Abstract:
A prosthetic joint is disclosed that includes a plurality of elements, which may be provided in kit form, that can be assembled to form either a single-axis joint or a double-axis joint depending on whether an adaptor is used to join first and second elements of the joint.

Description:
FIELD OF THE INVENTION 
     The present invention is directed toward a prosthetic joint, and more specifically, toward a prosthetic joint that can be configured as either a single- or double-axis joint. 
     BACKGROUND OF THE INVENTION 
     The joints of a human body are subject to substantial stresses, and as people age, their joints often function less effectively than when they were younger. Injury and disease can also affect joint function. It is becoming increasingly common to replace natural joints in the human body with artificial ones when the natural joints wear out or no longer function properly. Artificial hips and knees are widely used, and other joints such as the elbow are also replaced on occasion. 
     Most artificial joints include a stem or anchor portion that is inserted into the bone on either side of the damaged joint and a pair of bearing surfaces at the protruding ends of the stems that interact with one another to form a joint. Various joints in the body are generally replaced with structurally similar artificial joints; thus a knee joint will generally be replaced with a hinge joint and a hip joint will be replaced with a ball-and-socket joint. In some cases, however, such as with elbow joints, it may be desirable to replace the natural joint with an artificial joint structurally different from the original joint to improve the function of the patient&#39;s joint. Thus a natural single-axis elbow joint is sometimes replaced with a prosthetic device that includes two pivotal axes. In this case, a stem embedded in an ulna connects to a central joint element at a first location and a stem embedded in a humerus connects to the central joint element at a second location spaced apart from the first location so that both posts pivot about different, normally parallel, axes. Such bi-axial elbow joints and the benefits and uses thereof are described in greater detail in U.S. Pat. Nos. 5,314,484 and 5,376,121 which patents are hereby incorporated by reference. 
     The type of replacement joint selected by a surgeon will depend on many factors including the age, health and activity level of the patient and the size and condition of the bones adjacent the joint being replaced. Unfortunately, it is often difficult to determine which of these joint types should be used until a patient&#39;s joint has been exposed during surgery. This is especially true in elbow replacement surgery where a the need for a double axis joint is often not evident until the damaged joint can be directly examined. Thus, a surgeon may need to obtain both types of joints prior to a surgery even though only one joint will be used. Because double-axis elbows are used less frequently that single-axis joints, and are also more expensive than single-axis joints, surgeons may tend to use a single-axis joint even in cases where a double-axis joint would be more appropriate. Moreover, because a surgeon may need to partially install or modify one of the artificial joints before determining that a different device would be preferable, it may be necessary to discard one of the two prostheses at a considerable cost. 
     It is known to provide certain types of prosthetic joints in kit form which kits include a plurality of different elements, some or all of which may be used to form a given joint depending on the condition of the natural joint as revealed by surgery. For example, U.S. Pat. No. 6,027,534 describes a modular elbow kit that includes three different bearing elements. A first element is used when the elbow joint is to be configured in a constrained mode and a second and third element are used instead of the first element when the joint is to function in an unconstrained mode. Beneficially, the same kit can be used in a wide variety of patients. Stocking identical kits is generally less expensive that stocking a variety of different prosthetics, and, as a majority of the items in each kit will be used in every surgery, waste is minimized. 
     It would be therefore be desirable to provide a kit for forming a prosthetic joint that could be assembled to produce either a single-axis joint or a double-axis joint. 
     SUMMARY OF THE INVENTION 
     This problem is overcome by the present invention which comprises a prosthetic joint configurable as either a single-axis joint or a double-axis joint. While the subject invention could be used in various parts of the body, it finds particular utility as an elbow joint, and hereinafter, the invention will primarily be described in terms of an elbow joint, it being understood that it could also function in other locations in the body such as the knee. 
     In general terms, the invention comprises the provision of an adaptor for use with a single-axis joint to convert the single-axis joint to a double-axis joint when called for. The adaptor may be sold by itself or as part of a kit with the single-axis joint. An ordinary single-axis joint includes a first element insertable in a first bone, such as a humerus and a second element insertable into a second bone such as an ulna. The distal end of the humeral component and the proximal end of the ulnar component extend from the respective bones, and the distal end of the humeral element has a first shape and the proximal of the second element has a second shape complimentary to the first shape. By complimentary, it is meant that the first shape mates or fits with the second shape to form a joint. Thus a sphere and a depression would be complementary shapes (mating like a ball-and-socket joint) as would a single arm receivable between a pair of spaced-apart arms (a hinge joint). The typical joint also includes a pin or similar connector for pivotably joining the distal end of the humeral element to the proximal end of the ulnar component. To convert the single-axis joint to a double axis joint, a connector or adaptor is provided that has a first end having a shape complementary to the shape of the distal end of the humeral component and a second end having a shape complementary to the shape of the ulnar component which adaptor can thus be placed between the ends of the humeral and ulnar components and pivotally connected to each to form a double axis joint. In the preferred embodiment, the complementary shapes are described as a first end of a first element that is received between the spaced apart arms of a second element; however other complementary shapes could be used as well. 
     In a preferred embodiment, the invention comprises a humeral component having a stem portion for insertion into the interior of a humerus and a second end, an ulnar component having a first end for insertion into the interior of an ulna and a second end, and a connector for pivotably joining the second ends to form a joint. A first connector comprises a pin that directly connects the second ends of the components to form a single-axis joint while a second, alternate, connector comprises a spacing element that has a first portion connectable to the second end of the humeral element with a pin and a second portion connectable to the second end of the ulnar element with a pin to form a double-axis joint. The first portion of the spacing element is generally similar in shape to the second end of the ulnar element while the second portion of the spacing element is generally similar in shape to the second end of the humeral element. 
     The second end of the humeral element includes a pair of parallel, spaced apart arms each having a bore which bores are coaxially aligned. The second end of the ulnar element is somewhat narrower than the spacing between the arms of the humeral element and includes a bore of approximately the same diameter as the bores in the humeral element arms so that when the bore in the ulnar element is aligned with the bores in the humeral element and a pin is inserted through the aligned bore, a joint is formed. A bearing insert is also preferably used between the ulnar and humeral elements to reduce wear and keep the ulnar element properly spaced with respect to the humeral element. 
     The connector of the preferred embodiment is generally Y-shaped and includes two parallel arms that extend from a body portion in a first direction and a third arm that is centered between and parallel to the first and second arms but which extends from the body portion in a direction opposite to the first and second arms. To form a double-axis joint, the third arm of the connector is connected between the arms of the humeral element with a pin and the second end of the ulnar element is connected between the parallel arms of the connector with a pin to form a double-axis joint. The prosthesis is sold in kit form so that a surgeon need obtain only one kit, and the surgeon can install the joint with or without the connector depending on the condition of the natural joint as revealed by surgery. 
     It is therefore a primary object of the present invention to provide an artificial joint configurable as either a single-axis joint or a double-axis joint. 
     It is another object of the invention to provide a method of installing an artificial joint as either a single-axis joint or a double-axis joint. 
     It is a further object of the invention to provide an adaptor for converting a single-axis joint to a double axis joint. 
     It is still another object of the invention to provide a kit for assembling a prosthetic joint. 
     It is still a further object of the invention to provide a prosthetic joint kit that includes a first element for connection to a first bone, a second element for connection to a second bone, and two connectors, either of which can be used to pivotably connect the first and second elements. 
     In furtherance of the foregoing objects, a prosthetic elbow is disclosed that includes a humeral component and an ulnar component adapted to pivotably engage the humeral component and an adaptor having a first end pivotably connected to the ulnar component and a second end pivotably connected to the humeral component. 
     Also disclosed is a kit assembleable in a first configuration to form a single-axis prosthetic joint and in a second configuration to form a double-axis prosthetic joint that includes a first component having a proximal end insertable into a first bone and a distal end, a second component having a distal end insertable into a second bone and a proximal end, and an adaptor connectable between the first component and the second component. The kit is assembled by connecting the first component directly to the second component to form a single-axis joint or by connecting the adaptor between the first component and the second component to form a double-axis joint. 
     A method of assembling a prosthetic joint is also disclosed that includes the steps of providing a first joint component having a first end adapted to be inserted into the interior of a first bone and a second end, a second joint component having a first end adapted to be inserted into the interior of a second bone and a second end, a first connector for forming a single-axis pivotal connection between the first component and the second component, and a second connector for forming a double-axis pivotal connection between the first component and the second component. Then one of the first and second connectors is selected and used to connect the first component to the second component. 
     A double-axis prosthetic joint is also described that is formed from a first component having a proximal end adapted to be mounted in a first bone and a distal end comprising a pair of spaced apart arms and a second component having a distal end adapted to be mounted in a second bone and a proximal end including a bore. The joint also includes a connector for pivotably connecting the first component to the second component which connector has a first end having a bore which is pivotably mounted between the first component spaced apart arms and a second end comprising a pair of spaced apart arms. The second component distal end is pivotably mounted between the connector second end spaced apart arms. 
     Another aspect of the invention comprises a prosthetic joint kit including a first component having a first end and a second end comprising a pair of spaced apart arms and a second component having a first end and a second end comprising a bore. The kit also includes a first connector for pivotably connecting the first component directly to the second component and a second connector for pivotably connecting the first component indirectly to the second component. 
     Another aspect of the invention comprises a method of converting a single-axis prosthetic joint to a double-axis prosthetic joint that includes the steps of providing a first joint element having a first end insertable into a bone and a second end having a first shape, and a second joint element having a first end insertable into a bone and a second end having a second shape complementary to the first shape. The second end is pivotably connectable to the first joint second end to form a single-axis prosthetic joint. A connector is also provided that has a first end having a shape complementary to the first shape and a second end complementary to the second shape that can be used to pivotally attach the first joint element second end to the connector first end, and the second joint element second end to the connector second end to form a double-axis prosthetic joint. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and aspects of the invention will be better understood from a reading of the detailed description of the invention provided below together with the following drawings. 
     FIG. 1 is an exploded top plan view of an artificial joint according to the present invention. 
     FIG. 2 is an exploded side elevational view of the artificial joint of FIG.  1 . 
     FIG. 3 is a perspective view of an artificial joint according to the present invention configured as a single-axis joint. 
     FIG. 4 is a perspective view of an artificial joint according to the present invention configured as a double axis joint. 
     FIG. 5 is a perspective view of a pin and clip for connecting the elements of the subject artificial joint. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only and not for the purpose of limiting same, FIGS. 1 and 2 shows the elements of an artificial joint  10  according to the present invention, namely, a first or humeral component  12 , a second or ulnar component  14 , an adaptor or connector  16  and two bearing inserts  18 . The preferred embodiment of the invention comprises an artificial elbow joint, and therefore, various components are described as being connectable to a humerus in a person&#39;s upper arm and an ulna in a persons forearm. The terms “proximal” and “distal” are used herein relative to the portion of the human body in which the joint will be installed, even though a body it not shown in the figures. Thus, for example, the proximal end of the humeral component is the end that will be inserted into a humerus when the joint is in place in a body and the distal end of the humeral component will extend from the humerus. 
     All components described below, with the exception of inserts  18  are formed from a surgical grade metal, steel or titanium or alloys thereof, for example, while inserts  18  are formed from a standard implant-grade high molecular weight polyethylene. 
     Humeral component  12  includes a proximal end  22 , a distal end  24  and a head  26 . A portion  27  of distal end  24  is roughened or coated with a granular material to provide a larger surface area for bone to attach to as it grows around the stem. Head  26  includes a first wall  28  from which extends a first arm  30  and a second arm  32  parallel to the first arm and spaced apart therefrom by a first distance. Arms  30  and  32  have ends  34  and  36 , inner walls  38  and  40 , and outer walls  42  and outer wall  44 , respectively. First arm  30  includes a bore  50  extending between inner wall  38  and  42  while second arm  32  includes a bore  52  coaxially aligned with bore  50  and extending between inner wall  40  and outer wall  44 . Outer walls  42  and  44  each include U-shaped notches  54  extending inwardly from ends  34  and  36 . A stop plate  56  is also provided on the distal end of the humeral component for limiting the angular movement of the assembled joint. 
     Ulnar component  14  includes a distal end  58  and a proximal end  60  having a head  62  and a portion  64  roughened or coated with a granular material to provide a larger surface area for connection to an ulna. Head  62  includes parallel sidewalls  66 ,  68  connected by a bore  70  and a rounded end wall  72 . 
     Adaptor or connector  16  includes a body portion  76  having a first wall  78  from which a first arm  80  and a second arm  82  extend and a third arm  83  that extends from the opposite side of the body portion from the first and second arms. Arms  80  and  82  have ends  84  and  86 , inner walls  88  and  90 , and outer walls  92  and  94 , respectively. First arm  80  includes a bore  100  extending between inner walls  88  and outer wall  92  while second arm  82  includes a bore  102  coaxially aligned with bore  100  and extending between inner wall  90  and outer wall  94 . Outer walls  92  and  94  include U-shaped notches  103  surrounding the opening of bores  100  and  102 . Third arm  83  includes a rounded end wall  104  and first and second parallel sidewalls  106 ,  108  and a bore  110  extending between the first and second sidewalls. 
     Bearing inserts  18  are generally U-shaped and include a body portion  112 , first and second arms  114 ,  116  extending from the body portion, and a projection  117  extending from the opposite side of body portion  112 . Arms  114 ,  116  include ends  118 ,  120 , inner walls  122 ,  124  having inwardly facing bosses  123 ,  125 , and outer walls  126 ,  128  respectively. The bosses  123 ,  125  have outer widths sized to fit within bores  70  and  110  of the connector and the ulnar component in a manner that allows the connector and the ulnar component to be pivotably supported by the bosses. First arm  114  includes a bore  130  that extends through the first arm and boss  123  and second arm  116  includes a bore  132  coaxially aligned with first bore  130  that extends through the second arm  116  and the second boss  125 . 
     The parts described above can be assembled in one of two ways to form either a single-axis joint as shown in FIG. 3 or a double-axis joint as shown in FIG.  4 . Preferably, all elements are sold together in kit form so that a surgeon performing a joint replacement will have all the necessary pieces for forming the type of joint dictated by the condition of the patient&#39;s natural joint. Pins  134 , one of which is shown in FIG. 5, are provided for pivotably connecting the various elements of the kit which pins include a first end  136 , a cylindrical body  138 , and a second end  140  with an annular groove  142  spaced inwardly from end  140 . A clip  144  engages annular groove  142  to secure the pin as will be described below. 
     When it is determined that a single-axis joint is needed, the artificial joint is assembled as follows: the arms  114 ,  116  of bearing insert  18  are spread so that head  62  of ulnar portion  14  can be inserted between bosses  123 ,  125 . The insert is then allowed to return to its unflexed shape with bosses  123 ,  125  projecting into bore  70 . Insert  18  is next inserted into the gap between first and second arms  30 ,  32  of humeral portion  12  with projection  117  of the insert abutting first wall  28  of the humeral portion and with outer wall  126  of first bearing insert first leg  114  adjacent inner wall  38  of the first leg of the humeral portion and outer wall  128  of the first bearing insert second arm  116  adjacent inner wall  40  of the second leg of the humeral portion with bores  130 ,  132  of the bearing insert aligned with humeral portion first leg bore  50  and humeral portion second leg bore  52 . A pin  134  is the inserted through the aligned bores until first end  136  enters the U-shaped notch  54  on the side of first arm  30  and the second end  140  extends from bore  52  in second arm  32 . A clip  144  having a diameter greater than the width of U-shaped notch  54  in arm  32  is then snapped around annular groove  142  to prevent pin  134  from being withdrawn through the bores in the annular element. The humeral and ulnar components of the joint are then installed in a humerus and an ulna in the standard manner. 
     When it is determined that a double-axis joint is needed, connector  16  and a second bearing insert  18  are installed between the humeral element  12  and the ulnar element  14 . The arms  114 ,  116  of a first bearing insert  18  are spread so that third arm  83  of adaptor  16  can be inserted therebetween and the insert is then released to allow bosses  123 ,  125  to project into bore  110  of the adaptor. The adaptor and insert are then placed between the first and second arms  30 ,  32  of the humeral element with bores  50 ,  52  of the humeral component aligned with the adaptor bore  110  and attached with a pin  134  as described above. A second bearing insert  18  is then attached to head  62  of ulnar element  14  by spreading the arms of the insert and placing the bosses  125 ,  123  of the insert into bore  70  of ulnar element  14 . The bearing element mounted to head  62  of ulnar element  14  is next placed into the gap between arms  80 ,  82  of adaptor  16  with bore  70  of the ulnar element aligned with the bores  100 ,  102  in the adaptor arms  80 ,  82 , and the adaptor is fastened to the ulnar element using a pin as described above. The joint thus formed has a first pivotal axis at the first pin connecting the humeral element to the connector and a second pivotal axis at the second pin that connects the ulnar element to the second end of the connector. 
     The invention has been described in terms of a preferred embodiment, it being understood that numerous obvious modifications and additions to this embodiment will become apparent to those skilled in the relevant arts upon a reading and understanding of this description. It is intended that all such modifications and additions be a part of the subject invention to the extent that they are included within the scope of the several claims appended hereto.