US 7842037 B2
A bone fixation device comprises a beam including plurality of stacked flexible members. At least one locking member is provided in engagement with the plurality of stacked flexible members. The at least one locking member is configured to retain the plurality of stacked flexible members together in either a locked relationship or an unlocked relationship. In the locked relationship, the at least one locking member compress the plurality of stacked flexible members together. The plurality of stacked flexible members are configured to bend when a threshold force is applied to the beam, provided the plurality of stacked flexible members are in an unlocked relationship. When the plurality of stacked flexible members are in an unlocked relationship, the threshold force is insufficient to bend the plurality of stacked flexible members.
1. A bone fixation device comprising:
a) a beam comprising plurality of flexible members, wherein the plurality of flexible members are configured to bend when a threshold force is applied to the beam and the plurality of flexible members are in an unlocked relationship; and
b) a plurality of locking members configured to compress the plurality of flexible members together and into a locked relationship, wherein the threshold force applied to the beam is insufficient to bend the plurality of flexible members in the locked relationship;
wherein each locking member in the plurality includes a top portion and a bottom portion, the top portion and the bottom portion of each locking member cooperating to define a first channel and a second channel;
wherein the plurality of locking members are arranged end to end such that the first channels of each locking member are aligned to form a first passage and the second channels of each locking member are aligned to form a second passage;
wherein the plurality of flexible members of the beam comprise filaments arranged in a first stacked grouping and a second stacked grouping, the first stacked grouping being positioned in the first passage and the second stacked grouping being positioned in the second passage;
wherein the top portion and the bottom portion of each locking member are configured to move between a first relative position and a second relative position with respect to each;
wherein, in the first relative position, the top portion and the bottom portion are spaced apart from each other a distance so that the filaments of the first stacked grouping and the second stacked grouping are in an unlocked relationship in which the filaments of the first stacked grouping are able to move with respect to each other in the first channel and the filaments of the second stacked grouping to move with respect to each other in the second channel, respectively;
wherein, in the second relative position, the top portion and the bottom portion of the locking members are positioned with respect to each other to compress the filaments of the first stacked grouping together in the first channel and into the locked relationship and to compress the filaments of the second stacked grouping together in the second channel and into the locked relationship such that the filaments of the first stacked grouping and the second stacked grouping are prevented from moving with respect to each other.
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This application relates generally to the field of orthopedics, and more specifically to bone plates and systems for stabilization and compression of fractured or otherwise damaged bones.
Bone plates for internal fixation of fractured bones should generally conform to the contours of the fractured bone surface. This is especially true for compression plates that are screwed tightly against the bone. Matching the plate shape to the bone contours is important with compression plates in order to allow proper distribution of loads between the bone and the plate during healing of the fracture. It is also desirable for the plate to have a low profile and to blend with the bone surface as much as possible so as not to irritate or interfere with surrounding soft tissues, nerves, tendons, vessels, etc.
One type of bone plate for acetabular and other pelvic fractures is called a reconstruction bar. Conventional reconstruction bars are generally formed from a biocompatible metal that may be bent by the surgeon using special tools in order to configure the bar to conform to the bone. Typically the surgeon first forms a thin metal template by hand to conform to the bone surface at the fracture site. Working through an open incision, the surgeon bends the template to approximate the desired shape, places the template against the bone surface, removes the template, adjusts the shape of the template and repeats these steps until the template closely matches the shape of the bone surface. Then the surgeon, sometimes with the help of an assistant, uses a number of special forming tools to bend the reconstruction bar to be implanted into approximately the same configuration as the template, visually holding the bar and template side-by-side to assess when the bar is adequately similar to the template. This procedure may take several minutes of time and a significant amount of skill. The bar may then be attached to the bone using conventional cortical screws. It is not likely that the bar shape exactly matches the bone surface shape, so tightening of the bone screws may draw the bar against the bone surface, thereby inducing bending preloads at various locations along the bar due to the spring-back characteristic of the bar material. Alternatively, the bar may be implanted with significant gaps between various locations of the bar and the bone surface, resulting in the uneven transfer of loads between the bone and bar construct. Therefore, it would be advantageous to provide a reconstruction bar that may be implanted more quickly by the surgeon, requires fewer ancillary tools, is more conformable and contoured to the bone surface and is at least as effective as a fixation device compared to conventional reconstruction bars.
Another issue currently faced by orthopedic device manufacturers is the need to provide a full line of bone plates for a large variety of bone fractures and patient anatomies. The manufacturing costs associated with forming each rigid, one-piece bone plate is significant due largely to the need to configure the plate to approximately match the bone surface shape. Furthermore, a large product inventory must be provided to the user (hospitals) to be prepared for the many types of fractures and patient anatomies to be treated. Accordingly, it would be advantageous to provide bone plates that have broader indications, where each plate may be suitable for a larger variety of fractures and patient anatomies than currently available plates. Potentially, such bone plates may be produced at lower costs than current plates and inventories reduced without compromising surgical outcomes.
A bone fixation device comprises a beam including plurality of flexible members. The plurality of flexible members extend generally parallel to a curvilinear axis defined along the length of the bone fixation device. The plurality of flexible members are provided in one or more groupings that engage at least one locking member. The locking member is configured to retain the flexible members together in either a locked relationship or an unlocked relationship. In the locked relationship, the locking member compresses the flexible members together. The beam provided by the flexible members is configured to bend when a threshold force is applied to the beam, provided the flexible members are in an unlocked relationship. When the flexible members are in a locked relationship, the beam has an increased resistance to bending such that application of the threshold force is insufficient to bend the plurality of stacked flexible members and alter the shape of the bone fixation device.
In one embodiment, the at least one locking member comprises a first portion configured to engage a first side of the beam and a second portion configured to engage an opposite second side of the beam. The flexible members are arranged within the grouping in a stacked configuration. The first portion and the second portion are configured to clamp together, thus compressing the flexible members. The at least one locking member also comprises a hole extending through the first portion and the second portion. The hole is configured to receive a bone screw configured to draw the first and second portions together to clamp tightly to the flexible members while also securing the bone fixation device to the damaged bone.
The bone fixation device provides for a method of stabilizing a damaged bone. The method comprises providing a plurality of stacked flexible members and at least one locking member. The method further comprises bending the plurality of stacked flexible members to conform surfaces of the bone fixation device to the contours of the damaged bone. After the step of bending, the plurality of stacked flexible members are locked together using the at least one locking member. In particular, the plurality of stacked flexible members are compressed in order to lock the plurality of stacked flexible members together.
The above described features and advantages, as well as others, will become more readily apparent to those of ordinary skill in the art by reference to the following detailed description and accompanying drawings.
With reference to
As shown in
The filament forming the coil 30 may be formed from a spring steel, a stainless steel, a shape memory metal such as nitinol, titanium alloy, a polymer or other suitable biocompatible material. The cross-sectional shape of the filament forming the coil 30 may be any of numerous cross-sectional shapes. For example, in the embodiment of
As shown in
In other embodiments, the flexible members 24 may also be arranged within each grouping in configurations other than vertical stacks. For example, the flexible members 24 may be held together in a bundled configuration having an approximately circular cross-sectional shape (not shown).
With reference again to
With reference to
With reference now to
The bottom half 42 of the locking member 26 includes a generally planar lower surface 72 with the hole 50 extending through the lower surface 72. A sidewall 74 extends from the edges of the lower surface toward the top half 40. Slots 76 are formed within the sidewalls 74 to provide for the channels 46 to extend through the locking member 26. Grooves 78 are formed in the sidewalls 74 to receive the tabs 68 of the top half 40 of the locking member. In particular, the teeth 69 of the tabs 68 are configured to engage shelves 79 in the grooves 78 of the bottom half 42, thus loosely securing the top half to the bottom half. The arrows 58 in
The channels 46 formed through a locking member 26 may include features to help maintain the locking member 26 in place upon the beam 22. For example, as shown in
When a bone screw is placed in the hole 50 of each locking member 26A, 26B, and used to compress the top half 40 of each locking member 26 toward the bottom half 42, the plurality of flexible members 24 are also compressed together. The plurality of flexible members 24 only permit a certain amount of compression, such that a gap G2 (G2<G1) still exists between the top half and the bottom half following compression by the bone screw. With the top half 40 and bottom half 42 of each locking member 26A, 26B clamping down on the flexible members 24, the flexible members 24 are fixed together and not permitted to move relative to each other, thereby greatly increasing the stiffness of the beam 22 at that location. Accordingly, the threshold force that would formerly cause the first locking member 26A to move relative to the second locking member 26B is no longer sufficient to bend the beam 22, and a much greater force is required to move the first locking member 26A relative to the second locking member 26B. This locking feature allows the flexible bone plate 20 to be bent by the hands of a human in the unlocked position by adjusting the position of adjacent locking members 26, while preventing the bone from being bent by the hands of a human in the unlocked position.
As set forth in the preceding paragraph, the beam 22 in the bone plate 20 has one measure of stiffness in an unlocked position and a different measure of stiffness in an unlocked position. In general, the strength of any beam is a function of a beam stiffness factor associated with each mode of beam loading/deflection. The stiffness factor may be defined as the product of the modulus of elasticity E of the beam material times the moment of inertia I about the neutral axis in the direction of the beam deflection. Given a beam material, a comparison of the moments of inertia for the proposed and conventional reconstruction bars may help predict the usefulness of the proposed material as a flexible member 24 for the beam 22 in the disclosed bone plate 20. For example, if a one-millimeter square wire is used to form each flexible member 24, the sum of the individual bending moments of inertia about the neutral axis of the four beams in the vertical direction is about 0.33 mm4. Using such wire for the beam described for
In operation, the flexible bone fixation device 20 is configured for attachment to a fractured or otherwise damaged bone.
After the bone fixation device 20 is bent to the desired shape, the surgeon then starts the process of securing the bone fixation device to the bone. Starting at one end of the bone fixation device, the surgeon uses the holes 50 in the locking members 26 as a guide to drill a hole in the bone. The surgeon then inserts a bone screw through the hole and into the bone. When the bone screw is tightened in the locking member 26, the locking member compresses the plurality of flexible members together, placing the plurality of flexible members in a locked relationship at that location along the curvilinear axis of the bone fixation device 20. The surgeon follows this procedure to the opposite end of the bone fixation device until all of the locking members secure the plurality of flexible members in a locked relationship, and the bone screws are fixed to the bone. Alternatively, the surgeon may fully insert a bone screw in a hole in the middle of the bone fixation device 20 and proceed to fully insert the next bone screw in an adjacent hole in either direction, until all the screws are fully inserted. Furthermore, in some surgical applications, it may be desirable to partially insert all the bone screws into the holes of the fixation device 20, and then to tighten each screw starting from either end of the device 20, or the middle of the device 20. For each of the above-described procedures, it is generally desirable to position each locking member against the bone surface prior to fully tightening the bone screw through the locking member. However, there may be some surgical situations where the surgeon prefers to attach the fixation device to the bone surface with a gap between the bone surface and at least some of the locking members.
With the above described procedure, a bone fixation device is provided that is easily bent to match the contours of the bone surface. The forces required to bend the bone plate may be provided by the human hand. Because the bone fixation device is easily shaped, and no tools are required to bend the bone fixation device, the time needed to perform the surgical procedure installing a bone fixation device is reduced. In addition, because a single bone fixation device may be bent into numerous shapes, there is a reduced need to have bone fixation devices of various shapes on hand, and hospital inventories of bone fixation devices may be reduced.
In the embodiment of
The stem portion 144 of each laminate 124 also includes a plurality of holes 146. The holes 146 in each laminate layer are aligned to allow a bone screw or other fixation device to pass through the aligned holes. The laminates 124 on the stem portion 144 may be initially provided with or without the stem holes 146.
If holes 146 are not initially provided in the stem portion 144, the surgeon may drill each hole through the laminates 124 and into the bone in a single step. However, before drilling any hole 146 the surgeon first presses the portion of the laminates that will receive the hole against the bone surface to properly bend the laminates into alignment with the bone. In this embodiment, the upper flexible member, such as laminate 123 in
Alternatively, if the holes 146 are initially provided in the stem portion 144, the holes 146 are spaced apart according to a pre-determined configuration. In this embodiment, the holes 146 in the bottom flexible member 124 that contacts the bone surface, such as hole 147 in laminate 125 shown in the cutaway portion of
With pre-formed holes in the bone fixation device 120, the surgeon begins attaching the device 120 to the bone starting at the set of holes near the head 140 of the bone fixation device 120. The surgeon pushes the laminates 124 against the bone surface at that location and use the smaller hole 146 in the bottom laminate 125 to guide the bone drill. The surgeon may then immediately insert a bone screw through all the laminates at that location and tighten the screw, thereby locking the laminates together at that location. The surgeon may then proceed to the next hole location and repeat the procedure until all the screws are in place. As described above, the upper laminate holes provide significant clearance for the screw threads while the holes in the bottom laminate 125 are configured to engage the screw threads. Although the laminates may shift with respect to each other as the surgeon shapes the plurality of flexible members to conform to the bone contours, the differently sized holes still allow for passage of the bone screw. Once the bone screws are tightened, compressing the laminates 124 against the bone, the beam 122 is in the rigid/locked condition and configured for fixation of the bone fracture.
The laminates 124 shown in
In other embodiments, the laminates 124 of the bone fixation device 120 of
In one embodiment, the laminates 124 of
In the above-described embodiments, the surfaces of the flexible members or laminates may be treated or provided with any one of numerous processes, coatings, or features to enhance the frictional lock achievable when fixed together in the rigid condition. For example, the surfaces of the flexible members may be provided with a rough texture, such as may be obtained by sand blasting, or a multiplicity of tiny projections, teeth, serrations, or other structural features. A bonding agent such as a moisture activated cement or glue may be coated or otherwise disposed on the surfaces of the flexible members, such that once the implant is placed in the wet environment of the body, the bonding agent becomes active, and cures fully several minutes or hours later to increase the rigidity of the construct. The bonding agent may also be activated by heat, UV radiation, or other energy source.
Although the present invention has been described with respect to certain preferred embodiments, it will be appreciated by those of skill in the art that other implementations and adaptations are possible. For example, although the flexible members disclosed herein have been shown stacked in a vertical fashion, the flexible members may also be positioned laterally relative to one another. In addition, the shapes of the locking members and the flexible members may vary according to the desired surgical application. For example, the locking members 26 shown in