generally referring to fig1 an anterior or palmar view of the bones of the wrist carpus 20 of a right hand is shown , palm side up . the bones that form the carpus of the wrist 20 include a proximal carpal row 22 and a distal carpal row 24 . proximal carpal row 22 is adjacent the radius 26 and the ulna 28 of the wrist and includes a scaphoid bone 30 , a lunate bone 32 , a triquetrum bone 34 , and a pisiform bone 36 . the radial carpal joint 38 is that space between the proximal carpal row 22 and the articulating distal radius 26 . the distal carpal row 24 includes a hamate bone 40 , a capitate bone 42 , a trapezoid bone 44 , and a trapezium bone 46 . the midcarpal joint 48 of the wrist extends between the distal and proximal carpal rows . the extrinsic palmar carpal ligaments are shown in fig1 a , the intrinsic ligaments are shown in fig1 b and the dorsal extrinsic ligaments are shown in fig1 c . normal wrist movement is very complex and involves , in part , motion at the midcarpal joint and in part motion at the radiocarpal joint . additionally , there is a predicable well orchestrated rotational motion specific and different for each carpal bone which is generated by the bone &# 39 ; s shape and by its ligamentous and capsular attachments . for example , in radial deviation of the wrist the scaphoid distal pole rotates in a palmar direction , in a sense making &# 34 ; room &# 34 ; for the distal carpal row to pass over the proximal row . likewise , in ulnar deviation the normal scaphoid rotates dorsally , away from the palm , tethered by its neighboring lunate and surrounding capsule , in a sense making &# 34 ; room &# 34 ; for the distal carpal row to pass more easily &# 34 ; under &# 34 ; the proximal row . in pathological conditions such as severe wrist sprains , the ligaments are disrupted and the synchronous carpal kinematics are impaired . this may lead to pain , arthritis and advanced collapse of the carpus , i . e ., slac ( scapho - lunate advanced collapse ) wrist . a similar fate of slac may occur secondarily to scaphoid fracture non - union or avascular necrosis . during the surgical replacement of a carpal bone ( scaphoid or lunate ) those ligaments which are not already disrupted must be cut . unless those ligaments are reconstructed or substituted , the same fate may ensue : instability of the prosthesis , surrounding carpal arthritis and eventual carpal collapse . too frequently this is the fate of current &# 34 ; unrestrained &# 34 ; carpal prostheses . in accordance with the present invention , a &# 34 ; restrained &# 34 ; prosthesis , the complex carpal motion will be preserved and collapse with arthritis prevented . in fig2 - 6 , the prosthesis is generally denoted by the numeral 52 and comprises a body member 54 contoured to resemble the shape of the carpal bone which it replaces . in fig2 a and 2b , denoting respectively a scaphoid prosthesis and a lunate prosthesis , the body member includes first and second independent channels , 56 and 58 , and ligamentous means 60 are positioned within the channels for tethering prosthesis 52 to adjacent tissues , including carpal bone as well as dorsal and palmar capsule . fig3 a and 3b illustrate the three - dimensional structures of the carpus . the geometric axes of the hand , x , y and z axes are shown as 90 ° perpendicular planes of reference . to maintain reproducibility , for example on an x - ray , the following anatomic landmarks are chosen to create these axes : the x - axis represents a best fit line between the ulnar and radial styloids on a pa view . the y - axis is a best fit line through the length of the 3rd metacarpal shaft . the z - axis is simply a plane perpendicular to both the x and y axes . by creating these axes one has a mathematical tool and language to describe any coordinate or direction within the carpus . for example , each channel within a given carpal prosthesis has definable coordination on the x , y and z axes . returning now to fig2 a and continuing with the example of the scaphoid prosthesis , first channel 56 may be said in this embodiment to lie on an imaginary tether axis 62 , essentially the z axis ( dorsal to palmer ) in fig3 a and 3b . the second channel 58 ( fig2 a ) may be said in this embodiment to lie slightly obliquely to the x and y axes , articulating with the trapezium and lunate . in the preferred embodiment illustrated , channel 58 is curved to correspond generally to the curvature of the body member i . e ., along its long axis , proximal pole to distal pole . also , in the illustrated embodiment , channel 56 is substantially perpendicular to channel 58 , and the two channels intersect at a single point within the body member . in alternative embodiments , the channels need not be intersecting , nor need they be completely perpendicular . in fig2 a , each ligamentous means 60 extends through first and second channels 56 and 58 , and emerges from the openings at each end of the channels . in the illustrated embodiments , the channels may be ovoid in cross - section in order to protect the body member against stress risers . the edge of each channel opening may be rounded to remove any sharp interface against the ligamentous means . nevertheless , if desired , the channels may be circular or of any other cross - sectional shape which preserves the above desirable characteristics . also , the channels may be used : 1 ) without a porous coating or other affixation means ; 2 ) with a porous coating ( 70 ) to provide surface to facilitate tissue ingrowth between the ligamentous means and the prosthesis ; or 3 ) with or without a porous coating , but with adhesive to anchor the ligamentous means . ligamentous means 60 in fig2 a is placed through channels of the body member and is surgically attached to adjacent ligaments , capsule , or bone ( see fig4 ). ligamentous means 60 may be made of dacron or any other ingrowth receptive fabric ( including teflon ), native tendon graft ( e . g ., palmerus longus ), capsule , or bone - capsule - bone graft . for example , when ligamentous means 60 are secured to an adjacent carpal bone ( fig5 ), various techniques may be used including suturing the ligamentous means directly to the adjacent intrinsic ( interosseous ) ligament . for example , ligamentous means 60 of a scaphoid prosthesis 52a could be sutured to the scaphotrapezial ligament 76 and the scapholunate ligament 78 which are located between trapezial bone 46 and scaphoid bone 30 ( which has been replaced by prosthesis 52a ) and scaphoid bone 30 ( prosthesis 52a ) and lunate bone 32 , respectively , as shown in fig6 . an alternative technique would include removal of a very small area of cartilage and endosteum to expose raw cancellous bone . drill holes would then be placed in the bone for passage of suture and a suture placed in the end of the ligamentous means . the suture would be passed through the drill holes pulling the ligamentous means firmly against , or through , the scarified bone and the sutures tied to each other in a horizontal mattress fashion . this technique of suturing is similar to that described by julio taleisnick , m . d . ( journal of hand surgery , 17a , march 1992 , pages 354 - 359 , &# 34 ; a technique for direct repair of the scapho - lunate interrosseous ligament &# 34 ;). an alternate technique to suture the ligamentous means to adjacent bone may include use of small bone anchors , e . g ., mitek ® anchors which are available from surgical products , inc . of norwood , mass ., or to secure the ligamentous means by an interference screw . similarly , the lunate prosthesis could be secured by ligamentous means in a similar fashion to its adjacent carpal bones , i . e ., scaphoid ( and / or scapholounate ligament ) and the triquetrum ( and / or lunotriquetral ligament ). in a less preferred alternate embodiment , body member 54b includes one or both of the ligamentous means secured to its outer periphery 92 by means of eyelets 80 ( fig7 ) movably restraining the prosthesis to adjacent tissues . in use , prosthesis 52 is surgically implanted into a wrist for replacing a damaged carpal bone using standard surgical procedures . if the native intrinsic and extrinsic ligaments are intact , they are divided as the damaged carpal bone is removed , preserving neighboring ligament and capsular attachments . the properly sized prosthesis is then inserted into and properly positioned within the space created by the excised carpal bone such that one axis of the ligamentous means 60 is oriented towards the palmar or dorsal capsule 51 ( fig4 - 6 ). the prosthesis is next oriented along the second axis by inserting it in normal articulating alignment with its neighboring carpal bones . those articulating ends represent the exits for the second tethering channel through which the ligamentous means have been placed . finally , the ligamentous means are fixed to adjacent capsule and intrinsic ( interosseous ) ligament or bone ( see fig4 - 6 ). the following is a description of the method by which the ligamentous means through channel 56 is fixed to the dorsal and palmar capsule . in this method , referring again to fig2 a , the ligamentous means through channel 58 attaching to bone substitute for the &# 34 ; intrinsic ligaments &# 34 ; ( i . e ., short interosseous ligaments ), and the ligamentous means through channel 56 substitute for the extrinsic ligaments ( i . e ., dorsal and palmar capsular attachments ). in order to secure ligamentous means through channel 56 sutures attached to the ligamentous means at each end may be sewn directly to capsule and at either or both ends . alternatively , the suture may be brought through capsule , then skin , and tied down in a standard fashion over a button . after many weeks of healing the pull - out suture and button would be removed leaving the secured ligamentous means in place . fig8 and 9 illustrate a scaphoid and lunate prosthesis , 52a and 52b , respectively , after to their implantation in a wrist . first referring to fig8 scaphoid prosthesis 52a is tethered by ligamentous means 60 by way of channel 58 , to trapezium bone 46 and lunate bone 32 . scaphoid prosthesis 52a is also tethered by a second ligamentous means 60 to the dorsal and palmar capsules by way of channel 56 . this second ligamentous means would be perpendicular to the plane of the figure ( i . e ., in and out of the plane of the paper ). referring to fig9 lunate prosthesis 52b is shown tethered by way of its two channels by ligamentous means 60 to scaphoid bone 30 and triquetrum bone 34 and by the other ligamentous means to the dorsal and palmar capsules . again , this second ligamentous means is illustrated perpendicular to the figure . therefore , it should be recognized that , while the invention has been described in relation to a preferred embodiment thereof , those skilled in the art may develop a wide variety of structural details without departing from the principles of the invention . accordingly , the appended claims are to be construed to cover all equivalents falling within the scope and spirit of the invention .
a carpal bone prothesis comprising a body member made of a biocompatible , medically inert material which is designed to be restrained along at least two independent axes . in one important embodiment , the body member includes at least two independent channels and ingrowth receptive ligaments which extend through the channels and are attached to adjacent carpal bones along the first axis and to the dorsal and palmar capsules along the second axis .