Abstract:
A novel and improved canine elbow prosthesis and method of implanting same including a unique bi-compartmental prosthesis having bone receiving members and transverse pegs which may be implanted with a minimally invasive surgical technique.

Description:
BACKGROUND  
       [0001]     The article of manufacture and method relate broadly to a joint prosthesis and method of implanting same, and more particularly to a canine elbow prosthesis and novel and improved method of implanting same.  
         [0002]     The elbow joint is a hinge-type synovial joint formed where the distal end of the humerus articulates with the proximal end of the radius and ulna. Elbow dysplasia is a common debilitating condition that affects many dogs. The current surgical techniques result in an unacceptable failure rate of the implant due to the technical difficulties associated with the implantation procedure as well as excessive post-surgical physical therapy needs as a result of the invasiveness of the procedure and the abundance of soft tissue damage.  
         [0003]     There is therefore a need for a novel and improved joint arthroplasty that involves a minimally invasive surgical technique with a novel implant. The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools and methods which are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above described problems have been reduced or eliminated, while further embodiments are directed to other improvements.  
       SUMMARY  
       [0004]     The embodiments and methods set forth are exemplary and not for purposes of limitation. The present embodiments and methods are designed to provide a novel and improved elbow joint prosthesis and method of implanting same incorporating a first member having a first articulating surface portion of substantially hyperbolic paraboloid-shaped configuration as well as an opposite first bone fixation portion. A second member having a second articulating surface portion complementary to the first articulating surface portion, the second articulating surface portion having intersecting concave and convex surfaces defining alternate upwardly and downwardly curved projections as well as an opposite second bone fixation portion. The first and second members form an articulating prosthetic joint implant. The implant utilizes unique bone-stabilizing pegs as well as bone-receiving beads promoting bone ingrowth and reducing aseptic loosening. The anatomical duplication of the joint preserves flexion and extension while reducing excessive pulling of ligaments.  
         [0005]     Methods are also provided for a novel and improved joint arthroplasty. One such method offered by way of example but not limitation, for implanting an elbow endoprosthesis comprises the steps of exposing a medial humeral condyle of a subject, drilling a hole through the medial condyle, removing a condylar crown of the condyle, resurfacing articulating surfaces of the joint, implanting the prosthesis and reattaching the condylar crown to the medial humeral condyle by applying pressure therebetween. The medial approach in elbow joint arthroplasty, which is usually the area most affected by elbow dysplasia is proposed. This will result in a lower failure rate of the implant due to superior biomechanics of the implant, a lower degree of invasion of the joint capsule and ligamentous structure while reducing periarticular scarring. Resurfacing arthroplasty results in less structural damage to the joint, provides good trabecular structure to support the implant without subsidence, low infection rates and little bleeding. The current implant may be inserted without disarticulating the joint thereby enabling an earlier return to weight bearing and walking while providing for a minimally invasive technique. The implantation of a bicompartmental prosthesis with only one implantation step is novel and reduces trauma to the subject.  
         [0006]     The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those skilled in the art upon a reading of the Specification and study of the Drawings. In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the Drawings and by study of the following Description. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is an exploded view in perspective of an embodiment of a joint prosthesis;  
         [0008]      FIG. 2  is a side view of the implant of  FIG. 1  including the canine humerus, radius and ulna;  
         [0009]      FIG. 3  is a top plan view of the humeral component as shown in  FIG. 1 ;  
         [0010]      FIG. 4  is a side view of the humeral component shown in  FIG. 1 ;  
         [0011]      FIG. 5  is a cross-sectional view about line  5 - 5  of the humeral component shown in  FIG. 3 ;  
         [0012]      FIG. 6  is an elevational front view of the humeral component shown in  FIG. 1 ;  
         [0013]      FIG. 7  is a bottom plan view of the humeral component of  FIG. 1 ;  
         [0014]      FIG. 8  is a top plan view of the radioulnar component shown in  FIG. 1 ;  
         [0015]      FIG. 9  is a side view of the radioulnar component shown in  FIG. 1 ;  
         [0016]      FIG. 10  is a cross-sectional view taken about line  10 - 10  of the radioulnar component shown in  FIG. 8 ;  
         [0017]      FIG. 11  is an elevational front view of the radioulnar component shown in  FIG. 1 ;  
         [0018]      FIG. 12  is a rear view of the radioulnar component shown in  FIG. 1 ;  
         [0019]      FIG. 13  is a bottom plan view of the radioulnar component shown in  FIG. 8 ;  
         [0020]      FIG. 14  is a top plan view of the retaining element shown in  FIG. 1 ;  
         [0021]      FIG. 15  is a side view of the retaining element shown in  FIG. 1 ;  
         [0022]      FIG. 16  is a perspective view of a positioning system;  
         [0023]      FIG. 17  is a side view of the positioning system shown in  FIG. 16 ;  
         [0024]      FIG. 18  is a side view of a positioning system;  
         [0025]      FIG. 19  is an exploded diagrammatic view of the positioning system shown in  FIG. 18 ;  
         [0026]      FIG. 20  is a perspective view of a medial epicondylar osteotomy guide;  
         [0027]      FIG. 21  is a top plan view of the medial epicondylar osteotomy guide shown in  FIG. 20 ;  
         [0028]      FIG. 22  is a side view of the medial epicondylar osteotomy guide shown in  FIG. 20 ;  
         [0029]      FIG. 23  is a perspective view of an alignment guide and Center of Rotation post;  
         [0030]      FIG. 24  is a top plan view of the alignment guide shown in  FIG. 23 ;  
         [0031]      FIG. 25  is an exploded view of the alignment guide and a drill guide; and  
         [0032]      FIG. 26  is a top plan view of the drill guide shown in  FIG. 25 . 
     
    
       [0033]     Exemplary embodiments are illustrated in referenced Figures of the drawings. It is intended by the embodiments and Figures disclosed herein are to be considered illustrative rather than limiting.  
       DESCRIPTION  
       [0034]     In the embodiments shown in  FIGS. 1 through 15 , there is provided an implant  11  with a humeral condylar component  13  and a radioulnar component  29 . The humeral component  13  includes a first articulating surface portion  17  of substantially saddle-shaped configuration, as shown in  FIGS. 6 and 7 , and an opposite first bone fixation portion  14 , as shown in  FIGS. 3 and 4 . Geometrically, the saddle-shaped configuration of the first articulating surface portion  17  is broadly in the form of a hyperbolic paraboloid where sections parallel to and above the X-Y coordinates (horizontal plane) are hyperbolas symmetrical with the X axis, and sections parallel to and below the X-Y plane are hyperbolas symmetrical with the Y axis. Sections parallel to the other two coordinate planes are parabolas wherein those parallel to the X-Z plane open upward, while those parallel to the Y-Z plane open downward. See  FIG. 6 . The humeral condylar component  13  is made of cobalt-chrome (Co—Cr), molybdenum and titanium, Ti-alloy or ceramic but may also be made of other materials. The first articulating surface  17  as shown in  FIG. 7  has a longitudinally extending angular groove  15  and simulates or approximates the natural shape of a canine trochlea humeri which is a medially located, pulley-shaped member on a canine. The groove  15  extends diagonally across the surface and extends at an acute angle to an imaginary line through a major axis of the first articulating surface portion  17 .  
         [0035]     The first bone fixation portion  14  of the humeral component  13  has a concave form  21  that is opposite to the first articulating surface  17  and includes transversely extending peg members or protuberances  23 . The peg members  23  may be hollow or have shallow openings  22  at one end with the open end extending up to outer peripheral edges  16  of the first bone fixation portion  14 . The openings  22  are designed to receive a retaining piece  47  which will be discussed in more detail at a later point. The pegs  23  typically are evenly spaced and extend transversely to a major axis of the humeral component  13 . The peg members  23  may extend the width of the component  13  and in this embodiment do not extend beyond an outer peripheral edge  16  of the humeral component  13 . Alternatively, the peg members  23  could extend beyond the outer edges of the component. The first bone fixation portion  14  may also include porous members, such as, PCA beads  27  which also promote bone growth. The PCA beads are manufactured by Bio-Vac, Inc of Michigan, USA. Other possible fixation members include hydroxyl apatite (HA) coating, titanium plasma spray coating or Resorbably Blast Media Coating to name a few. Bony fixation of prosthetic implants is encouraged with surface extensions, such as, the peg members  23  and beaded porous ingrowth surfaces. A proximal portion  20  of the humeral component  13  which is the first bone fixation portion  14  contacts a distal surface  28  of the humerus  12  providing for an interference fit between the bone fixation portion and the humerus  12 . See  FIG. 2 .  
         [0036]     The radioulnar component  29  has opposing surfaces including a second articulating surface portion  31  and a second bone fixation portion  33 . The radioulnar component  29  is half-moon shaped and is slightly tapered at a posterior end. The second articulating surface portion  31  has a saddle-shaped configuration that faces cranially. The articulating surface portion  31  contains a medial ridge member  37  having intersecting convex and concave surfaces defining alternate upwardly and downwardly curved projections. The ridge member  37  simulates a canine trochlear notch and is complementary to the groove  15  of the first articulating surface portion of the humeral component  13 . The ridge  37  as shown in  FIG. 8 , extends diagonally across the concave surface at a mid-level portion between the concave and convex surfaces and extends at an acute angle to an imaginary line through a major axis of the second articulating surface portion  31 . The angular extension of the ridge  37  approximates the natural angular extension of a trochlear notch.  
         [0037]     As shown in  FIG. 1 , the first articulating surface portion  17  of the humeral component  13  forms an articulating system with the second articulating surface portion of the radioulnar component  29 . The radioulnar component  29  as shown in  FIGS. 9 and 10  is made of two pieces, namely, the second articulating surface portion  31  which is made of ultra-high molecular weight polyethylene but may also be made of other materials and the second bone fixation portion  33  which is composed of cast cobalt chrome molybdenum, titanium or ceramic, as well as other materials. This allows the articulating surfaces of the humeral and radioulnar components  17  and  31  to have metal-on-plastic contact. Other combinations may be used without departing from the intent of providing a smooth, articulating surface.  
         [0038]     The second bone fixation portion  33  of the radioulnar member  29  contains at least one porous peg member  40  with a hollow opening  41  to aid in implant positioning and bone reabsorption. As with the transversely extending peg members  23  of the humeral component  13 , the porous peg members  40  of the radioulnar component  29  also may be transversely extending along a major axis of the radioulnar component  29 . Further, the porous peg members  40  in this embodiment as shown in  FIG. 12  do not extend beyond the outer peripheral edge  42  of the second articulating surface portion  31  of the radioulnar component  29 . This is by way of example, but the porous peg members may also extend beyond the outer peripheral edges of the radioulnar component. As with the humeral component  13 , the second bone fixation portion  33  of the radioulnar component  29  may also integrate porous beads  45  to promote bone ingrowth. A distal portion of the radioulnar component  29  which is the second bone fixation portion  33  contacts proximal surfaces of the ulna  51  and radius  53  providing for an interference fit between the second bone fixation portion  33  and the radius and ulna.  
         [0039]     In one embodiment, the groove  15  and ridge member  37  are not centered but the complementary components are longitudinally extending and intersect a major axis only at the center as discussed previously, requiring a different joint prosthesis for the right and left joints. It will be evident that in another embodiment, the prosthesis including humeral and radioulnar components, which is isometric, can be used for a right or left joint arthroplasty with the complementary components extending longitudinally along a centered vertical plane.  
         [0040]     The articulating surfaces of the humeral and radioulnar components are polished to a smooth finish promoting unencumbered articulation between the two surfaces. The bone fixation portions of the humeral and radioulnar components contain the porous peg members  23  and  40  as well as the porous beading  27 ,  45  on their surfaces to promote bone ingrowth. The humeral and radioulnar components  13  and  29 , respectively, are releasably linked together with an aligning or retaining piece or retainer  47  as shown in  FIGS. 1, 14  and  15  which aids in positioning of the implant  11  within the joint cavity  48  as shown in  FIG. 2  and is removed once the implant is securely in place. The implant retainer  47  serves multiple functions. Due to the complex articular surfaces of the humeral and radioulnar components, it is necessary that when placed in the subject, both components be oriented at the proper depth and in the correct state of articulation. The canine elbow is typically aligned at 90° flexion. The implants, to function correctly together, should both be at their respective 90° of flexion. The retaining piece  47  has four posts  49 ,  50 ,  52  and  54  that releasably link the humeral component  13  and the radioulnar component  29 . See  FIG. 1 . The posterior ulnar post  49  on the retainer  47  is slightly larger and is slightly angled which compensates for the tapering in the posterior end of the radioulnar component  29  and assures that the implants cannot go in crooked or at an angle to the sagittal plane that exists at the elbow at the point of intersection between the center line of the humerus and the center line of the radioulnar component. The retainer  47  also functions as a tool in which one can press or hammer upon an extension  44  of the retainer  47  to assure maximum insertion into the joint cavity of the implant  11 . Due to the nature of the implant, the radioulnar component  29  relies heavily upon the press-fit nature of the component to insure stability. The humeral component  13  is captured between the medial and lateral epicondyles preventing movement laterally on a frontal or transverse plane.  
         [0041]     As embodied and broadly described herein, the elbow arthroplasty of the present embodiment includes a humeral component  13  and a complementary radioulnar component  29  as well as the retaining piece  47 . There will also be described a novel and improved method for implantation as well as embodiments of a positioning device  55  as shown in  FIGS. 16-19  with an angular support arm  66  and a drill guide  81 ; an osteotomy guide  93  as shown in  FIGS. 20-22  and an alignment and drill guide  103  and  105 , respectively, as shown in  FIGS. 23-26  for the installation of the implants. Broadly, the positioning device  55  immobilizes and positions a joint for prosthesis implantation. The positioning device  55  is adjustable so that different size joints may be positioned. The positioning device  55  in combination with the drill guide  81  allows for accurate drilling on a joint while the positioning device in combination with a burr and a base  59  allow for accurate removal of cartilage and minimal subcondylar bone from a joint.  
         [0042]     The implant  11 , instruments and method are useful in the treatment of degenerative joint disease in canines as well as other species including humans and allow for a minimally invasive implantation technique. The joint capsule is not disarticulated during the process and the ligaments and muscles remain attached to the condylar crown. The bicompartmental prosthesis is implanted in one stage as opposed to separate stages which involve securing the implant in consecutive steps to the humerus, radius and ulna.  
         [0043]     In one method, a radiographic evaluation including X-rays as well as arthroscopic surgery are performed on the subject to determine the degree of disease and to measure and estimate the proper size of implant to be used in the procedure. A Mylar overlay, not shown, is also used to determine the size of the implant necessary. The ulna  51  and the radius  53  are fused to allow fixation of the radioulnar component to the radius and ulna.  
         [0044]     The subject is then stabilized with the positioning device  55  as shown in  FIGS. 16 and 20 . The positioning device consists of a tray or base  56  having numerous apertures which in one embodiment includes opposing spaced arcuate slots  57 ,  57 ′ for insertion of a lower cylindrical end  58 ′ of an adjustable post member  58 . A lock nut  58 ″ is threadedly adjustable to establish the desired effective height of the post  58 , and the post  58  is both slidable and rotatable with respect to the tray  56 . The tray  56  also includes a linear slot  60 , also adapted to receive a post member  61  that is adjustable in the same manner as the post  58 . The arc section post  58  supports an upwardly facing, saddle-shaped radioulnar cradle  62  with a clamp or strap  69  and the linear section post  61  supports an upwardly facing, saddle-shaped humeral cradle  63  with a clamp or strap  69 ′. The tray  56  includes the base  59  that is designed to support and immobilize the epicondyle of a subject. The arc-shaped slots  57 ,  57 ′, linear slot  60  in combination with the post members  58 ,  61  and the base  59  allow for a subject joint to be taken through 120° of rotation without having to reposition the patient. This will be discussed at a later stage. Further, the opposing arc sections  57 ,  57 ′ allow for immobilization and rotation of the reverse joint from a medial or lateral aspect. For example, the positioning system  55  with the opposing arc-shaped slots  57 ,  57 ′ allow for immobilization of a subject&#39;s left or right joint, also allowing for approach from a medial or lateral aspect. The linear section post  61  is both slidable and rotatable to accommodate a variety of appendage sizes.  
         [0045]     The positioning device  55  also includes a support post  67  over which one end of an adjustable arm  66  fits. The arm  66  includes a universal swivel  66 ′ at its center and opposite ends so as to be capable of twisting as well as moving vertically and horizontally. A free end of the arm  66  includes a clamp  83  that enables attachment of a resurfacing component such as a drill or handpiece  72 . In this instance the handpiece is manufactured by Blackstone Industries, Inc. of Bethel, Conn. enabling a user to attach, for example, a burr or drill. The handpiece may take many forms and is not limited to the device shown but is designed to allow attachment of a tool for accomplishing a multitude of tasks such as, the accurate removal of bone and cartilage. The handpiece  72  has a flexible shaft  74  running to an electric motor, not shown. The handpiece  72  is clamped to the adjustable arm  66  with clamp  83  and enables the user to accurately remove cartilage and bone from a vertical or horizontal position, virtually removing operator error. The swivel arm may take many forms but is designed to enable an approach from virtually any angle while providing stabilization. The adjustable arm  66  as well may take different forms and may be positioned at various angles once again to allow for varied approaches in stabilization. The arm  66  may hold a multitude of tools including lasers, light sources and scalpels to name a few.  
         [0046]     It will be evident that the positioning device  55  is also conformable for use with the drill guide  81  as shown in  FIGS. 18-19 . The drill guide  81  has an arm  75  extending horizontally and upwardly as shown in  FIG. 18 . The drill guide  81  attaches to the base  59  at a variety of possible locations, shown in  FIGS. 16-19  at  65 , depending upon the size of the joint and location of the center of rotation on the particular subject. The base  59  has an upper flat surface  77  including 3, 2.5 mm holes  68  that are 2 mm to 6 mm off-center, in 2 mm intervals, approximately 45° cranial and distal, depending upon the elbow, that allows for a 2.5 mm drill  64  to pass through. A 2.5 mm center of rotation (COR) post  70  as shown in  FIGS. 23 and 25  is inserted through the drilled opening in the joint to aid in positioning of the joint during the drilling and burring process.  
         [0047]     Attached to the drill guide  81  is a drill guide arm  79  which lines up with one of three holes  68  located on the surface  77  of the base  59 . A thumbscrew  76  attaches the vertical arm  75  to the base  59 . The drill guide arm  79  possesses a drill guide hole  80  through which the 2.5 mm drill bit will fit. This aids in drilling off-center holes for optimizing the location of the center of rotation of the elbow. See  FIG. 19 . The drill guide  81  is typically used in conjunction with the positioning system  55  for accurate drilling purposes.  
         [0048]     As an example, the humerus  12  of a canine is placed in the humeral cradle  63  and secured, the fused radius  53  and ulna  51  of the canine is secured in the radioulnar cradle  62  and secured, exposing the canine&#39;s medial joint for osteotomy. The joint is placed on the base  59  and is stabilized. As referred to earlier, a 2.5 mm hole, “COR hole” is drilled through the epicondyle, medial to lateral, using the drill guide arm  75  and passing a 2.5 mm drill  64  through the drill guide hole  80 , the epicondyle and the corresponding hole  68  in the base  59 . The COR hole aids in proper positioning of the implant as well as positioning of the alignment and drill guides. Once the COR hole is drilled, the osteotomy guide  93  as shown in  FIGS. 20-22  is clamped to the medial epicondyle of the subject. The osteotomy guide  93  is a hemostat-like instrument having a first end  84  that establishes a contact point with the joint, typically along the articular cartilage on the cranial side of the humerus. A second end  85  having an osteotomy plate  86  including a cutting groove  87  that lies along the same horizontal plane as the contact point  84  and a serrated portion  88  which clamps onto the epicondyle. A saw blade, not shown, is inserted through the cutting groove  87  and intersects with the contact point  84  that has been secured to the caudal ridge of the distal end of the humerus. The guide allows for accurate bone cutting without removing excessive bone which tends to result in subsidence. The osteotomy guide also minimizes invasion of the joint capsule. Once the medial epicondyle has been osteotomized, not shown, the cut portion which is the condylar crown is reflected back along with the attached muscles and ligaments, exposing the distal medial humeral condyle.  
         [0049]     The next step involves attaching the alignment guide  103  as shown in FIGS.  23  to  25  with the COR post  70  to the positioning system  55 . The 2.5 mm hole which was previously drilled accommodates the COR post  70  through the epicondyle. The COR post  70  is inserted through the 2.5 mm hole, into the base  59  and the alignment guide  103  is attached by sliding the alignment guide  103  over the COR post  70  at point  80 ′ as shown in  FIG. 23 . The guide  103  is rotated until cranial peg hole  129  lines up with the cranial proximal ulnar and the caudal portion of the radius. K-wires are inserted down through respective holes  104  and  106  in the alignment guide and into the joint, locking the guide in the desired position. The alignment guide  103  is in the same shape as a cross-section of the entire implant at a 90° articulation.  
         [0050]     A specially designed burr saw  64 ′ shown in  FIGS. 16 and 17  is inserted into the handpiece  72 . The handpiece is clamped to the arm  66  with clamp  83 . The burr saw  64 ′ is designed with a slightly larger head  64 ″ which acts as an “end mill” or “router bit” to accurately remove remaining cartilage and minimal subcondylar bone while preserving good trabecular structure. Subsidence typically occurs when the compressive stresses or trabecular bone struts exceed the strength of the bone, resulting in microfractures and resorption of trabeculae. Resurfacing of the trochlea humeri and the trochlear notch of the radius and ulna is performed with the burr saw  64 ′ and a depth measuring device or depth limiting stop, not shown, is used to insure proper depth penetration. The burr saw removes the large arc-shaped portion  109  within the alignment guide  103 , leaving four smaller areas consisting of the openings  129 ,  130 ,  131 ,  132  that accommodate the peg members  23  and  40  of the implant  11  for the drill  64  to remove.  
         [0051]     Due to the insertion of the implant from the medial aspect, the humeral and radioulnar articulating surfaces may be resurfaced without having to break or otherwise open or expose the articulating surfaces of the elbow joint. The removal of articular cartilage as well as a minimal amount of subcondylar bone on both sides of the joint simultaneously without having to disarticulate the joint allows for a minimally invasive procedure.  
         [0052]     Once the alignment guide  103  has been inserted and the majority of resurfacing is complete, a drill guide plate  112  is placed on a top surface  91  of the implant alignment guide  103 . It slides down over the COR post  70  at point  80 ″ and has four holes  129 ′,  130 ′,  131 ′,  132 ′ that line up with the holes  129 ,  130 ,  131 ,  132  on the alignment guide. It is then locked in place by a screw  113  passing through the drill guide  112  and into the alignment guide  103  at points  90 ,  90 ′. Using the angular support arm  66  and the handpiece  72 , a specified drill size is chosen and inserted into the handpiece  72 . The drill bit  64  is lined up with the opening  80  in the arm guide  75  and four holes are drilled corresponding with the holes  129 ′,  130 ′,  131 ′,  132 ′ on the drill guide plate  112 . The drill guide plate  112  is then removed.  
         [0053]     The implant  11  is lined up with the implant retaining plate  47  in place, all four holes lining up with the four horizontal pegs  23 ,  40  located on the first bone fixation portion  14  of the humeral component  13  and the second bone fixation portion  33  of the radioulnar component  29 . This allows the implant  11  to be inserted where the cancellous articulating surfaces have been removed. Using a hammer device, not shown, the implant  11  will be tapped into place within the elbow joint. With the pegs running horizontally, the implant may not rotate on a sagittal plane while inside the elbow. The horizontal pegs also prevent the implant from sliding side to side based on a press-fit of the joint.  
         [0054]     The implant is set on the distal medial humeral condyle and is impacted or pounded so that there is almost no distance between the implant and the bone. Optimally, the implant is set within 1 mm of the bone. If there is more than 1 mm. of space between the implant  11  and the bone, there is typically poor bone ingrowth. Cementless fixation is utilized in our method but is set forth as an example, not as a limitation. Once the implant is in place, the medial epicondylar crown, including the attached ligaments and muscles, is reattached, not shown, using a 3.5 mm cancellous screw and a spiked washer, both not shown. The cancellous screw is manufactured by Veterinary Orthopedic Implant or Synthes and New Generation Devices. The spiked washers are also manufactured by Veterinary Orthopedic Implants and Synthes.  
         [0055]     While a number of exemplary aspects, embodiments and methods have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions and subcombinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and subcombinations as are within their true spirit and scope.