WO2009132341A1

WO2009132341A1 - Fixation device and method for soft tissue grafts

Info

Publication number: WO2009132341A1
Application number: PCT/US2009/041808
Authority: WO
Inventors: Christopher B. Connor; Bruce D. Beynnon; Brandon Johnson; Matthew Lankowski; Charles W. Morin; Huy K. Nguyen; Michael J. Rosen
Original assignee: The University Of Vermont And State Agricultural College
Priority date: 2008-04-25
Filing date: 2009-04-27
Publication date: 2009-10-29

Abstract

An expandable medical device for surgical implantation that secures the ends of a soft tissue graft in a tunnel made in bone, such as in ligament replacements. The graft material is positioned between the bone and the flexible portion of the fork component with intimate contact with the bone surface during the device expansion. Movement of a plug component into the fork component causes expansion of the device perpendicular to the bone tunnel. The device expansion is also perpendicular to the graft, so the axial tension of the graft does not change during the expansion process and can be monitored during surgery immediately before the expansion process. Expansion within the bone tunnel causes stabilization of the device, maximizes the graft-bone contact, and secures the graft without the device being substantially installed on the exterior surface of the bone or compromising the cortical bone surface outside of the bone tunnel.

Description

FIXATION DEVICE AND METHOD FOR SOFT TISSUE GRAFTS

RELATED APPLICATION DATA

[0001] This application claims the benefit of priority of U.S. Provisional Patent Application Serial No. 61/047,889, filed April 25, 2008, and titled Fixation Device For Soft Tissue Grafts, which is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

[0002] The present invention generally relates to the field of medical implants. In particular, the present invention is directed to a fixation device for soft tissue graft.

BACKGROUND

[0003] Repair of joints through replacement of torn ligaments and tendons is a frequently performed medical procedure. For example, the anterior cruciate ligament (ACL) of the knee is frequently injured. As a result, over 200,000 ACL reconstruction surgeries per year are performed in the United States.

[0004] There are two basic forms of ACL reconstruction, soft tissue grafts and bone-patellar tendon-bone grafts. Current problems with soft tissue grafts include slippage of the graft at the tibial fixation site and healing complications due to graft abrasion against the bone tunnel wall. Difficulties with bone-patellar tendon-bone grafts include post-operative pain due to the bone graft healing process and substantial pain at the donor graft site, although interference screw fixation is relatively secure.

[0005] In the example of an anterior cruciate ligament, the ligament holds the femur and the tibia together. A natural ACL would connect these bones within the knee joint. When this ligament is torn, and a graft replacement must be emplaced, sites for affixing the graft on these two bones must be selected so that the graft can perform the function of the natural ACL. The process of affixing the graft ends at a particular site is known as anchoring.

[0006] Soft tissue grafts must be anchored. Anchoring serves two purposes; positioning of the graft for proper function, and provision of an environment where tissue growth can more securely anchor the graft over time. An ideal anchoring method would be unobtrusive, easy to install, effective over time, and allow for normal functioning after recovery from the surgical grafting procedure. The soft tissue graft must be properly tensioned to function properly, so the anchoring device must allow for setting this tension during the installation procedure and maintaining the tension for the effective life of the graft.

[0007] One method of anchoring a graft involves creation of a contiguous tunnel through the adjacent bones. The length of the soft tissue grafts passes through the bone tunnel, and must be secured in or on each bone. A variety of surgical screws and nails can be used to secure the soft tissue graft ends to the outside of the bone in the bone's cortical layer. The securing devices are installed outside of the close confines of the joint. This technique is made feasible because of the bone tunnel.

[0008] Alternatively, a graft anchoring device may be used that fits within the bone tunnel. These devices have an inherent advantage of avoiding installation into a surface region of bone that would naturally be free of obstructions. The graft fixation device is less noticeable and less irritating placed within the bone tunnel. In the past, many of these devices have suffered from disadvantages, e.g., difficulty in applying the correct tension to the soft tissue graft and maintaining that tension during device installation. Maintaining that tension if the device shifted position within the bone tunnel before healing had secured the graft has also proven problematic.

SUMMARY OF THE DISCLOSURE

[0009] One exemplary embodiment of the present invention is an apparatus for securing a tissue graft against a bone surface in a bone hole. The apparatus includes: a clamping member including a base portion and a plurality of clamping fingers extending from the base portion, each of the plurality of fingers having an inside surface and an outside surface, each of the plurality of clamping fingers being configured and dimensioned to clamp a tissue graft portion between the outside surface and a corresponding bone surface by application of a force transverse to the bone surface; a pressure member disposed to slidingly engage the inside surfaces of the plurality of clamping fingers, the pressure member configured and dimensioned to apply an outwardly directed force to the plurality of clamping fingers in response to translation of the pressure member with respect to the clamping member; and a translational driving mechanism cooperating between the clamping member and the pressure member. [0010] Another embodiment of the present invention is a fixation device for securing a tissue graft to a surface of a tunnel formed in a bone. The fixation device comprises a stationary insert with an expandable clamping surface positioned to confront the surface of a tunnel formed in a bone when the insert is disposed in the tunnel; and a translatory plug adjustably coupled to the stationary insert and designed so as to coact with the expandable clamping surface as a consequence of relative axial, non-rotational movement between the stationary insert and the translatory plug such that the plug drives the expandable clamping surface outwardly toward the surface of the bone tunnel.

[0011] Yet another embodiment of the present invention is a method of attaching a tissue graft to an interior surface of a tunnel in a bone. The method comprises positioning a tissue graft in a bone tunnel having a longitudinal axis; positioning an expandable component having guiding passages in the bone tunnel such that the tissue graft is positioned between the surface of the bone tunnel and the guiding passages; and expanding the expandable component within the bone tunnel in a direction transverse to the longitudinal axis of the bone tunnel while substantially preventing movement of the expandable component in a direction parallel to the longitudinal axis.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] For the purpose of illustrating the invention, the drawings show aspects of one or more embodiments of the invention. However, it should be understood that the present invention is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein:

FIG. 1 shows a perspective view of an embodiment of a plug component of a graft fixation device;

FIG. 2 shows a perspective view of an embodiment of a fork component of a graft fixation device;

FIG. 3 shows an exploded perspective view of an embodiment of a graft fixation apparatus as it may be assembled; and

FIG. 4 shows a cutaway view of an embodiment of the device installed in a surgical environment inside a bone. DETAILED DESCRIPTION

[0013] Embodiments of the soft tissue fixation device disclosed herein are intended to secure soft tissue grafts to bone utilizing a tunnel made in the bone. While the device may be successfully used in connection with ACL reconstruction, it may also be used in connection with a wide variety of other surgeries involving the grafting of soft tissue. In use, embodiments of the device compress the soft tissue graft against the sides of the bone tunnel, providing good contact between graft and bone to enhance the healing process which is necessary for the long-term stability of the graft. Embodiments of the device are able to achieve this compression without inducing axial movement of the graft during the compression process, which might otherwise disturb the desired degree of tension of the graft or damage the graft or surrounding tissue.

[0014] The figures show various views of a version of a soft tissue fixation device, or views of separate components of such a soft tissue fixation device, for securing soft tissue, such as a hamstring tendon graft in a bone tunnel. Reference numbers will be carried forward between drawings when the same part or component appears in more than one drawing.

[0015] FIG. 1 is an illustration of a plug 100 component of a soft tissue fixation device according to an embodiment of the invention. Plug 100 has four channels 105 positioned symmetrically around the circumference of a plug sidewall 110, and which extend the entire length of the plug sidewall and vary in depth, from a plug base 115 to a plug tip 120, being deeper in depth near the plug tip. An axis of symmetry that extends from plug base 115 to plug tip 120 is a longitudinal center axis.

[0016] Plug 100 has a general cylindrical sidewall and profile with channels 105 formed in the surface. The portions of plug sidewall 110 which do not compose channels 105 act as separators 130 between the channels, and define the sides of the channels. The depth of channels 105 is defined by two distinct sections of each channel. A first channel section 135, beginning at plug base 115 and ending before reaching plug tip 120, is rectangular and parallel to the longitudinal center axis. A second channel section 140, is a continuation of the first channel section 135 and ending at plug tip 120, but in addition has a second, inner portion of lesser width than the first channel section. The inner portion is centered along the longitudinal axis, and with sides parallel to the sides of the first channel section, but with a greater depth at the end of second channel section 140 adjacent to plug tip 120 than the depth of first channel section 135. Thus in an exemplary embodiment, channels 105 are deeper at the tip end than the base end. The length of first channel section 135 is roughly one-third to two-thirds of the total length of plug 100 in this version of the device. Other versions may have one or more channel sections with a more complicated function of channel depth to achieve the same function during interaction with other components described below.

[0017] The depths of channels 105, first channel section 135, and second channel section 140, are measured as the distance from the surface of revolution defined by sidewall separators 130 formed by revolution about the longitudinal center axis of plug 100, measured perpendicular to the longitudinal center axis, to the bottoms of channel 105, first channel section 135, or second channel section 140, respectively. In one exemplary embodiment where the plug is formed from a cylinder and the channel is cut into the cylinder surface parallel to the cylinder longitudinal axis, the depth of a channel at any given longitudinal axial distance would be the distance from the point on the cylinder perimeter centered over the channel, to the bottom of the channel, measured along a radial vector perpendicular to the longitudinal axis.

[0018] Plug 100 has a cylindrical plug cavity 145 extending from the surface of plug tip 120 along the longitudinal center axis, but not necessarily penetrating through to plug base 115. Plug cavity 145 may be threaded to receive a corresponding threaded connector, or may be otherwise designed to accommodate some connecting mechanism. If the connecting mechanism does not require plug cavity 145, it may be absent.

[0019] FIG. 2 is an illustration of a fork 200 according to an embodiment of the invention of a soft tissue fixation device. Fork 200 has a fork base 205 and a fork tip 210. An axis of symmetry that runs between fork base 205 and fork tip 210 is a longitudinal center axis. The distance between fork base 205 and fork tip 210 may vary based upon the clinical variables and in vivo structures, such as the size of the bone and the length and diameter of the bone tunnel.

[0020] Flexible members 215 form finger- like projections connected to fork base 205 at their attached end 220, and are free at their free tip 225. The free tip 225 of the flexible members defines the position of the fork tip 210. Generally, the number of flexible members 215 on fork 200 will match the number of channels 105 on plug 100, though of course some channels could go unused, and thus the number of channels could exceed the number of flexible members without altering the principles of operation. Flexible members 215 will slidingly engage the corresponding channels of plug 100 during the insertion, translation, and fixation procedure. The width of each flexible member 215 should therefore be small enough to fit within the width of first channel section 135 and second channel section 140 of plug channels 105. The free ends of flexible members 215 and the width of channels 105 at plug tip 120 may therefore be shaped to ease the engagement process between flexible members 215 and plug tip 120.

[0021] Fork base 205 may include graft openings 230 at the edge of fork base 205. Graft openings 230 aligned with each flexible member 215 provide passage for a strand of the soft tissue graft being affixed. This allows separate axial tension to be placed on the graft strand independent of the device after fork 200 and plug 100 are emplaced in the bone tunnel, but before they are engaged. FIG. 2 also shows an embodiment of fork 200 designed to complement plug 100 in FIG. 1. Flexible members 215 align with channels 105 and are positioned such that translatory engagement of plug 100 into fork 200 will cause the flexible members to bend in conformity to the channel depth as the plug engages. Centered fork cavity 235 in fork base 205 allows for simple access to a connecting mechanism from the fork base end of the fixation device and passage of the mechanism through fork 200 to plug cavity 145.

[0022] FIG. 3 is an exploded view of an embodiment of the graft fixation device 300 showing how plug 100 of FIG. 1 and fork 200 of FIG. 2 align and engage, including components for a connecting mechanism. Plug 100 and fork 200 are oriented so that their longitudinal center axes coincide, and that plug tip end 120 points toward the fork tip end 210.

[0023] In the exemplary embodiment shown in FIG. 3, a threaded rod 305 and hex nut 310 comprise a connecting mechanism for plug 100 and fork 200. Threaded rod 305 will securely thread into plug cavity 145 (not seen in this view) at one end, while the opposite end of the threaded rod passes through fork cavity 235, and the threads are engaged by hex nut 310. The hex nut 310 may be accessed from outside the bone tunnel, enabling plug 100 and fork 200 engagement after emplacement in the bone tunnel. Alternative threaded fasteners, such as screws, or other mechanisms such as ratcheting toothed structures for secure engagement as are well known in cable-ties, may be easily substituted for threaded rod 305 and hex nut 310. [0024] Further engagement of the threads on threaded rod 305 by hex nut 310 will cause plug 100 to move axially toward fork 200. Alignment between channels 105 and flexible members 215 during the axial movement will cause the flexible members to be deflected transversely outward from the longitudinal center axis, typically, but not necessarily, in a direction substantially perpendicular to the longitudinal axis. This will occur essentially simultaneously for each flexible member 215 as the sloped bottoms of channels 105 act as wedges when plug 100 engages fork 200, forcing the flexible members apart and expanding the radial dimensions of graft fixation device 300.

[0025] FIG. 4 shows a cutaway of one version of the device installed within a bone tunnel 405 formed within two bones. In one application, upper bone 410 may represent a femur, and lower bone 415 may represent a tibia, in which case soft tissue graft 420, represented by multiple strands, is a repair of an anterior cruciate ligament of a knee joint. The strands are looped over a cross -pin 425 that intersects bone tunnel 405 in upper bone 410. Bone tunnel 405 is formed by drilling or other suitable bone removal techniques, and has at least one opening to the exterior of each bone. The bone which holds the fixation device generally has two openings in the bone tunnel, as the bone tunnel fully penetrates the bone, permitting insertion of the device from one end, and passage of soft tissue graft 420 to the other bone through the other end. In FIG. 4, bone tunnel 405 penetrates lower bone 415, but dead ends within upper bone 410. This creates two openings in lower bone 415, but only a single opening in upper bone 410.

[0026] Soft tissue graft 420 must be secured in upper bone 410 and lower bone 415 in order to stabilize the joint in a manner approximating the natural ligament or soft tissue that would normally be present in an uninjured joint. The securing mechanism in upper bone 410 shown in FIG. 4 is a cross-pin 425, though many other approaches can be envisaged.

[0027] The orientation of components will be described based upon the distance or direction to the opening of the bone tunnel in lower bone 415 farthest from the opening in upper bone 410. This opening will be defined as the "proximal" opening in lower bone 415. The second opening in lower bone 415 is the "distal" opening. Components residing within bone tunnel 405 inside lower bone 415 with a tip and base may either have their tip end oriented toward the proximal opening or their base end toward the proximal opening. [0028] Graft fixation device 300 is emplaced within bone tunnel 405 such that the strands of soft tissue graft 420 pass along the outside of the sidewalls of both plug 100 and fork 200. The strands are threaded through plug channels 105 and outside flexible members 215 and through graft openings 230 in fork 200. Plug 100 is oriented within bone tunnel 405 so that plug tip 120 is oriented toward the proximal opening of lower bone 415 and plug base 115 is oriented toward the distal opening of lower bone 415.

[0029] Fork 200 is oriented so that flexible members 215 are attached to fork base 205 on the distal side of the fork base, and the free ends of the flexible members point toward the distal end of lower bone 415 and therefore point toward plug tip 120. Fork base 205 is shaped to fit snugly at the proximal opening of bone tunnel 405 in lower bone 415. This may be accomplished by proper selection of the diameter of fork base 205 and appropriate tapering of the base to match a corresponding taper that may be imparted to the proximal opening of the bone tunnel, or existence of shoulders or other structures to engage the cortical or trabecular bone tissue of lower bone 415 and prevent fork base 205 from slipping axially in the bone tunnel.

[0030] With threaded rod 305 passing through centered fork cavity 235 and engaged with plug 100, the engagement of hex nut 310 will draw plug 100, tip first, into fork 200. Flexible members 215 will align with and follow the contour of channels 105, and pass underneath the strands of soft tissue graft 420 that pass through plug channel 105, continue through graft openings 230 in fork base 205 and exit the proximal end of bone tunnel 405. As flexible members 215 are forced transversely away from the longitudinal center axis of the device and toward the bone tunnel wall, the soft tissue graft strands will be pinned and immobilized between the flexible members and the wall of the bone tunnel. This transverse movement of flexible members 215 away from the longitudinal center axis may, in one implementation, be substantially perpendicular with respect to the longitudinal center axis. In other implementations, the movement may occur at an angle with respect to the longitudinal center axis.

[0031] This graft immobilization occurs with minimal axial motion due to the predominantly perpendicular movement of elongate flexible members 215 at the point where it contacts the graft strands. When soft tissue graft 420 is pre-tensioned, the fixation of the strands in this manner maintains the level of tension. Because the ends of the soft tissue graft strands can exit bone tunnel 405 with graft fixation device 300 in the bone tunnel, pre-tensioning can occur prior to causing plug 100 and fork 200 to engage. Each graft strand is placed in close contact with the surface of the bone tunnel along the length of flexible members 215, which encourages healing and fixation of the ligament. The surface of elongate flexible members 215 that contacts the graft strands may, if desired, be textured or roughened by abrasive means or other methods well known in the art, to better grip the graft strands. Symmetric arrangement of elongate flexible members 215 around the radial perimeter of the graft fixation device will generate uniform axial and radial forces. This reduces the likelihood of dislodging graft fixation device 300 in bone tunnel 405. Excess length of soft tissue graft 420 may be trimmed where it exits the proximal hole of bone tunnel 405, as may excess length of threaded rod 305. Increased surface area of the tapered portion of the sidewall of fork base 205, such as circumferential grooves in the surface, can provide structure to encourage the strength of the healed fixation of graft and device.

[0032] While the foregoing description of plug 100 and fork 200 utilize descriptions of channels as rectangular, surfaces as flat or cylindrical, or other geometric descriptions, it should be appreciated that alternative shapes and surfaces may be substituted. For example, a channel may be square rather than rectangular. The foregoing embodiment was intended to illustrate structures that performed the proper functions and would be relatively easy to machine. Graft fixation device 300 can be made from surgical-grade metals like titanium or some stainless steels, surgical-grade synthetic materials such as poly-L-lactide (PLLA), for strength, biocompatibility, and durability, or materials which may eventually be reabsorbed into the regenerating bone tissue once healing is complete.

[0033] The shapes of channels formed in plug 100 and the shapes of elongate flexible members 215 in fork 200 need to interact in a cooperative manner such that when plug tip 120 of plug 100 is properly aligned and axially drawn into the distal end of fork 200, the elongate flexible members 215 are guided into second channel section 140, preferably in the second channel. Continued longitudinal axial movement of plug 100 will cause elongate flexible members to deflect outwardly relative to the longitudinal axis, as the free ends of elongate flexible members are guided up the bottom of second channel section 140 and eventually into first channel section 135. The outward flexing of elongate flexible members 215 pins soft tissue grafts between the elongate flexible members and the wall of the bone tunnel, affixing the graft tissue without undue change in the longitudinal axial tension caused by graft fixation device movement within the bone tunnel during the graft procedure.

[0034] Exemplary embodiments have been disclosed above and illustrated in the accompanying drawings. It will be understood by those skilled in the art that various changes, omissions and additions may be made to that which is specifically disclosed herein without departing from the spirit and scope of the present invention.

Claims

What is claimed is:

1. An apparatus for securing a tissue graft against a bone surface in a bone hole, the apparatus comprising: a clamping member including a base portion and a plurality of clamping fingers extending from said base portion, each of said plurality of fingers having an inside surface and an outside surface, each said plurality of clamping fingers being configured and dimensioned to clamp a tissue graft portion between said outside surface and a corresponding bone surface by application of a force transverse to the bone surface; a pressure member disposed to slidingly engage said inside surfaces of said plurality of clamping fingers, said pressure member configured and dimensioned to apply an outwardly directed force to said plurality of clamping fingers in response to translation of the pressure member with respect to said clamping member; and a translational driving mechanism cooperating between said clamping member and said pressure member.

2. The apparatus of claim 1, wherein said pressure member is formed with wedge shaped surfaces corresponding to each of said inside surfaces of said plurality of clamping fingers to force corresponding ones of said plurality of clamping fingers outwardly in response to relative translation between said clamping member and said pressure member.

3. The apparatus of claim 2, wherein each of said plurality of clamping fingers is configured and dimensioned to clamp a tissue graft portion between said outside surface and a corresponding bone surface by application of a force substantially perpendicular to the bone surface.

4. The apparatus of claim 2, wherein said base portion of said clamping member is tapered to resist axial movement deeper into the bone hole.

5. The apparatus of claim 1, wherein said translational driving mechanism includes at least one threaded fastener.

6. The apparatus of claim 1, wherein said clamping member includes means for maintaining the tissue graft in alignment with said plurality of clamping fingers.

7. A fixation device for securing a tissue graft to a surface of a tunnel formed in a bone, the device comprising: a stationary insert with an expandable clamping surface positioned to confront the surface of a tunnel formed in a bone when said insert is disposed in the tunnel; and a translatory plug adjustably coupled to said stationary insert and designed so as to coact with said expandable clamping surface as a consequence of relative axial, non-rotational movement between said stationary insert and said translatory plug such that said plug drives said expandable clamping surface outwardly toward the surface of the bone tunnel.

8. The fixation device of claim 7, wherein said stationary insert includes a base with a tapered sidewall disposed to confront the surface of the bone tunnel when the fixation device is in use, and further wherein said stationary insert includes a plurality of openings in said base for aligning a tissue graft positioned between said expandable clamping surface and the surface of the bone tunnel with said expandable clamping surface.

9. The fixation device of claim 8, wherein said stationary insert further includes a plurality of radially-flexible members attached to said base, wherein said at least one of said plurality of openings is aligned with corresponding ones of said radially-flexible members.

10. The fixation device of claim 9, wherein said translatory plug has a plurality of sidewall channels, each for receiving at least one of said radially-flexible members of said stationary insert and configured such that when said translatory plug moves axially in a first direction relative to said stationary insert said plurality of sidewall channels drive said radially-flexible members towards the surface of the bone tunnel.

11. The fixation device of claim 7, further comprising a securing mechanism connected to said translatory plug and said stationary insert for causing said translatory plug to move toward or away from said stationary insert.

12. The fixation device of claim 11, wherein said securing mechanism includes at least one threaded fastener.

13. The fixation device of claim 9, wherein said expandable clamping surface resides on a radially outermost surface of said plurality of radially-flexible members.

14. The fixation device of claim 7, wherein said stationary insert further has a substantially cylindrical base connected to said expandable clamping surface, said cylindrical base formed with a retaining shoulder, said retaining shoulder having a shape and size selected to prevent movement of said retaining shoulder into the bone tunnel.

15. The fixation device of claim 7, wherein said stationary insert includes an annular base with an extended shoulder for overlapping cortical bone at the entrance to the bone tunnel, said shoulder having a greater diameter than any portion of the bone tunnel.

16. A method of attaching a tissue graft to an interior surface of a tunnel in a bone, the method comprising:

positioning a tissue graft in a bone tunnel having a longitudinal axis; positioning an expandable component having guiding passages in the bone tunnel such that the tissue graft is positioned between the surface of the bone tunnel and the guiding passages; and expanding the expandable component within the bone tunnel in a direction transverse to the longitudinal axis of the bone tunnel while substantially preventing movement of the expandable component in a direction parallel to the longitudinal axis.

17. The method as recited in claim 16, further comprising the step of securing the expandable component in an expanded state to secure the tissue graft between the expandable component and the surface of the bone tunnel.

18. The method as recited in claim 17, whereby said securing of the expandable component is achieved by driving a plug inside the expandable component so as to expand the expandable component.

19. The method as recited in claim 16, wherein the tissue graft includes a plurality of strands and said expanding of the expandable component occurs while simultaneously retaining the tissue graft strands in mutually spaced relation.

20. The method as recited in claim 16, wherein said expanding of the expandable component is performed without relative rotational movement between the plug and the expandable component.

21. The method as recited in claim 16, further wherein said expanding of the expandable component is performed so that the expandable component expands in a direction substantially perpendicular to the longitudinal axis of the bone tunnel.

22. The method as recited in claim 16, further wherein said expanding of the expandable component is performed without relative rotational movement between the tissue graft and the expandable component.