Patent Publication Number: US-2007118138-A1

Title: Alignment and connection device of femur cutter and tibia cutter and method of knee arthroplasty using the same

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an alignment and connection device for aligning and connecting the femur cutter and tibia cutter in knee arthroplasty and a method of knee arthroplasty using the device. More particularly, the present invention relates to an alignment and connection device of femur cutter and tibia cutter by which it is possible to minutely follow the determined extension gap and three-dimensionally connect the alignment of femur cutter and tibia cutter, and a method of knee arthroplasty using the device.  
      2. Description of the Related Art  
      Knee arthroplasty has become one of the most commonly performed surgeries, in which a damaged or deformed knee joint due to congenital deformation, traumatic injuries, diseases, degenerative arthritis, etc. is removed and replaced with an artificial joint. In such a knee arthroplasty, accurate cutting of the damaged knee joint is very important to prevent side effects after surgery and prolong the life of the replaced artificial knee joint.  
       FIG. 1  is a view showing an ideal cutting of extension gap. As shown in the drawing, in order to cut an extension gap ideally, the femur and tibia should be aligned in agreement to a mechanical axis so that the bottom end cut surface of femur  11  and the top end cut surface of tibia  12  are maintained in parallel each other.  
      We will take a look at the conventional knee arthroplasty, in which, as shown in  FIG. 2   a , a femur cutter  21  is mounted on the bottom end of femur  11  using alignment device (not shown) and the bottom end of the femur  11  is independently cut through a cutting groove  21 - 1 . Next, as shown in  FIG. 2   b , a tibia cutter  22  is mounted on the top end of tibia  12  using alignment device (not shown) and the top end of the tibia  12  is independently cut through a cutting groove  22 - 1 . That is, in the conventional knee arthroplasty, the femur cutter  21  and tibia cutter  22  are mounted independently to the femur  11  and the tibia  12 , then the femur  11  and tibia  12  are cut independently of each other. However, the conventional arthroplasty of cutting by aligning the femur  11  and the tibia  12  independently has a problem in that since in the actual surgery the femur  11  and the tibia  12  are not aligned in agreement to the mechanical axis, the cut surface of the femur bottom end and the cut surface of the tibia top end are not in parallel, so it is impossible to cut the extension gap accurately.  
      To make up for this drawback, the present applicant filed a patent application for an alignment and connection device  30  for connecting the alignment of femur cutter and tibia cutter and had it registered as Korean Patent No. 399489. As shown in  FIG. 3 , the alignment and connection device has a latching part  31  on the top and a pinhole part  32  on the bottom formed into a body by a side plate  33 , and a fixation part has a plurality of pinholes  34  formed at a predetermined interval for pins P to be inserted.  
      Knee arthroplasty using the alignment and connection device according to the aforementioned patent will be briefly described with reference to  FIG. 4  and  FIG. 5 . In such a replacement surgery, a femur cutter  21  is mounted on the bottom end of the femur  11  with pins, and then a latching part  31  of an alignment and connection device  30  is inserted into the cutting groove  21 - 1  of the femur cutter  21  and pins P are inserted into the pinholes of the alignment and connection device  30  for a tibia  12  to be driven. Thereafter, the alignment and connection device  30  is separated from the femur cutter  21  and pins P, and the tibia cutter  22  is mounted on the tibia  12  with the pins P that were driven into the tibia  12 . Then, around the knee joint, the femur cutter  21  and the tibia cutter  22  are mounted in parallel each other on the bottom end of the femur  11  and the top end of the tibia  12 , as shown in  FIG. 5 . Therefore, the cut surface of the femur bottom end and the cut surface of the tibia top end can be in parallel each other.  
      For reference, an extension gap is the gap between the cutting groove  21 - 1  of the femur cutter  21  and the cutting groove  22 - 1  of the tibia cutter  22  in  FIG. 5 . In other words, the extension gap is the sum of the cut length of the femur bottom end and the cut length of the tibia top end. In a normal surgery, the cut length of the femur bottom end is 8 mm and the cut length of the tibia top end is determined by the surgeon depending on the condition of the patient. Meanwhile, in surgery, since the position of the cutting groove  22 - 1  of the tibia cutter  22  is determined by the position of the pins P inserted into the pinholes  34  and driven into the tibia  12 , the reference point of the extension gap becomes the position of the pinholes  34  of the alignment and connection device  30  for the pins P to be inserted. For example, if the surgeon determines the extension gap at 20 mm depending on the extent of damage of the patient&#39;s knee joint, the cut length of the femur bottom end becomes 8 mm and the cut length of the tibia top end becomes 12 mm. If you select any one of pinholes  34  that corresponds to the cut length of the tibia top end, and insert pin P, then eventually, the gap between the cutting groove  21 - 1  of the femur cutter  21  and the cutting groove  22 - 1  of the tibia cutter  22  becomes 20 mm.  
      Like this, the aforementioned patent uses the alignment and connection device  30  to make it possible for the cut surface of the bottom end of the femur  11  and the cut surface of the top end of the tibia  12  to be in parallel because the alignment of the femur cutter  21  and the tibia cutter  22  is not made independently of each other but in mutual connection.  
      However, the alignment and connection device  30  according to the aforementioned patent has a problem in that it is not possible to minutely follow the extension gap determined. As we have seen, the reference point of the extension gap is the position of the pinholes  34  of the alignment and connection device for pins P to be inserted, but these pinholes  34  are formed at an interval so it is not possible to follow the extension gap minutely and continuously. For example, if the surgeon determined the extension gap at 19.5 mm (the cut length of the femur bottom end: 8 mm, the cut length of the tibia top end: 11.5 mm) but there is no pinhole that corresponds to the extension gap, then the problem is you cannot determine the reference point of the extension gap required. Therefore, an alignment and connection device that can follow the determined extension gap minutely is required.  
      Another problem is that the alignment and connection device  30  according to the aforementioned patent cannot precisely compensate for the length of lax ligament if the ligament of knee joint becomes lax. For example, the surgeon determined the extension gap at 20 mm (the cut length of the femur bottom end: 8 mm, the cut length of the tibia top end: 12 mm). But in the case of the ligament being 0.5 mm lax, the extension gap selected is 19.5 mm (the cut length of the femur bottom end: 8 mm, the cut length of the tibia top end: 11.5 mm) to cut the femur and tibia, and finally an artificial knee joint of 20 mm (femur replacement: 8 mm, tibia replacement: 12 mm) is inserted to extend the ligament. Thus, the length of lax ligament can be compensated for. However, this device has a problem that the length of lax ligament cannot be precisely compensated for because pinholes  34  are formed at an interval as mentioned above. Therefore, in case the ligament of knee joint is lax, an alignment and connection device that can easily compensate for the lax ligament length is required.  
      In addition, according to the alignment and connection device  30  according to the above patent, the cut surface of the femur bottom end to be cut and the cut surface of the tibia top end to be cut are not aligned three-dimensionally. That is, the device has a problem in that it was possible to maintain parallel alignment of the femur  11  and the tibia  12  on the coronal axis, but it is not possible to maintain parallel alignment of the femur  11  and the tibia  12  on the sagittal axis and the rotation synchronization of the femur  11  and the tibia  12  on the transverse axis. For reference, parallel alignment on the coronal axis means the alignment on the mechanical axis of the femur and tibia when the knee joint is seen directly in front, as shown in  FIG. 6 . And parallel alignment on the sagittal axis means the alignment on the mechanical axis of the femur and tibia when the knee joint is seen laterally. And rotation synchronization on the transverse axis means the rotation synchronization of the tibia with respect to the femur when the knee joint is seen from top. Here, in the alignment and connection device  30  as shown in  FIG. 5 , it is possible to align the tibia in parallel with the femur with respect to the mechanical axis on the coronal axis, but on the sagittal axis, it is not possible to align the tibia in parallel with the femur with respect to the mechanical axis, so the tibia could be cut inclined on the sagittal axis. And it is not possible to synchronize the tibia with the rotation of the femur, so there is a fear that the tibia could be cut in rotation with respect to the femur. Therefore, an alignment and connection device by which it is possible to connect by three-dimensional alignment and synchronization of the femur cutter and the tibia cutter is required.  
     SUMMARY OF THE INVENTION  
      It is an object of the present invention to solve the aforementioned problems by providing an alignment and connection device of femur cutter and tibia cutter by which it is possible to minutely follow the extension gap determined.  
      It is another object of the present invention to provide an alignment and connection device of femur cutter and tibia cutter by which it is possible to align the femur cutter and the tibia cutter three-dimensionally.  
      It is yet another object of the present invention to provide a method of knee arthroplasty using the alignment and connection device.  
      In accordance with the present invention, there is provided an alignment and connection device of femur cutter and tibia cutter comprising: a fixation part in which a guide slot is formed in front center and a through hole for a locking pin to be inserted is formed on the side of the guide slot and an indicating line is marked thereon; a supporting part which is assembled slidably to the guide slot of the fixation part, and having a slider marked with specifications corresponding to the extension gap determined and a lug portion inserted into the cutting groove of the femur cutter; and a fixing means for fixing the supporting part to the fixation part.  
      Further, in accordance with the present invention, there is provided a Method of knee arthroplasty comprising the steps of: determining the extension gap based on the extent of damage of the knee joint of the patient; adjusting the slider of the alignment and connection device based on the extension gap determined, then fixing the slider to the fixation part with a fixing means; mounting the tibia cutter on the bottom end of the femur and driving a selective rotation prevention pin into the rotation center point of the femur top end; inserting the lug portion of the alignment and connection device into the cutting groove of the femur cutter simultaneously with inserting the first and second selective rotation prevention holes of the alignment and connection device into the selective rotation prevention pin driven into the tibia; inserting the inclination identifying pin into the inclination identifying slot formed on the bottom of the fixation part of the alignment and connection device, then adjusting the inclination of the inclination identifying pin and the tibia axis; inserting a locking pin into the through hole formed on front side of the fixation part of the alignment and connection device and driving it into the tibia; separating the selective rotation prevention pin and the alignment and connection device respectively from the tibia and femur cutter; mounting a tibia cutter with the locking pin driven into the tibia; cutting the femur bottom end through the femur cutter mounted on the femur, bending the femur in a bended state with respect to the tibia, and inserting again the separated alignment and connection device onto the locking pin driven into the tibia; positioning a cutting block size determination device in the femur such that the guide is placed on the top of the lug portion of the alignment and connection device and the bent part is placed on the first anterior cortex of the femur cut in advance; adjusting the cutting block size determination device to determine the size of the cutting block; cutting with the determined cutting block the posterior condyle, posterior chamfer, anterior chamfer and anterior cortex of the femur; and replacing an artificial knee joint between femur and tibia after cutting the top end of tibia by tibia cutter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Other objects and aspects of the present invention will become apparent from the following description of embodiments with reference to the accompanying drawings in which:  
       FIG. 1  is a view illustrating an ideal bone cutting of extension gap;  
       FIG. 2   a  is a view for describing mounting a femur cutter on the bottom end of the femur using a conventional alignment device;  
       FIG. 2   b  is a view for describing mounting a tibia cutter on the top end of the tibia using a conventional alignment device;  
       FIG. 3  is a perspective view of a conventional alignment and connection device;  
       FIGS. 4 and 5  are drawings for describing a knee arthropolasy using the conventional alignment and connection device shown in  FIG. 3 ;  
       FIG. 6  is a view for describing a coronal axis, sagittal axis, transverse axis, and mechanical axis;  
       FIG. 7  is a perspective view showing an assembled state of an alignment and connection device according to the present invention;  
       FIG. 8  is a perspective showing a disassembled state of an alignment and connection device according to the present invention;  
       FIG. 9  is a cross-section taken along line A-A′ of  FIG. 7 ;  
       FIG. 10  is a view showing how an alignment and connection device according to the present invention is mounted;  
       FIG. 11  is a view showing how an alignment and connection device and a cutting block size determination device according to the present invention are mounted on a tibia and femur respectively;  
       FIG. 12  is a view showing how a cutting block is mounted on a femur. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The present invention will be described in detail with reference to the accompanying drawings.  FIG. 7  is a perspective view showing an assembled state of an alignment and connection device according to the present invention, and  FIG. 8  is a perspective view showing a disassembled state of the alignment and connection device according to the present invention, and  FIG. 9  is a cross-section taken along line A-A′ of  FIG. 7 . For the sake of convenience, the same symbols are given to the constituents that are the same with the conventional device.  
      Referring to  FIGS. 7 through 9 , an alignment and connection device  100  according to the present invention includes a fixation part  110 , supporting part  120  and a fixing means  130 .  
      The fixation part  110  includes a guide slot  111  formed in front center. To the guide slot  111  is slidably assembled a slider  121  of the supporting part  120  which will be described later. On both sides of the guide slot  111  are formed a pair of through holes  112 , and into the through holes  112  are inserted locking pins  113  before driven into the top end of tibia  12 . And on both sides of the front of the fixation part  110  are marked indicating lines  114  for indicating the specifications marked on the slider  121 . It is preferable that an inclination identifying slot  115  for an inclination identifying pin  116  to be inserted is formed in a predetermined length on the bottom of the fixation part  110 , in order to be able to identify whether the sagittal axis is inclined. It is also preferable that an extension gap preview slot  117  is formed above the through hole  112  of the fixation part  110  so as to preview the extension gap. Also, part of the rear side of the fixation part is preferably in a predetermined round  118  form so as to come into close contact with the front protrusion of the tibia.  
      The supporting part  120  is slidably assembled to the guide slot  111  of the fixation part  110 , and the upper end of the supporting part  120  is configured so as to be inserted in the cutting groove  21 - 1  of the femur cutter. Specifically, the supporting part  120  comprises the slider  121  that is slidably assembled to the guide slot  111  of the fixation part  110  and a lug portion  122  that is inserted into the cutting groove  21 - 2  of the femur cutter  21 . Also, on the front of the slider  121  are marked specifications  123  corresponding to the extension gap determined.  
      It is preferable that the contact surface of the slider  121  and the guide slot  111  is in an inwardly tapered form, but it is not limited to this, and a stepped form is also possible. Furthermore, on the upper side of the slider  121  is formed a first selective rotation prevention hole  124 , and on the upper side of the guide slot  111  of the fixation part  110  is formed a second selective rotation prevention hole  119  that corresponds to the first selective rotation prevention hole  124 . Here, the first and second selective rotation prevention holes  124  and  119  are provided lengthwise in a long hole, and the top end of the second selective rotation prevention hole  119  is formed in an open end as shown in drawing. The first and second selective rotation prevention holes  124  and  119  are provided to be inserted onto a selective pin  125  that was driven in advance in the rotation center of the tibia top end, as will be described later. The diameter of the selective rotation prevention pin  125  is formed substantially equal to or less than the width of the first and second selective rotation prevention holes  124  and  119 .  
      Meanwhile, as shown in  FIG. 9 , a longitudinal slot  126  is formed on the rear side of the slider  121 , and a protruding pin  140  introduced into the long slot  126  can be forcibly inserted into the fixation part  110  from the back. Due to the forcibly inserted protruding pin  140 , the slider  126  and the fixation part  110  can be prevented from breaking away each other.  
      It is preferable that the fixing means  130  is a locking bolt to be inserted into the screw hole  127  of the slider  121 .  
      The operation of the alignment and connection device according to the present invention will be described together with the description of the method of knee arthroplasty.  
      In the method of knee arthroplasty using the alignment and connection device according to the present invention, first the slider  121  is adjusted to fit the extension gap determined by the surgeon, and then the slider  121  is fixed to the fixation part  110  with the locking bolt  130 . That is, as shown in  FIG. 7 , if the surgeon determined the extension gap at 20 mm (the cut length of the femur bottom end: 8 mm, the cut length of the tibia top end: 12 mm) according to the condition of the patient, the slider  130  is fixed to the fixation part  110  with the locking bolt  130  such that the indicating line of the fixation part indicates the graduation  12  of the slider  121 . Then, the length from the actual extension gap preview slot  117  to the lug portion  122  becomes 20 mm, the extension gap. That is, the graduation listed on the slider  121  shows the cut length of the tibia top end to be cut. At this time, the extension gap is the length of the lug portion  122  from the preview slot  117 . However, the present invention is not limited to this, but may as well be designed such that the graduation itself listed on the slider  121  shows the extension gap, which is the sum of the cut length of the femur bottom end and the cut length of the tibia top end.  
      When the slider  121  is fixed according to the extension gap, the femur cutter  21  is mounted on the bottom end of the femur  11  with the pin  23  and the selective rotation prevention  125  is driven into the rotation center point of the top end of the tibia  12 , as shown in  FIG. 10 . Then, the lug portion  122  of the alignment and connection device  100 , and the first and second selective rotation prevention holes  124  and  119 , are inserted and left into the cutting groove  21 - 1  of the femur cutter  21 , and the selective rotation prevention pin  125  driven into the tibia  12 , respectively. At this time, since the diameter of the selective rotation prevention pin  125  is substantially equal to or less than the width of the first and second selective rotation prevention holes  124  and  119 , and the selective rotation prevention pin  125  is driven into the rotation center of the tibia top end, the alignment and connection device  100  is aligned while maintaining the rotation synchronized on the transverse axis with respect to the femur cutter  21 .  
      Thereafter, the inclination identifying pin  116  is inserted into the inclination identifying slot  115  formed on the bottom of the fixation part  110 , and the extent of agreement of the inclination identifying pin  116  and the tibia axis is checked. If the inclination identifying pin  116  and the tibia axis are inclined at a predetermined angle (that is, if the alignment on the sagittal axis is not agreed), the tibia  12  is moved to make the tibia axis agree with the inclination identifying pin  116 . At this time, because the selective rotation prevention pin  125  driven into the tibia can be moved up and down within the selective rotation prevention hole  124  with the rotation center point of the tibia as the hinge point, the alignment and connection device can be maintained in parallel arrangement also on the sagittal axis with respect to the femur cutter  21 .  
      Meanwhile, parallel arrangement on the coronal axis also can be accomplished by minutely moving the tibia left or right of the inclination identifying pin  116 .  
      Like this, when alignment with respect to the three axes (coronal axis, sagittal axis and transverse axis) is accomplished, the locking pin  113  is inserted into the through hole  112  formed on front side of the fixation part  110  while maintaining the alignment and is driven into the tibia  12 . Because the alignment and connection device  100  has a 3-axis alignment accomplished, the locking pin  113  driven into the tibia  12  has also a 3-axis alignment accomplished. Drive the locking pin  113  into the tibia and separate the selective rotation prevention pin  125  and the alignment and connection device  100  from the tibia  12  and the femur cutter  21 , respectively. Then, only two locking pins  113  will remain. Thereafter, mount the tibia cutter  22  with the locking pin  113  remaining in the tibial  12 . Then, as shown in  FIG. 5 , the femur  11  will have the femur cutter  21  mounted, and the tibia  12  will have only the tibia cutter  22  mounted. Although not shown, the three-dimensional shape of  FIG. 5  shows alignment accomplished three-dimensionally. Also, the position of the cutting groove  22 - 1  of the tibia cutter  22  comes into position corresponding to the position of the preview hole  117  of the alignment and connection device  100 .  
      As mentioned above, the alignment and connection device according to the present invention has the following advantages.  
      First, it can provide an alignment and connection device that can minutely follow the extension gap determined. That is, in the conventional alignment and connection device, the extension gap is followed by pinholes with intervals, so it was not possible to follow the extension gap minutely, but in the alignment and connection device according to the present invention, the extension gap is followed by the slider and the sliding method of the fixation part, so it has an effect that the extension gap can be followed linearly and continuously.  
      Second, if the ligament of knee joint becomes lax, the length of lax ligament can be easily compensated for. As mentioned above, the alignment and connection device according to the present invention can follow the extension gap continuously, so it has an effect that surgery is possible by easily changing the extension gap as much as the length of ligament to be compensated for.  
      Third, it can provide an alignment and connection device that can connect by three-dimensional synchronization of the alignment of the femur cutter and tibia cutter. That is, the present invention can make rotation synchronization on the transverse axis by the selective rotation prevention pin, and can accomplish parallel alignment on the sagittal axis and minute parallel alignment on the coronal axis by the inclination identifying pin, so it has an effect that connection is possible by three-dimensional synchronization of the alignment of the femur cutter and tibia cutter.  
      After the femur cutter  21  and the tibia cutter  22  are mounted on the femur  11  and the tibia  12  respectively, the alignment and connection device  100  according to the present invention and the cutting block size determination device according to the PCT Application No. PCT/KR2004/000703 filed by the present applicant are used in surgery of knee arthroplasty, which will be described below. Note: The cutting block size determination device and circumferential explanation on this are described in detail in PCT Application No. PCT/KR2004/000703 which is herein incorporated by reference.  
      After the femur cutter  21  and the tibia cutter  22  are mounted respectively on the femur  11  and the tibia  12 , the bottom end of the femur  11  is cut by the femur cutter  21 . As shown in  FIG. 11 , after the femur  11  is bent in a bended state with respect to the tibia  12 , the removed alignment and connection device  100  is inserted again onto the locking pin  113  driven into the tibia  12 . Next, the cutting block size determination device  200  disclosed in PCT Application No. PCT/KR2004/000703 is positioned in the femur  11  with the primary anterior cortex  11 - 1  cut in advance to determine the cutting block size.  
      Here, in the cutting block size determination device  200 , make a guide  201  be placed on the top of the lug portion  122  of the alignment and connection device and a bent part  202  be placed on the primary anterior cortex  11 - 1  cut in advance. When the cutting block size determination device  200  is positioned in the tibia  11  like this, it judges the graduation of a body  204  indicated by the indicating line of the slider  203  to determine the cutting block size. Next, as shown in  FIG. 12 , the posterior condyle  11 - 2 , the posterior chamfer  11 - 3 , the anterior chamfer  11 - 4  and the anterior cortex  11 - 5  of the femur are cut with the cutting block  300  of determined size.  
      Thereafter, the top end of the tibia  12  is cut by the tibia cutter  22 , and an artificial knee joint is replaced between the cut femur and tibia.  
      As described above, according to the alignment and connection device of the present invention, there is provided an alignment and connection device by which it is possible to follow the determined extension gap minutely, compensate for the length of lax ligament easily, and connect by three-dimensionally synchronizing the alignment of femur cutter and tibia cutter. In addition, the knee arthroplasty using such an alignment and connection device has effects of preventing side effects after surgery and prolonging the life of the replaced artificial knee joint.  
      While the present invention has been described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the present invention as defined by the following claims.