in fig1 a small - bone fixation pin or compression wire 1 is seen to comprise essentially a smooth - walled shank portion 2 , with an adjoining distal threaded portion 3 . the outside diameter of the threaded portion 3 is smaller than the outside diameter of the shank portion 2 ; the diameter of the threaded portion is preferably constant , except for a sharp distal end 5 , for self - tapping entry into bone tissue . between the threaded portion 3 and the shank portion 2 , as seen in fig2 a frusto - conical shoulder or step 2 serves as an abutment for a bone fragment a which is to be fixed onto the remainder of the main bone b , by advancing the threaded portion 3 into the main bone . the half - angle of conical shoulder convergence , i . e ., with respect to the central axis of pin 1 , is suitably in the range 30 ° to 60 °, and is preferably about 45 °. alternatively , and as shown in fig3 a compression wire or pin may have a substantially radial shoulder 4 &# 39 ; between its smooth shank 2 ( diameter d 1 ), adapted for drill - chucked drive , and its reduced self - tapping threaded end 3 ( of diameter d 2 ), in which case , a fixation as in fig2 will be understood to use the radial shoulder 4 &# 39 ; for larger - area contact with the fragment a to retain a predetermined retaining force of fragment a against the remainder b of the same bone . fig3 further serves to identify overall length l 1 and threaded length l 2 , as well as to indicate at α , the ground angle of convergence of the self - tapping distal end of threaded portion 3 ; the angle α is suitably about 45 degrees . to obtain an idea of the sizes involved , it is pointed out that a fixation pin 1 , may for example , have a length of 100 - mm , with the threaded portion 3 having a length of 15 - mm and the shank portion 2 a length of 85 - mm . the diameter of the threaded portion can be 1 . 4 to 1 . 6 - mm when , for example , the diameter of the shank portion 2 is 2 - mm . more specifically , and by way of example , a fixation pin 1 should be of such overall length ( l 1 ) as to permit well - chucked engagement to the shank portion 2 , with a generous allowance of exposed shank , for unobstructed viewing by the surgeon ; this can be taken to mean at least a viewable 25 - mm length of shank to the shoulder region 4 , when chucked to a portable drill . and to provide the surgeon with a range of fixation pins sufficient for the wide variety of small - bone fractures encountered in practice , it is currently preferred to provide sets or kits of such pins , in three standardized shank diameters , namely 1 . 5 - mm , 2 . 0 - mm and 3 - mm diameter respectively , and to provide all pins to the same overall length ( l 1 ) of at least 100 - mm and preferably 120 - mm . in general , it is considered suitable to provide the outer diameter d 2 of all threaded ends 3 at a 70 to 80 percent relationship to the shank diameter , and to provide progressively stepped increments of thread length ( l 2 ) in a full assortment that is preferred for each shank diameter . thus , for a small 1 . 5 - mm diameter shank - size assortment , thread length ( l 2 ) is selectable from a preferred group of eight pins , ranging in 2 - mm increments from 7 - mm to 21 - mm , wherein all threads are of 1 . 2 - mm diameter , all to serve for fixation of the smallest fragments in small bones . thus also , for a large 3 - mm diameter shank - size assortment , thread length ( l 2 ) is selectable from another preferred group of eight pins , ranging in 5 - mm increments from 20 - mm to 55 - mm , wherein all threads are of 2 . 2 - mm diameter , all to serve for fixation of larger fragments in relatively large bones . the intermediate or 2 - mm diameter shank assortment is currently preferred to serve intermediate situations , wherein thread length is in small ( e . g . 2 - mm ) increments in a range 11 - mm to 25 - mm , and in larger ( e . g . 5 - mm ) increments for greater threaded lengths , all with 1 . 6 - mm thread diameter . with the indicated orders of dimensional magnitude , and after a selected pin has been driven to fix a bone fragment , the shank portion 2 can easily be cut off by suitable nippers so that protruding regions of the threaded portion or of the shank portion can easily be removed . depending upon the externally exposed shape or condition of a particular bone fragment to be secured to the remainder of the same bone , the invention is shown in fig4 to permit optional employment of a washer 6 , which , as in the case of all or any pins of the invention , is also preferably and suitably of stainless steel . in fig5 diametric dimensions d 1 and d 2 identify the sizes and size relationships discussed above for the shank and threaded portions ( 2 , 3 ) of the pin of fig3 namely , with a radial shoulder 4 &# 39 ; between shank 2 and the threaded end 3 . washer 6 is flat and features a bore of diameter d 3 to clear the threads of portion 3 and a conical counterbore or chamfer at both ends of the bore . the outer diameter d 4 of the washer may suitably be 1 . 5 to 2 . 5 times the shank diameter d 1 . the inner diameter of the chamfer is the bore diameter d 3 , which is less than the shank diameter d 1 ; and the outer diameter d 5 of the chamfer exceeds the shank diameter d 1 , to an extent which is at least as great at the radial clearance between the washer bore and the thread diameter d 2 . in these circumstances , the driven fit of shoulder 4 &# 39 ; to washer 6 , with washer 6 compressing bone fragment a to bone remainder b , may be a perfectly centered engagement of the circular rim of shoulder 4 &# 39 ; to the adjacent chamfer , as shown ; and it is also possible for washer 6 to be slightly angled ( i . e ., tilted ) in self - adaption to a local profile or other feature at washer contact with fragment a , in which case , shoulder 4 &# 39 ; engagement to the adjacent chamfer of the washer will be at only slight departure from the circle - to - cone engagement for the perfectly centered situation . in any event , the slight tilting of washer 6 with respect to a normal to the central axis of the pin will in no sense impair a shank - driven washer compression of bone fragment a to bone remainder b . in fig5 the same washer 6 , with like preferably 45 - degree chamfers at opposite ends of its bore , is shown in combination with a pin as in fig1 and 2 , namely with a conical transition 4 between shank and threaded ends of the pin . the involved cone - to - cone engagement is self - centering , and washer is urged to assume an orientation perpendicular to the pin axis when shank 2 is driven to apply fragment - fixation compression over the area of the fracture x . in fig6 washer 6 &# 39 ; has a distal face 7 that is concave , being suitably a circular or parabolic arc of revolution about the axis of the bone pin . the axial depth d of the concavity 7 may be about one - third of the axial extent of washer 6 &# 39 ;. the small - bone fragment a is of course enlarged but is seen to present a concave shape for washer ( 6 &# 39 ;) engagement with the convex shape of the bone fragment , in close conformance with the concave depth and curvature of the distal face 7 of the washer . this is as it should be for the fracture x as shown in fig6 wherein bone - engagement via distal face 7 provides an enlarged area of bone - fragment support and compression surrounding the region of threaded - portion ( 3 ) engagement to bone at a and at b . it is realized , however , that not all bone fragments will present a convex shape that is so well accommodated by the distal face 7 that has been described . to best equip the orthopedic surgeon who must deal with whatever confronts him , the invention is to be understood as being available in kit form , wherein at least one and preferably several washers 6 are provided for each bone screw , pin , or wire 1 , and wherein the several washers 6 differ as to axial depth d of the concavity 7 . the surgeon has further opportunity to adapt the described washer 6 to particular circumstances of small bone fragment contour , in that the washer 6 may be bent as necessary by pliers or other tools which are standard equipment for the orthopedic surgeon . thus , if need be , a washer 6 &# 39 ;, of preselected axial depth d of its otherwise spherical distal face 7 may be bent to distort the distal face 7 into a more complex curvature wherein the curvature is , for example , ( i ) of relatively short - focus parabolic nature in a first longitudinal section which includes the pin axis and ( ii ) of longer - focus parabolic nature in a second longitudinal section , taken 90 degrees from the first longitudinal plane . a kit of the nature indicated preferably includes a set of small - bone pins or compression wires 1 , wherein there is at least one pin or wire 1 of each of several shank ( 2 ) diameters , illustratively of 3 - mm , 2 - mm , and / or 1 . 5 - mm diameter , with thread ( 3 ) diameters of 2 . 2 - mm , 1 . 6 - mm , and / or 1 . 2 - mm , respectively , in ranges of incrementally stepped thread lengths , as noted above for each of the respective thread lengths . such a kit would also include washers 6 ( and / or 6 &# 39 ;) at least to fit the 3 - mm and 2 - mm shank sizes indicated , and with at least two different axial depths d for each of these shank sizes . in the case of the 3 - mm shank size , washers 6 are suitably of 6 - mm or 4 - mm diameter d 4 ; and in the case of the 2 - mm or 1 . 5 - mm shank size , washers 6 are suitably of 3 - mm or 4 - mm diameter d 4 . each compression wire of the invention provides sufficient length of smooth - walled shank to enable chucked engagement to a standard portable drill , preferably of so - called &# 34 ; cordless &# 34 ; variety . procedurally , each wire can be installed in a single driven self - tapping operation with entry into both the small bone fragment and the larger remainder of the same bone , from which the small fragment was broken . the wire is set , upon driven rotational entry into the bone , to the extent of shoulder compression of the fragment a to the anchored remainder b of the same bone . in the course of driving the pin through the fractured bone , reduction is maintained by pressure applied to the fragment ; and the shoulder keeps the bone fragment from back - sliding when the shoulder reaches the cortex of the fragment . after wire - threading ( pin - threading ) purposes have been served , the shank portion is no longer necessary and can be readily severed from the installed remainder , using a conventional wire - snip tool , as closely offset as possible from the shoulder 4 ( 4 &# 39 ;) region , which is relied upon to retain the fixation of fragment a to remainder b . fig7 a to 9b provide illustration of a variety of uses of the invention , which in all cases not only simplifies and shortcuts the process and time required for fragment fixation , but also enables greatly enhanced and assured durability of the fixated product , i . e ., with compression - wire implantation . in fig7 a , two large compression - wire implants 10 , 11 , e . g . 3 - mm wire size , are shown with shanks cut off after self - tapping thread advance to the point of shoulder - driven fragment engagements to other fragments a &# 39 ;, a &# 34 ; and to the tibial remainder b , in the case of a tibial pilon fracture . and in fig7 b , a single compression - wire implant 12 of the same large wire size , is seen to be retaining a fragment a to bone remainder b in reduction of a medial malleolar fracture . in fig8 a , first and second medium - size compression - wire implants 13 , 14 , e . g . 2 - mm wire size , with shanks cut off after implantation , are shown retaining an outer fragment a to remainder bone b and to another fragment a &# 39 ;, for the case of an intra - articular distal radius fracture . and in fig8 b , a single compression - wire implant 15 of the same medium - size wire , is seen to be retaining a fragment a to remainder bone b in reduction of a proximal radius fracture . in fig9 a , a single small and short compression - wire implant 16 , e . g . 1 . 5 - mm wire size , with shank cut off after implantation , is shown retaining a mallet finger a to remainder bone b . and in fig9 b , a single , relatively elongate compression wire 17 of small - wire size is shown fixing a fragment a to remainder bone b , in reduction of an intra - articular phalangeal fracture .
the invention contemplates a compression wire for fixated retention of a fractured small bone fragment in an osteosynthesis procedure . the wire comprises a smooth - walled shank portion and an adjoining threaded portion , of lesser diameter than the diameter of the shank portion , there being a step - down shoulder between the shank portion and the threaded portion . the shank portion is adapted for chucked engagement to a portable rotary drill , and the distal end of the threaded portion is configured for self - tapping entry into and threaded implantation in bone . the implantation is complete when the shoulder engages cortex tissue of the fragment , holding the same in compression against remainder structure of the fractured bone . once implanted , the shank may be nipped by a cutter tool at relatively close offset from the shoulder .