Abstract:
An interlocking intramedullary nail assembly including an intramedullary nail, a first lag screw, a second lag screw and a locking screw. The first and the second lag screws are arranged to mate with one another and are received by the intramedullary nail at opposite ends of a transverse through bore passing through a distal portion of the nail. The interlocking screw is used to operatively couple the first lag screw and second lag so as to fix the first and the second lag screws to the nail.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an improved intramedullary nail and method for stabilizing fractures of the femur. More specifically, the present invention relates to a surgical interlocking intramedullary nail including an interlocking screw assembly for immobilization of distal femur parts involved in fractures occurring in the condylar and supracondylar portions of the femur.  
           [0003]    2. Description of the Prior Art  
           [0004]    It is known that bone parts or fragments involved in fractures of the femur are difficult to stabilize satisfactorily. Since the femur functions as a weight bearing bone, the femoral fractures often take longer to heal and there is potential for greater complications in setting the fracture than in non-weight bearing bones. Furthermore, it is well understood that patients that remain inactive following surgery have an increase in the risk of serious complications including the development of blood clots and pneumonia. Therefore after stabilizing a femoral fracture, early mobilization of a patient is necessary so that the femur will heal quickly, with stronger repair and less likelihood of complications.  
           [0005]    In treating a femoral fracture, it is standard practice to use a fixation device adapted to facilitate recovery of the fractured bone. The fixation device provides immobilization of the bone fragments and stabilization of the fractured femur, thus providing earlier mobilization and weight bearing of a patient. The fixation device is attached to or inserted into the femur and cooperates with the bone fragments and the femoral shaft to stabilize the bone. As the bone heals, the fixation device allows the bone fragments to compress into each other so the fragments grow together to restore the bone.  
           [0006]    Two prevalent types of femoral fractures are supracondylar or “T-type” condylar fractures about the distal femur. A number of different fixation devices, both external and implantable, have been devised for fixation of supracondylar and condylar fractures. In the past, treatment of condylar or supracondylar fractures consisted of stabilizing the bone portions with plates and screws. However, in using plates and screws, invasive surgery is required and includes considerable dissection of the thigh in order to expose the fracture so as to attach the plates and screws. The resultant devasculariztion of the distal portion of the femur has lead to a high frequency of complications of delayed union of the bone sections, osseous fracture and infection. Additionally, due to the muscular stresses in the region of the condylus and supracondylus, the treatment may involve undesirable post-operative procedures and complications including the bending or breaking of the plates, loosening of the screws and migration of the femoral shaft.  
           [0007]    Recently, intramedullary (IM) nailing has become a standard procedure for treating supracondylar and condylar fractures. In its basic form, IM nailing consists of driving a rod-like nail into the intramedullary bone canal of the femur to stabilize transverse fractures of the femur. However, such IM nails often fall short to provide effective fixation or immobilization for supracondylar and condylar fractures since they fail to sufficiently compress bone fragments. Improvements have been made on IM nails to further stabilize the bone fragments by introducing interlocking cross-bolts or screws through the nail that are fixed on both sides of the fracture.  
           [0008]    Despite their advantages over plate and screw fixation devices, there are still complications that arise with interlocking IM nails. One difficulty is that the screws may loosen, creating a decrease in screw fixation which results in screw toggling, or in a worst case scenario, complete screwing out of the nail. Another difficulty results from the oblique position of the condyles with respect to the shaft of the femur. Since the fixation of the screws is often transverse to the femoral shaft, the screws do not extend through the major mass of the cancellous bone of each condylus. Furthermore, the sizes of many current screws used with the IM nails do not achieve sufficient purchase in the bone. Stabilizing the fracture is further compounded by the fact that the bone is often of poorer quality.  
           [0009]    Known IM nails have been designed for treatment of condylar and supracondylar fractures. For example, U.S. Pat. No. 5,779,705 issued to Matthews and U.S. Pat. No. 6,010,505 Asche et al., which are herein incorporated by reference in their entirety, each disclose an intramedullary device having an IM nail and interlocking bolts or screws to grip and stabilize the femoral condyles with respect to the femoral shaft. The disclosures of the references are considered to establish the state art for condylus and supracondylus IM nails. Each of the devices disclosed thereby addresses the desirability of compression in the treatment of femoral fractures and emphasizes compression of the condyles with respect to the femoral shaft.  
           [0010]    Matthews discloses an intramedullary nail incorporating a Cruciate arrangement of two obliquely crossing locking bolts such that each condyle of the femur is gripped by an individual bolt. The Cruciate or staggered/crossed configuration of holes permits two distal locking bolts to be inserted.  
           [0011]    Asche et al. discloses a supracondylar bone nail that has an elongated shank with two bends. The first bend begins at a distance from the distal end of about a quarter or a third of the length of the nail at an angle of about 8°. The second bend begins in the last third of the nail length if looking from the distal end and has an angle of approximately 3°. The nail includes transverse bores in the distal and proximal end which are adapted to accommodate screws.  
           [0012]    Although effective results have been achieved with the above noted IM nails, problems of internal fixation still persist. Therefore, it is desirable to modify an IM nail so as to achieve greater internal fixation of the condyles and mitigate screw loosening and toggling.  
         SUMMARY OF THE INVENTION  
         [0013]    To meet the above noted desires, it is an object of the present invention to provide an interlocking intramedullary nail for fixation of the distal femur which overcomes certain disadvantages of the prior art devices while maintaining their advantages. The present invention provides an interlocking intramedullary nail that aims to achieve greater fixation and immobilization of condylus and supracondylus fractures of the femur.  
           [0014]    According to one embodiment of the present invention, the interlocking intramedullary nail comprises an intramedullary nail, a first lag screw, a second lag screw and a locking screw, all being adapted to accommodate one another. The nail is configured to be inserted from a distal end of the femur below the condylus and has a distal end with a transverse bore extending therethrough. The first lag screw has a distal end with a cylindrical first portion and an axial through hole. The first lag screw is arranged to be inserted into one end of the transverse bore. The second lag screw has an axial through hole and is adapted to receive the cylindrical portion of the first lag screw at another end of the transverse bore. The locking screw is adapted to be inserted into the axial through hole of the second lag screw so as to thread onto the first lag screw and the second lag screw.  
           [0015]    According to a second embodiment, the interlocking intramedullary nail has at least one transverse distal bore that is angled with respect to a longitudinal axis of the nail such that the first and second lag screws extend obliquely from the intramedullary nail.  
           [0016]    According to another variant of the invention, the first lag screw and the second lag screw each may include a major external thread diameter having a taper. Further, according to yet another variant of the invention, the first lag screw and the second lag screw each may include a minor external thread having a taper. Still further, according to another embodiment of the invention, the first lag screw and the second lag screw each may include a major external thread diameter having a taper and a minor external thread diameter having a taper.  
           [0017]    For a better understanding of the present invention, together with other and further objects thereof, reference is made to the following description, taken in conjunction with the accompanying drawings describing the preferred embodiments thereof.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 shows an elevation cutaway view of an intramedullary nail according to the present invention showing its location in a distal end of a femur;  
         [0019]    [0019]FIG. 2A is a side view of an embodiment of the intramedullary rod according to the present invention;  
         [0020]    [0020]FIG. 2B is a cross-sectional view of the embodiment of the intramedullary rod of FIG. 2A;  
         [0021]    [0021]FIG. 3A is a side view of another embodiment of the intramedullary rod according to the present invention;  
         [0022]    [0022]FIG. 3B is a cross-sectional view of the embodiment of the intramedullary rod of FIG. 3A;  
         [0023]    [0023]FIG. 4A is a side view of a first embodiment of a first lag screw according to the present invention;  
         [0024]    [0024]FIG. 4B is a cross-sectional view of the first embodiment of the first lag screw of FIG. 4A;  
         [0025]    [0025]FIG. 5A is a side view of a first embodiment of a second lag screw according to the present invention;  
         [0026]    [0026]FIG. 5B is a cross-sectional view of the first embodiment of the second lag screw of FIG. 5A;  
         [0027]    [0027]FIG. 6 is a side view of a second embodiment of a first lag screw according to the present invention;  
         [0028]    [0028]FIG. 7 is a side view of a second embodiment of a second lag screw according to the present invention;  
         [0029]    [0029]FIG. 8 is a side view of a third embodiment of a first lag screw according to the present invention;  
         [0030]    [0030]FIG. 9 is a side view of a third embodiment of a second lag screw according to the present invention;  
         [0031]    [0031]FIG. 10 is a plan view of an embodiment of the present invention showing the intramedullary nail installed in the distal portion of the femur along with a guiding lance;  
         [0032]    [0032]FIG. 11 depicts a step in the embodiment of FIG. 10;  
         [0033]    [0033]FIG. 12 depicts a next step in the embodiment of FIG. 11;  
         [0034]    [0034]FIG. 13 depicts a next step in the embodiment of FIG. 12;  
         [0035]    [0035]FIG. 14 depicts an assembled, cross-sectional view of an assembled intramedullary nail. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0036]    As shown in FIG. 1 according to a preferred embodiment of the invention, the distal portion of a femur  52  is shown which accommodates an intramedullary nail  10  with an elongate first lag screw  26  and a second lag screw  36 . The first lag screw  26  and the second lag screw  36  receive a locking screw  62 . The nail  10  is installed within the medullary or marrow canal  66  of the femur  52  in accordance with known medical procedures.  
         [0037]    [0037]FIG. 2A is a side view of one embodiment of the nail  10 . The basic structure of the nail  10  includes a distal portion  12  having a distal end  14  and a proximal portion  16  having a proximal end  18 . The distal portion  12  has at least one transverse bore  20  and the proximal portion  16  has at least one transverse bore  22 .  
         [0038]    [0038]FIG. 2B shows a cross-sectional view of FIG. 2A. The transverse bore  20  is generally arranged at a 90° angle with respect to the longitudinal axis of the nail  10 . The nail  10  is provided with an axial through hole  50  along its longitudinal axis.  
         [0039]    [0039]FIGS. 3A and 3B show another embodiment of the nail  10  whereby a transverse bore  24  extends at an angle with respect to the longitudinal axis of the nail  10 .  
         [0040]    One preferred embodiment of the first lag screw of the invention is shown in FIGS. 4A and 4B. According to this embodiment, the first lag screw  26  divides into an outer threaded portion  27  at a first end and an outer cylindrical portion  32  at a second end. The outer threaded portion  27  and the outer cylindrical portion  32  are axially spaced along the length of the first lag screw  26 . The outer threaded portion  27  has a constant outer diameter  28  and a minor diameter  30  located at the roots of the threads which progressively decreases from the first end to an end of the outer threaded portion  27  that is adjacent to the outer cylindrical portion  32 . FIG. 4B shows a cross-sectional view of FIG. 4A along the plane D-D illustrating the internal configuration of the first lag screw  26 . The first lag screw  26  internal configuration includes an axial bore  34  which includes a first threaded portion  70  extending axially from the second end a predetermined distance into the first lag screw  26 .  
         [0041]    Corresponding to the embodiment of the first lag screw  26  in FIGS. 4A and 4B, FIGS. 5A and 5B show a second lag screw  36  for mating with and receiving the first lag screw  26 . Similar to the first lag screw  26  in FIGS. 4A and 4B, the threaded portion of the second lag screw  36  has a constant threaded outer diameter  28 . The outer threaded portion also includes a minor diameter  30  located at the roots of the threads  30  and progressively decreases from a first end to a second end of the second lag screw  36 .  
         [0042]    [0042]FIG. 5B shows a cross-sectional view of FIG. 5A along the plane E-E illustrating the internal configuration of the second lag screw  36 . The internal configuration of the second lag screw  36  includes an axial through hole  38  having a screw seat  42  located at a first end and a mating portion  40  located at a second end. The screw seat  42  and the mating portion  40  are axially spaced along the length of the screw. The mating portion  40  is adapted to cooperate with the first outer cylindrical portion  32  of the first lag screw  26 . The mating portion  40  includes a recess formed by the second lag screw  36  and extends into the second lag screw  36  a predetermined distance. The recess of the mating portion  40  is dimensioned to accommodate the first outer cylindrical portion  32  of the first lag screw  26 . Moreover, the screw seat  42  acts as a stop for a locking screw as it is threaded onto the first lag screw  26  and the second lag screw  36 . The screw seat  42  includes a recess formed by the second lag screw  36  and extends axially from the first end into the second lag screw  36  a predetermined distance.  
         [0043]    [0043]FIGS. 6 and 7 each show another embodiment of both the first lag screw  26  and the second lag screw  36 . Specifically, the threaded outer diameter  28  and the inner threaded diameter  44  each have diameters that remain constant. The internal configuration of the first lag screw  36  and the second lag screw  44  is the same as illustrated in FIGS. 4B and 5B respectively.  
         [0044]    [0044]FIGS. 8 and 9 each show yet another embodiment of both the first lag screw  26  and the second lag screw  36 . Specifically, in FIG. 8 the major external thread portion  46  of the first lag screw  26  progressively decreases from the first end to the end adjacent to the outer cylindrical portion  32 . The minor diameter  48  at the roots of the threads of the first lag screw also progressively decreases from the first end to the end adjacent to the outer cylindrical portion  32 . FIG. 9 shows that the major external thread portion  46  of the second lag screw  36  progressively decreases from the first end to the second end. Morever, the minor diameter  48  at the roots of the threads of the second lag screw  36  also progressively decreases from the first end to the second end.  
         [0045]    Intramedullary nails in accordance with this invention are introduced into the femur through the knee. After exposing the femur, the nail is inserted through a bore which is in line with the axis of the intramedullary canal. FIG. 10 shows a nail  10  that has been inserted into the intramedullary canal  66 . A pilot through hole is drilled through the femur along the axis of a distal transverse bore  20 . In a preferred embodiment of the present invention, a guide wire  50  is passed through of the distal transverse bore  20 .  
         [0046]    [0046]FIG. 11 shows the first lag screw  26  inserted axially along the guide wire  50  into one side of the distal transverse bore  20 . Upon insertion into the nail  10 , the cylindrical portion  32  of the first lag screw  26  extends through the distal transverse bore  20 .  
         [0047]    [0047]FIG. 12 shows the second lag screw  36  inserted axially along the guide wire  50  on another side of the distal transverse bore  20 . The second lag screw  36  receives and engages the cylindrical portion  32  (not shown) of the first lag screw  26 .  
         [0048]    [0048]FIG. 13 shows a locking screw  62  being inserted axially along the guide wire  50 .  
         [0049]    [0049]FIG. 14 shows the locking screw  62  as received by the locking screw receiving bore  42  of the second lag screw  36 . The locking screw  62  is threaded onto the axial through hole  34  of the first lag screw so as to operatively couple the nail  10 , the first lag screw  26  and the second lag screw  36 .  
         [0050]    Typically, the nails may be manufactured in varying lengths from a biologically inert material which is sterilizable and has the appropriate mechanical strength and stiffness. It will be understood that any or all of the elements constituting the present invention may be included in a kit provided to a medical practitioner. Still further advantages of the present invention should be readily apparent to those of skill in the art based upon the written description provided above.  
         [0051]    It should be noted that the invention is not limited for use in the condylar and supracondylar regions of the femur. The intramedullary nail and the interlocking screws can be adapted to stabilize fractures of other bones throughout the human body.  
         [0052]    Although multiple preferred embodiments of the invention have been described above, it is to be understood that various modifications could be made to the embodiments by any person skilled in the art without departing from the scope of the invention as defined in the claims that follow, and that the various embodiments could be used interchangeably with other embodiments.