Patent Publication Number: US-2021161524-A1

Title: Fixation assembly and method of use

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/385,624, filed on Apr. 16, 2019, which is a continuation of U.S. patent application Ser. No. 14/594,953, filed on Jan. 12, 2015. The entire contents of those applications are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to the field of implant devices, and more particularly, to a fixation assembly for joining bones by applying uniform compression through multi-point fixation. 
     BACKGROUND OF THE INVENTION 
     Implant devices, such as intramedullary nails, plates, rods, screws, Kirschner wires (K-wires), and screw-and-washer assemblies are often used to repair or reconstruct bones and joints affected by trauma, degeneration, deformity, fractures, and disease, such as Charcot arthropathy caused by diabetes in some patients, Hallux Valgus deformities, failed Keller Bunionectomies, Rheumatoid Arthritis, injuries, and severe deformities. Infections and wound complications are a major concern in the aforementioned procedures. Wound closure is technically demanding for the surgeon, and devices that add surface prominence, such as plates or exposed screws, add to the difficulty by requiring greater tissue tension during incision reapproximation. This increases the risk of postoperative wound infections and dehiscence that may ultimately result in limb amputation. 
     Various implants have been utilized for surgical treatment of these bones and joints, including bone screws. Implants have also been utilized to treat severe deformities in the metatarsal and phalangeal bones, including multiple screws and plates. These multiple screws and plate implants have been commonly used in a first metatarsal-phalangeal fusion procedure to fuse the first metatarsal to the first phalangeal bone in hallux valgus deformities, failed Keller bunionectomies, rheumatoid arthritis, and other types of severe deformities in the metatarsal and phalange bones. While these devices allow fixation and promote fusion, they do not deliver restoration of the arch in a Charcot foot, they are not effective in metatarsal-phalangeal (MTP) fusion procedures, nor do they deliver uniform compression for various predetermined angles of compression. 
     Particularly, screw implants in MTP procedures are ineffective in delivering sufficient compression to the bones in the foot, preventing screw head break out, or delivering effective bending resistance. Moreover, hard to control dorsiflexion and valgus angles as well as skin irritation from proximity to the skin prevents these screw implants from being readily utilized for surgical treatment. Yet further, plate implants used with bone screws too have the same drawbacks as fixed varus and valgus angles, lack of direct compression across the MTP joint, and skin irritations from proximity to the skin reduce the effectiveness of these implants. 
     Still further, use of K-wires, screws, screw-and-washer assemblies, and plates for the reduction and internal fixation of arthrodesis, osteotomy, intra-articular and extra-articular fractures, and non-unions of bones and joints of the hand, foot, arm, leg and various other body parts are ineffective in delivering the strength necessary to maintain sufficient reduction and/or fixation of the fractured bone, maximizing cortical bone contact, retaining bones in most anatomically correct position, preventing screw head break out, minimizing the size of the incision(s) necessary to install the hardware, minimizing soft tissue and tendon disruption and/or displacement, stabilizing fixation of the fracture, easing mobility for the patient, and eliminating hardware profiles. 
     There is therefore a need for a fixation assembly and method of use that overcomes some or all of the previously delineated drawbacks of prior fixation assemblies. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to overcome the drawbacks of previous inventions. 
     Another object of the invention is to provide a novel and useful fixation assembly that may be utilized to treat bones in a human body. 
     Another object of the invention is to provide a system for compressing bones using a fixation assembly. 
     Another object of the invention is to fuse bones through the use of an intraosseous assembly. 
     Another object of the invention is to provide a novel fixation assembly that is securely assembled by securing a screw member to a post member via a tapered connection or engagement. 
     Another object of the invention is to provide a fixed acute angle fixation assembly for bone fixation. 
     Another object of the invention is to provide a fixation assembly that provides sufficient strength, delivers a highly stable fixation, and maintains reduction of a fractured bone. 
     Another object of the invention is to provide a fixation assembly that maximizes cortical bone contact. 
     Another object of the invention is to provide a fixation assembly that fixates to the subchondral bone and/or the cortical bone. 
     Another object of the invention is to provide a fixation assembly that retains and realigns bones in anatomically correct positions. 
     Another object of the invention is to provide a fixation assembly that reduces and/or eliminates unnecessary hardware. 
     Another object of the invention is to provide a fixation assembly that minimizes the size of the incision(s) necessary to install the fixation assembly. 
     Another object of the invention is to provide a fixation assembly that minimizes soft tissue and tendon disruption and/or displacement. 
     Another object of the invention is to provide a fixation assembly that allows for early post procedure mobilization of the patient. 
     Another object of the invention is to provide a fixation assembly that reduces and/or eliminates hardware profiles. 
     Another object of the invention is to provide a method for the reduction and fixation of arthrodesis, osteotomy, intra-articular and extra-articular fractures and non-unions of bones and joints of the hand, foot, arm, leg and various other body parts. 
     In one embodiment of the invention, a fixation assembly for bone fixation is provided comprising a post member coupled to a screw member. The post member comprises a head portion connected to an anchoring portion, wherein the head portion is offset from the anchoring portion by a first angle. The head portion may comprise a curved body annularly extending from a first end to a second end, wherein the first end is separated from the second end by a slot, and wherein the curved body defines a tapered annular bore therein. The anchoring portion comprises a first leg extending from the first end of the curved body and a second leg extending from the second end of the curved body. The screw member comprises a tapered bulbous portion connected to a threaded elongated portion. The screw member is coupled to the post member by advancing the elongated portion of the screw member through the tapered bore of the post member until the tapered bulbous portion of the screw member abuts the tapered bore of the post member thereby creating an interference fit. The first angle of the post member determines the angle of fixation of the post member with respect to the screw member. The fixation assembly of the present invention translates uniform compression to first and second bone segments (i.e., a first bone and a second bone, or first and second bone fragments of a single bone). 
     Broadly, the methods of the invention for joining and compressing a first bone segment to a second bone segment comprises: creating a first hole in the first bone segment and a second hole in the second bone segment along a first longitudinal axis; creating a depression below the cortex of the first bone segment by removing bone material from the first bone segment; creating third and fourth parallel holes in the first bone segment along a second longitudinal axis; advancing the first and second legs of the post member into the third and fourth parallel holes in the first bone segment; pressing the head portion of the post member into the depression in the first bone segment; and advancing the screw member through the bore of the post member and into the first hole in the first bone segment and the second hole in the second bone segment until the bulbous portion of the screw member abuts the bore of the post member. 
     Instruments are also disclosed for use in practicing the invention. Numerous variations may be practiced in the preferred embodiment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A further understanding of the invention can be obtained by reference to a preferred embodiment set forth in the illustrations of the accompanying drawings. Although the illustrated embodiment is merely exemplary of systems and methods for carrying out the invention, both the organization and method of operation of the invention, in general, together with further objectives and advantages thereof, may be more easily understood by reference to the drawings and the following description. The drawings are not intended to limit the scope of this invention, which is set forth with particularity in the claims as appended or as subsequently amended, but merely to clarify and exemplify the invention. 
       For a more complete understanding of the invention, reference is now made to the following drawings in which: 
         FIG. 1  is a perspective view of a fixation assembly according to an embodiment of the invention; 
         FIG. 2A  is a front perspective view of a post member of the fixation assembly shown in  FIG. 1  according to an embodiment of the invention; 
         FIG. 2B  is a front view of the post member shown in  FIG. 2A  according to an embodiment of the invention; 
         FIG. 2C  is a rear view of the post member shown in  FIG. 2A  according to an embodiment of the invention; 
         FIG. 2D  is a side view of the post member shown in  FIG. 2A  according to an embodiment of the invention; 
         FIG. 2E  is a top view of the post member shown in  FIG. 2A  according to an embodiment of the invention; 
         FIG. 2F  is a bottom view of the post member shown in  FIG. 2A  according to an embodiment of the invention; 
         FIG. 3A  is a perspective rear view of a post member of the fixation assembly shown in  FIG. 1  according to an alternate embodiment of the invention; 
         FIG. 3B  is a front view of the post member shown in  FIG. 3A  according to the alternate embodiment of the invention; 
         FIG. 3C  is a rear view of the post member shown in  FIG. 3A  according to the alternate embodiment of the invention; 
         FIG. 3D  is a side view of the post member shown in  FIG. 3A  according to the alternate embodiment of the invention; 
         FIG. 3E  is a top view of the post member shown in  FIG. 3A  according to the alternate embodiment of the invention; 
         FIG. 3F  is a bottom view of the post member shown in  FIG. 3A  according to the alternate embodiment of the invention; 
         FIG. 4  is a front view of a screw member of fixation assembly shown in  FIG. 1  according to an embodiment of the invention; 
         FIG. 5A  is a perspective view of an instrument used to couple the fixation assembly shown in  FIG. 1  to the bones according to an embodiment of the invention; 
         FIG. 5B  is a side view of the instrument shown in  FIG. 5A  according to an embodiment of the invention; 
         FIG. 5C  is a top view of the instrument shown in  FIG. 5A  according to an embodiment of the invention; 
         FIG. 5D  is a bottom view of the instrument shown in  FIG. 5A  according to an embodiment of the invention; 
         FIG. 5E  is a rear view of the instrument shown in  FIG. 5A  according to an embodiment of the invention; 
         FIG. 5F  is a front view of the instrument shown in  FIG. 5A  according to an embodiment of the invention; 
         FIG. 6  is a cross-sectional view of the instrument taken along line  6 - 6  in  FIG. 5C ; 
         FIG. 7  is a flow chart depicting illustrative steps of a method of coupling the fixation assembly shown in  FIG. 1  to bones according to an embodiment of the invention; and 
         FIGS. 8A-8F  depict details of certain steps of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention may be understood more readily by reference to the following detailed description of preferred embodiment of the invention. However, techniques, systems, and operating structures in accordance with the invention may be embodied in a wide variety of forms and modes, some of which may be quite different from those in the disclosed embodiment. Consequently, the specific structural and functional details disclosed herein are merely representative, yet in that regard, they are deemed to afford the best embodiment for purposes of disclosure and to provide a basis for the claims herein, which define the scope of the invention. It must be noted that, as used in the specification and the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly indicates otherwise. 
     Referring now to  FIG. 1 , there is shown a fixation assembly  100  which is made in accordance with the teachings of the preferred embodiment of the invention. As shown, the fixation assembly  100  includes a screw member  102  adapted to be locked to a post member  101 . Fixation assembly  100  is used to translate intraosseous and uniform compression to bone segments (i.e., a plurality of bones or a plurality of bone fragments of a single bone) for treating and fusing deteriorated, damaged, or fractured bones in the human body. In particular, fixation assembly  100  may be used for the reduction and internal fixation of arthrodeses, osteotomies, intra- and extrarticular fractures and nonunions of the small bones and joints of the foot and ankle. Fixation assembly  100  preferably delivers the strength necessary to maintain sufficient reduction and/or fixation of a fractured bone, maximizes cortical bone contact, retains bones in an anatomically correct position, prevents screw head break out, minimizes the size of the incision(s) necessary to install the hardware, minimizes soft tissue and tendon disruption and/or displacement, stabilizes fixation of the fracture, eases mobility for the patient, provides early post-operation mobilization of the fracture bone, and reduces and/or eliminates hardware profiles. Moreover, fixation assembly  100  generally provides a more stable and rigid fixation than the prior art because it is fixed to the strongest bone near the fracture and because it redistributes the force normally placed on the head of a screw along the assembly. 
     For example, fixation assembly  100  may be used to join a first bone  105  having a proximal end  107  and side surface  109  to a second bone  106  having a distal end  108 , and specifically, to join the proximal end  107  of first bone  105  with distal end  108  of second bone  106 . The fixation assembly  100  can be used to joint any bones of the hand and the foot, as well as for internal fixation of any other bones in the human body, including, but not limited to, the talus and navicular bones in the talonavicular joint, the calcaneus and cuboid bones in the calcaneocuboid joint, the metatarsal and cuneiform bones in the metatarsocuneiform joints, the tibia and talus bones in the tibiotalar joint, metatarsal osteotomies, as well as the metatarsals and the phalanges. The fixation assembly  100  may be further used to joint bone fragments of a single bone to treat bone fractures. It should be appreciated that screw member  102  and post member  101  of fixation assembly  100  may be provided at several sizes, lengths or widths, for the internal fixation of a variety of bone sizes in the human body. 
     Post member  101  comprises an anchoring portion  104  aligned along longitudinal axis  110  extending along the length of post member  101  for anchoring post member  101  in bone  105 . Post member  101  further comprises a head portion  103  aligned along longitudinal axis  112  and offset from the anchoring portion  104  and longitudinal axis  110  at an angle A. Angle A determines the angle of fixation of post member  101  with respect to the screw member  102 . Angle A is provided at various angles depending on the bone fragments that are being compressed. Angle A may be any angle less than 90 degrees and is preferably in the range of about 30 degrees to about 75 degrees. Screw member  102  is aligned along longitudinal axis  111  and is fixed to the post member  101  at angle B. Angle B may be any angle less than 90 degrees and is preferably in the range of about 15 degrees to about 60 degrees. Angle B causes the fixation assembly  100  to “hook” into bones  105  and  106  and translate uniform compression applied to the bones through multi-point fixation. In particular, fixation assembly  100  distributes compressive forces across a wide surface area providing orthogonal multi-plane fixation and bicortical cross screw fixation to bones. In a locked position, screw member  102  compresses bones  105  and  106 , while the post member  101  acts as an intraosseous bicortical anchor, which lags bones  105  and  106  together in a parallel fashion in directions D 1  and D 2 . Beneficially, fixation assembly  100  maintains compression even if the cortical bridge of the bone is compromised. 
     It should also be appreciated that the fixation assembly  100  is implanted through a minimal incision and is provided to be substantially within the bone (i.e., intraosseous), thereby reducing the disruption to the plantar tissues while at the same time minimizing the tension on the skin. This allows for improved wound closure, reduced operating room time, reduction in the number of incisions required, and reduction in the total length of incisions. Fixation assembly  100  may also be utilized with graft material (i.e., autograft, allograft or other biologic agent). Furthermore, it should be appreciated that a plurality of fixation assemblies, such as fixation assembly  100 , may be inserted into any of the bones of the body, such as but not limited to, radial, humerus, tibia, and femur, in order to fixate fractures, without limiting the scope of the invention. For example, the orientation of fixation assembly  100  and method of use may be utilized to fixate a distal radius fracture by rigidly fixating two fixation assemblies  100  to the subchondral bone and/or cortical bone and applying acute angle compression to the fracture. This orientation and method of use maintains reduction of the fracture by realigning the bone to its natural anatomical position, which allows for quicker healing time and earlier mobilization of the patient. 
     Post member  101  of fixation assembly  100  is shown in greater detail in  FIGS. 2A-2F , where  FIG. 2A  is a front perspective view of the post member  101 ,  FIG. 2B  is a front view thereof,  FIG. 2C  is a rear view thereof,  FIG. 2D  is a side view thereof,  FIG. 2E  is a top view thereof, and  FIG. 2F  is a bottom view thereof. Post member  101  preferably comprises unitary elongated body  200  extending from a first end  206  to a second end  207 . Post member  101  is aligned along longitudinal axis  110 , which is longitudinally coextensive the length of post member  101 . Post member  101  may be made of materials known in the art, including titanium, titanium alloy, stainless steel, cobalt chrome, PEEK, and resorbable polyactic acid (PLA). Also, post member  101  may be coated with an osteoconductive material, such as, for example, plasma spray or other similar types of porous materials, that are capable of supporting or encouraging bone ingrowth into the material. It should be appreciated that the length of the post member  101  may be selected of varying lengths to allow a surgeon to fuse different joints in the human body. 
     Post member  101  comprises a head portion  103  at its first end  206  fixed to an anchoring portion  104  at its second end  207 . Head portion  103  is aligned along longitudinally axis  112  and is offset from the anchoring portion  104  and longitudinal axis  110  by angle B. Angle A determines the angle for fixation of post member  101  with respect to the screw member  102  at angle B (shown in  FIG. 1 ). Angle A is provided at various angles depending on the bone fragments that are being compressed. Angle A may be any angle less than 90 degrees and is preferably in the range of about 30 degrees to about 75 degrees. Head portion  103  preferably comprises a curved body  213 . However, head portion  103  may comprise any other shape including a rectangular shape or a non-uniform shape. Curved body  213  annularly extends from a first end  216  to a second end  217 , separated by a slot  214 . Curved body  213  has an annular bore  212 , which traverses head portion  103  through its width and extends from a front face  210  to a rear face  211  of head portion  103  along longitudinal axis  111  (shown in  FIG. 1 ). Bore  212  annularly extends from a first end  216  to a second end  217 , wherein the first end  216  is separated from the second end  217  by slot  214 . Bore  212  is sized and shaped to receive a head of screw member  102  as is shown in  FIG. 1 . Bore  212  preferably comprises an inner wall  215  having a taper. Bore  212  tapers from front face  210  to rear face  211 —i.e., bore  212  has a diameter that decreases from front face  210  to rear face  211 . In a preferred embodiment, bore  212  comprises a Morse taper. 
     Anchoring portion  104  is adapted to be fixed transversely to a bone or a bone fragment as will be later described. Anchoring portion  104  comprises a first leg  201  and a second leg  202  extending along longitudinal axis  110 . First leg  201  extends from the first end  216  of curved body  213  to second end  207  of post member  101  and second leg  202  extends from the second end  217  of curved body  213  to second end  207  of post member  101 . First and second legs  201  and  202  are preferably substantially parallel and substantially cylindrical in shape. First and second legs  201  and  202  may comprise other shapes. For example, first and second legs  201  and  202  may comprise a rectangular cross-section, or a semi-circular cross-section as shown in  FIGS. 3A-3F . Each of the first and second legs  201  and  202  preferably has a smooth exterior surface and comprises a substantially uniform diameter. Alternatively, first and second legs  201  and  202  may comprise a taper. First and second legs  201  and  202  of the post member  101  create a wide profile across first bone  105  because the first and second legs  201  and  202  are offset with respect to one another. The wide profile assists in providing a better-secured anchor. First and second legs  201  and  202  preferably terminate at first and second tips  221  and  222 , respectively. Each of the first and second tips  221  and  222  may comprise a conical shape terminating at a point for ease of insertion of legs  201  and  202  into the bone. First and second tips  221  and  222  may comprise other shapes, as shown for example in  FIGS. 3A-3F . 
       FIGS. 3A-3F  illustrate an alternative embodiment of post member  300 , where  FIG. 3A  is a perspective rear view of the post member  300 ,  FIG. 3B  is a front view thereof,  FIG. 3C  is a rear view thereof,  FIG. 3D  is a side view thereof,  FIG. 3E  is a top view thereof, and  FIG. 3F  is a bottom view thereof. Post member  300  preferably comprises unitary elongated body  320  extending from a first end  306  to a second end  307 . Post member  300  comprises a head portion  303  at its first end  306  fixed to an anchoring portion  304  at its second end  307 . 
     Head portion  303  comprises a curved body  313  annularly extending from a first end  316  to a second end  317 , separated by a slot  314 . Curved body  313  has an annular bore  312 , which traverses head portion  303  through its width and extends from the front face  310  to the rear face  311  of head portion  303 . Bore  312  is sized and shaped to receive a head of screw member  102  as is shown in  FIG. 1 . Bore  312  preferably comprises an inner wall  315  having a taper, which tapers from front face  310  to rear face  311  (i.e., bore  312  has a diameter that decreases from front face  310  to rear face  311 ). In a preferred embodiment, bore  312  comprises a Morse taper. 
     Anchoring portion  304  is adapted to be fixed transversely to a bone or a bone fragment as will be later described. Anchoring portion  304  comprises substantially parallel first and second legs  301  and  302 . First leg  301  extends from the first end  316  of curved body  313  to second end  307  of post member  300  and second leg  302  extends from the second end  317  of curved body  313  to second end  307  of post member  300 . First and second legs  301  and  302  comprise a semi-circular cross-section as shown in  FIG. 3F  formed by partially-flat front-facing surfaces  326  and  327 , oppositely disposed partially-flat rear-facing surfaces  328  and  329 , flat outer-facing surfaces  324  and  325 , and curved inner-facing surfaces  330  and  331 . First and second legs  301  and  302  may comprise a plurality of barbs  334  and  335  extending transversely from the partially-flat rear-facing surfaces  328  and  329 . Alternatively, the plurality of barbs  334  and  335  may be disposed on partially-flat front-facing surfaces  326  and  327 , oppositely disposed flat outer-facing surfaces  324  and  325 , curved inner-facing surfaces  330  and  331 , or any combinations thereof. In addition, the plurality of barbs  334  and  335  may be disposed around the entire circumference of first and second legs  301  and  302 . The plurality of barbs  334  and  335  are used to buttress legs  301  and  302  against the bone. First and second legs  301  and  302  preferably terminate at first and second tips  321  and  322 , respectively. Each of the first and second tips  321  and  322  may taper from oppositely disposed flat outer facing surfaces  324  and  325  to curved inner facing surfaces  330  and  331 , terminating at a point for ease of insertion of legs  301  and  302  into the bone. 
     As shown in  FIG. 4 , screw member  102  comprises a unitary elongated body  400  extending from a first end  403  to a second end  404  along longitudinal axis  111 . Screw member  102  may be made of materials known in the art, including titanium, titanium alloy, stainless steel, cobalt chrome, PEEK, and resorbable polyactic acid (PLA). Also, screw member  102  may be coated with an osteoconductive material, such as, for example, plasma spray or other similar types of porous materials, that are capable of supporting or encouraging bone ingrowth into the material. It should be appreciated that the length of the screw member  102  may be selected of varying lengths to allow a surgeon to fuse different joints in the human body. 
     Screw member  102  comprises an elongated portion  401  connected to a bulbous portion  402 . The elongated portion  401  is substantially cylindrical in shape with a substantially uniform diameter. However, elongated portion  401  may be tapered from the bulbous portion  402  to the second end  404  of the screw member  102 . Elongated portion  401  preferably comprises threads  412 , such as helical threads, which are circumferentially disposed on the exterior surface  410  of the elongated portion  401 . It should be understood that any commonly used threads for engaging and coupling may be used without limiting the scope of the invention. Elongated portion  401  may also be provided with a self-tapping leading edge  409  to provide elongated portion  401  with the ability to remove bone material during insertion of screw member  102  into bone. 
     Bulbous portion  402  preferably comprises a taper, such as a Morse taper, on its outer surface  411  with a diameter that decreases from first end  403  of the screw member  102  to the elongated portion  401 . The taper of bulbous portion  402  allows for a locked interference fit with tapered bore  212  (shown in  FIGS. 2A-2F ) when tapered bulbous portion  402  resides within tapered bore  212 , as shown in  FIG. 1 . 
     Moreover, bulbous portion  402  is substantially cylindrical in shape and has an aperture  407  aligned along axis  111  traversing the longitudinal length of bulbous portion  403 . Aperture  407  is provided to receive an instrument (not shown) for applying torque to screw member  102 . Aperture  407  may comprise any shape known in the art, including, a hexagonal-shaped aperture, a star-shaped aperture, a square-shaped aperture, or any other shaped aperture may be utilized without departing from the scope of the invention. 
     Screw member  102  is preferably cannulated along its longitudinal length having a bore  406  that traverses the screw member  102  along longitudinal axis  111  and extending from the first end  403  to the second end  404 . Bore  406  is provided to interact with a guide wire or a Kirschner wire (K-wire) by receiving the K-wire within the bore  406  to help guide and position the screw member  102  into the bone as will be later described. Preferably, the diameter of bore  406  is constant throughout the length of the screw member  102 . Different diameters and K-wire sizes may be used depending on the diameter of the bones that are being joined and the surgeon&#39;s preferences. Illustratively, the diameter of the K-wire is in the range of approximately 0.7 to 4.0 millimeters (mm), and more preferably approximately 0.9 to 1.6 mm. In another embodiment, screw member  102  may be provided without a bore  406  (i.e., the screw member  102  may be solid). 
       FIGS. 5A-5F  illustrate a preferred embodiment of an instrument  500  used to couple the fixation assembly  100  to the bones.  FIG. 5A  illustrates the perspective side view of the instrument,  FIG. 5B  illustrates a side view thereof, and  FIG. 5C  illustrates the top view thereof,  FIG. 5D  illustrates the bottom view thereof,  FIG. 5E  illustrates the rear view thereof, and FIG.  5 F illustrates the front view thereof.  FIG. 6  illustrate the cross-section of the instrument taken along line  6 - 6  in  FIG. 5C . Instrument  500  comprises a unitary elongated body  501 . Elongated body  501  includes a handle portion  502  extending from a first end  511  to a second end  512  and aligned with its length along longitudinal axis  510 . Handle portion  501  may be ribbed (not shown) or may comprise friction resistant material to assist the surgeon to manually apply torque to the instrument  500 . Alternatively, or in addition, handle portion  501  may be sized to receive a torque transmitting tool (not show). 
     Elongated body  501  further comprises a head portion  503  coupled to the handle portion  502 . Head portion  503  extends from a first end  513  to a second end  514  and is aligned with its length along longitudinal axis  515 . Head portion  503  and handle portion  501  are coupled at their corresponding first ends  511  and  513 . Head portion  503  and thereby longitudinal axis  515  is offset from the handle portion  502  and thereby offset from the longitudinal axis  510  by angle C. Angle C may be any angle less than 90 degrees and preferably it is substantially equivalent to angle B. As such, angle C is preferably in the range of about 15 degrees to about 60 degrees. Head portion  503  preferably comprises an oval cross-section transverse to longitudinal axis  515 . Head portion  503  further comprises a pair of parallel bores  505  and  506  that traverse head portion  503  along longitudinal axis  515  from the first end  513  to the second end  514 . In a preferred embodiment, bores  505  and  506  are sized, shaped, and spaced-apart to correspond to first and second legs  201  and  202  of post member  101 . Preferably bores  505  and  506  are substantially cylindrical in shape with a substantially uniform diameter. Head portion  503  further comprises a rasp portion  520  extending transversely from its front end  513 . Rasp portion  520  comprises a plurality of teeth  521  arranged in fan-like configuration. Teeth  521  are used to clear bone material as will be later described. In a preferred embodiment, the front surface of rasp portion  520  is aligned along longitudinal axis  516 . Front surface of rasp portion  520 , and thereby longitudinal axis  516 , are offset from the pair of parallel bores  505  and  506 , and thereby from longitudinal axis  515 , by angle D. Preferably angle D is substantially equivalent to angle A. As such, angle D may be any angle less than 90 degrees and is preferably in the range of about 30 degrees to about 75 degrees. As shown in  FIG. 6 , instrument  500  is cannulated having a bore  508  extending along longitudinal axis  510  of handle  502  from a first end  511  to a second end  512 . 
     The fixation assembly  100  of the present invention is utilized to join two bones or two bone fragments together and to translate compression between the bones.  FIGS. 7 and 8A-8F  depict illustrative operative technique of an embodiment of the invention used joint a first bone (or bone fragment)  105  to a second bone (or bone fragment)  106 . It will be understood that the operative technique is only illustrative, that the order of execution of some steps may vary, and that some steps may not need to be used in the treatment of a particular patient in accordance with the invention. 
     Initially, in step  710  an incision is made in the skin over first bone (or first bone fragment)  105  and second bone (or second bone fragment)  106 . The incision may be a dorsal longitudinal incision or a two semi-elliptical incision. Next, in step  712  and as shown in  FIG. 8A , a retrograde K-wire  805  is advanced diagonally into the side surface  109  of the first bone  105  and through its proximal end  107 . The K-wire  805  is further advanced through the distal end  108  of the second bone  106 . The K-wire  805  is advanced by the surgeon in a direction of the desired alignment of the fixation assembly  100  with respect to the first and second bones  105  and  106 . Then in step  714 , as shown in  FIG. 8B , the first and second bones  105  and  106  are drilled using drill bit  810  over the K-wire  805  to create a first hole  811  in the first bone  105  and a second hole  812  in the second bone  106 . The K-wire  805  is used to guide drill bit  810  into the desired alignment. Accordingly, the drill bit  810  used in the present invention is preferably cannulated such that it may fit over the K-wire  805 . The drill bit  810  may be driven manually or via a torque transmitting tool (not shown). Hole  811  extends from the side surface  109  to proximal end  107  of the first bone  105  and hole  812  extends through the distal end  108  into the second bone  106 . 
     In step  716 , as shown in  FIG. 8C , instrument  500  is advanced over the K-wire  805  by inserting the K-wire  805  inside the bore  508  of instrument  500  until rasp portion  520  contacts the side surface  109  of first bone  105 . Rasp portion  520  is used to remove bone material from side surface  109  to create a depression  825  in the side surface  109  of first bone  105  to fit the head portion  103  of post member  101 . Since the longitudinal axis  516  of front surface of rasp portion  520  is offset from the longitudinal axis  515  of pair of parallel bores  505  and  506  by angle D ( FIGS. 5A-5B ), the depression  825  is angled to receive the head portion  103  in a flush configuration ( FIG. 8E ). In a preferred embodiment, the depression  825  is created deep enough in first bone  105  such that the head portion  103  sits within the depression  825  and is located below the side surface  109 . The depth of depression  825  sets the depth the fixation assembly  100  is implanted into bones  105  and  106 . To create depression  825 , instrument  500  is partially rotated or wiggled back and forth in directions D 3  and D 4  by rotating handle  502  manually, or by connecting handle  502  to a torque transmitting tool (not shown). Rotating handle  502  rotates head portion  503  to scrape and remove bone material with teeth  521  of the rasp portion  520 . 
     Next, in step  718 , as shown in  FIG. 8D , parallel bores  505  and  506  in head portion  503  of the instrument are used to align a drill bit  833  with first bone  105  to create third and fourth holes  831  and  832  in first bone  105 . To create the holes, the head portion  503  is aligned with the first bone  105  and the drill bit  833  is inserted into each of the parallel bores  505  and  506  of head portion  503 . In a preferred embodiment, third and fourth holes  831  and  832  are parallel and extend transversely with respect to first bone  105 . After the third and fourth holes  831  and  832  are created, in step  720 , first and second legs  201  and  202  are inserted into third and fourth holes  831  and  832 , respectively, as shown in  FIG. 8E . Head portion  103  is then pressed into the depression  825  until it is flush with the cortex of the bone. In alternative embodiments, post member  101  may be inserted by impaction, by press fit, by reaming, or substantially any other similar strategy or technique. 
     In step  722 , the screw member  102  is advance over the K-wire  805 , as shown in  FIG. 8F , so that the K-wire guides the screw member  102  into first and second bones  105  and  106 . Specifically, the K-wire  805  is inserted into bore  406  in the screw member  102 , as shown in  FIG. 8F . Screw member  102  is advanced through the bore  212  of the post member  101  and through first and second holes  811  and  812  in the first and second bones  105  and  106 , respectively. Screw member  102  may be driven by inserting a torque transmitting tool into aperture  407  in the bulbous portion  403  and rotating the screw member  102 , thereby engaging threads  412  with the second bore  812  in the second bone  106 . Screw member  102  is rotatably advanced into the second bone  106  until the tapered bulbous portion  403  engages and locks with tapered bore  212  in head  103  of the post member  101 . Finally, the K-wire  805  is removed from bones  105  and  106  and the incision is closed. 
     As will be apparent to those skilled in the art, numerous variations may be practiced within the spirit and scope of the present invention. For example, a variety of different tools—screw drivers, wrenches, reduction instruments and drill guides—may be used in the practice of the invention. Fixation assemblies of different sizes and different shapes may be used. Likewise, different thread sizes and configurations may be used. There may also be variation in the procedure used to implant the fixation assembly in the bones. Certain steps can be omitted or combined with other steps and certain steps can be performed in a different order. For example, in some procedures it may not be necessary to use a K-wire or pre-drill holes in the bones. 
     While the invention has been described with reference to the preferred embodiment and alternative embodiments, which embodiments have been set forth in considerable detail for the purposes of making a complete disclosure of the invention, such embodiments are merely exemplary and are not intended to be limiting or represent an exhaustive enumeration of all aspects of the invention. The scope of the invention, therefore, shall be defined solely by the following claims. Further, it will be apparent to those of skill in the art that numerous changes may be made in such details without departing from the spirit and the principles of the invention. It should be appreciated that the invention is capable of being embodied in other forms without departing from its essential characteristics.