Abstract:
An arthroscopic sealing cannula having improved efficiency, access and reduced manufacturing costs is described herein. In particular, the present invention describes arthroscopic sealing cannulae in which the conventional thermal and chemical bonding means are eliminated and replaced with a mechanical joining system that utilizes mating fastener pairs integrally molded into the distal and proximal elements of a cannula so as to thereby provide a strong reliable joining of the elements. Such a mechanical system eliminates the need for costly capital equipment and specializing tooling as well as the material and environmental handling problems associated with conventional bonding techniques. Furthermore, in that the join may be readily confirmed through simple visual examination, the present invention also eliminates the need for complex, costly, and time-consuming validation procedures mandated by regulations in place to ensure proper integrity, strength, and reliability of the bond. Accordingly, arthroscopic sealing cannulae constructed in accordance with the principles of this invention are expected to have increased reliability and reduced manufacturing costs.

Description:
PRIORITY 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/959,557 filed Aug. 27, 2013. The entire content of this priority application is incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to an efficient and simplified cannula for endoscopic surgery. 
       BACKGROUND OF THE INVENTION 
       [0003]    Arthroscopic procedures generally involve the passage of elongated instruments through portals that facilitate access to the internally located surgery site. Because these sites are generally filled with liquid under pressure, the use of a sealing access device is required. It is required that this access device, commonly called a sealing cannula or simply a cannula, provide for easy insertion, manipulation and retraction of instruments, and while also maintaining a fluid seal to prevent uncontrolled escape of pressurized fluid from the site. This sealing must be maintained both when instruments are in use as well as when there are no instruments within the cannula passageway. Commercially available examples of such arthroscopy cannulae include the Clear-Trac cannulae by Smith and Nephew (Andover, Mass.), the Dri-Loc Disposable Cannulas by Stryker, Inc. (Kalamazoo, Mich.), and the Twist-In Cannulas by Arthrex, Inc. (Naples, Fla.). 
         [0004]    A typical arthroscopy cannula has three principle elements: an elongate tubular distal element which is positioned within an incision made in the skin of a patient, one or more elastomeric sealing elements which prevents escape of fluid from the fluid-filled joint space when elongate instruments are inserted into the cannula, and a proximal portion which retains the seal in its position in the fluid/instrument path. Typically, the one or more sealing elements are positioned in a cavity formed between the distal and proximal elements, and the distal and proximal elements are joined by ultrasonic welding, solvent bonding, or use of a bonding agent such as, for instance, epoxy, cyanoacrylate or other curable adhesive. The sealing elements are typically formed from an elastomeric material such as silicone. The distal and proximal elements are typically made from a rigid polymeric material, although in some cases the distal element is formed from a non-rigid polymeric material to allow the passage of irregularly shaped instruments. 
         [0005]    Joining of the distal and proximal elements by ultrasonic welding or solvent bonding is problematic in that the integrity of the bond is difficult to confirm. Regulatory agencies require that the joining process be validated, that is, through testing and statistical analysis demonstrating that the bond formed meets strength and reliability specifications. However, even when the joining process is validated, variations within the process may occur that weaken the bond to the point where failure may occur during use. Such variations that lead to failure are not detectable, and unless statistically designed on-going destructive testing of the finished product is performed during production, large numbers of product with weak bonds may be supplied to customers. The validation of the bonding process is a costly time-consuming procedure that gives only limited assurance of the bond integrity. 
         [0006]    A second problem in the art of arthroscopic cannulae arises with the use of irregularly shaped instruments, the passage of which can cause deformation of the sealing elements, thereby allowing pressurized fluid from the site to escape. This may also occur when sutures extending from the site through the cannula and exiting from the cannula&#39;s proximal end are placed under tension, as when tying knots. The escaping liquid frequently comes out as a stream directly at the surgeon who is passing the instruments or tensioning the suture. Because of this, some manufacturers have begun adding an auxiliary sealing means to the proximal end of the cannula to prevent leakage. One example of such a device is disclosed in U.S. Pat. No. 5,779,697 to Glowa et al. The Glowa device includes an elastomeric sealing member mounted to the proximal end of the cannula in addition to a more distally mounted elastomeric seal so as to prevent leakage when instruments are inserted, retracted or mis-aligned. This same approach is used in Instrument Cannulas by Arthrex, Inc. (Naples, Fla.) that are supplied to surgeons with a “no squirt” elastomeric member attached to the cannula&#39;s proximal end. An alternative approach to dealing with leakage due to deformation of the sealing element is taught by Morris et al in U.S. Pat. No. 7,993,355 wherein a suture organizing device is provided with an elastomeric “spray shield” that is removably mounted to the proximal end of a cannula, the spray shield being configured not to prevent leakage, but rather to deflect the flow of escaping pressurized fluid using deformable flaps formed in the element. Escaping liquid does not spray at the surgeon, but rather flows from the device as a low-velocity stream. The liquid may exit the device by deforming the flaps, or alternatively, through holes in the spray shield at the proximal end of the flap-forming slots. In either case, pressurized liquid escaping past the seal at high velocity exits the device as a low-velocity stream. Dooney et al in U.S. Patent Publication 2014/0121630 teaches the same spray shield approach but with the spray shield integral to the cannula. In particular, Dooney teaches “ . . . an adjacent outer “baffle-like dam” that prevents fluid pressure build-up and allows the fluid to leak out and not squirt out of the cannula”. The “baffle-like” dam has slots that form flaps, and holes for the escape of fluid in the same manner as Morris. While the constructions of the Dooney device is simple, Dooney teaches Cap  65  may be attached by any known method in the art, for example, by welding such as ultrasonic welding.” Known methods would include solvent bonding and adhesive bonding in addition to ultrasonic welding. However, the drawbacks of these joining methods have been previously herein described. 
         [0007]    In contemplating means to address the aforementioned problems, the skilled artisan must keep in mind that not all arthroscopic instruments are straight. Various devices such as shaver blades are curved, yet are advantageously brought to the surgical site via a cannula, Also, some devices, particularly some manual instruments, have irregular shaped distal portions which will not fit into a standard round cannula. To accommodate these devices, sealing cannulae having a flexible polymeric distal portion have been developed. The distal portions of these cannula will bend to accommodate curved devices placed within them, or their lumen will deform to allow the passage of devices which would not fit through a conventional circular cross-sectioned lumen. Commercial examples of such alternative sealing cannulae include the Clear-Trac Flexible Cannula System by Smith and Nephew, Inc. (Andover, Mass.), and the Hex-Flex Cannulas by Conmed, Inc. (Largo, Fla.). These cannulae have construction similar to that of rigid cannulae in that they require bonding between structural elements and may limit the degree of flexibility which may be imparted to the distal portion. This, in turn, limits the functionality of the cannula since a flexible cannula with a high degree of rigidity (resistance to deformation) will make passage of irregularly shaped or bent device difficult. 
         [0008]    Accordingly, there is a need in the art for a cannula that may be manufactured without ultrasonic welding, and without adhesive or solvent bonding. There is further a need for a cannula that incorporates an elastomeric spray shield and may also be manufactured without ultrasonic welding and without adhesive or solvent bonding. Finally there is also a need for a cannula with a flexible distal portion in which the properties of the distal portion are not limited by the assembly bonding process. 
       SUMMARY OF THE INVENTION 
       [0009]    In the course of researching the afore-mentioned problems in the arthroscopic arts, the present inventors discovered one could eliminate the need for a bond between the distal and proximal elements of a cannula through the use of a suitable mechanical joining means provided in the configuration of the elements. Specifically, one could configure the elements such that mating fastener pairs are integrally molded into the distal and proximal elements of a cannula so as to thereby provide a strong reliable joining of the elements. The finished devices may be visually inspected to ensure that the fastener pairs are properly engaged so as to ensure the integrity of the joining means. Assembly of a cannula constructed in accordance with the principles of this invention may be rapidly accomplished without requiring capital equipment and specialized tooling as in the case with ultrasonic welding of the components, and without the environmental and material handling problems inherent in solvent bonding. Accordingly, cannulae constructed in accordance with the principles of this invention will have increased reliability and reduced manufacturing costs. 
         [0010]    In accordance with the present invention, these same construction techniques—using integral fastener pairs on the proximal and distal elements—may be advantageously applied to cannulae that have a proximally positioned elastomeric spray shield integral to their assembly, and may also be applied to cannulae that have flexible distal assemblies, wherein the mechanical properties of the distal portion are not limited by the manufacturing methods used. 
         [0011]    Accordingly, it is an objective of the present invention to provide a cannula assembly comprising:
       a. a proximal hub element having (i) a central opening configured to receive surgical instruments, (ii) a planar annular body portion that includes a first component of a mating fastener pair, and (iii) a distally projecting flange portion;   b. a distal tubular element composed of (i) an elongate tubular distal portion, (ii) a flared proximal portion that includes a second component of the mating fastener pair, and (iii) a proximally facing raised rim extending from the flared proximal portion, and   c. one or more sealing membranes,
 
wherein components (a)-(c) are assembled together such that the first and second components of the mating fastener pair mechanically interlock so as to securely fasten the proximal hub element to the distal tubular element and prevent relative movement and/or disengagement thereof.
       
 
         [0015]    It is a further object of the present invention to provide novel spray shield assemblies for use with the cannulae of the instant invention and/or conventional arthroscopic cannula. 
         [0016]    It is yet a further object of the present invention to provide a proximal hub element and distal tubular element that are each integrally molded from a rigid polymeric material. Alternatively, the distal tubular element, particularly elongate tubular distal portion may be composed of a flexible, elastomeric material and designed to accommodate curved and irregularly shape instruments. The novel fastening and spray shield systems disclosed herein may be accommodated to fit either configuration. 
         [0017]    In a preferred embodiment, the fastener pair is composed of integral projecting hooks that mate with corresponding integral recessed elements. In a particularly preferred embodiment, the hooks and the recessed elements feature coordinating beveled portions or projections. Depending on the construction of the respective mating components of the fastener pair, the bond between the proximal and distal elements of the assembly may be permanent (i.e., as in a single use device). To that end, the present invention contemplates simple mechanical fits as well as thermal techniques such as heat staking to ensure irremovable engagement. Alternatively, the cannula assembly of the present invention may be designed for repeated disassembly (i.e., as in a multi-use device) and reassembly, for example with replacement sealing membranes or the like. 
         [0018]    These and other objectives are accomplished in the invention herein described, directed to a simplified, more efficient, low cost arthroscopy cannula. Further objects and features of the invention will become more fully apparent when the following detailed description is read in conjunction with the accompanying figures and examples. However, it is to be understood that both the foregoing summary of the invention and the following detailed description are of a preferred embodiment, and not restrictive of the invention or other alternate embodiments of the invention. In particular, while the invention is described herein with reference to a number of specific embodiments, it will be appreciated that the description is illustrative of the invention and is not constructed as limiting of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    Various aspects and applications of the present invention will become apparent to the skilled artisan upon consideration of the brief description of figures and the detailed description of the present invention and its preferred embodiments that follows: 
           [0020]      FIG. 1A  depicts an exploded proximal perspective view of a prior art arthroscopic sealing cannula. 
           [0021]      FIG. 1B  is a plan view of a prior art arthroscopic sealing cannula. 
           [0022]      FIG. 1C  is a perspective view of the prior art arthroscopic sealing cannula of  1 B. 
           [0023]      FIG. 2A  depicts an exploded proximal perspective view of a novel arthroscopic sealing cannula formed in accordance with the principles of this invention. 
           [0024]      FIG. 2B  is an exploded distal perspective view of the objects of  FIG. 2A . 
           [0025]      FIG. 3A  is a plan view of the distal element of the cannula of  FIGS. 2A and 2B . 
           [0026]      FIG. 3B  is a side elevational sectional view of the objects of  FIG. 3A  at location A-A of  FIG. 3A . 
           [0027]      FIG. 3C  is an expanded view of region A of  FIG. 3B . 
           [0028]      FIG. 4A  is a plan view of the proximal element of the cannula of  FIGS. 2A and 2B . 
           [0029]      FIG. 4B  is a side elevational sectional view of the objects of  FIG. 4A  at location A-A of  FIG. 4A . 
           [0030]      FIG. 4C  is an expanded view of region A of  FIG. 4B . 
           [0031]      FIG. 5A  is a perspective view of a cannula formed in accordance with the principles of this invention. 
           [0032]      FIG. 5B  is an expanded proximal end view of the objects of  FIG. 5A . 
           [0033]      FIG. 6A  is a plan view of the cannula of  FIG. 5A . 
           [0034]      FIG. 6B  is an expanded side elevational sectional view of the proximal portion of the objects of  FIG. 6A  at location A-A of  FIG. 6A . 
           [0035]      FIG. 6C  is an expanded view of region A of  FIG. 6B   
           [0036]      FIG. 7  is a side elevational view of the objects of  FIG. 6A . 
           [0037]      FIG. 8  is an expanded plan sectional view of the distal portion of the objects of  FIG. 7  at location B-B of  FIG. 7 . 
           [0038]      FIG. 9A  is a plan view of a first alternate embodiment cannula formed in accordance with the principles of the instant invention. 
           [0039]      FIG. 9B  is a side elevational sectional view of the objects of  FIG. 9A  at location A-A. 
           [0040]      FIG. 9C  is an expanded view of region A of  FIG. 9B . 
           [0041]      FIG. 10A  is an exploded perspective assembly view of the alternate embodiment cannula of  FIG. 9 . 
           [0042]      FIG. 10B  is a perspective view of the alternate embodiment cannula of  FIG. 9 . 
           [0043]      FIG. 11  is an exploded perspective assembly view of the components of a second alternate embodiment cannula formed in accordance with the principles of this invention prior to final assembly. 
           [0044]      FIG. 12A  is a distal perspective view of the objects of  FIG. 11  assembled in preparation for heat staking. 
           [0045]      FIG. 12B  is a side elevational view of the objects of  FIG. 12A . 
           [0046]      FIG. 13A  is a distal perspective view of the objects of  FIG. 12A  after completion of assembly by heat staking. 
           [0047]      FIG. 13B  is a side elevational view of the objects of  FIG. 13A . 
           [0048]      FIG. 13C  is a proximal perspective view of the objects of  FIG. 13A . 
           [0049]      FIG. 14  is a proximal perspective view of the tubular body element of a spray suppression assembly for assembly to a cannula constructed in accordance with the principles of this invention. 
           [0050]      FIG. 15  is a distal perspective view of the objects of  FIG. 14 . 
           [0051]      FIG. 16  is a distal axial view of the objects of  FIG. 14 . 
           [0052]      FIG. 17  is a plan view of the objects of  FIG. 14 . 
           [0053]      FIG. 18  is a proximal axial view of the objects of  FIG. 14 . 
           [0054]      FIG. 19  is a side elevational sectional view of the objects of  FIG. 14  at location A-A of  FIG. 17 . 
           [0055]      FIG. 20  is a side elevational view of a flexible polymeric spray shield for a spray suppression assembly for assembly to a cannula constructed in accordance with the principles of this invention. 
           [0056]      FIG. 21  is an axial view of the objects of  FIG. 20 . 
           [0057]      FIG. 22  is a perspective view of the objects of  FIG. 20 . 
           [0058]      FIG. 23  is a side elevational view of a retaining ring for a spray suppression assembly for assembly to a cannula constructed in accordance with the principles of this invention. 
           [0059]      FIG. 24  is a side elevational view of the objects of  FIG. 23 . 
           [0060]      FIG. 25  is a perspective view of the objects of  FIG. 23 . 
           [0061]      FIG. 26  is a perspective view of the exploded assembly of a spray suppression assembly for mounting to a cannula constructed in accordance with the principles of this invention. 
           [0062]      FIG. 27  is a proximal perspective view of the elements of  FIG. 26  assembled to form a spray suppression assembly for mounting to a cannula constructed in accordance with the principles of this invention. 
           [0063]      FIG. 28  is a distal perspective view of the elements of  FIG. 27 . 
           [0064]      FIG. 29  is a distal axial view of the shaver suppression assembly of  FIG. 27 . 
           [0065]      FIG. 30  is a side elevational view of the objects of  FIG. 27 . 
           [0066]      FIG. 31  is a proximal axial view of the objects of  FIG. 27 . 
           [0067]      FIG. 32  is a plan sectional view of the elements of  FIG. 27  at location A-A of  FIG. 30 . 
           [0068]      FIG. 33  is a proximal perspective depiction of the cannula of  FIGS. 1 through 8  and the spray suppression assembly of  FIGS. 24 through 32  positioned for assembly of the spray suppression assembly to the cannula. 
           [0069]      FIG. 34  is a distal perspective depiction of the objects of  FIG. 33 . 
           [0070]      FIG. 35  is a proximal perspective depiction of a cannula assembly composed of the cannula of  FIGS. 1 through 8  and the spray suppression assembly of  FIGS. 24 through 32 . 
           [0071]      FIG. 36  is a distal perspective view of the objects of  FIG. 35 . 
           [0072]      FIG. 37  is a plan view of the cannula assembly of  FIG. 35 . 
           [0073]      FIG. 38  is a side elevational sectional view of the objects of  FIG. 35  at location A-A of  FIG. 37 . 
           [0074]      FIG. 39  is a plan view of a flexible polymeric distal portion for a cannula constructed in accordance with the principles of the instant invention. 
           [0075]      FIG. 40  is a side elevational view of the objects of  FIG. 39 . 
           [0076]      FIG. 41  is an expanded axial sectional view of the objects of  FIG. 39  at location B-B of  FIG. 40 . 
           [0077]      FIG. 42  is an expanded side elevational sectional view of the objects of  FIG. 39  at location A-A of  FIG. 39 . 
           [0078]      FIG. 43  is a plan view of a proximal subassembly for an alternate embodiment cannula formed in accordance with the principles of this invention. 
           [0079]      FIG. 44  is a perspective view of the subassembly of  FIG. 43 . 
           [0080]      FIG. 45  is a side elevational view of the objects of  FIG. 43 . 
           [0081]      FIG. 46  is an expanded side elevational view of the objects of  FIG. 43  at location A-A of  FIG. 43 . 
           [0082]      FIG. 47  is a plan view of a retaining collar for an alternate embodiment cannula formed in accordance with principles of the instant invention. 
           [0083]      FIG. 48  is an axial view of the objects of  FIG. 47 . 
           [0084]      FIG. 49  is a side elevational sectional view of the collar of  FIG. 47  at location A-A of  FIG. 47 . 
           [0085]      FIG. 50  is a perspective view of the objects of  FIG. 47 . 
           [0086]      FIG. 51  is a proximal perspective view of an alternate embodiment cannula having a flexible distal portion and formed in accordance with the principles of the instant invention. 
           [0087]      FIG. 52  is a distal perspective view of the cannula of  FIG. 51 . 
           [0088]      FIG. 53  is a plan view of the objects of  FIG. 51 . 
           [0089]      FIG. 54  is an expanded side elevational sectional view of the objects of  FIG. 53  at location A-A of  FIG. 53 . 
           [0090]      FIG. 55  is an expanded axial sectional view of the objects of  FIG. 53  at location B-B of  FIG. 53 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0091]    Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present invention, the preferred methods, devices, and materials are now described. However, before the present materials and methods are described, it is to be understood that the present invention is not limited to the particular sizes, shapes, dimensions, materials, methodologies, protocols, etc. described herein, as these may vary in accordance with routine experimentation and optimization. It is also to be understood that the terminology used in the description is for the purpose of describing the particular versions or embodiments only, and is not intended to limit the scope of the present invention which will be limited only by the appended claims. Accordingly, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. However, in case of conflict, the present specification, including definitions below, will control. 
         [0092]    In the context of the present invention, the following definitions apply: 
         [0093]    The words “a”, “an” and “the” as used herein mean “at least one” unless otherwise specifically indicated. Thus, for example, reference to an “opening” is a reference to one or more openings and equivalents thereof known to those skilled in the art, and so forth. 
         [0094]    The term “proximal” as used herein refers to that end or portion which is situated closest to the user of the device, farthest away from the target surgical site. In the context of the present invention, the proximal end of the arthroscopic sealing cannula includes the hub region. 
         [0095]    The term “distal” as used herein refers to that end or portion situated farthest away from the user of the device, closest to the target surgical site. In the context of the present invention, the distal end of the arthroscopic sealing cannula includes the elongate lumened region that passes through the incision site. 
         [0096]    In the context of the present invention, the term “cannula” is used interchangeably to refer to the family of elongate surgical instruments that facilitate access across tissue to an internally located surgery site. 
         [0097]    The terms “tube” and “tubular” are used herein to a generally round, long, hollow component having at least one central opening often referred to as a “lumen”. 
         [0098]    In the context of the present invention, the terms “seal”, “sealing element” and “membrane” are used interchangeably to refer to any of the various shaped pieces or discs of rubber or other elastomeric material sealing the junction between two surfaces, particularly between the proximal and distal ends of an arthroscopic cannula of the present invention, or between an instrument placed in the lumen of the cannula and the cannula assembly so as to prevent liquid flow through the cannula. 
         [0099]    The terms “lengthwise” and “axial” as used interchangeably herein to refer to the direction relating to or parallel with the longitudinal axis of a device. The term “transverse” as used herein refers to the direction lying or extending across or perpendicular to the longitudinal axis of a device. 
         [0100]    The term “lateral” pertains to the side and, as used herein, refers to motion, movement, or materials that are situated at, proceeding from, or directed to a side of a device. 
         [0101]    The term “medial” pertains to the middle, and as used herein, refers to motion, movement or materials that are situated in the middle, in particular situated near the median plane or the midline of the device or subset component thereof. In the context of the present invention, the terms “protrusion” and “protuberance” are used interchangeably herein to refer to a projecting element, such as a raised ridge, spline, or rib, that mates and/or engages with a coordinated recessed element, such as a groove or slot. 
         [0102]    In the Examples below, the present invention makes reference to a mechanically fit and/or optionally heat-staked fastener pair that arises from the engagement of a distal hook element and a proximal recess element. However, the present invention contemplates the reversal of such elements, wherein the recesses are disposed on the distal tubular component and the hooks are disposed on the proximal hub element. 
         [0103]    In the Examples below, the present invention also makes reference to various lock-and-key type alignment mechanisms that serve to establish and maintain proper angular alignment between the proximal hub element and the distal tubular element, as well as the optional spray shield assembly. It will again be readily understood by the skilled artisan that the position of the respective coordinating elements (e.g., mating slots and protrusions) may be exchanged and/or reversed as needed. 
         [0104]    The instant invention has both human medical and veterinary applications. Accordingly, the terms “subject” and “patient” are used interchangeably herein to refer to the person or animal being treated or examined. Exemplary animals include house pets, farm animals, and zoo animals. In a preferred embodiment, the subject is a mammal. 
         [0105]    Hereinafter, the present invention is described in more detail by reference to the Figures and Examples. However, the following materials, methods, figures, and examples only illustrate aspects of the invention and are in no way intended to limit the scope of the present invention. For example, while the present invention makes specific reference to arthroscopic procedures, it is readily apparent that the teachings of the present invention may be applied to other minimally invasive procedures and are not limited to arthroscopic uses alone. As such, methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. 
       EXAMPLES 
       [0106]      FIGS. 1A through 1C  depict the construction of a typical prior art cannula, more particularly an arthroscopic sealing cannula. As best seen in  FIG. 1A , prior art cannula  90  has a rigid polymeric distal element  92 , one or more elastomeric membranes or seals  94 , and a rigid polymeric proximal element  96  which is bonded to distal element  92  by ultrasonic welding, solvent bonding, or an adhesive, ultrasonic welding being the preferred method. Slots  97  in proximal element  96  allow cannula  90  to be inserted and retracted from a surgeon-formed portal in the body of a patient using a specialized handle called an obturator that allows the surgeon to apply axial force and torque to cannula  90  as needed. Cannula  90  as shown is configured for assembly by ultrasonic welding of distal portion  92  to proximal portion  96  with proximal facing annular surface  93  having formed thereon an annular ridge  95  which functions as an “energy director” to aid in forming the bond. When subjected to pressure and ultrasonic vibration, localized melting of ridge  95  provides material that flows between the proximal facing surface  93  and the distal facing surface of proximal portion  96 . The size and configuration of annular ridge  95  is critical since if ridge  95  contains excess material the melted plastic may flow beyond the periphery of the joint, and if the material of the ridge  95  is deficient the bond may not have the specified strength. Deficiency in the material of ridge  95  (a common molding problem known as a “short shot”) may be due to changes in the parameters of the molding process used to form distal portion  92 . Should such changes occur and be undetected prior to assembly of device  90  by ultrasonic welding, a cannula  90  with less than specified bond strength may be shipped to surgeons and fail during use, the failure mode being separation of proximal portion  96  from distal portion  92  when an instrument is retracted from the cannula. Such failure requires immediate attention, namely immediate replacement of the cannula, which, in turn, extends the procedure time, an undesirable outcome for both the surgeon and the patient. Verifying the integrity of the bond requires destructive testing of cannula  90  since visual inspection cannot detect substandard bonds. Because of this, molding and ultrasonic welding parameters must be closely controlled and periodic destructive testing of cannula  90  during the bonding process is required. Such testing increases the cost of production for cannula  90  since a portion of the products produced must be destroyed to verify bond integrity. Additionally, the ultrasonic welding machine with its associated tooling (commonly called a “horn”) for transmitting ultrasonic energy to the part must be validated according to procedures which conform to FDA regulations. That is, parameters must be established for the welding machine and molded components which produce bonds having a predetermined strength. Validating the process, machine and tooling requires destructive testing of large numbers of welded assemblies. If the tooling is changed or the machine undergoes maintenance or repairs that may affect the calibration of its output controls, the process must be requalified, again, a process that is time consuming and again requires the destructive testing of large numbers of welded assemblies. 
         [0107]    Given the above-described issues associated with the status quo, replacing current bonding methods with mechanical fastening methods that may be visually inspected has significant benefits. In the course of researching alternatives, it was herein discovered one could produce a cannula in which interlocking features on distal and proximal elements of the cannula permanently and irretrievably affix the proximal portion to the distal portion in a manner which may be visually inspected. Accordingly, cannulae formed in accordance with the principles of the present invention do not use ultrasonic welding or bonding agents, but rather mechanical interlocking of features on the components to maintain the integrity of the final assembly. 
         [0108]      FIGS. 2A and 2B  depict an exploded view of an arthroscopic cannula  10  constructed in accordance with the principles of this invention. Cannula  10  has an elongate tubular distal element  100 , sealing elements  200 , and a proximal hub element  300 . Features of cannula  10  other than those related to mechanical joining of the distal and proximal elements, for example the external threads on the distal end, are like those of prior art devices and form no part of the present invention which is directed solely to the simple reliable joining of the respective elements. 
         [0109]    Distal element  100  has an elongate tubular distal portion  102  that may optionally be threaded. Proximal portion  104  locates and retains sealing elements  200  by means of pins  106  that engage with holes  202  in seal  200 . Hook portions  110  protrude proximally from proximal portion  104 . Proximal portion  104  also has alignment protrusions or splines  112  extending from proximal rim  114  of proximal portion  104  of distal element  100 . Alignment protrusions  112  cooperatively engage with the slots  304  in flange element  306  of proximal element  300  to establish and maintain angular alignment between distal element  100  and proximal element  300 . Recessed features  310  of proximal element  300  and hook portions  110  of proximal portion  104  of distal element  100  together form a fastener pair. Proximal face  322  of proximal element  300  has formed therein recessed features  310 . Proximal element  300  has a distal facing surface  330 . Referring to  FIGS. 3A through 3C  which depict distal element  100 , axial portion  116 , transverse portion  118 , and distally facing portion  120  together make up hook portions  110  of distal element  100 . Transverse portions  118  have formed thereon beveled surfaces  122 . As best seen in  FIGS. 4A through 4C , recessed features  310  of proximal element  300  have a medially extending portion  312 , proximally extending portion  314 , and distal-medial facing beveled surface  316 . 
         [0110]      FIGS. 5 through 8  depict cannula  10  fully assembled with proximal portion  300  irremovably mounted to distal element  100 .  FIGS. 6A through 6C  depict the mechanical interlocking of hook portions  110  of distal element  100  with recessed features  310  to prevent axial movement in the proximal direction of proximal element  300 . Assembly is accomplished in the following manner. Seal elements  200  are positioned in proximal portion  104  of distal element  100 . Proximal element  300  is aligned with distal element  200 , hook portion  110  of distal element being partially inserted into the openings of recessed features  310 . Axial force is applied to proximal element  300  so as to compress seals  200  and flex proximal portion  300 . Beveled surfaces  122  of hook portions  110  acting with beveled surfaces  316  of recessed portions  310  cause hook portions  110  to flex inward, the flexure increasing with increasing axial movement of proximal element  300  relative to axial element  100 . When proximal element  300  has been sufficiently advanced axially relative to distal portion  100 , portions  118  and  120  of hook portions  110  protrude proximally beyond portions  312  and  314  of recessed portions  310  such that hook portions  110  can return to their free-state (un-deflected) condition. With the hook portions in their free-state position, portions  118  and  120  of hook portions  110  and portions  312  and  314  of recessed portions  310  interlock in a manner that prevents proximal movement of proximal portion  300  relative to distal portion  100 . Additionally, portions  314  of recessed portions  310  in cooperation with portions  120  of hook portions  110  prevent deflection of hook portions  110  as would be required for disassembly of proximal element  300  from distal element  100 . As best seen in  FIG. 8 , distal facing surface  330  of element  300  is in contact with the proximal ends of pins  106  of distal element  100  thereby prevent distal axial movement of element  300 . Alignment protrusions  112  of distal element  100  and slots  304  of proximal element  300  maintain angular alignment between elements  100  and  300 . 
         [0111]    An alternate embodiment that may be optionally disassembled after assembly (that is, wherein proximal element  300  may be demounted from distal element  100  after assembly) is depicted in  FIGS. 9A through 9C . Except as specifically indicated, in all aspects cannula  12  is identical to cannula  10 . Portions  314  of recessed portions  310  and portions  120  of hook portions  110  have formed on them complimentary beveled surfaces  315  and  121  respectively such that by placing a blade-like device into the gaps between surfaces  119  of portions  118  of hook portions  110  and surfaces  303  of proximal element  300  and imparting a separating force between the surfaces, hook portions  110  may be deflected such that proximal element  300  is released from distal element  100 . Unlike cannula  10 , which is intended to be a single-use device, cannula  12  is intended as a reusable device. As such, it may be disassembled, with distal element  100  and proximal element  300  optionally formed from a more durable polymeric material such that following one or more uses, sealing elements  200  may be replaced and additional uses of cannula  12  realized. 
         [0112]    When a suture passing from a cannula is placed under tension, the seal is often deformed and pressurized fluid from within the joint sprays from the proximal end of the cannula. Frequently the stream of fluid will strike the surgeon. Referring now to  FIGS. 10A and 10B , alternate embodiment cannula  20  formed in accordance with the principles of this invention has a spray shield  400  to prevent streams of fluid which escape the seal  200  from spraying at the surgeon. Spray shield  400 , formed from a suitable elastomeric material, has radial slits  404  terminating in holes  402  so as to form spray-deflecting flaps between the slots, and holes through which fluid leaking from seal  200  may flow as a low-velocity stream. Spray shield  400  and seal  200  are positioned within mid-element  500 . The assembly of seal  200 , mid-element  500  and spray shield  400  is then positioned in the proximal end  104  of distal element  100  and proximal element  300  is mounted to element  100  in the same manner as for cannulae  10  and  12 . 
         [0113]    The joining of plastic components may also be reliably accomplished by heat-staking, a process in which one or more features of one of the components of the final assembly is thermally deformed so as to create a mechanical barrier to disassembly. For instance, an assembly may have mating features on its component elements such that, when assembled, a protuberance of a first element is positioned within an opening of a second element, the distal end of the protuberance extending beyond a surface of the second element. The protruding distal end of the protuberance is thermally deformed so as to locally increase its size so as to prevent retraction through the mating opening. Heat-staking is a reliable method for securing assemblies since the strength of an individual heat-staked element is determined by the dimensions of the deformed region and the shear strength of the polymeric material. Also, heat-staked components may be visually inspected to verify their integrity, a feature lacking on bonds formed by ultrasonic welding or other means. 
         [0114]      FIG. 11  depicts the components for an alternate embodiment cannula  30  formed in accordance with the principles of this invention and arranged for assembly. Proximal element  300  has formed thereon distally extending portions  340 . Distal element  100  has formed in the distal facing surface  142  of its proximal portion  104  holes  140  which are sized and positioned to receive portions  340  upon assembly.  FIGS. 12A and 12B  depict the elements of cannula  30  assembled with the distal portions of distally extending portions  340  protruding beyond surface  142  of proximal portion  104  of cannula distal portion  100 .  FIGS. 13A through 13C  depict cannula  30  after final assembly. As best seen in  FIG. 13B , the portions of portions  340  extending beyond surface  142  of distal element  100  have been thermally deformed (heat-staked) to a hemispherical shape having a proximal diameter larger than that of holes  140  of distal element  100 . This deformation prevents withdrawal of portions  340  from holes  140  and thereby preventing disassembly of cannula  30 . 
         [0115]    Cannula  20  of  FIGS. 10A and 10B , with its integral spray shield  400 , requires a distal element  100  and proximal element  300  formed in a manner which allows the assembly therebetween of mid-element  500  with sealing element  200  and spray shield  400 . This construction requires the construction of the molds configured to produce not only the distal element  100  and proximal element  300 , but also the mid-element  500 . Alternate embodiment cannulae with integral spray shields are anticipated in which cannulae  10  or  12  as previously described herein are modified through the additional of a proximally mounted spray suppression assembly. The benefits to be realized from this construction are reduced tooling and inventory costs since “standard” cannulae (that is, without spray shields) may be modified to produce cannulae with spray shields. Additionally, the tooling and manufacturing costs for the spray suppression assemblies are low since the configuration of the elements of the assemblies are designed for low-cost tooling and manufacturing. That is, while the elastomeric spray shield must be produced in its own injection mold, the two other rigid components may be molded in what is commonly called a “family mold”, that is, a single mold in which multiple related parts are formed simultaneously with each cycle of the molding machine. 
         [0116]      FIGS. 14 through 19  depict tubular body element  610  for a simplified spray suppression assembly  600  ( FIGS. 26 through 32 ) which may be assembled to cannula  10  ( FIGS. 1 through 8 ). Body element  610  has a tubular distal portion  612  having an inner diameter  614  sized to allow mounting of body element  610  to proximal element  300  of cannula  10 , and inwardly extending axial ridges  616  (commonly called “crush ribs”) on inner cylindrical surface  618  along with alignment key  619 . Proximal inwardly extending flange  614  of body element  610  has formed in its proximal face slots  620  having the form and function of slots  320  of proximal element  300  of cannula  10 . Flange  614  has formed on its distal surface flange  622  which forms a cylindrical pocket of diameter  624  that has formed therein alignment key  626 . Flange  614  defines a circular opening  628  of diameter  629 . Body  610  is formed of a suitable rigid polymeric material. 
         [0117]      FIGS. 20 through 22  depict a flexible polymeric spray shield  630  having a diameter and thickness selected to allow the placement of shield  630  in the cylindrical pocket formed by flange  614  of body element  610 , angular alignment of spray shield  630  to body  610  being established by alignment notch  632  of shield  630  and alignment key  626  of body  610 . Shield  630  has formed therein a pattern of radially extending slots  634  terminating in holes  636  so as to form therebetween deformable flaps  636 . 
         [0118]      FIGS. 23 through 25  depict a retaining ring  640  formed of a suitable rigid polymeric material having an outer diameter  642  slightly less than diameter  614  of distal portion  612  of body  610  Inner diameter  644  is approximately equal to diameter  629  of circular opening  628  of flange  614  of body  610 . 
         [0119]    As seen in  FIGS. 26 through 32  depicting spray suppression assembly  600 , spray shield  630  is positioned in the circular recess created by flange  622  of proximal flange  614  of body  610 , and is retained in that position by retaining ring  640  positioned within tubular portion  612  of body  610 . Retaining ring  640  has a diameter which causes interference between protruding axial ridges  616  of inner surface  618  of body  610  so as to prevent retaining ring  640  and spray shield  630  from being dislodged from body  610 . 
         [0120]      FIGS. 33 and 34  depict cannula  10  ( FIGS. 2 through 9 ) and spray suppression assembly  600  positioned for assembly wherein spray suppression assembly  600  is mounted to proximal element  300  of cannula  10 , interference between crush ribs  616  and the outer cylindrical surface of element  300  preventing demounting. Alignment key  619  of element  610  of assembly  600  and axial slot  301  of proximal portion  300  provide angular alignment between spray suppression assembly  600  and cannula  10 . As with previous embodiments, no solvent bonding or ultrasonic welding is used. As seen in  FIG. 38 , spray shield  630  is proximally displaced from seals  200  so as to create therebetween void  660 . Fluid leaking past sealing elements  200  fills void  600  thereby converting high velocity flow past sealing elements  200  into low velocity flow which escapes through the flaps formed by slits  634  and holes  636  thereby preventing spraying of fluids on the surgeon and surrounding area. 
         [0121]    Spray suppression assembly  600  relies on interference between crush ribs  616  of body  610  and retaining ring  640  and between crush ribs  616  and proximal element  300  to irremovably mount the elements one to another. In an alternate embodiment of the instant invention, crush ribs  616  are eliminated and irremovable assembly of the elements is accomplished by an interference fit between the respective cylindrical surfaces. In yet another embodiment, the spray suppression assembly may be removable from the cannula. 
         [0122]    In yet another alternate embodiment, the principles of the instant invention are applied to a cannula having a flexible distal portion able to accommodate curved instruments and those having irregularly shaped distal portions that will not fit through the lumen of a conventional rigid cannula. In the flexible cannulae of the instant invention, the rigid distal portion  100  of previous embodiments is replaced by an assembly having a rigid proximal portion and a flexible distal portion, the flexible distal portion being affixed to the rigid proximal portion without the use of bonding agents, but rather through a unique configuration of complementary features and a retaining collar. 
         [0123]    The elastomeric distal portion  700  for a cannula with a flexible distal portion according to the instant invention is depicted in  FIGS. 39 through 42 . Distal element  700  has an elongate distal tubular portion  702  which may optionally be threaded, and a proximal tubular portion  704  of outer diameter  710 , radial surfaces of radius  706  and laterally opposed flats  708 . 
         [0124]    The proximal assembly  740  for a cannula with a flexible distal portion according to the instant invention is depicted in  FIGS. 43 through 46 . Proximal assembly  740  is identical in form and function to cannula  10  except as described hereafter. Distal portion  742  of assembly  740  has formed on its distal end tubular portion  742  of outer diameter  744  with wedge-shaped ridges  746  formed on its outer radial surfaces, and laterally opposed flats  748  formed thereon. The form of distal portion  742  of proximal assembly  740  is complementary to the form of proximal portion  704  of distal element  700 . Diameter  744  of distal portion  742  of proximal assembly  740  may be greater than the sum of radii  706  of proximal portion  704  of elastomeric distal element  700  so that when elastomeric distal element  700  is mounted to distal portion  742  of proximal assembly  740  proximal portion  704  is stretched and wedge-shaped ridges  746  penetrate the inner radial surfaces of proximal portion  704  of elastomeric distal element  700 . 
         [0125]      FIGS. 47 through 50  depict a tubular collar  760  having an inner diameter  762  approximately equal to outer diameter  710  of proximal portion  704  of elastomeric element  700 , a radiused inner proximal edge  764  and a chamfered distal outer edge  766 . 
         [0126]    Cannula  70  having a flexible distal portion and formed in accordance with the principles of this invention is depicted in  FIGS. 51 through 55 . Elastomeric distal portion  700  is mounted to proximal assembly  740  as previously described. Collar  760  is positioned about proximal portion  704  of elastomeric distal element  700  so as to place portion  704  under compression and prevent demounting of element  700  from proximal assembly  740 . Collar  760  may be made from either a suitable polymeric or a suitable metallic material. In a preferred embodiment collar  760  is inelastically deformed after positioning on the assembly to produce increased compressive pressure on the assembly. 
       INDUSTRIAL APPLICABILITY 
       [0127]    As noted previously, the present invention is directed to a simplified, low cost arthroscopic sealing cannula having improved efficiency and reduced manufacturing costs. In particular, by replacing the conventional thermal and chemical bonding means with a mechanical joining system, the present invention provides for a substantial reduction in manufacturing costs, a dramatically simplified validation process as well as a reduced opportunity for failure. Cannulae formed in accordance with the principles of this invention may be assembled using integral fastener pairs formed with hooked sections, using heat-staked elements, or using pressed together elements that have interfering and/or friction fit features. The cannulae may optionally have a spray shield or may have a flexible distal element. The choice of the assembly method for a given device and combinations and variations of placement of these methods fall within the scope of this invention. 
         [0128]    The disclosure of each publication, patent or patent application mentioned in this specification is specifically incorporated by reference herein in its entirety. However, nothing herein is to be construed as an admission that the invention is not entitled to antedate such disclosure by virtue of prior invention. 
         [0129]    The invention has been illustrated by reference to specific examples and preferred embodiments. However, it should be understood that the invention is intended not to be limited by the foregoing description, but to be defined by the appended claims and their equivalents.