Ligament fixation device and method

An anchor for securing soft tissue within a bone tunnel having an inner wall includes a resilient body member that defines a soft tissue opening and has a first, leading end and a second, trailing end. The anchor also has at least one bone engaging element connected to the body member. The anchor is movable between a first, sliding position wherein the at least one bone engaging element slides along the inner wall of the bone tunnel and the anchor is movable within the bone tunnel, and a second, locking position wherein the at least one bone engaging element engages the inner wall of the bone tunnel to resist movement of the anchor within the bone tunnel. In one embodiment, two opposed bone engaging legs are connected to the body at the second trailing end and extend at an angle away from the longitudinal axis and in a direction from the leading end to the trailing end. A pull tool engaging element provided on the second, trailing end of the body between the two opposed bone engaging legs.

CROSS-REFERENCE TO RELATED APPLICATIONS 
Not Applicable. 
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
Not Applicable. 
BACKGROUND OF THE INVENTION 
The present invention relates to a device and method for attaching soft 
tissue such as a ligament or ligament graft to a bone. The device and 
method are particularly useful for fixing the soft tissue within a tunnel 
formed in a bone proximate to the natural point of attachment of the soft 
tissue. 
The complete or partial detachment of ligaments, tendons or other soft 
tissues from their associated bones within the body are relatively 
commonplace injuries, particularly among athletes. Such injuries are 
generally the result of excess stress being placed on these tissues. 
Tissue detachment may occur as the result of an accident such as a fall, 
overexertion during a work related activity, during the course of an 
athletic event or in any one of many other situations and/or activities. 
If, however, the ligament or tendon is completely detached from its 
associated bone or bones, or if it is severed as part of a traumatic 
injury, partial or permanent disability may result. Fortunately, a number 
of surgical techniques; exist for reattaching such detached tissues and/or 
completely replacing severely damaged tissues. 
One such technique involves the reattachment of the detached tissue using 
"traditional" attachment devices such as metal staples and cancellous bone 
screws. Such "traditional" attachment devices have also been used to 
attach tendon or ligament substitutes (often formed of autogenous tissue 
harvested from elsewhere in the body) to the desired bone or bones. 
Another technique is described in detail in U.S. Pat. No. 4,950,270 
entitled "Cannulated Self-Tapping Bone Screw", issued to Bowman et al. on 
Aug. 21, 1990, and specifically incorporated herein by reference. In this 
technique, the anterior cruciate ligament in a human knee, for example, is 
replaced and/or repaired by forming bone tunnels through the proximal 
tibia and/or distal femur at the points of normal attachment of the 
anterior cruciate ligament. A ligament graft with a bone block on at least 
one of its ends is sized to fit within the bone tunnels. A suture is then 
attached to the outer end of each bone plug and sutures on opposite ends 
of the graft structure are passed through the femoral and tibial bone 
tunnels. The femoral plug and the tibial plug are then inserted into their 
respective bone tunnels behind the sutures. The sutures are then drawn 
tight simultaneously in opposite directions. This procedure places the 
bone plugs in the desired position, and imparts the desired degree of 
tension to the ligament or ligament substitute. Finally, a bone screw is 
inserted between each bone plug and the wall of its associated bone tunnel 
so as to securely lock the bone plug in position by a tight interference 
fit. 
Another common ligament attachment technique is described in U.S. Pat. No. 
5,645,588 entitled "Graft Attachment Device," issued to Graf et al. on 
Jul. 8, 1997, and in U.S. Pat. No. 5,769,894 entitled "Graft Attachment 
Device and Method of Attachment," issued to Ferragamo on Jun. 23, 1998. 
This method uses a button-like device that rests on the outside of a bone, 
covering at least part of the opening to a bone tunnel. The button is 
first sutured to a portion of a ligament graft at a distance from the 
button, in effect suspending the graft from the button. The 
button-suture-graft construct is then pulled through the bone tunnel and 
the button is seated outside the far end of the tunnel with the ligament 
graft suspended within the tunnel. 
U.S. Pat. No. 5,356,413, entitled "Surgical Anchor and Method for Deploying 
the Same," issued to Martins et al. on Oct. 18, 1994, discloses a surgical 
anchor device having a metal anchor body with nickel-titanium alloy arcs 
located on a leading end of the body. One transverse bore on the leading 
end is used to place a suture which is used to pull the anchor into a bone 
tunnel. A second transverse bore located in the trailing end of the 
anchor. The ligament graft may be directly connected to the second bore, 
or the ligament graft may be suspended from the second bore by suture 
thread. 
The ligament fixation schemes described above have not been entirely 
successful. For example, rigid attachment using "traditional" attachment 
devices such as staples, sutures and screws often cannot be maintained 
even under normal tensile loads. Also, the use of sharp screws to create a 
locking interference fit between a bone plug and a bone tunnel can be 
problematic. For one thing, there is always the possibility of damaging 
the ligament during insertion of the screw. In addition, it can be 
difficult to maintain the desired tension on the ligament or repair 
material during insertion of the screw. 
Non-rigid fixation schemes, such as suspending a ligament graft from a 
suture button, also have drawbacks. Because the graft structure is not 
rigidly fixed within the bone tunnels, movement of the graft structure can 
disrupt the healing process. 
Despite the various ligament fixation methods known in the art, it would 
still be desirable to provide a ligament fixation device and method that 
can rigidly fix a ligament graft within a bone tunnel at a desired 
ligament tension for a time sufficient to allow the ligament graft to 
permanently fix itself to the bone. 
SUMMARY OF THE INVENTION 
The present invention provides an anchor for securing soft tissue within a 
bone tunnel having an inner wall. The anchor includes a resilient body 
member that defines a soft tissue opening and has a first, leading end and 
a second, trailing end. The anchor also has at least one bone engaging 
element connected to the body member. The anchor is movable between a 
first, sliding position wherein the at least one bone engaging element 
slides along the inner wall of the bone tunnel and the anchor is movable 
within the bone tunnel, and a second, locking, position wherein the at 
least one bone engaging element engages the inner wall of the bone tunnel 
to resist movement of the anchor within the bone tunnel. 
In one embodiment, the anchor of the invention is bioabsorbable and 
includes a resilient body defining a soft tissue opening and having a 
longitudinal axis, a first leading end and a second trailing end. Two 
opposed bone engaging legs are connected to the body at the second 
trailing end and extend at an angle away from the longitudinal axis and in 
a direction from the leading end to the trailing end. A pull tool engaging 
element is provided on the second, trailing end of the body between the 
two opposed bone engaging legs. 
The anchor body can be resilient and can deform in order tc move from the 
first to the second position in order to lock within a bone tunnel. In 
particular, the anchor body may deform in the area between the opposed 
bone engaging legs at the trailing end of the anchor body and cause the 
legs to extend farther outward to engage the wall of the bone tunnel. 
The anchor body can take the form of a broken circle having a break or gap 
at the leading end. As the anchor deforms from the first to the second 
position, the gap in the anchor body closes, and when closed, the anchor 
body resists further deformation. Stabilizing legs may also be provided on 
the anchor body on opposite sides of the gap. 
The anchor may deform from the first to the second position as a result of 
forces applied on the anchor such as tension on the soft tissue being 
anchored and engagement of tips at the end of the bone engaging legs with 
the walls of the bone tunnel.

DETAILED DESCRIPTION OF THE INVENTION 
An anchor 10 of the invention having a body 12 and at least one bone 
engaging element 18 is illustrated in FIGS. 1 and 2. The body 12 has a 
leading end 14 and a trailing end 16, the at least one bone engaging 
element 18 being connected to the body 12 in proximity to the trailing 
end. A longitudinal axis 20, generally coincident with the axis of a bone 
tunnel with which anchor 10 may be used, extends through the leading and 
trailing ends 14, 16. 
Body 12 is generally in the form of an incomplete circle having a 
transverse opening 22 sized to receive a ligament graft and a break or gap 
24 in the circle at the leading end 14 of the body 12. Transverse opening 
22 is sized to receive a ligament graft and may generally be about 0.240 
inch in diameter. The outer surface 26 of body 12 is rounded and the inner 
surface 28 of body 12 is chamfered so as not to present sharp edges that 
might damage a ligament graft. The leading end 14 of body 12 may include 
stabilizing legs 30 provided adjacent to gap 24. 
Exemplary anchor 10 has two opposed bone engaging members 18. These bone 
engaging members 18 are attached to a body 12 at its trailing end 16 and 
extend outward away from longitudinal axis 20 and downward in a direction 
from the leading edge 14 toward the trailing edge 16 of the body 12. On 
anchor 10, the outer surface 32 of each bone engaging member 18 extends at 
an angle of about 30.degree. with the longitudinal axis 20 and ends at a 
point 34 that is suitable to engage the inside of a bone tunnel to hold 
anchor 10 in place. 
A pulling element 36 is provided on the anchor of the invention so that a 
tool, such as a length of suture thread, can engage the anchor for the 
purpose of pulling it, and an attached ligament graft, through a bone 
tunnel for fixation. On anchor 10, the pulling element 36 is a slot 
defined between the bone engaging elements 18 at the trailing end 16 of 
body 12. 
Exemplary anchor 10 is formed from a resilient material that can be 
bioabsorbable. Exemplary non-absorbable materials for forming anchor 10 
include delrin and polysulfone. Bioabsorbable polymers or copolymers may 
be selected according to the desired adsorption or degradation time. That 
time, in turn, depends upon the anticipated healing time for the 
reattachment of soft tissue to the bone or other tissue which is the 
subject of the surgical procedure. Known biodegradable polymers and 
copolymers range in degradation time from about three months for 
polyglycolide to about forty-eight months for polyglutamic-coleucine. A 
common biodegradable polymer used in absorbable sutures is an absorbable 
copolymer derived from glycolic and lactic acids, such as a synthetic 
polyester chemically similar to other commercial available glycolide and 
lactide copolymers. Glycolide and lactide, in vivo, degrade and absorb by 
hydrolysis into lactic acid and glycolic acid which are then metabolized 
by the body. 
Exemplary anchor 10 is a unitary anchor and leg structure formed from a 
resilient material. It is generally sized that it can slide snugly within 
a bone tunnel to which a ligament is being fixed. In one embodiment, body 
12 has a diameter of about 0.400 inches and a depth of about 0.160 inches. 
The span of bone engaging legs 18 from tip 34 to tip 34 is about 0.460 
inches. The leg span may be greater than the diameter of the bone tunnel 
in which anchor 10 will be used, causing bone engaging legs 18 to flex 
inward when entering the tunnel. The circular wall of body 12 has a 
thickness of about 0.080 inches. The thickness of body 12 in region 52 
between pulling element 36 and transverse opening 22 is about 0.0495 
inches. Generally, an anchor 10 having these dimensions can conveniently 
be used in a bone tunnel having a diameter of about 0.400 inches. 
As illustrated in FIG. 1, resilient anchor 10 is in a first, sliding 
position in which anchor 10 is undeformed. As will be explained in greater 
detail below, resilient anchor 10 deforms in use into a second, locking 
position in which anchor 10 no longer slides in the direction of tension 
from the ligament, but is locked to the inner surface of a bone tunnel. 
In FIG. 2, anchor 10 is shown engaged with a ligament graft 38 which passes 
through transverse opening 22. Ligament graft 38 can be an actual 
ligament, it could also be fashioned from other soft tissue (such as a 
portion of a patella tendon), or it could be synthetic. Ligament graft 38 
can be secured to anchor 10 by passing an end of ligament graft 38 through 
transverse opening 22 and suturing the ligament end back to the ligament 
38. Attachment means other than sutures, including staples or clips for 
example, can also be used to secure ligament 38 through transverse opening 
22. Because transverse opening 22 is transverse to the direction of bone 
engaging legs 18, ligament 38 will not catch on bone engaging legs 18. 
A length of suture 40 is also engaged with anchor 10 as illustrated in FIG. 
3. Suture 40 may be attached to anchor 10 before or after ligament graft 
38 is secured. Suture 40 passes through pulling element 36 (FIG. 1) and 
each end of suture 40 extends from the pulling element 36 past the leading 
end 14 of anchor 10. If suture 40 is attached to anchor 10 after ligament 
38 is secured thereto, suture 40 can be attached by attaching one end to a 
needle and passing the needle and suture 40 through ligament 38, through 
pulling element 36, and through ligament 38 on the opposite side of 
pulling element 36. 
Application of the structure of FIG. 3, that is, anchor 10 having a 
ligament graft 38 and a length of suture 40 affixed thereto, to fix 
ligament graft 38 within a bone tunnel is illustrated in FIGS. 4 to 7. In 
these figures, a bone tunnel 42, shown in cut away, has been formed in a 
proximal tibia 44 and distal femur 46. Exemplary tunnel 42 passes through 
the normal attachment points of an anterior cruciate ligament in a 
normally functioning human knee, however, the methods and devices of the 
invention can be used to affix other ligaments or other soft tissues or 
soft tissue substitutes to bone. 
As shown in FIG. 4, fixation of ligament 38 within bone tunnel 42 can begin 
by drawing suture 40 into the distal end 48 of bone tunnel 42 in the 
tibia, proximally through the tunnel 42, and out the proximal end 50. As 
shown in FIG. 5, anchor 10 and ligament 38 can be drawn into bone tunnel 
42 by pulling on suture 40. It may be desirable for a surgeon to apply a 
tension on ligament 38 during this process so that ligament 38 remains 
firmly seated in transverse opening 22 of anchor 10. Anchor 10 slides 
snugly within tunnel 42 and the outer surface 32 of each bone engaging leg 
18 may contact the inner surface of tunnel 42 as anchor 10 slides therein. 
When anchor 10 reaches the desired location for fixation, illustrated in 
FIG. 6, the surgeon may stop pulling on suture 40 and thus stop sliding 
anchor 10 proximally into tunnel 42. 
When the anchor has reached, or slightly passed, the desired position, 
tension on suture 40 can be released while tension on ligament 38 is 
applied or maintained. With suture 40 tension removed and tension applied 
to ligament 38, anchor 10 deforms into a second, locking position 
illustrated in FIGS. 7 and 8. The tension applied though ligament 38 
causes the tips 34 of legs 18 to engage the inner surface of bone tunnel 
42. The tension on ligament 38 continues to pull on anchor 10, causing the 
anchor to deform. Legs 18 angle more acutely to extend legs 18 outward 
into bone. Simultaneously, body 12 deforms as its broken circle shape 
deforms to look more like a completed oval (see FIG. 8). When designed as 
shown in FIGS. 1 and 8, much of the deformation of anchor 10 from its 
first, sliding position to its second, locking position occurs in the 
region 52 between pulling element 36 and transverse opening 22 as this 
region of anchor 10 has the smallest cross sectional area. Anchor body 12 
can be configured, by sizing the gap 24 in the broken circle body 12, to 
allow a controllable amount of deformation before the gap 24 closes and 
the portions of anchor body 12 adjacent to stabilizing legs 30 meet. At 
this point, anchor 10, and thus ligament 38, is locked against distal 
movement, i.e. motion in the direction of ligament 38 tension. 
With the anchor 10 fixed in the desired position, suture 40 may be removed 
by cutting suture 40 or by pulling on one end to slide suture 40 out of 
contact with ligament 38 and with anchor 10. 
It is also possible, using the method and device of the invention, to 
adjust the position of the anchor 10 even after it has be locked into 
position. By pulling on suture 40 before it is removed, the anchor 10 can 
be pulled proximally within tunnel 42 and will resume its first, sliding 
position. If the new desired position is proximal, suture 10 can be pulled 
until the anchor reaches that position. If the new desired position is 
distal, the anchor 10 can be unlocked by pulling on the suture 40, then 
moved distally by supplying equal tension on the ligament while carefully 
sliding the anchor 10 in the distal direction. 
The distal end of ligament 38 can be fixed within the tibial portion of 
tunnel 42 by any means known in the art including use of another anchor 
10, use of other prior art anchors, staples, screws, or interference 
screws where a b)ne block is provided on the distal end of the ligament 
38. 
Anchor 10 of the invention can also be used with a ligament having a bone 
block on the proximal, and if desired also on the distal, end thereof. 
Similarly to the embodiment illustrated in FIGS. 8 and 9 of U.S. Pat. No. 
5,356,413, specifically incorporated herein by reference, a bone block on 
the end of a ligament or ligament graft can be suspended from an anchor 
such as anchor 10 by passing one or more suture threads through transverse 
opening 22 and connecting those sutures to the bone block by passing the 
sutures through preformed holes in the bone block. Alternatively, a bone 
block and ligament graft construct can be more rigidly secured using 
anchor 10 by using a tape to connect the bone block to the anchor. In this 
embodiment, a length of tape, such as one-quarter inch polyester tape, can 
be passed through transverse opening 22 and connected to the bone block at 
either end of the length of tape. The tape may be connected to the bone 
block using adhesive and/or tying the tape to the bone block using suture 
thread. 
It will be understood that the foregoing is only illustrative of the 
principles of the invention, and that various modifications can be made by 
those skilled in the art without departing from the scope and spirit of 
the invention. All references cited herein are expressly incorporated by 
reference in their entirety.