Funnel hole for intramedullary nail

Abstract

The intramedullary nail may include a shank having a centerline defined along its length. The nail may also include a channel having a channel axis transverse to the centerline. The channel may have an oval shape in a first cross-sectional plane perpendicular to the channel axis at the centerline and a tapered profile in a second cross-sectional plane including the channel axis. A proximal edge of the channel in the second cross-sectional plane may form a first angle with respect to the channel axis, and a distal edge of the channel in the second cross-sectional plane may form a second angle with respect to the channel axis that is different from the first angle.

Description

[Technical field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of the filing date of U.S. Provisional Patent Application No. 63 / 031,701, filed May 29, 2020, the disclosure of which is incorporated herein by reference. [Background technology]

[0002] Intramedullary nails are a known solution for treating injuries to bones, such as fractures or breaks. For example, it is known to use intramedullary nails to treat fractures in the body of the femur, or to use intramedullary nails in cooperation with lag screws to treat fractures in the femoral neck. Such intramedullary nails may have an elongated shape and include a relatively thin and cannulated shank extending from the head of the intramedullary nail, which is intended to pass through the medullary cavity of the bone to be treated. The cannulation through the entire length of the intramedullary nail is used by the surgeon to insert a k-wire to guide the intramedullary nail during insertion into the intramedullary canal of a long bone, such as the femur or tibia.

[0003] In some applications, one or more locking screws are inserted through the bone and corresponding channels located near the distal end of the shank. As the shank is driven into the bone, it may undergo an amount of deflection that is difficult to predict with certainty, so the exact location and angle at which the locking screw can be placed may vary from patient to patient. Additional steps may be required prior to inserting the locking screw, such as scanning or imaging the bone and nail after the nail is implanted, to determine the final location of the channel. Summary of the Invention

[0004] The nail may be designed such that a locking screw is inserted into a channel at the distal end of the nail after the nail is inserted into the long bone, taking into account any deflection that occurs in the nail during insertion. Deflection of the nail occurs because the intramedullary canal of the long bone is curved, causing the nail to follow the anatomy of the bone once inserted. Such an intramedullary nail may be designed such that a drill is inserted into or through the bone at a required position and angle relative to the head of the nail, without contacting the proximal or distal edges of the corresponding channel.

[0005] To this end, a portion of the channel may have a funnel shape. The channel may be of generally constant cross section, such as cylindrical, except for the funnel-shaped portion, and may extend in a direction perpendicular to the centerline of the nail. The funnel shape may be tapered, being wider on one side of the nail and narrower on the other side. The taper may be along only a portion of the depth of the channel, and the channel may include an inflection point separating the tapered portion from the constant-sized portion. The channel may be of constant width transversely of the nail's shank, but may taper from longer to shorter along the length of the nail's shank. Such a channel may thus have an oval shape at least at its wider end and through at least a portion of its depth.

[0006] In another aspect, the nail may include a shank with a centerline defined along its length. The nail may also include a channel with a channel axis transverse to the centerline. The channel may have an oval shape in a first cross-sectional plane perpendicular to the channel axis at the centerline and a tapered profile in a second cross-sectional plane that includes the channel axis. A proximal edge of the channel in the second cross-sectional plane may form a first angle with respect to the channel axis and a distal edge of the channel in the second cross-sectional plane may form a second angle with respect to the channel axis that is different from the first angle.

[0007] In some configurations, the opposing proximal and distal ends of the channel may be defined by circular ends that each extend along two non-parallel axes, and the opposing sides of the channel may be flat and each extend between the two circular ends to define an oval shape.

[0008] In some configurations, the channel has full internal threads.

[0009] In some configurations, the channel defines a circular opening in the surface of the shank.

[0010] In some configurations, each of the two non-parallel axes may intersect the centerline.

[0011] In some configurations, the first angle may be non-zero and the second angle may be zero.

[0012] In some configurations, the nail may include an oval opening in the shank that feeds into the channel, and at least a portion of the periphery of the oval opening may be chamfered.

[0013] In some configurations, the angle between the two non-parallel axes may be between 3° and 7°.

[0014] In some configurations, the angle between the two non-parallel axes may be 6.5°.

[0015] In another embodiment, the shank may be elastically deformable through a range of deflection of the distal tip of the shank in the second cross-sectional plane. The ratio of the deflection range of the distal tip of the shank to the overall length of the nail may be at least 1:30. A rectangular region may exist in the second cross-sectional plane that extends through the channel without intersecting the proximal or distal edges of the channel at any location within the tip travel range.

[0016] In some configurations, the ratio of the deflection range of the distal tip of the shank to the overall length of the nail may be 1:24.

[0017] In some configurations, the shank may define a bore extending along the centerline and dividing the channel into two aligned openings.

[0018] In another aspect, a method of treating an injury to a femur may include inserting an intramedullary nail into the femur generally along the anatomical axis of the femur. The intramedullary nail may include a shank, the shank having a centerline defined along its length. The shank may have a channel with a channel axis transverse to the centerline. The channel may have an oval shape in a first cross-sectional plane perpendicular to the channel axis at the centerline and a tapered profile in a second cross-sectional plane that includes the channel axis at the centerline. The method may also include inserting a screw through the femur at a predetermined location.

[0019] In some configurations, the nail may include an oval opening in the shank that feeds into the channel. The nail may be implanted into the femur with the oval opening oriented in an anterior direction relative to the femur.

[0020] In some configurations, the nail may be implanted in the femur such that the tapered profile narrows in a posterior direction relative to the femur.

[0021] In some configurations, the method may further include drilling through the femur and the channel in an anterior to posterior direction at the predetermined location on the femur.

[0022] In some configurations, the screw may engage at least a portion of the channel to accommodate deflection of the nail that occurs during implantation.

[0023] In some configurations, a method of designing an intramedullary nail may include evaluating an expected range of deflection of a shank of the intramedullary nail in a deflection plane corresponding to deflection of the intramedullary nail during a procedure for embedding the intramedullary nail in a bone. The method may include defining a fixed position for a cylindrical fixation element relative to a head of the intramedullary nail disposed at a proximal end of the intramedullary nail. The fixed position may be such that the cylindrical fixation element extends laterally relative to and intersects the shank at any position of the shank within the expected range of deflection. The method may also include selecting respective positions and angles for a proximal end of a channel disposed through a distal half of the shank and a distal end of the channel, such that the cylindrical fixation element disposed at the fixed position extends through the channel without intersecting the proximal or distal ends of the channel at any degree of deflection of the shank within the expected range of deflection.

[0024] In some configurations, the method may include defining an additional fixation location for an additional cylindrical fixation element. The method may include selecting respective locations and angles for proximal and distal ends of an additional channel disposed through a distal half of the shank such that the additional cylindrical fixation element disposed at the additional fixation location extends through the additional channel without intersecting the proximal or distal ends of the additional channel at all degrees of deflection of the shank within an expected range of deflection.

[0025] In some configurations, a method of treating an injury to a femur using an intramedullary nail may include inserting the intramedullary nail into the femur generally along the anatomical axis of the femur while allowing flexion of the intramedullary nail within the femur. The method may also include, after the intramedullary nail is inserted into the femur, inserting a screw through the femur and channel at a position and angle relative to the head of the intramedullary nail that corresponds to a fixation position of the cylindrical fixation element. [Brief description of the drawings]

[0026] [Figure 1A]FIG. 1 is a cross-sectional front view of an intramedullary nail according to a first configuration. [Figure 1B] FIG. 2 is a front view of an intramedullary nail according to a second configuration. [Figure 2A] FIG. 1B is a side view of the tip portion of the intramedullary nail of FIG. 1A. [Figure 2B] FIG. 2B is a cross-sectional view taken along line 2B-2B of FIG. 2A. [Figure 2C] FIG. 2B is another side view of the tip portion of the intramedullary nail shown in FIG. 2A. [Diagram 3] 1B is a cross-sectional front view of the intramedullary nail of FIG. 1A at three degrees of deflection. [Figure 4] FIG. 13 is a cross-sectional front view of a portion of an intramedullary nail according to a third configuration. [Diagram 5] FIG. 5 is a perspective view of a targeting device for use with the intramedullary nail of FIGS. 1A, 1B, or 4. [Figure 6] 6 is a cross-sectional front view of the targeting device of FIG. 5 for guiding a drill into the intramedullary nail of FIG. 1A, FIG. 1B or FIG. 4 through various stages of deflection. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] The intramedullary nail 10 shown in FIG. 1A includes a head 14, a conical section 16 that tapers from the head 14 to a narrower diameter, and a shank 18 extending from the conical section 16. The intramedullary nail 10 extends along a centerline X. Although the centerline X is shown as a straight line in FIG. 1A, the shank 18 is flexible relative to the head 14, i.e., the centerline X may have a curved profile depending on the flexed state of the shank 18. In an alternative configuration, such as that shown in FIG. 1B, the shank 18 may have a non-linear rest position, which may include, for example, a centerline X that curves toward a posterior direction P as the distance from the head 14 increases. Thus, the shank 18 may be able to curve further toward the posterior direction P than the opposite anterior direction A.

[0028] The distal portion 20 of the shank terminates at a point 22. The distal portion 20 shown herein is the distal-most half of the shank 18. The distal portion 20 includes at least one channel 28 extending therethrough. In the configuration shown, the distal portion 20 includes a first channel 28a and a second channel 28b that extend through the nail 10 from anterior to posterior. The second channel 28b is closer to the point 22 and has a greater width along the centerline X than the first channel 28a.

[0029] As shown in more detail in FIG. 2A, the first channel 28a has a first chamfered forward opening 34a, and the second channel 28b has a second chamfered forward opening 34b. Both forward openings 34a, 34b have an oval shape when viewed in the perspective of FIG. 2A, extending in a longitudinal direction parallel to the centerline X. Here, "oval" means any shape generally similar to the foregoing, including a stadium shape, an orthogonal projection of a capsule, two opposing semicircles or nearly semicircles, each connected at both ends by two parallel lines. However, "oval" is used in an approximate sense to account for the fact that the curved periphery of the shank 18 gives the forward openings 34a, 34b a non-flat profile.

[0030] 2B and 2C, the first channel 28a includes a first rear opening 38a and the second channel 28b includes a second rear opening 38b. The first rear opening 38a is circular and has a diameter equal to the lateral width of the first forward opening 28a, while the second rear opening 38b is oval and has the same lateral width as the second forward opening 28b, but has a smaller width parallel to the centerline X.

[0031] The first channel 28a defines a central orthogonal axis 46 that extends perpendicular to the centerline X and through a center point of the first rear opening 38b. A first distal edge 50a of the first channel 28a extends parallel to the central orthogonal axis 46. A distal portion of the first channel 28a defines a cylindrical shape centered on the central orthogonal axis 46. Additionally, the funnel shape of the first channel 28a is defined by a first skew axis 47 that is angled relative to the central orthogonal axis 46. Here, "angled" is used to mean that the first skew axis 47 extends at a non-zero angle relative to the central orthogonal axis 46. The first skew axis 47 extends parallel to a first bevel portion 51a of a proximal edge 54a of the first channel 28a. In a preferred configuration, the first skew axis 47 extends at an angle of 6.5° relative to the central orthogonal axis 46. In other configurations, the angle can range from 3.5° to 9.5°, or 4° to 8°, or 6° to 7°. The first beveled portion 51a extends distally and rearwardly from the first forward opening 34a to a first inflection point 52a where the first channel 28a reaches a circular cross-sectional shape. The volume from the first inflection point 52a to the first rear opening 38a is a cylindrical zone of the first channel 28a, as shown above. Also, the volume from the first inflection point 52a to the first forward opening 34a on the distal side of the first channel 28a between the central orthogonal axis 46 and the first distal edge 50a is a portion of the cylindrical volume of the first channel 28a, i.e., a semi-cylindrical shape. The volume from the first inflection point 52a to the first front opening 34a on the proximal side of the first channel 28a between the central orthogonal axis 46 and the first bevel portion 51a is the conical zone of the first channel 28a. Together, these three volumes make up the total volume of the first channel 28a.

[0032] The first bevel portion 51a also extends along the proximal-most end of the semi-cylinder defined by the first channel 28a, which extends along the first skew axis 47 between the first inflection point 52a and the first forward opening 34a. The first proximal edge 54a is collectively defined by the first bevel portion 51a, the first inflection point 52a, and the first orthogonal portion 53a. The first orthogonal portion 53a of the first proximal edge 54a extends parallel to the central orthogonal axis 46 between the first inflection point 52a and the first rear opening 38a. This causes the forward portion of the first channel 28a defined between the first forward opening 34a and the first inflection point 52a to have a funnel shape. In particular, a forward portion of the first channel 28a tapers narrower along the length of the shank 18 from the first proximal opening 34a to the first inflection point 52a, thereby defining a funnel shape. A rearward portion of the first channel 28a defined between the first inflection point 52a and the first rearward opening 38a has a cylindrical shape.

[0033] The first channel 28a is threaded along its inner surface as shown. Despite the change in the circumference of the first channel 28a, the first channel 28a is threaded at a constant pitch from the first rear opening 34a to the first rear opening 38a. Thus, an object having an external thread, such as a screw, may be threaded into the first channel 28a over the entire length of the first channel 28a. For further details regarding exemplary screws suitable for engaging any of the intramedullary nails of the present disclosure, reference may be made to International Application Publication No. WO 2019 / 111041, which corresponds to International Patent Application No. PCT / IB2017 / 057688, filed December 6, 2017. Because the angle between the first skew axis 47 and the central orthogonal axis 46 is relatively small, the threads of the screw will tightly engage with the threaded portion anywhere in the first channel 28a, regardless of whether the screw is not exactly parallel to the central orthogonal axis 46 which defines the threads of the first channel 28.

[0034] Similarly, the second channel 28b defines a second distal edge 50b extending perpendicular to the centerline X and a second proximal edge 54b. The second proximal edge 54b includes a second beveled portion 51b that cooperates with the second distal edge 50b to define a funnel shape, a second orthogonal portion 53b that extends parallel to the second distal edge 50b, and a second inflection point 52b between the second beveled portion 51b and the second orthogonal portion 53b. The second channel 28b defines a proximal orthogonal axis 56 and a distal orthogonal axis 58, both of which are perpendicular to the centerline X at respective locations. The distal portion of the second channel 28b defines one half of a cylinder centered about the distal orthogonal axis 58, and the proximal portion of the second channel 28b between the second inflection point 52b and the second posterior opening 38b defines one half of a cylinder centered about the proximal orthogonal axis 56. Thus, the second channel 28 has an oval cross-section between the second inflection point 52b and the second posterior opening 38b. The second channel 28b in the illustrated configuration is not threaded and may non-threadedly receive a transverse element, such as a locking screw or nail, for constraining movement of the intramedullary nail 10 within the bone.

[0035] The second beveled portion 51b extends distally and rearwardly from the second forward opening 34b to a second inflection point 52b. A second skew axis 57 is defined parallel to the second beveled portion 51b. In various configurations, the second skew axis 57 extends at an angle of 3° to 7°, or 6.5°, relative to the proximal orthogonal axis 56. The proximal portion of the second channel 28b between the second forward opening 34b and the second inflection point 52b defines one half of a cylinder centered about the second skew axis 57. Thus, the forward portion of the second channel between the second forward opening 34b and the second inflection point 52b has a funnel shape that narrows toward the centerline X as it extends further in the rearward direction P, but has a constant width with respect to a lateral direction perpendicular to the proximal orthogonal axis 56, the distal orthogonal axis 58, and the second skew axis 57.

[0036] The above description relates to the illustrated configuration, and other configurations of the nail 10 may differ in some respects to suit different applications. For example, in some alternative configurations, the orthogonal axes 46, 56 and 58, the distal edges 50a, 50b, and the orthogonal portions 53a, 53b of the proximal edges 54a, 54b extend at non-perpendicular angles to the centerline X at their respective locations along the centerline X.

[0037] The intramedullary nail 10 is flexible such that typical forces applied to the shank 18 during insertion of the intramedullary nail 10 into bone may cause the intramedullary nail 10 to deflect in either the anterior direction A or the posterior direction P within an expected range of deflection 62 shown in Figure 3. In various configurations, the expected range of deflection may be determined experimentally or by theoretical analysis of the intramedullary nail 10, such as by finite element analysis. Throughout the expected range of deflection 62, a first theoretical cylinder 60a extends through the first channel 28a and a second theoretical cylinder 60b extends through the second channel 28b. The funnel shape of the forward portion of the first channel 28a and the second channel 28b allows the distal portion 20 of the shank 18 to move throughout the expected range of deflection, while the first theoretical cylinder 60a and the second theoretical cylinder 60b remain stationary relative to the head 14 without the cylinders 60a, 60b crossing the boundaries of the proximal edges 54a, 54b or distal edges 50a, 50b of the channels 28a, 28b, respectively. This allows the nail 10 to be attached to a bone, and then a cylindrical drill bit having a diameter similar to the theoretical cylinders 60a, 60b in both channels 28a, 28b is inserted, and a cylindrical locking element, such as a bone screw, having a diameter slightly larger than the theoretical cylinders 60a, 60b is inserted in a predetermined position relative to the head 14 without measuring the actual deflection of the nail 10 in situ. Because the funnel shape of the channels 28a, 28b accommodates the theoretical cylinders 60a, 60b through the expected range of deflection 62, the drill or drills will not damage the channels 28a, 28b or any threads in the channels 28a, 28b, and a cylindrical locking element inserted through the bone in the same location relative to the head 14 as the cylinders 60a, 60b can be expected to extend through the channels 28a, 28b without interfering therewith and to engage a portion of the threaded channel to facilitate locking. Furthermore, because of the elongated threads of the first channel 28a, a carelessly inserted bone screw can be expected to thread into the first channel 28a regardless of the actual degree of deflection. Although the first channel 28a is shown as being fully threaded, in some alternative configurations the first channel 28a is only partially threaded.For example, in some configurations, only the distal half or the proximal half of the first channel 28a has threads.

[0038] In some configurations, the nail 10 may be configured such that the expected range of flexion 62 extends further in a posterior direction relative to the head 14 than in an anterior direction, as shown in FIG. 3. The flexibility of the nail 10 may vary as appropriate for a given treatment. For example, the flexibility of the nail 10 may depend on the size, shape and density of the bone in which the nail 10 is used, as well as the forces that the nail 10 is expected to be subjected to during treatment. In some configurations, the ratio of the total length of the nail 10 to the range of flexion 62 is at least 1:30. In further configurations, the ratio of the total length of the nail to the range of flexion is 1:24. FIG. 3 shows, from left to right, the distal portion 20 in a terminal anterior position, a middle position, and a terminal posterior position. The middle position is closer to the terminal anterior position than the terminal posterior position. In some configurations, it is three times further from the middle position to the terminal posterior position than from the middle position to the terminal anterior position. For example, the intramedullary nail 10 can be designed with an inclination toward backward bending by designing the intramedullary nail such that the center line X curves in a backward direction the further away from the head 14 it is in the neutral position, which means the position that the intramedullary nail 10 occupies when there is no external force.

[0039] Portions of an intramedullary nail 110 according to an alternative configuration are shown in FIG. 4. The shank 118 is cannulated and includes a bore 164 extending along a centerline X. Thus, the channel 128 extending through the shank 118 is provided by chamfered anterior and posterior openings 134, 138 on either side of the bore 164. The anterior opening 134 is defined between an anterior distal edge 150a and an anterior proximal edge 154a, and the posterior opening 138 is defined between a posterior distal edge 150b and a posterior proximal edge 154b. The posterior opening 138 has a circular cross-sectional shape, the cross-sectional shape of the anterior opening 134 having a thickness defined perpendicular to the centerline X, the thickness being equal to the diameter of the posterior opening 138. The anterior opening 134 has an oval cross-sectional shape such that the distance between the anterior proximal edge 150a and the anterior distal edge 154a is greater than the diameter of the posterior opening 138. 3, the nail 110 is designed such that the theoretical cylinder 160 at a given position relative to the head (not shown) of the nail 110 extends through the channel 128 even as the shank 118 flexes through the range of deflections expected to result from insertion of the nail 110 into bone. Specifically, the positions and angles of the respective edges 150a, 150b, 154a, 154b of the channel 128 allow the shank 110 to flex through the entire expected range of deflections while the theoretical cylinder 160 remains stationary without any of the edges 150a, 150b, 154a, 154b contacting the theoretical cylinder.

[0040] In other configurations, the distal portion 20 includes different numbers and configurations of front-to-back channels. For example, the distal portion 20 may include only one or more than two front-to-back channels, and the relative widths along the centerline X of the front-to-back channels may have any pattern along the centerline X. For example, the channel having the greatest width along the centerline X may be the middle or most proximal of the channels included in the distal portion.

[0041] The nail 10,110 according to any of the above examples may be designed according to experimentally derived or mathematically determined values. In particular, one or more sets of general dimensions of the nail 10,110, such as length and diameter, may be pre-determined. The range of curvatures of the nail 10,110 expected during an implantation procedure may be evaluated for each given set of general dimensions by experiment with a simulated implantation procedure, mathematically by finite element analysis, or the like, or by a combination of experimental and mathematical processes. The angles and dimensions of the channels through the nail 10,110 of various given general dimensions may then be determined taking into account the expected range of curvatures and diameters of the associated drill or bone screw. In particular, each channel may be positioned, angled and dimensioned such that for a given set of given general dimensions, the associated drill may be driven through the bone and channel at a pre-determined position and angle relative to the head of the nail 10,110 without damaging the channel or any threads inside the channel. Additionally, a bone screw may be engaged through the channel at a predetermined position and angle relative to the head of the nail 10, 110 after the nail 10, 110 is implanted for any position of the nail 10, 110 within the predicted curvature range. Thus, an intramedullary nail 10, 110 designed according to the above process may be implanted in bone and secured in place by a transverse bone screw without the intervening step of determining the actual degree of curvature of the nail 10, 110.

[0042] 5 shows a targeting device 200 for preparing a femur 210 for a retrograde guided target drilling procedure that secures the intramedullary nail 10,110 after it has been inserted into the femoral canal. The targeting device 200 includes a bracket 214 that can be connected to the head of the intramedullary nail 10,110. The bracket 214 holds an arm 218 of the targeting device 200 in a position that can be adjusted for specific use depending on the patient's anatomy. The arm 218 terminates in a block 222 that includes two guide holes 226a,226b for guiding drills and fasteners through the femur 210 and the intramedullary nail 10. The guide holes 226a,226b are specifically sized and positioned to match the channels 28a,28b of the intramedullary nail 10 to enable locking of the intramedullary nail 10 in the femur. That is, the block 222 is positioned relative to the femur 210 such that the guide holes 226a, 226b direct the drill and subsequent screw or pin into the channels 28a, 28b without the drill contacting the edges of the channels.

[0043] The guide hole 226a is cylindrical and angled 3° from an axis perpendicular to the centerline of the block 222 which is designed to be parallel to the centerline X of the nail 10 when the nail 10 is at rest or unflexed in the position (B) shown in FIG. 6. The 3° angle corresponds to the geometry of the channel 28a and when used with the channel 28a allows for pre-drilling with a drill (e.g., 4.2 mm) without any metal contact in the nail in either the flexed or unflexed state. Also shown in FIG. 6 are positions showing the nail in anterior flexion (A) and positions showing the nail in posterior flexion (C). The 3° angle of the guide hole 226a is consistent with the geometry and orientation of the channel 28a, such that a drill bit or screw passing through the guide hole 226a will pass through a central portion of the channel 28a along an axis that coincides with the first skew axis 47 or the central orthogonal axis 46, or along an axis between the first skew axis 47 and the central orthogonal axis 46, when the nail 10 is at rest, i.e., depending on the flexion of the nail. Because the guide hole 226a is inclined at 3°, the axis passing through the center of the guide hole 226a and the central orthogonal axis 46 of the first channel 28a intersects at the center of the uppermost portion of the cylindrical zone of the channel 28a, i.e., aligns with the first inflection point 52a. Guide hole 226b is similarly angled 3° relative to the proximal orthogonal axis 56 of second channel 28b to provide the same cooperation between guide hole 226b and second channel 28b as described above between guide hole 226a and first channel 28a. Guide hole 226b is oval for static / dynamic locking in second channel 28b.

[0044] With the guide hole 226a angled at 3°, the first channel 28a is configured such that a drill passing through the first channel 28a will not contact either the first bevel portion 51a or the first distal edge 50a, despite the deflection of the nail 10. This is shown in FIG. 6, where position (A) corresponds to a forward deflection of the nail 10, but the nail 10 is aligned such that the first distal edge 50a is closer to the drill bit. In position (C), which shows a rearward deflection of the nail 10, the nail 10 is aligned such that the first bevel portion 51a is closer to the drill bit. The 6.5° angle of the first bevel portion 51a and the 0° angle of the first distal edge 50a have been experimentally determined such that the 3° angle of the guide hole 226a may facilitate drilling without metal contact or any alteration of the female thread of the first channel 28a. The 0° angle of the first distal edge 50a represents the position of the locking hole without the funnel function, thereby representing the orientation of all circular holes perpendicular to the axis of the nail. The design is selected to remove minimal material compared to the circular holes of previous designs. This test looks at the range of deflection angles of the nail 10 given various femoral contours and shapes, focusing on the range of deflection angles for a zone that encompasses substantially all potential deflection values. This results in virtually no metal contact between the drill and the first channel 28a in all procedures. Thus, during targeting and drilling with the targeting device, the nail should not be damaged in either the undeflected or deflected position.

[0045] After the guide holes 226a, 226b are used to guide the drill through the femur 210, a fastener or screw 228 may be inserted through the drilled holes and the channels 28a, 28b, 128 to secure the nail 10, 110 to the femur 210. Because the channels 28a, 28b, 128 are oval, the screw 228 can engage the female threads of the channels 28a, 28b, 128 regardless of any flexure that may be present in the nail 10. For example, the channel 28a has a lateral width throughout that is the same as the diameter of the channel 28a in the cylindrical zone below the first inflection point 52a. This is even though the proximal-distal dimension of the channel 28a increases upward and away from the first inflection point 52a. Thereby, when the screw 228 is inserted in the terminal deflection state of the intramedullary nail 10, the screw 228 engages with the threads on the first bevel portion 51a or the first distal edge 50a in addition to the female threads on the lateral sides of the channel 28a and the cylindrical zone below the first inflection point 52a. At any angle between these ends, the screw 228 engages with at least the threads on the lateral sides of the channel 28a and the female threads on the cylindrical zone below the first inflection point 52a. Although the thread connection may not be a perfect match, the range of angles allows for the screw to thread within the channel 28a regardless of the angle at which the screw 228 is inserted. As the screw enters the cylindrical zone between the first orthogonal portion 53a and the first distal edge 50a below the first inflection point 52a, the cylindrical nature of this portion of the channel 28a reorients the screw so that it is ultimately positioned perpendicular to the axis of the nail as in a normal circular hole. Of course, in some instances, this reorientation of the screw may not result in a perfectly perpendicular orientation. In these instances, the geometry and contours of the channel 28a are utilized to facilitate secure locking of the screw 228 regardless of what deflections are present in the implanted nail 10, which eliminates the need for the user to be concerned with finely tuned and precise angulation of the screw insertion during the procedure.Of course, channel 28a is described herein as an example in this manner, and channels 28b and 128 are designed in the same manner while configuring their oval shapes.

[0046] Although the concepts herein have been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present disclosure. It is therefore to be understood that many modifications may be made to the illustrative embodiments and that other configurations may be devised without departing from the spirit and scope of the present disclosure as defined by the appended claims. The technical ideas grasped from the above-described embodiments will be described below. [Aspect 1] a shank having a centerline defined along a length thereof; 1. An intramedullary nail, wherein the shank has a channel with a channel axis perpendicular to the centerline, the channel having an oval shape in a first cross-sectional plane perpendicular to the channel axis at the centerline and a tapered profile in a second cross-sectional plane that includes the channel axis, whereby a portion of a proximal edge of the channel in the second cross-sectional plane forms a first angle with the channel axis and a distal edge of the channel in the second cross-sectional plane forms a second angle with the channel axis that is different from the first angle. [Aspect 2] The intramedullary nail of embodiment 1, wherein opposing proximal and distal ends of the channel are defined by circular surfaces each extending along two non-parallel axes, and opposing sides of the channel are flat and each extending between the two circular surfaces to define an oval shape. [Aspect 3] The intramedullary nail of embodiment 2, wherein the channel has a full thread therein. [Aspect 4] The nail of embodiment 2, wherein the channel extension defines a circular opening in a surface of the shank. [Aspect 5] The intramedullary nail of embodiment 2, wherein each of the two non-parallel axes intersects the center line. [Aspect 6] The nail of embodiment 2, wherein the first angle is non-zero and the second angle is zero. [Aspect 7] The nail of embodiment 2, wherein the nail includes an oval opening in the shank that feeds into the channel, at least a portion of an outer periphery of the oval opening being chamfered. [Aspect 8] The intramedullary nail according to aspect 2, wherein the angle between the two non-parallel axes is between 3° and 7°. [Aspect 9] The intramedullary nail according to embodiment 8, wherein the angle between the two non-parallel axes is 6.5°. [Aspect 10] the shank is elastically deformable through a range of deflection in the second cross-sectional plane, and a ratio of a distance traveled by a distal tip of the shank across the range of deflection to an overall length of the nail is at least 1:30; The intramedullary nail of embodiment 1, wherein at any position of the shank within the range of deflection, there is a rectangular area in the second cross-sectional plane that does not intersect with a proximal or distal edge of the channel. [Aspect 11] 11. The intramedullary nail of claim 10, wherein the ratio of the distance the distal tip of the shank travels between ends of the range of flexure to the overall length of the intramedullary nail is 1:24. [Aspect 12] The intramedullary nail of embodiment 1, wherein the shank defines a bore extending along the centerline and dividing the channel into two aligned passages. [Aspect 13] 1. A method of treating an injury to a bone, comprising: inserting an intramedullary nail into an intramedullary canal of the bone generally along an anatomical axis of the bone; The intramedullary nail comprises: a shank having a centerline defined along a length thereof; the shank has a channel with a channel axis perpendicular to the centerline, the channel having an oval shape in a first cross-sectional plane perpendicular to the channel axis at the centerline and a tapered profile in a second cross-sectional plane that includes the channel axis at the centerline; A method of treating an injury to a bone comprising inserting a screw through a predetermined location in the bone such that the screw threadably engages at least a portion of the channel. [Aspect 14] 14. The method of claim 13, wherein the intramedullary nail includes an oval opening in the shank that feeds into the channel, and the intramedullary nail is embedded in the bone with the oval opening oriented in an anterior direction relative to the bone. [Aspect 15] 15. The method of claim 14, wherein the intramedullary nail is embedded in the bone such that the tapered profile narrows in a posterior direction relative to the bone. [Aspect 16] 16. The method of embodiment 15, further comprising drilling through the bone and the channel at a predetermined location of the bone from the anterior direction to the posterior direction. [Aspect 17] 14. The method of claim 13, wherein the screw engages at least a portion of the channel to accommodate deflection of the nail that occurs during implantation. [Aspect 18] 1. A method of designing an intramedullary nail, comprising: assessing an expected range of deflection of a shank of the intramedullary nail in a deflection plane corresponding to a deflection of the intramedullary nail during a procedure for embedding the intramedullary nail in bone; defining a fixation location for a cylindrical fixation element relative to a head of the nail located at a proximal end of the nail, the fixation location being such that the cylindrical fixation element extends transversely to and intersects the shank at any location of the shank within the expected range of deflection; A method of designing an intramedullary nail comprising selecting respective positions and angles for a proximal end of a channel and a distal end of the channel disposed through a distal half of the shank, whereby the cylindrical fixation element disposed at the fixed position extends through the channel without intersecting the proximal end or the distal end of the channel at all degrees of deflection of the shank within the expected range of deflection. [Aspect 19] Further, providing additional fastening positions for additional cylindrical fastening elements, The method of embodiment 18, comprising selecting respective positions and angles for proximal and distal ends of an additional channel disposed through the distal half of the shank, such that the additional cylindrical fixation element disposed at the additional fixation position extends through the additional channel without intersecting the proximal or distal ends of the additional channel at any degree of deflection of the shank within the expected range of deflection. [Aspect 20] 19. A method of treating an injury to a bone using an intramedullary nail designed according to the method of claim 18, comprising: inserting the nail into the bone generally along the anatomical axis of the bone while allowing the nail to flex within the bone; After the nail is inserted into the bone, inserting a screw through the bone and channel at a position and angle relative to a head of the nail that corresponds to a locking position of a cylindrical fixation element.

Claims

1. a shank having a centerline defined along a length thereof; 1. An intramedullary nail, wherein the shank has a channel with a channel axis perpendicular to the centerline, the channel having an oval shape in a first cross-sectional plane perpendicular to the channel axis at the centerline and a tapered profile in a second cross-sectional plane that includes the channel axis, whereby a portion of a proximal edge of the channel in the second cross-sectional plane forms a first angle with the channel axis and a distal edge of the channel in the second cross-sectional plane forms a second angle with the channel axis that is different from the first angle.

2. 2. The intramedullary nail of claim 1, wherein opposing proximal and distal ends of the channel are defined by circular surfaces extending respectively along two non-parallel axes, and opposing sides of the channel are flat and extend respectively between the two circular surfaces to define an oval shape.

3. The nail of claim 2 , wherein the channel is fully internally threaded.

4. The nail of claim 2 , wherein the channel extension defines a circular opening in a surface of the shank.

5. The nail according to claim 2 , wherein each of said two non-parallel axes intersects said center line.

6. The nail of claim 2 , wherein the first angle is non-zero and the second angle is zero.

7. The nail of claim 2 , wherein the nail includes an oval opening in the shank that feeds into the channel, at least a portion of an outer periphery of the oval opening being chamfered.

8. The nail according to claim 2, wherein the angle between the two non-parallel axes is between 3° and 7°.

9. The nail according to claim 8, wherein the angle between the two non-parallel axes is 6.5°.

10. the shank is elastically deformable through a range of deflection in the second cross-sectional plane, and a ratio of a distance traveled by a distal tip of the shank between ends of the range of deflection to an overall length of the nail is at least 1:30; The nail of claim 1 , wherein at every location of the shank within the range of deflection there is a rectangular area in the second cross-sectional plane that does not intersect a proximal or distal edge of the channel.

11. The nail of claim 10, wherein the ratio of the distance the distal tip of the shank travels between ends of the range of flexure to the overall length of the nail is 1:

24.

12. The nail of claim 1 , wherein said shank defines a bore extending along said centerline and dividing said channel into two aligned passages.

13. A method for designing an intramedullary nail, comprising the steps of: assessing an expected range of deflection of a shank of the intramedullary nail in a deflection plane corresponding to a deflection of the intramedullary nail during a procedure for embedding the intramedullary nail in bone; defining a fixation location for a cylindrical fixation element relative to a head of the nail located at a proximal end of the nail, the fixation location being such that the cylindrical fixation element extends transversely to and intersects the shank at any location of the shank within the expected range of deflection; A method of designing an intramedullary nail comprising selecting respective positions and angles for a proximal end of a channel and a distal end of the channel disposed through a distal half of the shank, whereby the cylindrical fixation element disposed at the fixed position extends through the channel without intersecting the proximal end or the distal end of the channel at all degrees of deflection of the shank within the expected range of deflection.

14. Further providing an additional fixing position for an additional cylindrical fixing element, 14. The method of claim 13, further comprising selecting respective positions and angles for proximal and distal ends of an additional channel disposed through the distal half of the shank such that the additional cylindrical fixation element disposed at the additional fixation location extends through the additional channel without intersecting the proximal or distal ends of the additional channel at all degrees of deflection of the shank within the expected range of deflection.

15. A method for treating an injury to a bone using an intramedullary nail designed according to the method of claim 13, comprising: inserting the nail into the bone generally along the anatomical axis of the bone while allowing the nail to flex within the bone; After the nail is inserted into the bone, inserting a screw through the bone and channel at a position and angle relative to a head of the nail that corresponds to a locking position of a cylindrical fixation element.

16. A portion of the circular surface of the proximal end of the channel defines a semi-cylinder centered on a proximal axis along which the circular surface of the proximal end lies of the two non-parallel axes; 3. The nail of claim 2, wherein a portion of said circular surface of said distal end of said channel defines a semi-cylinder centered on a distal one of said two non-parallel axes along which said circular surface of said distal end lies.

Images