Device for inserting an implant

Abstract: An implant 20 comprising a specially adapted bone screw having a threaded shank portion 22 and a sleeve 42 which mates with and operates in cooperation with the threaded shank portion 22 is provided. Also provided is a driver 60 specially adapted for inserting and removing the implant 20 of the invention. A method of compressing a fracture in a bone is also provided. The implant 20 generates bone compression by itself and can be used either alone or with plates and washers. It is easily inserted into a fracture and also is easily removed from the fracture. The driver 60 which is specially adapted to be used in combination with the implant 20 of the invention aids in the ease of insertion and removal of the implant 20.

Description: This invention relates generally to drivers for screws, and relates more particularly to a specially adapted device for inserting the implant claimed in EP-B-0574517. In the prior art, many types of screw are known. More recently, in the field of orthopaedics, various developments have taken place. A number of these are described in an article by Raymond G Tronzo MD, entitled 'Hip Nails For All Occasions', Orthopedic Clinics of North America - Vol 5, No 3, July 1974. However, despite these developments a continuing need exists for improvements in bone screws and for drivers for inserting those screws, in particular for bone screws that are useful for fractures in small bones. US-A-2,312,869 discloses a surgeon's bone screw driver which is provided with means for retaining a conventional bone screw during insertion of the screw. Only one driving means is provided. The bone screw implant claimed in EP-B-0574517 is a variable length implant comprising in a non-removably connected relationship: (a) a threaded shank having: (1) a distal threaded shank portion having a distal end and (2) a proximal threaded shank portion having a proximal end and having threading with a diameter d'; (b) a sleeve having a head with a diameter D larger than d' and having a distal end and a proximal end and having an inner threading which threads with said proximal threaded shank portion, resulting in an implant having a maximum implant length and a minimum implant length; and (c) a connector means which non-removably connects said sleeve near said distal end of said sleeve with said proximal threaded shank portion near said proximal end of said proximal threaded shank portion but which permits said sleeve to move longitudinally with respect to said distal threaded shank portion after said maximum implant length is reached. According to the invention, a device for inserting an implant comprises: (a) a inner rod having a distal rod end and a proximal rod end and having a first driver means positioned at said distal rod end; (b) an outer cylindrical portion having a distal cylindrical end and a proximal cylindrical end and having a further cylindrical portion integrally attached to said proximal cylindrical end and having a second driver means positioned at said distal cylindrical end; and (c) locking means for locking said proximal rod end and said proximal cylindrical end with respect to each other in a fixed position, in which said second driver means is proximal to said first driver means, as desired but allowing said outer cylindrical portion to move with respect to said inner rod when said locking means is not locked. The device of the invention may be used in a method of compressing a fracture in a bone comprising: (a) drilling a hole into and through the proximal side of the fracture and into the distal side of the fracture; (b) "overdrilling" the proximal side of the fracture (i.e., drilling the same hole with a drill bit which is large enough to accommodate the shaft of the sleeve of the implant; (c) with the implant extended to its maximum length, placing the device of the invention (when in its locked position) so that the first driver means located on the inner rod and preferably also the second driver means are engaged with the implant and contact the proximal end of the threaded shaft portion of the implant and the head of the sleeve, respectively, and then rotating the handle so as to insert the implant into and through the proximal portion of the fractured bone and into the distal portion of the fractured bone; and (d) unlocking the driver of the invention, holding the inner rod of the driver steady (which holds the threaded shank steady), and then rotating the outer cylinder clockwise so that the implant has a length which is shorter than its maximum length and so that the fracture is compressed. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an exploded view of an implant of EP-B-0574517, showing the threaded shaft portion separated from the sleeve before it is non-removably connected to the sleeve, with the sleeve shown partially in cross-section. Fig. 2 is a pictorial representation of the implant of Fig. 1, with the sleeve and the threaded shaft portion non-removably connected together. Fig. 3 is a magnified view of the implant shown in Fig. 2, but with the sleeve portion of the implant shown partially in cross-section. Fig. 4 is a cross-sectional view taken along the lines 4-4 in Fig. 2. Fig. 5 is a pictorial representation of an embodiment of the driver of the invention, showing the locking means located on the handle of the device which locks into a preferably knurled portion of the outer cylindrical portion, the outer cylindrical portion having a special driver means at its distal end, and showing the inner rod portion having another special driver means at its distal end. When the knob is moved toward the tip of the screw driver, the driver goes from its unlocked to its locked position. Fig. 6 is a view partially in cross-section of the driver shown in Fig. 5 (with the driver in its locked position). Fig. 7 is a pictorial representation showing (with use of inner phantom lines) the driver means located at the distal end of the inner rod of the driver just prior to its contacting the proximal end of the threaded shank portion of the implant, at a point in time when the implant has its maximum length. Fig. 8 is an end view of Fig. 3 (viewed along lines 8-8 in Fig. 3). Fig. 9 is a pictorial representation in cross-section illustrating the first step in the method of inserting the implant into a fractured bone, a drill bit shown drilling a hole into and through the proximal portion of the fracture and into the distal portion of the fracture. Fig. 10 is a pictorial representation in cross-section illustrating the second step in the method of inserting the implant, a second drill bit having a larger diameter than that shown in Fig. 9 being used to "overdrill" (i.e., to accommodate the shaft of the sleeve) the proximal portion of the fracture. Fig. 11 is a pictorial representation in cross-section showing the distal portion of the threaded shank portion of the implant being inserted into the distal portion of the fracture by means of the driver means on the distal end of the inner rod of the driver (preferably together with the driver means on the distal end of the cylinder), these two driver means being mated with recesses in the implant, prior to the sleeve being threaded down onto the proximal portion of the threaded shank portion of the implant (the fracture being at this time not compressed). The driver of the invention at this time is in its locked position. Fig. 12 is a pictorial representation (partially in cross-section) showing the driver in its unlocked position with the driver means located at the distal end of the inner rod positioned adjacent to and engaged with the proximal end of the threaded shank portion and with the driver means located at the distal end of the outer cylindrical portion being located adjacent to and engaged with the recess in the head of the sleeve portion of the implant of the device of the invention. An arrow indicates the clockwise direction in which the driver will be turned so as to insert the implant. Fig. 13 is a pictorial representation of the implant after it has been fully inserted into a fracture and after the fracture has been compressed by the implant and after the driver has been removed. DETAILED DESCRIPTION OF THE INVENTION In Figure 1, showing an implant 20 prior to the time when the parts of the implant 20 are assembled together, a threaded shank portion 22 comprises a proximal threaded shank portion 24 and a distal threaded shank portion 26. The threads of proximal threaded shank portion 24 and distal threaded shank portion 26 are not identical, but rather are of different diameters, pitches, and profiles. The directions of the threads are the same (both preferably are the same and both preferably are right-handed). The length of the proximal threaded shank portion 24 (preferably machine thread) is slightly shorter than the length of the distal threaded shank portion 26 (preferably bone thread). These relative lengths can be modified as desired, depending upon the intended use. The diameter 32 of the proximal threaded shank portion 24 is slightly smaller than the diameter 34 of the distal threaded shank portion 26. At the proximal end 36 of proximal threaded shank portion 24 a cutout 38 is present and in a preferred embodiment is half-cylindrical. The cutout 38 can (if desired) have a rounded boundary 40. For clarity, sleeve 42 is shown separated from threaded shank portion 22, but this is at a time prior to the assembly of the implant. Sleeve 42 has an outer diameter 44 and an inner diameter 46. Sleeve 42 has internal threading 48 which mates with and threads with threading 25 of proximal threaded shank portion 24. Sleeve 42 has an outer surface 50 which is substantially smooth. At the proximal end of sleeve 42 is a head 52 which is integral with sleeve 42. Head 52 has an outer diameter 54 and has a recess 56 therein. Recess 56 is preferably in the shape of a slot but can be, if desired, of other shapes, for example, hexagonal. Outer diameter 54 will be larger than the diameter drilled in the proximal portion of the bone fracture during "overdrilling". The length 28 of proximal threaded shaft 24 should be no longer than the length of the sleeve 42 without including the length of head 52. The number of threads in internal threading 48 should be the minimum number of threads to function properly as a machine thread. And the hole 58 should be located just proximal to the last thread in internal threading 48. In Figure 2, sleeve 42 is shown partially threaded down onto proximal threaded shank portion 24. Proximal threaded shank portion 24 and distal threaded shank portion 26 are integral with each other. In Figure 2, a hole 58 in sleeve 42 is shown. Prior to assembly of the implant 20, a hole 58 is drilled into sleeve 42. After the sleeve 42 is assembled together with the threaded shank portion 22, the threaded shank portion 22 and the sleeve 42 are non-removably connected together when manufactured by any suitable means, for example, by deforming some of the threads 25 through hole 58 so that sleeve 42 cannot become disengaged from threaded shank portion 22. Another alternative is to deform proximal end 36 so as to prevent disengagement of sleeve 42 from threaded shank portion 22. In Figure 3, shown is a magnified view of the device of Figure 2, with a portion of sleeve 52 shown in cross-section. Cutout 38 is located at the proximal end 36 of proximal thread shaft portion 24, and hole 58 is located in sleeve 42. Proximal threaded shaft portion 24 is threaded within and engaged with internal threading 48 of sleeve 42. In Figure 4, taken along the lines 4-4 in Figure 2, proximal threaded shank portion 24 is threadably engaged within internal threading 48 of sleeve 42. Areas 59 are multiple areas of deformed threads which prevent future disengagement of the device. In Figure 5 is shown a driver which is especially suitable for inserting and removing the implant described above. Driver 60 has a handle 62, which is fixedly attached to an inner rod 64. Handle 62 has a slidable portion 66, which can be in the shape of any of a variety of structures, for example (as shown) a knurled portion of a cylinder or a knob. When slidable portion 66 is slid to its distal-most position within handle 62, a small rod 68 fixed thereto can be positioned so that it fits into one of a multiplicity of holes 70 in (preferably) knurled cylindrical portion 72. Knurled cylindrical portion 72 is integral with outer cylindrical portion 74, which fits over inner rod 64 and which has located at its distal-most end 76 a tab 78 for mating with the recess 56 in the head 52 of the sleeve 42. Outer cylindrical portion 74 can be in a locked position, wherein small rod 68 is locked within a hole 70. Outer cylindrical portion 74 can alternatively be in an unlocked position, wherein slidable portion 66 is retracted in a proximal direction so that small rod 68 is not engaged within a hole 70. Tab 78 is integral with distal-most end 76 of outer cylindrical portion 74. Locking mechanism 78 is shaped so that it can mate with recess 56 in head 52. The distal-most end 82 of inner rod 64 is shaped so that it can mate and engage with cutout 38 at proximal end 36 of proximal threaded shank portion 24. Outer cylindrical portion 74 can have at least two integrally attached portions having different diameters 84, 86, if desired; or alternatively, it can have one diameter throughout, which is integrally attached to preferably knurled cylindrical portion 72. Preferably, also, knurled cylindrical portion 72 has a multiplicity of holes 70 therein, into any one of which rod 68 can be engaged. In Figure 8, an end view taken along the lines 8-8 in Figure 3 shows head 52 of sleeve 42 with recess 56 therein and shows also proximal threaded shank portion 24 having proximal end 36 and cutout 38 (which is preferably in the shape of a half-cylinder) therein. In Figure 9, a proximal portion 88 of a fractured bone and a distal portion 90 of that bone are shown separated from each other. A hole is drilled into and through the proximal portion of the fractured bone and into the distal portion of the bone by a drill bit 92. In Figure 10, a larger diameter drill bit 94 is illustrated within that same bone so as to enlarge the hole in the proximal portion of that fractured bone thereby "overdrilling" the proximal portion of that bone to accommodate the shaft 42 of the sleeve. As illustrated in Figure 11, with the implant 20 in its fully extended position so that it has its longest possible length, the distal threaded shank portion 26 of the implant 20 is inserted into the distal portion 90 of the fracture and into its optimal position in the bone. The distal-most end 82 of inner rod 64 is shown engaged with the end 36 and cutout 38 of proximal threaded shank portion 24. Tab 78 meshes with and engages with recess 56 within head 52. In Figure 12, slidable portion 66 is retracted so that it is at its proximal-most position, small rod 68 (attached thereto) is retracted from hole 70, and knurled cylindrical portion 72 is now free to rotate. When knurled cylindrical portion 72 is rotated in a clockwise direction as indicated, the sleeve 42 of the implant 20 advances so as to shorten the overall length of the implant 30 and so as thereby to compress the fracture as force is exerted by head 54 down onto bone where head 54 contacts the bone. As shown in Figure 13, with the driver 60 removed, the implant 20 can be allowed to remain within the bone as desired. If its removal is desired, the driver 60 especially suitable for inserting the implant can be profitably used for removing the implant. In this event, the reverse of the procedure just described is used, with the distal-most end 82 of inner rod 64 being positioned to abut against and engage with proximal end 36 of proximal threaded shank portion 24 and with cutout 38 and (at the same time) such that locking mechanism 78 abuts against and engages with recess 56 in head 52 of sleeve 42 of implant 20. The driver 60 is at this time in its unlocked position and knurled cylindrical portion 72 is rotated in a clockwise or counter-clockwise direction to line up the nearest hole 70 with the rod 68. The screwdriver is then locked and turned as a unit counterclockwise to remove the screw. The device of the invention has several advantages. The first driver means located on the inner rod fits securely within the sleeve of the implant and mates with the proximal end of the threaded shank portion of the implant, so as to enable the threaded shank portion of the implant to be inserted into and through the proximal side of the fracture and into the distal side of the fracture and also enables the driver to prevent slippage of the driver while the outer cylindrical portion of the driver having a second driver means is used to thread the sleeve onto the implant so as to compress the fracture. That is, both the functions of inserting the screw and then lagging the fracture are accomplished by the same implant.

Claims: A device (60) for inserting an implant (20), said device (60) comprising: (a) an inner rod (64) having a distal rod end (82) and a proximal rod end and having a first driver means positioned at said distal rod end (82); (b) an outer cylindrical portion (74) having a distal cylindrical end (76) and a proximal cylindrical end and having a further cylindrical portion integrally attached to said proximal cylindrical end and having a second driver means (78) positioned at said distal cylindrical end (76); and (c) locking means (66, 68, 70) for locking said proximal rod end and said proximal cylindrical end with respect to each other in a fixed position, in which said second driver means (78) is proximal to said first driver means, as desired but allowing said outer cylindrical portion (74) to move with respect to said inner rod (64) when said locking means (66, 68, 70) is not locked. A device (60) according to Claim 1, wherein said first driver means comprises a structure adapted to engage with a proximal end (36) of a threaded shank portion (24) of an implant (20). A device (60) according to Claim 1 or 2, wherein said second driver means (78) comprises an end portion of a cylinder which is adapted to engage with a slot (56) in a proximal end of a sleeve (42) of an implant (20) and wherein said rod (64) fits within said cylinder. A device (60) according to Claim 1 which is adapted for inserting and removing an implant (20) having a threaded shank portion (24) which threads with a sleeve (42) having a head (52), said device (60) further comprising a handle (62); said first driver means fitting within said sleeve (42) of said implant (20) and mating with a proximal end (36) of said threaded shank portion (24) of said implant (20), said inner rod (64) being connected at said proximal rod end to said handle (62). A device (60) according to Claim 4, wherein said outer cylindrical portion (74) is adapted to house therewithin said inner rod (64) and said locking means (66, 68, 70) are located at said proximal cylindrical end and are adapted for locking said outer cylindrical portion (74) with said handle (62) when desired. A device (60) according to Claim 4 or Claim 5, wherein said second driver means (78) mates with a recess (56) in said head (52) of said sleeve (42) of said implant (20).

Inventors: ASNIS STANLEY E, CROMBIE JOHN S, LANE LEWIS B, ASNIS, STANLEY E., CROMBIE, JOHN S., LANE, LEWIS B.
Applicants: HOWMEDICA, HOWMEDICA INC.
Application year: 1992
Main classification: A61B17
IPC codes: A61B17