Patent Application
20220401138
The present invention generally relates to bone screws and, more particularly, to a bone fixation screw including an expandable portion and a removable core pin.
Orthopedic fastening devices, such as sutures, pins, screws and the like, are typically used in the treatment of many bone fractures. Such fasteners are used to hold distal and proximal bone fragments in accurate alignment with each other with the hope that the fragments will be sufficiently close together to permit the rapid bonding or fusing of the fragments together. These fasteners may also be used with orthopedic implants and orthopedic appliances such as, for example, a bone plate.
Conventional fasteners, however, have significant disadvantages when used in certain situations requiring compression of bones or fractures, such as, for example, ankle syndesmosis, LisFranc, joint fusions, and light fracture fixation. The specific amount of compression applied in these types of applications is critical. For example, when treating ankle syndesmosis, not enough compression leads to instability and over compression leads to subluxation of, for example, the talus.
The use of sutures is undesirable in some situations because sutures are too flexible and will not result in healing of soft tissue. Conventional screws and pins are too rigid, potentially causing fatigue and breakage. When a bone screw is employed, either to fasten two or more bone fragments together or to secure an orthopedic appliance (e.g., bone plate) to a bone surface, and the bone screw is tightened, initially, tension in the screw is relatively very high, and holds the bone fragments together. However, bone is a viscoelastic material and undergoes a phenomenon known as stress relaxation immediately after torque has been applied to the bone screw. The stress relaxation response is quite pronounced and causes immediate and rapid reduction in the bone screw tension and, hence, the force holding the bone fragments together. Furthermore, after a conventional bone screw is tightened, and the bone fragment is laterally displaced, as by bending, the rigidity of the bone screw causes the surrounding bone to fail because the bone has lower strength and stiffness than the bone screw. This can lead to failure of the fixation and eventual non-union or misalignment of the bone fragments at the fracture site.
One approach to overcome this problem has been the use of a bone screw having a helical portion, as described in U.S. Pat. No. 6,656,184 to White et al. In this reference, a conventional bone screw is modified to include an intermediate helical portion that requires the use of a resorbable material within the spaces of the helical portion when the helical portion is in a stressed state. The resorbable material is used to slowly induce transition of the pretention load after insertion into the desired location, e.g. fracture or joint. However, the use of a resorbable material has significant disadvantages, including, for example, the brittleness of the resorbable material and the unknown forces being applied to the bone at various points in time. Also, a bone screw having a helical portion relying on a resorbable material is not strong enough to initially insert into the desired bone location.
Thus, a need exists for a bone fixation screw that provides, for example, more stability than a suture construct and more flexibility than a conventional screw. There is also a need for a bone fixation screw that further provides, for example, a quantifying and known amount of compression force across the fracture at predetermined and predictable levels.
Briefly, a bone fixation screw constructed in accordance with one or more aspects of the present invention provides, for example, controlled and repeatable compression, the ability to work on its own or with plates and/or nails, stable fixation with limited flexibility and a simple and quick implant fixation system.
In one embodiment, a bone fixation screw constructed in accordance with one or more aspects of the present invention includes, for example, an expandable portion that could be stretched to a known force value and held with a removable core pin in the cannulation of the screw. The bone fixation screw would be provided to a surgeon in this form. The bone fixation screw could then be inserted across, for example, the fracture or joint. Once in place, the core pin is removed and the pre-tension load is transitioned across the fracture or joint at the predetermined level. Quantifying the amount of compression that is being induced across the fracture or joint is becoming more desirable so that a user does not under or over compress the fracture or joint, especially with ankle syndesmosis. A bone fixation screw constructed in accordance with one or more aspects of the present invention allows a user to apply a known compression force every time.
In one embodiment, a shorter core pin may be inserted to change the stiffness of the bone fixation screw after being implanted.
These, and other objects, features and advantages of this invention will become apparent from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings.
The present invention will be understood more fully from the detailed description given hereinafter and from the accompanying drawings of the certain embodiments of the present invention, which, however, should not be taken to limit the invention, but are for explanation, illustration and understanding only.
The present invention will be discussed hereinafter in detail in terms of various exemplary embodiments according to the present invention with reference to the accompanying drawings. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the present invention. It will be obvious, however, to those skilled in the art that the present invention may be practiced without some of these specific details. In other instances, well-known structures are not shown in detail to avoid unnecessary obscuring of the present invention.
Thus, all implementations described below are exemplary implementations provided to enable persons skilled in the art to make or use the embodiments of the disclosure and are not intended to limit the scope of the disclosure, which is defined by the claims. As used herein, the word “exemplary” or “illustrative” or “example”, and derivatives thereof, means “serving as an example, instance, or illustration.” Any implementation described herein as “exemplary” or “illustrative” or “example”, and derivatives thereof, is not necessarily and should not be construed as preferred or advantageous over other implementations. Moreover, in the present description, the terms “upper”, “lower”, “left”, “rear”, “right”, “front”, “vertical”, “horizontal”, and derivatives thereof shall relate to the invention as oriented in
Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. It is also understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification, are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise. While this invention is satisfied by embodiments in many different forms, there is shown in the drawings, and will herein be described in detail, one or more embodiments of the present invention with the understanding that the present disclosure is to be considered as exemplary of the principles and aspects of the invention and is not intended to limit the invention to the embodiments illustrated. The scope of the invention will be pointed out in the appended claims.
In short, a bone fixation screw constructed in accordance with one or more aspects of the present invention provides, for example, controlled and repeatable compression, the ability to work on its own or with plates and/or nails, stable fixation with limited flexibility and a simple and quick implant fixation system. A bone fixation screw constructed in accordance with one or more aspects of the present invention includes an expandable portion that could be stretched to a known force value and held with a removable core pin in the cannulation of the screw. The bone fixation screw would be provided to a surgeon in this form. The bone fixation screw would then be inserted across, for example, the fracture or joint. Once in place, the core pin is removed and the pre-tension load is transitioned across the fracture or joint at the predetermined level. Quantifying the amount of compression that is being induced across the fracture or joint is becoming more desirable so that a user does not under or over compress the fracture or joint, especially with ankle syndesmosis. A bone fixation screw constructed in accordance with one or more aspects of the present invention allows a user to apply a known compression force every time. In one embodiment, a shorter core pin may be inserted to change the stiffness of the bone fixation screw.
Distal portion 130 may include a threaded surface 132 formed on its outer surface 134. Threaded surface 132 may have a right-hand or left-hand turning orientation.
Head portion 110 includes an end surface 112 and a side surface 114. End surface 112 includes an opening to a recess 116 formed in head portion 110. In one example, recess 116 may be hex shaped for receiving a driving device, such as, for example, a hex driver. Although recess 116 is shown as being hex-shaped, it is envisioned that other configurations may be employed as well, such as different recess shapes or differently shaped male members to be engaged by a female drive mechanism. Head portion 110 may be a locking head that includes, for example, threads 118 on side surface 114 to, for example, attach to a bone plate.
Intermediate portion 150 includes a compressive member such as, but not limited to, an expandable portion 152. In one embodiment, expandable portion 152 may include a single helix 154, formed therein by any number of conventional methods, such as, but not limited to, wire electrical discharge machining. In an alternative embodiment, illustrated in
Core pin 170 is removably inserted into inner bore 156 of intermediate portion 150 through recess 116 in proximal head portion 110. Core pin 170 provides stability to bone fixation screw 100 as it is inserted into bone. As illustrated in
In an alternative embodiment illustrated in
Alternatively, bone fixation screw 100 may be employed into a stressed or unrelaxed state by inserting core pin 170 using first set of threads 180 screwed into the threads 122 in inner surface of inner bore 156 proximate head portion 110. In this example, illustrated in
As expandable portion 152 stretches, the amount of force required to continue to stretch goes up requiring an increasing amount of torque to continue to turn the core pin 170. One can calculate the torque level that produces a specific stretch force by using a torque to linear force equation inputting the pitch and diameter of the core pin threads. By using a torque limiting driver set to this predetermined torque value one can repeatedly set the tension force of the screw to the desired force.
There are various force levels that are desired based on known and available research. The desired force level may depend on, for example, the hardness and softness of the bone. Specific procedures may also call out for specific amounts of force based on known and available studies and research, so a bone constructed in accordance with one or more aspects of the present invention may be specifically design to a desired force level specific to the surgery. In one example, a bone fixation device 100 constructed in accordance with one or more aspect of the present may be stretched or expanded approximately two millimeters to create a pre-tension of forty pounds.
In one example, a bone fixation screw constructed in accordance with one or more aspects of the present invention may be pre-tensioned by a manufacturer to, for example, twenty pounds, thirty pounds, forty pounds, etc., and then packaged so that it would already be set for the amount of force needed by a surgeon. The screw could be stretched in a clean room to a desired force level and then a core pin 170 inserted to hold that force level.
In one example of use of bone fixation screw 100 when it is desired to fasten or secure two or more bone fragments or members together (see, e.g.,
At this point, bone fixation screw 100 contains the maximum amount of initial tension, and is comparable to the amount of initial tension achieved with a conventional bone screw. Once the bone fragments are fully apposed and bone fixation device 100 is fully inserted or seated, core pin 170 may be removed. When core pin 170 is removed, the pre-tension that was being held by core pin 170 is then transferred to the fragmented bones because the bones are now preventing bone fixation screw 100 from going back to its original length. In this configuration, the pre-tension force is effectively across the bone fragments.
Once bone fixation screw 100 has been inserted and core pin 170 removed, bone fixation screw 100 has transitioned the pre-tension load to the fragmented bones. To avoid having core pin 170 carry any of the load that is now being held by the fragmented bones, a shorter core pin 192, as illustrated in
Depending on the stiffness of shorter core pin 192, the overall stiffness of bone fixation screw will change. For example, if a more flexible bone fixation screw is desired, core pin(s) may be left out all together or a shorter core pin made from a more flexible material, such as, for example, polyethylene or PEEK, may be employed. Alternatively, if a stiffer bone fixation screw is desired, core pin(s) may be made from different metals, including, for example, a soft titanium allow to a very hard CoCrMo alloy.
In an alternative embodiment as illustrated in
A bone fixation screw constructed in accordance with one or more aspects of the present invention achieves several advantages over conventional and existing bone fixation screws or devices. For example, a bone fixation screw including an expandable portion and removeable core pins constructed in accordance with one or more aspects of the present invention provides a finite amount of compression that is known to be optimal clinically.
While several aspects of the present invention have been described and depicted herein, alternative aspects may be affected by those skilled in the art to accomplish the same objectives. Accordingly, it is intended by the appended claims to cover all such alternative aspects as fall within the true spirit and scope of the invention.
The present application claims priority to U.S. Provisional Application Ser. No. 63/213,269 filed on Jun. 22, 2021 (Attorney Docket No. 3768.112P1), which is incorporated herein by reference in their entireties
| Number | Date | Country | |
|---|---|---|---|
| 63213269 | Jun 2021 | US |
