Abstract:
Methods are provided for preparing a replacement graft for use in repairing a damaged ligament. The methods include harvesting the graft material, shaping it accordingly, assembling the graft by attaching sutures to the ends, and packaging the graft in a sterile container.

Description:
[0001]    This application is a divisional of U.S. application Ser. No. 09/461,829, filed Dec. 15, 1999, which claims priority under 35 U.S.C. § 119 (e) to U.S. Provisional Application Ser. No. 60/113,312, filed Dec. 22, 1998, which is expressly incorporated by reference herein.  
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to a convenient packaged ligament graft; more particularly to a sterilized preserved ready to use ligament graft; and most particularly to a convenient sterilized preserved ready to use ligament graft for replacement of a cruciate ligament. The present invention also relates to methods of preparing and using the same.  
         BACKGROUND AND SUMMARY OF THE INVENTION  
         [0003]    The prior art is replete with examples of cruciate ligament replacements. In replacing an anterior or posterior cruciate ligament, standard techniques often involve drilling bone tunnels through the tibia and femur, inserting replacement ligament material in the bone tunnels, and securing the ends. See, for example, U.S. Pat. No. 5,354,300, hereby incorporated by reference. The prior art also includes examples of replacement ligaments that have bone plugs at one or both ends. Replacement ligaments including bone plugs are particularly useful, as the bone plugs fuse into the prepared bone tunnel, healing quickly and providing a secure attachment for the replacement ligament. Replacement ligaments may be anchored in the bone tunnels by interference screw, cross-pin, tab-loop anchor, screw-and-washer, or a variety of other means. See, for example, U.S. Pat. Nos. 5,562,671 and 4,950,270, incorporated herein by reference.  
           [0004]    Prior art replacement ligaments often involve autografts, for which suitable material is harvested from elsewhere in the patient&#39;s body. The patella tendon is widely used for such graft material, as it can be harvested with bone plugs at both ends. However, patients often experience considerable pain at the donor site following harvest of this tendon. Furthermore, an autograft patella tendon is not always available for use, particularly in revision surgery. Autograft alternatives to the patella tendon include the semitendinosis and gracilis hamstring tendons, the central quadriceps tendon, and fascia lata. See, for example, Charles H. Brown Jr. and Joseph H. Sklar, “Graft Selection, Nonpatellar Alternatives Gain Popularity,” BioMechanics, June 1998, at 21; John P. Fulkerson and Rolf Langeland, “An Alternative Cruciate Reconstruction Graft: The Central Quadriceps Tendon,” Arthroscopy: The Journal of Arthroscopic and Related Surgery, June 1995, at 252, all hereby incorporated by reference. However, these replacement ligaments cannot be harvested with bone plugs at both ends. Thus, when using a replacement ligament of this type, the graft material is often sutured to a bone plug prior to insertion in the bone tunnel. Assembly of the replacement ligament during surgery uses significant operating room time and contributes considerably to the expense of such surgery.  
           [0005]    Allografts may be used as replacement ligaments. However, the supply of allograft patella tendons is limited. Even when patella tendons are available, additional preparation is often required prior to use. As with autografts, available allograft semitendinosis, gracilis, quadriceps, Achilles&#39; tendons, and flexor and extensor tendons (usually from the foot) require considerable additional preparation prior to use.  
           [0006]    According to the present invention, graft material is packaged for convenient use. Packaged, sterilized, ready-to-use replacement grafts are provided in a variety of lengths with pre-attached sutures for easy insertion and may be further pre-sutured to one or two bone plugs. Thus, a surgeon may select a graft of the appropriate configuration, length, and size for use during reconstructive surgery, thereby eliminating the surgery time previously spent on harvesting and/or constructing the graft.  
           [0007]    In one embodiment, the replacement ligament is provided with one bone plug. In another embodiment, the replacement ligament is provided with two bone plugs, one at each end. Such pre-attached bone plugs may improve the rate of incorporation of the soft tissue into a bone tunnel, thus improving healing rates. Long strands of sutures may be attached to one or both ends, in order to facilitate insertion. The replacement ligament material may include semitendinosis, gracilis, or quadriceps tendon, or other allograft or xenograft material. Other organic materials, such as small intestine submucosa (“SIS”), collagen scaffolds, or synthetic materials may be used. See, for example, U.S. Pat. Nos. 4,902,508 and 5,711,969, hereby incorporated by reference.  
           [0008]    According to another embodiment of this invention, replacement ligament could be provided without bone plugs. In this embodiment, the graft material may be cut to appropriate lengths and widths, looped, and sutured. This embodiment may be particularly appropriate for use with fixation techniques which do not use bone plugs, for instance in surgical situations wherein a crosspin is used to capture a looped replacement ligament.  
           [0009]    Still another embodiment of this invention is a method of preparing a replacement graft package, including the steps of harvesting the graft material, cutting and shaping it, then assembling, preserving, and packaging the replacement graft.  
           [0010]    The bone and tissue for use in this invention may be obtained from tissue banks, such as LifeNet, Virginia Beach, Va. The product may be preserved by freeze drying prior to packaging and reconstituted at the time of surgery. Water or a saline solution may be used for the reconstitution. Alternatively, the replacement ligament may be frozen without drying and thawed just prior to use.  
           [0011]    In another embodiment of the invention, the replacement ligament is used to repair a damaged cruciate ligament. A sterile graft of appropriate size is selected and inserted in pre-drilled femoral and tibial holes. After insertion, the graft can be fixed within the knee using fixation devices including interference screws, cross-pins, tab-loop anchors, and screws and washers.  
           [0012]    A final embodiment is a kit for repairing a damaged ligament comprising the pre-packaged ligament of this invention, pre-attached sutures, and a graft fixation devices including screws, cross-pins, tab-loop anchors, screws and washers, or other fixation devices.  
           [0013]    While this invention is described for use in reconstruction of the cruciate ligaments of the knee, it should be appreciated that the invention may be practiced in other manners as well, including in the replacement of other soft tissue, especially in the replacement of other ligaments.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a perspective view of a replacement ligament for use in this invention, wherein a single piece of graft material is looped three times around a pair of bone plugs;  
         [0015]    [0015]FIG. 2 is similar to FIG. 1, except showing a line drawing representing the graft material and illustrating the direction of looping;  
         [0016]    [0016]FIG. 3 is a sectional view along the line of  3 - 3  of FIG. 1;  
         [0017]    [0017]FIG. 4 is similar to FIG. 1, except the graft material comprises a single strand which is looped around each bone plug twice;  
         [0018]    [0018]FIG. 5 is a perspective view of an end of the replacement ligament of FIG. 4 showing the sutures extending through the construct;  
         [0019]    [0019]FIG. 6 is a sectional view along the line of  6 - 6  of FIG. 5;  
         [0020]    [0020]FIG. 7 is similar to FIG. 6, except showing an alternate graft material arrangement;  
         [0021]    [0021]FIG. 8 is an alternative embodiment of the replacement ligament for use in this invention, showing a replacement ligament without bone plugs;  
         [0022]    [0022]FIG. 9 is a sectional view along the line of  9 - 9  of FIG. 8;  
         [0023]    [0023]FIG. 10 is similar to FIG. 8, except the replacement ligament includes a looped end;  
         [0024]    [0024]FIG. 11 is similar to FIG. 8, except the replacement ligament includes one bone plug;  
         [0025]    [0025]FIG. 12 is a sectional view across  12 - 12  of FIG. 11.  
         [0026]    [0026]FIG. 13 is similar to FIG. 12, except showing an alternate graft material arrangement;  
         [0027]    [0027]FIG. 14 is similar to FIG. 11, except the replacement ligament includes bone plugs at both ends; and  
         [0028]    [0028]FIG. 15 shows the graft of FIG. 8 as it is being inserted and fixed into the knee of a patient.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]    [0029]FIG. 1 shows generally a replacement ligament  10  for use in this invention. In this embodiment, replacement ligament  10  comprises graft material  12  and a set of bone plugs  20  and  22 . Replacement ligament  10  of this invention also includes a set of interior sutures  32  for securing bone plugs  20  and  22  in place, and a set of end sutures  36  for use in insertion of replacement ligament  10  into a patient. Graft material  12  provides suitable flexibility and strength for ligament replacement, and bone plugs  20  and  22  are provided for bone ingrowth.  
         [0030]    Referring still to FIG. 1, end sutures  36  may be used to secure the ends of graft material  12  in place, while interior sutures  32  secure portions of graft material  12  together to create pockets for receiving the bone plugs  20  and  22 . Additionally, a long strand suture  30  may be secured to one or both ends of the replacement ligament. Such additional long strand sutures  30  may be used later to aid in insertion of replacement ligament  10  into prepared bone tunnels in the knee of the patient.  
         [0031]    [0031]FIG. 2 illustrates a method for constructing replacement ligament  10  of FIG. 1. Graft material  12  is wrapped around first bone plug  20  to second bone plug  22 , as shown by a line representing graft material  12   a.  Graft material  12   b  then loops back around second bone plug  22  and to first bone plug  20 . Finally, graft material  12   c  wraps around first bone plug  20  and back past second bone plug  22 . Thus, in this illustrative embodiment the graft material  12  is triple-stranded.  
         [0032]    [0032]FIG. 3 shows a cross section of FIG. 1 illustrating a possible placement of graft material  12   a,    12   b,  and  12   c  around bone plug  20 . As illustrated in FIGS. 1 and 3, bone plugs  20  and  22  are exposed on only approximately one third of the circumference. However, in other embodiments, more surface area of the bone plugs may be exposed. This may be accomplished by looping the replacement ligament  12  twice rather than three times, as illustrated in FIGS.  4 - 7 .  
         [0033]    An alternative embodiment of the present invention that provides additional bone surface area is shown in FIG. 4. In this embodiment, replacement ligament  10  is provided with two bone plugs  20  and  22 . Graft material  12  is double stranded. The first strand, graft material  12   a,  is located along a side  60  of bone plug  22 , extends to bone plug  20 , and is located along a side  61  of bone plug  20 . Graft material  12  then loops around a proximal end  45  of bone plug  20 , and the second strand, graft material  12   b,  is located along a second side  62  of bone plug  20 , and then extends to bone plug  22  at a side  63 . As illustrated, bone plug  20  is then secured to graft material  12  by a set of sutures  34  and  35 . Suture  34  extends from side  62  of bone plug  20  and passes completely through bone plug  20  to side  61  where optionally a stitch  48  is made. Suture  34  then returns to side  62 . As shown, suture  35 , is provided in the opposite orientation and extends from side  61  of bone plug  20  and passes completely through to side  62 . Suture  35  then passes back through bone plug  20  to side  61  where a knot  26  is tied. As described above, graft material  12  is also wrapped around bone plug  22 . Bone plug  22  is then secured to replacement ligament  12  by sutures  31  and  33  that pass completely through bone plug  22  in the same manner as sutures  34  and  35 . A set of bundle sutures  38 , preferably provided in a whip stitch  39 , may be used to secure ends  24  and  25  of graft material  12  beyond bone plug  22  at a distal end  46  of replacement ligament  10 . Additional long strand sutures  30  may be secured to the proximal and distal ends  45  and  46  of the replacement ligament  10 . It will be understood that the terms proximal and distal are used for convenience and represent the preferred orientation of replacement ligament  10  for use in anterior cruciate ligament repair. Alternative graft orientations may be required for particular applications or surgeon preference.  
         [0034]    [0034]FIGS. 5 and 6 further illustrate a construction in which graft material  12  is sutured to bone plug  20  of FIG. 4. As best seen in FIG. 5, suture  34  passes completely through bone plug  20  twice, first passing from side  62  through bone plug  20  to side  61 . Preferably a stitch  48  is then made on side  61 . The suture then passes back through bone plug  20  to side  62 . The ends of suture  34  are then tied in a knot  26 , thus securing the opposing strands  12   a  and  12   b  of graft material  12 . In the embodiments of FIGS.  4 - 6 , it is preferred that all strands of graft material  12  be secured to bone plug  20 . However, for some applications surgeons may prefer replacement ligaments for which the bone plugs are provided in pockets, rather than rigidly sutured to the graft material.  
         [0035]    In some fixation methods, it would be preferable to have bone exposed on both sides of the graft, as shown in FIGS.  4 - 6 . With other fixation methods, it may be preferable to have the greatest possible exposed surface area of bone plug  20  on one side, as seen in FIG. 7. FIG. 7 shows an alternative graft arrangement in which the graft strands  12   a  and  12   b  are placed together on one side of bone plug  20  and secured by suture  34 . Also, the replacement ligament may be provided in a straight single length and sutured to bone plugs without looping at all. Finally, by varying the size of the bone plugs in relation to the replacement ligament width, more of the circumference of the bone plug may be exposed without sacrificing necessary strength of the replacement ligament.  
         [0036]    Another embodiment is illustrated in FIG. 8. In this embodiment, a replacement ligament  10  is provided without bone plugs. Graft material  12  may be single-stranded or multiple-stranded. If graft material  12  is multiple-stranded as shown, the multiple strands may be created by bundling individual strands, by folding a strand back upon itself, or by a combination of both. FIG. 9 shows a cross section of FIG. 8 illustrating the multiple-stranded bundle created by the individual strands  14  and  16  folded back upon themselves and secured by bundle sutures  38 .  
         [0037]    Still referring to FIG. 8, multiple stranded replacement ligament graft distal end  46  maybe secured using bundle sutures  38 , preferably provided in a whip stitch  39 . As shown,  14   a,    14   b,    16   a,  and  16   b  are secured with bundle sutures  38  in a whip stitch  39  at both proximal and  45  and distal end  46 . Also as shown, long strand sutures  30  are provided as separate sutures. Alternatively, long strand sutures  30  may be provided as the ends of bundle sutures  38 . For some applications, long strand sutures  30  may be omitted. In the illustrative embodiment of FIGS. 8 and 9, the replacement ligament  10  is made of two individual strands  14  and  16 , which are folded back upon themselves at proximal end  45 , creating a quadruple-strand graft. However, it will be understood that other strand arrangements are within the scope of this invention.  
         [0038]    [0038]FIG. 10 shows an embodiment similar to that illustrated in FIG. 8. However, at proximal end  45 , a set of semi-bundle sutures  40  only partially bundle graft material  12 , creating a loop  42 . Loop  42  may be particularly useful for fixation methods which employ a cross pin. Alternatively, loop  42  may be provided in applications where autograft bone plugs are preferred. A similar loop may be provided at distal end  46 .  
         [0039]    [0039]FIG. 11 illustrates an embodiment of this invention which was prepared in a manner similar to the embodiment illustrated in FIG. 8, but includes one bone plug  20 . In this illustrative embodiment, bone plug  20  is included within the whip stitching  39  of bundle sutures  38  at distal end  46  of replacement ligament  10 . The whip stitching  39  of bundle sutures  38  may provide enough support to hold the bone plug  20  in place. Alternatively, bone plug sutures similar to those shown in FIG. 5 may be necessary to provide proper attachment strength. Other arrangements for bone plug  20  are possible within the scope of this invention. Also, the proximal end  45  of this embodiment may be looped as in FIG. 10, or closed as in FIG. 8.  
         [0040]    A cross section of FIG. 11, shown in FIG. 12, illustrates a possible placement of replacement ligaments  14  and  16  around bone plug  20 . The whip stitching  39  of the bundle sutures  38  secures bone plug  20  within the replacement ligament strands  14   a,    14   b,    16   a,  and  16   b.  FIG. 13 shows a cross section of an alternative arrangement to FIG. 12 wherein all four strands of ligaments  14  and  16  may be located on one side of bone plug  20 . The stitching of the bundle sutures is not shown. Alternatively, ligaments  14  and  16  may be secured with sutures similar to those shown in FIG. 7.  
         [0041]    As illustrated in FIGS.  11 - 13 , the graft material is provided in the quadruple strand arrangement of FIG. 8. However, other multiple strand arrangements may be suitable.  
         [0042]    [0042]FIG. 14 illustrates another embodiment which is similar to that illustrated in FIG. 11, as the replacement ligaments  14  and  16  are looped at proximal end  45  and bone plug  22  is incorporated within the whip stitching  39  of bundle sutures  38 . However, with the embodiment illustrated in FIG. 14, bone plugs  20  and  22  are provided on both ends. In this embodiment, the replacement ligaments  14  and  16  of proximal end  45  are held together with a set of bundle sutures  41 . As shown, the same sutures  41  are used to suture bone plug  20 . This embodiment ensures that bone plug  22  will not move during insertion into a patient&#39;s knee. Other methods of securing bone plug  20  are possible.  
         [0043]    According to another embodiment, allograft replacement ligaments may be prepared using patella tendons which are harvested with bone plugs (not shown). Preparation of these replacement ligaments includes pre-attached sutures to facilitate subsequent insertion. The sutures may be made of absorbable or non-absorbable suture material. These replacement ligaments are provided in a variety of sizes and are packaged and sterilized for convenient use. The package may also include graft fixation devices.  
         [0044]    In a method of construction of this invention, graft material may be obtained from a variety of sources including allograft, xenograft, or synthetic material. If allograft or xenograft material is used, it can be prepared by removing extraneous tissue, cutting the material to the proper size, and assembling into ready to use configurations, as described above. If bone plugs are provided, they are cut to the proper size, and they may be provided with slots to aid in suturing during assembly. The bone plugs may be allograft or xenograft bone material, or they may be made from bone substitutes such as hydroxyapatite, tri-calcium phosphate, or others.  
         [0045]    Prior to assembly, the replacement ligament material may go through a series of washes. Such washes may include ALLOWASH™ solution, sterile water, isopropyl alcohol, antibiotic solution, and a final rinse with sterile water. ALLOWASH™ as described in U.S. Pat. No. 5,820,581, hereby incorporated by reference, is a solution comprising three detergents, i.e., (1) polyoxyethylene-4-lauryl ether having the chemical formula C 9 H 19 (OCH 2 CH 2 ) 4 OH, (2) octylphenol-ethyleneoxide, and (3) poly(ethylene glycol)p-nonyl-phenol-ether. The &#39;581 patent also discloses various alternative cleaning solutions and washing protocols which may be used in the practice of this invention. The antibiotic solution may be a solution of endotoxin-free deionized/distilled water or ethanol, containing antibiotics, antiviral agents, hydrogen peroxide, permeation enhancers, organic acids, or a dilute solution of strong acids. Preferably, the antibiotic solution contains a mixture of bacitracin and polymyxin in sterile water. U.S. Pat. No. 5,797,871, hereby incorporated by reference, describes other methods of cleaning allograft bone. It should be understood that these and other techniques for cleaning the allograft tissue are within the scope of this invention.  
         [0046]    Following assembly, the graft material may be placed under tension. For example, a tension spring may be used. This tension keeps the replacement ligament in proper alignment during subsequent preservation and packaging. The spring or other tension device may be removed before packaging or just prior to use.  
         [0047]    Once the allograft or xenograft replacement ligaments have been washed, they are preserved. In one preferred embodiment of preparing the graft material, preservation is accomplished by a lyophilization cycle which may, for instance, last five days. Preferably, the replacement ligament is placed in sterile gauze within a sterile bottle prior to lyophilization, and the bottle is stoppered under vacuum following lyophilization to finish the packaging. When used, the replacement ligament may be reconstituted in either sterile water or saline, and such reconstitution may take approximately one hour under vacuum. For grafts which have been bottled under vacuum, this reconstitution may take place simply by introducing water or saline into the bottle by use of a sterile needle. Preferably, the needle would pierce the stopper without breaking the vacuum.  
         [0048]    Alternatively, following washing, the replacement ligaments may be preserved by being fresh frozen. In this method of preservation, the replacement ligaments preferably are placed in a peelable soft package. Air is removed from the package by suction, and the package can be heat-sealed. A second, slightly larger, soft package may be used for additional protection of the graft material. For further sterilization, the replacement ligaments may be irradiated as is known in the art, for example with gamma radiation. Finally, the replacement ligaments are stored frozen, for instance from about −70° C. to about −80° C., and may be distributed on dry ice. When needed, frozen grafts are thawed, preferably in sterile saline. Because fresh frozen replacement ligaments are not fully dried, the reconstitution step required for lyophilized grafts may be omitted.  
         [0049]    Various fixation devices, including interference screw, cross-pin, tab-loop anchor, screw-and-washer fixation devices, may be packaged with the replacement ligament, thus providing the surgeon with a kit for replacing a damaged ligament.  
         [0050]    Synthetic materials may also be used in the practice of this invention. The graft material and/or bone plugs may be made of synthetic materials, and the replacement ligament may be constructed using a similar variety of techniques. The replacement ligament of this embodiment is then sterilized, and it is packaged according to the requirements of the materials used. As with allograft or xenograft replacement ligaments, the synthetic replacement ligaments may be packaged with or without graft fixation devices.  
         [0051]    The replacement ligaments of this invention may be provided in a variety of lengths, with or without a variety of sizes of bone plugs. For ACL or PCL repair, lengths of 60 to 150 mm, preferably 90 to 100 mm may be used, with bone plugs preferably having a diameter of 6 to 10 mm. However, certain PCL techniques may require longer grafts, and individual patients or alternative fixation techniques may require grafts of larger or smaller sizes. Also, grafts for use in the replacement of other ligaments or other soft tissue may be larger or smaller. Thus, while sizes are disclosed, it will be understood that these sizes are merely typical of sizes needed for repair of the cruciate ligaments. Other sized grafts are within the scope of this invention.  
         [0052]    As an example of use, a replacement ligament  10  of this invention may be used to repair an anterior cruciate ligament. FIG. 15 illustrates the graft of the present invention after it has been inserted into the patient. The surgical site and the tibial tunnel  72  and femoral tunnel  70  are drilled as known in the art, see, for example, U.S. Pat. No. 5,671,695, incorporated herein by reference, preferably while replacement ligament graft  10  is reconstituting or thawing. After tibial and femoral tunnels  72  and  70 , respectively, have been drilled, a slotted guide pin (not shown) may then be passed through tibial tunnel  72  and into femoral tunnel  70 . The knee is placed in hyperflexion and the guide pin can be passed out the anterolateral femoral cortex, where it then exits the skin.  
         [0053]    Distal end long strand sutures  29  of the replacement ligament  10  are looped through the slotted guide pin eyelet (not shown) and pulled through the joint, exiting at the anterolateral femur. A pin puller, for example the DePuy Pin Puller (Cat. No. 2972-96-000), may be helpful in pulling the sutures through the joint. The graft is gently pulled into the tibial tunnel  72 . A guidewire is then passed through a stab wound made at the level of the tibial plateau and just medial to the patellar tendon and into the femoral tunnel  70  while maintaining a position along the femoral wall. At this point the knee is flexed an additional 15-20 degrees beyond the flexion angle used to drill the femoral tunnel  70  to accommodate the guidewire position. A fixation device  66 , such as the DePuy Phantom SofThread Screw, can be used to fix replacement ligament  10  into femoral tunnel  70 .  
         [0054]    After the guidewire has engaged the proximal aspect of the femoral tunnel  70 , it is tapped into femur  80  with a mallet, for example the DePuy Mallet (Cat. No. 2972-23-000), to avoid rotation of the guidewire and the fixation device. A second guidewire is then passed through the tibial tunnel  72  anterior to graft  10 . It may be useful to pull graft  10  back out of the tibial tunnel  72  to introduce the tibial wire.  
         [0055]    After both wires are in position, the graft is then pulled up the tibial tunnel  72  and into the femoral tunnel  70 . The proximal long strand sutures  30  are used to determine complete seating of graft  10  in femoral tunnel  70 . Once the graft is tensioned both proximally and distally, the fixation device  66  is inserted through an anteromedial puncture wound.  
         [0056]    The fixation device  66  is then advanced until the entire head is within femoral tunnel  70  and preferably countersunk beneath an edge of the femoral tunnel  70 . The knee is then placed at approximately 20-30 degrees of flexion. Graft  10  is loaded to 20 lbs. 20 times by pulling on the long strand sutures  30  exiting the tibial tunnel  72 . Using approximately 15 lbs. of preload, a tibial fixation device, for example tibial screw  67 , is inserted along the anterior graft surface and advanced with driver  78  until it is completely within the tibial tunnel  72 .  
         [0057]    The knee is checked for mobility and stability and when acceptable, the proximal sutures  30  are pulled through the skin and removed. Sutures and any excess graft material flush with the tibial tunnel  72  should be transected. However, care should be taken to not cut the sutures that hold the graft together. The wounds are then closed in a standard fashion. It is understood that the above is illustrative of a surgical technique employing replacement ligaments of this invention. Other surgical techniques are within the scope of this invention.  
         [0058]    Although the invention has been described with reference to certain preferred embodiments, variations and modifications exist within the scope of the present invention.