Abstract:
A two-piece cut block for performing a minimally invasive partial or total knee arthroplasty. The present invention comprises a cut block that can be inserted into an incision in two parts then assembled in vivo. The two-piece design allows the relatively large surgical instrument to fit into a small, minimally invasive, surgical incision

Description:
RELATED APPLICATIONS  
         [0001]    There are no related applications.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates generally to medical instruments for aiding in the implantation of an endoprosthetic implant. More specifically, the present invention relates to a cutting guide for preparing a distal femur to accept the femoral component of a uni-condylar total knee implant during a minimally invasive surgical procedure.  
           [0004]    2. Description of the Related Art  
           [0005]    Partial knee replacement surgery has become relatively common. According to traditional practice, such surgeries require a relatively large incision through the soft tissue above a patient&#39;s knee, through which the various aspects of the partial knee arthroplasty are performed. These aspects include removing diseased bone and cartilage from the patient&#39;s knee and preparing the distal femur and proximal tibial to receive synthetic implants. For example, when a patient&#39;s knee deteriorates, cartilage wears away and the patient becomes either bow-legged or knock-kneed, depending on which side of the knee, medial or lateral, is diseased. Accordingly, surgery must be performed to realign the knee by seating artificial implants to replace the diseased portion of the patient&#39;s knee. Part of such a surgery involves resecting bone from the diseased side of the distal femur, such that the bone is appropriately shaped to receive an articulating artificial femoral component. In order to make sure such cuts are properly performed, and that soft tissue is not unnecessarily damaged, instruments called cut guides, which are well known in the art, are removably attached to the appropriate section of the distal femur, and are used to provide a mechanical stop to the saws introduced into the surgical field to make appropriate cuts on the distal femur. Larger surgical incisions naturally involve greater damage to skin, muscle connective tissue and the like, collectively referred to herein as soft tissues. As damage to a patient&#39;s soft tissue is increased, so too, is the time required for the patient to recover from surgery. This fact can cause a variety of negative economic effects. For example, a longer recovery time for a partial knee arthroplasty patient means a longer hospital stay. Physicians and hospitals, therefore, can accommodate fewer surgeries, and thus, the price to patients and their insurers increases for each individual surgery. Moreover, longer recovery times result in patients missing more time from work which may result in economic detriments for both the patient and his or her employer. However, a smaller incision results in a smaller scar and a generally more pleasing aesthetic effect for the patient.  
           [0006]    Accordingly, minimally invasive surgical (“MIS”) techniques have become available, which greatly reduce the size of the incision. Such smaller incisions, in the range of about 6-10 millimeters, vastly reduce the amount of time necessary for the patient to fully recover from a partial knee surgery. Thus, a need exists for minimally invasive surgical instruments that fit into smaller incisions, yet still useful to surgeons.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention relates to a cutting guide for use in minimally invasive partial knee arthroplasty. In order to easily fit within the small incision of a minimally invasive surgical procedure, the cutting guide of the present invention comprises two pieces; a frame piece that removably attaches to a partially prepared distal femur; and a body piece that removably attaches to the frame piece. Both the frame piece and the body piece contain slots for accommodating surgical saws. These slots lie in mutual alignment when the body piece is removably attached to the frame piece. In use, the cutting guide of the present invention operates as a mechanical stop to saws and post drills used to perform the final preparations of the femur.  
           [0008]    An advantage of the present invention is that by separating the cutting guide into two pieces, a surgeon can insert each piece into a surgical incision separately. Because the incision must accommodate only one component at a time, it can be smaller than if it had to accommodate both pieces at once. A smaller incision results in less initial trauma to the patient and therefore a faster recovery time.  
           [0009]    Other advantages and features of the present invention will be apparent to those skilled in the art upon a review of the appended claims and drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1: perspective view of a partially prepared distal femur.  
         [0011]    [0011]FIG. 2: exploded perspective view of the two-piece cut block assembly of the present invention.  
         [0012]    [0012]FIG. 2A: perspective view of two piece cut block assembly attached to distal femor.  
         [0013]    [0013]FIG. 3: perspective view of the frame according to the present invention.  
         [0014]    [0014]FIG. 3A: side elevation view of a frame according to the present invention.  
         [0015]    [0015]FIG. 3B: front elevation view of a frame according to the present invention.  
         [0016]    [0016]FIG. 4: perspective view of a cut block according to the present invention.  
         [0017]    [0017]FIG. 4A: side elevation view of a cut block according to the present invention.  
         [0018]    [0018]FIG. 4B: top view of a cut block according to the present invention.  
         [0019]    [0019]FIG. 5: side elevation view of a two piece cut block assembly according to the present invention, attached to a distal femur.  
         [0020]    [0020]FIG. 6: side elevation view of a resected distal femur. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]    As used herein, the following locational definitions apply. Anterior and posterior mean nearer the front or nearer the back of the body respectively. Thus, for the knee joint described herein, anterior refers to that portion of the knee that is nearer the front of the body, when the leg is in an extended position. Proximal and distal mean nearer to or further from the root of the structure, respectively. For example, the distal femur is a part of the knee joint while the proximal femur is closer to the hip joint. Finally, the adjectives medial and lateral mean nearer the median plane or further from the median plane respectfully. The median plain is an imaginary vertical plane through the middle of the body that divides the body into right and left halves.  
         [0022]    Referring now to FIG. 1, there is shown a perspective view of a human knee showing the portion of the distal femur upon which the present invention can be used. FIG. 2 shows an exploded view of a two-piece cut block assembly according to the present invention. FIG. 2 also shows a perspective view of partially prepared distal femur  200  (i.e. a distal femur having one condyle removed in preparation to receive a femoral condylar implant). For convenience, all of the descriptions and figures herein show the present invention used on only one side of the femur. It will be apparent to those skilled in the art, however, that a two-piece cut block according to the present invention can be used with either side of the femur yet remain within the scope of the present invention.  
         [0023]    Referring now to FIG. 2, there is shown an exploded prospective view of the two-piece cut block assembly  200  of the present invention, wherein assembly  200  comprises frame  300  and body  400 . Turning now to FIG. 3, there shown a perspective view of frame  300 . Frame  300  comprises a generally arched anterior portion  310 . Frame  300  further comprises lateral leg  320  and medial leg  330  that extend from arched portion  310  in a posterior direction. Disposed between, legs  320  and  330  is cross member  340 . Cross member  340  comprises opposing ends  341  and  342 . End  342  of cross member  340  is fixedly attached to leg  330  such that leg  330  and cross member  340  are perpendicular. End  341  of cross member  340  is fixedly attached to leg  320  such that leg  300  and cross member  340  are perpendicular. Frame  300  further comprises anterior window  350 . Window  350  is bound posteriorly by cross member  340 , anteriorly by anterior portion  310 , and by legs  320  and  330  on its lateral and medial sides, respectively. Anterior to cross member  340 , are slot  360  and groove  370 . Slot  360  is cut through leg  320  from the medial side of leg  320  through the lateral side of leg  320  at an angle corresponding to the angle of a desired cut to make on a particular femoral condyle. Groove  370  is cut into the lateral side of leg  330  at an angle equal to that of slot  360  such that a desired portion of the medial side of leg  330  remains intact as shown in FIG. 3. Slot  360  and groove  370  are co-planer and of sufficient size to accommodate a surgical bone cutting device. Slot  360  and groove  370  are of equal anterior/posterior height.  
         [0024]    Frame  300  further comprises bone contacting surface  302  and free surface  301 . Frame  300  further comprises bore  380  shown in FIGS. 3 and 3B. As shown in FIG. 3, bore  380  is located near the apex of portion  310  of frame  300  such that bore  380  is in communication with free surface  301  and bone contacting surface  302 . As further shown in FIG. 3, frame  300  comprises threaded bore  385  through cross member  340 , bore  385  is also in communication between surfaces  301  and  302 , and is used with an insertion/removal instrument.  
         [0025]    Frame  300  further comprises posterior window  355 . Referring again to FIG. 3, legs  320  and  330  extend posteriorly beyond cross member  340  to bottom  390 . Bottom  390  is disposed generally parallel to cross member  340 . Bottom  390  extends between legs  320  and  330 . Bottom  370  comprises opposing ends  391  and  392 . End  392  of bottom  390  is fixedly attached to leg  330  such that leg  330  and bottom  390  are perpendicular. Similarly, end  391  of bottom  390  is fixedly attached to leg  320  such that leg  330  and bottom  390  are perpendicular. Posterior window  355  is bounded anteriorly by cross member  340 , posteriorly by bottom  390 , laterally by leg  320  and medially by leg  330 . Posterior to cross member  340  in frame  300  are slot  365  and groove  375 . Slot  365  is cut through leg  320  in a medial/lateral direction at a desired angle in a position posterior to cross member  340 . Groove  375  is cut posterior to cross member  340  through only a desired amount of the lateral side of leg  330  such that the medial side of leg  330  remains intact. Slot  365  and groove  375  are co-planar, and both slot  365  and groove  375  correspond to a desired angle for a second femoral condylar resection cut. Continuing to refer to FIG. 3, there is shown foot  305 . Foot  305  is connected to bottom  390  and protrudes perpendicularly from bone contacting surface  302  of frame  300  in a direction opposing free surface  301  of frame  300 .  
         [0026]    Referring now to FIG. 4, there shown cut block  400 . Block  400  comprises free surface  420  and frame contacting surface  410 . Free surface  420  is curved in the anterior/posterior plane. Frame contacting surface  410  includes groove  430 . Groove  430  comprises a preferably rectangular cross-sectional shape, and is shaped appropriately to receive cross member  340  of frame  300  when block  400  is disposed on frame  300  in such a way that frame contacting surface  410  of block  400  abuts free surface  301  of frame  300 .  
         [0027]    Block  400  further comprises grooves  430  and  440 . Groove  440  is positioned anteriorly to groove  430  and is in communication between free surface  420 , frame contacting surface  410  and the lateral side of block  400 . Groove  430  is positioned at an angle through block  400  corresponding to a desired angle for cutting the lateral portion of a femoral condyle. Referring still to FIG. 4, block  400  further comprises groove  440  positioned posteriorally to groove  430 . Groove  440  is also in communication with surface  420 , surface  410 , and the lateral side of block  400 .  
         [0028]    Referring still to FIG. 4, block  400  further comprises bores  470  and  480 . Bore  470  traverses slot  430  in a medial lateral direction such that surfaces  410  and  420  are in communication through bore  470 . Block  400  further comprises threaded bore  480 , which bore  480  is in communication between surfaces  410  and  420  of block  400 . Bore  480  is disposed in block  400  such that it is concentric and in communication with bore  385  of frame  300  as shown in FIG. 2. Preferably bore  480  and bore  385  comprise equal diameters. In addition, bore  470  of block  400  is disposed therethrough such that the assembly of frame  300  and bore  400  results in the longitude axis of bore  470  being collinear with the center of window  385 . In addition, bore  470  is disposed through block  400  along groove  430 , such that groove  430  lies along the diameter of bore  470 .  
         [0029]    In FIG. 5, there is shown a side elevational view of an assembly according to the present invention. As shown in FIG. 5, surface  410  block  400  is disposed against surface  301  of frame  300  such that block groove  440  is in co-planar with slot  360  and groove  370  while groove  450  is in co-planar with slot  365  and groove  375  of frame  300 . In addition, slot  430  of block  400  is positioned to receive cross member  340  of frame piece  300 . The alignment of the afore mention slot, allows a cutting device to be inserted therethrough in order to resect one condyle of the distal femur.  
         [0030]    During a partial knee replacement surgery, the two-piece cut block assembly is used as a cutting guide for surgical tools used to make the final cuts to distal femur  100  to prepare distal femur  100  to accept a femoral condylar implant. FIG. 5, shows assembled two piece cut block  1 , attached to distal femur  200 . A broad description of the surgery is as follows: After making an appropriate incision on the skin around the knee, the surgeon selects an appropriately sized frame  300  based on the size of the flat surface found on partially prepared distal femur  200 . Frame  300  is inserted through an incision such that bone contacting surface  302  of frame  300  is adjacent to distal femur  200 , and foot  305  is oriented toward the posterior side of distal femur  200 . With a properly sized frame  300  in place, the surgeon drills a hole through bore  380  and into distal femur  200 . The surgeon then inserts a holding pin  510 . At this point, distal femur  200  is still visible to the surgeon through frame windows  350  and  355 . Next, the surgeon inserts body  400  through the incision (not shown) such that frame contacting surface  410  abuts free surface  301  of frame  300 . Body  400  is disposed against frame  300  such that cross member  340  of frame  300  is seated inside slot  430 . Pads  491  and, are seated inside windows  350  and  385  respectively. Bore  480  is aligned with bore  385 , such that seated, body  400  cannot rotate with respect to frame  300 . Next, the surgeon drills a second hole, through bore  480  of body  400 , and through bore  385  into distal femur  200 . Another holding pin  510  is then inserted through this second series of holes to retain frame  300  and body  400  in place. Persons skilled in the art will appreciate that additional holes may be provided on either frame  300 , body  400  or both, through which additional holes may be drilled into femur  200  and through which additional holding pins  510  may be placed. Finally, the surgeon drills a hole through body posterior pin hole  470  and window  360  into distal femur  200 . At this point the surgeon leaves the drill in place.  
         [0031]    Now that the two piece guide block assembly is in place, the surgeon can begin to make the final cuts to distal femur  200  in order to prepare distal femur  200  to accept a condylar implant. First, the surgeon removes the drill from bore  470  and window  355 . Next, the surgeon inserts the blade of a surgical cutting device through cutting slots  440  and  360  and  370  and makes the appropriate cut to distal femur  200 . Next, the surgeon removes holding pin  510  from bores  385  and  480 . The surgeon then inserts the blade of a surgical cutting device through anterior cutting slots  450  and  365  and  375  and makes the appropriate cut to distal femur  200 . Next, the final holding pin  510  is removed from frame  300 . Thereafter, the surgeon removes body  400  from frame  300 , and frame  300  from distal femur  200 . Finally, the surgeon completes the remaining steps of the partial knee replacement, including installing a femoral condylar implant on a fully prepared distal femur  200 .  
         [0032]    It will be appreciated by those skilled in the art that the foregoing is a description of a preferred embodiment of the present invention and that variations in design and construction may be made to the preferred embodiment without departing from the scope of the invention as defined by the appended claims.