Intramedullary threaded nail for radial cortical fixation

Abstract

To provide a device and system for fixation of intra-articular and extra-articular fractures and non-unions of small bones and other small bone fragments.SOLUTION: The present invention relates to a threaded nail 10 with a robust length and a distal end with a cutting tip and longitudinal cutting flutes and a stepped diameter with cutting flutes at the transition point, and an optional cannulation along the central longitudinal axis of the nail.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to devices and systems for fixation of fractures and nonunions of small bones and other small bone fragments, and more particularly to a threaded nail having a robust length, a headless anterior end with a torque-transmitting recess, a posterior end with a cutting tip and longitudinal cutting grooves, and a cutting grooved intermediate stepped diameter at the transition point. Optionally, the device includes a cannulation along the central longitudinal axis of the nail. This intramedullary nail provides circumferential cortical fixation from the medial side along the entire shaft length, specifically for use in metacarpals and metatarsals. Thus, the implant achieves at least one circumferential friction fit with the medial cortex over at least 60%+ / -15% of the intramedullary canal length with penetration-assisted helical thread engagement along at least 80%+ / -15% of its length. [Background technology]

[0002] Metahand and midfoot injuries can have life-changing effects on victims as a result of loss of function, residual disability, and lengthy and arduous treatment protocols. Particularly for those who live a "hand to mouth" lifestyle, losing use of the foot or hand can make life difficult, sometimes impossible.

[0003] Current treatments include surgical internal fixation, such as plate fixation systems and wire fixation, or, in the case of non-displaced fractures, immobilization of the hand or foot in a cast without surgical intervention. These treatments require significant periods of time, i.e., weeks or months, during which the injured hand or foot cannot be moved. However, disuse during these periods can lead to serious problems with adhesions, muscle loss, proprioception, and neurological health. Furthermore, beyond the side effects of the treatment protocols, there are issues with compliance and challenges with daily living that result from not being able to use the hand or foot during these long periods of time.

[0004] Hand and foot injuries can occur during a variety of activities, including traffic accidents, accidental firearms discharges, and extreme sporting activities, but the risk of such traumatic events is more correlated with physical labor and low-wage jobs. Thus, the incidence and impact of such injuries are disproportionately distributed among lower-wage jobs and often involve workers who are already economically at risk. Thus, individuals who sustain injuries to their hands or feet often commit offenses that involve premature use of the injured limb or, in some cases, suffer income loss, including losing work altogether, which causes a rapid decline in the ability to "make ends meet," with the risk escalating from this injury to loss of home and family stability.

[0005] After all, it should be noted that the hands are paramount to all aspects of our humanity, helping to determine and define our relationship to society. Hand injuries, especially when they appear disfigured or disabled, can impede our perceptions and the relationships of our roles in society. Our hands are always visible to ourselves and to the world, and debilitating scars or irregularities such as scars, or even Frankenstein-like outlines from surgical instruments on the metacarpals, are visible and painful reminders of the traumatic event and its aftermath.

[0006] Conventional orthopedic implants used for small bones of the arms and legs have a different set of criteria than those for long bones and large joints. These bones tend to be smaller in diameter (commonly at the elbow and below, and at the knee) resulting in different ratios of cortical and cancellous bone, as well as problems with the overlying soft tissue, relatively large tendon nexus problems, ligament and nerve problems that complicate the surgical procedure. The present invention aims to solve these problems and provide a solution for surgical fixation of broken or fractured small bones with threaded nails for intramedullary fixation, most importantly for enabling a quick return to daily life and reducing disability, pain and rehabilitation.

[0007] One typical osseous implant site is the hand or foot, specifically the metacarpals and metatarsals. The hand structure consists of the navicular and other carpal bones, metacarpals, and phalanges that meet the radius and ulna at the wrist joint. The back of the hand contains the metacarpals. The metacarpals connect each finger and thumb to the hand, while the fingers and thumb are formed from bones called phalanges. The connections between the phalanges and metacarpals are called "phalangeal" joints or metacarpophalangeal joints (MCP joints) and act like hinges when bending the fingers or thumb. Each finger has three phalanges, which are separated by two joints called interphalangeal joints (IP joints). The proximal IP joint (PIP joint) is the joint closest to the MCP joint. The other joint closest to the tip of the finger is the distal IP joint (DIP joint). The thumb has only one IP joint. The joints are covered at the ends with articular cartilage. The foot has a similar structure and includes the talus, which connects the tibia and fibula of the lower leg, and the calcaneus of the foot, the midfoot consisting of the tarsal bones including the cuneiform bones (i.e., cuboid and navicular), metatarsals and phalanges.

[0008] Injuries to these bones in the limbs can result from sprains, fractures, or trauma and generally require reduction surgery to realign the damaged bone and stabilize it in place so that it can fuse in place.

[0009] Previously, surgical procedures to stabilize these fractured bones involved drilling pilot holes and inserting K-wires or smooth nails along the length of the bone to hold it in place while the bone heals. First, an opening is made in the metacarpal bone that extends through the fracture, and the nail is positioned by forcing it into the opening through the soft, spongy mid-bone to provide immobility to the bone portions on either side of the fracture. After a period of time, a subsequent operation is required to remove the nail from the bone. Problems with this procedure include the fact that the nail is not fixed into the bone, and in fact interacts primarily with the medullary tissue of the spongy mid-bone, and can migrate through the metacarpal bone and into the surrounding tissue. Sometimes this can result in soft tissue damage, such as tearing or damage to tendons or cartilage, and / or cause pain. Another problem with the nail is that it migrates, necessitating a subsequent operation to remove it. Additionally, the proximal end of the pin and nail can cause tendon irritation, tendon rupture, or skin irritation and infection.

[0010] One theoretical solution to this problem is to insert a screw into the bone, but placing the screw the entire length of the metacarpal bone (which is a relatively thin, delicate, and brittle bone) requires high torque. Such a procedure is lengthy and may result in bone damage or breakage of the screw's driving head, preventing full insertion into the opening created in the bone. Current screws are not specifically designed for intramedullary placement. For example, current screws are often not long enough and furthermore do not account for the narrow constriction of the metacarpal or metatarsal bones.

[0011] Thus, the present invention is directed to fixation of intra-articular and extra-articular fractures and non-unions of small bones and small bone fragments, including, for example, arthrodesis, bunionectomy and osteotomy of small joints, including the navicular bone and other carpal bones, metacarpals, tarsals, metatarsals, patella, ulna, styloid, capitellum, radial head and radial styloid, and preferably intramedullary fixation of metacarpal and phalangeal fractures, providing the surgeon with a reliable solution with a simple approach. The provision of a large length to diameter ratio (greater than 15:1, preferably greater than 20:1), different diameters (smaller diameter of 3-5 mm in the anterior length and even smaller diameter of 0.4-2 mm in the posterior length toward the nail head, as good examples being 3.2 / 3.6 or 4.0 / 4.5), and robust lengths (greater than 3.5 cm, preferably greater than 4 cm, or 5 cm + / - 1 or 0.5 cm, or up to 7.5 cm) accurately matches the position of the natural metacarpals and phalanges to provide strong, stable fixation and accurate reduction. Furthermore, the present invention contemplates filling the intramedullary canal substantially along its entire length (i.e., more than 45 length%, or more preferably more than 50 length%, more preferably more than 60 length% or 70 length%, and up to 80 length% or up to 98 length%). The design includes a front, or moving away from the nail end, section where the root and crest of the threads are of smaller outer diameter, but the inner cannulated section is relatively constant, if this front section is from 40-60% of the total length. The larger diameter section reinforces the area next to the torque receiving end of the nail, thus allowing more material to transmit torque within the device, and the cut grooves in the transition section between the two diameters keep the smaller front section from collapsing on itself. Thus, the device is designed to allow both insertion and removal by threading or unthreading the implant into the intramedullary canal.

[0012] Additionally, the present invention is unique in that the nail is designed to capture the medial cortical bone so that it not only extends substantially the entire length of the shaft (at least 60% including penetration beyond the isthmus), but is also used to achieve "radial" or "circumferential" fixation within the canal, preferably achieving 360° circumferential medial cortical fixation. This is novel for metacarpal applications since the metacarpal (and metatarsal) includes the "isthmus" of the metacarpal (and metatarsal) which is a narrowed, constricted area. Conventional screws and intramedullary implants are not designed to engage a sufficient length or to capture the inner wall of the canal circumferentially for a substantial entire length, but the present design includes a stepped diameter including a leading cutting tip and a middle cutting feature, which allows the present invention to ream the canal to a size such that it can be advanced into the canal. The canal is thus prepared for circumferential cortical fixation, which is unique to the present invention and relates to the use of an implant including a surface that is fixed to the medial cortical wall, or specifically to the use of an intramedullary shaft of the metacarpal bone of the metatarsal. The nail is intended to avoid the application of compressive forces along the entire length of the nail and can be used when there is a void or missing bone fragment in the bone, stabilizing the remaining gaping bone fragment to restore metacarpal length. The nail is available in two diameters, with both anterior and posterior diameter sections being substantially cylindrical, and importantly, is not tapered or conical to allow for maintenance of contact with the bore in the canal during removal of the device and easy removal by extracting the nail.

[0013] The present invention can be used in procedures that allow patients to return to work in as little as two weeks to the next day, including jobs ranging from manual laborers to caregivers, professional musicians, artists and professional athletes. Return to a convenient life and reduction in the risks of time off work, rehabilitation and daily life will be of great social relief. Summary of the Invention [Means for solving the problem]

[0014] The present invention solves the problems associated with repairing metacarpal or metatarsal fractures or dislocations by providing a unique combination nail and screw device that provides circumferential intramedullary cortical fixation, supports the bone from the inside (even when there is a bone gap of 0 to 2, 2.5 or even 3 cm along the length of the injured metacarpal), is sized and shaped to fit into the narrowing of the bone with at least one stepped diameter and grooved transitions between diameters, so that it can be inserted into the bone without damaging it, by providing a uniform lead headless design that can be positioned below the bone surface to avoid compression and possible irritation from protuberances, and by performing a cannulated surgical technique with an intramedullary implant designed to minimize soft tissue, cartilage and vascular trauma upon insertion and promote early active mobilization postoperative protocols for accelerated union and faster return to work.

[0015] Furthermore, the device is fixed in the bone to provide radially internal fixation, eliminating migration and the need for subsequent surgery to remove the device. Thus, the device provides a cannulated cylindrical core having an outer outer surface along its length (35 to 75, or even up to 120 or 130 mm long) that defines an inner diameter (minor diameter) relative to the outer edge of the threaded portion that defines the outer diameter (major diameter). The design includes one or more stepped sections at the rear section that allow for an increase in at least the outer or inner diameter, more preferably both the outer and inner diameters. Furthermore, the transition region includes longitudinal cut grooves (2-5, 3-10 mm long) to account for this increase at a certain length of the nail (i.e., 25% to 75%, preferably 35% to 60% of the total distance from the rear end) to allow for clearance of the narrowed or "necked" portion of the bone. The cannulated portion is generally a constant diameter along the entire length of the nail (for ease of manufacture) but may include two diameters, which may include an over grind at the larger diameter or trailing end of the nail that includes a torque transmission feature in the form of an internal or external hexagon or hexalobe or the like.

[0016] The device includes an anterior portion that has 2-5 cutting teeth at a beveled anterior tip and further includes additional longitudinal grooves along the long sides. These longitudinal grooves, like the other grooves, are intended for reaming cancellous intramedullary material and for scoring the inner surface of the intramedullary passage as well as locations for additional cancellous material present during surgery.

[0017] The thread defined between the major diameter and the minor diameter may suitably comprise a right-handed single start thread with a pitch of 3 to 5 mm, preferably at least 4.0 mm + / - 0.25, or a double start lead thread with the same lead value, the pitch value being half the lead value, and the secondary thread having a height less than that of the primary thread, i.e. 40% to 75% or 50% + / - 5% of the height of the primary thread. The leading and trailing flanks of the thread together form an angle of 5° to 60°, preferably 15° ± 10°, and are connected by a crest of 0.05 to 0.2 mm in length, spaced from the root diameter by a thread depth of 0.2 mm to 0.8 mm.

[0018] At its first or trailing end, the device includes a transmission recess that can be advanced by a suitable driver into the opening, such as a hex lobe or T10 transmission recess, to generate sufficient torque to penetrate into the cortical bone while avoiding damage to the thinner leading end of the nail with less material. [Brief description of the drawings]

[0019] [Figure 1] FIG. 2 is a top side view of a device according to the present invention. [Diagram 2] FIG. 2 is a side view of the device of FIG. 1. [Diagram 3] FIG. 2 is a cross-sectional view of the device of FIG. 1 taken along line AA. [Figure 4] FIG. 4 is a detailed view of FIG. 3 showing details of the thread features and thread geometry. [Diagram 5] FIG. 2 is a proximal end view of the device of FIG. 1. [Figure 6] FIG. 2 is an end view of the distal tip of the device of FIG. 1. [Figure 7] 2 is a detailed side view of a transition section of a blank forming the present invention, showing the intermediate cut groove of FIG. 1; FIG. [Figure 8] FIG. 2 is a detailed side view of the distal end of a blank forming the present invention showing the distal cut groove of FIG. 1. [Figure 9]FIG. 1 is a top view of a hand skeleton showing an implant of the present invention in place within a fractured metacarpal bone. [Figure 10] 1A-1C are diagrams of steps for measuring the metacarpal bones for use in the technique according to the invention; [Figure 11] 1A-1C are diagrams illustrating steps of inserting a guide wire in a retrograde manner to anatomically reduce fracture fragments according to the technique of the present invention. [Figure 12] FIG. 12 is a diagram of the guide wire entry point in FIG. 11 located in the dorsal third of the metacarpal head. [Figure 13] FIG. 13 is a diagram of the drilling step by passing a cannulated drill over the guide wire. [Figure 14] 1A-1D are diagrams illustrating steps of inserting an implant into a metacarpal bone according to the surgical technique of the present invention. [Figure 15] FIG. 2 is a side view of a second embodiment of the device of FIG. 1. [Figure 16] FIG. 16 is a cross-sectional view of the device of FIG. 15 taken along line CC. [Figure 17] FIG. 17 is a detailed view of FIG. 16 showing details of the thread features and thread profile. [Figure 18] FIG. 16 is a side view of a blank forming the present invention showing the transition section, intermediate cut groove and distal cut groove of FIG. [Figure 19] FIG. 16 is a proximal end view of the device of FIG. 15. [Figure 20] FIG. 16 is an end view of the distal tip of the device of FIG. 15. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] FIG. 1 illustrates an exemplary embodiment 10 of a threaded intramedullary nail of the present invention. The nail 10 may be formed from any suitable biocompatible material, such as surgical grade stainless steel, titanium, nickel-chromium alloys, nitinol, PEEK, hydroxyapatite, bio-glass, other biocompatible materials, or combinations of these materials. The nail 10 has a first or proximal end 12, a second or distal end 14, a shaft 16 including an outer surface 17, and a central portion 18 between the first end 12 and the second end 14. A cutting end 19 including a bevel and two, three or four teeth 19a is provided at the trailing end 14 (distal to the torque transmission recess and implanted in the proximal portion of the metacarpal bone), and a torque transmission surface 20 within a torque transmission recess 22 is formed within the apex of the first end 12.

[0021] The cutting edge 19 aids in cutting any remaining within the bone when the bone is drilled to receive the device 10, and further includes two to five radially equally spaced longitudinal cutting grooves 23 on its outer surface that extend longitudinally through the threads of the nail 10. In this embodiment, the drive surface 20 has a hex-lobe drive form, although any suitable drive form may be used. Other drive forms that may be used include slotted, Pozidriv, Robertson, Tri-Wing, Torq-Set, Spanner Head, Triple Square, and Hex Head.

[0022] The outer surface 17 has grooves or cut grooves 24 extending longitudinally, preferably along the longitudinal axis of the shaft 16. As used herein, "longitudinally extending" means that each groove 24 is elongated and extends along the shaft with one end closer to the first end 12 and the opposite end closer to the second end 14, although the grooves 24 may be formed at an angle, and are not necessarily formed along the longitudinal axis of the shaft 16, as is preferred. The grooves 24 preferably have edges that aid in boring the device 10 into the bone and anchoring the device 10 within the opening in the bone. The grooves 24 may also trap any debris remaining after the bone drilling process that creates the opening, which occurs when the device 10 is positioned in the opening.

[0023] The shaft 18 of the nail 10 of the present invention includes at least two sections of differing diameters, for example a proximal section extending over a length of approximately 15% to 30% of the total length of the device and located 25% to 75%, preferably 55-65% of the total distance from the distal end of the device 10. Additionally, the device provides a cannulated cylindrical core or shaft 18 having an outer exterior surface 17 along its length (provided in 5 mm increments from 35 to 75 mm) that defines an inner diameter relative to the outer edge of the threaded portion that defines the outer diameter. The design includes one or more stepped sections that allow for an increase of at least 0.25-1.0 mm in the outer or inner diameter, more preferably both the outer and inner diameters, in the proximal section. Additionally, the transition region includes longitudinal cut grooves (2-5 grooves, 3-10 mm in length) to allow for clearance of narrowed or "necked" portions of the bone and account for this increase over a certain length of the nail (i.e., 25% to 75%, preferably 50% to 60% of the total distance from the proximal end).

[0024] The device includes threads 25 defined between the outer diameter and the inner diameter, and may suitably include a right-handed single start thread with the same lead value and a pitch of 3 to 5 mm, preferably at least 4.0 + / - 0.25 mm. Alternatively, as shown in Figures 15, 16 and 17, the device may include a double start lead thread 125 having a first thread 126 and a second thread 127 with the same lead value, where the second thread 127 has a height of about 50% of the height of the first thread 126.

[0025] The leading and trailing flanks of the thread together form an angle of 5° to 60°, preferably 15±10°, and are joined by a crest having a length of 0.05 to 0.2 mm, spaced from the root diameter by a thread depth of 0.2 mm to 0.8 mm.

[0026] FIG. 9 shows a nail 10 according to the present invention in place in the fourth metacarpal bone, fixing a reduced fracture.

[0027] The first step of the surgical technique according to the present invention, shown in FIG. 10, is to determine the size of the metacarpal bone 30 in question for sizing the implant.

[0028] In FIG. 11, the bone fracture is aligned and then a guide wire 32 is inserted retrograde into the intramedullary canal.

[0029] FIG. 12 shows the optimal location 34 for guide wire insertion.

[0030] In FIG. 13, using the guide wire as a guide, with a cannulated drill 33, an opening is drilled into the metacarpal bone that extends through the fracture and provides sufficient space on either side of the fracture for proper positioning of the device 10.

[0031] 14, the drive recess is used to advance the device 10 into the opening in the metacarpal bone. The outer diameter of the threads 28 is slightly larger than the inner diameter of the opening in the bone, thereby threading the bone material at the threads 28 and providing an interference fit for the device 10.

[0032] Having thus described some embodiments of the present invention, other variations and embodiments that do not depart from the spirit of the present invention will become apparent to those skilled in the art. Accordingly, the scope of the present invention is not limited to any particular embodiment, but is instead set forth in the appended claims and their legal equivalents. Unless otherwise expressly stated in the written description or claims, the steps of any method recited in the claims can be performed in any order that achieves the desired results.

Claims

1. An intramedullary implant, a first portion extending from about 15% to about 30% of the length of the intramedullary implant, the first portion having a driver recess formed in a first end thereof; a second portion having one or more radially spaced apart cutting grooves; a central portion between the first portion and the second portion; Equipped with the diameter of the second portion is 0.4 mm to 2 mm smaller than the diameter of the first portion; the second portion includes a double lead thread; The intramedullary implant, wherein the threads of the first portion and the threads of the second portion have the same pitch.

2. An intramedullary implant as described in claim 1, wherein the double-thread lead thread comprises a first thread having a first pitch value and a second thread having a second pitch value.

3. An intramedullary implant as described in claim 2, wherein the first pitch value and the second pitch value are the same.

4. An intramedullary implant as described in claim 2, wherein the first thread has a first thread height and the second thread has a second thread height different from the first thread height.

5. An intramedullary implant as described in claim 4, wherein the second thread height is 30% to 75% of the value of the first thread height.

6. The intramedullary implant of claim 1, wherein the intramedullary implant comprises titanium or stainless steel.

7. The intramedullary implant of claim 1, wherein the intramedullary implant is configured to be placed in the navicular bone, capitellum, radial head, metacarpal bone, tarsal bone, metatarsal bone, or ulna.

8. The intramedullary implant of claim 1, wherein the intramedullary implant is provided with a cannula.

9. An intramedullary implant as described in claim 1, wherein the central portion has a plurality of radially spaced cutting grooves.

10. An intramedullary implant, a first end portion having a first outer diameter, the first end portion including a torque transmission feature; a second end portion having a second outer diameter, the second portion including at least one machined groove; a transition portion between the first end portion and the second end portion, the transition portion including at least one cutting groove; a cannula extending along the entire length of the intramedullary implant; Equipped with the intramedullary implant comprises a thread extending from the first end portion to the second end portion; The intramedullary implant, wherein the second outer diameter is 0.4 mm to 2 mm smaller than the first outer diameter.

11. An intramedullary implant as described in claim 10, wherein the threads include a double lead thread.

12. An intramedullary implant as described in claim 11, wherein the double-thread lead thread includes a first thread having a first pitch value and a second thread having a second pitch value, and the first pitch value and the second pitch value are the same.

13. An intramedullary implant as described in claim 11, wherein the first thread has a first thread height and the second thread has a second thread height different from the first thread height.

14. An intramedullary implant as described in claim 13, wherein the second thread height is 30% to 75% of the value of the first thread height.

15. An intramedullary implant as described in claim 10, wherein the ratio between the length of the intramedullary implant and the maximum outer diameter of the intramedullary implant is greater than 8:1.

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