Abstract:
An intramedullary nail for fixation and stabilization of a fractured bone that also allows for a controlled amount of longitudinal motion at the fracture site to encourage bone remodeling and healing is described. The intramedullary nail has a proximal portion and a distal portion that are coupled together in a manner by a biasing assembly that provides for a controlled movement of the proximal and distal portions relative to each other so that when a patient puts pressure on the bone, such as when walking, the fracture site compresses and the bone ends move together, and when the pressure is released from the bone, the bone ends are biased apart by a controlled amount.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. Application No. 61/725,429, filed Nov. 12, 2012 incorporated by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    This invention relates to an intramedullary nail for use in stabilizing and enhancing the healing of broken bones, and more particularly to an intramedullary nail that includes motion along its longitudinal axis so as to elicit an improved healing response in the bone in which the nail is placed. 
         [0003]    It is well known in the art that functional loading of skeletal bone results in changes to bone quality and quantity. Conversely, lack of mechanical loading has been found to lead to a loss of bone quality and quantity. 
         [0004]    When a bone fractures, one of two physiological processes are stimulated that provide for healing of the fracture. The first process is denoted enchondral ossification and occurs when there is strain at the fracture site. This process forms bone through a cartilage intermediate and is similar to the mineralization that occurs at the human growth plate. The second process is denoted intramembranous ossification and occurs when the fracture edges are not only in contact and opposed but also have minimal to no strain, that is, rigid fixation. In this process, little bone callus is seen as the fracture gap is consolidated by cutting “cones” that cross the fracture. Both processes essentially bridge the gap between the fracture elements. The bony healing process in humans takes approximately 6-8 weeks except bones with potentially compromised vascular supply or vascular watershed areas (such as, for example, the tibia, scaphoid, talus, and the like). After the initial healing process, the bone is comprised of woven bone and later remodels to lamellar bone. 
         [0005]    Typically, fractured bones are stabilized using various mechanical or surgical means to hold the fractured portions of the bone in alignment, Depending on the gap between the fracture ends, the body forms either granulation tissue (scar tissue), cartilage (enchondral ossification), or bone (intramembranous ossification). If the fracture gap is too large, the body heals via scar tissue—tough connective tissue that resists strain, and while not rigid, this tissue maintains the fragments in proximity to each other. Non-healed fractures, such as those with interposed scar tissue, can cause significant pain for the patient as there is still motion occurring between the previously fractured elements. Surgical intervention with opposition of the bones, possible use of a bone graft, and mechanical stabilization is usually necessary to help the fracture heal. 
         [0006]    One means of stabilizing a fractured bone is through the use of an intramedullary nail. For example, where the fracture is located in the tibia bone of the lower leg, the central portion of the bone, known as the medullary canal or space, is accessed. The current convention is to ream the medullary canal prior to insertion of an intramedullary nail. In other cases, the medullary canal may not be reamed. 
         [0007]    The intramedullary nail is inserted into the medullary canal and positioned as desired to align the fractured ends or edges of the bone and restore length, alignment, and rotation. Fixation screws, or locking screws, are usually used at both the proximal and distal ends of the nail to ensure that the intramedullary nail is a static construct with rotational stability. 
         [0008]    Various authors have posited whether allowing some motion at the fracture site would enhance the healing process by providing mechanical signals that would initiate an anabolic response to spur bone remodeling. The problem, however, is how to allow enough motion at the fracture site to enhance the healing process while still maintaining adequate stabilization of length, alignment, and rotation of the fractured bone ends. If too much motion occurs, the bone may not completely heal. 
         [0009]    What has been needed, and heretofore unavailable, is an intramedullary device that provides for adequate positioning and stabilization of the fractured ends or edges of a bone, while still allowing a measure of motion to occur at the fracture site to provide for enhanced healing of the fracture. The present invention satisfies these, and other needs. 
       SUMMARY OF THE INVENTION 
       [0010]    In a most general aspect, the invention provides an intramedullary nail that provides for fixation and stabilization of a fractured bone while still providing a controlled amount of motion in the longitudinal axis at the fracture site to encourage and hasten bone healing. 
         [0011]    In another aspect, the present invention includes an intramedullary nail, comprising: a distal portion and a proximal portion; a bias member or device disposed between the distal and proximal portions for biasing the distal and proximal portions apart along a longitudinal axis; and an adjusting assembly configured to engage the distal and proximal portions such that actuation of the adjusting assembly results in providing for a selected amount of motion along the longitudinal axis between the proximal and distal portions. In one alternative aspect, the distal and proximal portions are in a telescoping arrangement relative to each other. 
         [0012]    In still another aspect, the adjusting assembly is adjustable to allow a selected amount of motion along the longitudinal axis between the proximal and distal portions of the intramedullary nail, applying a compressive force along the longitudinal axis causes a combined length of the distal and proximal portions to be reduced, and reducing the compressive force allows the combined length of the distal and proximal portions of the intramedullary nail to increase. 
         [0013]    In yet another aspect, the invention further includes an alignment assembly that engages the proximal and distal portions of the intramedullary nail in a manner to maintain an alignment between the proximal and distal portions of the intramedullary nail. 
         [0014]    In still another aspect, the invention also includes an outer surface of the distal and proximal portions that is covered with a material that enhances healing of a fracture. In one alternative aspect, the material is zinc. 
         [0015]    In yet another aspect, the bias member is a spring. In an alternative aspect, the bias member is a compliant membrane. 
         [0016]    Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the features of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1A  is a side view of an embodiment of an intramedullary nail in accordance the present invention. 
           [0018]      FIG. 1B  is a cross-sectional side view of the intramedullary nail of  FIG. 1A . 
           [0019]      FIG. 1C  is a magnified view of a portion of the cross-sectional side view of  FIG. 1B  showing details of interconnection of the distal and proximal portions of the intramedullary nail of  FIG. 1A . 
           [0020]      FIG. 2A  is a side view of a distal portion of the intramedullary nail of  FIG. 1A . 
           [0021]      FIG. 2B  is a cross-sectional side view of the distal portion of the intramedullary nail of  FIG. 2A . 
           [0022]      FIG. 2C  is a magnified cross-sectional side view of a threaded proximal end of the distal portion of the intramedullary nail shown in of  FIG. 2B . 
           [0023]      FIG. 3A  is a side view of the proximal portion of the intramedullary nail of  FIG. 1A . 
           [0024]      FIG. 3B  is a cross-section of the proximal portion of the intramedullary nail of  FIG. 3A  showing internal details of the embodiment. 
           [0025]      FIG. 4A  is a side view of a threaded fastener used to hold the proximal and distal portions of the intramedullary nail of  FIG. 1A  together 
           [0026]      FIG. 4B  is a top view of the threaded fastener of  FIG. 4A . 
           [0027]      FIG. 4C  is a cross-sectional side view of the threaded fastener of  FIG. 4A . 
           [0028]      FIG. 5A  is a side view of a threaded fastener that may be inserted into a proximal end of the proximal portion of the intramedullary nail of  FIG. 1A . 
           [0029]      FIG. 5B  is a top view looking down at the proximal end of the threaded fastener of  FIG. 5A . 
           [0030]      FIG. 5C  is a cross-sectional side view of the threaded fastener of  FIG. 5A . 
           [0031]      FIG. 6A  is a side view of an alternative embodiment of an intramedullary nail in accordance the present invention. 
           [0032]      FIG. 1B  is a cross-sectional side view of the intramedullary nail of  FIG. 6A . 
           [0033]      FIG. 6C  is a magnified view of a portion of the cut-away view showing details of interconnection of the distal and proximal portions of the intramedullary nail of  FIG. 6A . 
           [0034]      FIG. 7A  is a side view of a distal portion of the intramedullary nail of  FIG. 6A . 
           [0035]      FIG. 7B  is a cross-sectional side view of the distal portion of the intramedullary nail of  FIG. 7A . 
           [0036]      FIG. 7C  is a magnified cross-sectional side view of a threaded proximal end of the distal portion of the intramedullary nail shown in of  FIG. 7B . 
           [0037]      FIG. 8A  is a side view of the proximal portion of the intramedullary nail of  FIG. 6A . 
           [0038]      FIG. 8B  is a cross-section of the proximal portion of the intramedullary nail of  FIG. 8B  showing internal details of the embodiment. 
           [0039]      FIG. 9A  is a side view of an embodiment of a threaded fastener used to hold the proximal and distal portions of the intramedullary nail of  FIG. 6A  together 
           [0040]      FIG. 9B  is a top view of the threaded fastener of  FIG. 9A . 
           [0041]      FIG. 9C  is a cross-sectional side view of the threaded fastener of  FIG. 9A . 
           [0042]      FIG. 10A  is a side view of a compressible/extensible member for providing a bias between the distal and proximal portions of an embodiment of an intramedullary nail in accordance with the present invention. 
           [0043]      FIG. 10B  is a cross-sectional side view of the compressible/extensible member of  FIG. 10A . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0044]    Referring now to the drawings in detail, in which like reference numerals indicate like or corresponding elements among the several figures, there is shown in  FIG. 1A  an exemplary embodiment of an intramedullary nail  10  in accordance with the present invention. Nail  10  includes a distal portion  15  and a proximal portion  20 . As will be discussed in more detail below, the distal and proximal portions are engaged in a manner that allows each portion to move a limited amount independently of the other portion. 
         [0045]    Distal portion  15  includes an end port  25  disposed at a distal end of the distal portion  15 . A fixation hole  30  is also disposed near the distal end of distal portion  15 . Fixation hole  30  is sized to receive a screw or other fastener that may be used to attached distal portion  15  to bone surrounding distal portion  15  when the nail  10  is positioned within the medullary space of a bone so as to fixate and stabilize a fracture in the bone. 
         [0046]    Referring now to  FIGS. 1A and 1B , a lumen  45  extends from the end port  25  through the nail  10  to a proximal end  47  of proximal portion  20 . When implanting nail  10  within a medullary space of a bone, such as, for example, but not limited to, a tibia or a femur, it is common to use a guidewire to ensure that the nail can be properly positioned, even when the medullary space may be dis-continuous due to the severity of a fracture in the bone. Lumen  45  provides for placing the nail  10  along the guidewire, and then sliding the nail  10  along the guidewire until the nail  10  is properly positioned, The guidewire may then be withdrawn from the nail  10 . The distal most end of distal portion  15  may be chamfered to provide reduced friction between the nail and the medullary space of the bone when the nail is inserted into and through the intramedullary space of the bone. The chamfer may be, for example, 15 degrees. 
         [0047]    A threaded fastener  40  is also shown in  FIGS. 1A and 1B . Fastener  40  engages threads  50  disposed in a proximal end of the proximal portion  20  of intramedullary nail  10 . Fastener  40  may be threaded into the threads in the proximal portion to provide a surgeon with a means for removing the nail  10  from the medullary space. 
         [0048]    Referring now  FIG. 1C , as well as  FIGS. 2A-C  and  3 A-B, additional details of the distal and proximal portions of the nail  10  are described. A proximal end of the proximal portion  15  includes a portion  60  having a reduced diameter compared to the outer diameter of the remainder of the distal portion  15 . Given this reduction in diameter, a land  65  is formed at a junction of the reduced portion  60  and the remainder of distal portion  15 . A proximal end of reduced diameter portion  60  also has a threaded portion  70  having male threads for engaging corresponding female threads  80  of adjustment nut  75  ( FIG. 1C ). 
         [0049]    Proximal portion  20  ( FIGS. 3A-B ) includes a distal portion  115  and a proximal portion  120 . While lumen  45  extends through both portions, distal portion  115  is offset along a longitudinal axis from proximal portion  120  by an angle phi (Φ) so as to produce a bend in the nail  10  that facilitates placement of the nail through the top of the bone, for example, a tibia bone, and then down through the medullary space of the bone. This angular offset will be dependent on the bone to be stabilized. For example, a femur may require different angulation than a tibia, and thus nails to be used to stabilize a femur will have a different offset than a nail intended for use in a tibia. In one embodiment, for example, intended for implantation within a tibia bone, the angle phi may be 10 to 12 degrees, and preferable 11 degrees. 
         [0050]    Proximal portion  120  of proximal portion  20  may also include a bore  35  sized to receive a screw or other fastener for fixing the proximal portion  120  to the portion of bone adjacent proximal portion  120 . This allows the proximal portion  20  to be fixed in such a manner to still allow for limited movement between distal portion  15  and proximal portion  20 . 
         [0051]    As seen in  FIG. 3A , the distal portion  115  of proximal portion  20  may also include a chamfered segment  125  located at a distal end  105  of distal portion  115  of proximal portion  20 . The angulation Θ of this chamfer may be, for example, 11 degrees. 
         [0052]    Referring now  FIG. 3B , proximal end  100  of proximal portion  120  of proximal portion  20  is threaded with threads  50  to receive fastener  40  ( FIG. 1A ). The diameter of lumen  45  in proximal portion  120  of proximal portion has a first diameter that may, but does not have to be, consistent throughout the length of proximal portion  120 . This diameter of lumen  45  may remain the same through the angulation between distal portion  115  and proximal portion  120  of proximal portion  20 . At some point distal to the beginning of the angulation in the segment designated  135 , the diameter of lumen  45  decreases. This reduction in diameter forms a land  82  at the junction of lumen  45  of the proximal portion and the diameter of the lumen of segment  135 . At a point distal to land  82 , the diameter of lumen  45  through segment  135  is further reduced in segment  145 , forming land  84  at the junction between the distal end of segment  135  and the proximal end of segment  145 . Finally, at a point distal to land  84 , the diameter of the lumen increases at a transition to segment  130 . This enlargement of the lumen creates land  87  at the junction between the lumen of segment  145  and the enlarged lumen of segment  130 . It will be understood that while exact dimensions of the various lumens and segments have not been specified, they may vary depending on the overall dimensions of the nail  10  and the fasteners used to join proximal portion  20  and distal portion  15 , while still providing a lumen through the entire length of the intramedullary nail  10  to allow the nail to be positioned with an intramedullary space of a fractured bone using a guidewire passing through the lumen of the intramedullary nail. 
         [0053]    Further detail of the relationship between the various lumen diameters and segments can be understood by referring to the magnified view of  FIG. 1C . This view shows how the various lumen diameters and segments of the distal portion  115  of the proximal portion  20  of intramedullary nail  10  cooperate with segment  60  of the proximal end of distal portion  15  of intramedullary  10  to provide for limited motion between the distal portion  15  and proximal portion  20  of the intramedullary nail  10  to promote bone remodeling and healing. As shown, segment  60 , including threaded area  70  extend into the lumen located at the distal end  105  of proximal portion  15 . In this configuration, a space is formed between land  65  of the distal portion  15  and land  87  of proximal portion  20  of intramedullary nail  10 . This space allows a bias means, such as a spring, to be disposed between proximal portion  20  and distal portion  15  of intramedullary nail  10  to bias the two portions apart when the spring is compressed. 
         [0054]    Adjustment nut  75  is a threaded nut having a head  200  and a body  205 , and is shown in detain in  FIGS. 4A-C . See The diameter of the body  205  is sized to be slidingly, rotationally and removably received within the lumen diameter of segment  135  of the proximal portion  115  of proximal portion  20 . Head  200  has a diameter that is larger than the diameter of body  205 , the diameter being sized to be slidably, rotatably and removably received within the lumen of area  140 , and able to pass through the angulation between proximal portion  120  and distal portion  115  of proximal portion  20  of intramedullary nail  10 . The distal edge of adjustment nut  75 , when inserted into the distal portion  20  of intramedullary nail  10  is advanced and engages threads  70  of distal portion  15  with threads  80 . A proximal end of head  200  of adjustment nut  75  includes a means  210  for engaging adjustment nut  75  so that nut  75  may be rotated in a clockwise or counterclockwise direction. Means  210  may be, for example, a hexagonally shaped indentation for receiving a suitably sized hexagonal Allen driver, or it may be slotted, or crossed, or having another suitably shaped indentation for receiving a customized driving tool. 
         [0055]    Rotating adjustment nut  75  in a clockwise direction causes the nut to be drawing onto the threads  70 , which in turn compresses spring  85  due to the abutment of the distal edge of the head  200  of adjustment nut  75  with land  82 . Adjustment nut  75  may continue to be tightened until the spring is completely compressed, or when the distal edge of body  205  of adjustment nut  75  abuts against land  84 . Similarly, rotating adjustment nut  75  in a counter-clockwise direction will loosen adjustment nut  75 , resulting in distal portion  15  of nail  10  moving away from proximal portion  20  of nail  10  due to the bias imparted by spring  85 . 
         [0056]    It will be understood that the threads  70  and  80  may be reversed so that rotating adjustment nut  75  in a counter-clockwise direction draws threads  70  into threads  80  to compress spring  85 , and rotating adjustment nut  75  in a clockwise direction reduces the compression of spring  85 , without departing from the intended scope of the invention. 
         [0057]    Additionally, spring  85  is intended as a biasing member, whose function may be carried out by a variety of means besides a spring. For example, spring  85  may be replaced with a reversibly compressible material, such as a polymer. Moreover, the entire arrangement between the proximal portion  20  and distal portion  15  may be constructed in a fashion different from that described above, so long as there is a bias member or device between the two portions that may be adjusted to provide a desired amount of motion between the two portions. In an alternative embodiment, the bias member may be a compound bias member comprising a resilient polymer and a mesh of plastic, metal or other suitable material. In still another embodiment, the bias member may be a compliant membrane. 
         [0058]    When the bias means is fully compressed, there is intended to be no relative movement between the distal portion  15  and the proximal portion  20 . Loosening adjustment nut  75  reduces the amount of compression of spring  85 , allowing for a controlled amount of longitudinal movement of the two portions relative to each other. Alternatively, the bias member may be used to put the fracture under compressing. In this embodiment, the distal portion of the nail is fixed to the bone with a screw, the proximal portion is held while the adjustment nut is tightened, so that the distal portion and proximal portions of the nail pull on the ends of the fracture, 
         [0059]      FIGS. 5A-C  illustrate details of fastener  40 . Fastener  40  has a head  250  and a threaded body  255 . The threads of threaded body  255  are sized to engage threads  50  disposed within the bore of proximal end  100  of proximal portion  20 . This allows fastener  40  to be threaded into proximal end  100  to provide a means for extracting nail  10  from a medullary space. Head  250  of fastener  40  also includes an indentation  260  shaped and sized to receive a driver, such as, for example, but not limited to, a hexagonally shaped driver, to provide for rotating the fastener  40  in clockwise and counter-clockwise directions. 
         [0060]    In another embodiment, fastener  40  may be formed in the shape of a “handle” that has a threaded distal end and a proximal end having a handle-like shape to facilitate installation of the nail. For example, the proximal end of the handle shaped fastener may be, for example, in the shape of a “T” shape or the like, During installation, the distal end of the fastener would be threaded into the nail, and the nail placed at the entrance of the intramedullary canal. The handle shape of the proximal end of the fastener provides an area or surface which could be struck by a striking implement, and would facilitate driving the nail in the intramedullary canal of the bone. The striking implement could be, for example, a hammer, mallet or the like. The handle-like shape of the proximal end of the fastener  40  could then be used to facilitate rotation of the fastener to remove the fastener from the intramedullary nail  10  once the nail was properly positioned and stabilized within the intramedullary space of the bone. 
         [0061]    The embodiment of the intramedullary nail described above is constructed of materials know to be biocompatible. Examples of suitable materials are various types of stainless steel or titanium alloys, such as Ti-6Al-4V, Cobalt chromium or the like. 
         [0062]    The intramedullary nail will typically be cylindrical in shape, but may be an elongated body having another shape, such as a hexagonal, ovoid or other suitable external shape depending on the needs of the surgeon. The distal and proximal portions  15 ,  20  will typically be arranged in a telescoping relationship. Moreover, a means for maintaining the proximal and distal portions  15 ,  20  of intramedullary nail  10  in alignment may also be provided, such as by using a spline mounted on one of the portions to engage a keyway disposed in or on the other portion. In the case where the nail is not cylindrical, the shape of the portions may be self-aligning, such as where the overall outer profile of the nail is hexagonal. 
         [0063]    Referring now to  FIG. 6A  another exemplary embodiment of an intramedullary nail  300  in accordance with the present invention is shown. Intramedullary nail  300  includes a distal portion  305  and a proximal portion  310 . As will be discussed in more detail below, the distal and proximal portions are engaged in a manner that allows each portion to move a limited amount independently of the other portion. 
         [0064]    Distal portion  305  includes an end port  315  disposed at a distal end of the distal portion  305 . A fixation hole  320  is also disposed near the distal end of distal portion  305 . Fixation hole  320  is sized to receive a screw or other fastener that may be used to attached distal portion  305  to bone surrounding distal portion  305  when the intramedullary nail  300  is positioned within the medullary space of a bone so as to fixate and stabilize a fracture in the bone. 
         [0065]    Referring now to  FIGS. 6A-B , a lumen  345  extends from the end port  315  through the intramedullary nail  300  to a proximal end  347  of proximal portion  310  to facilitate implanting the intramedullary nail using a guidewire, as described above. The distal most end of distal portion  305  may be chamfered to provide reduced friction between the nail and the medullary space of the bone when the nail is inserted into and through the intramedullary space of the bone. The chamfer may be, for example, 15 degrees, but other angulations may be used to suit the particular bone size or fracture type into which the intramedullary nail is being implanted. 
         [0066]    The interior of proximal end  347  of the proximal portion  310  of intramedullary nail  300  may also include threads  350 . A fastener may be threaded into the threads  350  to provide a surgeon with a means for removing the nail  300  from the intramedullary space of the bone. 
         [0067]    Referring now  FIG. 6C , as well as  FIGS. 7A-C  and  8 A-B, additional details of the distal and proximal portions of the nail  300  are described. A proximal end of the distal portion  305  of nail  300  includes a portion  360  having a reduced diameter compared to the diameter of the remainder of the distal portion  305 . Given this reduction in diameter, a land  361  is formed at a junction of the reduced portion  360  and portion  362 . Portion  362  has an increased diameter relative to portion  360 , but that diameter is less than the outer diameter of distal portion  305 . The junction between portion  362  and the remainder of distal portion  305  thus forms a land  365 . A proximal end of portion  360  also has a threaded portion  370  having male threads for engaging corresponding female threads  380  of adjustment nut  375  ( FIG. 6C ). 
         [0068]    Proximal portion  310  ( FIGS. 8A-B ) includes a distal portion  415  and a proximal portion  420 . While lumen  45  extends through both portions, distal portion  415  is offset along a longitudinal axis from proximal portion  420  by an angle phi 2  (Φ 2 ) so as to produce a bend in the nail  300  that facilitates placement of the nail through the top of the bone, for example, a tibia bone, and then down through the medullary space of the bone. This angular offset will be dependent on the bone to be stabilized. For example, a femur may require different angulation than a tibia, and thus nails to be used to stabilize a femur will have a different offset than a nail intended for use in a tibia. In one embodiment, for example, intended for implantation within a tibia bone, the angle phi 2  may be 10 degrees. 
         [0069]    As is evident from  FIGS. 8A-B , besides major sections portion  415  and portion  420 , proximal portion  310  may include additional segments, such as segment  450 ,  455 ,  460 ,  465 ,  470 ,  475  and  480 . The geometric shape of these segments may be consistent with the shapes of portions  415  and  420 , or they may be varied to facilitate use of the intramedullary nail  300 . In the embodiment shown, for example, segment  450 , which forms the most proximal segment of portion  420  of intramedullary nail  300  may be a cylinder having a constant outer diameter, but also may have a chamfer disposed on the proximal end  400  of segment  450 . This chamfer ensures that once the nail is implanted in a bone, the proximal end of the nail will not unduly extend from the top of the bone, but will instead more readily blend with the contour of the bone. 
         [0070]    As shown in  FIG. 8A , segment  455  may have a proximal end that has an outer diameter substantially equal to the outer diameter of the distal end of segment  450 . The outer diameter of segment  455  tapers along its length to a reduced outer diameter at its distal end. The taper may be, for example, but not limited to, five degrees. 
         [0071]    In some embodiments, such as the embodiment of  FIG. 8A , proximal portion  310  may also include a segment  460 . This segment may have a consistent outer diameter, beginning at the distal end of segment  455  and ending at the proximal end of segment  465 , or the outer diameter may change depending on the design of the nail. 
         [0072]    Segment  465  includes angulation phi 2 , as described above. There may also be a segment  480  interposed between segment  470  and segment  465 . The length and outer diameter of this segment are dependent upon the over length of the nail and the design requirements as described above. 
         [0073]    Segment  470  may also be included. As shown, segment  470  may taper from its proximal end to its distal end, as required for the design of the nail. In the example shown, the taper is two degrees. Segment  475  comprises the distal end of proximal portion  310 . 
         [0074]    It will be understood by those skilled in the art that the various segments described above may or not be present in an embodiment of the intramedullary nail of the present invention. For example, depending on the length of the nail, one or both of segments  460  and  480  may be omitted without departing from the scope of the invention. Additionally, segments  470  and  455  may be need to be tapered, and indeed, may be omitted from the nail, depending on the design of the nail for a particular bone size or length or fracture situation. 
         [0075]    Proximal portion  420  of proximal portion  310  may also include a bore  325  sized to receive a screw or other fastener for fixing the proximal portion  420  to the portion of bone adjacent proximal portion  420 . This allows the proximal portion  420  to be fixed in such a manner to still allow for limited movement between distal portion  305  and proximal portion  310 . 
         [0076]    Referring now  FIG. 8B , proximal end  400  of proximal portion  310  is threaded with threads  350  to receive a fastener or handle-like tool as described above to facilitate installation and removal of intramedullary nail  300  from the intramedullary space of a bone. The diameter of lumen  345  in proximal portion  420  of proximal portion  310  has a first diameter that may, but does not have to be, consistent throughout the length of proximal portion  420 . This diameter of lumen  345  may remain the same through the angulation between distal portion  415  and proximal portion  420  of proximal portion  310 . 
         [0077]    At some point distal to the beginning of the angulation in the segment designated  535 , the diameter of lumen  345  decreases. This reduction in diameter forms a land  382  at the junction of lumen  345  at the proximal end of segment  545  and the diameter of the lumen at the distal end of segment  135 . The diameter of lumen  345  increases at junction between the distal end of segment  545  and the proximal end of segment  530 . This change in lumen diameter results in the formation of a land  387 . 
         [0078]    It will be understood that while exact dimensions of the various lumens and segments have not been specified, they may vary depending on the overall dimensions of the nail  300  and the fastener used to join proximal portion  310  and distal portion  305 , while still providing a lumen through the entire length of the intramedullary nail  300  to allow the nail to be positioned with an intramedullary space of a fractured bone using a guidewire passing through the lumen of the intramedullary nail. 
         [0079]    Further detail of the relationship between the various lumen diameters and segments can be understood by referring to the magnified view of  FIG. 6C . This view shows how the various lumen diameters and segments of the distal portion  415  of the proximal portion  310  of intramedullary nail  300  cooperate with area  360  of the proximal end of distal portion  305  of intramedullary  300  to provide for limited motion between the distal portion  305  and proximal portion  310  of the intramedullary nail  300  to promote bone remodeling and healing. As shown, area  360  includes threaded area  370  extends into the lumen located at the distal end  405  ( FIG. 8A ) of proximal portion  310 . In this configuration, a space is formed between land  365  of the distal portion  305  and land  387  of proximal portion  310  of intramedullary nail  300 . This space allows a bias means, such as a spring, to be disposed between proximal portion  3100  and distal portion  305  of intramedullary nail  300  to bias the two portions apart when the spring is compressed. 
         [0080]    Adjustment nut  375  is a threaded nut having a proximal end  600 , a distal end  605 , and a body  610 , and is shown in detail in  FIGS. 9A-C . The diameter of the body  615  is sized to be slidingly, rotationally and removably received within the lumen diameter of segment  535  of the proximal portion  415  of proximal portion  310 , and is able to pass through the angulation between proximal portion  420  and distal portion  415  of proximal portion  310  of intramedullary nail  300 . In this embodiment, the outer diameter of body  610  is constant from proximal end  600  to distal end  605 , although some deviation may be allowed so long as the adjustment nut  375  is able to slide through lumen  345 . 
         [0081]    Adjustment nut  375 , when inserted into the distal portion  305  of intramedullary nail  300  engages threads  370  of distal portion  305  with threads  380 . The proximal end of adjustment nut  375 , as shown in  FIG. 9B , includes a means  615  for engaging adjustment nut  375  so that nut  375  may be rotated in a clockwise or counterclockwise direction with a suitable tool. Means  615  may be, for example, a hexagonally shaped indentation for receiving a suitably sized hexagonal Allen driver, or it may be slotted, or crossed, or having another suitably shaped indentation for receiving a customized driving tool. 
         [0082]    Rotating adjustment nut  375  in a clockwise direction causes the nut to be drawing onto the threads  370 , which in turn compresses spring  385  due to the abutment of the distal end  605  of adjustment nut  375  with land  382 . Adjustment nut  375  may continue to be tightened until the spring is completely compressed. Similarly, rotating adjustment nut  375  in a counter-clockwise direction will loosen adjustment nut  375 , resulting in distal portion  305  of nail  300  moving away from proximal portion  310  of nail  300  due to the bias imparted by spring  385 . 
         [0083]    It will be understood that the threads  370  and  380  may be reversed so that rotating adjustment nut  375  in a counter-clockwise direction draws threads  370  into threads  380  to compress spring  385 , and rotating adjustment nut  375  in a clockwise direction reduces the compression of spring  385 , without departing from the intended scope of the invention. As described above, while bias means is shown as spring  375  in this embodiment, other biasing devices or materials may be utilized, such as a reversibly compressible polymer, and the like. 
         [0084]      FIGS. 10A-C  illustrate one embodiment of a biasing device or means  700  that may be used with the various embodiments of the present invention. In this embodiment, the biasing means  700  is depicted as a spring. As noted above, however, other types of biasing members or devices or means may be employed. Where a spring is used, the coils of the spring may be consistent, or the spring may be formed in such a way that the spring constant K of the spring varies along the length of the spring, thus imparting variable biasing force depending on how much the spring is compressed or extended. This variance may be accomplished in various way, as is known to those skilled in the art. For example, the spacing between coils of the spring may differ along the longitudinal length of the spring, or the diameter of the coil wire may vary. 
         [0085]    In still another embodiment, the size and/or resiliency of the bias member may be selected depending on bone size and patient weight to achieve a desired load-deflection. Different bias members could have different load-deflection curves, allowing a surgeon to choose the bias member that fits a particular situation, including fracture type, complexity, patient weight and bone dimensions. 
         [0086]    In yet another embodiment, the any of the various embodiments of the nail of the present invention may be covered or coated with a suitable biocompatible material which may have healing enhancement properties. The nail may be coated with, for example, but not limited to, zinc. Alternatively, the nail may be coated with a material or drug, or a combination of material or drug, to enhance bone formation or to promote healing of the fracture. In still another embodiment, the outer surface of the nail of any of the various embodiments may be textured to enhance implantation, or hold a coating or drug or combination of the two to enhance healing of the fracture. 
         [0087]    Various procedures for using an intramedullary nail of the present invention are described in the literature and are well known in the art. For example, an method for reducing a tibial shaft fracture is contained in Trafton, Peter G. “Tibial Shaft Fractures .” (Elsevier Science (USA) 2003), the entirety of which is intended to be incorporated by reference herein. 
         [0088]    Other information discussing the scientific rationale supporting the advancement over the prior art represented by the inventors various embodiments of the present invention are also attached hereto, and are intended to be incorporated in their entirety by reference herein. 
         [0089]    While several particular forms of the invention have been illustrated and described, it will be apparent that various modifications can be made without departing from the spirit and scope of the invention.