Abstract:
A method and apparatus are provided for attaching a cranial flap ( 20 ) to a skull ( 10 ). The cranial flap ( 20 ) and the skull ( 10 ) are spaced apart by a kerf ( 22 ) defined by a first kerf edge ( 24 ) on the cranial flap and a second kerf edge ( 28 ) on the skull. The apparatus comprises at least one attachment device ( 30 ) made of a bioabsorbable polymeric material and having a head portion ( 40 ), a main body portion ( 32 ), and an end portion ( 50 ). The end portion ( 50 ) is deformable from an axially extending first condition to a radially extending second condition by heating the end portion and forming the end portion around the first kerf edge ( 24 ), which clamps the attachment device ( 30 ) to the cranial flap ( 20 ). The main body portion ( 32 ) includes a first surface portion ( 36 ) that attaches to the first kerf edge ( 24 ) and a second surface portion ( 38 ) that attaches to the second kerf edge ( 28 ). The attachment device ( 30 ) is positionable in the kerf ( 22 ) to secure the cranial flap to the skull by frictional engagement between the first surface portion ( 36 ) against the first kerf edge ( 24 ) and frictional engagement between the second surface portion ( 38 ) against the second kerf edge ( 28 ).

Description:
FIELD OF THE INVENTION 
     The present invention is directed to a method and apparatus for attaching a cranial flap to a skull, from which the cranial flap was removed, during surgery. 
     BACKGROUND OF THE INVENTION 
     Surgical operations involving the human skull, such as brain surgery or craniofacial surgery, require that a section of the skull be removed. Typically, a number of burr holes are first drilled into the skull and which outline the section of the skull to be removed. A cutting tool is then inserted into one of the burr holes and a cut, or osteotomy, is made from one burr hole to then next burr hole until a loop is completed. The loop of osteotomies forms an opening in the skull and defines the section of the skull to be removed. The section of the skull to be removed is commonly referred to as a cranial flap. Because the blade on the cutting tool typically has a width of 1-2 mm, a kerf is formed between the opening in the skull and the cranial flap. Thus, the periphery of the cranial flap is smaller than the opening in the skull. 
     When the surgical procedure inside the skull is complete, the cranial flap must be replaced in the opening in the skull and re-attached to the skull. A number of methods are known for re-attaching the cranial flap to the skull. One known method uses stainless steel wire as a suture material. Other known methods utilize plates and associated screws made from either titanium or a bioabsorbable polymer. Still other known methods employ rivet-type fasteners made of titanium or a biocompatible polymer such as acetyl resin. 
     A major disadvantage of the known methods for reattaching a cranial flap that use a metallic material is that the metal creates large artifacts in any subsequent CT scans and radiographs. It is also disadvantageous to use a permanent (non-bioabsorbable) fastener that protrudes more than 1-2 mm from the surface of the skull because the fasteners then become visible as unsightly bumps under the patient&#39;s skin. 
     SUMMARY OF THE INVENTION 
     The present invention is an apparatus for attaching a cranial flap to a skull during surgery. The cranial flap and the skull are spaced apart by a kerf defined by a first kerf edge on the cranial flap and a second kerf edge on the skull. The apparatus comprises at least one attachment device made of a bioabsorbable polymeric material. The at least one attachment device has a head portion, a main body portion, and an end portion that is deformable upon heating to a predetermined temperature. The end portion of the at least one attachment device has a first condition in which the end portion extends axially from the main body portion and a second condition in which the end portion extends radially from the main body portion and engages an inner surface of the cranial flap. The end portion is deformable from the first condition to the second condition during surgery by heating the end portion and forming the end portion around the first kerf edge of the cranial flap to clamp the at least one attachment device to the cranial flap. The main body portion of the at least one attachment device includes a first surface portion that attaches to the first kerf edge on the cranial flap and a second surface portion that attaches to the second kerf edge on the skull. The at least one attachment device is positionable in the kerf between the cranial flap and the skull to secure the cranial flap to the skull by frictional engagement between the first surface portion against the first kerf edge and frictional engagement between the second surface portion against the second kerf edge. 
     The present invention also provides a method for re-attaching a cranial flap to a skull during surgery. The method utilizes an attachment device made of a bioabsorbable material that is formable upon heating to a predetermined temperature. The attachment device has a head portion, a main body portion, and a deformable end portion extending axially from the main body portion. The attachment device is placed adjacent the cranial flap so that the head portion engages an outer surface of the cranial flap and the main body portion engages a first kerf edge of the cranial flap. The end portion of the attachment device is heated to a predetermined temperature and subsequently bent around the cranial flap so that the end portion extends radially and engages an inner surface of the cranial flap. The cranial flap is then pressed into an opening in the skull created by the removal of the cranial flap so that frictional engagement between the main body portion of the attachment device and the cranial flap and frictional engagement between the main body portion of the attachment device secures the cranial flap to the skull. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other features of the present invention will become apparent to those skilled in the art to which the present invention relates upon reading the following description with reference to the accompanying drawings, in which: 
     FIG. 1 is a perspective view of a human skull illustrating several apparatuses for attaching a cranial flap in accordance with multiple embodiments of the present invention; 
     FIG. 2 is a perspective view of an apparatus for attaching a cranial flap in accordance with a first embodiment of the present invention; 
     FIG. 3 is a sectional view of the apparatus of FIG. 2 at an early stage in the attachment process; 
     FIG. 4 is a view similar to FIG. 3 illustrating a subsequent stage in the attachment process; 
     FIG. 5 is a sectional view taken along line  5 — 5  in FIG. 1; 
     FIG. 6 is a perspective view of an apparatus for attaching a cranial flap in accordance with a second embodiment of the present invention; 
     FIG. 7 is a perspective view of an apparatus for attaching a cranial flap in accordance with a third embodiment of the present invention; and 
     FIG. 8 is a plan view of the apparatus of FIG.  7 . 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention is directed to a method and apparatus for attaching a cranial flap to a skull, from which the cranial flap was removed, during surgery. As representative of the present invention, FIG. 1 illustrates a human skull  10  on which surgery is being performed. 
     To access a particular region inside the skull  10 , the surgeon drills a number of burr holes  12 , only two of which are visible in FIG. 1, in the skull. A cutting tool (not shown) is then inserted into a first one of the burr holes  12  and a cut  14  is made in the skull  10  from the first one of the burr holes to another of the burr holes. Additional cuts  14  in the skull  10  are made between the other burr holes  12  until a loop is completed. In the representative illustration of FIG. 1, there are three cuts  14 . It should be apparent that more than three burr holes  12  and three cuts  14  may be made at the discretion of the surgeon. 
     The loop of cuts  14  in the skull  10  forms an opening (not numbered) in the skull and defines a cranial flap  20  to be removed. While making the cuts  14 , the width of the cutting tool forms a kerf  22  between the cranial flap  20  and the skull  10 . Hence, the cranial flap  20  is slightly smaller than the opening in the skull  10 . When the surgical procedure inside the skull  10  is complete, the cranial flap  20  is replaced in the opening in the skull and secured to the skull according to the method and apparatus described below. 
     A first embodiment of an attachment device  30  for securing the cranial flap  20  to the skull  10  is illustrated in FIG.  2 . The attachment device  30  according to the first embodiment is designed to fit into one of the burr holes  12  in the skull  10 , as is described further below. The attachment device  30  is made of a bioabsorbable polymeric material, such as polylactide (PLA), polyglycolide (PGA), or a co-polymer of polylactide and polyglycolide. The attachment device  30  has a main body portion  32 , a head portion  40 , and a deformable end portion  50 . 
     The main body portion  32  of the attachment device  30  has a generally cylindrical outer surface  33 . An upper section  34  of the outer surface  33  has a plurality of circumferentially extending teeth  35 . The teeth  35  extend through diametrically opposed first and second surface portions  36  and  38  in the upper section  34  of the outer surface  33 . In accordance with the embodiment of FIG. 2, the first and second surface portions  36  and  38  comprise arcuate segments. Further, the main body portion  32  preferably has an axial length L 1  that is between 3 mm and 5 mm to allow the attachment device  30  to adapt to various skull thicknesses. 
     The head portion  40  of the attachment device  30  has a domed outwardly facing surface  42  and a planar inwardly facing surface  44  (FIG.  3 ). The head portion  40  preferably has an axial thickness T 1  of no more than 2 mm to reduce the visibility of the head portion while the attachment device  30  is being absorbed. 
     The end portion  50  of the attachment device  30  includes generally parallel first and second side surfaces  52  and  54 . The end portion  50  has a first condition in which the end portion extends axially from the main body portion  32 . The end portion  50  further has a second condition, illustrated in FIG. 4, in which the end portion extends generally radially from the main body portion  32 , and the first side surface  52  faces in an upward (as viewed in the Figures) direction A. The end portion  50  of the attachment device  30  is deformable from the first condition to the second condition by heating the end portion. 
     To re-attach the cranial flap  20  to the skull  10 , at least one attachment device  30  is first secured to the cranial flap. As shown in FIG. 3, the attachment device  30  is placed next to the cranial flap  20  so that the teeth  35  on the first surface portion  36  of the main body portion  32  of the attachment device engage a first kerf edge  24  on the cranial flap. Further, the inwardly facing surface  44  on the head portion  40  of the attachment device  30  is brought into engagement with an outer surface  25  of the cranial flap. The attachment device  30  is positioned so that the first side surface  52  on the end portion  50  lies underneath and generally parallel to the first kerf edge  24  on the cranial flap  20 . 
     In accordance with the first embodiment of the invention, the cylindrical main body portion  32  of the attachment device  30  fits into one of the burr holes  12  in the skull  10 . The first kerf edge  24  has an arcuate shape formed by the drill bit (not shown) used to create the burr hole, and the first surface portion  36  on the main body portion  32  of the attachment device  30  adjoins this arcuate first kerf edge. 
     Next, the end portion  50  of the attachment device  30  is heated to a predetermined elevated temperature by a suitable heat source such as a heat gun  60 , an exhaust nozzle  62  of which is illustrated schematically in FIG.  4 . The predetermined elevated temperature to which the end portion  50  is heated will depend on the glass transition temperature of the specific bioabsorbable polymeric material of the attachment device  30 , but will likely be in the range of 50-100° C. 
     Upon being heated to the predetermined elevated temperature, the end portion  50  of the attachment device  30  is deformed into the second condition illustrated in FIG. 4 by bending the end portion around the first kerf edge  24  of the cranial flap  20  in the direction of arrow B. The end portion  50  of the attachment device  10  is bent in the direction of arrow B until the first side surface  52  on the end portion engages an inside surface  26  on the cranial flap  20 . As the end portion  50  of the attachment device  30  cools and re-hardens in the position shown in FIG. 4, the attachment device becomes clamped to the cranial flap  20 . Cooling of the end portion  50  may be accelerated using a fan (not shown) or other suitable device. 
     In order to use the attachment device  30  for attaching the cranial flap to the skull, additional attachment devices should be secured around the periphery of the cranial flap  20 . It should be understood that it is not necessary that one or more attachment devices be located to fit in a burr hole  12 . The number and location of additional attachment devices to be used are decisions made by the surgeon either before or during surgery. The surgeon may use several of the attachment devices  30  according to the first embodiment of FIGS. 2-5 or, alternatively, may utilize additional attachment devices constructed in accordance with either the second embodiment (FIG. 6) or the third embodiment (FIGS. 7 and 8) of the present invention. 
     An attachment device  130  constructed in accordance with the second embodiment of the invention is illustrated in FIG.  6 . As is best seen in FIG. 1, the attachment device  130  is designed to fit into the kerf  22  that extends between two of the burr holes  12  in the skull  10 . As with the first embodiment, the attachment device  130  is made of a bioabsorbable polymeric material, such as polylactide (PLA), polyglycolide (PGA), or a co-polymer of polylactide and polyglycolide. The attachment device  130  (FIG. 6) has a main body portion  132 , a head portion  140 , and a deformable end portion  150 . 
     The main body portion  132  of the attachment device  130  has a generally square shape including diametrically opposed first and second surface portions  136  and  138 . Further, the main body portion  132  has an axial length that is between 3 mm and 5 mm to allow the attachment device  130  to adapt to various skull thicknesses. 
     The head portion  140  of the attachment device  130  has a domed outwardly facing surface  142  and a planar inwardly facing surface  144  for engaging the outer surface  25  of the cranial flap  20 . Like the attachment device  30  of FIG. 3, the head portion  140  preferably has an axial thickness of no more than 2 mm to reduce the visibility of the head portion while the attachment device is being absorbed into the skull. 
     The end portion  150  of the attachment device  130  includes generally parallel first and second side surfaces  152  and  154 . The end portion  150  has a first condition in which the end portion extends axially from the main body portion  132 . The end portion further has a second condition in which the end portion  150  extends generally radially from the main body portion  132  and the first side surface  152  faces upward. The end portion  150  of the attachment device  130  is deformable from the first condition to the second condition by heating the end portion to a predetermined elevated temperature. 
     The attachment device  130  is secured to the cranial flap  20  in same manner as the attachment device  10  of the first embodiment and therefore is not separately illustrated. The attachment device  130  is placed next to the cranial flap  20  so that the teeth  135  on the first surface portion  136  of the main body portion  132  of the attachment device engage the first kerf edge  24 . The inwardly facing surface on the head portion  140  of the attachment device  150  is brought into engagement with the outer surface  25  of the cranial flap  20 . The attachment device  130  is positioned so that the first side surface  152  on the end portion  150  lies underneath and generally parallel to the first kerf edge  24  on the cranial flap  20 . 
     The end portion  150  of the attachment device  130  is then heated to a predetermined elevated temperature by a suitable heat source, such as the heat gun  60  shown schematically in FIG.  4 . Upon being heated to the predetermined elevated temperature, the end portion  150  of the attachment device  130  is deformed into the second condition by bending the end portion around the first kerf edge  25  of the cranial flap  20  in the direction of arrow B. The end portion  150  of the attachment device  130  is bent in the direction of arrow B until the first side surface  152  on the end portion engages the inside surface  26  on the cranial flap  20 . As the end portion  150  of the attachment device  130  cools and hardens, the attachment device becomes clamped to the cranial flap  20 . Cooling of the end portion  150  may be accelerated using a fan (not shown) or other suitable device. 
     An attachment device  230  constructed in accordance with the third embodiment of the invention is illustrated in FIGS. 7 and 8. As is best seen in FIG. 1, the attachment device  230  is designed to fit into the kerf  22  that extends between two of the burr holes  12  in the skull  10 . As with the first embodiment, the attachment device  230  is made of a bioabsorbable polymeric material, such as polylactide (PLA), polyglycolide (PGA), or a co-polymer of polylactide and polyglycolide. The attachment device  230  (FIG. 7) has a main body portion  232 , a head portion  240 , and a deformable end portion  250 . The attachment device  230  is basically an elongated version of the attachment device  130  of FIG. 6, but with a few additional features. 
     The head portion  240  of the attachment device  230  has a domed outwardly facing surface and a planar inwardly facing surface  244 . As shown in FIGS. 7 and 8, the head portion  240  further includes a plurality of relief slots  246  located along the periphery of the head portion. The relief slots  246  make it easier for the head portion  240  to bend laterally, as is indicated by arrows C and D in FIG. 8, so that the attachment device  230  can adapt to a curved section of the kerf  22 . The head portion  240  preferably has an axial thickness of no more than 2 mm to reduce the visibility of the head portion while the attachment device  230  is being absorbed. 
     The main body portion  232  of the attachment device  230  has a generally rectangular shape including diametrically opposed first and second surface portions  236  and  238  having teeth  235 . Further, the main body portion  232  preferably has an axial length that is between 3 mm and 5 mm to allow the attachment device  230  to adapt to various skull thicknesses. 
     The end portion  250  of the attachment device  230  includes generally parallel first and second side surfaces  252  and  254 . The end portion  250  further includes a plurality of relief notches  256  located along a bottom edge  258  of the end portion. The relief notches  256  make it easier for the end portion  250  to bend laterally as indicated by arrows C and D, so that the attachment device  230  can adapt to a curved section of the first kerf edge  24  on the cranial flap  20 . 
     As with the previous embodiments, the end portion  250  has a first condition in which the end portion extends axially from the main body portion  232 . The end portion  250  further has a second condition in which the end portion extends generally radially from the main body portion  232  and the first side surface  252  faces upward. The end portion  250  of the attachment device  230  is deformable from the first condition to the second condition by heating the end portion to a predetermined elevated temperature. 
     The attachment device  230  is secured to the cranial flap  20  in same manner as the attachment device  30  of the first embodiment and therefore is not separately illustrated. The attachment device  230  is placed next to the cranial flap  20  so that the teeth  235  on the first surface portion  234  of the main body portion  232  of the attachment device engage the first kerf edge  24 . The inwardly facing surface  244  on the head portion  240  of the attachment device  230  is brought into engagement with the outer surface  25  of the cranial flap  20 . The attachment device  230  is positioned so that the first side surface  252  on the end portion  250  lies underneath and generally parallel to the first kerf edge  24  on the cranial flap  20 . 
     Next, the end portion  250  of the attachment device  230  is heated to a predetermined elevated temperature by a suitable heat source, such as the heat gun  60  shown schematically in FIG.  4 . Upon being heated to the predetermined elevated temperature, the end portion  250  of the attachment device  230  is deformed into the second condition by bending the end portion around the first kerf edge  24  of the cranial flap  20  in the direction of arrow B. The end portion  230  of the attachment device  250  is bent in the direction of arrow B until the first side surface  252  on the end portion engages the inside surface  26  on the cranial flap  20 . As the end portion  250  of the attachment device  230  cools and hardens, the attachment device becomes clamped to the cranial flap  20 . Cooling of the end portion  250  may be accelerated using a fan (not shown) or other suitable device. 
     With a suitable number of attachment devices  30 ,  130  and/or  230  secured to the cranial flap  20 , the cranial flap is then placed into the opening in the skull  10  in the same orientation as the cranial flap was removed from the opening. For the sake of clarity, only the attachment device  30  is further described, but it should be understood that the attachment devices  130  and  230  function in the same manner. 
     When the cranial flap  20  is placed into the opening in the skull  10 , the second surface portion  38  on the main body portion  32  of the attachment device  30  engages a second kerf edge  28  on the skull  10  (see FIG.  5 ). The cranial flap  20  is then pressed into the opening in the skull until the cranial flap becomes flush with the skull. As the cranial flap  20  is pressed into the flush position illustrated in FIG. 5, the teeth  35  on the first surface portion  36  of the attachment device  30  grip the first kerf edge  24  on the cranial flap  20 . Simultaneously, the teeth  35  on the second surface portion  38  of the attachment device  30  grip the second kerf edge  28  on the cranial flap  20 . Frictional engagement between the first surface portion  36  and the first kerf edge  24  and between the second surface portion  38  and the second kerf edge  28  cause the cranial flap  20  to be wedged in the opening in the skull  10 . This frictional engagement secures the cranial flap  20  to the skull  10 . 
     The method and apparatus disclosed above has several advantages. The method and apparatus saves valuable time during surgery. Screws and plates, known in the art, are not required. The bioabsorbable material of the attachment devices  30 ,  130 , and  230  do not show up permanently in CT scans. Finally, the attachment devices  30 ,  130  and  230  leave no permanent unsightly bumps under the patient&#39;s skin. 
     From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. For example, it will be apparent to those skilled in the art that a bioabsorbable screw or tack of some kind may be used to further secure the head portion of the attachment devices disclosed herein to the either the cranial flap or the skull. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.