Patent Abstract:
The invention is directed toward a portable surgical workstation and kit of accessory devises for cartilage implant formation comprising a base, a vise assembly mounted to the base, the vise assembly comprising a fixed jaw member and a moveable jaw member, each jaw member defining grasping surfaces for holding a bone workpiece. A shaft drive is threadably connected to the moveable jaw member and rotatably mounted in the fixed jaw member for transporting the moveable jaw toward and away from the fixed jaw. An articulated guide assembly is mounted to the fixed jaw member, the articulated guide means including a sleeve member and a plurality of moveable interconnected members selectively rotatable on a ball joint. A miter assembly defining a slot of a width to receive a surgical saw is mounted to at least one of the jaw members. The kit of accessory devices comprises a plurality of different diameter bushings which fit in the sleeve member and a plurality of different diameter cylindrical core cutter assemblies sized to fit in each respective sized bushing and a donor cutter guide adapted to fit in said sleeve.

Full Description:
RELATED APPLICATIONS 
       [0001]    There is no related application. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       REFERENCE TO SEQUENCE LISTING, A TABLE OR A COMPUTER PROGRAM LISTING COMPACT DISC APPENDIX 
       [0003]    None. 
       BACKGROUND OF THE INVENTION 
       [0004]    1. Field of Invention 
         [0005]    The present invention is generally directed toward the surgical treatment of articular chondral defects and is more specifically directed toward a surgical workstation for producing an allograft cartilage implant plug having a cartilage face and bone body. 
         [0006]    2. Description of the Prior Art 
         [0007]    Articular cartilage injury and degeneration present medical problems to the general population which are constantly addressed by orthopedic surgeons. Every year in the United States, over 500,000 arthroplastic or joint repair procedures are performed. These include approximately 125,000 total hip and 150,000 total knee arthroplastics and over 41,000 open arthroscopic procedures to repair cartilaginous defects of the knee. 
         [0008]    In the knee joint, the articular cartilage tissue forms a lining which faces the joint cavity on one side and is linked to the subchondral bone plate by a narrow layer of calcified cartilage tissue on the other. Articular cartilage (hyaline cartilage) consists primarily of extracellular matrix with a sparse population of chondrocytes distributed throughout the tissue. Articular cartilage is composed of chondrocytes, type II collagen fibril meshwork, proteoglycans and water. Active chondrocytes are unique in that they have a relatively low turnover rate and are sparsely distributed within the surrounding matrix. The collagens give the tissue its form and tensile strength and the interaction of proteoglycans with water give the tissue its stiffness to compression, resilience and durability. The hyaline cartilage provides a low friction bearing surface over the bony parts of the joint. If the cartilage lining becomes worn or damaged resulting in lesions, joint movement may be painful or severely restricted. Whereas damaged bone typically can regenerate successfully, hyaline cartilage regeneration is quite limited because of it&#39;s limited regenerative and reparative abilities. 
         [0009]    Articular cartilage lesions generally do not heal, or heal only partially under certain biological conditions due to the lack of vascularity. The limited reparative capabilities of hyaline cartilage usually results in the generation of repair tissue that lacks the structure and biomechanical properties of normal cartilage. Generally, the healing of the defect results in a fibrocartilaginous repair tissue that lacks the structure and biomedical properties of hyaline cartilage and degrades over the course of time. Articular cartilage lesions are frequently associated with disability and with symptoms such as joint pain, locking phenomena and reduced or disturbed function. These lesions are difficult to treat because of the distinctive structure and function of hyaline cartilage. Such lesions are believed to progress to severe forms of osteoarthritis. Osteoarthritis is the leading cause of disability and impairment in middle-aged and older individuals, entailing significant economic, social and psychological costs. Each year, osteoarthritis accounts for as many as 39 million physician visits and more than 500,000 hospitalizations. By the year 2020, arthritis is expected to affect almost 60 million persons in the United States and to limit the activity of 11.6 million persons. 
         [0010]    There are many current therapeutic methods being used. None of these therapies has resulted in the successful regeneration of hyaline-like tissue that withstands normal joint loading and activity over prolonged periods. Currently, the techniques most widely utilized clinically for cartilage defects and degeneration are not articular cartilage substitution procedures, but rather lavage, arthroscopic debridement, and repair stimulation. The direct transplantation of cells or tissue into a defect and the replacement of the defect with biologic or synthetic substitutions presently accounts for only a small percentage of surgical interventions. The optimum surgical goal is to replace the defects with cartilage-like substitutes so as to provide pain relief, reduce effusions and inflammation, restore function, reduce disability and postpone or alleviate the need for prosthetic replacement. 
         [0011]    Lavage and arthroscopic debridement involve irrigation of the joint with solutions of sodium chloride, Ringer or Ringer and lactate. The temporary pain relief is believed to result from removing degenerative cartilage debris, proteolytic enzymes and inflammatory mediators. These techniques provide temporary pain relief, but have little or no potential for further healing. 
         [0012]    Repair stimulation is conducted by means of drilling, abrasion arthroplasty or microfracture. Penetration into the subchondral bone induces bleeding and fibrin clot formation which promotes initial repair, however, the tissue formed is fibrous in nature and not durable. Pain relief is temporary as the tissue exhibits degeneration, loss of resilience, stiffness and wear characteristics over time. 
         [0013]    The periosteum and perichondrium have been shown to contain mesenchymal progenitor cells capable of differentiation and proliferation. They have been used as grafts in both animal and human models to repair articular defects. Few patients over 40 years of age obtained good clinical results, which most likely reflects the decreasing population of osteochondral progenitor cells with increasing age. There have also been problems with adhesion and stability of the grafts, which result in their displacement or loss from the repair site. 
         [0014]    Transplantation of cells grown in culture provides another method of introducing a new cell population into chondral and osteochondral defects. Carticel® is a commercial process to culture a patient&#39;s own cartilage cells for use in the repair of cartilage defects in the femoral condyle marketed by Genzyme Biosurgery in the United States and Europe. The procedure uses arthroscopy to take a biopsy from a healthy, less loaded area of articular cartilage. Enzymatic digestion of the harvested tissue releases the cells that are sent to a laboratory where they are grown for a period ranging from 2-5 weeks. Once cultivated, the cells are injected during a more open and extensive knee procedure into areas of defective cartilage where it is hoped that they will facilitate the repair of damaged tissue. An autologous periosteal flap with cambium layer is sutured around the defect to seal the transplanted cells in place and act as a mechanical barrier. Fibrin glue is used to seal the edges of the flap. This technique preserves the subchondral bone plate and has reported a high success rate. Proponents of this procedure report that it produces satisfactory results, including the ability to return to demanding physical activities, in more than 90% of patients and that biopsy specimens of the tissue in the graft sites show hyaline-like cartilage repair. More work is needed to assess the function and durability of the new tissue and determine whether it improves joint function and delays or prevents joint degeneration. As with the perichondrial graft, patient/donor age may compromise the success of this procedure as chondrocyte population decreases with increasing age. Disadvantages to this procedure include the need for two separate surgical procedures, potential damage to surrounding cartilage when the periosteal patch is sutured in place, the requirement of demanding microsurgical techniques, and the expensive cost of the procedure which is currently not covered by insurance. 
         [0015]    Osteochondral transplantation or mosaicplasty involves excising all injured or unstable tissue from the articular defect and creating cylindrical holes in the base of the defect and underlying bone. These holes are filled with autologous cylindrical plugs of healthy cartilage and bone in a mosaic fashion. The osteochondral plugs are harvested from a lower weight-bearing area of lesser importance in the same joint. Reports of results of osteochondral plug autografts in a small numbers of patients indicate that they decrease pain and improve joint function, however, long-term results have not been reported. Factors that can compromise the results include donor site morbidity, effects of joint incongruity on the opposing surface of the donor site, damage to the chondrocytes at the articular margins of the donor and recipient sites during preparation and implantation, and collapse or settling of the graft over time. The limited availability of sites for harvest of osteochondral autografts restricts the use of this approach to treatment of relatively small articular defects and the healing of the chondral portion of the autograft to the adjacent articular cartilage remains a concern. 
         [0016]    Transplantation of large allografts of bone and overlying articular cartilage is another treatment option that involves a greater area than is suitable for autologous cylindrical plugs, as well as for a non-contained defect. The advantages of osteochondral allografts are the potential to restore the anatomic contour of the joint, lack of morbidity related to graft harvesting, greater availability than autografts and the ability to prepare allografts in any size to reconstruct large defects. Clinical experience with fresh and frozen osteochondral allografts shows that these grafts can decrease joint pain, and that the osseous portion of an allograft can heal to the host bone and the chondral portion can function as an articular surface. Drawbacks associated with this methodology in the clinical situation include the scarcity of fresh donor material and problems connected with the handling and storage of frozen tissue. Fresh allografts carry the risk of immune response or disease transmission. Musculoskeletal Transplant Foundation (MTF) has preserved fresh allografts in a media that maintains a cell viability of around 50% at 35 days for use as implants. In the current technology frozen allografts lack cell viability and have shown a decreased amount of proteoglycan content, however, they are commonly used for large defects. 
         [0017]    A number of United States patents have been specifically directed towards the manufacture of plugs or cores which are implanted into a cartilage defect. U.S. Pat. No. 6,591,591 issued Jul. 15, 2003 describes a precut bone plug for use in allograft core transplantation surgery which has a tissue bank harvest the graft using a coring trephine with teeth having an inner diameter between 0.5 mm to 0.1 to create a bone core with a hyaline cartilage layer in approximately 7.9 mm, 9.9 mm, 11.9 mm diameters. Alternatively a donor harvester having a cutter tube with a straight cutting edge windows and depth markings with a torque handle on the proximal end may be used to obtain an allograft core as is shown in U.S. Pat. No. 5,919,196 issued Jul. 6, 1999. U.S. Pat. No. 6,592,588 issued Jul. 15, 2003 discloses instruments for cutting a bone core by cutting or punching having collared pins disposed within the harvester for removal of the harvester cores. 
         [0018]    U.S. Pat. No. 4,565,192 issued Jan. 21, 1986 shows a multi-plate device with fixed pins and movable pins for cutting a portion of a patella during knee surgery. U.S. Pat. No. 5,092,572 discloses an allograft vise with a “V” shaped vise face and moveable vise plates. The vise is affixed to a table and can be provided with spherical vise plates having a sharp tripod support for a femur. 
         [0019]    U.S. Pat. Nos. 6,488,033 and 6,852,114 (a divisional application of the &#39;033 patent) issued respectively Dec. 3, 2002 and Feb. 8, 2005 are directed toward an osteochondral transplant workstation for cutting a core out of an allograft bone held in an adjustable vise with a lubricated rotary cutting bit. The core is removed from the bit, held in a specially designed set of pliers, and cut to size by a saw blade to fit into a blind bore which has been oriented and drilled into the patient&#39;s arthritic defect area. This workstation while an improvement over existing procedure is cumbersome to use and requires experience and training use. 
         [0020]    The present invention was designed to overcome prior art procedures and provide a simple to use core preparation devise which accurately fits into the patient&#39;s bore area to form a uniform cartilage surface for the patient. 
       SUMMARY OF THE INVENTION 
       [0021]    A workstation for the preparation of osteochondral allograft cartilage implants having a portable plastic base with a fixed jaw member and a moveable jaw member to hold the allograft full or hemi condyle being cut to provide replacement cores. An articulated guide assembly for a variable size positioner and cutter is mounted on the fixed jaw body and a miter for a surgical saw is formed on one side of the fixed jaw and moveable jaw. 
         [0022]    It is an object of the invention to provide a surgical workstation for forming osteochondral allograft plugs with a cartilage layer which are of the correct size for insertion into a blind bore in a patients knee to repair a cartilage defect. 
         [0023]    It is also an object of the invention to provide a surgical workstation allowing the creation of a cartilage repair implant which has a cartilage layer contoured to the defect site and is easily placed in a defect area by the surgeon to form a continuous cartilage surface in the defect area. 
         [0024]    It is still another object of the invention to provide a surgical workstation for creating a cartilage implant core during surgery which has load bearing capabilities. 
         [0025]    It is further an object of the invention to provide a surgical workstation which can be easily used by the surgeon to create correctly dimensional and contoured cartilage implants. 
         [0026]    It is yet another object of the invention to provide a surgical workstation which can be easily cleaned and sterilized. 
         [0027]    It is still another object of the invention to provide a workstation with a miter so that accurate core lengths for the implant can be obtained. 
         [0028]    It is a further object of the invention to provide a surgical workstation which holds the full or hemi condyle in a fixed stable position allowing a uniform core to be cut from the hemi condyle. 
         [0029]    These and other objects, advantages, and novel features of the present invention will become apparent when considered with the teachings contained in the detailed disclosure along with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]      FIG. 1  is a perspective view of the osteochondral allograft cartilage implant forming workstation with an exploded cutter positioning and guide assembly; 
           [0031]      FIG. 2  is a perspective exploded view of the workstation of  FIG. 1  including a bushing for the guide sleeve; 
           [0032]      FIG. 2A  is a perspective exploded view of another embodiment of the workstation of  FIG. 2  showing drill guide holes for optional additional fixation of the hemi condyle including a bushing for the guide sleeve; 
           [0033]      FIG. 3  is a side perspective view of the workstation shown in  FIG. 1  with the cutter guide assembly in place holding the core cutter and a hemi condyle mounted in the vise jaws; 
           [0034]      FIG. 4  is an opposite side perspective view of the workstation from that shown in  FIG. 3 ; 
           [0035]      FIG. 5  is a perspective view of the allograft cartilage implant workstation using a positioner to establish donor plug position and axis; 
           [0036]      FIG. 6  is a perspective view of the osteochondral allograft cartilage implant workstation with bushing, cutter and slotted wrench tool shown in exploded position; 
           [0037]      FIG. 7  is a side elevational view of the workstation shown in  FIG. 6  with the cutter, cutter holder and hemi condyle shown in cross section and the cutter shown cutting the allograft cartilage implant core; 
           [0038]      FIG. 7A  is an alternate embodiment of a side elevational view of the workstation shown in  FIG. 7  showing the jaws of the vise with chamfered bores used to receive wire fixation or drill bit for fixation; 
           [0039]      FIG. 8  is a side elevational view of the workstation shown in  FIG. 7  with the cutter removed and a saw blade isolating the donor plug by cutting same to desired length; 
           [0040]      FIG. 9  is a partial enlarged perspective view of the plug length trim with the handle of the saw shown in phantom; and 
           [0041]      FIG. 10  is a reversed view cross section taken through the center of  FIG. 4  with cutter, bushing and hemi condyle removed. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0042]    The term “tissue” is used in the general sense herein to mean any transplantable or implantable tissue such as bone. 
         [0043]    The terms “transplant” and “implant” are used interchangably to refer to tissue (xenogeneic or allogeneic) which may be introduced into the body of a patient to replace or supplement the structure or function of the endogenous tissue. 
         [0044]    The terms “autologous” and “autograft” refer to tissue or cells which originate with or are derived from the recipient, whereas the terms “allogeneic” and “allograft” refer to tissue which originate with or are derived from a donor of the same species as the recipient. The terms “xenogeneic” and “xenograft” refer to tissue which originates with or are derived from a species other than that of the recipient. 
         [0045]    The present invention is directed towards a cartilage repair implant forming workstation. The preferred embodiment and best mode of the invention is shown in  FIGS. 1 ,  2 ,  3 - 7 , and  8 - 10 . In the inventive workstation  20 , a workpiece in the form of an allograft hemi condyle  210  from which an allograft plug or core  200  with a cartilage cap  202  and a subchondral bone portion  204  is prepared for implantation into a patient. 
         [0046]    The portable workstation  20  is constructed with a plastic or metal base  22  having integral upwardly angled handles  24 . The angled handles  24  define grasping cutouts  26  and the base  22  defines a centrally located slot  28  which is stepped as shown in  FIGS. 1 ,  2 ,  6  and  10  to receive a shoulder screw  66  which retains the traveling jaw  60  of vise  29  in the slot  28 . Located on each side of slot  28  are tracks  30  which receive the rails  64  of the traveling jaw  60 . The bottom surface of the base is provided with small ½ inch legs (not shown) at each corner of the base  22  which together with the grasping handles provide stability to the workstation during the cutting operations. Mounted on the top surface of base  22  is a solid fixed jaw  40  of the vise  29  having a planar top surface  42 , a planar side surface  43 , a rear grasping surface  44  and a front angled surface  45 . The top surface  42  is planar and the associated transverse work piece grasping surface  44  (or allograft work piece engaging surface) is formed with a angular cutout  46  which receives the notch of the allograft hemi condyle  210  which has been precut prior to surgery for easy insertion into the vise  29 . The top portion  48  of the grasping wall defines a plurality of vertically positioned parallel teeth  50  as best seen in  FIG. 2 . If desired, a plurality of parallel throughgoing drill or wire guide bores  51  as seen in  FIG. 2A  with chamfered hole lead ins  55  are drilled through the top portion  48  for additional fixation of the hemi condyle  210 . This fixation is accomplished by wires  170  as shown in  FIG. 7A  or by the drill bit itself inserted through both jaws and the base of the hemi condyle  210 . 
         [0047]    As shown in  FIG. 10 , a central throughgoing bore  52  is cut through the middle of the fixed jaw  40  parallel to the top surface of the base  22  to receive the shaft  81  which drives the moving jaw  60 . A shaft retainer lug  54  is mounted in a groove  53  cut in the fixed jaw body adjacent the throughgoing bore  52  and extends into an arcuate groove  85  cut in the end of the shaft to keep shaft  81  in a fixed position within the fixed jaw  40 . A vertical bore  49  is cut into the top surface  42  of the fixed jaw body and extends down into the fixed jaw body to receive the post  92  of the articulated arm assembly  90 . A side bore  47  is cut into the side  43  of the fixed jaw body and communicates with the vertical bore  49  allowing contact of the end of shaft  59  of attachment knob  58  with the post  92  of the articulated arm assembly  90  to secure the post  92  of the articulated arm assembly at a fixed height within the fixed jaw  40 . The bottom of the fixed jaw  40  is secured to the base  22  by means of recessed securement bolts  31  screwed into the bottom of the base through the recessed bores  27  in the base which are aligned with threaded blind bores  59  cut into the bottom of the fixed jaw as best seen in  FIG. 10 . 
         [0048]    The moveable or traveling jaw  60  has a bottom surface  62  defining two parallel rails  64  which slide in the tracks  30  formed in the base  22 . A blind bore  66  is cut into the bottom surface of the slot  28  and is axially aligned with blind stepped bore  67  cut into the bottom of the traveling jaw body. The stepped bore  67  is threaded to receive the threaded end  69  of shoulder screw  68  which retains the traveling jaw  60  in the slot  28 . 
         [0049]    The surface of the top wall  70  of the moveable jaw  60  is planar and the associated transverse grasping wall  72  is formed with a angular cutout  74  which receives the notch of the allograft bone workpiece  210 . The hemi condyle  210  can be mounted into the vise  29  on either axis. A planar side surface  77  forms one side of the moveable jaw  60  and a miter assembly  79  forms the opposite side of the moveable jaw. The top portion  75  of the grasping wall  72  defines a plurality of vertically positioned parallel teeth  76  as seen in  FIG. 9 . A plurality of parallel throughgoing drill or wire guide bores  51 ( a ) as seen in  FIG. 2A  with chamfered hole lead ins are drilled through the top portion  75  and are axially aligned with bore holes  51  in the fixed jaw body for additional fixation of the hemi condyle  210 . This fixation is accomplished by wires  170  as shown in  FIG. 7A  or by the drill bit itself inserted through both jaws and the base of the hemi condyle  210 . 
         [0050]    A throughgoing bore  78  is cut through the moveable jaw body and is axially aligned with the throughgoing bore  52  of the fixed jaw body to receive threaded shaft portion  82 . The thread on the shaft is an acme or convention type thread. Shaft assembly  80  comprises shaft  81  formed into threaded shaft portion  82  and a smooth surfaced shaft portion  84  with the distal smooth portion  84  of the shaft defining an arcuate groove  85  which holds shaft retainer lug  54  holding the shaft  81  fixed in place in the fixed jaw  40 . The proximal portion of shaft  81  has a knob  86  mounted thereto which is held in place by a securement cross pin  88  which is best shown in  FIG. 10 . The proximal end of the knob  86  defines a wrench lug  87  which is adapted to receive a slotted wrench tool for tightening the vise  29 . 
         [0051]    An articulated arm assembly  90  as best seen in  FIG. 10  is mounted to the fixed jaw body as previously noted. The articulated arm assembly  90  comprises a post  92  which is indexed for ease of height adjustment as shown in  FIGS. 1 and 2 , the distal end of the post  92  ending in an upper ball joint  93  upon which an articular arm  94  is mounted. The articular arm is positioned and locked to a designated axis as established with a sizer/positioner tool  300  as shown in  FIG. 5 . The articulare arm  94  is “T” shaped with tapered threaded ends  95  and  95 ( a ), each of which defines a central recess  96  holding an acetal bearing pad  98  which respectively bears against ball joints  93  and  124 . The arm  94  has an integral finger tab  97 . Mounted over the lower threaded end  95  is a lower bearing lock body  100  which defines a conical threaded bore  102  sized to be threaded over the lower threaded end  95  and has an integral opposing finger tab  104  for locking end  95  in place against ball joint  93 . Mounted over the upper threaded end  95   a  is an upper bearing lock body  110  which defines a conical threaded bore  112 , the lock body  110  having an integral opposing finger tab  114  for locking end  95 ( a ) in place against ball joint  124 . The upper bearing lock  110  holds a positional collar  120  which has an extending arm  122  with a ball joint  124  secured to the distal end which is held in a fixed position by the upper bearing lock body  110 . The collar  120  defines a central throughgoing bore  126  which can hold interchangeable bushings  130  as shown in  FIG. 6-8  ranging in size from 15, 18, 20, 22, 25, 30 and 35 mm in diameter. The bushings in turn are adapted to hold core cutter blades  144  ranging from 15, 18, 20, 22, 25, 30 and 35 mm in diameter. 
         [0052]    A plug or core cutting assembly  140  comprising an arbor  142 , chuck  144  and cylindrical cutting blade  146  are shown in  FIGS. 7 ,  7 A. The core trimmer is formed in the fixed jaw  40  and the moveable jaw  60  as best seen in  FIG. 9 . Each jaw side portion  47 ,  79  defines an aligned miter slot  142 ,  144  which establishes a perpendicular cut to match the bottom of the recipient counterbore with the exterior side  145  of miter side portions  47 ,  79  defining finger clearance reliefs  146 . The miter slot is of sufficient width to receive a standard type surgical saw blade  160 . The top surface  148  of each of the miter sections has a flat planar section  150  and a downward angled flat surface  152  with the ends being provided with a scale  154  set to the allograft plug length. 
         [0053]    In operation, the lesion or defect is removed by cutting a counterbore in the patient of a predetermined diameter and depth in the defect area with a cannulated boring bit. An allograft hemi condyle is placed between the jaws of the vise to hold the condyle in the desired position. A donor cutting guide is placed over the allograft condyle in the same position and orientation as the original cartilage removed from the defect area and then a coring bit and arbor is used to obtain an allograft plug of the same diameter as the diameter of the core cut into the defect area of the patient as seen in  FIG. 1 . The core is then removed from the allograft condyle by sawing the condyle transversely with a surgical saw as seen in  FIG. 8  to make the allograft plug an independent entity. The plug is then trimmed to length by the surgical saw in the miter cutting area as shown in  FIG. 9  or when held by forceps. 
         [0054]    The plug  200  which has been cut to the desired length is placed in the bore which has been cut in the lesion area of the bone of the patient with the upper surface of the cartilage cap  202  being slightly proud or substantially flush with the surface of the original cartilage  202  remaining in the area. The length of the osteochondral plug  200  can be the same as the depth of the bore or less than the depth of the bore If the plug  200  is the same length, the base of the plug implant is supported and the articular cartilage cap  202  is level with the articular cartilage of the patients bone surface. If the plug is of a lesser length, the base of the plug implant is not supported but support is provided by the wall of the bore or respective cut out area as the plug is interference fit within the bore or cut out area with the cap being slightly proud or flush with the articular cartilage depending on the surgeon&#39;s preference. With such load bearing support the graft surface is not damaged by weight or bearing loads which can cause micromotion interfering with the graft interface producing fibrous tissue interfaces and subchondral cysts. 
         [0055]    The principles, preferred embodiments and modes of operation of the present invention have been described in the foregoing specification. However, the invention should not be construed as limited to the particular embodiments which have been described above. Instead, the embodiments described here should be regarded as illustrative rather than restrictive. Variations and changes may be made by others without departing from the scope of the present invention as defined by the following claims:

Technology Classification (CPC): 1