united states and most other countries, AO/ASIF guidelines for skeletal fixation have become the standard of care for trauma fracture and osteotomy treatment fixation techniques. Under these AO/ASIF guidelines, surgeons plan and perform surgery to achieve a predetermined end result of bone healing and skeletal function.

Problems can arise when the fracture site or fusion site is not sufficiently stable during healing. Screws and plates may be used alone or in combination, depending on the nature of the fracture. One purpose of osteosynthesis implants is the anatomical reduction of fractures. Another object is to minimize or eliminate inter-chip movement. Yet another object includes increasing or maximizing blood supply to the fracture site by reducing or minimizing collateral vessel damage. Continuous compression therapy may also be osteoinductive due to its piezoelectric effect on the osteoblasts themselves. Excessive inter-fragment movement leads to the formation of fibrous unmineralized scar tissue (leading to unbonded or pseudoarticular joints) as opposed to bone regeneration. Unmineralized scar tissue fails to support the load and loses skeletal function. A sufficient blood supply must be maintained to support bone metabolism, bone regeneration, and remodeling of the fracture site. Current standards of care include bone engaging devices made of stainless steel or titanium.

The use of stainless steel or titanium in bone-engaging devices has a long history and a considerable record of success. However, over time, the stainless steel and titanium fixation constructs (screws and plates) no longer maintain compression on the fracture fragment. A reduction in pressurization of certain standard material constructions has been observed to reach thirty-two percent (32%) in a two week period. As the necrotic surface of the fracture is resorbed, non-load bearing gaps are created between the fragments, thereby reducing compression and increasing the risk of inter-fragment migration and scar tissue formation. Loss of compression is generally contrary to the goal of fracture fixation, and in particular, to the goal of bone engaging implants. Improvements that help maintain a compressive load on the fracture site over a longer healing period are desired.

Disclosure of Invention

The present application relates generally to fracture repair and bone fusion, and more particularly to osteosynthesis implants for fracture/fusion repair and methods of their use and manufacture. Fracture repair devices, systems, and methods include devices, systems, and methods for repairing intentional fracture sites for reconstruction purposes, such as, but not limited to, osteotomies. Bone fusion of the surgical resection joint throughout the body is included within the scope of the present invention. The fracture fixation devices, systems, and methods of the present invention help maintain a compressive load on the fracture site for a longer period of time as compared to prior devices. In certain embodiments, the use of shape memory materials, including nickel titanium, provides improved fracture repair characteristics. The invention also includes methods of use and methods of manufacture of such bone fixation devices and systems.

In one embodiment, the bone fixation device of the present invention includes an elongated member having a responsive zone. The elongated element is a plate, nail, or in an alternative embodiment a bone screw. The elongate member is adapted to be coupled to a bone such that the responsive zone is positioned adjacent a fracture site or fusion site in the bone. The responsive zone is adapted to apply a predetermined pressure to the bone when coupled thereto. In a preferred embodiment, the responsive zone comprises a shape memory material, which may be nickel titanium or nitinol.

In some embodiments, the elongate element comprises nitinol, while in other aspects, the responsive zone is pseudo-elastic at body temperature. In this manner, the elongated member may be used to apply a predetermined force at the fracture site. In some embodiments, the responsive zone is positioned substantially in the middle of the elongated member. In one aspect, the responsive zone has a cross-section that is smaller than a cross-section of the end of the elongated member. This configuration helps to position the stress or pressure in the elongated member at a predetermined location, particularly at the responsive zone.

In certain aspects, the bone fixation device further comprises a coupler adapted to couple the elongate element to the bone. The connector may include one or more bone screws, which in some embodiments include a shape memory material. In certain embodiments, the elongate member has first and second end portions, each end portion having at least one aperture adapted to receive a coupler therethrough for coupling the member to bone. Other embodiments may use two, three, four, or more holes in one or both end portions to fixedly couple the device to a fractured bone.

The invention also provides a bone fixation system. In one embodiment, the system includes an elongated element having a responsive zone of shape memory material, for example, in its pseudo-elastic state, and a coupler adapted to couple the elongated element to a bone such that the responsive zone is positioned in the bone adjacent a fracture site. In some embodiments, the system includes a removable clamp adapted to hold the elongate element responsive zone at a predetermined position prior to coupling the element to the bone, and may also be adapted to be removed from the elongate element after the element is coupled to the bone. In one aspect, the responsive zone is adapted to apply a predetermined pressure to the bone when the elongate member is coupled to the bone.

The invention also provides methods of stabilizing a fractured bone. In one such embodiment, the method includes providing an elongate element, which may be a plate, intramedullary or extramedullary nail, bone screw, pin, or related device. The elongated member has a responsive zone of shape memory material such that the responsive zone is adapted to apply a predetermined pressure to the bone when coupled thereto. The method includes coupling an elongate element to the bone such that the responsive zone is positioned in the bone adjacent the fracture site.

In one aspect, the method includes applying a force to an elongated element, elongating the responsive zone a predetermined amount, holding the element in an elongated position, coupling the element to the bone such that the elongated responsive zone is positioned adjacent the fracture site, and releasing the elongated element. In certain aspects, the elongated member can be released by removing the clamp. As a result, stresses formed in the responsive zone may be applied to the bone, helping to stress, stabilize, heal, etc. the fracture site and fusion site.

In a particular aspect, coupling the elongate element to the bone comprises: a first coupler is attached to the member and to the bone on a first side of the fracture site, and a second coupler is attached to the member and to the bone on a second side of the fracture site. In this manner, the responsive zone is positioned adjacent to the fracture site. In one aspect, the force applied to the elongated element to elongate the responsive zone by a predetermined amount corresponds to a predetermined compressive force to be applied to the fractured bone when the element is coupled thereto. Further, the shape memory material may be nitinol or other shape memory material compatible with the human body.

In one aspect, embodiments of the present invention provide a bone fixation system. The system can include a bone fixation device having a response zone, and a clamping member configured to be at least partially received within a lumen of the bone fixation device, the lumen being disposed along an axial length of the bone fixation device. The clamp is adjustable between a first mode in which a first amount of strain is induced or maintained in the response zone along the axial length of the bone fixation device and a second mode in which a second amount of strain is induced or maintained in the response zone along the axial length of the bone fixation device. The clamping member may be removably coupled to the bone fixation device. In some cases, the clamp includes an end cap and an inner post. The end cap is adjustably engaged with the bone fixation device at a first portion of the end cap and adjustably engaged with the inner post at a second portion of the end cap. Relatedly, the end cap is threadably engaged with the bone fixation device at the end cap first portion and threadably engaged with the inner post at the end cap second portion. In certain aspects, a central longitudinal axis defined by the lumen of the bone fixation device is collinear with a central longitudinal axis defined by the inner strut. Relatedly, a central longitudinal axis defined by the lumen of the bone fixation device is collinear with a central longitudinal axis defined by the end cap.

The bone fixation device may be, for example, an intramedullary or extramedullary nail, a screw, a plate, a pin, a compression rod, a spinal fixation device, or the like. The responsive zone can have physical properties similar to human tissue. In some cases, the physical property is a modulus, such as an elastic modulus. For example, the modulus can have a value ranging from about 10Gpa to about 70 Gpa. In some cases, the human tissue is bone. Typically, the responsive zone comprises a shape memory material, which may be a shape memory alloy. The shape memory alloy can include nickel alloys, copper alloys, and the like. In some cases, the shape memory alloy includes nickel titanium alloy, copper zinc aluminum alloy, copper aluminum nickel alloy, and the like. The responsive zone is configured to provide a predetermined compressive force at the fracture site when the clamp is removed or deactivated. Similarly, the responsive zone is configured to return to a preset length when the clamp is removed or deactivated.

In another aspect, embodiments provide a bone fixation device that includes a machined responsive zone having hardness values in the range of from about 5HRB to about 60HRC on the Rockwell B and C scale. The responsive zone may comprise nitinol. In yet another aspect, embodiments provide a method of preparing a bone fixation system. The method can include providing a bone fixation device having a response region, inserting a clamp at least partially into a lumen of the bone fixation device, the lumen disposed along an axial length of the bone fixation device, and inducing, controlling, or adjusting a strain in the response region along the axial length of the bone fixation device with the clamp. The method can further include threadably engaging an end cap of the clamp with the bone fixation device at a first portion of the end cap and threadably engaging the end cap with the inner post of the clamp at a second portion of the end cap.

In yet another aspect, embodiments include a method of positioning a bone fixation device in a patient. Such a method can include, for example, providing a bone fixation device having a first portion, a second portion, and a responsive zone disposed therebetween, and inserting a clamp at least partially into a lumen of the bone fixation device. The lumen may be disposed along an axial length of the bone fixation device. The method may further include inducing, maintaining, controlling, or adjusting a strain along an axial length of the bone fixation device in the responsive zone with the clamp, coupling the bone fixation device to the bone of the patient by attaching a first portion of the device to a first bone site and attaching a second portion of the device to a second bone site. The bone typically includes a fracture site disposed between first and second bone locations. The method can also include securing the bone fixation device to the outer strut assembly, removing the clamp from the bone fixation device, and removing the outer strut assembly from the bone fixation device. The bone fixation device is capable of remaining coupled to a bone of a patient and allowing release of the responsive zone, thereby transmitting a compressive force through the bone fixation device to a fracture or fusion site of the bone of the patient.

In one aspect, embodiments include a method of processing a shape memory material for use in a bone fixation device. The method may include, for example, treating the shape memory material with a first treatment, transforming the shape memory material from a first state to a second state, machining the shape memory material while in the second state, and treating the machined shape memory material with a second treatment to transform the shape memory material from the second state to a third state. The first treatment comprises a first thermal cycle at a temperature of about 600 ℃ for at least 5 minutes. The first treatment further includes a second thermal cycle at a temperature ranging from about 200 ℃ to about 550 ℃ for at least 5 minutes. In certain embodiments, the first state has a first hardness value, the second state has a second hardness value, and the first hardness value is between about 100% and about 500% of the second hardness value. The first state can have a first shape recovery value, the third state has a third shape recovery value, and the third shape recovery value is at least 95% of the first shape recovery value. In some cases, the shape memory material includes a shape memory alloy such as nickel titanium alloy, copper zinc aluminum alloy, copper aluminum nickel alloy, and the like. The third state comprises an optimal pseudo-elastic property curve of the shape memory material. In certain aspects, the first state has a first hardness value, the third state has a third hardness value, and a difference between the first hardness value and the third hardness value is less than about 3HRC on a rockwell C scale. In some cases, the difference may be less than about 10 HRC.

In another aspect, embodiments include a method of preparing a bone fixation device. The method may include providing a bone fixation device including a shape memory material and machining the shape memory material while its temperature is maintained at or above an austenite transformation temperature. In certain aspects, the shape memory material remains in the hard austenite phase and does not transform to the malleable austenite phase during machining.

Additional embodiments and features are set forth in part in the description which follows and, in part, will be apparent to those skilled in the art from the description or may be learned by practice of the invention. The features and advantages of the invention may be realized and obtained by means of the instruments, combinations, and methods described in the specification.

Drawings

FIG. 1A is an overall view of a dynamic compression bone screw according to an embodiment of the present invention;

FIGS. 1B and 1C are simplified views of steps for forming the dynamic compression bone screw shown in FIG. 1A;

FIGS. 2A-2C schematically illustrate the use of the dynamic compression bone screw of FIG. 1A for repairing a bone fracture;

FIG. 3A is a side view of the dynamic compression bone screw of FIG. 1A;

fig. 3B and 3C are enlarged views of the screw head and threaded portion, respectively, for the bone screw shown in fig. 3A;

FIG. 3D is a longitudinal cross-sectional view of the bone screw shown in FIG. 3A;

FIG. 3E is a top view of the bone screw shown in FIG. 3A;

fig. 3F is an overall view of the bone screw shown in fig. 3A;

FIG. 3G is an overall view of the dynamic compression bone screw of an alternative embodiment of the present invention;

FIG. 4 is an overall view of two bone fixation devices of an embodiment of the present invention;

fig. 5A is an overall view of the bone fixation device shown in fig. 4;

FIGS. 5B-5I are additional views of the fixture shown in FIG. 5A, including a bottom view (FIG. 5A), a top view (FIG. 5B), a longitudinal cross-sectional view (FIG. 5C), an enlarged bottom view (FIG. 5D) of the expansion region, an end view (FIG. 5E), and a side view (FIG. 5F);

FIGS. 6A and 6B are general views of a fixation device coupled to a bone having a fracture site;

FIGS. 7A and 7B are exploded and assembled overall views, respectively, of a bone fixation system using an embodiment of the present invention of the fixation device shown in FIG. 4;

FIG. 8 is an overall view of a bone fixation device of an alternative embodiment of the present invention;

FIGS. 9A and 9B are graphs of material properties of a bone fixation screw and device according to an embodiment of the present invention; and

FIGS. 10A and 10B are diagrammatic illustrations of features of a bone screw and fixation device in accordance with an embodiment of the present invention;

FIGS. 11 and 11B illustrate an end cap of an embodiment of the present invention;

fig. 12 shows an inner post of an embodiment of the present invention;

fig. 13A and 13B illustrate a bone fixation system according to an embodiment of the present invention;

FIG. 14 illustrates a clamp or external fixation device of an embodiment of the present invention;

FIG. 15 shows a retaining bar of an embodiment of the present invention;

FIG. 16 illustrates a bone fixation device according to an embodiment of the present invention;

FIG. 17 illustrates a patient's leg and a clamp and retaining bar of an embodiment of the present invention;

FIG. 18 illustrates a patient's leg, a clamp and retaining rod of an embodiment of the present invention, and a bone fixation device;

FIG. 19 illustrates a patient's leg, a clamp and retaining bar of an embodiment of the present invention, a bone fixation device, and a cross pin;

FIG. 20 illustrates a patient's leg and a bone fixation device of an embodiment of the present invention;

FIG. 21 illustrates a patient's leg, the clamp and retaining bar of an embodiment of the present invention, a cross pin, a bone fixation device, and a bone screw;

FIGS. 22A and 22B illustrate a patient's leg, a clamp and retaining rod of an embodiment of the present invention, a cross pin, a bone fixation device, and a bone screw;

FIG. 23 illustrates a patient's leg, a bone fixation device and bone screws of an embodiment of the present invention;

fig. 24A to 24H illustrate a typical intramedullary nail having exemplary dimensions;

FIG. 25 shows a graph of hardness versus heat treatment for an embodiment of the present invention.

Detailed Description

It is known that when a bone is fixed and a compressive force is applied to a fracture or fusion fixation device, the force between the ends of the fragments decreases rapidly as a function of time. Ideally, the fixation device is capable of maintaining a compressive force that allows continuous healing by reducing the fracture gap, and stability of the fracture gap. If this does not occur, loss of compression may result in lack of union and stabilization of the fracture site, which in turn slows healing. The fracture fixation device is placed in place to stabilize the fracture site, however if the compressive force is not present, minor movement between the fracture ends may occur. This in turn may lead to unnecessary resorption, which may lead to non-bonding of the bone or the presence of large voids. These reasons show the importance of the device to actively match changes in the body and have a similar response to bone.

Embodiments of the present invention include bone fixation devices, including plates, bone nails such as intramedullary nails, bone screws, and the like, which are capable of providing stable compression (spontaneous dynamic compression) of a bone fracture over time. The dynamic compressive force is stable or substantially stable as a function of resorption of the bone surface at the fracture site, facilitating promotion of bone healing and reduction of unbound rate. Certain bone fixation devices of the present invention will allow approximately six percent (6%) relaxation prior to loss of pressure. In contrast, typical stainless steel or titanium bone screws lose their compressive force after about one percent (1%) resorption at the fracture surface.

Fig. 1A-2C illustrate a dynamic compression bone screw 100 according to an embodiment of the present invention. Bone screw 100 shown in fig. 1A is further described in conjunction with fig. 3A-3F. In a particular embodiment, the bone screw 100 is formed from a shape memory alloy of nickel titanium, known as nitinol. As shown in fig. 1B and 1C, the screws are made from nitinol blanks or blocks and may be heat treated to produce the desired characteristics. Shape memory alloys such as nitinol have the ability to recover a large strain (e.g., about 6%) by heating (shape memory) or by gradual unloading (pseudo-elasticity). The present invention uses the greater strain capacity and recovery characteristics of shape memory alloys, such as nitinol, for bone repair with novel devices, systems and methods. In one embodiment, a fixation device such as screw 100 is machined from a shape memory material such as nitinol that is heat treated to be pseudo-elastic at body temperature. The overall screw geometry, response element geometry, and material heat treatment will be specified to maintain the compressive force required as a function of the condition of the fracture or fusion site.

The shape memory effect of nitinol is a temperature induced phase transformation between a malleable martensite (lower temperature) phase and a harder austenite (higher temperature) phase having a desired preset shape. The use of thermally driven phase changes helps certain embodiments of the present invention to produce the desired bone fixation results. The pseudo-elastic effect of nitinol refers to its return to its pre-set austenitic configuration upon unloading after elastic deformation. The initiation of the superelastic behavior of nitinol requires the formation of stress-induced martensite (SIM) from the austenite phase, for example, by the application of an external load or stress. The reduction of the external load or stress induces the formation of the austenite phase, thus forming its pre-set configuration. Nitinol is capable of accumulating large deflections (strains) under nearly constant loads (stresses). A relatively flat region of nitinol load versus deflection may be used with certain devices of the present invention.

Certain embodiments of the present invention utilize the stress/strain (modulus) of nickel titanium shown in fig. 9A. These characteristics of nickel titanium facilitate, for example, the improvement and use of improved total joint implants. This property of nickel titanium reduces the stress of the connection of the entire bone to the implant, resulting in a longer implant life. Embodiments of the present invention, particularly those using nickel titanium, help the bone to maintain a load, which promotes healing by reducing stress/strain and shear forces and helps the smaller implant to maintain the same or similar stability as the larger implant in a similar fixation area.

Formation of the SIM within the responsive zone of the screw 100 or other bone engaging implant and device may be accomplished prior to or as a result of surgical placement. For bone screw 100 depicted in fig. 1A, the responsive zone of the screw would be designed to initiate SIM formation as a result of the installation process. This occurs at least in part due to the elongation forces applied to the screw when the screw is in use. Additional details on the response region are discussed in connection with fig. 3A-3F.

One technique for fracture fixation is the passage of a lag screw through the apposition end of a fracture in the cortical bone. Inserting the screw through the fracture site helps create dynamic behavior in the screw. As shown in fig. 2A, the bone screw 100 is inserted at an angle relative to the fracture site 210. Screw 100 is rotated to draw the two bone fragments 220 toward one another, creating a compressive force therebetween. The rotational torque used to rotate screw 100 translates into axial compression between bone fragments 220. The result is proper alignment of bone fragments 220 as shown in fig. 2B. Screw 100 maintains a compressive force on bone fragments 220 for a longer period of time than conventional bone screws made of steel, titanium, or the like. As a result, a more fully healed fracture site 210 is obtained (fig. 2C). During healing and bone resorption, the force generated by existing screws can be reduced such that a reduced compressive force acts on the fracture site 210 over time. In contrast, the bone screw 100 of the present invention is a dynamic screw that is capable of maintaining a high compression value for a longer period of healing. Advantages of screw 100 include better promotion of direct bone healing, reduced non-union at high risk fracture sites, and reduced bone implant site resorption. In certain embodiments, at least some of these advantages are achieved by using a shape memory material, such as nitinol, that has an inherent stress/strain similar to bone.

Fig. 3A-3F illustrate further details of bone screw 100 according to an embodiment of the present invention. It will be apparent to those skilled in the art that specific examples are illustrated in fig. 3A-3F, and that the invention is not limited to the dimensions and configurations shown therein. As best seen in fig. 3A, 3D and 3F, the bone screw 100 has a shank portion 110 having a reduced thickness or radius compared to the radius or thickness of the threaded portion 120 or the head portion 130. In this manner, the reduced area of rod portion 110 allows stress to be concentrated on rod portion 110, which allows rod portion 110 to elongate to form a responsive element or region. In one embodiment, elongation of shaft portion 110 occurs during the process of insertion into a fractured bone, as shown in fig. 2B. Bone screw 100 is capable of positioning the force generated by the SIM over the fracture site through the use of a responsive element or shaft portion 110. The non-responsive screw portion (e.g., head 130) remains substantially strain free and generates little force on the bone due to the SIM.

In an alternative embodiment, the bone screw 300 shown in fig. 3G has a substantially uniform diameter at the shank portion 310. In this embodiment, only the stem portion 310 is made of a shape memory material with a threaded end portion 320 that includes a harder region that is less affected by elongation.

Referring now to fig. 4, a bone fixation device 400 according to an embodiment of the present invention will be described. The bone fixation device 400 allows for longer and greater sustained compressive forces. For example, current bone plates applied to fracture surfaces tend to lose compression force within two days to two weeks after surgery, thus slowing the healing process. Other problems with existing plates (e.g., offset and stiffness) also result in a greater chance of re-fracture and slow healing. In one embodiment of the present invention, the bone fixation device 400 comprises a shape memory alloy that may be nitinol or the like. The fixation device 400 is a dynamic device that can change over time with the human body into which it is inserted. In a preferred embodiment, device 400 comprises nitinol, in part because of its ability to recover to large strains over time. In one embodiment, this is accomplished by fabricating the device 400 with a responsive zone portion 410. In certain embodiments, the total cross-sectional area of the responsive zone 400 is smaller than the non-responsive zone of the device 400. The responsive zone 410 is used to locate the elongation of the device 400 in that zone. In one embodiment, device 400 is elongated based on the application of a force similar to or the same as the force required to stabilize the fracture to which device 400 is applied. The device 400 will elongate based on the force required to stabilize the fracture and apply the necessary healing force. After the device 400 is elongated, it is held in an elongated state, in one embodiment, by an external clamp or similar structure, to prevent return movement of the device 400. After the device 400 is secured to the fracture site, the clamp or other retaining mechanism may be removed. Further details on the use of the apparatus 400 are discussed in connection with fig. 7A and 7B.

Fig. 5A-5I illustrate various views of the apparatus 400 or portions of the apparatus 400, according to particular embodiments of the present invention. Dimensions including length, width, thickness and radius of curvature may also be varied within the scope of the invention as shown in the figures. More specifically, the figures include a longitudinal cross-sectional view (fig. 5C), a top view (fig. 5B), a bottom view (fig. 5A), a side view (fig. 5F), an end view (fig. 5E), and an enlarged bottom view of the extended region 410 of the device 400. In a preferred embodiment, device 400 is attached to a bone having a fracture site such that responsive zone 410 is disposed adjacent to the fracture site. This arrangement can be seen in fig. 6A and 6B.

As shown, device 400 has one or more holes 430 disposed on each side of response zone 410 so that device 400 can be coupled to fractured bone 600. Although fig. 6A and 6B illustrate four holes 430 on each side of the fracture site, a greater or lesser number of holes 430 may be used within the scope of the invention. In some embodiments, the holes 430 are adapted to receive screws or other fixation elements that secure the device 400 to the bone 600. With respect to coupling of device 400 to bone 600, it is preferable to position responsive zone 410 across or adjacent to fracture site 610. This may include attaching one end of the device 400 to one bone segment 620 and attaching a second end of the device 400 to the opposite bone segment 620. In certain embodiments, the screws or fixation elements used to couple device 400 to bone segments 620 include bone screws, which may be made of stainless steel, titanium, or the like. In particular embodiments, the screws or fixation elements used to couple device 400 to bone 600 comprise a shape memory alloy such as nitinol.

Fig. 7A and 7B illustrate a bone fixation system 700 according to an embodiment of the present invention. The system 700 includes the fixture 400 and the clamp 710 as previously described. Although FIG. 7A illustrates one example of a clamp 710, other clamp types are within the scope of the present invention. Moreover, alternative devices may be used in place of clamp 710 provided that the alternative devices are capable of being attached to device 400 and preferably capable of maintaining device 400 in a desired position or elongated state. In operation, an elongation force is applied to the device 400 to stretch or elongate the device 400 to a predetermined length. As described further below, the application of the predetermined force is determined, at least in part, by the force required to provide a healing effect to the bone to which the device 400 is to be applied. Once the device 400 is elongated to a desired length, the clamp 710 is used to hold the device 400 in the elongated position. The clamp 710 maintains the extended position of the device 400 until the device 400 is attached to the fractured bone. Once device 400 is attached to the fractured bone, clamp 710 may be removed from device 400. In this manner, device 400 is attached to the fracture site and upon release of clamp 710, device 400 provides the desired compressive force at the site of the fracture. Again, in certain embodiments, the device 400 also includes a shape memory material, and in particular embodiments, nitinol. Preferably, the application of the compressive force is of sufficient duration to aid healing and avoid some or all of the other problems associated with prior devices constructed of stainless steel, titanium or similar materials.

In the illustrated embodiment, clamp 710 includes a body member 712, first and second device engaging members 714, and a wedge element 716. In one embodiment, the device-engaging members 714 are configured such that screws, lugs, posts, etc. 718 extending from the members 714 pass at least partially through corresponding holes 430 in the device 400. The body component 712 is then coupled to the device-engaging component 714 such that the wedge element 716 is positioned therebetween. Force is applied to wedge element 716 by rotating or depressing pressure applicator 720, which in one embodiment is a screw. A force is applied to wedge 716 in the direction shown by arrow 722 resulting in an outward force being applied to component 714 as shown by arrow 724. As can be seen in fig. 7A, the force indicated by arrow 724 results in an elongation force being applied to the device 400 through the use of screws, lugs, or posts 718. By controlling the physical relationship between pressure applicator 720 and member 714, the elongation force on device 400 can be controlled. The coupling configuration of the clamp 700 to the device 400 is generally shown in FIG. 7B.

In another embodiment, a separate device or system is used to apply the elongation force to the device 400. This may be accomplished, for example, by pulling on opposite ends of the device 400 to create an elongation force similar to that represented by arrow 724. Once the device 400 has been elongated by a predetermined amount, a clamp 710 may be coupled to the device 400 in a manner substantially as described above to maintain the device 400 in the elongated position. In this embodiment, the pressure applicator 720 is operated such that the screw, lug or post 718 engages the aperture 430 to hold the device 400 in a predetermined elongated state. Again, device 400 is then coupled to bone 600, preferably with responsive zone 410 positioned across or adjacent to fracture site 610. This may include attaching one end of the device 400 to one bone segment 620 and attaching a second end of the device 400 to the opposite bone segment 620. Once the device 400 is coupled to the bone 600, the clamp 700 is removed.

The invention also provides bone fixation rods, nails, and the like. In one embodiment, the bone fixation rod or nail 800 has a first end 810 and a second end 812 such that an intermediate section 814 is disposed therebetween. In one embodiment, some or all of the rods 800 comprise a shape memory alloy, which in a preferred embodiment comprises nitinol. For example, in one embodiment, the intermediate section 814 comprises nitinol. In this manner, the intermediate segment 814 is a responsive zone having features generally described herein. In another embodiment, one or both of first end 810 and second end 812 comprise nitinol. In yet another embodiment, the entire rod 800 is nitinol.

In one embodiment, rod 800 is a dynamic intramedullary nail. Such a device may be used, for example, for degenerative tibiocalcaneus-calcaneus fusion. The nail 800 addresses the problem of fusion or fracture site compression, as well as vascular preservation issues, substantially as described in connection with the previous embodiments. For example, rod 800 may provide dynamic compression on the fusion site in a manner that allows for the use of smaller rods 800 or staples. The use of a rod or peg 800 that is smaller in diameter than existing titanium or like pegs will help preserve the intraosseous/bone marrow blood supply.

As shown in fig. 8, a rod or nail 800 is inserted into a bone 850. In one embodiment, insertion of shaft 800 is accomplished by deburring the medullary canal of the bone and hammering or driving nail 800 into place. The nail 800 may then be locked relative to the bone using one or more interference or locking screws 820. Although the embodiment shown in fig. 8 depicts a single screw 820 near end 810 and two screws 820 near end 812, one skilled in the art will recognize that the number of screws 820 may vary within the scope of the present invention. Also, the interference or locking screw 820 may include a nail, pin, or the like. The dimensions of rod 800 and screw 820, including length, width, diameter, and thickness, may vary within the scope of the present invention and may be determined, at least in part, by the particular bone and/or joint into which the device is inserted or attached.

In some embodiments, spike or rod 800 is designed to allow release of a responsive element or region portion thereof, allowing rod or spike 800 to shorten. This is accomplished, at least in part, by having the responsive zone of rod 800 comprise a shape memory alloy such as nitinol and screw 300 as described above. In this manner, release of the responsive element portion of the nail 800 pulls the locking screws 820 together on opposite sides of the responsive zone. Resulting in dynamic compression on bone 850. In one embodiment, the responsive zone, which may include the ends 810, 812 and/or the intermediate section 814, is positioned at a desired location within the bone 850 or joint 860 to facilitate bone healing. For example, the responsive zone may be positioned across or adjacent a fracture site within bone 850, may be positioned within joint 860, or other location where increased and/or maintained dynamic pressure is desired.

The bone fixation device of the present invention, including the nail 800, screw 300, and plate 400, may be inserted with one or more sets of instruments that are also included within the scope of the present invention. For example, the implanted instruments may include screws and plates, hammers or other compression devices, clamps or other retaining devices, torquing devices such as screwdrivers, torque wrenches, and the like for inserting screws, rods, and plates. In one embodiment, a torque wrench is provided with a preload device that allows the surgeon to determine if the screw 300 has activated a pseudo-elasticity when inserted at the fracture site.

FIG. 9A depicts a stress-strain diagram for living tissue and a nickel titanium alloy. Nickel titanium, and in particular nitinol, has desirable strain recovery characteristics. The temperature at which nitinol recovers is known as the transition temperature (T)_t). Various heat treatments may be performed on the material to determine the phase transition temperature. Then, at least in part, according to T_tAnd the ambient temperature T_a(e.g., atmospheric temperature, body temperature, etc.) may demonstrate the pseudo-elastic (PE) and Shape Memory (SM) properties of the material. When T is_aGreater than T_tWhen this occurs, the PE state is observed. Permanent strain is observed when the material is stretched with an applied force. When the force is removed, the material recovers strain. When T is_tGreater than T_aWhen it is time, the SM state is observed. The material is deformed above Ta and remains deformed until the temperature is above T_tUntil now. According to some implementations of the inventionFor example, these features are useful for constructing a fixation device. Fig. 9B depicts the results of the inventors' experiments showing the effect of total strain on the unloading curve of SIM nitinol.

The force a surgeon may attempt to place on the fracture site 210 or 610 with a screw 100, nail 800, plate 400, or other fixation device within the scope of the present invention may be limited to F_R. The physician is also able to determine the predetermined change in the length of relaxation/resorption (Δ L) required to maintain fracture stability. This may include determining the distance or amount that the bone and/or surrounding tissue will relax during healing. From this information, the cross-sectional area and length of a bone fixation device, such as screw 100, nail 800, and/or device 400, respectively, may be calculated.

Using equation (1) below, the cross-sectional area can be calculated. Using equation (2) below, the total length of the response element can be calculated. In these equations, A is the cross-sectional area, F_RIs a doctor-specified restoring force, σ_RIs the tensile recovery stress (material property), L is the length of the response region or element, Δ L is the physician-specified change in length of the response region or element, andis the tensile strain (material property). To meet the needs of the physician, the total length and cross-sectional area are used for the manufacture of the plate or screw. Fig. 10A and 10B show examples of possible areas and lengths that may be decided by the physician.

A＝F_R/σ_R (1)

In a preferred embodiment, the responsive element or responsive region has a smaller cross-sectional area than the non-responsive portion. The reduction in area allows the stress to be placed on the responsive element or region, which in turn only elongates the responsive element or region. By using this responsive element or region, applicants are able to localize stress-induced martensite (SIM) induced forces at the fracture site, while the non-responsive element remains substantially unstrained and exerts minimal force on the bone due to the SIM.

Several devices and systems of the present invention have evolved from Shape Memory Alloys (SMA) to respond positively to changes in the human body, particularly bones. In certain embodiments, the inventors studied and used SMA nitinol. Nitinol is biocompatible with endoskeletal structures, and is strong and durable. Several embodiments of the present invention take advantage of the material properties of nitinol.

The following discussion covers the steps of producing dynamic compression bone screws, nails, bone fixation devices or plates, and other effective devices made from nitinol, as well as machining of nitinol devices. A brief description of the heat treatment, composition and deformation techniques used will be set forth. Those skilled in the art will recognize that the fabrication techniques described are merely representative of certain embodiments of the present invention.

Pretreatment of materials

It is desirable to develop accurate stress-strain responses for each state of nitinol. The following is a procedure for identifying the specific composition of the nitinol SMA of the embodiments of the present invention.

1. Rods of hot rolled Ti-50.9% at% Ni and cold drawn Ti-50.9% at% Ni were obtained with the specified metals.

2. Electrical Discharge Machining (EDM) is used to cut material from the rod into the desired bone plate, nail and screw shapes. This process allows machining operations to be minimized in sampling. The sample was cut into a dogbone for tension and a rectangular block for compression. All tests were performed under a single strain control.

3. Based on Ti₃Ni₄Use of a precipitant to alter the martensite start (M)_s) And end (M)_f) Temperature, and austenite start (A)_s) And end (A)_f) Temperature, various heat treatments were performed on the hot rolled material. The results were judged by the peak phase transition observed by differential scanning calorimetry.

4. With respect to the heat treatment, various stress-strain responses were examined. This allows certain characteristics to be exploited in the design. The use of various heat treatments allows for varying stress recovery and strain recovery.

5. Using the material response in its loaded condition, the cross-sectional area is designed as discussed briefly in connection with fig. 10A-10B.

Bone explosion nail/nail

Certain embodiments of the bone fixation devices of the present invention have been developed to be aggressively adapted for resorption of a fracture site. One such bone screw manufacturing process of the present invention is provided below. The manufacture of other fixtures within the scope of the present invention follows a similar or identical process.

1. Using the above 1-5 manufacturing results, the actual design of the response element or response region can be determined. The specific calculation of the responsive element of the bone screw is briefly discussed in connection with fig. 10A-10B and is discussed in greater detail in the previously incorporated provisional application No. 60/563952.

2. The nitinol rod is sent to electrical discharge machining to be formed into a smaller cylindrical section. At this point, no heat treatment has been performed and the material is in its class receiving state.

3. The smaller cylinders are heat treated at about 600 c for about 30 minutes, which in turn reduces the hardness and places the material in a more easily machined state.

4. The screws were machined, such as on a lathe, at a cutting speed similar to stainless steel (e.g., approximately 300 RPMs). At the same time, the nitinol is filled with cutting fluid to reduce the work hardening effect of the cutting surface.

5. After machining, the final part is heat treated to the appropriate temperature based on the material characteristics and design metallographic phase listed above. In a specific embodiment, the heat treatment associated with a material composition of 50.9 is performed at about 350 ℃ for about 1.5 hours.

6. The screws were autoclaved and set. The reactive element is stretched using the principle of screw head and thread.

Bone fixation device or plate

Increasing the large area of stabilization at the fracture site may require the use of bone fixation devices or bone plates. The device or plate may be used with bone screws. The bone fixation device or plate is actively adapted to the resorption of the fracture site and to the compensation of the resorption at the screw head and the thread. The following is a description of a nitinol bone plate used to develop embodiments of the present invention.

1. Using the manufacturing results 1-5, the actual design of the response element can be decided. Details of the response element are briefly discussed in connection with fig. 10A-10B and in more detail in provisional application No.60/563952, previously incorporated by reference.

2. The stress/strain maps are used to tailor the final compression force required by the plate in response to the bone, based on the fracture type and the predetermined amount of resorption.

3. The nitinol rod is fed through an electrical discharge machining into the final design of the plate. At the same time, the material is in its class receiving state without heat treatment.

It is possible to machine the plate on a rolling mill using the "softening" heat treatment described above. The bar is cut into smaller rectangles and then heat treated at about 600 c for about 30 minutes, which in turn reduces the hardness and puts the material in a more "easy to machine" state.

4. After the discharge mechanical removal, the plate leaves its oxide layer.

5. Based on the results of the material characterization phase, the class receiving bone plate is heat treated to obtain the desired properties. Similar to the screw, the heat treatment associated with the material composition of 50.9 is carried out at about 350 ℃ for about 1.5 hours.

6. Once the application of the panel is known, it is stretched to a predetermined strain using external means and held in place with braces.

7. The entire device is then sterilized with high pressure and finally placed at the fracture site.

Other Nitinol devices including responsive elements

Other devices may benefit from the use of nitinol or other SMA in the positive response element. For example, interlocking intramedullary nails may be formed. The nail is similar in design to a screw and contains similar responsive elements. This design comes from the properties of nitinol discussed herein. Other devices that can incorporate a responsive element include artificial disc replacements for use in the patient's spine. The responsive element can be designed to allow for different forces between specific vertebrae. For example, a person with a larger upper torso has a different stress distribution between the upper and lower vertebrae than a person with a smaller torso. Other uses of SMA such as nitinol are also used to create a positive response element.

Bone fixation systems and methods of use and manufacture

In certain embodiments, a bone fixation system can include a fixation device having a responsive zone bone, and a clamp having an end cap and an inner post. Fig. 11A and 11B illustrate an end cap 1110 of an embodiment of the present invention. The end cap 1110 includes a first portion 1112 and a second portion 1114. In some embodiments, the end cap may be designed to couple with or be located at the distal end of the intramedullary nail and provide additional support to the clip. The end caps may also provide for attachment of the inner struts. In some cases, the end cap may be made of Ti6A1-4V and can have an internally threaded cavity or other threaded surface. Fig. 12 shows an inner post 1210 of one embodiment of the present invention. Inner post 1210 includes a first section 1212 and a second section 1214. Generally, the end cap 1110 and the inner post 1210 are configured for adjustable cooperation. For example, the end cap first portion 1112 and the inner post first portion 1212 may be threadably engaged. In some embodiments, the inner post may be designed to be positioned inside the intramedullary nail and provide an obstacle or impediment to premature recovery of the nail. The inner post may be threaded into the end cap and may be designed to allow the guide bar to be inserted inside the post and peg configuration. In some cases, the inner post is made of Ti6A1-4V and has an internally threaded cavity or other threaded surface.

Fig. 13A and 13B illustrate a bone fixation system 1310 according to one embodiment of the present invention. Bone fixation system 1310 includes a bone fixation device 1320 having a response region 1322 and a clamp member 1330 having an end cap 1340 and an inner post 1350. The clamping member 1330 is partially disposed within a lumen of the bone fixation device 1320, wherein the lumen is disposed along an axial length of the bone fixation device 1320. Clamping member 1330 is adjustable to a first mode, as shown in fig. 13A, that induces or maintains a first amount of strain in response region 1322 along the axial length of bone fixation device 1320. Similarly, clamping member 1330 is adjustable to a second mode, as shown in fig. 13B, that induces or maintains a second amount of strain in response region 1322 along the axial length of bone fixation device 1320. Typically, adjustment to or between the first or second modes includes adjusting the length of the clamp 1330. In some cases, the amount of strain in the first or second mode may be zero. Clamp 1330 is operable to prevent, inhibit, or control or adjust recovery in response region 1322. Clamping member 1330 can be removably coupled with bone fixation device 1320. It is recognized that the device may be provided in a covered state, wherein the device is held in tension by the end caps and inner struts.

As seen in fig. 13A and 13B, the end cap first portion 1342 is adjustably engaged or coupled with the bone fixation device 1320, and the end cap second portion 1344 is adjustably engaged or coupled with the inner post first region 1352. Relatedly, the end cap first portion 1342 can be threadably engaged with the bone fixation device 1320, and the end cap second portion 1344 can be threadably engaged with the inner post first region 1352. In some embodiments, a central longitudinal axis 1326 defined by the lumen of the bone fixation device 1320 can be collinear with the central longitudinal axis 1356 defined by the inner post 1350. In certain embodiments, the central longitudinal axis 1326 can be collinear with the central longitudinal axis 1346 defined by the end cap 1340. It is recognized that the bone fixation device can include any of a variety of orthopedic devices such as nails, screws, plates, rods, compression rods, spinal and other fixation devices, and the like.

The responsive zone 1322 can be fabricated or adapted to have physical properties similar to those of human tissue, such as bone. For example, the physical property may be a modulus value, such as an elastic modulus value. In some cases, the modulus of the response region may be in the range from about 10GPa to about 70 GPa. Response region 1322 can include a shape memory material, which can be a shape memory nickel or copper alloy. The shape memory material may include nickel-titanium alloy, copper-zinc-aluminum alloy, copper-aluminum-nickel alloy, and the like. In some embodiments, responsive zone 1322 is configured to provide a predetermined or preset compressive force on the fracture site when the clamp is removed or not used. For AO, for example, the predetermined or preset pressurization force may be in a range from about 2kN to about 4 kN. It is recognized that the therapeutic load may be within, below, or above this range. Relatedly, the responsive zone 1322 can be configured to cover a predetermined or preset length, such as when the clamping member 1330 is removed or not in use, so that tension is no longer applied to the bone fixation device 1320. In certain embodiments, the present invention provides a bone fixation device comprising a machined responsive zone having hardness values in the range of from about 5HRB to about 60HRC on the Rockwell B and C scale.

Embodiments of methods for preparing a bone fixation system are also presented. For example, the bone fixation system 1310 may be prepared by providing a bone fixation device 1320 having a response region 1322 and inserting the clamp member 1330 at least partially within the inner lumen of the bone fixation device 1320. Strain in the response region 1322 along the axial length of the bone fixation device 1320 may be induced, maintained, or adjusted by providing the clamping member 1330 in an appropriate configuration. In some embodiments, the bone fixation device 1320 is an intramedullary nail fabricated from nitinol by using a series of heat treatments to reduce the hardness of the bulk material. After staple manufacture, the staple may be aged to induce a pseudo-elastic response from the bulk material at body temperature (e.g., about 37 ℃). The staple may be designed such that only the responsive element will be stretched during the elongation process. This can allow major recovery of resorption to occur at the fracture site. The nail may be designed to recover immediately or soon after unloading, and then a clamp or other internal retention system may be designed to cover and retain the stretched area of the nail.

Fig. 14 illustrates an external fixation device or clamp device 1410 that is designed to maintain the bone fixation device in a stretched form when the clamp is removed therefrom. In some embodiments, the clamping member may be designed to maintain the stretched form of the intramedullary nail when the inner post is removed therefrom. External fixation devices or clamps can also provide the functionality of implanting and locking the screw arrangement. The clamp can be pre-set so that the screw hole of the intraosseous nail aligns with the screw hole in the clamp outside the leg, helping to lock the screw placement through soft tissue and bone. Fig. 15 shows a retaining rod 1510 that can be used to secure the end cap relative to the clamp and prevent or inhibit premature nail migration or migration within the intramedullary canal. The intramedullary nail, the inner post, and the end cap may be designed to slide over the retaining rod until the flange of the end cap contacts the rod. This can lock the intramedullary nail in place and help align the clamp in place. The clamp may be configured in any of a number of suitable shapes. The clip may have a "U" shape.

In certain embodiments, the present invention provides methods of disposing a bone fixation device in a patient. The bone fixation device 1610 illustrated in FIG. 16 is coupled to the clamp 1615 and includes a first portion 1620, a second portion 1630, and a responsive zone 1640 disposed therebetween. In some embodiments, this can represent stretching and holding of the staple, such that the staple remains secured by the inner struts and end caps. The clamp 1615 is partially disposed within a lumen of the device 1610, wherein the lumen is disposed along an axial length of the device 1610. The clamp 1615 may be configured to induce or maintain strain in the response region 1640 along the axial length of the device 1610.

In an exemplary procedure, the surgeon performs a standard technique of preparing the patient's ankle and ankle-binding heel joint. Fig. 17 illustrates outer strut assembly 1710, which includes clamp 1720 and retaining bar 1730. Also shown here with respect to outer strut assembly 1710 is a patient's lower leg 1740. The outer strut assembly can help the surgeon properly align the ankle where the procedure is performed. By using appropriately placed wires, the surgeon can enlarge the hole in the intramedullary cavity to the appropriate size for the outer diameter of the intramedullary nail. In some embodiments, the clamp may be placed on a patient's foot or other body part and connected to the intramedullary nail via an end cap at the distal end of the body part (e.g., the distal end of an ankle).

As shown in fig. 18, the bone fixation device 1810 may be placed adjacent to or within a patient's bone 1820 and the first portion 1830 of the device 1810 may be coupled with the retention bar 1830. In some embodiments, the stretched intramedullary nail construct is inserted into the intramedullary canal until the construct contacts the retaining rod. The retaining bar can be used to align the staple into the correct position when contact occurs between the construct and the bar. Fig. 19 shows cross pin 1910, which effectively couples bone fixation device 1920 with a first location 1922 of a patient's bone 1930 and stabilizes bone 1930 relative to clamp 1940. The cross pin may also be used to similarly secure a second location of a patient's bone to the bone fixation device and may include a drill tip. Typically, the bone includes a fracture site disposed between first and second bone locations. Thus, bone fixation device 1920 can be fixed relative to clamp 1940. In some embodiments, once the intramedullary nail is embedded and aligned inside the medullary canal, the surgeon can drill 2-3 holes, placing a cross pin through the proximal side of the tibia. The cross pin may be designed to transfer the load from the inner post or pin to a fixed point of the clamp. As seen in fig. 20, once the cross pin is installed, the surgeon can pre-load the clamp by removing the inner post 2010 using an appropriate device such as an allen key or a hand tool. With the struts removed, the load is transferred through the intramedullary nail and the end caps into the clamp. The surgeon can monitor the outer post and staple placement.

As shown in fig. 21, after the internal strut has been removed and the load transferred to the clamp, the surgeon can first install the calcaneus screw 2110 on the distal end of the ankle and then can place the proximal/tibial side locking screw. The bone screws can allow compression through the ankle. As seen in fig. 22A and 22B, once the screws have been installed on both ends of the intramedullary nail, end cap 2210 may be slowly loosened or removed by using a suitable tool, such as an allen key. The progressively loosened end cap 2210 can transfer loads from the outer post 2220 to the intramedullary nail and ankle. In some embodiments, multiple screws may be installed before the end cap is completely removed. After the end cap is completely removed, the cross bar or pin can be removed and replaced with a bone screw 2310 to secure the remainder of the nail, as shown in fig. 23. Once the end cap is removed, the staples are in a dynamic state and a constant compressive force is applied at the fusion site. The solid end cap can then be placed into the nail to secure the distal end. The surgeon can then suture the remaining incisions and prepare for post-operative work. The jig is then removed and removed from the patient's foot. The nail is fully loaded and installed.

The techniques described herein may be used in any part of the body where dynamic axial compressive loading is desired. For example, these methods may be used to treat fractures of longer fractures, including fractures of the humerus, radius, tibia, and femur. Advantageously, these techniques provide repeatable, true dynamic loading for application from an external fixture. Relatedly, these techniques can be used in a relative application to apply dynamic distraction forces at the fracture site. For example, such relative applications may be used in limb lengthening surgery or for larger "long bone defect implants", such as in humeral replacement status in non-skeletal adult patients following osteosarcoma resection. These systems and methods may also be used to apply controlled dispensing/pressurizing increments driven by radio frequency or magnetic operation. Moreover, the systems and methods can be used to couple the responsive zone with existing or current implants, such as the entire hip or the entire knee, to allow for greater latitude or error in the state of differential limb length after joint replacement. In certain embodiments, these techniques allow for adjustment after the implant has been placed and the patient individual's resorptive bone response has occurred for months or years. It is recognized that these methods may be accomplished in a variety of controlled pressurization/extension modes involving the internal implant.

Fig. 24A-24H illustrate a typical intramedullary nail having exemplary dimensions. FIG. 25 illustrates various hardness responses that may be obtained from aging of nickel titanium. Hardness may relate to the machinability of the material. In certain embodiments, the softer the material, the easier it is to machine. Stiffness peaks when a shape memory material such as nickel titanium exhibits pseudoelasticity (superelasticity). Thus, the material is difficult to machine. The material may be assisted in aging to a low hardness state, machining it, then removing the low hardness state and readjusting it to a high hardness state.

In one embodiment, a method of processing a shape memory material for a bone fixation device can include processing the shape memory material with a first process to transform the shape memory material from a first state to a second state, machining the shape memory material while in the second state; and processing the machined shape memory material with a second process to transform the shape memory material from the second state to a third state. Typically, the process is designed to establish or optimize pseudo-elastic or shape memory properties in the material. The first treatment may include a first thermal cycle at a temperature of about 600 ℃ or above for at least 5 minutes, or in some cases from about 5 minutes to about 1.5 hours. It is recognized that the duration and temperature may vary depending on the type of material to be processed. The first treatment may also include a second thermal cycle at a temperature of 300 ℃, 350 ℃, 400 ℃, 450 ℃, 500 ℃ or 550 ℃, or between about 200 ℃ and about 550 ℃, for at least 5 minutes, or in some embodiments, from about 5 minutes to about 1.5 hours. In certain embodiments, the first state has a first hardness value, the second state has a second hardness value, and the first hardness value is between about 100% and about 500% of the second hardness value. Relatedly, in some cases, the first state has a first shape recovery value, the third state has a third shape recovery value, and the third shape recovery value is at least 95% of the first shape recovery value. The shape memory material can include a shape memory alloy such as nickel titanium alloy, copper zinc aluminum alloy, or copper aluminum nickel alloy, or any precipitated shape memory alloy.

The third state can have an optimal pseudoelastic or superelastic property profile for the shape memory material. Similarly, the third state may also have an optimal shape memory state. In certain embodiments, the first state can have a first hardness value, the third state can have a third hardness value, and the difference between the first hardness value and the third hardness value can be less than about 3HRC on the rockwell C scale. In some cases, the difference may be less than about 10 HRC.

In another embodiment, the invention provides a method of preparing a bone fixation device. The method includes providing a bone fixation device including a shape memory material, and machining the shape memory material while a temperature of the shape memory material is maintained at or above an austenite or r-phase transformation temperature. In certain embodiments, the shape memory material retains a hard austenite phase without transforming to malleable austenite during machining.

Various embodiments of the present invention have now been described in detail. It will be appreciated, however, that the invention may be practiced otherwise than as specifically described in the foregoing discussion, and that certain changes and modifications may be practiced within the scope of the appended claims. The scope of the invention is therefore intended to be limited not by these specific examples, but rather by the scope of the following claims.

Claims (11)

1. A bone fixation device, comprising:

an elongated element comprising a responsive zone, the element adapted to be coupled to a bone such that the responsive zone is positioned adjacent a fracture site or fusion site in the bone;

wherein the responsive zone is adapted to apply a predetermined pressure to the bone when coupled thereto;

wherein the responsive zone comprises a shape memory alloy;

wherein said shape memory alloy is produced by performing a first heat treatment operation on said shape memory alloy, said first heat treatment operation comprising heating said shape memory alloy between 500 ℃ and 550 ℃ for 5 minutes to 1.5 hours;

wherein the shape memory alloy is manufactured by subjecting the shape memory alloy to a machining operation after the first heat treatment operation;

wherein the shape memory alloy is fabricated by subjecting the shape memory alloy to a second heat treatment operation after the machining operation.

2. The bone fixation device of claim 1 wherein the responsive zone comprises nitinol.

3. The bone fixation device of claim 1 wherein the elongate element comprises nitinol.

4. The bone fixation device as in claim 1 wherein the responsive zone is pseudoelastic at 37 ℃.

5. The bone fixation device as in claim 1 wherein the responsive zone is positioned substantially in the middle of the elongated member, the responsive zone having an overall cross-section that is smaller than the cross-section of the ends of the elongated member.

6. The bone fixation device of claim 1 further comprising a coupler adapted to couple the elongate member to a bone.

7. The bone fixation device as in claim 6, wherein the coupler comprises at least one bone screw.

8. The bone fixation device of claim 7 wherein the bone screw comprises a shape memory material.

9. The bone fixation device of claim 1 wherein the elongate member comprises a plate having first and second end portions, each end portion including at least one aperture adapted to receive a coupler therethrough for attaching the plate to the bone.

10. The bone fixation device of claim 1 wherein the elongate element comprises a bone screw.

11. The bone fixation device as in claim 1 wherein the elongated member comprises a nail.