Abstract
A soft tissue fixation system, most typically applicable to orthopedic joint repairs, such as anterior cruciate ligament (ACL) knee repair procedures, comprises an implant which is placeable in a tunnel disposed in a portion of hone, wherein the tunnel is defined by walls comprised of bone. A first member is deployable outwardly to engage the tunnel walls for anchoring the implant in place in the tunnel, and a second member is deployable outwardly to engage tissue material to be fixed within the tunnel. The second member also functions to move the tissue material outwardly into contact with the tunnel walls to promote tendon-bone fixation. Extra graft length is eliminated by compression of the tendon against the bone at the aperture of the femoral tunnel, which more closely replicates the native ACL and increases graft stiffness. The inventive device provides high fixation of tendon to bone and active tendon-bone compression. Graft strength has been found to be greater than 1,000 N (Newtons), which is desirable for ACL reconstruction systems.
Claims
1. A method of securing soft tissue in a bone tunnel in a femur, the method comprising: positioning an anchor in a bone tunnel in a femur alongside a first length of soft tissue and a second length of soft tissue, the anchor having a distal end, a proximal end, and a longitudinal axis; outwardly deploying, in the bone tunnel and relative to the longitudinal axis of the anchor, a first compression pad and a second compression pad so as to compress the first length of soft tissue between the first compression pad and a wall of the bone tunnel at the proximal end of the anchor and the second length of soft tissue between the second compression pad and the wall of the bone tunnel at the proximal end of the anchor; and outwardly deploying, in the bone tunnel and relative to the longitudinal axis of the anchor, a first arm and a second arm so that the first arm and the second arm contact the wall of the bone tunnel proximate the distal end of the anchor for anchoring the anchor in the bone tunnel.
2. The method of claim 1, wherein the first length of soft tissue and the second length of soft tissue comprise a tendon graft.
3. The method of claim 1, wherein the first arm and the second arm displace bone in the wall of the bone tunnel.
4. The method of claim 1, wherein the first arm and the second arm extend into bone in the wall of the bone tunnel.
5. The method of claim 1, wherein the first arm includes a first fin at a distal end of the first arm and the second arm includes a second fin at a distal end of the second arm.
6. The method of claim 5, wherein, after outwardly deploying the first arm and the second arm in the bone tunnel, the first fin and the second fin both point toward the distal end of the anchor.
7. The method of claim 1, wherein, along the anchor, the first compression pad and the second compression pad are longitudinally spaced apart from the first arm and the second arm.
8. The method of claim 1, wherein the first compression pad and the second compression pad are located on opposite sides of the anchor.
9. The method of claim 8, wherein the first compression pad and the second compression pad outwardly deploy relative to one another in a first plane, and wherein the first arm and the second arm outwardly deploy relative to one another in a second plane, the first plane being perpendicular to the second plane.
10. The method of claim 1, wherein the anchor is sized for deployment through a 5-8 mm cannula.
11. The method of claim 1, wherein said outwardly deploying the first compression pad and the second compression pad and said outwardly deploying the first arm and the second arm is caused by advancing, in the bone tunnel, a first anchor member within a second anchor member along the longitudinal axis of the anchor.
12. The method of claim 11, wherein the first anchor member comprises a compression wedge.
13. The method of claim 1, wherein the first length of soft tissue and the second length of soft tissue comprise a ligament graft.
14. The method of claim 1, wherein the first arm and the second arm penetrate into bone in the wall of the bone tunnel.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIG. 1 is an isometric view of an embodiment of a device constructed in accordance with the principles of the present invention;
(2) FIG. 2A is a top view of the device of FIG. 1 in an undeployed configuration;
(3) FIG. 2B is a side view of the device of FIG. 2A;
(4) FIG. 3A is a top view of the device of FIG. 1, wherein the deployment screw is starting to deploy the compression pads;
(5) FIG. 3B is a side view of the device of FIG. 3A;
(6) FIG. 4A is a top view of the device of FIG. 1, wherein the compression pads have been fully deployed;
(7) FIG. 4B is a side view of the device of FIG. 4A;
(8) FIG. 5 is a top view of the device of FIG. 1, wherein the wedge is starting to deploy the arms;
(9) FIG. 6 is a top view of the device of FIG. 1, wherein the wedge is halfway engaged;
(10) FIG. 7A is a top view of the device of FIG. 1, wherein the implant has been fully deployed;
(11) FIG. 7B a side view of the device of FIG. 7A;
(12) FIG. 8 is a view illustrating the implant of FIG. 1, as it is deployed in the femoral tunnel of a patient;
(13) FIG. 9A is a view illustrating tendon compression as effected by embodiment of FIGS. 1-7;
(14) FIG. 9B is a detail view of a portion of FIG. 9A denoted by a circle labeled as 9B;
(15) FIG. 10 is a perspective view, in isolation, of a deployment screw for use in the embodiment of FIGS. 1-7;
(16) FIG. 11A is a perspective view of a compression pad for use in the embodiment of FIGS. 1-7;
(17) FIG. 11B is a perspective view of a second compression pad;
(18) FIG. 12 is a perspective view of the body of the implant of FIGS. 1-7;
(19) FIGS. 13A and 13B are perspective views of arms for use in the embodiment of FIGS. 1-7;
(20) FIGS. 14A and 14B are perspective views of the wedge for use in the embodiment of FIGS. 1-7;
(21) FIGS. 15A and 15B are perspective views of modified embodiments of the implant of FIGS. 1-7 with arms flipped to engage with the cortical surface during a soft tissue repair procedure;
(22) FIGS. 16A and 16B are perspective views of yet another embodiment of the implant of the invention, wherein the body is used as the wedge;
(23) FIG. 17 is a table summarizing the performance of an implant constructed in accordance with the principles of the present invention, as shown in FIGS. 1-7;
(24) FIG. 18 is an isometric view of a further modified embodiment of the invention;
(25) FIG. 19 is an exploded view of the embodiment of FIG. 18;
(26) FIG. 20 is a plan view of the embodiment of FIG. 18, in an undeployed configuration;
(27) FIG. 21 is a side view of the embodiment of FIG. 20;
(28) FIG. 22 is a plan view of the embodiment of FIG. 20, wherein the deployment screw is starting to deploy the compression pads;
(29) FIG. 23 is a side view of the embodiment of FIG. 22;
(30) FIG. 24 is a view illustrating the implant of FIGS. 18-23 deployed in a femoral tunnel;
(31) FIG. 25 is a detailed view similar to FIG. 24, showing tendon compression performed by the deployed inventive device;
(32) FIG. 26 is a perspective view of the deployment screw;
(33) FIG. 27 is a view showing the body of the implant;
(34) FIG. 28 is a view similar to FIG. 27, but showing the implant from a different orientation;
(35) FIG. 29 is an isometric view of an arm in accordance with the invention;
(36) FIG. 30 is an isometric view from a different orientation than FIG. 29, showing the arm;
(37) FIG. 31 is a view of the wedge of the invention;
(38) FIG. 32 is a data table;
(39) FIG. 33 is an isometric view of another embodiment of the invention, comprising an undeployed cortical fixation implant;
(40) FIG. 34 is an isometric view of the cortical fixation implant of FIG. 33, from a different orientation;
(41) FIGS. 35 and 36 are top and side views, respectively, of the cortical implant of FIGS. 33 and 34;
(42) FIGS. 37 and 38 are top and side views, respectively, of the cortical implant of FIGS. 33 and 34, wherein the implant is beginning to be deployed;
(43) FIGS. 39 and 40 are top and side views, respectively, of the cortical implant of FIGS. 37 and 38, wherein the implant is in a deployed state;
(44) FIGS. 41 and 42 show a deployment sequence for the cortical fixation implant;
(45) FIG. 43 is an isometric view of the body of the implant of FIG. 33, showing integrated compression pads;
(46) FIG. 44 is a cross-sectional view of the body of FIG. 43, taken along the lines 44-44 of FIG. 45;
(47) FIG. 45 is a side view of the implant of FIG. 43;
(48) FIG. 46 is a perspective view of the wedge of the invention;
(49) FIGS. 47 and 48 are views of the arm of the invention;
(50) FIG. 49 is a perspective view of the compression wedge of the invention;
(51) FIG. 50 is a perspective view of the deployment screw of yet another embodiment of the inventive implant; and
(52) FIGS. 51-52 are isometric views of an additional embodiment of a cortical implant of the invention, wherein FIG. 51 shows the device in its undeployed configuration and FIG. 52 shows the device in its deployed configuration;
(53) FIGS. 53-54 are isometric views of still another embodiment of a cortical implant of the invention, wherein FIG. 53 shows the device in its undeployed configuration and FIG. 54 shows the device in its deployed configuration; and
(54) FIG. 55 is a view of the femur and tibia of a patient's leg, showing a substantially completed ACL repair.
DETAILED DESCRIPTION OF THE INVENTION
(55) Referring now more particularly to the drawings, procedures and anchoring devices for repairing soft tissue are illustrated. In FIG. 1, one embodiment of an implant 10, constructed in accordance with the principles of the present invention, is shown. The implant 10 comprises a deployment screw 12, which protrudes through a pair of compression pads 14 and 16. The implant 10 comprises a body 18, through which the deployment screw 12 also protrudes. The deployment screw 12, at its distal end, is threaded into a wedge 20.
(56) The left compression pad 14 slides into the right compression pad 16, and they attach to one another. Two pins 22 attach a pair of arms 24 to the body 18. There is a track 26 on each side of the wedge 20, best seen in FIG. 14A. Each wedge track 26 attaches to a track post 28 (FIG. 13B) on a corresponding one of the arms 24. The wedge tracks 26 function to prevent the wedge from rotating during deployment of the implant.
(57) The compression pads 14, 16 slide into a pair of body tracks 30 (FIG. 12) in the body 18, which allow the pads 14, 16 to expand when the deployment screw 12 is rotated clockwise, as shown in FIGS. 2-4. The body tracks 30 also prevent the pads 14, 16 from rotating.
(58) In FIG. 10, the deployment screw 12 is shown in detail. This screw 12 comprises a quad lead section 32, with four separate thread starts. This means that, for every single turn on the screw, the linear distance it travels is four times what a single lead screw would be. This feature enables the user to turn the screw fewer times than would be required with a single start thread, approximating the same number of turns that the user would need during the implantation of an interference screw such as the above described Smith & Nephew RCI screw. Often, during implantation, an interference screw requires a notch to be placed at the edge of the femoral tunnel aperture to allow the screw to start engaging into the bone. Advantageously, the need for this step is eliminated when deploying the implant of the present invention, resulting in a substantially easier implementation procedure.
(59) Accordingly, the present invention is easy to deploy as an interference screw, and requires fewer steps than in prior art approaches. The deployment screw 12 also provides a rigid backbone to support the implant. A screw head or compression pad deployer 34 deploys the compression pads 14, 16 as the screw 12 moves axially into the implant. Another feature of the screw 12 is a load transfer disk 36 that transfers some of the axial load from a junction between the screw head 34 and the body 18 to a junction between the load transfer disk 36 and the body 18. This load transferring feature allows for thinner side walls or struts 38 on the body 18 due to a decreased load on struts 38 (FIG. 12), which, in turn, allows a larger tendon to fit between the deployment screw 12 and the body 18.
(60) With reference now particularly to FIGS. 11A and 11B, the compression pads 14 and 16 are shown in greater detail. The left and right compression pads 14, 16, respectively, compress the tendons against the femoral tunnel wall to promote tendon-to-bone healing at the aperture of the tunnel. Unlike current approaches for more intimate tendon-to-hone contact that only reduce the space between the tendon and the tunnel wall, the present invention actively compresses the tendons against the bone tunnel. Compression pad tracks 40 engage the body tracks 30 and interlock them to the body 18. This joint also provides torsional resistance while moving the implant into place, and during initial deployment until the arms 24 start to engage with the bone. There are engagement slots 42 in each compression pad 14, 16, as shown, that engage with a deployment device that keep the implant 10 from rotating until the arms 24 engage the bone. The two compression pads 14, 16 snap together using compression pad snaps 44 to prevent premature deployment of the pads.
(61) Now referring to FIG. 12, the body 18 functions to trap the tendons on either side of the deployment screw 12. The compression pads 14, 16 engage the body tracks 30 and provide torsional strength to the body while inserting the implant into the femoral tunnel, thus allowing the compression pads 14, 16 to expand parallel to one another. The struts 38 also provide structural support for the deployment screw 12, wedge 20, and arms 24 to deploy against.
(62) The arms 24 have a few key design features, as best shown in FIGS. 13A and 13B. Fins 46 on the top of each arm provide torsional strength for the wedge-to-arm junction. The fins 46 also allow easier insertion into the femoral tunnel when inserting into a femoral tunnel that is drilled off-axis from the tibial tunnel. The portion of the arm 24 that engages with the bone has a tapered edge 48 which allows for ease of bone displacement during deployment. A support rib 50 disposed along the length of the arm 24 is also tapered for ease of bone displacement, and provides structural support during axial loading. Torsion pins 52 engage with a torsion hole 54 to provide additional torsional strength while the implant is being implanted into the femoral tunnel.
(63) FIGS. 14A and 14B show, in greater detail, particular constructional features of the wedge 20. The wedge 20 is threaded with a female quad lead thread 56 that matches the male quad lead thread 32 of the deployment screw 12. The track posts 28 engage with the wedge tracks 26 to provide torsional strength through deployment. A tapered nose 58 on the wedge 20 allows easier off-axis insertion into the femoral tunnel.
(64) Referring now to FIGS. 2-9, a preferred method of using the disclosed inventive implant will now be discussed. In FIGS. 2A and 2B, the implant 10 of FIG. 1 is shown in its undeployed orientation. A preferred procedure for deploying the implant is generally similar in many respects to the procedure disclosed in U.S. Patent Application Publication No. 2006/0155287, herein already expressly incorporated by reference.
(65) Thus, to accomplish tendon fixation using the exemplary methods and devices described herein, standard surgical preparation of the site and/or arthroscopic portals for access to the procedural region are performed. The joint is dilated with arthroscopic fluid if the procedure is to be performed arthroscopically. With open procedures, the device may easily be manipulated and deployed with a single hand. For arthroscopic procedures, the deployment device is introduced through a standard 5, 6, or 8 mm cannula placed into the joint. A range of preferred cannula sizes would be 2-11 mm.
(66) The procedures described herein are specifically adapted to repair of the ACL in a patient's knee. However, it should be kept in mind that the implants described herein may be used in numerous other soft tissue repair applications, using surgical procedures which are adapted to those applications.
(67) FIGS. 8 and 9A illustrate, from two different orientations, a hamstring ACL reconstruction, wherein the implant 10 is utilized to secure the ACL graft proximal to the femur 60 and distal to the tibia 62 of a patient. To deploy the implant 10, a bone tunnel 64 is drilled completely through the tibia 62 and partially through the femur 60. An actuator (not shown) is employed to insert the implant 10 distally through a tibial inlet aperture 66 and through the tibial tunnel 64, so that the implant 10 is finally disposed in a portion of the tunnel 64 which is within the femur 60, distal to a femoral aperture 68, as shown in FIGS. 8 and 9A.
(68) Now with respect to FIGS. 3 and 3A, once the implant 10 is in place within the femoral tunnel 64, as shown in FIG. 8, the deployment screw 12 is actuated (rotated) in order to advance the screw 12 axially distally into the implant body 18, and thus begin to deploy or expand the compression pads 14 and 16 outwardly. FIGS. 4 and 4A depict the next step, wherein advancement of the deployment screw 12 has caused the compression pads 14, 16 to fully deploy. As noted above, the screw head or compression pad deployer 34 acts to deploy the compression pads 14, 16 as it moves distally into the implant 10, as shown.
(69) As the deployment screw 12 continues to move distally through the implant 10, the distal end of the screw 12, comprising the male quad lead section 32 (FIG. 10), engages the female quad lead thread 56 of the wedge 20 (FIG. 14B). Continued axial distal movement of the screw 12 causes the threaded sections 32 and 56 to cooperate to move the wedge 20 axially in a proximal direction, as shown in FIG. 5. This proximal movement of the wedge 20 causes the arms 24 to begin to deploy outwardly. In FIG. 6, the wedge 20 is shown in a position where it is about halfway engaged within the separating arms 24.
(70) In FIGS. 7A and 7B, the wedge 20 is fully proximally engaged with the body 12 of the implant 10, such that the arms 24 are, consequently, fully deployed. In FIG. 8, the implant 10 is shown in this fully deployed condition.
(71) FIGS. 9A and 9B illustrate tendon compression as effected by the deployed implant 10. In these figures, tendons 70 are compressed by deployed compression pads 14, 16 against the femoral tunnel wall in order to promote tendon-to-bone healing at the aperture of the tunnel. Advantageously, the inventive approach actively compresses the tendons against the hone tunnel.
(72) Alternative implant designs are shown in FIGS. 15 and 16. In particular, FIGS. 15A and 15B illustrate an alternative embodiment (with like elements being labeled with like reference numerals to those used in connection with the embodiment of FIG. 1) wherein the arms 24 are flipped to the other side of the body 18. The modified arms 24 are designed to permit the tendons (not shown) to pass by them and engage with the cortical bone. The arm-to-body joint is a pin-less design with a track way in the body that secures the arm 24 in place.
(73) FIGS. 16A and 16B illustrate yet another modified embodiment wherein, once again, like elements are labeled with like reference numerals as those used in connection with the earlier embodiments. In this embodiment, the implant 10 uses the body 18 as a wedge.
(74) Testing has been done by the inventors to verify the functionality of the disclosed invention of FIGS. 1-7. As shown in FIG. 17, the inventors found that pull-out forces for the implant 10 were significantly higher than those of a predicate device, the RCI interference screw available from Smith & Nephew.
(75) In FIGS. 18-21 there is shown another implant embodiment 110, wherein like elements are identified with like reference numerals as for the embodiment of FIGS. 1-14, preceded by the numeral 1. As shown, the deployment screw 112 protrudes through the compression pads 114 and 116, which are each integrated into the body 118. The deployment screw 112 is threaded at its distal end into the wedge 120. Two pins 122 attach a pair of arms 124 to the body 118, as shown.
(76) As noted above, in this embodiment the compression pads 114, 116 are integrated into the body 118. This feature permits the use of a shorter implant than is the case for the implant of FIG. 1. A track 126 in the wedge 120 attaches to track posts 128 on the arms 124 (FIG. 29), which keep the wedge 120 from rotating during deployment. The compression pads expand as the implant is deployed. In particular, the screw 112 expands the pads 114, 116 outwardly by siding on a compression taper 72 (FIG. 27), as shown in FIGS. 20-23. Moreover, as the deployment screw 112 rotates, the wedge 120 expands the arms 124 as also shown in FIGS. 20-23. Once the screw 112 is fully seated, the expanded arms 124 fully engage with adjacent cancellous bone 74, thus locking the anchor in place, as shown in FIG. 24.
(77) The deployment screw 112 (FIG. 26) has a male quad lead section 132 with four separate thread starts, as in the prior disclosed embodiment. This means that for every one rotation of the screw, the linear distance it travels is four times that which a single lead screw would travel. This enables the user to turn the screw fewer times than would be required with a single start thread, approximating the same number of turns that the user would need during the implantation of an interference screw such as the RCI screw available from Smith & Newphew. Oftentimes, during implantation, an interference screw such as the RCI screw requires a notch to be placed at the edge of the femoral tunnel aperture to permit the screw to start engaging the hone. However, the present invention avoids the need for such a step, resulting in an easier implantation procedure. The invention is easy to deploy as an interference screw, and requires fewer steps. The deployment screw 112 also provides a rigid backbone to support the implant. A reverse threaded hex 75 is preferably provided to drive the screw.
(78) The screw head or compression pad deployer 134 deploys the compression pads 114, 116 as the screw 112 advances axially into the implant. Another feature of the screw is the provision of a load transfer disk 136 that transfers some of the axial load from the screw head 134 to body junction to the disk to body junction. This allows for thinner side walls or struts 138 on the body 118 due to the decreased load on the struts, which in turn allows a larger tendon to fit between the deployment screw 112 and the body 118.
(79) As shown in FIG. 25, the compression pads 114, 116 compress the tendons 170 against the femoral tunnel wall to promote tendon-to-bone healing at the aperture of the tunnel. Unlike prior art approaches for more intimate tendon-to-bone contact that only reduce the space between the tendon and the tunnel wall, the present invention actively compresses the tendons against the bone tunnel. The compression pads 114, 116 in this embodiment are integral with the body 118.
(80) The body 118 functions to trap the tendons 170 on either side of the deployment screw 112. The struts 138 are split, as shown at reference numeral 76 (FIG. 28), to allow the integrated compression pads 114, 116 to expand and compress the tendon against the bone tunnel. They also provide structural support for the deployment screw 112, wedge 120, and arms 124 to deploy against.
(81) The arms 124 include a few key design features, as particularly shown in FIGS. 29 and 30. Fins 146 on the top provide torsional strength for the wedge 120 to arm 124 junction. They also allow easier insertion into the femoral tunnel when inserting into a femoral tunnel that is drilled off-axis from the tibial tunnel. The portion of the arm 24 that engages with the bone has a tapered edge 148 which allows for ease of bone displacement during deployment. The support rib 150 along the length of the arm 124 is also tapered for ease of bone displacement and provides structural support during axial loading. The torsion pins 152 engage with a torsion hole 154 to provide additional torsional strength while inserting into the femoral tunnel.
(82) As in the prior embodiment, the wedge 120 is threaded with a female quad lead thread 156 that matches the complementary threads 132 on the deployment screw 112. The track posts 128 on the arms 124 engage with the wedge track 126 to provide torsional strength through deployment. A tapered nose 158 allows easier off-axis insertion into the femoral tunnel.
(83) FIG. 32 is a table similar to that of FIG. 17, presenting data generated by the inventors which indicates that pull-out forces for the implant 110 were significantly higher than those of a predicate device, the RCI interference screw available from Smith & Nephew.
(84) Still another embodiment of the inventive implant is illustrated in FIGS. 33-54, wherein like elements to those of the prior embodiments are identified by like reference numerals, preceded by the numeral 2. This embodiment 210 utilizes the cortical bone for fixation in combination with tendon-to-bone compression. In this version of the invention, the deployment screw 212 is offset to one side of the implant 210, for the purpose of permitting easier passing of tendon through the orifice. This implant deploys in two steps. The deployment screw 212 is rotated clockwise as an arm 78 and wedge 220 slide together across tapered faces 80 (FIG. 46) and 82 (FIG. 48) until they lock together with their respective cortical locks 84, 86. The wedge 220 and the arm 78 lock into place by filling a majority of the cross section of the femoral tunnel. Thus, the implant is free to move in the femoral tunnel, allowing tactile feedback to ensure engagement of a cortical tab 88 with the cortex.
(85) The screw is then rotated so that it is advanced the remainder of the way, and the compression wedge 90 engages with the compression pads, thereby pressing the tendon against the bone tunnel wall. A track 92, 94 in the compression pads 214, 216 and compression wedge 90 prevents the compression wedge from engaging unevenly. A progression of deployment of the implant 210 is illustrated in FIGS. 35-42. FIGS. 43-50 illustrate various components of the embodiment. In the undeployed state, the arm is engaged with the wedge with the arm's track posts 228 engaging with a T-bar 96 of the wedge 220. This prevents the arm 78 from moving during insertion. Also, to prevent the wedge 220 from rotating during deployment, the track post 228 is inserted into a torsion slot 100.
(86) Modified cortical fixation implant designs are illustrated in FIGS. 51-54. FIGS. 51 and 52 illustrate a modified wedge and only one arm which allows engagement with the cortical bone. FIGS. 53 and 54 illustrate the same embodiments as in FIGS. 51 and 52, wherein the screw is to one side of the implant.
(87) FIG. 55 has been incorporated into this application to illustrate a substantially completed ACL repair procedure. FIGS. 8 and 9, as well as FIGS. 24 and 25 and FIGS. 41 and 42, illustrate the installation of the femoral anchor of the present invention, in various embodiments. However, as one skilled in the art would understand, to complete the repair procedure further steps are necessary. Once the femoral anchor has been deployed and installed, as previously described, the anchored tendons 70 extend proximally from the femoral tunnel through the tibial tunnel and out through tibial aperture 66. To complete the procedure, a tibial anchor 102 is preferably installed, to anchor the tendon bundles in place, as shown in FIG. 55. Once this anchor is in place, the proximal ends of the tendon bundles are trimmed to complete the procedure. This portion of the ACL reconstruction procedure is fully explained in co-pending U.S. application Ser. No. 11/725,981, which has already been fully and expressly incorporated by reference herein. Any suitable tibial anchor 102 may be used in conjunction with femoral anchors of the type disclosed in this application, but the tibial anchors shown and described in the '981 patent application are presently preferred.
(88) Accordingly, although exemplary embodiments of the invention has been shown and described, it is to be understood that all the terms used herein are descriptive rather than limiting, and that many changes, modifications, and substitutions may be made by one having ordinary skill in the art without departing from the spirit and scope of the invention.
