Abstract:
The outer periphery of a head section ( 11   e ) of a medical screw ( 11 ) is provided with an inverse external screw thread ( 11   h ) that is formed in the opposite screw direction from that of a screw thread ( 11   b ) provided to a tip section ( 11   a ). An inverse internal screw thread ( 14   a ) provided to the leading end of a rod-shaped body constituting an extraction jig ( 14 ) is rotated in the opposite direction from the screw direction of the screw thread ( 11   b ) so as to be screwed onto the inverse external screw thread ( 11   h ) and thereby integrate the screw ( 11 ) and the extraction jig ( 14 ). The screw ( 11 ) is gently extracted from the bone fracture site (D) and is removed from the body by rotating the extraction jig in the reverse direction from the insertion direction of the screw ( 11 ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a medical screw for joining a fracture site and a withdrawal operating jig for a medical screw. 
       BACKGROUND ART 
       [0002]    PTL 1 discloses a medical screw  1  having a hollow hole, which is referred to as a cannulated screw as illustrated in  FIG. 12 . The screw  1  is used for joining a fracture site in a medical field in the related art, is provided with a screw thread portion  1   b  formed on an outer surface of a distal end portion  1   a,  is provided with a drill blade  1   c  formed at an extremity thereof, and is provided with a through hole  1   d  extending along a center axis along an entire length thereof. A rotational operating portion if formed of, for example, a hexagonal depression is provided at an entry of the through hole  1   d  of a head portion  1   e  of the screw  1 , and the fracture site is joined by screwing the screw thread portion  1   b  into a bone by fitting a distal end portion of a driver-type rotational operation jig into the rotational operating portion if and rotating the same. 
         [0003]    A procedure of screwing the screw  1  of the related art into the bone starts with piercing a metallic guide pin  2  through an incised skin A and a subcutaneous structure B in a fracture site D of a bone C substantially orthogonal to the fracture site D under anesthesia as illustrated in  FIG. 13 . A distal end of the guide pin  2  is pointed like a drill, is pieced through the skin A and the subcutaneous structure B as is, and is screwed into the bone C by being rotated by a motor or the like when the distal end comes into abutment with a bone cortex surface E of the bone C. 
         [0004]    Subsequently, an upper end of the guide pin  2  is inserted into the through hole  1   d  on the distal end portion  1   a  side of the screw  1 , and the screw  1  is pushed inward while being guided along the guide pin  2 . The upper end of the guide pin  2  projected further upward from the head portion  1   e  of the screw  1  is inserted into a through hole  3   b  of a rotational operation jig  3 . Subsequently, as illustrated in  FIG. 14 , the screw  1  is pushed inward of the skin A and the subcutaneous structure B by the rotational operation jig  3 , and is rotated clockwise by a manual operation using a grip portion  3   c  of the rotational operation jig  3  after the distal end portion  1   a  of the screw  1  has come into abutment with the bone cortex surface E. With a rotation of the screw  1 , the screw thread portion  1   b  is screwed into an interior of the bone C along the guide pin  2  while drilling the bone C with the drill blade  1   c  provided at the distal end thereof. The screw  1  may be screwed by the rotational operation jig  3  such as a medical electric drill or the like. 
         [0005]    By screwing the screw  1  into the bone C while observing an X-ray TV monitor with radioscopy, the screw thread portion lb penetrates through the fracture site D and starts unification. Then, as illustrated in  FIG. 15 , when the head portion  1   e  of the screw  1  reaches the bone cortex surface E, fixation of the fracture site D by the screw  1  is achieved. 
         [0006]    The rotational operation jig  3  is pulled out from the guide pin  2 , and finally, the guide pin  2  is withdrawn from the bone C, and then the skin A or the like is sutured, whereby a joining process on the fracture site D with the screw  1  is completed. 
         [0007]    Since the fracture site D is united after an elapse of several months from the joining process, a process of withdrawing the screw  1  which has completed its role is performed. After the skin A and the subcutaneous structure B have incised, the screw  1  is taken out from the bone C by loosening the screw thread portion  1   b,  which is screwed in, by fitting a distal end portion  3   a  of the rotational operation jig  3  into the rotational operating portion if of the screw  1  and rotating the same counterclockwise. In this case, a withdrawal guide pin is preferably inserted into the screw  1  to guide the rotational operation jig  3  to the head portion le of the screw  1 . 
         [0008]    At a time when the fracture site D is unified by the fixation of the screw  1 , callus is generated newly around the head portion  1   e  of the screw  1  in many cases, so that the head portion  1   e  of the screw  1  may be buried in the callus. In this case, since the callus becomes an obstacle which makes the rotational operation jig  3  difficult to fit into the rotational operating portion if of the screw  1 , the callus needs to be removed. 
         [0009]    The screw thread portion  1   b  of the screw  1  is pulled out from the bone C by rotating the rotational operation jig  3  counterclockwise after the rotational operation jig  3  is fitted correctly into the rotational operating portion  1   f.  At the time of being pulled out, the screw  1  is moved upward by a reaction force of the bone C until the screw thread portion  1   b  screwed into the bone C reaches the bone cortex surface E. However, in the case where the screw  1  is still buried in the subcutaneous structure B, the screw thread portion  1   b  runs idle and thus puling out of the screw  1  becomes difficult. 
         [0010]    In the case where the screw  1  comes off the bone C when screwing the screw  1  at the time of joining the fracture site D and thus is screwed into the subcutaneous structure B as well, the screw  1  needs to be pulled out once to retry screwing. At this time, even though the screw  1  is rotated counterclockwise, the screw thread portion  1   b  runs idle and thus the screw  1  cannot be pulled out. 
         [0011]    Furthermore, if several months have been elapsed from the joining process, the bone C having the screw  1  screwed therein may reject the metal, and thus a gap may be formed between the bone C and the screw  1 . In such a case as well, the screw thread portion  1   b  runs idle and thus cannot be pulled out easily even though the screw  1  is rotated. 
         [0012]    PTL 2 discloses an orthopedic screw having the same function as the medical screw  1 , and describes that a reverse internal thread portion having a thread in a reverse direction to a direction of the screw thread formed at the distal end portion, is formed inside a head portion of the orthopedic screw, and the screw is pulled out by engaging an operating jig with the reverse internal thread portion and rotating the screw in a reverse thread direction. 
         [0013]    The screw can be pulled out easily by using this orthopedic screw, because a withdrawal operating jig is integrated with the orthopedic screw via the reverse internal thread portion and the screw thread can be loosened from the bone by rotating the operating jig in the reverse direction. 
       CITATION LIST 
     Patent Literatures 
       [0014]    PTL 1: JP-A-10-272142 
         [0015]    PTL 2: JP-T-2011-500215 
       SUMMARY OF THE INVENTION 
     Technical Problem 
       [0016]    However, the reverse internal thread portion of the orthopedic screw disclosed in PTL 2 is formed inside the head portion of the screw. Therefore, if a foreign substance, for example, callus, is adhered to inside of the head portion, the reverse internal thread portion has a disadvantage of becoming incapable of functioning unless the foreign substance is removed. Removal of the foreign substance is very troublesome, and proper engagement of the operating jig with the reverse thread portion cannot be achieved as long as the foreign substance remains in the head portion. Therefore, the foreign substance needs to be completely taken out from the head portion, and this is a big problem in the surgical operation which needs to be quick. 
         [0017]    It is a first object of the invention to solve the above-described problem and provide a medical screw which can be withdrawn easily and quickly from inside the bone by using a reverse external thread portion formed on an outer periphery of a head portion after the bone has unified or at the time of replacement. 
         [0018]    It is a second object of the invention to provide a withdrawal operating jig for a medical screw configured to achieve a withdrawal of the medical screw described above reliably, easily, and quickly. 
       Solution to Problem 
       [0019]    A medical screw according to the invention for achieving the above described objects is a medical screw formed of a metallic material for joining a fracture site and including: a screw thread portion formed on an outer surface of a distal end portion; and an external thread portion formed on an outer periphery of a head portion which is provided at a rear end portion and whose top portion bulges in an arcuate shape, in which the external thread portion is formed in a reverse direction to a direction of a thread of the screw thread portion. 
         [0020]    A withdrawal operating jig for a medical screw according to the invention is a withdrawal operating jig for withdrawing a medical screw from a fracture site, the medical screw including: a screw thread portion formed on an outer surface of a distal end portion; and an external thread portion formed on an outer periphery of a head portion provided at a rear end portion and swelled in an arcuate shape at a top portion thereof, in which the external thread portion provided on the head portion being formed of a metallic material so as to have a thread formed in a reverse direction to a direction of a thread of the screw thread portion, including an engaging portion formed into an internal thread portion configured to engage the external thread portion provided on the outer periphery of the head portion of the medical screw at a front end portion of a rod-shaped member. 
       Advantageous Effects of Invention 
       [0021]    According to the medical screw and the withdrawal operating jig for a medical screw according to the invention, since the external thread portion formed in the reverse direction to the direction of the thread of the screw thread portion is provided in the periphery of the head portion of the medical screw, even though there is a foreign substance such as callus adhered to the outer periphery of the head portion, the foreign substance can be removed easily from the external thread portion. In addition, at the time of the withdrawal, the internal thread portion of the withdrawal operating jig provided in a reverse direction is engaged with the external thread portion of the head portion. Accordingly, the medical screw and the withdrawal operating jig are easily integrated, so that the medical screw can be taken out of the body easily and quickly by being loosen by a further rotation in a reverse direction to the direction of screwing-in of the medical screw. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0022]    [ FIG. 1 ]  FIG. 1  is a cross-sectional view of a medical screw of an embodiment. 
           [0023]    [ FIG. 2 ]  FIG. 2  is a perspective view of a screwing-in operating jig. 
           [0024]    [ FIG. 3 ]  FIG. 3  is an explanatory drawing illustrating a state in which the medical screw is screwed into a fracture site. 
           [0025]    [ FIG. 4 ]  FIG. 4  is an explanatory drawing illustrating a state in which callus is formed in the vicinity of a head portion. 
           [0026]    [ FIG. 5 ]  FIG. 5  is a cross-sectional view illustrating a principal portion of a callus separation operating jig. 
           [0027]    [ FIG. 6 ]  FIG. 6  is an explanatory drawing illustrating a removal of the callus by the callus separation operating jig. 
           [0028]    [ FIG. 7 ]  FIG. 7  is an enlarged plan view illustrating a modification of the head portion of the medical screw. 
           [0029]    [ FIG. 8 ]  FIG. 8  is a perspective view of another callus separation operating jig. 
           [0030]    [ FIG. 9 ]  FIG. 9  is a cross-sectional view of a principal portion of a withdrawal operating jig. 
           [0031]    [ FIG. 10 ]  FIG. 10  is an explanatory drawing illustrating a state of inserting the withdrawal operating jig. 
           [0032]    [ FIG. 11 ]  FIG. 11  is an explanatory drawing illustrating a state of withdrawing the medical screw from inside a bone. 
           [0033]    [ FIG. 12 ]  FIG. 12  is a perspective cross-sectional view of a medical screw of the related art. 
           [0034]    [ FIG. 13 ]  FIG. 13  is an explanatory drawing in a state in which a guide pin is inserted into the fracture site. 
           [0035]    [ FIG. 14 ]  FIG. 14  is an explanatory drawing of a state in which the medical screw of the related art is inserted into a subcutaneous structure. 
           [0036]    [ FIG. 15 ]  FIG. 15  is an explanatory drawing illustrating a state in which the medical screw of the related art is screwed into the fracture site. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0037]    The invention will be described in detail with reference to embodiments illustrated in  FIG. 1  to  FIG. 11 . 
         [0038]      FIG. 1  is a cross-sectional view of a medical screw  11  of an embodiment. A distal end portion  11   a  of the tube-shaped screw  11  formed of a metallic material such as titanium is provided with a screw thread portion  11   b,  which is a right-handed thread, formed on an outer surface thereof and is provided with a drill blade  11   c  at an extremity thereof. The screw thread portion  11   b  may be provided not only on the distal end portion  11   a,  but also on the outer surface entirely in a longitudinal direction of the screw  11 . 
         [0039]    A rear end portion  11   d  is provided with a head portion  11   e  at a distal end thereof, and is provided with a rotational operating portion  11   f  formed into, for example, a cross-shaped plus groove configured to fit in a distal end portion of a screwing-in operating jig, which will be described later, at a center portion of a top surface of the head portion  11   e.  A through hole  11   g  having a predetermined diameter is provided along a center axis from the distal end portion  11   a  to the head portion  11   e  of the screw  11 , and the through hole  11   g  is configured to allow insertion of a guide pin and a withdrawal guide pin, which have been described in conjunction with the related art. 
         [0040]    The through hole  11   g  has a substantially circular shape in cross section, has the same diameter from the distal end portion of the screw  11  to a rear end portion thereof, and has an inner diameter on the order of 2 mm. The head portion  11   e  is provided with a reverse external thread portion  11   h  on an outer periphery thereof as a left-handed thread in a reverse direction to a direction of the screw thread portion  11   b.    
         [0041]    The shape of the top portion of the head portion  11   e  is preferably swelled upward, for example, in an arcuate shape, so that a callus separation operating jig and a withdrawal operating jig, which will be described later, can be easily guided to the reverse external thread portion  11   h.    
         [0042]    The entire length of the screw  11  is, for example, on the order of 30 to 60 mm. However, it is desired to provide a plurality of types having different lengths and thicknesses and select one suitable for the size of a fracture site and the position of the fracture site such as a finger bone or a femur as needed. However, the screws  11  in all sizes preferably have the head portions  11   e  having the same outer diameter in order to be used commonly for the callus separation operating jig and the withdrawal operating jig, which will be described later. 
         [0043]      FIG. 2  is a perspective view of a screwing-in operating jig  12 , which is provided with a plus portion projecting from a distal end portion  12   a  thereof and being configured to fit the rotational operating portion  11   f  of the screw  11 , and a through hole  12   c  having a circular shape in cross section extending from the distal end portion  12   a  to a grip portion  12   b  at a rear end. The inner diameter of the through hole  12   c  substantially matches the inner diameter of the through hole  11   g  of the screw  11 , and is configured to allow insertion of the guide pin therein. 
         [0044]    When screwing the screw  11  into a bone C, a skin A or the like is incised, and then a guide pin  2  inserted into the bone C is inserted through the through hole  11   g  of the screw  11  and the through hole  12   c  of the screwing-in operating jig  12 , and the distal end portion  12   a  of the screwing-in operating jig  12  is fitted into the rotational operating portion  11   f  of the screw  11  while being guided by the guide pin  2  as illustrated in  FIG. 3 . Then, by rotating the screwing-in operating jig  12  clockwise in a direction of the right-handed thread by a manual operation or electrically, the drill blade  11   c  of the screw  11  drills the bone C to cause the screw thread portion  11   b  to be screwed into the bone C. Then, by continuing screwing until the head portion  11   e  reaches a bone cortex surface E, a fracture site D is joined. Subsequently, the screwing-in operating jig  12  and the guide pin  2  are pulled out and the skin A and the like is sutured, so that the joint with the screw  11  is completed. 
         [0045]    By forming the shape of the depressed-shaped rotational operating portion  11   f  of the screw  11  into a depressed plus groove as illustrated in  FIG. 1 , the distal end portion  12   a  of the screwing-in operating jig  12  can be fitted to the rotational operating portion  11   f  of the screw  11  and rotated even though the size of the plus shape of the distal end portion  12   a  of the screwing-in operating jig  12  is different to some extent. 
         [0046]    The shape of the distal end portion  12   a  of the screwing-in operating jig  12  may be formed into a minus shape, and in this case, the shape of the rotational operating portion  11   f  of the screw  11  needs only to be a depressed linear shape or a cross shape, and the rotational operating portion  11   f  can be rotated even though the size is different to some extent from the minus shape of the distal end portion  12   a.  Alternatively, the shape of the depressed-shaped rotational operating portion  11   f  may be a shape which allows fitting of the rotational operation jig  3  having a polygonal shape such as a hexagonal shape as described in the description of the related art without problem. However, in this case, the screw  11  cannot be rotated unless the screwing-in operating jig  12  has the distal end portion  12   a  having a shape which completely fits. 
         [0047]    In the case where the fracture site D is unified after an elapse of several months and thus the screw  11  which is no longer necessary is taken out, the skin A needs to be incised to allow the callus separation operating jig, the withdrawal operating jig, which will be described later, and the screw  11  to pass through a subcutaneous structure B and the skin A. However, since the skin A and the subcutaneous structure B extend to some extent, an incision of the skin A and the subcutaneous structure B on the order of 4 mm in outer diameter above the head portion  11   e  is sufficient. 
         [0048]    In the vicinity of the head portion  11   e  of the screw  11 , callus F is formed with an elapse of time as illustrated in  FIG. 4 , so that the head portion  11   e  may be buried in the callus F. In this case, in order to remove the callus F in the periphery of the head portion  11   e,  a callus separation operating jig  13  as illustrated in  FIG. 5  is used as needed. The callus separation operating jig  13  is a screw driver-type jig provided with a plurality of tongue-shaped blade portions  13   b  having an elasticity arranged in an annular shape at a distal end of a shaft portion  13   a,  and is configured to have an insertion hole  13   d  from a distal end thereof to a grip portion  13   c  so as to allow insertion of the withdrawal guide pin. 
         [0049]    As illustrated in  FIG. 6 , a withdrawal guide pin  2 ′ is pierced into the bone C, the withdrawal guide pin  2 ′ is inserted into the through hole  11   g  of the screw  11 , and the callus separation operating jig  13  is pushed therein along the withdrawal guide pin  2 ′. Subsequently, the blade portion  13   b  is rotated by the grip portion  13   c  to remove the callus F in the periphery of the head portion  11   e  to completely expose the reverse external thread portion  11   h  provided in the outer periphery of the head portion  11   e.  In the case where the blade portion  13   b  of the callus separation operating jig  13  is inserted so as to extend along the surface of the head portion  11   e , the callus F can be separated easily. By separating and removing the callus F in the periphery of the head portion  11   e , engagement of the withdrawal operating jig, which will be described later, with the reverse external thread portion  11   h  of the head portion  11   e  is enabled. 
         [0050]      FIG. 7  is an enlarged plan view of a head portion  11   e  of a medical screw  11  of a modification. A plurality, three for example, of groove portions  11   i  for separating the callus are formed on the periphery of the head portion  11   e  of the screw  11  from the top portion to the side in a direction orthogonal to a peripheral direction, and depressed guide portions  11   j  are provided at positions from the top portion to the groove portions  11   i.    
         [0051]    When a pin or the like is inserted from above the groove portions  11   i  covered with the callus F via the guide portions  11   j  and opened forcedly, the fragile callus F adhered to the periphery of the head portion  11   e  can be separated easily, so that the reverse external thread portion  11   h  can be exposed. The presence of the groove portions  11   i  does not affect engagement of the reverse external thread portion  11   h.    
         [0052]    It is also possible to use a callus separation operating jig  13 ′ as illustrated in  FIG. 8  to cause the groove portions  11   i  to operate. In other words, the callus separation operating jig  13 ′ has, for example, resiliency at a distal end of a rod body portion  13   e,  and is provided with three metallic pins  13   f  arranged at positions matching the groove portion  11   i  of the head portion  11   e  of the screw  11 . An insertion hole, which is not illustrated, for allowing insertion of the withdrawal guide pin  2 ′ is provided at a center portion from the distal end of the rod body portion  13   e  to a grip portion  13   g.    
         [0053]    When removing the callus F formed on the outer periphery of the screw  11 , the callus F can be pushed outward and separated easily by a resilient force of the metallic pins  13   f  only by inserting the metallic pins  13   f  of the callus separation operating jig  13 ′ into the groove portions  11   i  via the push-in guide portion  11   j  along the arcuate-shaped swelling of the head portion  11   e.    
         [0054]      FIG. 9  is a cross-sectional view of a principal portion of a withdrawal operating jig  14 . The withdrawal operating jig  14  includes a cap nut portion  14   b  having a reverse internal thread portion  14   a  on an inner side thereof as an engaging portion at a front end portion of the rod-shaped member, and the reverse internal thread portion  14   a  is configured to engage the reverse external thread portion  11   h  of the screw  11 . An insertion hole  14   e  for allowing the withdrawal guide pin  2 ′ to be inserted therethrough is formed at center portions of a shaft portion  14   c  and a grip portion  14   d  of the withdrawal operating jig  14 . 
         [0055]    As illustrated in  FIG. 10 , the skin A or the like is incised and an upper end of the withdrawal guide pin  2 ′ pierced into the bone C is inserted into the insertion hole  14   e  of the withdrawal operating jig  14 . By moving the withdrawal operating jig  14  downward along the withdrawal guide pin  2 ′, the reverse internal thread portion  14   a  of the withdrawal operating jig  14  is guided to the head portion  11   e  of the screw  11  and brought into abutment with the reverse external thread portion  11   h.  In this case, by using the withdrawal guide pin  2 ′ as the withdrawal operating jig  14 , and forming the top portion of the head portion  11   e  into an arcuate shape, the reverse internal thread portion  14   a  is guided correctly to the reverse external thread portion  11   h.    
         [0056]    Subsequently, the withdrawal operating jig  14  is rotated counterclockwise, that is, in a reverse thread direction by the grip portion  14   d,  the reverse internal thread portion  14   a  of the withdrawal operating jig  14  is sufficiently screwed into the reverse external thread portion  11   h  of the screw  11 , and the withdrawal operating jig  14  is unified with the screw  11 . 
         [0057]    When the withdrawal operating jig  14  is further rotated counterclockwise subsequently to the unification, the screw  11  can be taken out by loosening the screw thread portion  11   b  of the screw  11  with respect to the bone C as illustrated in  FIG. 11 . Even though the screw  11  is withdrawn out from the bone C and runs idle, since the screw  11  is integrated with the withdrawal operating jig  14 , the screw  11  can be pulled out of the body by puling the withdrawal operating jig  14  upward as is. Finally, the withdrawal guide pin  2 ′ is withdrawn and the skin A or the like is sutured, whereby the screw  11  is completely taken out. 
         [0058]    After the screw  11  has pulled out, there remains a void in the bone C. However, the void is filled up by the bone C with an elapse of time. 
         [0059]    In the description of the embodiment given above, the screw thread portion  11   b  of the screw  11  is the right-handed thread and the reverse external thread portion  11   h  is the left-handed thread. However, this relationship may be vice versa. 
         [0060]    Although the guide pin  2  and the withdrawal guide pin  2 ′ are described as separate members, these members may be the same member, and these are not an absolutely imperative member. When the guide pin  2  and the withdrawal guide pin  2 ′ are not used, the through hole  11   g  of the screw  11 , the insertion hole  13   d  of the callus separation operating jig  13 , and the insertion hole  14   e  of the withdrawal operating jig  14  are not necessary. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           2 ,  2 ′ guide pin 
           11  medical screw 
           11   a  distal end portion 
           11   b  screw thread portion 
           11   c  drill blade 
           11   d  rear end portion 
           11   e  head portion 
           11   f  rotational operating portion 
           11   g  through hole 
           11   h  reverse external thread portion 
           11   i  groove portion 
           11   j  guide portion 
           12  screwing-in operating jig 
           13 ,  13 ′ callus separation operating jig 
           14  withdrawal operating jig 
           14   a  reverse internal thread portion 
           14   b  cap nut portion 
           14   c  shaft portion 
           14   d  grip portion  14   e  insertion hole