Patent Publication Number: US-2013253664-A1

Title: Antimicrobial containment cap for a bone anchored prosthesis mounting

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to improvements in external or exoskeletal prosthetic devices and systems of the type utilizing an implanted, bone anchored mounting post having or carrying an externally protruding or externally exposed fixator structure for removable attachment of a prosthesis such as a prosthetic limb or the like. More particularly, this invention relates to an antimicrobial containment cap for use in combination with a bone anchored prosthesis mounting system, wherein the containment cap supports and retains a selected antimicrobial agent against the skin of an amputee substantially at the exit site or tissue interface of the fixator structure extending through the skin, to reduce or eliminate risk of infection. 
     Socket type prosthetic limbs such as prosthetic arm and leg structures for use by amputees are generally well known in the art, wherein a prosthesis is constructed with an open-ended and typically padded socket structure for receiving and supporting the post-surgical stump of a residual amputated limb. By way of example, a socket type prosthetic leg includes such open-ended socket structure at an upper end thereof for receiving and supporting the post-surgical upper leg of a transfemoral amputee. Various straps and/or other fasteners are provided for securing the prosthetic leg to the amputated limb to accommodate walking mobility at least on a limited basis. Such prosthetic limbs can be an important factor in both physical and mental rehabilitation of an amputee. 
     However, socket type prosthetic limbs are associated with a number of recognized limitations and disadvantages. In particular, the socket style prosthesis inherently couples mechanical loads associated with normal ambulatory activity through a soft tissue interface defined by the soft tissue covering the end or stump of the residual amputated limb, but wherein this soft tissue interface is structurally unsuited for this purpose. While many different arrangements and configurations for the requisite straps and other fasteners have been proposed for improved transmission and distribution of these mechanical loads to bone structures for improved secure and stable prosthesis attachment, to correspondingly accommodate a more natural ambulatory movement, such arrangements have achieved only limited success. In addition, compressive loading of this soft tissue interface often results in blisters, sores, chafing and other undesirable skin irritation problems which have been addressed primarily by adding soft padding material within the socket structure. But such soft padding material undesirably increases the extent of the soft or non-rigid interface between the amputated limb and prosthesis, all in a manner that is incompatible with an optimally secure and stable prosthesis connection, As a result, particularly in the case of a prosthetic leg, traditional socket style connection structures and methods have generally failed to accommodate a normal walking motion. 
     In recent years, improved external or exoskeletal prosthetic devices have been proposed, wherein the external prosthesis is structurally linked by means of a bone anchored mounting system directly to patient bone. In such devices, a rigid mounting post is surgically implanted and attached securely to patient bone as by means of osseointegration or the like. This implanted mounting post extends from the bone attachment site and includes or it attached to a fixator pin or post structure that protrudes through the overlying soft tissue at the end of the residual amputated limb. Thus, one end of the fixator pin is externally exposed for suitable and secure attachment to a prosthetic limb or the like. In such bone anchored mounting systems, mechanical loads on the prosthetic limb during ambulation are transmitted by the rigid components including the external fixator pin and the implanted mounting post directly to patient bone. As a result, conventional mechanical loading of the soft tissue interface is avoided, and substantially improved and/or normal patient movements are accommodated. In addition, the requirement for compressive loading of the soft tissue at the end of the amputated limb is significantly reduced, to correspondingly reduce incidence of blisters and other associated skin irritation problems. 
     Although use of a bone anchored mounting system offers potentially dramatic improvements in secure and stable prosthetic limb attachment, and corresponding improvements in amputee lifestyle, the exit site or interface between the externally protruding fixator pin and the soft tissue at the end of the residual limb inherently subjects the amputee to a significant and on-going risk of infection. That is, the soft tissue interface with the externally protruding fixator pin is difficult to seal and protect against entry of microbial infection-producing organisms. The difficulties in adequately sealing this tissue-pin interface are compounded by the presence of multiple and typically random and irregular-shaped small skin folds formed in the soft tissue at the end of the residual limb, and thus present in the immediate vicinity of the tissue-pin interface. These small skin folds unfortunately provide multiple shallow channels or pathways which are difficult to keep clean, many of which lead directly to the tissue-pin interface. Infection at this tissue-pin interface can produce serious complications including eventual loosening and failure of the bone anchored mounting post. 
     There exists, therefore, a significant need for improvements in and to external or exoskeletal prosthetic devices of the type utilizing a bone anchored mounting system, wherein the risk of infection at the soft tissue interface with an externally protruding fixator pin is substantially reduced and/or eliminated. The antimicrobial containment cap of the present invention fulfills these needs and provides further related advantages. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, an antimicrobial containment cap is provided for use in combination with a bone anchored prosthesis mounting system. Such bone anchored mounting system includes an implanted bone anchored mounting post adapted for secure and stable affixation to patient bone, wherein the implanted mounting post carries or is connected to a fixator pin which protrudes through soft skin tissue and the like covering the end or stump of a residual amputated limb and is adapted for secure and stable attachment to an external or exoskeletal prosthesis such as a prosthetic limb or the like. The containment cap is interposed between the external prosthesis and the soft tissue at the end of the residual limb, and carries and retains a selected antimicrobial agent against the amputee&#39;s skin in a position generally closely overlying and substantially circumscribing the host tissue exit site or interface between soft tissue and the fixator pin. The containment cap, which is adapted for quick and easy periodic removal for cleaning and/or replenishment of the antimicrobial agent, thus safeguards the tissue-pin interface against infection. 
     In one preferred form, the containment cap comprises a generally cup-shaped structure having an open-ended configuration defining a cavity adapted for receiving and supporting the selected antimicrobial agent. In a preferred embodiment, the antimicrobial agent may be carried by or embedded or impregnated within a disk-shaped member formed from a relatively soft and resilient material such as a fibrous batting or gauze or foam material having a size and shape for seated reception into the open-ended cap cavity. The containment cap further incorporates fastener means for removable attachment locked onto the external fixator pin, such as a central cylindrical hub depending from a cap base wall. A set screw or the like may be fastened through the depending hub into engagement with the fixator pin, when the containment cap is slidably or rotatably fitted onto the fixator pin with the soft disk-shaped, agent-carrying member contacting or in close proximity to the soft tissue of the residual limb substantially at the tissue-pin interface. The fixator pin protrudes through and beyond the containment cap to define a free end exposed for suitable removable attachment to the associated prosthesis, such as a prosthetic leg or arm for an amputee. 
     In use, the containment cap closely overlies the soft tissue interface with the externally protruding fixator pin, to retain the antimicrobial agent against and in close proximity with this soft tissue interface throughout normal usage of the prosthesis. The selected antimicrobial agent may comprise any selected medicant in ointment, gel, lotion or other form chosen for killing any selected infection-causing organism or organisms, or other medicant such as a conditioning or anti-inflammation agent or the like. Upon removal of the prosthesis, the containment cap can be quickly and easily removed from the fixator pin for appropriate cleaning of the residual limb soft tissue and/or cap surfaces, as well as replenishment and/or replacement of the infection-preventive agent. 
     Other features and advantages of the present invention will become apparent from the following more detailed description, taken in connection with the accompanying drawing which illustrate, by way of example, the principals of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate the invention. In such drawings: 
         FIG. 1  is an exploded and partially fragmented perspective view showing the antimicrobial containment cap of the present invention in combination with a bone anchored prosthesis mounting post for use in removable external attachment to an exoskeletal prosthesis, such as a prosthetic leg; 
         FIG. 2  is a fragmented perspective view illustrating an upper leg portion of a transfemoral amputee, including a bone anchored prosthesis mounting post defining an externally protruding fixator post member for use in removable attachment of an exoskeletal prosthesis; 
         FIG. 3  is an enlarged sectional view of the antimicrobial containment cap of the present invention; 
         FIG. 4  is an elevation view, shown partially in vertical section, showing the antimicrobrial containment cap mounted onto the externally protruding fixator post; 
         FIG. 5  is an exploded and partially fragmented perspective view depicting surgical implantation of the bone anchored mounting post; 
         FIG. 6  is an enlarged sectional view similar to  FIG. 3 , but illustrating one alternative preferred form of the invention; and 
         FIG. 7  is an enlarged sectional view similar to  FIGS. 3 and 6 , but showing a further alternative preferred form of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     As shown in the exemplary drawings, an antimicrobial containment cap referred to generally in  FIG. 1  by the reference numeral  10  is provided for use with a bone anchored mounting system of the type having an implanted mounting post  12  designed for secure and stable attachment to an external or exoskeletal prosthesis  14 , such as a prosthetic limb or the like for an amputee. The containment cap  10  carries and retains a selected medicant in a position for contacting soft tissue substantially at the exit site or tissue interface with an externally protruding fixator pin or post  16  adapted for removable connection to the external prosthesis  14 . The containment cap  10  is designed for significantly reducing or eliminating risk of infection at this soft tissue interface with the externally protruding fixator pin  16 . 
     The antimicrobial containment cap  10  of the present invention is particularly designed for use with external or exoskeletal prosthetic fixation or mounting systems of the type having the internal, implanted bone anchored mounting post  12  which is surgically attached to and securely supported by patient bone, as by means of osseointegration or the like. For example, with reference to the illustrative drawings as viewed in  FIGS. 1-2  and  4 - 5 , the bone anchored mounting post  12  comprises an elongated tube or rod formed typically from a high strength and biocompatible metal or the like adapted for secure affixation within the intramedullary canal  18  of a long patient bone  20  such as by seated implantation into a lower end of an amputated femur in the case of a transfemoral amputee. The mounting post  12  extends from the amputated end of the patient bone  20  through the adjacent and associated soft tissue  24  which overlies the amputated bone end and defines the stump of the residual amputated limb. Importantly, the mounting post  12  extends further, in a one-piece or multi-piece construction, through this soft tissue  24  of the residual limb to define the externally protruding fixator pin  16  for attachment in any suitable manner (not shown herein) to the exoskeletal prosthesis  14 , such as a prosthetic leg in the case of a transfemoral amputee. 
     The implanted bone anchored mounting post  12  and associated externally protruding fixator pin  16  beneficially accommodate direct mechanical support of the prosthesis  14  and associated direct mechanical loading by the patient bone  20  during normal use such as during ambulatory movements. In other words, such mechanical loads are transmitted from the prosthesis  14  directly via the rigid linkage defined by the fixator pin  16  and the mounting post  12  to the patient bone  20 , wherein ambulatory loading is substantially carried by the bone  20  in a normal anatomical manner. By contrast, the soft tissue  24  at the end of the residual limb is substantially unloaded, compressively or otherwise, since the soft tissue  24  is not required to bear or transmit these mechanical loads. As a result, the bone anchored mounting system beneficially provides a more stable and more secure attachment of the prosthesis  14  to the amputee in a manner capable of accommodating more normal and more natural ambulatory movements. By avoiding significant mechanical loading of the soft tissue  24 , soft tissue blistering and chafing and other skin irritation problems associated with a traditional soft tissue loaded prosthesis interface are substantially reduced and/or eliminated. In addition, by mechanically linking and supporting the prosthesis  14  from the patient bone  20 , amputees have reported a significant increase in perception of the prosthesis  14  as an actual and natural body part—a highly desirable factor referred to as “osseoperception.” 
     The antimicrobial containment cap  10  of the present invention is designed for mounting along the externally protruding portion of the fixator pin  16  substantially at the soft tissue interface with said fixator pin  16 , and interposed between the residual limb soft tissue  24  and the associated prosthesis  14 . Accordingly, in a preferred orientation as shown, the containment cap  10  may be sized and shaped for substantially nested positioning within an upwardly open socket  26  ( FIG. 1 ) formed in or defined by an upper end of the associated prosthesis  14 , whereby the cap  10  is substantially concealed from view during normal use. The containment cap  10  is, in the preferred form, mounted onto the fixator pin  16  but in a manner that does not interfere with the desired direct transfer of mechanical loads by the fixator pin  16  and associated mounting post  12  from the prosthesis  14  to the patient bone  20 . In other words, the containment cap  10  may be carried by the fixator pin  16  in a manner that does not result in substantial compressive loads applied to the cap  10  or to the soft tissue  24  of the residual limb. Importantly, the containment cap  10  supports and retains the selected medicant such as an antimicrobial agent in substantial contact or in close proximity with the soft tissue  24 , substantially at the tissue interface with the protruding fixator pin  16 , to reduce and/or eliminate risk of infection. 
     As shown best in  FIGS. 1 ,  3  and  4 , the containment cap  10  comprises (in one preferred form) a substantially cup-shaped body  28  defining an open-ended or upwardly open cavity  30  including a generally circular base wall  32  joined at its perimeter with a short, upstanding side wall  34  of generally cylindrical shape. A central bore  36  is formed in the base wall  32  and defines a passage through a short, vertically oriented mounting hub or mounting collar  38  protruding downwardly therefrom. A radially oriented threaded port  40  is formed in the mounting collar  38  for thread-in reception of a fastener such as a set screw  42  or the like. 
     In use, the above-described containment cap  10  is mounted onto the exposed end of the fixator pin  16  by slidably fitting the pin  16  through the hub bore  36 . The cap  10  is adjustably positioned along the length of the fixator pin  16  to position and preferably seat an upper margin  44  of the side wall  34  firmly but with a relatively light force against the soft tissue  24  of the residual limb. When suitably positioned, the set screw  42  or the like can be appropriately advanced within the threaded port  40  to engage the fixator pin  16 , thereby locking the containment cap  10  in place on the fixator pin  16 . 
     Prior to such positional adjustment and positional locking of the containment cap  10  onto the fixator pin  16 , the selected medicant such as the selected antimicrobial agent is placed into the cap cavity  30 . Accordingly, when the cap  10  is locked onto the fixator pin  16  as described above, the medicant carried thereby is positioned substantially against the soft patient  24  located at and surrounding or circumscribing the soft tissue interface with the fixator pin  16  at the exit site of the pin  16  from the tissue  24  at the end of the residual limb. Importantly, since this soft tissue  24  typically incorporates numerous relatively small or shallow ridges and folds and associated intervening channels  46  ( FIG. 2 ) extending typically in a generally radial direction relative to the fixator pin  16 , and thus defining typically hard-to-clean pathways leading to the pin-tissue interface, the presence of the medicant at this location beneficially deters and/or eliminates risk of undesirable infection. 
     In the preferred form, the antimicrobial agent can be carried by and/or embedded within a soft and resilient member  48  such as a disk-shaped fibrous or gauze or foam pad. Such pad  48  may be formed with a size and shape for slide-fit reception into the cap cavity  30 , and may include a central bore  50  for slide-fit reception over the fixator pin  16  as the containment cap  10  is mounted thereon. The pad  48  may have a thickness for slight compression against the soft tissue  24  upon final positioning of the cap  10 , thereby insuring relatively intimate medicant contact with the pin-tissue interface. 
     The selected medicant such as the selected antimicrobial agent may be provided in any convenient form such as an ointment or gel or salve or the like, suitable for carrying by the soft pad  48  against the soft tissue  24 . Various medicants may be used, such as antibacterial or antibiotic compounds and/or combinations thereof suitable for killing infection-causing organisms at the pin-tissue interface. Alternative medicants can be used, including but not limited to conditioning or anti-inflammation agents and the like. 
     Upon periodic and typically normal removal of the prosthesis  14  from the fixator pin  16 , the containment cap  10  can be removed quickly and easily from the fixator pin  16  for convenient cleaning and/or replenishment of the medicant and/or soft pad  48 , or alternately for disposal and replacement of these components. In this regard, the containment cap  10  may be constructed from a metal material suitable for cleaning and re-use, or alternately from a lightweight plastic material or the like conducive to single usage followed by disposal. The soft pad  48  may also be designed for cleaning and re-use with medicant replenishment, or alternately for single usage and disposal. When removed from the fixator pin  16 , the soft tissue  24  is conveniently exposed for cleaning. 
       FIG. 5  depicts one preferred form for the bone anchored mounting post  12  and associated fixator pin  16  with the containment cap  10  for assembly therewith. As shown, the bone anchored mounting post  12  comprises an elongated and generally tubular component  60  having longitudinally extending external flutes  62  formed thereon, and a closed upper end  64 . Outer surfaces of the post  12  may be constructed to include porous bone ingrowth surfaces (not shown) for improved osseointegration, if desired. This mounting post  12  is sized and shaped for suitable surgical implantation and secure affixation within the medullary canal  18  of the patient bone  20 , such as an amputated femur. Persons skilled in the art, however, will recognize and appreciate that alternative mounting post configurations and affixation techniques, including but not limited to thread-in post structures, may be used. 
     The fixator pin  16  shown in  FIG. 5  includes an upper end  66  having a suitable size and configuration for seated reception and secure affixation as by press-fitting into the open lower end of the post  12 . A radially enlarged flange  68  may be formed on the pin  16  to provide an enlarged and stable stop for seating against the lower end of the amputated bone  20 . The fixator pin  16  protrudes coaxially with the implanted anchoring post  12  downwardly from the stop flange  68  for passage through the soft tissue  24  ( FIGS. 1 ,  2  and  4 ) at the end of the residual limb, and appropriate removable attachment of the containment cap  10  and associated prosthesis  14 , as previously shown and described herein. As shown, this externally protruding end of the fixator pin  16  may have a noncircular cross sectional shape, such as the squared cross sectional shape as shown in  FIG. 5 , for suitable secure attachment to the external prosthesis  14  (not shown). 
       FIGS. 6 and 7  illustrate alternative preferred forms of the containment cap  10  of the present invention, wherein components corresponding with those shown and described in  FIGS. 1-5  are identified by common reference numerals. In this regard,  FIG. 6  illustrates one preferred alternative containment cap configuration  110 , wherein the disk-shaped and medicant-supporting soft pad  48  is carried by a circular base wall  32  in the absence of an upstanding cylindrical side wall  34  of the type shown and described in  FIGS. 1 ,  3  and  4 .  FIG. 7  shows another alternative preferred containment cap form  210  constructed according to  FIGS. 1 ,  3  and  4  but wherein the upper margin  44  of an upstanding cap side wall  34  merges with a radially outwardly extending support flange  70  defining a broad-based surface area for contacting the soft tissue  24  at the end of the residual limb. In both embodiments of  FIGS. 6 and 7 , the modified containment caps  110  and  210  are adapted for removable mounting onto the fixator pin  16  in substantially the same manner as previously shown and described, to support and retain the soft pad  48  and associated antimicrobial agent carded thereby against the pin-tissue interface. 
     Although various embodiments and alternatives have been described in detail for purposes of illustration, various further modifications may be made without departing from the scope and spirit of the invention. For example, although shown and described in connection with a bone anchored mounting post protruding from the patient&#39;s body, persons skilled in the art will recognize and appreciate that the containment cap may be used with other rigid and nonrigid structures protruding from the human body. By way of further example, it will be recognized and appreciated that the containment cap may incorporate vented ports as depicted in dotted lines by reference numeral  80  in  FIGS. 3 ,  6  and  7  to accommodate air flow to and ventilation of the pin-tissue interface. Accordingly, no limitation on the invention is intended by way of the foregoing description and accompanying drawings, except as set forth in the appended claims.