Abstract:
A device and method for resecting a distal portion of a femur comprises a distal cutting guide [ 98],  a valgus guide [ 102],  and a variable collet [ 10].  The distal cutting guide [ 98]  is configured to overlie an anterior portion of the femur and comprises a slot for guiding a cutting tool across a distal portion of the femur. The valgus guide [ 102]  is configured to connect to the distal cutting guide [ 98] . The valgus guide [ 102]  is configured to align the slot of the distal cutting guide[ 98]  at the proper varus/valgus angle. The variable collet [ 10]  is configured to attach to an intramedullary rod and the valgus guide [ 102].  The variable collet [ 10]  comprises a port [ 30]  for receiving the intramedullary rod. The port [ 30]  is angularly adjustable with respect to the valgus guide [ 102]  such that adjusting the port [ 30]  adjusts the varus/valgus angle of the distal cutting guide [ 98].

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/828,158, filed Oct. 4, 2006. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates generally to cutting guides and blocks for bone preparation of a femur and, more particularly, distal cutting guides for preparation of the distal portion of the femur. 
         [0004]    2. Related Art 
         [0005]    In preparing the knee for implantation of a prosthesis in knee replacement surgery (either total knee replacement or partial knee replacement), the distal femur requires cuts on the bone in precise locations and precise planar angles. In many instances, the first cut may be a distal cut on the femur. Further cuts, including anterior, posterior, and any intermediate angled cuts, may be referenced from the distal cut. Thus, the distal cut may be used to orient all other cuts on the distal portion of the knee. Properly aligning the distal cutting block prior to making the distal cut may create a better fit and better performance of knee prosthesis. 
         [0006]    Fixation of the cutting block to the femur has been accomplished by intramedullary (IM) rods or by pinning the guide to the femur. The IM rod may also be used as an alignment guide to orient a distal cutting guide. However, a surgeon does not align the cutting block perpendicular to the IM canal (the anatomical axis of the femur). Instead, the surgeon may align to a default angular offset that is built in to the cutting guide and is fixed within the cutting guide. Thus, if the surgeon desires to adjust the angle between the IM canal and the cutting guide (which affects the varus/valgus angle between the femur and tibia) then a different cutting block may be required having a different fixed cutting guide orientation. Additional cutting guide orientations require those blocks to be sterilized and present in the operating room at the time of surgery. This increases the possibility of error and may increase operating room time. 
         [0007]    Other cutting blocks may include variability in the cutting guides relative to the pinned portions of the cutting block, but these cutting guides generally offset the plane of the cutting guides relative to the cutting blocks. Such changes may affect the amount of the resection and result in improper installation and performance. 
         [0008]    Thus, there remains a need in the art for an easily adjustable distal cutting block for locating distal cutting guides for proper angle and depth of the distal resection. 
       SUMMARY OF THE INVENTION 
       [0009]    It is in view of the above problems that the present invention was developed. A device and method for resecting a distal portion of a femur may comprise a distal cutting guide, a valgus guide, and a variable collet. The distal cutting guide is configured to overlie an anterior portion of the femur and comprises a slot for guiding a cutting tool across a distal portion of the femur. The valgus guide is configured to connect to the distal cutting guide. The valgus guide is configured to align the slot of the distal cutting guide at the proper varus/valgus angle. The variable collet is configured to attach to an intramedullary rod and the valgus guide. The variable collet comprises a port for receiving the intramedullary rod. The port is angularly adjustable with respect to the valgus guide such that adjusting the port adjusts the varus/valgus angle of the distal cutting guide. 
         [0010]    Another embodiment comprises a locking portion configured to fix the variable collet to the intramedullary rod. 
         [0011]    Yet another embodiment comprises a depth gage configured to adjust the depth of the distal cutting guide relative to the femur. 
         [0012]    Alternatively, the depth gage may be further configured to fix the distal cutting guide to the valgus guide. 
         [0013]    Another embodiment of the distal cutting guide includes a unicondylar distal cutting guide. 
         [0014]    In yet another embodiment, the port has a first end and a second end, the first end configured to receive an end cap and the second end configured with a spherical surface, the spherical surface being a bearing surface configured to rotate the port within the collet. 
         [0015]    Another embodiment further comprises a tensioner portion configured to tension the port such that the tension is generated from a force exerted oppositely on the spherical surface and the end cap. 
         [0016]    Yet another embodiment further comprises a bias member configured to bias the tensioner portion. 
         [0017]    Alternatively another embodiment of the valgus guide is fixed at an angle other than a perpendicular angle to the variable collet thereby aligning the slot of the distal cutting guide at a nonperpendicular angle to the anatomical axis of the femur. 
         [0018]    Another embodiment further comprises indicia on the collet at the port to adjustably align the varus/valgus angle of the distal cutting guide. 
         [0019]    A method of resecting a distal portion of a femur may comprise driving an intramedullary rod in the intramedullary canal of the femur. Another step may align a slot over an anterior portion of the femur. A step attaches a guide to the intramedullary rod. Another step attaches the slot to the guide. The slot is angularly adjustable with respect to the guide such that adjusting the guide adjusts the varus/valgus angle of the slot. 
         [0020]    Another embodiment further comprises the step of locking the guide to the intramedullary rod. 
         [0021]    Yet another embodiment further comprises the step of adjusting the depth of the slot relative to the femur. 
         [0022]    An embodiment further comprises the step of fixing the slot to the guide. 
         [0023]    Alternatively, the slot guides a unicondylar distal cutting tool. 
         [0024]    In another embodiment, the method step of attaching the slot to the guide step further comprises rotating the guide relative to a bearing surface to adjust the varus/valgus angle of the slot with respect to the guide. 
         [0025]    In yet another embodiment, the method step of locking further comprises the step of tensioning the guide such that the guide is fixed to the intramedullary rod. 
         [0026]    In another embodiment, the method further comprises the step of biasing the guide in tension such that a force is required generally along the axis of the intramedullary rod to tension the guide. 
         [0027]    Alternatively, the guide is fixed at an angle other than a perpendicular angle to the intramedullary rod thereby aligning the slot at a nonperpendicular angle to the anatomical axis of the femur. 
         [0028]    Another embodiment further comprises the step of indicating the varus/valgus angle of the guide. 
         [0029]    The invention has several advantages over prior devices and techniques which may be addressed by some of the embodiments. First, the number of necessary cutting blocks may be limited. Second, accurate placement, which may lead to better performance of the knee prosthesis is allowed from the ability to adjust the varus/valgus angle. Other advantages of the embodiments may also be apparent from the type of cutting block used. 
         [0030]    Further features, aspects, and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    The accompanying drawings, which are incorporated in and form a part of the specification, illustrate embodiments of the present invention and together with the description, serve to explain the principles of the invention. In the drawings: 
           [0032]      FIG. 1  is an embodiment of a variable collet; 
           [0033]      FIG. 2  is a side view of the variable collet of  FIG. 1 ; 
           [0034]      FIG. 3  is another view of the variable collet of  FIG. 1 ; 
           [0035]      FIG. 4  is a cutaway of the variable collet of  FIG. 1 ; 
           [0036]      FIG. 5  is a cutaway of the variable collet of  FIG. 1  showing a separate orientation of the collet; 
           [0037]      FIG. 6  is an exploded view of the variable collet of  FIG. 1 ; 
           [0038]      FIG. 7  is another exploded view of  FIG. 6 ; 
           [0039]      FIG. 8  is a cutaway of the exploded view of  FIG. 6 ; 
           [0040]      FIG. 9  is a variable collet attached to an IM rod and a femur; 
           [0041]      FIG. 10  is a variable collet attached to a femur; 
           [0042]      FIG. 11  is a variable collet attached to a unicondylar cutting guide; and 
           [0043]      FIG. 12  is a distal view of a variable collet. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0044]    Referring to the accompanying drawings in which like reference numbers indicate like elements,  FIG. 1  is an embodiment of a variable collet  10 . The variable collet  10  includes an IM rod guide  12 , an upper tensioner portion  14 , a lower locking portion  16  and a distal cutting frame  18 . The IM rod guide  12  includes a tensioner cap  20  and a varus/valgus indicator  22 . The distal cutting guide frame  18  includes distal block assembly receiving slots  24 , intracondylar guides  26  and a set screw  28 . The collet  10  is configured to slide over an IM rod to position a distal cutting block in the proper orientation. The IM rod guide  12  orients the angle between the IM rod and the distal cutting block. The locking portion locks the angle in place. The distal cutting frame  18  sets the plane for the distal cutting guide. 
         [0045]    The distal cutting block (examples of which are shown in  FIGS. 9-12 ) is oriented in a plane defined by the receiving slots  24 . The receiving slots are fixed with respect to the locking portion  16 . The receiving slots  24  may be perpendicular to the locking portion  16  or may be placed at an angle to the locking portion  16 . The angular offset may be set to align the distal cutting block along the mechanical axis of the femur. The varus/valgus indicator  22  may indicate the angle either relative to the offset, or relative to the actual varus/valgus angle. 
         [0046]    In  FIG. 1 , the embodiment is offset 6 degrees from perpendicular. 
         [0047]    Changing the angle of the IM rod guide  12 , then, rotates the varus/valgus angle from the 6 degree offset value built into the collet  10 . While the embodiment shown is at 6 degrees, any choice of offset may be given. Changing the offset may be beneficial based upon the population of likely surgical candidates. The minimum and maximum varus/valgus angle is determined from the amount of rotation the IM rod guide  12  can achieve in the collet  10 . The range of angles from the offset may be equally spaced from the offset, for example, by setting the offset at an expected average for a population, then variation from the average, assuming a normal distribution, would allow for most of the population to be easily adjustable from the average. If, however, the population has a skewed distribution, then the average may not be best accounted for by offsetting the angle so that the range encompasses as many possible members of the population as possible. Instead, the skew may dictate setting the angle closer to the longer tail of the distribution to allow for the variable collet  10  to be used on as many people as possible. 
         [0048]    Once the angle is set, then the locking portion  16  is rotated to lock the IM rod guide  12  in place. The locking portion  16  rotates relative to the tensioner portion  14 . The tensioner portion  14  extends from the locking portion  16 . The tensioner portion  14  presses against the tensioner cap  20  and the varus/valgus indicator  22  to lock the IM rod guide  12 . The tensioner portion  14  may be any device that puts tension on the IM rod guide  12  to lock the IM rod guide  12  in place with respect to the receiving slots  24 . 
         [0049]    The distal cutting guide frame  18  sets the depth and orientation of the cutting guide. The depth is set by the intracondylar guides  26 . The guides  26  position the receiving slots  24  above the intracondylar notch. The collet  10  slides down the IM rod until the intracondylar guides  26  rest in the notch. The receiving slots set the angle of the distal block relative to the IM rod. The set screw  28  may be used to fix the cutting block to the frame  18 . 
         [0050]    Turning now to  FIG. 2 ,  FIG. 2  is a side view of the variable collet  10  of  FIG. 1 . The collet  10  shows the intracondylar guides  26  are displaced anteriorly and posteriorly from the center of the collet  10 . The indicators  22  also may be located on both anteriorly and posteriorly (A/P plane). The cutting block guides  24  are also oriented in the A/P plane so that the distal cutting block does not rotate in the A/P direction. The other portions of the collet  10 , including the locking portion  16 , the IM rod guide  20  and the upper tensioner  14  are generally cylindrical so that rotation may be achieved with the surgeon&#39;s fingers. However other shapes may be used for ease of use, such as hexagonal cross sections (like a bolt). 
         [0051]    The upper face of the tensioner portion  14  may be rounded. The surface may be rounded to accommodate the rotation of the IM rod guide  12 . The arc of the surface may be an arc having a radius the length of the IM rod member. This allows for the IM rod member to rotate without having to change the tension in the tensioner portion  14 . 
         [0052]    Turning now to  FIG. 3 ,  FIG. 3  is another view of the variable collet  10  of 
         [0053]      FIG. 1 . The IM rod guide  12  includes an IM rod port  30  and varus/valgus indicia  32 . The IM rod port  30  receives an IM rod. The port  30  extends fully through the collet  10 , passing through the locking portion  16  and the cutting guide frame  18 . The indicia  32  may display numerical values for varus/valgus angle or may set a plus/minus from the offset. The indicia  32  may include indices for any number of possible settings. The example shown has an index for the offset, one for a more varus orientation, and one for a more valgus orientation. While there are only three indices, the amount of variation is not limited to only those three positions. The collet  10  may be set to any value within the range from varus to valgus angles rotatable in the collet  10 . 
         [0054]    The angular range of the collet  10  is controlled by a tensioner slot  34 . The tensioner slot  34  sets the range of motion of the IM rod guide  12  in the medial-lateral direction. The walls of the tensioner slot  34  limit the motion. 
         [0055]    The set screw  28  is threaded into the distal cutting guide frame  18 . The set screw may be a hex head screw which may be tightened onto the cutting block assembly to hold the assembly rigid to the collet  10 . An indention on the tensioner  14  may allow for clearance of a tool to set the set screw  28 . Other tightening mechanisms (like a thumb wheel, a cam, etc.) may be used instead of the hex head set screw  28 . 
         [0056]    Turning now to  FIG. 4 ,  FIG. 4  is a cutaway of the variable collet of  FIG. 1 . The IM rod guide  12  includes an IM rod tube  36  and a wave spring  42 . At one end, the IM rod tube  36  has a threaded tube portion  38  which threads into the tensioner cap  20 . At the other end, a spherical end portion  40  is the rotating surface between the tube  36  and the frame  18 . The frame  18  also includes a threaded frame portion  44  which threads into the locking portion  16 . The wave spring  42  is positioned between the locking portion  16  and the tensioner portion  14 . The wave spring  42  biases the tensioner portion  14 . Other connections may be used to exert force from the locking portion  16  to the tensioner portion  14 . 
         [0057]    The tensioner cap  20  is pressed against the tensioner portion  14  by rotating the locking portion  16 . The locking portion  16  rotates on the threaded portion  44  upward to press against the wave spring  42 . The wave spring biases and pushes the tensioner portion  14  against the tensioner cap  20 . When the tensioner portion  14  presses against the tensioner cap  20 , the IM rod tube  36  is tensioned between the interface at the tensioner cap  20  and tensioner portion  14  and the interface between the spherical end portion  40  and the cutting guide frame  18 . 
         [0058]    In  FIG. 4 , the IM rod tube is fully rotated to the left (corresponding to the negative orientation from the indicia shown in  FIG. 2 . In contrast, turning now to  FIG. 5 ,  FIG. 5  is a cutaway of the variable collet  10  of  FIG. 1  showing a separate orientation of the collet  10 . The IM tube rod  36  is fully rotated to the right (corresponding to the positive orientation from the indicia shown in  FIG. 2 . The tensioner cap  20  abuts the tensioner slot  34  on the left side of the slot  34 . The spherical end portion  40  allows for the tube  36  to be rotated while maintaining contact with the frame  18 . 
         [0059]    Turning now to  FIG. 6 ,  FIG. 6  is an exploded view of the variable collet  10  of  FIG. 1 . The tube  36  is inserted from below through the frame  18 . The locking portion  16  is threaded onto the frame  18 . The spring  42  and tensioner portion  14  are placed within the locking portion  16 . The tensioner portion  14  is free to rotate within the locking portion  16 . The tensioner cap  20  is threaded onto the threaded tube portion  38  to connect all portions of the collet  10  between the spherical end portion  40  and the tensioner cap  20 . 
         [0060]    Turning now to  FIG. 7 ,  FIG. 7  is another exploded view of  FIG. 6 . The locking portion  16  includes a cavity  50  to receive the wave spring  42  and the tensioner portion  14 . Additionally, the rectangular cross section of the tensioner cap slot  34  is shown. The tensioner portion  14  is hollow to allow for the tube  36  to rotate. The tensioner slot  34  guides the IM tube  36  to only move in one direction. The rod tube  36  is received between the intracondylar guides  26 . 
         [0061]    Turning now to  FIG. 8 ,  FIG. 8  is a cutaway of the exploded view of  FIG. 6 . The wave spring  42  rests between a locking portion abutting surface  60  and a tensioner portion abutting surface  64 . The tensioner portion  14  includes a threaded frame portion recess  66  configured to receive the threaded portion of the frame when the locking portion  16  is rotated and translates along the axis of the frame  18 . 
         [0062]    A flat  70  on the set screw  28  retains the set screw within the frame  18 . The flat also creates the interference fit between the frame  18  and the distal cutting block assembly. The flat is oriented at the angle of the slots  24  so that the entire flat surface  70  contacts the block assembly. 
         [0063]    A spherical recess  72  on the frame  18  receives the IM rod  36 . The spherical recess  72  is the surface which allows for rotation of the IM rod  36 . The center of rotation of the IM rod is the center of the spherical recess  72 , which is generally below the collet  10 . 
         [0064]    Turning now to  FIG. 9 ,  FIG. 9  is a variable collet attached to an IM rod  74  and a femur  78 . A distal cutting block assembly  76  is attached to the collet  10 . In this embodiment, the distal cutting block assembly  76  is a cutting block for a primary total knee arthroplasty (TKA). However, other distal blocks, for example a revision or a unicompartmental cutting block, may alternatively be used depending on the type of surgical procedure being performed. The TKA cutting block  76  align along condyles  80  of the femur  78 . 
         [0065]    The cutting block assembly  76  may include a valgus alignment guide  81  and a distal cutting guide  82 . The valgus alignment guide  81  includes floating spikes  84  and collet receiving slots  86 . A cam  88  connects the distal cutting guide  82  to the valgus alignment guide  81 . The cam  88  may be a thumb knob retaining member or any other connector to attach the distal cutting guide  82  to the valgus alignment guide  81 . The floating spikes  84  may couple the valgus alignment guide  81  to the condyles  80  of the femur  78 . 
         [0066]    The collet  10  is placed over the IM rod  74  and lowered to the femur  80 . The valgus alignment guide  81  is slid into the collet  10 . The collet receiving slots  86  are slidably received along the receiving slots of the collet  10 . The distal cutting guide  82  is attached perpendicularly to the valgus alignment guide  81 . The cam  88  fixes the distal cutting guide  82  to the valgus alignment guide  81 . 
         [0067]    Turning now to  FIG. 10 ,  FIG. 10  is a variable collet  10  attached to a femur  78 . The femur  78  has already been prepared with an anterior resection  94 . The distal cutting guide  82  may further include a depth gage  90  and spike holes  92 . The depth gage  90  sets the depth of the distal cutting guide  82 . The cam  88  fixes the depth of the cutting guide  82 . When the depth is set, the surgeon may use spikes to fix the distal cutting guide  82  to the femur  78 . The IM rod  74  and the collet  10  may then be removed before the distal cut is made. If additional depth is needed, then the depth of the distal cutting guide  82  may be adjusted by using the same holes in the femur, but using the adjacent spike holes  92 . The distal cutting plane is then defined by the slot within the distal cutting guide  82 . 
         [0068]    The center of rotation of the collet  10  is approximately aligned with the cutting slot of the distal cutting guide  82 . 
         [0069]    Turning now to  FIG. 11 ,  FIG. 11  is a variable collet  10  attached to a unicondylar distal cutting guide  98 . Spikes  100  fix the cutting guide  98  to the bone. The slot for making the distal cut for a unicondylar distal cutting guide  98  is positioned for cutting a single condyle  80  of the femur  78 . 
         [0070]    Turning now to  FIG. 12 ,  FIG. 12  is a distal view of a variable collet  10 . A valgus alignment guide  102  may not have floating spikes as in previous embodiments. The valgus alignment guide  102  still aligns within the slots of the collet  10 . Additionally, spikes  100  may have grooves which allow for extraction of the spikes from the guide  98 . 
         [0071]    In surgery, the surgeon first places the IM rod in the intramedullary canal. The variable collet, valgus alignment guide and distal cutting block are assembled and attached to the IM Rod. Then the valgus angle is adjusted as necessary. In one embodiment, when an anterior cut is already made, the adjustment aligns the lateral side of the distal cutting block either equal to or slightly proximal to the transition point. The transition point is the most distal point of the anterior cut on the lateral side. The variable collet is adjusted by first loosening the locking portion and then by pushing down on the tensioner portion to adjust to a different angle. 
         [0072]    Next, the depth of the distal cutting guide is set. In one embodiment, the depth may be determined by using shims Femoral shims (for example, −2, 0 or +2 mm), assess the amount of distal resection. The 0 mm shim represents 9 mm of distal resection, which is equal to the thickness of the femoral implant. If this is chosen, this will be a measured resection. If necessary, more or less distal bone may be resected to account for flexion/extension stability. 
         [0073]    Once the angle and the depth are set, then pins or spikes may be used to fix the cutting block to the femur. The variable collet, valgus alignment guide and IM rod may be removed for better visibility. The distal portion of the condyle or condyles may then be resected. The pins may then be removed and the guide removed from the femur. 
         [0074]    In view of the foregoing, it will be seen that the several advantages of the invention are achieved and attained. 
         [0075]    The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. 
         [0076]    As various modifications could be made in the constructions and methods herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.