Abstract:
The present invention relates to an orthopedic plate and screw system and instruments for surgical fixation of a small bone or bones including specifically the small bones of the spine. The plate facilitates three dimensional contouring to provide for a variety of applications and to accommodate individual variation in bone shape. The plate has a modified x shape including a central trunk portion including one or more screw holes along a longitudinal axis and a set of divergent upper and an oppositely extending set of divergent lower arms, each arm including screw holes which are placed at a radially equal distance but which diverging asymmetrically from the longitudinal axis relative to its paired upper or lower mate. The screws of the system are self-starting, self-tapping screws including the option of partial or full cannulation. In a further embodiment, the plate is intended for use through the length of the spine.

Description:
CROSS-REFERENCE 
     This application claims the benefit of priority under 35 U.S.C. §119 of U.S. Provisional Application Ser. No. 60/691,171 filed on June 16, 2005 and U.S. Provisional Application Ser. No. 60/648,364 Jan. 28, 2005 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an orthopedic plate for surgical repair or reconstruction of a bone in instances where it is desirable to have convergent screw fixation with screws that placed by the plate so as to be unlikely to impinge on each other. 
     BACKGROUND OF THE INVENTION 
     The field of orthopedic medicine has grown tremendously in the past fifty years as surgical techniques, implants and instrumentation have developed and been improved. The medical companies have tended to focus their attention on the largest market areas so that some areas of the body, such as the spine, knees and hips, have received intense focus from the large medical companies. While the small bones are frequently subject to the need for re-constructive surgery for example, as a result of trauma, to counteract the effects of aging or to repair congenital deformities, this area has typically not received the same degree of attention from the medical companies as joint replacement, trauma and spinal areas. Consequently, the products available to the small bone surgeon often represent scaled down versions of products designed for the large long bone market which are not adequate for the fine bones and delicate procedures required of the small bone surgeon. Additionally, while there is a wide variety in the exact shape and mass of all bones, these variations become more problematic in providing orthopedic implants for small bone applications since there is less room on and about the bone for the surgeon to place and fix the construct. These bones are finer and have less surface area for placement of an implant, and less mass for the placement of screws and as a result, individual variations become more problematic for implants of stock design. 
     While some of the spinal companies have focused on hardware intended for use in the cervical and thoracic areas of the spine, some of the same problems exist in these areas as have been previously listed, thus the present invention is also useful in a slightly modified, and more robust form for use in the spine. 
     One problem that needs to be avoided in the delicate environment of the congested bone area, such as the metacarpals, the metatarsals, and the cervical region of the spine, is the interference of screws, with other screws, and with the function of ligaments and tendons. It may be desirable to design an orthopedic plate so that securing screws converge in order to cause compression or increase the pullout strength, it is difficult when a screw impinges on or conflicts with the desired placement of another screw. Some surgeons prefer bicortical fixation in which a screw is sized so that the distal end is secured in cortical bone giving the screw better purchase, however, other surgeons may prefer to avoid placing a screw so that it projects beyond the outer surface of the anchoring bone. These factors are complicated by the relative lack of soft tissue and the presence of ligaments and tendons in these small or congested bone areas. Consequently, the less forgiving biological environment in which the small bone or cervical surgeon works requires greater procedural precision and calls for specialized implants and tools. 
     The present invention is designed to meet the specific needs of the small bone surgeon to facilitate effective and repeatable procedures which provide for ease of use and a range of function for this specific area of specialization. The present invention could serve for the treatment of a broad range of indications including relatively straightforward fracture repair following trauma in an otherwise healthy individual where screws are used alone or with plates to maintain the integrity of the bones while they heal, as well as for more complex surgeries such as reconstruction to correct congenital or age related deformation. Reconstruction often includes arthrodesis or partial or total fusion which involves removal of a joint and the use of a mechanical-biological construct to keep the bones immobile while fusion occurs. Further small bone surgeons may be called upon to achieve soft-tissue balancing by readjusting the length of tendons and ligaments or to reshape the bone itself through removal or repositioning in a procedure known as an “ostetomy”. In an aging or diabetic population, these procedures may also involve dealing with the difficulties of poor quality bone and/or compromised soft tissue. 
     These surgeons typically include sub-specialists such as hand surgeons and feet and ankle and podiatric surgeons, but can also include general orthopedic surgeons who may be called upon to perform procedures on the small bones. 
     The present invention provides a plate with asymmetrical and bi-planar screw fixation and further designed to facilitate three dimensional contouring to provide for a variety of applications and to accommodate individual variation in bone shape. The plate is designed specifically for the small bone market, i.e. for use in bones distal to the elbow and knee, including, for example, the ulna, radius, tibia, fibula, as well as the metacarpals, carpals, metatarsals, tarsals, and phalanges, and in a further embodiment for the spine. The plate can be used in applications previously mentioned, for example those that require fixation to a single bone such as the stabilization of a fracture or the plate can be used across two or more bones so as to facilitate total or partial fusion. The plate is configured to bend laterally, longitudinally, and to wrap or spiral about its longitudinal axis so that it can be molded to an optimal shape for small bone procedures. The plate is designed to provide optimal stabilization of fractures and osteotomies by providing multi-planar fixation that allows for better pull-out and limited axial loading to the bone. The plate is further designed to accelerate fusion success by reducing or eliminating torsional or twisting stresses to the bone segments during the healing process. In addition, when desired, the plate can be shaped so as to apply a compressive, or even a tensile, force, for example, along the longitudinal axis of a bone. 
     The plate has a central trunk portion including one or more screw holes separated by a waist shaped linking portion along a longitudinal axis and a set of upper and lower arms including screw holes which are placed at a radially equal distance but which diverge asymmetrically from the longitudinal axis to avoid conflicts in the screw placement of the paired arm, specifically, so that the screws of a set of arms do not impinge on each other. The plate is radiused with a curvature corresponding generally to the curvature of a bony surface. The upper pair of arms, and the lower pair of arms continue this curvature and the through holes are placed so that the angle of the longitudinal axis of the screws converge in the direction of the distal end of the screw. The screw holes are placed with the longitudinal axis perpendicular a tangent to the top surface of the arm with the effect that the longitudinal axes of the screws converge in the direction of the distal end. This increases the pull-out strength of the screws. Further the screw holes are concavely rounded to allow for multi-axis orientation of the low profile, rounded screw in the hole, which can be oriented with a conical shape about the longitudinal axis of the screw hole having an angle of at least 20°, preferably at least 25°, and most preferably about 30°. 
     The screws do not in fact conflict since each of the arms in a pair form a different angle to the central trunk so that the longitudinal axis of the screws are offset from each other along the length of the plate. The pre-bent configuration of the plate is designed to increase operating room efficiency by facilitating commonly desirable shapes while maintaining the required strength and by permitting bending without deforming the screw holes. This results in making customization in anticipation or during surgery easier. 
     The screws useful with the plate of the present invention are self-starting, self-tapping screws including the option of partial or full cannulation. The screws include a cutting end having multiple flutes, and preferably 2 or 3 flutes about a conical recess. The screws further include a partial taper of the inner diameter in the proximal end over the first several thread turns, for example over 2-8, and preferably over 3-5 turns in order to increase the fatigue life of the screw as well as providing potential physiological advantages in use. The screw head is a rounded low profile head. The screws further include a torque driving recess that may be a hexagon, a torx shape, or a modification of a torx shape, i.e. a multilobe shape having from 3 to 12 lobes, and preferably having 4 to 8 rounded recesses or lobes. The recess can be of a constant size in the direction of the longitudinal axis, or can taper inward along the longitudinal axis of the screw toward the bottom of the recess. 
     The instruments for use with the system are well-balanced and ergonomically designed with sufficiently long handles to place the surgeon&#39;s hands outside of the line of radiation and designed to reduce fatigue in the operating room. 
     The plate system of the present invention is thus designed to fit a range of needs of the surgeon operating on the small bones (specifically including the small bones of the spine) to allow him or her to perfect a variety of techniques using a set of instruments and a customizable plate and screw construct. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top view of an alpha orthopedic plate in accordance with the invention; 
         FIG. 2  is a cross-section of the plate taken along line  2 - 2 ; 
         FIG. 3  is a cross-section of the plate taken along line  3 - 3 ; 
         FIG. 4  is a cross-section of the plate taken along line  4 - 4 ; 
         FIG. 5  is a cross section of the plate taken along line  5 - 5 ; 
         FIG. 6  is a perspective view of a screw used with the present system; 
         FIG. 7  is a detail of the torque receiving recess of the screw shown in  FIG. 6 ; 
         FIG. 8  is a cross-section of the screw of  FIG. 6  taken along line  6 - 6 ; and 
         FIG. 9  is a top view of a second embodiment of an orthopedic plate in accordance with a further aspect of the invention. 
         FIG. 10  is a top view of a beta version of the first embodiment of a plate in accordance with the invention; 
         FIG. 11  is a cross section of the plate of  FIG. 10  taken along line  11 - 11 ; 
         FIG. 12  is a top view of an alpha version of a third embodiment of a plate in accordance with the invention; 
         FIG. 13  is a cross section of the plate of  FIG. 12  taken along line  13 - 13 ; 
         FIG. 14  is a top view of a beta version of the third embodiment of a plate in accordance with the invention; 
         FIG. 15  is a cross section of the plate of  FIG. 14  taken along line  15 - 15 ; 
         FIG. 16  is a top view of an alpha version of a fourth embodiment of a plate in accordance with the invention; 
         FIG. 17  is a cross section of the plate of  FIG. 16  taken along line  17 - 17 ; 
         FIG. 18  is a top view of the beta version of the fourth embodiment of the plate in accordance with the invention; 
         FIG. 19  is a cross section of the plate of  FIG. 18  taken along line  19 - 19 ; 
         FIG. 20  is a top view of an alpha version of a fifth embodiment of a plate in accordance with the invention; 
         FIG. 21  is a cross section of the plate of  FIG. 20  taken along line  21 - 21 ; 
         FIG. 22  is a top view of the beta version of the fifth embodiment of the plate in accordance with the invention; 
         FIG. 23  is a cross section of the plate of  FIG. 22  taken along line  23 - 23 ; 
         FIG. 24  is a top view of an alpha version of a sixth embodiment of a plate in accordance with the invention; 
         FIG. 25  is a cross section of the plate of  FIG. 24  taken along line  25 - 25 ; 
         FIG. 26  is a top view of the beta version of the sixth embodiment of the plate in accordance with the invention; 
         FIG. 27  is a cross section of the plate of  FIG. 26  taken along line  27 - 27 ; 
         FIG. 28  is a top view of an alpha version of a seventh embodiment of a plate in accordance with the invention; 
         FIG. 29  is a cross section of the plate of  FIG. 28  taken along line  29 - 29 ; 
         FIG. 30  is a top view of the beta version of the seventh embodiment of the plate in accordance with the invention; and 
         FIG. 31  is a cross section of the plate of  FIG. 30  taken along line  31 - 31 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The plate  10  of the present invention is shown having a asymmetric shape which can be thought of as being similar to the Greek letter χ with foreshortened opposing diagonal legs extending from a central trunk portion  12  defining the longitudinal axis of the plate. The trunk portion  12  includes one or preferably more screw holes  14  along the longitudinal axis. The number of screw holes in the trunk portion  12  will depend on the length of the plate, and may range from 0 to 6, and more preferably from 2 to 4. In one embodiment the holes are compression holes. The screw holes  14  are preferably slotted or elongated with a larger radius area  11  on each of the screw holes facing in the same direction, and a smaller radius area  13  which has a shallower lip to allow the plate to be set initially and subsequently to be slide into a different position as the screws are tightened down. This allows compression to be applied across the middle of the trunk section. Further, the screw holes include annular rings  15  of increased thickness in the vertical direction about through holes  14 . 
     The through holes  14  in the trunk portion  12  have a longitudinal axis that is perpendicular to plane tangent to the top radius of the plate. The area linking the screw holes has a decreased width so as to define a waist area  26  that will bend laterally (or “curve”) relative to the longitudinal axis and which will bend longitudinally to form a curved area in and out of the plane of the plate. This thinner area also facilitates twisting of the plate so as to allow the plate to spiral, or wrap around it longitudinal axis. The increased annular area around the through bores resists deformation when a bending device is used to apply a force to the plate through the screw holes. 
     The plate  10  also includes at least one set, and preferably two opposing sets of arms  20 . As viewed in  FIG. 1 , these sets of arms can be viewed as a set of upper and lower arms, although it is understood that the orientation of the plate can vary even after the plate has been fixed to the bone so that the terms upper and lower are only used to distinguish the pair on one side of the trunk portion  12  from the pair on the other side of the trunk portion  12 . The arms can also be thought of as a first  22  and second  23  set of diagonally opposing arms which correspond in shape and size. The plate is bilaterally asymmetrical, meaning that the right half and the left half are not the same. Neither is the top of the plate the same as the bottom half of the plate, but the plate has a transverse mirror symmetry, meaning that while they are not the same, the half on one side of a transverse plane if a mirror image of the half on the other side of the plane. This means that the plates exhibit a handedness, and are presented as an alpha and a beta version, which correspond roughly to a left and right version. It should also be understood that the plates can have a single set of arms at one end of the plate and a truncated trunk portion. Each of the arms in a set includes screw holes  24  which are placed at a radially equal distance but which diverging asymmetrically from the longitudinal axis of the plate  10 . More specifically, each set of arms includes one arm that defines a smaller angle of divergence α from the longitudinal axis of the trunk portion than the angle of divergence of the other arm β. For example, the first angle shown in  FIG. 1  at α may be from about 5° to about to 25°, and more preferably from about 10° to about to 20° and most preferably from about 12° to about to 16°, while the second angle shown at β from about 10° to about to 35°, and more preferably from about 15° to about to 30° and most preferably from about 22° to about to 26° with a preferred difference in the angles beings from about 2° to about to 20°, and more preferably from about 4° to about to 16° and most preferably from about 8° to about to 12°. 
     In addition to the angled arms of this asymmetrical dog-bone shape facilitating a variety of useful positions in the small bone area, the plate of the present invention is sized to fie the needs of the small bone specialist. For small bone usage, the total length of the plate along its longitudinal axis is from about 25 mm to about 80 mm, depending on the number of screw holes in the trunk portion. The total width is from about 12 mm to about 18 mm, width an inferior radius of curvature of about 8 mm to about 12 mm and a concentric radius on the superior side. Typically, the waist area measures from about 7.5 mm to about 10 mm from the center of the larger, i.e. about 3.8 mm, radiused portion of the holes. The trunk portion has a width of about 7 mm to about 9 mm wide at the wider parts and about 3 mm to about 5 mm wide at the narrower waist portion. The longer arm has a length along the longitudinal axis of the plate from the center of the screw hole to the center of the plate for a two-hole trunk of from about 12 mm to about 16 mm, with a width of about 3 mm to about 5 mm. The shorter arm has a comparable length of from about 7 mm to about 15 mm with a narrowed width of about 2.5 to about 5 mm. In a further embodiment the plate could be modified for use in the long bones with a length of up to about 400 mm with a width of up to about 50 mm, and proportional sizes for the arms and thickness. 
     On the inferior side, or the side that would be facing the bone surface in use, the arms continue the radius of curvature of the trunk portion. The superior or top side of the plate has a similar radius of curvature as the top surface of the plate has an outline that corresponds with the shape of the bottom of the plate (excluding the optional thickened annular area surrounding the screw holes which would act to shield these holes against deformation during bending.) The screw holes also include a rounded concavity to mate with the rounded shape of the head of the screw to allow of variable axis positioning. The screw holes  24  are placed with the longitudinal axis perpendicular a tangent to the top surface of the arm with the effect that the longitudinal axes of the screws converge in the direction of the distal end. This increases the pull-out strength of the plate/screw construct. Since the arms are asymmetrical relative to each other, and in particular since they diverge from the longitudinal axis of the trunk portion at differing angles, conflicts in the positions of paired screws is avoided so that the screws of a set of arms typically do not impinge on each other. This is even more important in instances where the plate is bent around the longitudinal axis so as to wrap around the longitudinal axis of the bone. 
     The arms  20  also each include a screw hole  24  which, like the trunk portion  12  has a linking portion  26  that joins the screw hole to the trunk portion. Again this design facilitates the desired bending while resisting deformation of the screw holes  24  when they are used with the bending instrument to contour the plate. While the angle of the arms  20  of each one of a pair of a respective set of arms  22  and  23  varies so as to create a bilateral asymmetry, meaning that the plate is not symmetrical with respect to a plane that passes through the longitudinal axis in the vertical direction from the superior (the top side relative to the bone) to the inferior side (the side facing the bone), the “first plane”. However, the position of the arms in each set is preferably flipped so that the symmetry of the plate shape about a plane transverse to the first plane is a mirror image, this is defined herein as transverse mirror symmetry. The screws holes of the trunk portion can include means to induce a compressive force in one direction, such as a ramped area on each screw hole. These ramped areas would be ramped on the same side of the holes looking down from the top of the plate. Typically the first screw implanted stabilizes and the second screw is used to achieve compression. Further the length of each of the arms of a pair will vary so that the radial length of the center of the screw hole to the intersection with the longitudinal axis will be the same. As shown in  FIGS. 2-4 , the plate includes a radial curve about the longitudinal axis. The radius is typically about 10 mm with a transverse dimension from the edge of one arm to the edge of the other arm of an upper or lower pair being about 15 or 16 mm for typical small bone usage, and the screw bore having a longitudinal axis of about 24° to an plane passing through the longitudinal axis of the plate. The bores are typically about 3.75 mm for a 3.5 mm diameter screw for small bones excluding the smallest of applications which would include phalanges. Again, for the smallest application as well as long bone embodiments the screws and corresponding screw holes could be sized to range from a 1.5 mm diameter screw up to a 7.5 mm diameter screw. In a further embodiment, the bore could be threaded. 
       FIG. 4  shows a screw  30  used with the plate system of the present invention. The distal end of the screw includes a cutting tip  32  which is self-starting and self-tapping. This aspect is defined by a conical recess and a plurality of flutes  33 . These screws  30  can optionally include partial or full cannulation  34 . The head of the screw is spherical and includes a torque driving recess, such as a modified multilobe shape as is shown in  FIG. 5 . The screw has a cancellous thread with a constant major diameter and a minor diameter that tapers proximally in order to increase fatigue life of the screw and to improve compression and compensate for bone resorption. 
     An additional embodiment of the plate in accordance with the present invention is shown in  FIG. 9 . This plate  110  shares the same features as the design show in  FIG. 1 , but is somewhat more robust, with less tapering at the trunk portion  112 . The plate includes opposing pairs of asymmetrical arms,  120 , which can again be viewed as upper  122 , and lower  123  arms, each including a set of screw holes  124  The trunk area  112  further includes slotted screw holes  114  which can be similarly used to cause a compression between them. The bottom side is radiused as for the small bone area, but with a gentler curvature of radius. 
       FIG. 10  is a beta version of the plate shown in  FIG. 1 . Thus, it is a mirror image of the plate, with corresponding elements such as a trunk portion  12 ′, a pair of angled arms  20 ′ at either end each having a screw hole  24 ′, and the trunk portion  12 ′ having two compression slots  14 ′ that can be used to apply a compressive force in the direction indicated by the arrow  17 ′ by placing the screw near the front of the slot, or can be used at a neutral compression by placing the screw in the middle of the slot when they are first put in.  FIG. 11  is a cross-section of the plate of  FIG. 10 . 
       FIGS. 12 through 14  illustrate an embodiment of the plate  310 ,  310 ′ with a shorter trunk  312 ,  312 ′ that serves principally to join the two ends bearing the arms  320 ,  320 ′ and including a single narrowed waist area  326 ,  326 ′. The arms  320 ,  320 ′ each include screw holes  324 ,  324 ′ which are rounded and provide the option of conical multi-axis fixation as shown and described for the first embodiment.  FIGS. 16 through 19  illustrate an embodiment of a plate  410 ,  410 ′ having two opposing pairs of arms  420 ,  420 ′ each including the multi-axis screw hole  424  and having a relatively short trunk portion  412 ,  412 ′ having a single compression slot  414 ,  414 ′.  FIGS. 20 through 23  illustrate both the alpha and beta version of an embodiment of the plate  510 ,  510 ′ which have the pairs of asymmetrical arms  520 ,  520 ′ and including a central trunk area  512 ,  512 ′ with three compression slots  514 ,  514 ′ separated by narrowed waist areas  526 ,  526 ′.  FIGS. 24 through 27  illustrate both the alpha and beta version of an embodiment of the plate  610 ,  610 ′ which have the corresponding diagonally opposing arms  622  and  623 , and  622 ′, and  623 ′ and including a central trunk area  612 ,  612 ′ with three compression slots  614 ,  614 ′ separated by narrowed waist areas  526 ,  526 ′.  FIGS. 28 through 31  illustrate an alpha and beta version of the plate  710 ,  710 ′ having only a single pair of arms  720 ,  720 ′ and a trunk portion  712 ,  712 ′ optionally having one or more compression slots  714 ,  714 ′. 
     While in accordance with the patent statutes, the best mode and preferred embodiment have been set forth, the scope of the invention is not limited thereto, but rather by the scope of the attached claims.