Abstract:
A bone plate assembly has the screws on one plate, either distal or proximal to the fracture, placed through round holes perpendicular to long axis of a first bone thus securing the plate rigidly to the bone on one side relative to the fracture. The screw holes can be either threaded on non-threaded. On the other side of the fracture, the bone fragment is first secured with an inclined screw placed from less than 90 to 10 degrees towards the fracture. As the screw is tightened it advances away from the fracture pulling the first bone, securely attached, plate towards the fracture site and thus compressing the fracture.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to bone plates for fracture repair and improved methods of repair. 
       BACKGROUND OF THE INVENTION 
       [0002]    Fractures of normal bone usually result from injuries which frequently also involve surrounding tissues. Not all fractures can be treated conservatively as in number of instances treatment by immobilization, traction and other non-surgical methods results in non-unions, delayed unions and malunions. Prolonged immobilization can also lead to stiffness and degeneration of adjacent joints. For these reasons surgical treatment of fractures is often resorted to Anatomical reduction and bone immobilization by internal fixation with plates and screws. This is highly successful, but it too has its limitations not the least of which is stress-shielding. Anatomical reduction and compression of the fracture site with rigid internal fixation are generally achieved by the use of metallic dynamic compression sliding plates and screws. The plates are equipped with elongated holes with angulated sides. This allows bone to move independently of the plates. The holes in the bone plate are configured so as to allow the plate to glide in response to the pressure applied by the screw head and to push the bone fragments to achieve compression of bone fragments against each other. Such fixation usually produces good clinical results. A relatively recent addition to the internal rigid fracture fixation was the advent of locking plates. With conventional plates, screws can move independently from the plate, they may loosen with time. Premature screw loosening produces fracture instability, loss of fracture gap and non-union. Plate to bone compression and friction from the movement of the plate may negatively impact on the blood supply essential to fracture healing and formation of fracture callus, both external and internal. Osteoporotic bone may not be able to withstand high screw torque required to maintain screw-compression plate construct. With locking plates, the screws and plates form a single complex reducing the possibility of hardware failure since the motion between, screws, bone and plate is eliminated. The plate screw assembly distributes stress along the entire length of the plate, thus making it more suited for osteopenic bone and multi segment fractures. Locking screws are not better or worse than conventional screws. They are different. Locking screws use the screw pullout strength more effectively, but cannot compress fractures as conventional screws can. Hybrid plate fixation provides advantages of both techniques. Bridge plating can be performed with conventional, locked or hybrid fixation. The longer the bridge or comminuted segment, the more empty holes in currently available plates. Empty holes can double or triple the plate stresses by concentrating the stress which reduces fatigue life of the plate. 
         [0003]    It is well understood that bone healing can also occur as a result of flexible osteosynthesis which provides only relative stability. This method of bone fixation is typically employed in comminuted fractures. The goal of this technique is to maintain length of the bone, its angulation and keep the end portions of fractured bones or joints in correct position without directly lifting or manipulating the fracture zone itself. This can be achieved with locking screws, which as we said do not have the capacity to compress bone fragments. 
         [0004]    As is well known to those skilled in the art the bones where fractures occur as well as the types of the fractures vary greatly. Many fractures do not respond well to only rigid internal fixation with compression alone or flexible osteosynthesis with angular stability alone. This precipitated the development of bone plate assemblies which incorporate screws that allow compression or lock into the threaded plate hole. These have been the subject to several patents and publications known to those skilled in the art. 
         [0005]    US Pat. No. 8,632,545 B2 discloses the invention relating to a bone plate with a combination hole which can receive a bone screw that can be used to fix bone fragments and also be securely locked in a relationship of angular and axis stability with the bone plate. The invention discloses a bone plate system wherein the bone plate comprises a plurality of holes at least one of which is a combination hole that can receive screw capable of either locking or compressing the plate. 
         [0006]    US Pat. No. 6,669,701 discloses a bone plate with at least one hole with a substantially circular outer periphery and a second portion defining an elongated outer periphery, with threads extending over an angle of 100 to 270 degrees at the upper surface of the bone plate and 180 to 230 degrees at the lower surface of the bone plate. The bone plate as disclosed in this patent has only a partial thread in the hole which does not encompass the diameter of the hole completely. 
         [0007]    US Pat. No. 8,226,693 reveals an orthopaedic bone bridge for internally fixing and stabilizing fractured bones. It includes first and second bone plates attached to bone by screws. Plates are placed on the opposite sides of the fractures. The plates are mounted on a pair of elongated hollow legs on which the plates are mounted. The second plate is slidably engaged and is movable with respect to the first plate. A cable is attached to the first plate and extends through the legs and around the second plate. The cable provides tensile form between the plates when they are pulled apart thus compressing the fractured bone fragments by forming a bone bridge. 
         [0008]    US Pat. No. 5,057,111 reveals non-stress shielding bone healing device which can be with screws, pins or nails for attaching the device to the bone. At least one of two or more openings in the plate is a relaxation opening shaped in part as a truncated spherical section. The plate is preferably a polymer member formed of viscoelastic or resorbable materials. 
         [0009]    It is well understood that bone screws used in bone plate assemblies to compress bone fragments also compress the bone plate to underlying bone. This result in stress shielding and undesirable osteopenia or osteoporosis in the bone beneath the plate. The second undesirable effect of compression plates which span the fracture site is the inhibition of the formation of the external callus with consequent weakening of the fracture site. 
         [0010]    Bearing these facts in mind the prior art reveals the need for an improved and radically different system of bone plate assemblies. 
       SUMMARY OF THE INVENTION 
       [0011]    The object of the invention is to provide bone plate assemblies secured with screws through threaded or unthreaded holes on a principles different from those employed in a prior art. A bone plate assembly has the screws on one plate, either distal or proximal to the fracture, placed through round holes perpendicular to long axis of a first bone thus securing the plate rigidly to the bone on one side relative to the fracture. The screw holes can be either threaded on non-threaded. On the other side of the fracture, the bone fragment is first secured with an inclined screw placed from less than 90 to 10 degrees towards the fracture. As the screw is tightened it advances away from the fracture pulling the first bone, securely attached, plate towards the fracture site and thus compressing the fracture. The degree of compression is determined by the angle at which it is placed which in turn determines the distance the screw will travel, and pull the already attached plate. Once desired degree of compression is achieved the second plate is further attached with screws placed through the holes at right angles. The holes can be threaded or unthreaded. If the compressing hole is unthreaded a jig or guide directing the placement of the screw at a predetermined angle is another embodiment of the invention. If the hole in the compression plate is with screws, the screws are placed at a predetermined angle. The plate can be marked with the angle θ of the screw and the distance the screw will traverse before the bone fracture placement is complete. 
         [0012]    Still another embodiment of the invention is a curvature in the plate which will lay over the actual fracture site thus preventing pressure directly on the fracture site. This is done to prevent inhibition of the external callus formation. The portion of the plate over the fracture site is devoid of holes in order to provide maximum strength to the construct. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The invention will be described by way of example and with reference to the accompanying drawings in which: 
           [0014]      FIG. 1  is a top view of the bone plate made according to the present invention attached to a fractured bone. 
           [0015]      FIG. 2  is a cross sectional view of the fractured bone and bone plate of  FIG. 1 . 
           [0016]      FIG. 2A  is an end view of the bone plate of the present invention fixed to a bone. 
           [0017]      FIG. 3  is a cross sectional view of one embodiment of the bone plate of the present invention showing a hole having angled threads to guide the bone screw. 
           [0018]      FIGS. 3A and 3B  are side views of exemplary bone screws. 
           [0019]      FIG. 4  is a cross sectional view of an exemplary bone screw with an angled head and the bone plate of the present invention. 
           [0020]      FIG. 5  is a cross sectional view of a second embodiment bone plate of the present invention attached to a fractured bone. 
           [0021]      FIG. 6  is a top view of an exemplary screw head for use with the bone plate of the present invention. 
           [0022]      FIGS. 7A-7E  are photographs of side and top views of the bone plate of the present invention being installed on a simulated bone. 
           [0023]      FIG. 8  is a cross sectional view of the drill guide shown with the bone plate of the present invention. 
           [0024]      FIG. 9  is a top view of an exemplary plate marked at various angles and corresponding compression distances. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    With reference to  FIGS. 1-7E , the present invention relates to bone plates  3 , bone screws  4 ,  5 ,  7 , and bone plate assemblies used for stabilization and controlled compression of fragments of fractured bone  8 . The principles on which this invention is based are different from those described and employed in prior art. In prior art compression is achieved by exerting pressure on the slanted rims of elongated holes in compression plates (dynamic compression plates) and sliding the bone fragment towards another fragment of a fracture bone. The degree of compression is determined empirically, it is not controlled. The present invention employs slanted screws  5  and holes  2  in the plates  3 . While one end  3 A of the plate  3  is securely attached to a distal or proximal segment  8 A of a fracture bone  8  the other side of the plate  3 B exerts a pulling force on a fragment  8 B secured to the plate  3  through the motion of the screw  5  placed at acute angles θ to the bone fragment  8 B. The screw  5  pulls the plate  3  with the attached bone fragment  8 A towards the fracture  9  thus compressing it. As the screw  5  placed at an acute angle θ is screwed into the bone  8  it travels away from the fracture  9  pulling the plate  3  with it. The distance the head  5 A of the screw  5  will travel will depend on the angle θ the screw  5  is being placed into the bone fragment  8 B. Thus the distance (d) the plate  3  will travel and exert compression on the fracture  9  is known in advance. The greater the distance (d) the greater is the degree of compression. 
         [0026]    This procedure is best illustrated by the simulation exhibited in  FIGS. 7A-7D . In  7 A, the cut bone sections  8 A and  8 B are longitudinally widely spaced as well as vertically offset. The bone  8 A is fixed to the plate  3  by the screws  4  perpendicularly fastened to the bone  8 A. The inclined screw  5  is shown in the bone fragment or section  8 B extending from the compression hole  2 C. As the screw  5  tightens, the distance (d) between the bone sections  8 A,  8 B decreases, see  FIG. 7B . On further tightening, the bone sections  8 A,  8 B are abutting and in compression shown in  FIG. 7C .  FIG. 7D  shows a frontal side view of the bone sections  8 A,  8 B and the aligned and compressed fracture  9 .  FIG. 7E  is a top perspective view showing the screws  7  completing the fixation of the plate  3  to the bone  8 B. 
         [0027]    The human skeleton is made up of bones that typically have shafts and heads. It is well understood that fractures of bones are treated differently depending on various factors. Some of these are position of the fracture, number of fragments, condition of bone and damage to the surrounding tissues. Osteopenia and osteoporosis are particularly important consideration. Open treatment of fractures generally employs systems or assemblies of metallic plates with holes to receive the screws. The treatment itself usually includes steps of compressing fractured fragments towards each other. Recent advances in this field include bone plates with holes with threads to accommodate screws with threaded heads, shown in  FIG. 3A , which lock the bone plate with the screws thus preventing screw loosening , a relatively frequent occurrence, particularly in osteopenia and osteoporotic bones. 
         [0028]    The bone plate  3  of the invention comprises an upper surface  3 C and a lower surface  3 D. The lower surface  3 D is the surface in contact with the underlying bone  8 . The plate  3  has a plurality of holes  2  to receive the screws  4 ,  5 ,  7 . The holes  2 , except for the compression holes  2 C are designed to accommodate screws  4 ,  7  for placement perpendicular to underlying bone  8 . These holes  2  can be threaded holes  2 T to accommodate threaded screw heads or unthreaded holes  2 . One or two screw holes  2 ,  2 T are compression holes  2 C which are placed at acute angles θ to the long axes of the bones  8 . The angles θ are directed away from the fractures  9 . As the screws  5  are being screwed in place the head  5 A of the screw  5  travels in the direction away from the fracture  9  site. It pulls the plate  3  with it. The distance (d) the screw  5  and head  5 A of the screw will travel is determined by the angle θ at which the screw  5  is placed. The hole  2 ,  2 C can be threaded holes  2 T to accommodate the placement of the screw  5 , as shown in  FIG. 4 . Proximal portion of the holes  2  can be larger in diameter than the rest of the screw formed as a countersunk hole as illustrated, generally or a counterbored hole as shown in  FIG. 4 . The angle θ of the compression screw hole  2 C as well as the distance the head  5 A of the screw  5  will travel can be marked on the plate  3 , shown in  FIG. 9 . Preferably, this is done in order to allow the surgeon to choose the plate  3  with a predictable compression distance (d). The screw at a 60 degree angle will advance the distal fragment 5 mm, at 70 degree angle it will advance it 2 to 3 mms, at 80 degrees it will advance it 1 mm and at 90 degrees it will, of course, not advance it at all. Another refinement we can add is placing the threads for the locking plates at different angles in the compressing hole. 
         [0029]    If the plate  3  has a compression hole  2 C without threaded screw hole  2 T, the angle θ at which the screw  5  is placed can be determined by jigs or guides  15 , shown in  FIG. 8 , designed to pre-drill holes to place screws  5  at various acute angles θ. 
         [0030]    The plates  3  can be made of different thickness (t), preferably from 2 to 5 mm. The plates  3  preferably are concave on the sides to fit the contour of bone  8 , as shown in  FIG. 2A . 
         [0031]    With reference to  FIG. 4 , the screw  5  as shown has a flat head  5 A shown horizontal to the upper surfaces  4 C nested in a counterbored hole  2 D. The threaded shaft of the screw  5  is inclined by the angle θ. This is one optional assembly. 
         [0032]    As shown in  FIG. 5 , in another exemplary embodiment, the bone plates  3  of present invention have upper surface  3 C and the lower surface  3 D which is concave, said concave lower surface  3 D being the bone contacting surface. The plate  3  has a plurality of holes  2  with at least one hole  2  being a compression hole  2 C extending at an angle θ from the upper  3 C to the lower surface  3 D. The mid-portion  20  of the plate is devoid of holes and is a bowed or curved structure with the curve extending above and away from the bone  8 . This mid-portion  20  of the plate  3  is placed over the fracture  9  site, and optionally instead of being contoured to the surface of the bone it can be flat. This mid-portion  20  of the plate  3  does not touch the underlying fracture  9  or bone fragments  8 A or  8 B of the bone  8 , thus preventing the inhibition of the external callus encountered with current art compression plates. 
         [0033]    With reference to screws, the screws  4 ,  5 ,  7  may have any type of mechanical apertures for torqueing and tightening such as common Phillips head, slotted flat or pan heads or Allen heads or as shown in  FIG. 6  a faceted head with radially extending pedal like slots or channels  23  from a hole  24  to which a complimentary tool (not shown) can be used to drive the screws in place. 
         [0034]    The plate  3  with the curved mid-portion  20  can be made sufficiently thick so as to be rigid. Alternative and optionally, the plate  3  can be made thin enough to be flexed slightly toward the bone  8  by the surgeon after the first screws  4  are placed in the plate  3  at that end  3 A. By flexing the curved mid-portion  20  inwardly slightly, this lengthens the plate  3  ever so slightly so when the one or more compression screws  5  are placed and the surgeon releases the curved mid-portion  20  the plate  3  shortens slightly to provide a spring loaded additive compressive feature. This effectively allows the plate  3  to mimic dynamic bone fracture plates. 
         [0035]    Variations in the present invention are possible in light of the description of it provided herein. While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. It is, therefore, to be understood that changes can be made in the particular embodiments described, which will be within the full intended scope of the invention as defined by the following appended claims.