Abstract:
A hip fracture device providing distance limited dynamization, load controlled dynamization and combinations of both dynamization methods by varying components. The hip fracture device includes a plate having a head portion and a shaft portion. A barrel projects from the head portion of the plate and a screw is inserted in the barrel. A friction pin is slidably connected with the screw, and an end cap is fixed to the head portion of the plate. The friction pin is fixedly connected with the end cap. The screw slides over the friction pin and toward the end cap when a load is applied on the fracture device. The load required for further sliding of the screw over the friction pin increases incrementally as the screw slides towards the end cap.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of the filing date of U.S. Provisional Patent Application No. 60/925,399 filed Apr. 19, 2007, the disclosure of which is hereby incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to an apparatus and method for the treatment of fractures of the proximal femur including the neck of the femur and the intertrochantric region. 
       BRIEF DESCRIPTION OF THE PRIOR ART 
       [0003]    Referring to  FIG. 1 , the femur  1 , otherwise known as the thigh bone, generally comprises an elongate shaft extending from the hip to the knee. The proximal end of the shaft  3  includes a head  5 , a neck  7 , a greater trochanter  8  and a lesser trochanter  9 . Internal fixation of femoral fractures in general is one of the most common orthopedic surgical procedures. Fractures of the proximal portion of the femur (hip fractures) generally include femoral neck fractures and intertrochanteric fractures. Fractures of the femur which extend into the neck of the bone are often treated with screws that thread into the femoral head and extend generally parallel to the femoral neck axis A-A to a plate on the lateral side of the shaft  3 . 
         [0004]    A conventional fracture fixation system for femoral neck fracture is disclosed in U.S. Pat. No. 3,107,666 (the &#39;666 Patent). The fracture fixation system of the &#39;666 Patent has a sleeve and a nail that is inserted in the sleeve. A plastic ring is disposed between the sleeve and the nail. The plastic ring frictionally engages the internal cylindrical surface of the sleeve and the external surface of the nail. The friction creates resistance to relative movement between the sleeve and the nail. However, upon the force acting on the system exceeding a threshold, relative movement between nail and sleeve is permitted. 
         [0005]    Other conventional screw and plate systems typically apply a static compressive force across the fracture. It has been found that allowing the screw to travel along its axis in response to loading by the patient further encourages the growth of strong bone to heal the fracture. Screws of this type, known as dynamic compression screws, must provide axial movement while preventing angular rotation or lateral movement across the fracture. One shortcoming of dynamic compression screws is that unless the travel is appropriately limited, the neck of the femur may be undesirably shortened. Therefore, it is desirable to adjustably control the extent of axial movement (distance limited dynamization) and to adjustably provide a force that resists travel (load controlled dynamization). It is especially advantageous if the resisting force increases with the extent of travel. 
         [0006]    As used herein, when referring to bones or other parts of the body, the term “proximal” means closer to the heart and the term “distal” means more distant from the heart. The term “inferior” means toward the feet and the term “superior” means towards the head. The term “anterior” means towards the front part of the body or the face and the term “posterior” means towards the back of the body. The term “medial” means toward the midline of the body and the term “lateral” means away from the midline of the body. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention fills the need described above by providing hip fracture devices allowing distance limited dynamization, load controlled dynamization and the combination of the distance limited dynamization and load controlled dynamization and methods of using these devices. 
         [0008]    The hip fracture device has a plate and screw assembly. By replacement of modular components in the screw assembly the extent of axial travel and the force resisting travel may be adjusted interoperatively. 
         [0009]    In one aspect of the present invention, the hip fracture device uses a fixed barrel and modular end caps to variably limit the extent of axial travel of the screw within the barrel while restraining the screw to be coaxial with the barrel. 
         [0010]    In another aspect of the invention, a friction pin mounted to an end cap progressively engages a bore in the screw to provide load controlled dynamazation. 
         [0011]    In another aspect of the invention, the hip fracture device includes a plate having a head portion and a shaft portion. A barrel projects from the head portion of the plate and a screw is inserted in the barrel. A friction pin is slidably connected with the screw, and an end cap is fixed to the head portion of the plate. The friction pin is fixedly connected with the end cap. The screw slides over the friction pin and toward the end cap when a load is applied on the fracture device. The load required for further sliding of the screw over the friction pin increases incrementally as the screw slides towards the end cap. 
         [0012]    Another aspect of the invention is a method of repairing a fracture between the head and neck of a femur. The method includes the steps of affixing a plate having a head portion and a shaft portion on the femur, the plate having openings in the head portion and the shaft portion. A barrel is inserted in the opening in the head portion and a screw is inserted in the barrel. An end cap is inserted in the opening having the barrel inserted therein, and a friction pin is inserted between the end cap and the screw. The screw can slide over the friction pin and towards the end cap, and the load required for further sliding of the screw over the friction pin increases incrementally as the screw slides towards the end cap. 
         [0013]    In another aspect, the invention provides a kit for repairing a fracture between the head and neck. The kit includes at least one plate, the plate having a head portion and a shaft portion, and openings formed in the head portion and the shaft portion. The kit also includes at least one barrel configured for insertion in the opening in the head portion, and at least two screws each having a central bore, each bore having a different diameter. Also included are at least two friction pins, each pin having an external diameter that matches the diameter of one of the central bore in one of the screw, and at least two end caps, each end cap having a first bore that matches the diameter of one of the friction pins. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0014]      FIG. 1  is a frontal elevation view of a hip fracture device implanted in a proximal femur. 
           [0015]      FIG. 1A  shows another embodiment of a bone plate that may be used with the hip fracture device of  FIG. 1 . 
           [0016]      FIG. 2  is a close up view of a portion of  FIG. 1 . 
           [0017]      FIG. 3  is a sectional lateral view as shown in  FIG. 1  with the end cap removed. 
           [0018]      FIG. 4  is a view as in  FIG. 2  showing an end cap with a long shaft. 
           [0019]      FIG. 5  is a view as in  FIG. 2  showing an end cap with a short shaft. 
           [0020]      FIG. 6  is a view as in  FIG. 2  showing a friction pin placed between an end cap and a hip screw. 
           [0021]      FIG. 7  is a view as in  FIG. 2  showing the friction pin engaged in the end cap and the hip screw with the hip screw at the farthest distance from the end cap. 
           [0022]      FIG. 8  is a view as in  FIG. 2  showing the friction pin engaged in the end cap and the hip screw with the hip screw having moved axially towards the end cap. 
           [0023]      FIG. 9  shows the hip screw after it has moved further axially towards the end cap as compared to the position shown in  FIG. 8 . 
           [0024]      FIG. 10  shows the hip screw after it has moved farthest axially towards the end cap such that the top of the hip screw is touching the end cap and cannot move any further. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    Referring to  FIG. 1 , a hip fracture device  21  includes a locking plate  11  and one of more (preferably three) screw assemblies  31 . The hip fracture device  21  may be used for fixing bone fractures, particularly femoral neck fractures including Gaarden III/IV type fractures. 
         [0026]    The locking plate  11  generally conforms to the lateral portion of the proximal femur  1  and is attached to the femur by at least one cortical interlocking screw  15  passing through holes  13  in the subtrochanteric shaft region  3  of the femur  1 . The interlocking screws  15  serve to attach the plate  11  to the femur  1 . The plate  11  also has one or more stepped bores  17  for each screw assembly  31 . The major diameter of the stepped bore  17  incorporates a screw thread for fastening the screw assembly  31 . The minor diameter of the stepped bore  17  creates a shoulder  19  at the junction of the major and minor diameters. Each stepped bore  17  is aligned with the axis of each of the screw assemblies  31 .  FIG. 1A  shows a plate  11 A. Plate  11 A is a variation of design of plate  11 , and includes a slot  13 A. Plate  11 A may be used in place of plate  11 . A guide wire may be inserted through slot  13 A and into the femur  1 . The guide wire may be used to position the plate  11 A in a desired alignment on the surface of the femur  1 . The compression screw embodiments disclosed hereafter may be used with the bone plate  11 A. 
         [0027]    The screw assemblies  31  incorporate a hip screw  33 , a barrel  41 , an end cap  51  and an optional friction pin  61 . The friction pin may also be referred to as a spring pin. At least one screw assembly  31 , in conjunction with the plate  11 , provides angular stability in the indicated direction to counteract the moment created on the femoral neck  7  by the normal force F resulting from loads on the femoral head  5 . The screw assembly  31  also provides angular stability in all other directions. Rotational stability about the head axis A-A is achieved if more than one screw assembly  31  is connected to the plate  11 . Typically the hip screw assembles  31  are oriented parallel to the femoral neck axis A-A as shown. 
         [0028]    Hip screw  33  is typically cannulated with a bore  37 . Non-cannulated versions may have a blind bore  37  at the distal end. The screw  33  has a central shaft  34  defining a minor external diameter and an external flange  38  defining a major external diameter at the distal end of the screw. Formed internal to flange  38  are rotational features such as a hex socket  39 . Threads  35 , suitable for anchoring to bone, are formed at the proximal end of the screw  33  and engage the cancelleous bone of the femoral head  5 . 
         [0029]    Referring to  FIG. 2 , barrel  41  is generally cylindrical in shape with an external diameter  43  corresponding to the minor diameter of the stepped bore  17  in plate  11 . The barrel  41  has a sliding fit in the stepped bore  17  and rests on the shoulder  19 . Located at the distal end of barrel  41  is an external flange  49  that is a sliding fit with the major diameter of stepped bore  17  and engages shoulder  19  to prevent movement of the barrel  41  in the proximal direction along the screw assembly axis. The barrel  41  has a stepped bore  45  with major diameter  46  and minor diameter  47 . The minor diameter  47  creates a shoulder  48  at the junction of the major diameter  46  and minor diameter  47 . The minor diameter  47  is a sliding fit with central shaft  34  of the screw  33  and the shoulder  48  engages the external flange  38  to limit movement of the screw  33  in the proximal direction along the screw assembly axis. 
         [0030]    A head  52  is formed in a distal portion of the end cap  51 . The head  52  has a major diameter  53  and external machine threads formed on the major diameter  53  for fastening with the mating threads of the bore  17  of the plate  11 . Formed internal to head  52  are rotational features such as a hex socket  59 . The proximal region of the end cap  51  is a shaft  55  with a minor diameter  56  providing a slip fit with major diameter  46  of the barrel  41 . The shaft  55  has a proximal end  58  which may abut the end of the flange  38  to limit movement of the screw  33  in the distal direction along the screw assembly axis. The end  58  has a blind bore  57 . 
         [0031]    The friction pin  61  is provided for load controlled dynamization. The friction pin  61  is typically a roll pin with a slot  67  ( FIG. 3 ) that, when present, is press fit in bore  57  and is also a sliding interference fit with the bore  37  of the screw  33 . The bore  57  is sized to firmly retain the friction pin. The bore  37  is sized to provide a controlled frictional resistance to resist movement of the screw  33  in the distal direction along the screw assembly axis as will be further described in conjunction with  FIGS. 7-10 . 
         [0032]    All the various diameters and bores of the screw assembly  31  are concentric about the axis of the assembly as depicted in  FIG. 3 , which does not show the end caps  51  or the hex socket  39 . The various concentric sliding fits allow the screw  33  to move only along its axis, that is, parallel to the axis A-A. 
         [0033]    Assembly of the device  21  on femur  1  proceeds as follows. First, the plate  11  is fixed at the proximal femur  1  at the lateral region of the shaft  3 . The femur  1  is prepared by drilling holes sized for insertion of the screw  31  and the barrel  41 . The barrel  41  is then inserted into the bore  17  of the plate  11  until its final position where the flange  49  is seated against the shoulder  19  formed between the major and minor diameters of the bore  17 . The screw  33  is then inserted into the barrel  41  and turned into the bone until the screw flange  38  is seated against the barrel shoulder  48 . By turning several additional turns of the compression screw  33  a femoral head fragment that includes the femoral head  5  is pulled against the distal fracture surface of the femur  1  and the fracture is initially compressed. 
         [0034]    By selecting from a kit of various configurations of end caps  51  and friction pins  61 , the extent and force required for dynamization can be adjusted by the surgeon at this point in the operation. Should the surgeon desire static locking of the fragment in order to strictly limit travel and prevent shortening of the femoral neck, an end cap  51   a  with a longer shaft  56   a  is used to prevent distal motion of the screw  33  as shown in  FIG. 4 . Here the end cap  51   a  is in contact with the end of screw  33  and therefore no axial movement of the femoral head fragment is allowed.  FIG. 5  shows how caps  51  with various lengths of shaft  56  may be used to allow distance limited sliding of the screw  33 . In  FIG. 5 , there is a space between the end of the end cap  56  and the opposing end of the screw  33 . Therefore, the screw  33  and consequently the femoral head fragment can move axially towards the cap end  56 . The maximum travel in this case is equal to the space between the end of the end cap  56  and the opposing end of the screw  33 . This distance limited sliding of the femoral head fragment allows for fragment opposition and postoperative dynamic fracture site compression by weight bearing while limiting excessive femoral neck shortening. 
         [0035]    As shown in  FIG. 6 , when friction pin  61  is added, the screw assembly  31  provides load controlled sliding of the screw  33 . This sliding allows femoral head fragment opposition and postoperative dynamic fracture site compression by weight bearing while limiting the load on the fracture site, limiting the travel based on the load, and preventing stress induced resorption of the bone. The initial friction created by the friction pin  61  and the bore  37  can be varied by selecting from a kit of pins with varying diameters according to the patients weight, bone structure and the type of fracture. Thus, a heavier patient with larger bones may be fitted with a pin that creates more friction. 
         [0036]    The hip fracture device  21  shown in  FIG. 6  provides load controlled sliding of the femoral head fragment in order to allow for fragment apposition and postoperative dynamic fracture site compression by weight bearing while limiting the load on the fracture site and preventing stress induced resorption of the bone. The control mechanism provides increasing resistance with increasing sliding distance. This is caused by the progressively greater length of the friction pin  61  engaged by the bore  37  during sliding as depicted in  FIGS. 7-10 . Sliding of screw  33  stops when either the resistance becomes equal to the body weight induced force or when the distance limit is reached. 
         [0037]    When multiple screw assemblies  31  are used, the installation steps are repeated and the resistance may be varied by using the friction pins in some or all of the assemblies. Typically, the distance limits are the same for all the assemblies. 
         [0038]    In use, the plate  11  is fixed to the bone by inserting cortical screws  15  through holes  13  and into the subtrochantric shaft region. Using methods known to one skilled in the art, one or more stepped holes are drilled from the lateral side of femur into the femoral head portion. The holes are sized to accept screw  33  and barrel  41 . Next, a barrel  41  is inserted in a hole  13  and a screw  33  is inserted in the barrel. If more then one screws are to be used, the process may be repeated at this time or later. Next, the screw  33  is rotated in the femoral head fragment thereby attaching it to the fragment. The rotation is continued after the screw  33  has bottomed on the shoulder  48  resulting in closing of the fracture gap. The screw may be rotated further to apply initial compression to the fracture site. Next, the end cap  51   a  ( FIG. 4 ) is inserted in the hole  13  and screwed in place. The end cap  51   a  may be of such length that its proximal end rests on the end of the screw  33  to prevent any axial movement of screw  33 . If the end cap is of a shorter length, the screw  33  would be allowed to slide back in axial direction. The sliding movement would be stopped when the screw  33  touches the end cap  56 . 
         [0039]    Alternatively, as shown in  FIG. 7 , one end of the friction pin  61  is inserted in the bore  37  of the screw  33  and the other end is inserted in the bore  57  of end cap  51 , thereby clamping the friction pin  61  between the end cap  51  and screw  33 . Upon application of load, for example, by putting body weight on the hip and thus device  21 , the friction pin  61  may be pushed further into the bore  37 . As the friction pin  61  is pushed further in the bore  37 , as seen in  FIGS. 8 and 9 , increasingly greater load is required for axial movement of the screw  33  towards cap  51 . Once the screw  33  touches the end cap  51 , as seen in  FIG. 10 , any further axial travel of the screw  33  is prevented. 
         [0040]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention.