WO2013156816A2

WO2013156816A2 - Osteotomy implant, instrumentation and associated methods of use

Info

Publication number: WO2013156816A2
Application number: PCT/IB2012/051948
Authority: WO
Inventors: Jean-Pierre ETCHERVERS; Loïc GIROD; Mael COCAIGN
Original assignee: Etchervers Jean-Pierre; Girod Loic; Cocaign Mael
Priority date: 2012-04-18
Filing date: 2012-04-18
Publication date: 2013-10-24

Description

OSTEOTOMY IMPLANT, INSTRUMENTATION AND ASSOCIATED METHODS OF

USE

FIELD OF THE INVENTION

E0001] This invention pertains to fusion cages for internal bo e fixation.

BACKGROUND OF THE INVENTION

Ϊ0002] Certain medical conditions can be treated by the stabilization and/or correction of angular deviations in a single bone, or between two adjacent bones in the foot. For example, performing a basal open-wedge osteotomy on the first metatarsal is indicated to correct hallux valgus with substantial metatarsus primus varus. An Evans osteotomy may be performed on the heel to correct flat feet. In other examples, a Cotton osteotomy may be performed on the first cuneiform to correct various conditions, such as flat feet, hallux limitus and hallux valgus. When performing these and other surgeries, multiple bones or multiple segments of a single bone may require stabilisation with a device, such as plates, wedges, or interposition implants. Each of these types of devices can come with certain drawbacks .

[0003] Plates, for example, often cause irritation of surrounding soft tissues, which may necessitate removal of the plate. Operative techniques for implanting plates are also often incompatible with a minimally invasive, approach. This can result in more soft tissue damage and require, a larger incision, leading to increased recovery time, increased hematoma and post-operative pain, and larger scars. Plates also come in different sizes and configurations, which may not always correspond to the dimensions required for a particular case. The. complexity of plate implantation, which generally requires at least four screws, multiple K-wires to place the plate, and other associated instruments and assemblies, is another disadvantage often seen with plate systems. Finally, a plating system should not be used alone to fix an open-wedge osteotomy since a large void would be left between the opposing sides of the osteotomy. The void would generally need to be filled with living bony material or bone substitute to complete the osteosynthesis process of the osteotomy. Using a plating system alone without filling the bone void could delay and threaten optimal healing, possibly leading to non-union or even mal -union of the bone segments.

[0004] Wedges and interposition implants may solve some of the problems associated with plate implants, but these too often leave something to be desired. For example, although they can address the problem of the empty cavity of open wedge osteotomies, they are generally made of non-resorbable materials which limit the effectiveness of bony colonization of the cavity. Also, despite a large range of products, wedges and interposition implants still can fail to precisely fit a specific patient's anatomy. Further, wedges and interposition implants are often used as a secondary fixation to another method, such as a plating system, and thus can fail to obviate problems associated with the primary implant.

[0005] It would be beneficial to provide an internal bone fixation system that has a small number of implant sizes which can fit a large range of patient anatomies and surgical requirements .

[0006] It would further be beneficial to provide an internal bone fixation system compatible with a minimally invasive surgical technique.

[0007] It would also be useful to provide an internal bone fixation system that allows enhanced bone growth processes to reduce the time required for osteosynthesis and to improve the stability of the surgical correction without necessarily having to harvest bone in a separate step.

[0008] It would further be advantageous to provide an internal bone fixation system that requires a relatively small number of operating steps to shorten and simplify the surgery. BRIEF SUMMARY OF THE INVENTION

[0009] In one embodiment of the invention, a fusion cage system includes an im lant. The implant includes a cylindrical shaft having a circumference, an interior cavity, a trailing end, a leading end including an opening to the interior cavity. The implant further includes self -tapping threads positioned along the circumference of the cylindrical shaft, the self -tapping threads being interrupted by at least one fenestration in the cylindrical shaft. The implant further includes self-coring teeth at the leading end of the cylindrical shaft. The implant, of the fusion cage system may also include an interior cavity having an open end at the leading end of the implant and an end wall at. the trailing end of the implant .

[0010] The self-tapping threads of the implant may not fully extend to the leading end of the implant, and also may not fully extend to the trailing end of the implant.

[0011] The self-coring teeth of the implant can include an outer surface and an inner surface, the outer surface of the teeth extending farther than the inner surface of the teeth in a direction of the leading end of the cylindrical shaft of the implant .

[0012] The fusion cage system can also include one or more stabilizing wires. The cylindrical shaft of the implant can include two or more fenestrations spaced at generally regular intervals around the circumference of the cylindrical shaft, the two or more fenestrations being configured to receive the two or more stabilizing wires therethrough. The trailing end of the cylindrical shaft can include one or more markings corresponding to the location of at least one or more fenestration to assist in guiding the stabilizing wires through the fenestrations of the implant.

[0013] The fusion cage system can further include an insertion guide/retractor . The retractor includes a tubular shaft having a circumference, a trailing end, a leading end, and an inner bore. The retractor also includes a first prong at the. leading end of the retractor and a second prong at the leading end of the retractor, the first and second prongs being configured to maintain an osteotomy open, during an implantation procedure.

[0014] The inner bore of the retractor can be configured to receive the implant therethrough. The retractor can further include an extension member extending from the tubular shaft of the retractor, the extension member including two or more apertures configured to guide two or more stabilizing wires.

[0015] The fusion, cage system can also include, an implant inserter having a length between a proximal end and a distal end, the implant inserter adapted to engage the trailing end of the implant. The inserter may be sized to be positioned within the inner bore of the retractor.

[0016] Another embodiment of the present invention includes a method, of performing surgery. The steps include providing an implant comprising a cylindrical shaft, having a circumference, an interior cavity, a trailing end, and a leading end, the leading end including an opening to the interior cavity. The implant further comprises self-tapping threads positioned along the circumference of the cylindrical shaft, the self- tapping threads being interrupted by at least one fenestration in the cylindrical shaft. The implant further comprises self- coring teeth at the leading end of the cylindrical shaft. A further step includes inserting the leading end of the implant into a first and second portion of a bone, the first and second portions of the bone being separated by an osteotomy in the bone. A further step includes advancing the self -tapping threads and self-coring teeth of the implant through the first and second portions of the bone such that a section of the first portion and a section of the second portion are positioned within the cavity of the implant. [0017] The method can further include inserting a first stabilizing wire through each of a first and second fenestration of the implant, the first and second fenestrations being located on generally diametrically opposed sides of the cylindrical shaft.

[0018] The method can still further include inserting a second stabilizing wire through each of a third and fourth fenestration, the third and fourth fenestrations being located on generally diametrically opposed sides of the cylindrical shaft .

[0019] The step of advancing the self-coring teeth of the implant, through the first and second portions of the bone can cause bone chips to be guided toward the osteotomy in the bone . The bone chips can be caused to be. guided toward the cavity of the implant positioned within the osteotomy.

[0020] The step of inserting the leading end of the implant into the first and second portion of the bone can include passing the implant through a retractor, the retractor holding open the osteotomy while the implant is inserted into the bone ,

[0021] The trailing end of the implant can include an end wall of the internal cavity, and the step of advancing the implant through the first and second portions of the bone can continue until the sections of the first and second portions of the bone, contact the end wall of the trailing end.

[0022] A further embodiment of the invention includes a method of performing surgery including providing an implant with a cylindrical shaft having a circumference, an interior cavity, a trailing end, and a leading end, the leading end including an opening to the interior cavity. The implant also includes self-tapping th eads positioned along the circumference of the cylindrical shaft, the self-tapping threads being interrupted by at least one fenestration in the cylindrical shaft. The implant further includes self-coring teet at. the leading end of the cylindrical shaft. The method further includes the step of inserting the leading end of the implant into a first and second portion of a bone, the first and second portions of the bone being separated by an osteotomy in the bone. The method further includes the step of advancing the self-tapping threads and self-coring teeth of the implant through the first and second portions of the. hone without pre-drilling or pre-shaping either the first or second portion of the bone .

[0023] The cylindrical shaft can further include a plurality of fenestrations extending from an outer surface of the cylindrical shaft to the interior cavity of the cylindrical shaft, at least one of the fenestrations having a non-zero rake angle.

[0024] The self-tapping thread includes a proximal end, the proximal end of the self-tapping thread may not fully extend to the trailing end of the cylindrical shaft. The step of advancing the implant through the first and second portions of the bone continues until the proximal end of the self--tapping thread is fully implanted into at least one of the first or second portions of the bone.

[0025] The step of inserting the leading end of the implant into the first and second portion of the bone can include passing the implant through a retractor, the retractor holding open the osteotomy while the implant is inserted into the bone .

[0026] The step of inserting the leading end of the implant into the first and second portion of the bone can further includes transmitting torque from an inserter to the implant. The torque can be transmitted from the inserter to the implant with a motorized drill, by hand, or both.

[0027] The method can further include inserting a first stabilizing wire through each of a first and second fenestration of the implant, the first and second fenestrations being located on generally diametrically opposed sides of the cylindrical shaft, and inserting a second stabilizing wire through each of a third and fourth fenestration, the third and fourth fenestrations being located on generally diametrically opposed sides of the cylindrical shaft. The. trailing end of the implant includes at least one marking, each of the at least one markings indicating a location of a corresponding fenestration.

[0028] In another embodiment of the invention, an internal bone fixation system includes an implant, a retractor, and an inserter. The implant includes a cylindrical shaft having a circumference, an interior cavity, a trailing end, a leading end including an opening to the interior cavity. The implant further includes self-tapping threads positioned along the circumference of the cylindrical shaft, the self -tapping threads being interrupted by at least one fenestration in the cylindrical shaft. The implant further includes self-coring teeth at the leading end of the cylindrical shaft. The retractor includes a tubular shaft having a circumference, a trailing end, a leading end, and an inner bore. The retractor also includes a first prong at the leading end of the retractor and a second prong at the. leading end of the retractor, the first and second prongs being configured to maintain an osteotomy open during an implantation procedure. The inserter is configured to fit within the inner bore of the retractor. The retractor can include an extension member, the extension member" containing a plurality of apertures.

[00293 The internal bone fixation system can also include a plurality of guide wires, the guide wires being configured to be inserted through the apertures of the extension member.

[0030] The internal bone fixation system can also include a plurality of stabilizing wires, the stabilizing wires being configured to be. inserted through the fenestrations in the cylindrical shaft of the implant. [0031] In another embodiment of the invention, an internal bone fixation kit. includes a retractor, an inserter, and a plurality of implants of different sizes adapted for fixation of various-sized bones. Each implant includes a cylindrical shaft having a circumference, an interior cavity, a trailing end, a leading end including an opening to the interior cavity. Each implant further includes self-tapping threads positioned along the circumference of the cylindrical shaft, the self-tapping threads being interrupted by at least one fenestration in the cylindrical shaft. Each implant further includes self -coring teeth at the leading end of the cylindrical shaft.

[0032] The kit can also include a plurality of retractors of different sizes, the retractors each having a circumference, a trailing end, a leading end, and an inner bore. Each retractor also includes a first prong at the leading end of the retractor and a second prong at the leading end of the retractor, the first arid second prongs being configured to maintain an osteotomy open during an implantation procedure. The plurality of retractors may have first and/or second prongs of different sizes.

[0033] The kit can also include a plurality of wires. The plurality of wires can include a first set of wires of a first diameter configured to be inserted through the fenestrations in the implant, to stabilize the osteotomy. The plurality of wires can also include a second set of wires of a second diameter be configured to be inserted through apertures in the retractor to stabilize the retractor.

[0034] In a further embodiment of the invention, a method of performing surgery includes providing an internal bone fixation kit. The kit includes a plurality of implants of different sizes, each implant includes a cylindrical shaft having a circumference, an interior cavity, a trailing end, and a leading end, the leading end including an opening to the interior cavity. Each implant also includes self -tapping threads positioned along the circumference of the cylindrical shaft, the self-tapping threads being interrupted by at least one fenestration in the cylindrical shaft. Each implant further includes self -coring teeth at the leading end of the cylindrical shaft. The kit further includes an inserter configured to insert one of the plurality of implants into a bone. The method includes the step of choosing one of the plurality of implants and inserting the leading end of the chosen implant into a first and second portion of the bone, the first and second portions of the bone being separated by an osteotomy in the bone. The. method further includes the step of advancing the self -tapping threads and self-coring teeth of the chosen implant through the first and second portions of the bone such that a section of the first portion and a section of the second portion are positioned within the cavity of the chosen implant .

[00351 The kit can further include a plurality of retractors of different sizes, each retractor being configured to hold open an osteotomy in a defined range by virtue of the tapered prongs. The step of inserting the leading end of the chosen implant into the first and second portion of the bone includes choosing one of the plurality of retractors and passing the chosen implant through the chosen retractor, the chosen retractor holding open the osteotomy while the chosen implant is inserted into the bone.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIG. 1-2 illustrate perspective views of a fusion cage implant according to one embodiment of the invention.

[0037] FIG. 3 illustrates a vertical sectional view of the implant of FIG. 2 across Section 3-3.

[0038] FIG. 4 illustrates a horizontal sectional view of the implant of FIG. 1 across Section 4-4.

3 [0039] FIGS. 5-6 illustrate perspective views of the teeth of the implant shown in FIGS, 1-2.

[0040] FIG, 7 illustrates a perspective view of the leading end of a fusion cage implant according to one embodiment of the invention,

[0041] FIGS. 8-9 illustrate fusion cages implanted into a bone .

[0042] FIG. 1.0 shows a perspective view of a retractor and insertion tool according to one embodiment of the invention.

[0043] FIG, 11 shows a sectional view of the retractor and insertion tool shown in FIG. 10.

[0044] FIGS. 12-13 illustrate differently sized retractor and insertion tools within an osteotomy.

[0045] FIG. 14 shows a perspective view of an inserter and t being inserted through a retractor and insertion tool.

[0046] FIG. 15 shows the retractor and insertion tool of FIG. 10 engaged with stabilizing wires.

[0047] FIG. 16 shows a perspective view of the inserter shown in FIG. 14.

[00483 FIG. 17 shows a sectional view of the leading end of an inserter mated with the trailing end of a fusion cage implant .

[0049] FIGS. 18-20 illustrate various views of a fusion cage implant with stabilizing wires extending through the implant ,

[0050] FIGS. 21-23 illustrate various views of a fusion cage implant in bone with stabilizing wires extending through the implant and bone .

[0051] FIGS, 24-25 illustrate bottom views of the teeth of the. implant .

DETAILED DESCRIPTION

[0052] In one embodiment of the invention, an internal bone fixation system includes an osteotomy cage 100, a retractor and insertion guide 200, and an inserter 300. The system may further include K-wires 400.

[00533 Referring to FIGS, 1-7, an osteotomy cage generally includes a cylindrical shaft body 110 with a trailing end 120 and a leading end 130, a thread 140, enestrations 150, and teeth 160.

[0054] The thread 140 preferably begins at a distance Di from the leading end 130 of the body 110, such that the external circumference of the leading end 130 of the body 110 is threadless for a distance D_x . This distance Di preferably corresponds to the thickness of the cortical bone layer at the intended implantation site. For purposes of illustration and not limitation, the distance Ό could be on the order of about 1mm-4mm for a foot, and as large as approximately 6mm for the tibia. Starting the threads a distance Di from the leading end 130 of the body 110 allows for the osteotomy cage 100 to pass through the cortical bone, with a high drilling speed, without having the thread engage the cortical bone. Similarly, the thread 140 preferably ends at a distance D₂ from the trailing end 120 of the body 110. This distance D₂ may be based, for exa.mp.le, on the outer shape and the convexity of the bone subject to implantation. This provides a threadless outer circumference near the trailing end 120 which limits the amount of sharp implant edges that might otherwise cause irritation of nearby soft, tissue. The pitch of the thread 140 is preferably chosen as a function of the design of teeth 160 to adjust the advance of the implant based on the amount of bone to be removed. This helps reduce the likelihood that bone over- accumulates in the teeth during drilling, thus helping to avoid overheating and other undesirable cutting conditions that might otherwise damage the surrounding bone and threaten a rapid fusion of the bone.

[0Q553 Multiple fenestrations 150 are spaced about the circumference of the body 110, each fenestration 150 extending through the thickness of the body 110. Stated in another way, the fenestrations 150 create a channel between the outer circumference and an inner cavity of the body 110. Preferably, the fenestrations 150 are dimensioned to extend at least through the ends of the thread 140 at both the trailing end 120 and leading end 130 of the body 110, as illustrated, for example, in FIG. 1. This configuration results in sharp edges where the thread 140 interfaces with the fenestration 150, creating a self tapping thread 140 that diminishes the torque necessary to drive the implant, reducing the likelihood that the implant overheats or is otherwise damaged during implantation. The fenestrations 150 preferably do not extend radially through the body 110, but rather have a cutting axis A_f that is offset from the radial axis A, which is defined by a line extending from a point on the cutting surface to the longitudinal axis of the implant body 110. The angle between the cutting axis and the radial axis is defined as the rake angle. This rake angle, or cutting angle, is best see in FIG. 4 in the context of the fenestrations and in FIGS. 24-25 in the context of the teeth. In this embodiment, the rake angle may have, a non-zero value, such that the rake angle may be greater or less than 0 degrees. This further reduces the torque necessary to drive the implant and helps increase the likelihood that bone material removed by virtue of the rotating threads 140 may be guided toward the inner cavity of the implant body 110.

[0056] The fenestrations 150 also allow for optional insertion of K-wires 400 through the entirety of the body 110 of the implant. Preferably, the fenestrations 150 are substantially evenly spaced around the circumference of the body 110 and configured such that a K-wire 400 can enter a fenestration 150 on one side of the body 110 and exit through another fenestration 150 on the other side of the body. However, the exact configuration of the number, spacing, and orientation of the fenestrations 150 is a matter of design choice .

[0057] The circumference of the lea.ding end 130 of the implant body 110 includes a plurality of teeth 160, as best seen in FIGS. 5-7. The teeth 160 of the implant body 110, illustrated in FIG. 5 with a saw-blade configuration, provide a self-coring functionality to the implant, enabling insertion of the implant without the need for pre-drilling or pre- shaping the bone. The gullets 170, or space between the teeth 160, are preferably sized to store at least the ma.ximum volume of bone chips cut by a tooth 160 during insertion. This volume can be calculated as a function of the pitch of the threads and the cutting area of the implant (i.e. diameter of the implant and thickness of the walls of the implant) . As best understood referring to FIGS. 8-9, this corresponds to the volume of bone that would be cut by a single tooth 160 from the point of entry into the bone until the gullet 170 storing the bone material is aligned with the osteotomy such that the bone material can leave the gullet 170 and enter the osteotomy. This volume can be calculated, for example, by assuming that the osteotomy opening is narrow and that the amount of bone chips stored, in the gullet 170 is entirely emptied into the osteotomy during each pass. In addition to helping fill the osteotomy with quality autologous bone debris, appropriately sizing the volume of the gullet 170 helps to maintain the ability of the teeth 160 to make a clean cut and thus helps to avoid overheating of the surrounding bone during the implantation process .

[00583 The number of teeth 160 at the leading end of the implant body 110 can be a function of the outside diameter of the implant. For purposes of illustration, and not limitation, for each millimeter of diameter of the implant, between about 1 and 1.5 teeth can be included. This helps provide an optimum cutting operation in which less heat is generated and the cut is more accurate. An additional feature of the teet 160 is a rake angle (best seen in FIGS. 24-25) on each tooth 160 that enables bone chips to be guided into the osteotomy during implantation.. The rake angle a can be, for purposes of illustration and. not limitation, between about 10-30°, preferably about 17°.

[00591 In one embodiment of the invention for use with the foot, for the correction of hallux valgus deformities, the diameter of the body 110 of the implant 100 is approximately between IImm and 13mm including the thread 140. The length of the body 110 from trailing end 120 to leading end 130 is approximately 10mm in one embodiment, with the thickness of the walls of the body 110 being about ,8mm. These dimensions are exemplary and may be modified as a matter of design choice. For example an implant of smaller dimensions may be more suitable for use in the hand bones. Alternatively, a substantially larger version of implant 100 may be suitable for use in a. long bone, such as a tibia.

[0060] The implant 100 is inserted into the bone such that the walls of the implant body 110 capture a. living bone core between the osteotomy and the implant body 110. This living bone core, as best seen in FIGS. 8-9, provides enhanced stability to the osteotomy, particularly since the implant 100 itself forms the living bone core during insertion of the im lant. Another result of preserving a living bone core inside the implant is that it provides additional stability and strength when hazardous loads are applied (e.g. transverse loads, shear loads} or in cases of breakage of the bony hinge of the osteotomy, allowing for osteosynthesis in some of even the most severe cases .

[0061] As the implant 100 is inserted into bone, the teeth 160 and threads 140 cut away bone. Bone cut by the teeth 160 is stored in the. gullet 170 until passing the osteotomy

(during rotation of the implant. 100) , at which point the bone stored in the gullet 170 is guided into the osteotomy. Similarly, bone cut by the threads 140 is guided into the osteotomy by way of the fenestrations 150. By virtue of simply inserting the implant 100 into bone, the osteotomy is filled with bone chips that will assist in the fusion process and enhance stability of the osteotomy. This avoids the necessity of harvesting additional autologous bone and the attendant pain and morbidity, and further avoids the need for any additional bone substitute that likely would have inferior osteosynthesis capabilities compared to autologous bone.

[0062] Additionally, the diameter of the implant 100 can be sized as a function of the osteotomy opening. For example, an implant of a first range of diameters could be used for hallux valgus corrections while an implant of a second range of diameters would be used for Evans osteotomies. Appropriately sizing an implant for a specific correction helps to entrap a minimum section of living bone.

[0063] Other attendant benefits include eliminating bone shaping steps, eliminating the necessity of reamers or drill bits for the implant and reducing the risk of metal debris production. These benefits result in savings in time and costs as well as reducing the likelihood of contamination during the procedure. This also helps to limit mismatches between the implant size and the prepared housing, for example by reducing the likelihood of over drilling, under drilling, size mistakes, and implantation along the wrong axis. This, in turn, helps to maximize the integration of the implant within the bone surrounding the osteotomy, enhances the fusion process, and reduces the risk of breaking the internal bone core .

[QQ64] Referring now to FIGS. 10-15, the internal bone fixation system can also include a retractor and insertion guide 200. The retractor 200 includes a tubular shaft 210. The leading end of the tubular shaft 210 has two prongs 220 on diametrically opposed portions of the tubular shaft 210. The prongs 220 function to hold an osteotomy open during insertion of the osteotomy cage 100, Multiple retractors 200 with prongs 220 of different widths can be included in a set or a kit to increase the likelihood that retractors 200 are available to fit a variety of osteotomy sizes. For example, FIGS. 12-13 show retractors 200 with prongs 220 of different widths that correspond to osteotomies of different sizes. Preferably, a set of retractors 200, each with prongs 220 of a different width, are included to increase the likelihood that a retractor 200 is available to fit a particular osteotomy size. With each retractor 200, a range of angular corrections can be achieved by virtue of the tapered feature of the prongs 220. In certain embodiments of the invention, fox- example for use with indications other than an open wedge osteotomy, the retractor and insertion guide 200 can alternately be used without the prongs 220,

[0065] The retractor 200 includes an inner bore 230 extending through the shaft 210. The inner bore 230 is configured to allow passage of the fusion cage through the inner bore 230 once the retractor 200 is in place with prongs 220 in the osteotomy. The inner bore 230 can also accommodate an inserter, for example a screwdriver, 300. An extension member 240 extends from the shaft 210 of the retractor 200 and includes a plurality of apertures 250. Each aperture 250 is capable of accepting a K-wire 400, at the operator's discretion, to increase the stability of the retractor 200. The tubular shaft 210 can also include a plurality of openings 260 to enable an operator to control the position of the osteotomy cage 100 and inserter 300 while they are within the inner bore 230 of the retractor 200.

[00663 Referring to FIGS. 16-17, the internal bone fixation system can also include an inserter, for example screwdriver 300. The. inserter 300 includes a head 310 that mates with a corresponding shape on the trailing end 120 of the osteotomy cage 100. For example, the head 310 may have a tapered hexagonal shape which mates with a corresponding hexagonal shape on the trailing end 120 of cage 100. The head 310 of the inserter 300 enables transmission of torque to the osteotomy cage 100 and also helps reta.in the osteotomy cage 100 in position during handling. It should be noted that although a hexagonal shape is preferred, other shapes are permissible. The trailing end 320 of the inserter 300 includes markings that indicate when the inserter 300 has progressed to the point where it would be preferable to switch from motor drilling to hand controlled drilling to allow for finer control of the insertion. The external diameter of the inserter 300 preferably matches the internal diameter of the inner bore 230 of the retractor 200 to allow the inserter 300 to slide and guide within the retractor 200. The proximal end 330 of the inserter 300 enables a quick connection with a handle or with a motor to drive the inserter 300 during insertion of the osteotomy cage 100.

[0067] Although embodiments of the invention are described herein with respect to osteotomy surgeries, it is also within the scope of the disclosure to use the devices and instrumentation described herein for other indications, such as arthrodesis or closing osteotomies,

[0068] In one embodiment, the present invention includes a method for performing an osteotomy procedure, including a surgeon making an incision, for example in the foot, creating an open-wedge osteotomy in the bone, and distracting the osteotomy as is known in the art. While this invention is described for use in the foot, it is envisioned that the present invention may be used in other anatomy, such as the hand, or various bones of the. body such as the tibia. Once distracted, the surgeon can choose the most appropriately sized retractor 200 and insert the prongs 220 of the retractor 200 into the osteotomy, as shown in FIGS. 12-13, At this point, if the surgeon requires more stability in the system, he may, at his discretion, insert K-wires 400 through the apertures 160 of the extension member 240 of the retractor 200. The K-wires 400 can then be further anchored into the bone to provide extra stability.

[0069] Once the retractor 200 is in place, the surgeon mates the head 310 of the inserter 300 with the correspondingly shaped recess in the trailing end 120 of an appropriately sized osteotomy cage 100 for the particular anatomy. The osteotomy cage 100 and inserter 300 are placed through the inner bore 230 of the retractor 200 and the leading end 130 of the osteotomy cage 100 is placed in proximity to the incision. The proximal end 330 of the inserter 300 is attached to a motor drill (not shown) and drilling begins. As the drilling ensues and the osteotomy cage 100 enters the. bone, the inserter 300 moves toward the leading end of the retractor 200 through the inner bore 230. As the inserter 300 continues to progress, markings, for example on the trailing end 320 of the inserter 300, indicate that the osteotomy cage 100 has moved far enough into the bone such that finer hand control of the inserter 300 would be preferable. At this point, the surgeon can grasp the inserter 300 by hand with an appropriate handle and complete insertion of the osteotomy cage 100.

[0070] During insertion of the osteotomy cage 100, the teeth 160 self-core the bone without the need to pre-drill or shape the bone. As the teeth 160 initially pass through the cortical bone, the leading end 130 of the implant body 110 is unthreaded, allowing for faster initial drilling without causing overheating. Also as the self -coring teeth 160 rotate into the bone, bone chips created from the drilling are stored within the gullets 170 of the teeth 160. During rotation, when a particular gullet 170 has moved through rotation to the point where it is at the osteotomy in the bone, the bone chips are guided from the gullet 170 into the space of the osteotom .

[0071] As drilling continues, the threads 140 on the implant body 110 begin to contact the bone. The fenestrations 150 give the threads 140 a self-tapping f nctionality to enhance drilling and reduce heating of the system. As the threads 140 move through the bone, bone chips are stored in the fenestrations 150 until a fenestration 150 reaches the space of the osteotomy. Once the fenestration 150 is lined up with the osteotomy, the bone chips are guided, with the help of the rake angle, into the. osteotomy.

[0072] Drilling continues until the implant body 110 has moved far enough into the bone. At this point, the trailing end 120 of the implant body 110 is near the surface of the bone. Because the trailing end 120 of the implant body 110 is threadless for a distance D₂, the implant body 1.10 is less likely to cause irritation of the tissue near the surface of the bone .

[0073] Once the implant body 110 is at the proper depth as determined by the surgeon, the insertion is complete. However, the. surgeon may, at his discretion, choose to further fix the osteotomy by means of stabilizing wires 400, as seen in FIGS. 18-23. This additional step is likely to be used in the worst cases when the surgeon feels that the fixation brought by the implant alone could be insufficient to guarantee a fixation stable enough to promote osteosynthesis. This case may be seen with a highly osteoporotic bone or a broken bony hinge, for exam le .

[0074] If the stabilizing wires 400 are to be used, indicia 410, such as laser markings, on the distal face of the implant body 110 enable the surgeon to target the fenestrations 150 that the stabilizing wires 400 are to traverse. Although one stabilizing wire 400 can be used with the implant body 110, preferably two stabilizing wires 400 are inserted in a cross fashion to result in sufficient stabilization of the two bone parts. The sharp ends of the stabilizing wires 400 preferably do not go past the cortical layer of bone such that contact with soft tissue is avoided. The rounded ends of the stabilizing wires are preferably as flush as possible with the opposite cortical layer, while still leaving enough room for an instrument to engage the stabilizing wire 400 if it is to be further manipulated, such as if the stabilizing wire 400 must be removed. During insertion of the stabilizing wires 400 through the fenestrations 150 of the implant body 110, it is not necessary for the stabilizing wires 400 to make or maintain contact with the edges of the implant body 110 that define the fenestrations 150. The wires 400 are capable of stabilizing the two bone pa.rts by virtue of. bone-- to-bone contact on either side of the implant body 110 by the stabilizing wires 400, and are not intended to affix to, engage, or otherwise secure the implant body 110. If a stabilizing wire 400 does make contact with the implant body 110, that contact is incidental to insertion and most, if not ail, the stabilizing effect is provided by the bone-to-bone contact of the stabilizing wires 400.

[0Q75] Another embodiment of the invention includes an internal bone fixation system suitable for carrying out the various methods described herein, such as an open -wedge osteotomy. The internal bone fixation system includes an osteotomy cage 100, a retractor and insertion guide 200, and an inserter 300. The system may further include K-wires 400.

[0076] The osteotomy cage 100, already described in detail above, is implanted into sections of a bone surrounding an osteotomy, capturing an internal bone core and causing' the osteotomy to fill with autologous bone chips automatically by virtue of the implantation and further resulting in stabilization of the osteotomy. The retractor 200 is configured to hold the osteotomy open during implantation. The retractor 200 also has an inner bore 230 that receives and guides the implant 100 and further can receive the inserter 300 that drives the implant 100 into the bone. The inserter 300, which can be for example a screwdriver, mates with a trailing end 120 of the implant 100 and allows torque to be transmitted from the inserter 300 to the implant 100. This torque can be provided by a motorized drill, for example, or manually with an appropriate handle.

[0077] The system optionally includes K-wires 400. The K- wires 400 can be used to stabilize the retractor 200 while the implant 100 is being implanted, The K-wires 400 can additionally or alternatively be used to stabilize the osteotomy once the implant 100 has been implanted into the bone. For example, a first set of K-wires 400 with a first diameter can be provided for stabilization of the osteotomy, and a second set of K-wires 400 with a second diameter can be provided for stabilization of the retractor 200 during implantation. The surgeon may also choose to forego the use of K-wires 400 altogether.

[0078] In another embodiment of the invention, an internal bone fixation kit is provided. The kit can include a plurality of implants 100 of different sizes to increase the likelihood of an optimal fit between the implant 100 and the osteotomy. Each kit could be for a different indication. For example, one kit. could be used for performing an Evans osteotomy, while a second kit could be used for performing a Cotton osteotomy. In one example, a kit to treat hallux valgus de ormities can include an implant body 110 10mm long, with a range of diameters between 11mm and 13mm (with the threads 140 included), and the walls of the body are about .8mm. The kit can include implants 100 that are larger and smaller than this for use in larger or smaller osteotomies and/or larger or smaller bones or anatomical locations. For a specific kit for a specific indication, each implant 100 in the kit includes a recess in the trailing end 120 that is the same size and shape for each implant, in the kit.

[OQ793 A kit for a specific indication further includes a single inserter, for example a screwdriver, 300. Because the recess in the trailing end 120 of each implant 100 in a kit for a specific indication is the same size, only a single inserter 300 is needed in the. kit.

[0080] The kit can also include a plurality of retractors 200 of different sizes, as described above. The retractors 200 each have a set. of prongs 220 that have a different width. During an implantation procedure, a surgeon can choose a retractor 200 from the set which most. appropriately corresponds to the size of the osteotomy in. the bone. Preferably, the kit includes multiple retractors 200 of different sizes to allow for the range of correction of the specific indication. For example, for purposes of illustration and not limitation, a kit. for treating hallux valgus could include a number of retractors 200 to allow for a range of correction between about 2mm-7mm, a kit for performing a Cotton osteotomy could include retractors 200 to allow for a range of. correction between about 3mm- 7mm, and a kit for performing an Evans osteotomy could include retractors 200 to allow for a range of correction between about 4mm- 12mm. However, the specific number of retractors 200 provided in a kit and the range of corrections permitted by the retractors 200 is largely a matter of design choice.

[0081] The kit further includes a plurality of K-wires 400. The K-wires 400 can be optionally used to stabilize the osteotomy after the implant 100 is implanted in the bone, to stabilize the retractor 200 during the implantation procedure, or both. The kit preferably includes a first set of K-wires 400 of a first diameter for use with the retractor 200 and a second set of K-wires 400 of a second diameter for use wi h he ostepto v and implant 10.0,

C0 823 Although the invention herein ^' s been described with reference to particular eiiibodimeftts,· it is to he understood that these

are merely illustrative of the pr.inad.ples and applications of the present invention. It is therefore to he understood tha n mer s modifications nay foe tnade to the Illustrative embodimen s an that other arrangements may he devised without departing from the spirit and scope of the present invention s defined by: the appended cla ms .

33

Claims

1. A method of performing surgery, the steps comprising :

providing an implant comprising;

a cylindrical shaft having a circumference, an interior cavity, a trailing end, and a leading end, the leading end including an opening to the interior cavity; self-tapping threads positioned along the circumference of the cylindrical shaft, the self-tapping threads being interrupted by at least one fenestration in the cylindrical shaft; and

self-coring teeth at the leading end of the cylindrical shaft;

inserting the leading end of the implant into a first and second portion of a bone, the first and second portions of the bone being separated by an osteotomy in the bone; and

advancing the self-tapping threads and self-coring teeth of the implant through the first and second portions of the bone such that a section of the first portion and a section of the second portion are positioned within the cavity of the im lant .

2. The method of claim 1, further comprising;

inserting a first stabilizing wire through each of a first and second fenestration of the implant, the first and second fenestrations being located on generally diametrically opposed sides of the cylindrical shaft.

3. The method of claim 1, wherein the step of advancing the self--coring teeth of the implant through the first and second portions of the bone causes bone chips to be guided toward the osteotomy in the bone.

4. The method of claim 3, wherein the bone chips are caused to be guided toward the cavity of the

positioned within the osteotomy .

5. The method of claim 1, wherein the step of inserting the leading end of the implant into the first and second, portion of the bone includes passing the implant through a retractor, the retractor holding open the osteotomy while the implant is inserted into the bone .

6. The method of claim 1, wherein the trailing end includes an end wall of the internal cavity, wherein the step of advancing the implant through the first and second portions of the bone continues until the sections of the first and second portions of the bone contact the end wall of the trailing end.

7. A method of performing surgery, the steps comprising: providing an implant comprising;

a cylindrical shaft having a circumference, an interior cavity, a trailing end, and a. leading end, the leading end including an opening to the interior cavity; self-tapping threads positioned along the circumference of the cylindrical shaft, the self-tapping threads being interrupted by at least one fenestration in the cylindrical shaft; and

self --coring teeth at the leading end of the cylindrical shaft ;

advancing the self-tapping threads and self-coring teeth of the implant through the first and second portions of the bone without pre-drilling or pre-shaping either the first or second portion of the bone.

8. The method of claim 7, wherein the cylindrical shaft further comprises;

a plurality of fenestrations extending from an outer surface of the cylindrical shaft to the interior cavity of the cylindrical shaft, at least one of the fenestrations having a nonzero rake angle.

9. The method of claim 7, wherein the self - tapping thread includes a. proximal end, the proximal end of the self-tapping' thread not fully extending to the trailing end of the cylindrical shaft.

10. The method of claim 9, wherein the step of advancing the implant through the first and second portions of the bone continues until the proximal end of the self-tapping thread is fully implanted into at least one. of the first or second portions of the bone.

11. The method of claim 7, wherein the step of inserting the leading end of the implant into the first and second portion of the bone includes passing the implant through a retractor, the retractor holding open the osteotomy while the implant is inserted into the bone.

12. The method of claim 11, wherein the step of inserting the leading end of the implant into the first and second, portion of the bone further includes transmitting torque from an inserter to the implant.

13. The method of claim 12, wherein the torque is transmitted from the inserter to the implant with a motorized drill .

14. The method of claim 12, wherein the torque is transmitted from the inserter to the implant by hand.

15. The method of claim 12, wherein the inserter is sized to fit within the retractor.

16. The method of claim 7, further comprising;

17. The method of claim 16, wherein the trailing end of the implant includes at least one marking, each of the at least, one markings indicating a location of a corresponding fenestration .

18. A method of performing surgery, the steps comprising :

providing an internal bone fixation kit comprising;

a plurality of implants of different sizes, each implant comprising:

a cylindrical shaft having a circumference, an interior cavity, a trailing end, and a leading' end, the leading end including an opening to the interior cavity;

self -tapping threads positioned along the circumference of the cylindrical shaft, the self- tapping threads being interrupted by at least one fenestration in the cylindrical shaft; and sel -coring teeth at the leading end of the cylindrical shaft; and

an inserter configured to insert one of the plurality of implants into a bone;

selecting one of the plurality of implants and inserting the leading end of the chosen implant into a first and second portion of the bone, the first and second portions of the bone being separated by an osteotomy in the bone; and

advancing the self-tapping threads and self-coring teeth of the chosen implant, through the first and second portions of the bone such that a section of the first portion and a section of the second portion are positioned within the cavity of the chosen implant ,

13. The method of claim 18, wherein the kit further includes a plurality of retractors of different sizes, each retractor being configured to hold open an osteotomy, wherein the step of inserting the leading end of the chosen implant into the first and second portions of the bone includes choosing one of the plurality of retractors and passing the chosen implant through the chosen retractor, the chosen retractor holding open the osteotomy while the chosen implant is inserted into the bone.