Stand alone intervertebral fusion device

Abstract

An angled fixation device, such as an angled screw. This angled fixation device may be used by the surgeon to secure a spacer to a spinal disc space. The proximal end portion of the angled fixation device is driven perpendicular to the anterior wall of the spacer, and so is parallel to the vertebral endplates and in-line with the inserter. The distal end portion of the angled fixation device is oriented at about a 45 degree angle (plus or minus 30 degrees) to the vertebral endplate it enters.

1 . An intervertebral device comprising:
 a) an intervertebral spacer having an anterior wall, a posterior wall, and first and second side walls connecting the anterior and posterior walls, the anterior wall having an anterior surface, an upper surface and a lower surface, a first throughhole extending upwards from the anterior surface and a second throughhole extending downwards from the anterior surface,
 b) a first screw received in the first throughhole, the first screw having a distal tip, an intermediate shaft having a threadform thereon, and a proximal head, 
   wherein the shaft of the first screw is angled.   
     
     
         2 . The device of  claim 1  wherein the angled shaft is made of a flexible material. 
     
     
         3 . The device of  claim 1  wherein the angled shaft includes a joint. 
     
     
         4 . The device of  claim 1  wherein the angled shaft includes a universal joint. 
     
     
         5 . The device of  claim 1  wherein the angled shaft includes a ball-and-socket joint. 
     
     
         6 . The device of  claim 1  wherein the spacer comprises a cage consisting essentially of the posterior wall and the first and second side walls, and the anterior wall is a separately manufactured faceplate that is mated to the cage. 
     
     
         7 . The device of  claim 1  wherein the first throughhole extends upwards through the upper surface of the anterior wall, and the second throughhole extends downwards through the lower surface of the anterior wall. 
     
     
         8 . The device of  claim 1  wherein the anterior wall comprises a posterior surface, and the first throughhole extends upwards through the posterior surface of the anterior wall, and the second throughhole extends downwards through the posterior surface of the anterior wall. 
     
     
         9 . The device of  claim 1  further comprising:
 c) a second screw received in the second throughhole, the second screw having a distal tip, an intermediate shaft having a threadform thereon, and a proximal head, 
 wherein the shaft of the second screw is angled. 
 
     
     
         10 . A medical implant comprising:
 c) a wall having an upper surface and a lower surface, and a front surface, and a first hole extending into the wall from the front surface,   d) a first screw received in the first hole and having a distal tip, an intermediate shaft having a first thread, and a proximal head,   
       wherein a portion of the shaft is disposed at an angle to the first hole. 
     
     
         11 . The implant of  claim 10  wherein the first hole extends into the wall at an angle that is not perpendicular to the front surface. 
     
     
         12 . The implant of  claim 10  wherein the shaft of the first screw is angled. 
     
     
         13 . The implant of  claim 10  wherein the shaft of the first screw is flexible. 
     
     
         14 . A method of fixing a medical implant having a wall having a front surface and a first hole extending into the wall from the front surface, the method comprising the steps of:
 d) implanting the implant in a patient, and   e) inserting a first screw having a shaft into the first hole,   
       wherein a portion of the shaft is disposed at an angle to the first hole during insertion. 
     
     
         15 . The method of  claim 14  wherein the shaft is flexible. 
     
     
         16 . An intervertebral device comprising:
 a) an intervertebral spacer having an anterior wall, a posterior wall, and first and second side walls connecting the anterior and posterior walls, the anterior wall having an anterior surface, an upper surface and a lower surface, a first throughhole extending upwards from the anterior surface and a second throughhole extending downwards from the anterior surface,
 b) a first nail received in the first throughhole, the first nail having a distal tip, an intermediate shaft having a plurality of barbs thereon, and a proximal head, 
   wherein the shaft of the first nail is angled.   
     
     
         17 . An intervertebral device for insertion into a disc space defined by opposing vertebral endplates, comprising
 i) an intervertebral spacer comprising:
 a) an anterior wall having an upper surface and a lower surface, an anterior surface, and a first throughhole extending upwards from the anterior surface and a second throughhole extending downwards from the anterior surface, 
 b) a posterior wall having an upper surface and a lower surface, and 
 c) first and second side walls connecting the anterior and posterior walls, each side wall having an upper surface and a lower surface, 
   ii) a first bone anchor received in the first through hole,   iii) a second bone anchor received in the second through hole,   wherein the upper and lower surfaces of the anterior wall contact the opposing vertebral endplates,   wherein at least one of the upper and lower surfaces of the anterior wall comprises a controlled subsidence feature,   wherein the anterior wall is characterized by a material having an intrinsic strength, the remainder of the spacer is characterized by a material having an intrinsic strength, and the intrinsic strength of the material of the anterior wall is greater than the intrinsic strength of the material of the remainder of the spacer.   
     
     
         18 . The device of  claim 17  wherein each of the upper or lower surfaces of the anterior wall comprises a controlled subsidence feature. 
     
     
         19 . The device of  claim 18  wherein the controlled subsidence feature acts to increase contact area between the spacer and the endplates as subsidence increases. (is this the definition of “controlled subsidence”?) 
     
     
         20 . The device of  claim 17  wherein the controlled subsidence feature comprises an acutely angled projection extending outwards from the upper or lower surface of the anterior wall. 
     
     
         21 . The device of  claim 17  wherein the controlled subsidence feature is selected from the group consisting of a pyramid, a cone and a wedge. 
     
     
         22 . The device of  claim 17  wherein the anterior wall comprises attachment features for attaching to the side walls. 
     
     
         23 . The device of  claim 22  wherein at least one side wall comprises a controlled subsidence feature. 
     
     
         24 . An intervertebral device for insertion into a disc space defined by opposing vertebral endplates, the device having an anterior-most surface and comprising
 i) an intervertebral cage comprising:
 a) a posterior wall having an upper surface and a lower surface, and 
 b) first and second side walls connecting the anterior and posterior walls, each side wall having an upper surface and a lower surface, 
   ii) a faceplate attaching to each of the side walls and forming the anterior-most surface of the device, the faceplate having an upper surface and a lower surface, and an anterior surface,   iii) a first bone anchor extending upwards and posteriorly from the cage and   iv) a second bone anchor extending downwards and posteriorly from the cage,   wherein the upper and lower surfaces of the faceplate contact the opposing vertebral endplates,   wherein at least one of the upper and lower surfaces of the faceplate comprises a controlled subsidence feature.   
     
     
         25 . An intervertebral device for insertion into a disc space defined by opposing vertebral endplates, comprising
 i) an intervertebral spacer comprising:
 a) an anterior wall having an upper surface and a lower surface, an anterior surface, and a first throughhole extending upwards from the anterior surface and a second throughhole extending downwards from the anterior surface, 
 b) a posterior wall having an upper surface and a lower surface, and 
 c) first and second side walls connecting the anterior and posterior walls, each side wall having an upper surface and a lower surface, 
   ii) a first bone anchor received in the first through hole,   iii) a second bone anchor received in the second through hole,   wherein the upper and lower surfaces of the anterior wall contact the opposing vertebral endplates,   wherein the upper and lower surfaces of the anterior wall define an anterior wall height, and wherein the upper and lower surfaces of the posterior wall define a posterior wall height, and   wherein the anterior wall height is greater than the posterior wall height.   
     
     
         26 . The device of  claim 25  wherein at least one of the upper and lower surfaces of the faceplate comprises a controlled subsidence feature. 
     
     
         27 . A method of inserting an intervertebral device into a disc space, wherein the device comprises,
 i) an intervertebral spacer comprising:
 a) an anterior wall having an upper surface and a lower surface, an anterior surface, and a first throughhole extending upwards from the anterior surface and a second throughhole extending downwards from the anterior surface, 
 b) a posterior wall having an upper surface and a lower surface, and 
 c) first and second side walls connecting the anterior and posterior walls, each side wall having an upper surface and a lower surface, 
   ii) a first bone anchor received in the first through hole,   iii) a second bone anchor received in the second through hole,   wherein at least one of the upper and lower surfaces of the anterior wall comprises a controlled subsidence feature,   wherein the anterior wall is manufactured as a separate component from a remainder of the spacer,   the method comprising the steps of:
 a) creating the disc space between opposing vertebral endplates, and 
 b) inserting the device into the disc space so that the upper and lower surfaces of the anterior wall contact the opposing vertebral endplates. 
   
     
     
         28 . The method of  claim 27  wherein the anterior wall is characterized by a material having an intrinsic strength, the remainder of the spacer is characterized by a material having an intrinsic strength, and the intrinsic strength of the material of the anterior wall is greater than the intrinsic strength of the material of the remainder of the spacer. 
     
     
         29 . An intervertebral device for insertion into a disc space defined by opposing vertebral endplates, comprising
 i) an intervertebral spacer comprising:
 a) having an anterior wall having an upper surface and a lower surface, an anterior surface, and a first throughhole extending upwards from the anterior surface and a second throughhole extending downwards from the anterior surface, 
 b) a posterior wall having an upper surface and a lower surface, and 
 c) first and second side walls connecting the anterior and posterior walls, each side wall having an upper surface and a lower surface, 
   ii) a first bone anchor received in the first throughhole, the first bone anchor having a distal tip, an intermediate shaft, and a proximal head,   iii) a second bone anchor received in the second throughhole, the second bone anchor having a distal tip, an intermediate shaft, and a proximal head,   wherein at least one of the first and second bone anchors has an enhanced fixation feature.   
     
     
         30 . The device of  claim 29  wherein the first throughhole extends upwards through the upper surface of the anterior wall, and the second throughhole extends downwards through the lower surface of the anterior wall. 
     
     
         31 . The device of  claim 29  wherein the anterior wall comprises a posterior surface, and the first throughhole extends upwards through the posterior surface of the anterior wall. 
     
     
         32 . The device of  claim 31  wherein the second throughhole extends downwards through the posterior surface of the anterior wall. 
     
     
         33 . The device of  claim 29  wherein the bone anchor is a screw coated with bone ingrowth substance. 
     
     
         34 . The device of  claim 29  wherein the bone anchor is a fenestrated screw for use with either cement and/or biologic injections and/or bone ingrowth materials. 
     
     
         35 . The device of  claim 29  wherein the bone anchor is an expanding screw to prevent migration. 
     
     
         36 . The device of  claim 29  wherein the bone anchor is a cannulated screw for use in percutaneous or other minimally invasive procedures. 
     
     
         37 . The device of  claim 29  wherein the bone anchor is a resorbable screw. 
     
     
         38 . The device of  claim 29  wherein the bone anchor is a screw coated with an anti-bacterial agent. 
     
     
         39 . The device of  claim 29  wherein the bone anchor is a nail having fins extending therefrom. 
     
     
         40 . The device of  claim 29  coated with an anti-bacterial agent. 
     
     
         41 . An intervertebral device for insertion into a disc space defined by opposing vertebral endplates, comprising
 i) an intervertebral spacer comprising:
 a) an anterior wall having an upper surface and a lower surface, an anterior surface, and a first through hole extending upwards from the anterior surface and a second through hole extending downwards from the anterior surface, 
 b) a posterior wall having an upper surface and a lower surface, and 
 c) first and second side walls connecting the anterior and posterior walls, each side wall having an upper surface and a lower surface, 
   ii) a first bone anchor received in the first through hole,   iii) a second bone anchor received in the second though hole,   wherein the anterior wall is made of a first material and a remainder of the spacer is made of a second material,   wherein the material of the anterior wall has a stiffness, the material of the remainder of the spacer has a stiffness, and the stiffness of the anterior wall material is less than the stiffness of the material of the remainder of the spacer.   
     
     
         42 . The device of  claim 41  wherein the spacer comprises a hollow between the walls, and wherein the device further comprises iv) bone graft contained within the hollow. 
     
     
         43 . An intervertebral device for insertion into a disc space defined by opposing vertebral endplates, comprising
 i) an intervertebral spacer comprising:
 a) having an anterior wall having an upper surface and a lower surface, an anterior surface, and a first hole extending from the anterior surface to the upper surface and a second hole extending from the anterior surface to the lower surface, 
 b) a posterior wall having an upper surface and a lower surface, and 
 c) first and second side walls connecting the anterior and posterior walls, each side wall having an upper surface and a lower surface, 
   ii) a first bone anchor received in the first hole, the first bone anchor having a distal tip, an intermediate shaft, and a proximal head,   iii) a second bone anchor received in the second hole, the second bone anchor having a distal tip, an intermediate shaft, and a proximal head,   wherein the anterior wall comprises a metallic material and a remainder of the spacer comprises bone graft.   
     
     
         44 . The device of  claim 43  wherein the anterior wall consists essentially of a metallic material and a remainder of the spacer consists essentially of bone graft. 
     
     
         45 . An intervertebral device for insertion into a disc space defined by opposing vertebral endplates, comprising
 i) an intervertebral spacer comprising:
 a) having an anterior wall having an upper surface and a lower surface, an anterior surface, and a first hole extending from the anterior surface to the upper surface and a second hole extending from the anterior surface to the lower surface, 
 b) a posterior wall having an upper surface and a lower surface, and 
 c) first and second side walls connecting the anterior and posterior walls, each side wall having an upper surface and a lower surface, 
   ii) a first bone anchor received in the first hole, the first bone anchor having a distal tip, an intermediate shaft, and a proximal head,   iii) a second bone anchor received in the second hole, the second bone anchor having a distal tip, an intermediate shaft, and a proximal head,   wherein the anterior wall is made of a first material and a remainder of the spacer is made of a second material, and   wherein the anterior wall is fixed into the remainder of the spacer so that it does not float.   
     
     
         46 . The device of  claim 45  wherein the anterior wall is made of a metallic material. 
     
     
         47 . The device of  claim 46  wherein the anterior wall comprises a titanium alloy. 
     
     
         48 . The device of  claim 47  wherein a remainder of the spacer comprises allograft bone or bone substitute. 
     
     
         49 . The device of  claim 47  wherein the remainder of the spacer comprises a polymer. 
     
     
         50 . The device of  claim 47  wherein a remainder of the spacer comprises allograft bone. 
     
     
         51 . An intervertebral device for insertion into a disc space defined by opposing vertebral endplates, comprising
 i) an intervertebral spacer comprising:
 a) having an anterior wall having an upper surface and a lower surface, an anterior surface, and a first hole extending from the anterior surface to the upper surface and a second hole extending from the anterior surface to the lower surface, 
 b) a posterior wall having an upper surface and a lower surface, and 
 c) first and second side walls connecting the anterior and posterior walls, each side wall having an upper surface and a lower surface, 
   ii) a first screw received in the first hole and having a distal tip, an intermediate shaft having a first thread, and a proximal head,   iii) a second screw received in the second hole and having a distal tip, an intermediate shaft having a second thread, and a proximal head,   wherein the anterior wall has a first hole surface having a first ring extending therefrom,   wherein the first thread has a proximal end portion having a proximal side wall that runs substantially parallel to the ring.   
     
     
         52 . The device of  claim 51  wherein the first ring abuts the proximal side wall to prevent backout. 
     
     
         53 . The device of  claim 52  wherein the ring is sized to allow for passage of the first thread to allow for screw advancement. 
     
     
         54 . The device of  claim 51  wherein the first ring is fully circumferential. 
     
     
         55 . The device of  claim 51  wherein the first ring is partially circumferential. 
     
     
         56 . The device of  claim 51  wherein the first ring is an integral portion of the anterior wall. 
     
     
         57 . The device of  claim 51  wherein the first ring is manufactured separately from the anterior wall. 
     
     
         58 . A medical implant comprising:
 a) a wall having an upper surface and a lower surface, and a front surface, and a first hole extending into the wall from the front surface,   b) a first screw received in the first hole and having a distal tip, an intermediate shaft having a first thread, and a proximal head,   
       wherein the wall has a first hole surface having a first ring extending therefrom, 
       wherein the first thread has a proximal end portion having a proximal sidewall that runs substantially parallel to the ring. 
     
     
         59 . A method of fixing an implant comprising a wall having a front surface and a first hole extending into the wall from the front surface, wherein the wall has a first hole surface having a first ring extending therefrom,
 the method comprising the steps of:
 a) placing the implant against a bone, and 
 b) selecting a first screw having a distal tip, an intermediate shaft having a first thread, and a proximal head, wherein the first thread has a proximal end portion having a proximal sidewall that runs substantially parallel to the ring, 
 c) inserting a first screw through the first hole and into the bone. 
   
     
     
         60 . The method of  claim 59  wherein the first screw is inserted into the bone so that the proximal end portion of the first thread is advanced past the ring. 
     
     
         61 . The method of  claim 59  wherein the first screw is inserted into the bone so that the ring is disposed between the proximal end portion of the first thread and the proximal head. 
     
     
         62 . An intervertebral implant comprising:
 a) an intervertebral spacer having an anterior wall, a posterior wall, and first and second side walls connecting the anterior and posterior walls, the anterior wall having an anterior surface, an upper surface and a lower surface, wherein the anterior surface has a tapered section defining an upward sloping surface and a downward sloping surface,   b) a first fin having a proximal section, an intermediate section and a distal section,   c) a compression cap having a first portion and a second portion,   wherein the first fin contacts the upward sloping section of the tapered section of the anterior face,   wherein the distal section of the first fin extends above the upper surface of the anterior wall, and   wherein the proximal section of the first fin contacts the first portion of the compression cap.   
     
     
         63 . The implant of  claim 62  wherein the anterior wall further comprises a threaded hole located between the upward and downward sloping surfaces thereof, wherein the compression cap comprises a distal thread, and wherein the threaded hole threadably receives the thread of the compression cap. 
     
     
         64 . The implant of  claim 62  further comprising:
 d) a second fin having a proximal section, an intermediate section and a distal section, 
 
       wherein the second fin contacts the downward sloping section of the tapered section of the anterior face, 
       wherein the distal section of the second fin extends below the lower surface of the anterior wall, and 
       wherein the proximal section of the second fin contacts the second portion of the compression cap. 
     
     
         65 . The implant of  claim 64  wherein the spacer further comprises a hollow portion between the anterior and posterior walls, wherein bone graft is contained within the hollow, and wherein the fins impart compression onto the bone graft. 
     
     
         66 . The implant of  claim 62  wherein the first fin comprises a concave surface and an opposing convex surface. 
     
     
         67 . The implant of  claim 66  wherein the convex surface of the first fin contacts the upward sloping surface of the tapered portion of the anterior surface of the anterior wall. 
     
     
         68 . The implant of  claim 66  wherein at least one of the concave and convex surfaces of the first fin has a tooth extending therefrom. 
     
     
         69 . The implant of  claim 66  wherein at least one of the concave and convex surfaces of the first fin has a plurality of teeth extending therefrom. 
     
     
         70 . The implant of  claim 66  wherein at least one of the concave and convex surfaces of the first fin has a groove therein. 
     
     
         71 . The implant of  claim 66  wherein the first fin further comprises at least one side surface extending between the concave and convex surfaces, wherein the at least one side surface comprises a tooth thereon. 
     
     
         72 . The implant of  claim 62  wherein the distal section of the first fin is forked. 
     
     
         73 . The implant of  claim 62  wherein the distal portion of the first fin is tapered. 
     
     
         74 . The implant of  claim 62  wherein the proximal portion of the first fin has wings extending laterally therefrom. 
     
     
         75 . The implant of  claim 74  wherein the wings are flexible. 
     
     
         76 . The implant of  claim 62  wherein the proximal section of the first fin contacts the upward sloping section of the tapered section of the anterior face. 
     
     
         77 . The implant of  claim 62  wherein the intermediate section of the first fin contacts the upward sloping section of the tapered section of the anterior face. 
     
     
         78 . The implant of  claim 62  wherein the first fin extends above the upper surface of the anterior wall at an angle defined by the upward sloping section of the anterior wall. 
     
     
         79 . The implant of  claim 62  wherein at least of the anterior wall, posterior wall, and first and second side walls of the intervertebral spacer further comprise upper and lower surfaces that are toothed. 
     
     
         80 . The implant of  claim 62  wherein each of the anterior wall, posterior wall, and first and second side walls of the intervertebral spacer further comprise upper and lower surfaces that are toothed. 
     
     
         81 . The implant of  claim 64  wherein the spacer comprises bone extending continuously between the anterior and posterior walls, and wherein the fins impart compression to the bone. 
     
     
         82 . An intervertebral device for insertion into a disc space defined by opposing vertebral endplates, comprising:
 i) an intervertebral spacer comprising:
 a) an anterior wall having an upper surface and a lower surface, an anterior surface, and a first hole extending from the anterior surface, 
 b) a posterior wall, and 
 c) first and second side walls connecting the anterior and posterior walls, 
   ii) a first screw received in the first hole and having a distal tip, an intermediate shaft having a first thread, and a proximal head, and   iii) a retaining plate slidably mounted to the anterior surface of the spacer in a first and a second slidable position, the plate having a first hole,   wherein, in the first slidable position, the first hole of the plate aligns with the first hole of the spacer to allow passage of the screw therethrough, and   wherein, in the second slidable position, the first hole of the plate mis-aligns with the first hole of the spacer to prevent back out of the screw.   
     
     
         83 . The device of  claim 82  wherein the plate is slidable in a medial-lateral direction across the anterior face of the spacer. 
     
     
         84 . The device of  claim 82  wherein the plate is slidable in an upper-lower direction across the anterior face of the spacer. 
     
     
         85 . The device of  claim 82  wherein the spacer and plate include a locking feature adapted to retain the holes in a mis-aligned state. 
     
     
         86 . The device of  claim 85  wherein the locking feature comprises a locking arm. 
     
     
         87 . The device of  claim 85  wherein the locking feature comprises a ball detent. 
     
     
         88 . The device of  claim 85  wherein the locking feature locks in a medial-lateral direction. 
     
     
         89 . The device of  claim 85  wherein the locking feature locks in an anterior-posterior direction. 
     
     
         90 . The device of  claim 85  wherein the locking feature locks in an upper-lower direction. 
     
     
         91 . The device of  claim 85  wherein the locking feature comprises a protrusion and a recess. 
     
     
         92 . The device of  claim 82  wherein the plate further comprises first and second sidewalls, wherein the first sidewall comprises a living spring. 
     
     
         93 . The device of  claim 82  wherein the plate further comprises first and second sidewalls, and wherein the device further comprises a stand-alone compression spring or leaf spring disposed between the sidewalls. 
     
     
         94 . The device of  claim 82  wherein the second sidewall of the plate comprises a feature for mating with a grabber instrument. 
     
     
         95 . The device of  claim 82  wherein the second sidewall of the plate comprises a chamfer. 
     
     
         96 . The device of  claim 82  wherein the first hole of the plate comprises a chamfer. 
     
     
         97 . The device of  claim 96  wherein the chamfer is adapted to mate with the distal tip of the screw. 
     
     
         98 . An intervertebral device for insertion into a disc space defined by opposing vertebral endplates, comprising:
 i) an intervertebral spacer comprising:
 a) having an anterior wall having an upper surface and a lower surface, an anterior surface, and a first screwhole extending from the anterior surface to the upper or lower surface of the anterior wall, 
 b) a posterior wall having an upper surface and a lower surface, and 
 c) first and second side walls connecting the anterior and posterior walls, each side wall having an upper surface and a lower surface, 
   ii) a first screw received in the first screwhole and having a distal tip, an intermediate shaft having a first thread, and a proximal head,   iii) a washer having a body portion, an aperture, a proximal face and a distal face, the washer positioned anterior to the anterior face so that its aperture aligns with the first screwhole;   wherein the shaft of the screw is received in the aperture of the distal washer.   
     
     
         99 . The device of  claim 98  wherein the distal face of the washer comprises a projection extending distally therefrom. 
     
     
         100 . The device of  claim 98  wherein the anterior wall has a recess corresponding to the projection, and the projection is received in the recess. 
     
     
         101 . The device of  claim 98  wherein the washer has a peripheral contour, and the anterior face has a recess matching the peripheral contour, and wherein the washer is received in the recess. 
     
     
         102 . The device of  claim 98  wherein a proximal end portion of the first thread has a parallel sidewall. 
     
     
         103 . An intervertebral device for insertion into a disc space defined by opposing vertebral endplates, comprising
 i) an intervertebral spacer comprising:
 a) having an anterior wall having an upper surface and a lower surface, an anterior surface, and a first hole extending from the anterior surface to the upper surface and a second hole extending from the anterior surface to the lower surface, 
 b) a posterior wall having an upper surface and a lower surface, and 
 c) first and second side walls connecting the anterior and posterior walls, each side wall having an upper surface and a lower surface, 
   ii) a first screw received in the first hole and having a distal tip, an intermediate shaft having a first thread, and a proximal head comprising at least one flange extending therefrom, the flange having a proximal face and a distal face.   
     
     
         104 . The device of  claim 103  wherein the distal face of the flange comprises a projection extending distally therefrom. 
     
     
         105 . The device of  claim 103  wherein the anterior wall has a recess corresponding to the projection, and the projection is received in the recess. 
     
     
         106 . The device of  claim 103  wherein the flange has a peripheral contour, and the anterior face has a recess matching the peripheral contour, and wherein the flange is received in the recess. 
     
     
         107 . The device of  claim 103  wherein a proximal end portion of the first thread has a parallel sidewall.