Abstract:
A graft preparation board that enables an exact tensioning of soft tissue grafts. The graft preparation board allows the amount of tensile load to be easily determined so that the operator can precisely control the amount of tension to be applied. The graft preparation board also enables higher tensions to be placed on graft tissues to be used in surgery.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not applicable. 
     FIELD OF THE INVENTION 
     The present invention relates to a device and method for preparing graft tissue for tissue replacement surgery. More specifically, the invention relates to a preparation board for tensioning graft tissue prior to implantation at an injury site. 
     BACKGROUND 
     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. In the case of a partial detachment, commonly referred to under the general term “sprain”, the injury will frequently heal itself, if given sufficient time, and if care is taken not to expose the injury to any undue stress during the healing process. 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. 
     A typical surgical correction of a tendon or ligament injury involves the fixed attachment of the tendon or ligament substitute (often formed of autogenous tissue harvested from elsewhere in the body) to the area of normal bony attachment so that regrowth and reattachment of the tendon or ligament substitute to the bone is enabled. Attachment of the ligament substitute to the bone is ensured by the use of bone attachment means using “traditional” attachment devices such as metal staples, sutures over buttons and cancellous bone screws. Such “traditional” attachment devices have also been used to attach tendon or ligament substitutes to the desired bone or bones. The ligament substitute to bone attachment means must be rigidly situated so that regrowth of the ligament substitute in the bony area of the attachment point is undisturbed. 
     A common type of injury to the knee is the tearing of the anterior cruciate ligament (ACL). Located in the center of the knee joint and running from the femur (thigh bone) to the tibia (shin bone), through the center of the knee, the ACL is the major stabilizing ligament of the knee. Surgical treatment of a torn anterior cruciate ligament usually involves an arthroscopic surgical reconstruction of the injured ligament. A number of different types of tissues can be utilized to reconstruct the ACL, the most common of which involves harvesting the central third of the patellar tendon with a bone block at each end of the tendon graft. After harvesting the tissue, drill guides are used to place holes into the tibia and femur. By placing the drill holes at the attachment sites of the original ligament, when the graft is pulled through the drill hole and into the knee, it will be placed in the same position as the original ACL. After pulling the graft through the drill holes and into the joint to replace the torn ACL, the graft is then held in place with bioabsorbable screws or metallic screws. New blood vessels are allowed to grow into the graft and the site is allowed to heal. 
     While the patellar tendon is the most widely used autograft tissue, surgical morbidity associated with its harvest has led to an increase in the use of alternate grafts. Currently proposed alternatives include double stranded hamstring tendons and other soft tissue grafts for creating composite grafts. An exemplary technique for using double stranded hamstring tendons requires pretensioning the tendons on a graft preparation board until they are ready for use. This pretensioning process involves holding the graft tissue across the board and applying a tensile load to the tissue. Before the composite graft is implanted, the tendons can be whip stitched at their ends while under tension to create a secure bundle and prevent fraying. 
     Once the tendon graft is prepared, the tendons may be doubled over, and then inserted, doubled end first, through a drilled tibial tunnel. Attachment means, such as the ligament fixation device disclosed by Wenstrom, Jr. in U.S. Pat. No. 6,152,928, may be used to secure the doubled end to the opening of the femoral socket. Sutures from the whip stitched ends provide a means by which the composite graft can be connected to an in situ tensioner and the composite graft tensioned and the knee ranged approximately 12 to 14 times from extension to flexion. While maintaining tension and spreading apart the individual strands of the composite graft, the soft tissue graft can be fixed to the anterior tibia. Fixation may be achieved by inserting an expandable sheath up the tibial tunnel, into the opening resulting from the spreading and tensioning of the strands. Fixation may be achieved, for example, by screwing an expander screw into the sheath to engage the sheath with the strands and tibia. 
     Regardless of whether a patellar tendon or a double stranded hamstring tendon is used, one important factor in ensuring the success of the ACL surgery is the adequacy of tensioning of the graft tissue during its preparation. Current graft preparation boards for pretensioning harvested graft tissue, such as the one disclosed by Schmieding in U.S. Pat. No. 5,415,651, comprise a pair of rudimentary holding blocks that are linearly displaceable along a track. Each end of the graft tissue is secured to a block. Each block is held in position in one of a plurality of predetermined holes along the track by a vertical pin. To effect tensioning of the graft, the pins are released and the blocks moved apart by a fixed length along the track. When the pin or pins align with one of the holes along the track, the blocks are resecured. 
     Though such a preparation board may provide adequate tensioning of the graft tissue for some types of graft preparations, there is no means to precisely control the amount of tension to be applied. Further, the boards currently available do not allow the user to measure with accuracy the amount of tension being applied. There is thus a need for a graft preparation board that enables the operator to easily to control and monitor the amount of tension to be applied to the graft tissue. There is also a need for a graft tensioner that is able to place higher tensions than normally possible by simply pulling axially on one end of a soft tissue graft. 
     SUMMARY OF THE INVENTION 
     The present invention avoids the aforementioned problems associated with current graft tension boards by providing a graft preparation board that enables an exact tensioning of soft tissue grafts. In the present invention, the amount of tensile load can be easily determined so that the operator can precisely control the amount of tension to be applied. The present graft preparation board also enables higher tensions to be placed on the tissues to be used in surgery. 
     In one embodiment of the present invention, the graft preparation board has a platform on which there is a first unit and a second unit. On the second unit is a second grasping element for securing an opposite end of the tissue graft. The first unit includes a tensioning device which comprises a base member and a translating element that extends through the base member. The translating element is connected at one end to a head that extends into a first grasping element for securing an end of a tissue graft. Translating element is connected at an opposite end to a grip. Extending between the grip and base member is a spring mechanism. By deploying the grip, the spring mechanism can be tensioned as the translating element is moved, effecting a linear displacement of the translating element with respect to the head and base member. In this particular embodiment, the translating element can comprise a sliding threaded shaft, and the grip can comprise a knob such that, when the knob is turned, the sliding threaded shaft translates with respect to the head and the base member when the spring mechanism is tensioned. 
     In another embodiment of the present invention, the translating element can include a sliding shaft having notches or grooves instead of threads that would enable the shaft to incrementally ratchet to allow the first grasping element any number of predetermined distances with respect to base member. It is envisioned that the tensioning device of the present invention could work as well with a pulley or reel system for the translating system. 
     In one aspect of the present invention, the first and second units may be translatable along the length of the platform. For instance, first and second units can be slidable along a track that extends on the platform. Each unit can be locked in position on the track. The board may include indicia along the side of the platform for determining the length of the graft tissue held between the first and second grasping elements. 
     In another aspect of the present invention, the first and second grasping elements can comprise jaws. However, first and second grasping element can also be hooks, pins, or posts for engaging an end of the graft tissue to be prepared. 
     In yet another aspect of the present invention, the base member can include a window having indicia representing units of tension (lbs. and N) surrounding the window. Within the window is an indicator for reading the amount of tensile load being applied to the graft tissue being held within the first and second grasping elements. 
     Further features of the invention, its nature and various advantages, will be more apparent from the accompanying drawings and the following detailed description of the drawings and the preferred embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of one embodiment of a graft preparation board of the present invention; 
     FIG. 2 is a detailed view of the tensioning device of FIG. 1; and 
     FIG. 3 is yet another perspective view of the tensioning device of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIG. 1, a graft preparation board  10  is shown having a platform  12  on which there sits a first unit  20  and second unit  30  for preparing and tensioning a graft tissue  5  prior to implantation. The first unit  20  can be translatable, or linearly displaceable with respect to the platform  12 . As illustrated, first unit  20  is slidable along a track  14  that extends the length of the platform  12 . On the first unit  20  is a first grasping element  22  for holding one end of graft tissue  5 . As detailed in FIGS. 2 and 3, in this embodiment the first grasping element  22  comprises a pair of jaws that can be opened and locked shut by adjusting threaded nut  24  extending through the jaws. First unit  20  can also include a locking mechanism  26  for holding the first unit  20  stationary on the platform  12 . 
     Also on platform  12  is a second unit  30  that includes a second grasping element  32  for holding an opposite end of graft tissue  5 . Second grasping element  22  comprises a pair of jaws that are opened and locked with threaded nut  34 . Second unit  30  can also be slidable along the track  14  of platform  12 . By having either or both first  20  and second units  30  translatable, first unit  20  and/or second  30  unit can be moved to accommodate the particular length of the graft tissue  5  to be tensioned. This enables the units  20 ,  30  to hold the graft tissue  5  taut against the platform  12 , regardless of length. Indicia  16  representing units of length (inches, cm, etc.) can be provided along the side of the platform  12  for reading the length of tissue  5 . 
     Graft preparation board  10  also includes a tensioning device  40  on first unit  20 . As shown in FIGS. 2 and 3, tensioning device  40  comprises a base member  42  and a translating element extending through the base member  42 . The translating element enables the first grasping element  22  to be linearly displaced with respect to the first unit  20 , which is connected to a flange  44  extending from base member  42 . In this particular embodiment, the translating element comprises a sliding threaded shaft  50  that is attached at a distal-most end to a head  28  extending from first grasping element  22 . At the proximal-most end of threaded shaft  50  is a grip such as a knob  54 . Tensioning device  40  also includes a spring mechanism  60  on the sliding threaded shaft  50  between the knob  54  and base member  42 . 
     In use, sliding threaded shaft  50  can translate with respect to both the head  28  and the base member  42  when tension is applied. If no tension exists, i.e., spring mechanism  60  is not compressed, when knob  54  is rotated, then the head  28  can translate with respect to the sliding threaded shaft  50  and base member  42 . In this instance, the sliding threaded shaft  50  does not translate with respect to the base member  42 . However, where an initial tension exists, i.e., the spring mechanism is compressed, then both the head  28  and the sliding threaded shaft  50  can translate with respect to each other, and with respect to the base member  42  when knob  54  is rotated. 
     First unit  20  and tensioning device  40  of graft preparation board  10  not only provide controlled induction of tensile load on the graft tissue  5 , but can also measure the exact tensile load according to the translation of the sliding threaded shaft  50  relative to the base member  42 , as calculated by the displacement of spring mechanism  60 . As shown in FIG. 3, base member  42  includes a cut-away window  46  surrounding which are indicia  48  representing units of tensile load, e.g., lbs, N. Extending through window  46  is a portion of sliding threaded shaft  50  having thereon an indicator, or marking  52 . Marking  52  can be a groove machined into the sliding threaded shaft  50 , or just a superficial marking on the sliding threaded shaft  50 . 
     To tension the graft tissue  5  held between first grasping element  22  and second grasping element  32 , the knob  54  can be rotated so that spring mechanism  60  is displaced with respect to base member  42 . In doing so, the first grasping element  22  is moved with respect to the distal-most end of the threaded shaft  50 , thereby effectively stretching the graft tissue  5 . That is, as tensile load is applied, the length of spring mechanism  60  becomes compressed as the tensile load pulls sliding threaded shaft  50  and first grasping element  22 , and moving indicator  52  on sliding threaded shaft  50  further down and towards a distal-most end of window  46 . The amount of compression, as measured by the spring&#39;s displacement, will be reflected in the position of the indicator or marking  52  on shaft  50  which, when lined up with indicia  48 , can be read for determining the tensile load being placed on tissue graft  5 . 
     While the first and second grasping elements  22 ,  32  are illustrated with jaws, it is contemplated that grasping elements can also comprise hooks, pins, or posts for engaging an end of the graft tissue  5  to be prepared. Though not shown, it is contemplated that the present invention can be used with graft tissue  5  having terminal bone blocks as well. Further, translating element may include a shaft having notches or grooves instead of threads that would enable shaft  50  to incrementally ratchet the first grasping element  22  any number of predetermined distances with respect to base member  42 . It is envisioned that the tensioning device  40  of the present invention could work as well with a pulley or reel system for the translating system. 
     Graft tissue  5  to be prepared can be tensioned on the board  10  of the present invention until such time as the tissue  5  is ready for implantation. Before the composite graft is implanted, the tissue can be whip stitched at their ends to create a secure bundle and prevent fraying. Sutures from the whip stitched ends provide a means by which the composite graft can be connected to an in situ tensioner and the composite graft tensioned post implantation. This will provide adequate tensioning of the composite graft for optimal functioning at the implantation site. 
     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.