Void filling joint prosthesis and associated instruments

Abstract

A method of forming a bone void for receipt of a prosthesis, comprising the steps of: inserting a stem of a reaming guide assembly into an intramedullary canal of a bone, the reaming guide assembly having first and second reamer guides disposed adjacent to each other, the first and second reamer guides being connected to an end of the stem; reaming the bone through the aperture of the first reamer guide to form a first bone void; inserting the lobe trial into the first bone void; and reaming the bone through the aperture of the second reamer guide to form a second bone void.

Claims

1. A method of preparing a distal femur for receipt of a prosthesis comprising: reaming a distal end of a femur via a conical reamer to so as to form a conical bone void at a distal end of the femur, the conical bone void having a lateral boundary thereof defined by the conical shape of the conical reamer, the lateral boundary being disposed at a lateral extent of the bone void furthest from a longitudinal axis of the bone void; and inserting a void filling prosthesis into the bone void such that a conical leg extending from a body of the void filling prosthesis conforms to the lateral boundary of the conical bone void.

2. The method of claim 1, further comprising implanting a femoral component onto the distal femur after inserting the void filling prosthesis into the bone void such that a stem connected to the femoral component is inserted into the femur through an opening of the body and a cam box of the femoral component is positioned between the conical leg and another conical leg of the void filling prosthesis.

3. A method of preparing a distal femur for receipt of a prosthesis comprising: reaming through a distal end of the femur via an intramedullary reamer such that a shaft thereof extends from the distal end of the femur; reaming the distal end of the femur over the shaft of the intramedullary reamer via a cannulated reamer such that the cannulated reamer forms a central opening of a bone void at a distal end of the femur; removing the cannulated reamer and intramedullary reamer from the bone; inserting a stem of a reaming guide into the intramedullary canal after the removing step; reaming the distal end of the femur via a conical reamer coupled to the reaming guide to form a first offset opening of the bone void; and inserting a void filling prosthesis into the bone void, the void filling prosthesis being conically shaped and conforming to the central and first offset openings of the bone void when implanted therein.

4. The method of claim 3, wherein the central opening has a greater cross-sectional dimension than an opening formed by the intramedullary reamer.

5. The method of claim 4, further comprising: inserting a reamer guide assembly into the central opening so that a portion of the reamer guide assembly extends from the central opening, the reamer guide assembly having a longitudinal axis and first and second passageways extending therethrough, the first and second passageways each defining a guide axis offset from the longitudinal axis of the reamer guide.

6. The method of claim 5, wherein: reaming the first offset opening of the bone void includes driving the conical reamer along the guide axis defined by the first passageway into the distal end of the femur.

7. The method of claim 6, further comprising: inserting the conical reamer into the first passageway prior to reaming the first offset opening by passing a shaft of the conical reamer through a first slot in a side of the reamer guide assembly that communicates with the first passageway.

8. The method of claim 7, further comprising: inserting the conical reamer into the second passageway by passing the shaft of the conical reamer through a second slot in a side of the reamer guide assembly that communicates with the second passageway, and driving the conical reamer along the guide axis defined by the second passageway into the distal end of the femur to form a second offset opening, the void filling prosthesis conforming to the second offset opening when implanted in the bone void.

9. The method of claim 8, further comprising: inserting a stabilizer member into the first offset opening prior to reaming the second offset opening so that the stabilizer member is coupled to the reamer guide assembly and extends from the first passageway of the reamer guide assembly into the first offset opening.

10. The method of claim 9, further comprising: sliding a bushing disposed over the shaft of the conical reamer into the first passageway once the reamer shaft is disposed within the first passageway, the bushing having an external dimension substantially corresponding to an internal dimension of the first passageway so as to constrain movement of the bushing transverse to the guide axis of the first passageway.

11. The method of claim 10, wherein reaming the first offset opening includes sliding the conical reamer relative to the bushing while the bushing remains disposed within the first passageway.

12. The method of claim 3, wherein the void filling prosthesis includes a central body and a pair of legs extending away from the central body.

13. The method of claim 12, wherein the legs of the void filling prosthesis each have a conically shaped exterior surface that tapers inwardly toward the central body.

14. The method of claim 13, wherein the exterior surface of each of the legs includes a porous material.

15. The method of claim 12, wherein the central body has an outer surface that is at least partially conical.

16. A method of preparing a distal femur for receipt of a prosthesis comprising: removing a first femoral prosthesis previously implanted on a distal end of the femur; reaming through a distal end of the femur via an intramedullary reamer such that a shaft thereof extends from the distal end of the femur; reaming the distal end of the femur over the shaft of the intramedullary reamer via a cannulated reamer such that the cannulated reamer forms a first portion of a bone void at a distal end of the femur; removing the intramedullary reamer and cannulated reamer from the bone; inserting an elongate member of a reamer guide into the bone void after the removing step; reaming the distal end of the femur with a reamer coupled to the reamer guide to form a second portion of the bone void; and inserting a void filling prosthesis into the bone void, the void filling prosthesis conforming to the first and second portions of the bone void when implanted therein.

17. The method of claim 16, wherein the inserting step includes inserting a central body of the void filling prosthesis into the first portion of the bone void and a leg of the void filling prosthesis into the second portion of the bone void, the leg extending from the central body.

18. The method of claim 17, wherein inserting the void filling prosthesis into the bone void includes aligning an opening that extends through the entirety of the central body with an intramedullary canal of the femur.

19. The method of claim 18, further comprising: implanting a second femoral prosthesis onto the distal femur such that a stem connected to the second femoral prosthesis is inserted into the femur through the opening of the central body.

20. The method of claim 17, wherein exterior surfaces of the leg and central body are conically tapered.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:

(2) FIG. 1 shows a perspective view of one embodiment of a void filling prosthesis.

(3) FIG. 2 shows a front view of the void filling prosthesis of FIG. 1.

(4) FIG. 3 shows another perspective view of the void filling prosthesis of FIG. 1.

(5) FIG. 4 shows a side perspective view of the void filling prosthesis of FIG. 1.

(6) FIG. 5 shows a top perspective view of another embodiment of a void filling prosthesis of FIG. 1.

(7) FIG. 6 shows a bottom perspective view of the void filling prosthesis of FIG. 5.

(8) FIG. 7 shows a side view of the void filling prosthesis of FIG. 1 interfacing with a femoral component.

(9) FIG. 8 shows a rear view of the void filling prosthesis of FIG. 1 interfacing with a femoral component.

(10) FIG. 9 shows a side view of the void filling prosthesis of FIG. 5 interfacing with a femoral component.

(11) FIG. 10 shows a top perspective view of the void filling prosthesis of FIG. 5 interfacing with a femoral component.

(12) FIGS. 11-19 show a method and instrumentation for forming a bone void to receive the prostheses of FIG. 1 and FIG. 5.

DETAILED DESCRIPTION

(13) FIGS. 1-4 depict a first embodiment of a void filling prosthesis 10. The void filling prosthesis 10 includes a central body 11, a medial leg 13, and a lateral leg 12. In another embodiment, the void filling prosthesis 10 may include a central body and only a medial leg 13 or lateral leg 12. The central body 11 is generally cylindrical. However, this cylindrical shape may take the form of a portion that has a constant diameter and a portion that is slightly tapered such that it is generally frustoconical. The central body 11 includes an aperture 18 that extends through the central body 11 in order to allow the passage of an IM stem of a femoral component 30. This aperture 18 forms a wall 19, which is integrated with the lateral and medial legs 12, 13 forming a monolithic structure.

(14) The lateral and medial legs 12, 13 may be offset posteriorly from a median transverse axis of the central body 11. Further, the lateral and medial legs 12, 13 may be located in close proximity, but may be separated generally by a space 17 that penetrates through both legs and forms a saddle-like structure in order to provide clearance for a femoral cam box 33 of a femoral component 30. This space 17 forms inner surfaces 15a-d that abut the femoral cam box 33 when implanted. These inner surfaces 15a-d may be flat, planar walls, or they may be terraced to provide surfaces conducive for bonding with bone cement. Further, inner surface 15d may be obliquely angled with respect to the longitudinal axis of the central body 11 in order to account for the angle of the IM stem (not shown) with respect to the cam box.

(15) Further geometric features may be incorporated into the medial and lateral legs 12, 13 in order to provide clearance for the structure of the femoral component 30. For instance, inclined surfaces 14a-d may be fashioned into each leg in order to provide clearance for a bone interface surface 35 of the femoral component 30.

(16) The remainder of the lateral and medial legs 12, 13 that has not been shaped to form clearance space is depicted as having a generally frustoconical profile. This geometric profile is preferred in order to conform more closely to bone voids created by the reaming instrumentation. However, this is merely an example of a geometry that the medial and lateral legs 12, 13 may form. The legs 12, 13 may have other geometries, such as box-like geometries. Further, the medial and lateral legs 12, 13 may be symmetric with respect to one another, or they may be asymmetric where one leg 12, 13 may be larger than the other 12, 13 and/or one leg 12, 13 may have a different geometry. A conical structure 16a-b may be disposed at one end of each of the lateral and medial legs 12, 13. This conical structure 16a-b may help prevent rotation of the prosthesis 10 when implanted in the bone and help the prosthesis 10 settle into the proper orientation and more closely conform to the void formed by the reaming instruments.

(17) Referring to FIGS. 1-4 and 7-8, each leg 12, 13 is shown to include two removable portions 20a-d at an end of each leg 12, 13. While two removable portions 20a-d are shown, this is merely an example. Each leg 12, 13 may include any number of selectively removable portions 20a-d, including just one. Alternatively, one leg 12, 13 may include at least one selectively removable portion 20a-d while the other leg 12, 13 may have no selectively removable portions 20a-d. Where one or more selectively removable portions 20a-d is removed from a leg 12, 13, the length of the leg 12, 13 is decreased in order to make room in the joint cavity for a bone augment, for example. This removability provides the operator the operating room capability and flexibility to configure the void filling device 10 to work in conjunction with a bone augment, or alternatively work where no augment is needed. Thus, each selectively removable portion 20a-d is shaped to conform to the geometries of the void filling prosthesis 10 as though they will never be removed. Further, where these portions 20a-d are not removed, they provide structural support to the prosthesis 10.

(18) Where there are multiple selectively removable portions 20a-d, they are layered along the length of each leg 12, 13 as far as needed to accommodate a bone augment. Each selectively removable portion 20a-d may have a first section 22a-d made from a weaker material and a second section 21a-f made from a stronger material, where the two sections 21a-f, 22a-d are layered along the length of each leg 12, 13. In a preferred embodiment, the weaker and stronger material may be made from the same metallic material, but the weaker material may have a higher porosity than that of the stronger material allowing for a seamless transition between these two sections 21a-f, 22a-d, but providing a region for easy separation. Separation is made easier by the fact that the more porous material is easier to separate and that the two sections 21a-f, 22a-d are visually recognizable indicating the separation location. In one embodiment, the separation location may be designated by a small chamfer to receive a cutting blade between the first section 22a-d of one selectively removable portion 20a-d and the second section 21a-f of another selectively removable portion 20a-d. An example of the porous metallic material may be titanium, titanium alloy, stainless steel, cobalt chrome alloys, tantalum or niobium formed by direct laser remelting as described in U.S. Pat. No. 7,537,664 titled “Laser-Produced Porous Surface,” the entirety of which is incorporated-by-reference herein fully set forth herein and which is assigned to the same entity as the present invention. Additional examples are disclosed in U.S. application Ser. No. 11/027,421, filed Dec. 30, 2004, Ser. No. 11/295,008, filed Dec. 6, 2005, and Ser. No. 13/441,154, filed Apr. 6, 2012, and U.S. Pat. Nos. 8,350,186 and 8,147,861, the entireties of which are incorporated-by-reference herein as if fully set forth herein.

(19) In an alternative embodiment, the weaker material may have the same porosity as the stronger material, but may be constructed from a material that has a lower modulus than the stronger material. In another embodiment, the entire void filling prosthesis 10 may be constructed from a porous metallic material including the selectively removable portions 20a-d with little or no variations in the porosity, but that the selectively removable portions 20a-d have score marks to designate the cutting points. In a further embodiment, the first section 22a-d may have an outer shell that is the same porosity as the remainder of the void filling prosthesis 10, and an interior portion constructed from the weaker material.

(20) These selectively removable portions 20a-d may be removed by cutting along the weaker section 22a-d generally parallel and adjacent the stronger section 21a-f of another selectively removable portion 20b, 20d that is more proximate the central body using a cutting device. For instance a cutting device may be a guillotine-like device, an example of which is disclosed in U.S. application Ser. No. 12/002,002, filed Dec. 13, 2007, the entirety of which is incorporate-by-reference herein as if fully set forth herein. Where the selectively removable portion 20b, 20d is the last selectively removable portion along the length of that particular leg 12, 13, the leg 12, 13 may have a layer of stronger material 21c, 21f just adjacent to the weaker section 22b, 22d of that selectively removable portion 20b, 20d to facilitate removal.

(21) The remainder of the void filling prosthesis 10 may also be partially constructed from porous metallic material as described above. In one embodiment, the surfaces in contact with the femoral component 30, such as internal surfaces 15a-d, may be constructed of solid metallic material, such as titanium as an example, while the remainder of the void filling prosthesis 10 may be constructed of porous metallic material.

(22) FIGS. 5 and 6 depict an alternative embodiment wherein the bone void filler 10′ does not include selectively removable portions 20a-d, but has substantially the same geometries as prosthesis 10. This embodiment may also be constructed from the same materials as that of prosthesis 10, including portions of porous metallic material. Further, this embodiment may also be constructed from solid metal or high strength polymeric material.

(23) FIGS. 7-10 depict the interface between the void filling prosthesis 10, 10′ and a femoral component 30. The femoral component 30 may be any femoral component 30, for example a femoral component 30 utilized in a posterior stabilized or total stabilized total knee prosthesis, for example the Scorpio® TS femoral component (Howmedica Osteonics, Mahwah, N.J.).

(24) The void filling prosthesis 10, 10′ may be placed in contact with the femoral component such that aperture 18 of the central body 11 is placed over a stem portion of the femoral component 30 and the inner surfaces 15a-d are placed in contact with the cam box 33. In one embodiment, bone cement is placed between the inner surfaces 15a-d and the cam box 33 to provide for additional support. Such inner surfaces 15a-d may be terraced to provide more surface area for bonding to the cement.

(25) In one embodiment, the distal ends of the legs 12, do not contact the bone contacting surface 35 of the femoral component in order to provide some space for bone cement to flow and to provide space so that the operator can make minor corrections to the rotation of the femoral component 30.

(26) A set of guided instruments may be provided to form the bone void to receive the void filling prosthesis. Included in this set of instruments may be an IM reamer 40, a boss reamer 50, a reamer guide assembly 60, an alignment handle 90, an alignment pin 100, a lobe reamer assembly 110, and a lobe trial 120.

(27) The IM reamer 40, as depicted in FIG. 11, may include a shaft 42 that includes a plurality of depth indicators 44 situated along the length of the shaft 42 at designated intervals, and a reamer head 43 disposed at one end of the shaft. The other end of the shaft 41 may be configured to interface with a torque applying device, such as the chuck of a drill.

(28) The boss reamer 50, as depicted in FIG. 12, may include a cannulated shaft 52 that includes a boss reamer head at one end. The other end 51 of the shaft 52 may be configured to interface with a torque applying device, such as the chuck of a drill. The internal diameter of the cannulated shaft 52 is such that the shaft 52 may be slid over the IM reamer shaft, but generally not the IM reamer head, and rotated with respect to the IM reamer. The boss reamer head may also be cannulated to slide over the IM reamer shaft 42 and may have a cutting diameter substantially similar to the diameter of the central body 11.

(29) The reamer guide assembly 60, as depicted in FIGS. 13-19, may include a trial stem 70 and a reamer guide 80. The reamer guide generally includes a base 82, a support shaft 81, and a guide block 88. The trial stem 70 may be connected to one end of the base 82. In one embodiment, this connection may be a threaded connection, ball-detent connection or any other connection as is known in the art. The other end of the base 82 includes an abutment surface 89 and the support shaft 81 extending from the base 82 at an outward angle with respect the longitudinal axis of the trial stem 70. The support shaft 81 then bends such that the remainder of the support shaft 81 is generally parallel to the longitudinal axis of the trial stem 70. Integrated into the end of the guide shaft 81 is the guide block 88. The guide block 88 generally includes a handle hole 83 extending through the guide block 88 for receipt of an alignment handle 90 (described below), an alignment pinhole (not shown) for receipt of an alignment pin 100 (described below), and a first and second lobe reamer guide 84, 85. The first and second lobe reamer guides 84, 85 are generally disposed between the handle hole 83 and alignment pinhole. Both the first and second lobe reamer guides 84, 85 include a passageway 86a, 86b that is substantially cylindrical and a side-slot 87a, 87b extending through the sides of each of the lobe reamer guides 84, 85 into the passageway 86a, 896b. The longitudinal axes of the passageways 86a, 86b extend to a location on the abutment surface 89. Further, these longitudinal axes may be provided at various angles with respect to the longitudinal axis of the trial stem 70 in order to ream different bone void dimensions.

(30) The alignment handle 90, as depicted in FIGS. 14-19, is generally an elongate shaft with a flange disposed 91 along its length for abutting against the guide block 88. The alignment pin 100 is preferably a ⅛″ diameter pin with a length long enough to extend beyond the epicondyles when inserted into the guide block 88. While ⅛″ diameter is preferred so as to not obstruct the epicondyles from the operator's view, any diameter pin may be used.

(31) The lobe reamer assembly 110, as depicted in FIGS. 15-17 and 19, includes a lobe reamer head 117, a reamer shaft 116, a depth stop collar 112, and a bushing 113. The lobe reamer head 117 is disposed at one end of the reamer shaft 116, while the other end 111 of the shaft 116 is configured to interface with a torque applying device. The depth stop collar 112 is fixed to the reamer shaft 116 opposite the end of the lobe reamer head 117. The reamer shaft 116 has a diameter small enough to fit through the side-slot 87a, 87b of the first and second reamer guides 84, 85. The bushing 113 is disposed along a portion of the reamer shaft 116 between the reamer head 117 and depth stop collar 114 such that the bushing 113 can slide back and forth between the reamer head 117 and depth stop collar 112. The bushing 113 is generally cylindrical and includes a first segment 115 and second segment 114 where the second segment 114 generally has a larger diameter than the first segment 115. The diameter of the first segment 115 may be dimensioned to slide into and fit tightly within the passageway 86a, 86b of the first and second lobe reamer guides 84, 85.

(32) The lobe trial 120, as shown in FIGS. 18 and 19, includes a lobe trial head 125 and a first shaft segment 124 and a second shaft segment 122. The lobe trial head 125d is disposed at the end of the first shaft segment 124 and generally has a frustoconical shape with a portion removed along its length. The lobe trial head 125 is dimensioned to substantially match the bone void formed by the reamer head 116 and to substantially match at least one leg 12, 13 of the void filling prosthesis 10. While the lobe trial head 125 is depicted as having this shape, the lobe trial head 125 may have any shape depending on the shape of the reamer head 116 and the legs 12, 13 of the void filling prosthesis 10. The first shaft segment 124 has a diameter less than that of the second shaft segment 122 and is dimensioned to be capable of passing through the side-slot 87a, 87b of the first and second lobe reamer guides 84, 85. The second shaft segment 122 is dimensioned such that it can tightly fit and slide within the passageway 86a, 86b of the first and second lobe reamer guides 84, 85. An impact surface 121 is formed at the opposite end of the lobe trial 120 as that of the lobe reamer head 125. The impact surface 121 is a relatively broad and flattened surface so that the operator can impact the lobe trial 70 in order to seat the lobe trial head 125 into a bone void.

(33) In one embodiment of the present invention, a method for forming a void in bone to receive the void filling prosthesis 10, as illustrated by FIGS. 11-19. In this embodiment, the instruments, as described above, are utilized. While FIGS. 11-19 and the following description of the method are directed toward the preparation of a bone void within a femur, it is to be understood that this is merely an example. The following method may be utilized to prepare a bone void in any long bone.

(34) Referring to FIG. 11, the IM reamer 40 is depicted as reaming along the IM canal of a femur 200 until the bone 200 is flush with the requisite depth indicator 44. While it appears from FIG. 11 that the IM reamer 40 is passing through a femoral component, the femoral component is merely a depiction of the femur 200. With the IM reamer 40 remaining within the IM canal, the boss reamer 50 is slid over the shaft of the IM reamer, as shown in FIG. 12. The operator reams along the IM reamer shaft 42 until the boss reamer head 53 abuts the IM reamer head 40, thereby preventing further travel into the femur bone 200. The IM reamer and boss reamer 50 are then removed from the IM canal in preparation for further bone forming.

(35) Referring to FIG. 13, the reamer guide assembly 60 is assembled. In such assembly, the operator may select a trial stem 70 to match the IM reamer head diameter, and then attach the trial stem 70 to the reamer guide 80. In another embodiment, the IM reamer 40 may be attached to the reamer guide 80, thus taking the place of the trial stem 70. Attachment may be by a threaded engagement, with a ball detent, or any other engagement known in the art. Once the reamer guide assembly 60 is assembled, the trial stem 70 is inserted into the portion of the IM canal that was reamed by the IM reamer 40, and the base of the reamer guide 82 is inserted into the portion of bone reamed by the boss reamer 50. The operator may further seat the reamer guide assembly 60 to the proper depth by impacting the end of the guide block 88. The proper depth may be indicated when the reamer guide assembly 110 no longer moves when impacted and generally where the bone is flush with the bend in the support shaft 81.

(36) Referring to FIG. 14, with the reamer guide assembly 60 firmly seated within the IM canal, the alignment handle 90 is placed in the handle hole 83 until the flange 91 abuts the guide block 88, and the alignment pin 100 is placed in the alignment pinhole such that the alignment pin 100 extends from both sides of the guide block 88 beyond the periphery of the femur. The operator will then grip the alignment handle 90 and rotate the reamer guide assembly 60 within the IM canal until the alignment pin 100 is aligned with the transepicondylar axis or any axis of the operator's preference.

(37) Referring to FIG. 15, once alignment is achieved the lobe reamer assembly 110 is loaded into the first lobe reamer guide 84. This is achieved by moving the bushing 113 so that it abuts the depth stop collar 112, thereby exposing the reamer shaft 116 proximate to the reamer head 117. The reamer shaft 116 is then side-loaded through the side-slot 87a and into the passageway 86a. The resulting configuration should be such that the reamer head 116 is located on one side of the first lobe reamer guide 84 and the bushing 113 located on the other side, as shown in FIG. 15. The first segment 115 of the bushing 113 is then slid into the passageway 86a until the second segment 113 abuts the first lobe reamer guide 84, as shown in FIG. 16. The reamer head 116 is then advanced into the distal femur by applying a torque to the reamer shaft 115 until the depth stop collar 112 abuts the bushing 113 and the reamer head 116 abuts the abutment surface 82, as shown in FIG. 17. The reamer head 116 is then retracted from the femur and the reamer assembly 110 removed from the first lobe reamer guide 84 through the side-slot 87a.

(38) Referring to FIG. 18, the lobe trial 120 is then loaded into the passageway 86a of the first lobe reamer guide 84 in a similar fashion as the lobe reamer assembly 110. The first shaft segment 124 of the lobe trial 120 is passed through the side-slot 87a and into the passageway 86a. The lobe trial head 125 is then advanced into the first bone void. As the lobe trial head 125 is advanced, the second shaft segment 123 is advanced into the passageway 86a and the lateral protrusion 123 is advanced into the side-slot 87a. The lateral protrusion 123 ensures that the lobe trial 120 has the proper rotational alignment and also acts as a stop to prohibit rotation. In one embodiment of the lobe trial 120, the lateral protrusion 123 may be a pin that extends through the second shaft segment 122 and into a hole located in the first lobe reamer guide 84 to prevent both rotational and translational movement. The operator may then impact the impact surface 121 to fully seat the lobe trial 120. The lobe trial 120 may remain in place while a second bone void is formed in order to provide additional stability during reaming, as seen in FIG. 19.

(39) Referring to FIG. 19, the lobe reamer assembly 110 is side-loaded into the second lobe reamer guide 85 as previously described. The reamer head 117 is then advanced into the distal femur by applying a torque to the reamer shaft 116 until the depth stop collar 112 abuts the bushing 113 and the reamer head 117 abuts the abutment surface 89, thereby forming a second bone void for receipt of the void filling prosthesis 10.

(40) While this method has generally been described herein as utilizing one lobe reamer assembly 120 to form both bone voids, more than one lobe reamer assembly 110 having different geometries may be used depending on the geometry of the void filling prosthesis 10.

(41) Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.