Abstract:
A reamer for reaming a joint between at least two bones comprises a housing, a plurality of cutting blades, and a power source. The housing is configured to be inserted within the joint. The plurality of cutting blades is configured to couple to the housing. The plurality of cutting blades creates a cutting surface. The power source is coupled to the housing and configured to deliver motion to the cutting blades such that the cutting blades cut at least one bone of the at least two bones. The method of resurfacing a bone comprises the steps of placing a reamer substantially within a bone joint. The reamer has a housing and a plurality of cutting blades. The cutting blades are configured to bear upon a bone surface. Motive force is delivered to the housing. The motive force drives the plurality of cutting blades to ream the bone surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/942,604, filed Jun. 7, 2007 the disclosure of which is hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates generally to implants and processes in joint surgery, particularly knee surgery, and more particularly tibial preparation. In certain embodiments, the invention relates to tibial resurfacing guided by soft tissue. 
         [0004]    2. Related Art 
         [0005]    Tissue guided knee replacement requires instrumentation that is quite different from conventional knee replacement instrumentation due to minimal exposure, minimal bone and cartilage to be removed and soft tissue based resection. In the past, knee implants were fitted to a patient by the surgeon making measured resections by using fixed cutting blocks or by using a medial and lateral jig to control the reaming surface or mill type cutter. 
         [0006]    Tissue guided total knee arthroplasty (TKA) requires a reaming tool to remove condylar cartilage and bone while not disturbing the natural kinematics of the patients knee. The reaming device should be small enough to fit in knee joint via an MIS approach and located on the prepared proximal tibia below the unprepared distal femur. The reaming device should be able to power itself or be powered by an external source. Finally the device should be able to function while being precisely manipulated by the surgeon performing the procedure. 
         [0007]    With respect to the power systems for these tools, surgical motorized power systems of the past were a large control box wired into a motor via a long cable. The motor speed controls were either integral to the control box, in the motor hand piece or foot pedal operated. These designs generally require the surgeon to hold the motor while performing the procedure. 
         [0008]    Past and current tissue guided surgery focuses on separate implants to address bi &amp; tri-compartment knee osteoarthritis. Instrumentation is focused on reaming technology only and does not focus much on resection based instrumentation. 
       SUMMARY 
       [0009]    It is in view of the above problems that the present invention was developed. An embodiment may include a reamer for reaming a joint between at least two bones comprises a housing, a plurality of cutting blades, and a power source. The housing is configured to be inserted within the joint. The plurality of cutting blades is configured to couple to the housing. The plurality of cutting blades creates a cutting surface. The power source is coupled to the housing and configured to deliver motion to the cutting blades such that the cutting blades cut at least one bone of the at least two bones. 
         [0010]    In one aspect of the invention, the cutting surface is a planar surface. 
         [0011]    In another aspect of the invention, the power source is coupled to the housing through a flexible drive shaft. 
         [0012]    In yet another aspect of the invention, the cutting blades are barrel cutters. 
         [0013]    Another aspect of the invention includes cutting blades oscillating in a first direction. 
         [0014]    In another aspect of the invention, teeth on the cutting blades are oriented obliquely to the first direction. 
         [0015]    In yet another aspect of the invention, the teeth have a V shaped cross section in order to cut in a forward and backward direction. 
         [0016]    Another aspect of the invention includes a lavage port configured to lavage biomatter from the joint. 
         [0017]    In another aspect of the invention, a crankshaft configured to oscillate the cutting blades. 
         [0018]    In yet another aspect of the invention, the reamer reams at least two bones simultaneously. 
         [0019]    Another aspect includes the power source coupled to a patient. 
         [0020]    Another aspect of the invention provides a method of resurfacing a bone comprises the steps of placing a reamer substantially within a bone joint. The reamer has a housing and a plurality of cutting blades. The cutting blades are configured to bear upon a bone surface. Motive force is delivered to the housing. The motive force drives the plurality of cutting blades to ream the bone surface. 
         [0021]    In another aspect of the invention, the cutting blades form a planar cutting surface. 
         [0022]    In yet another aspect of the invention, the power is delivered to the housing through a flexible drive shaft. 
         [0023]    In one aspect, the cutting blades are rotated. 
         [0024]    Alternatively, the cutting blades are oscillated in a first direction. 
         [0025]    In yet another aspect, teeth on the cutting blades are oriented obliquely to the first direction. 
         [0026]    In yet another aspect of the invention, the teeth have a V shaped cross section in order to cut in a forward and backward direction. 
         [0027]    Another aspect of the invention provides the step of lavaging the joint while the reamer is reaming 
         [0028]    Yet another aspect provides the step of reaming at least two bones simultaneously. 
         [0029]    Additionally, an aspect may provide the step of mounting a power source on a patient. 
         [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 example of a straight edge barrel reamer according to an aspect of the invention; 
           [0033]      FIG. 2  is an example of a modular bone reamer according to an aspect of the invention; 
           [0034]      FIG. 3  is an example of an alternating bone reamer including a plurality of reamer blades; 
           [0035]      FIG. 4  is an example of an embodiment of one of the reamer blades of  FIG. 3 ; 
           [0036]      FIG. 5  is an example of an embodiment of two alternating reamer blades of  FIG. 3  depicting a reverse tooth pattern; 
           [0037]      FIG. 6  is an example of an embodiment of a crankshaft for driving the alternating reamer blades of  FIG. 5 ; 
           [0038]      FIG. 7  is an example of a partial view of the reamer blades of  FIG. 5  mounted on the crankshaft of  FIG. 6 ; 
           [0039]      FIG. 8  is an example of a partially assembled modular reamer according to an aspect of the invention; 
           [0040]      FIG. 9  is an example of an embodiment of a cartridge of a modular reamer; 
           [0041]      FIG. 10  is an example of parts of an embodiment of a modular housing; 
           [0042]      FIG. 11  is an example of an embodiment of a pair of reamers attached to a motor mounted on a leg; and 
           [0043]      FIGS. 12 through 18  are embodiments of reamers and power sources. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0044]    Currently most paradigms of tissue guided knee surgery impose the use of separate implants to address bi or tri-compartment disease. This is usually seen as a patello-femoral joint (PFJ) implant and two unicompartmental implants or a combination of the implants. By using a monolithic implant combined with femoral preparation by tissue guided techniques as well as traditional measured resection advantages of both may be realized 
         [0045]    A monolithic femoral component may be used to address bi or tri-compartment disease that is instrumented to the femur using both tissue guided reaming as well as measured resection. Less bone and cartilage may be removed using tissue guided reaming. The system may better restore the patient&#39;s natural kinematics. The monolithic femoral component can address bi compartment by replacing either the PFJ and either the medial or lateral condyle with a material thickness of 3 mm to 6 mm in the distal and posterior condylar regions which transitions to normal femoral implant thickness. The same design would be used for tri-compartmental disease except the implant would cover both condyles and the PFJ. 
         [0046]    The implant would be instrumented beginning with tissue guided reaming on one or both femoral condyles (after bi-uni tibial plateau resection). Once the required amount of tissue has been reamed from the posterior and distal condylar regions, reaching slightly onto the anterior cortex, asymmetric unicompartmental implant trials that match the amount of tissue removed (3 mm to 6 mm thick) are placed onto the femur. The monolithic femoral implant trial may be sized and placed on the femur. Joint line and balance are reassessed. If all is correct then the surgeon must assess if the patella should be resurfaced. If so then the patella is resurfaced and joint line and balance is reassessed. If the balance and the joint line are proper, the monolithic femoral implant is implanted (possibly with a femoral unicompartmental implant) and with two tibial unicompartmental-implants. 
         [0047]    Referring to the accompanying drawings in which like reference numbers indicate like elements,  FIG. 1  illustrates an example of a straight edge barrel reamer  10  according to an aspect of the invention. The barrel reamer  10  may be used in a modular reamer. The modular reamer may ream condylar cartilage and bone using the barrel reamer  10 . Because the device is modular, in-vivo assembly, multiple choices of reaming cartridges and disposable reamer cartridges may be used. 
         [0048]    The straight edge reamer  10  includes cutting teeth  12  located along the circumference of the reamer  10  and extending along the axis of the reamer  10 . A shaft  14  extends the length of the reamer  10 . The teeth  12  extend radially outward from the shaft  14  of the reamer  10 . At the axial ends of the shaft  14 , positive mating surfaces  16  may connect the reamer  10  to a drive mechanism. The positive mating surfaces  16 , in one embodiment, may be flats along the circumference of the shaft  14 . 
         [0049]    While the teeth  12  of the current embodiment extend axially along the shaft  14 , other embodiments may include teeth that extend both axially and circumferentially along the shaft such that the teeth spiral along the length of the shaft. Similarly, while the teeth have a cross section that is generally triangular in this embodiment, the cross section of the teeth may have other shapes. Such changes may allow the teeth to better move debris along the shaft, cut in only one direction, cut in both directions, or balance forces along the length of the shaft. 
         [0050]    Turning now to  FIG. 2 ,  FIG. 2  is an example of a modular bone reamer  20  according to an aspect of the invention. The reamer  20  includes a drive component  22  connected to a reaming component  24  through a connection  28 . The drive component  22  is a multiple use component that contains the gears and connections necessary to attach power to the reaming component  24  and distribute the power to the reaming component  24 . The reaming component  24  includes a cartridge  30  supporting a plurality of barrel cutters  32  and a tissue protector  34 . Gears  38  connect the drive component  22  to the barrel cutters  32 . Further components may include but are not limited to fixation components and distraction components. 
         [0051]    The drive component  22  is attached to the modular reaming component  24  via a positive locking mating surface that allows the drive component&#39;s gears  38  to mesh with those of the drive component  22  through the connection  28 . Once the two components have been secured together a drive shaft may be attached to the drive component  22  and locked into place. The drive shaft is attached to a drive motor that powers the assembly. Once the components have been assembled the modular reamer  20  is placed in the joint where the reaming barrel cutters  32  may contact the condylar cartilage. Once the reamer  20  has been placed in the correct location the motor is energized and the drive shaft begins to turn drive gears in the drive component  22 . This, in turn, turns the gears  38  in the modular reamer cartridge  24  which turns the barrel cutters  32 . The turning of the barrel cutters  32  removes the cartilage and bone of the condyle. 
         [0052]    The modular bone reamer  20  is designed to fit into a knee joint and ream either the proximal tibia or the distal femur and can be located in either the medial or lateral compartments or both compartments simultaneously. 
         [0053]    The body of the drive component  22  can be either straight or angled to allow for single condylar reaming or bi-condylar reaming or custom fit for patient anatomical needs. The reaming surface is comprised of rotating cylindrical cutters that may have multiple methods of operation including opposite directions of rotation or same directions of rotation if idlers are employed in the drive assembly. The actual reaming blades are straight barrels with straight cutting edges that are parallel to the axis of the barrel or they could be conventional helical fluted cutters. Vast cutter geometries may be used with certain designs most suitable for particular applications. Rotation is achieved by powering directly meshed spur gears that are attached to the cutters. This method of driving the cutters helps balance the reaming forces in the joint and maintain as much efficiency as possible by not having idler gears. 
         [0054]    By making the reaming device modular it could be possible to reduce costs to the patient by having a multi-use drive component where the patient would not have to incur the cost of a single use device. This allows for a less expensive reaming component to be a single use device that attaches to the drive component for each surgical procedure. This configuration also increases the number of reaming solutions by having a reusable drive body that multiple designs of reaming cartridges may attach and allowing the reaming system to meet several different needs of the doctors and patients. The possible different types of devices that could be attached to the drive component are reaming carriages with different number of cutters, different lengths of cutters, alternating cutters, belt cutters and different configurations of barrel cutters. Finally the modularity of the reamer will allow the surgeon to assemble the device in-vivo and/or in-situ thus allowing for a smaller incision on the patient. 
         [0055]    Other modular reamers could use different cutting geometry such as alternating cutting blades or a belt like cutting surface. Other mechanical means, in addition to the drive shaft, could be used to transfer power/energy to the reamers. The cartridge may also be modular so that the barrel cutters may be added or located in various stages (i.e. click on barrel sections that allow the reamer to adjust from a single barrel reamer to a plurality of reamers, oriented in different directions). 
         [0056]    Turning now to  FIG. 3 ,  FIG. 3  is an example of an alternating bone reamer  40  including a plurality of reamer blades  42 . The balanced alternating bone reamer  40  is designed to ream femoral condylar cartilage and bone by the use of an even number of alternating reverse toothed cutting blades that reciprocate opposite to each other during the reaming process. This function of the even numbered alternating cutting reamers  42  resects the tissue while not upsetting the natural kinematics of the patient&#39;s knee. 
         [0057]    The balanced alternating bone reamer  40  is designed in this embodiment to fit into the knee joint and ream either the proximal tibia or the distal femur and can be located in either the medial or lateral compartments or both compartments simultaneously. The balanced alternating bone reamer  40  is comprised of a reamer housing  44  and even number of alternating reaming blades  42  with a reverse tooth pattern  48 , a crank shaft  50  that moves the reaming blades in an alternating manner and a lavage portals  52  located on the housing  44  and allowing the flow of fluid under and through the blades  42 . Further components may include but are not limited to tissue protectors, fixation features and distraction features. 
         [0058]    The net external force of the cutting blade system is essentially zero, and thus a balanced system. As half of the blades  42  are cutting in a forward direction, the other half of the blades  42  are cutting in a backward direction. Thus, the force of the forward moving blades  42  cutting against the bone and cartilage are approximately equal to the forces exerted from the bone and cartilage acting upon the blades  42  moving in the opposite direction. Such a setup may keep the bone reamer  40  from chattering or moving within the joint. 
         [0059]    The housing  44  is modular to allow for the internal parts (crankshaft, gearing, reaming blades  42  and bushings) to be assembled and inserted. The major portions of the housing  44  are positively locked together once assembled. The anterior portion of the modular housing can have from two to five power ports that allow power to be applied to the crankshaft from the medial, lateral, anterior, superior and inferior aspects of the reamer  40  or any combination of the five aspects. Alternatively, the reamer may have internal mating features that would allow the optional connection of power from any of an assortment of directions, (eg medial or lateral or anterior). This would then embody a single reamer with application to different compartments or surgeon preference on how to connect power. 
         [0060]    Other embodiments may include an odd number of reaming blades. The blades may have straight teeth as opposed to oblique. The blade tooth geometry may be varied or different. The blades may even become an adequately roughened surface. The blades may articulate with a cam shaft and spring/bumper resistance to create the opposing forces to the cam shaft. The blades may articulate with an internal cam shaft in place of the crankshaft that would articulate on a closed journal in the blade as opposed to the open journal this design has. The crankshaft may be modular. Instead of alternating reaming blades, the reamer may alternate superiorly facing saw blades. 
         [0061]    Turning now to  FIG. 4 ,  FIG. 4  is an example of an embodiment of one of the reamer blades of  FIG. 3 . The blades  42  are kept on in place inferiorly and superiorly by two or more transverse cross bars that intersect the reaming blades  42  through transverse slots  60  located on the side of the reaming blade  42 . The blades  42  are constrained transversely by the sides of the housing. A crankshaft slot  62  receives the crankshaft, as described below. 
         [0062]    Teeth of the reamer blade  42  have a generally V shaped cross section. The V-shaped cross section of the teeth  66  allow the teeth to cut in both a forward and backward direction. By separating the teeth  66  from each other, bone material may slide between the teeth  66  and be flushed out by the lavage. The teeth  66 , in this embodiment, are also oriented obliquely relative to the direction of the movement of the blade  42 . Both the cross section and orientation of the blade  42  may be adjusted in other embodiments. 
         [0063]    Turning now to  FIG. 5 ,  FIG. 5  is an example of an embodiment of two alternating reamer blades  42  of  FIG. 3  depicting a reverse tooth pattern. The reamer blades  42  have reverse oblique oriented teeth  70 . One reamer blade  42  is forward positioned and the other is reverse positioned showing how the blades  42  reciprocate. The teeth  70  are obliquely oriented in opposite directions which may help to minimize the external forces by balancing out the lateral forces in opposite directions between the blades  42 . In other words the tooth pattern of one blade is opposite to that of the blade located next to it. The cutting teeth are oblique to the long centerline of the blades with a tissue evacuation portion located between each tooth. 
         [0064]    Turning now to  FIG. 6 ,  FIG. 6  is an example of an embodiment of a crankshaft for driving the alternating reamer blades of  FIG. 5 . The crankshaft includes a plurality of journals  74  to receive blades. The crank shaft  50  that drives the reaming blades  42  is powered by a power system that delivers power to the reamer  40  either medially, laterally or anteriorly. The design of the crankshaft  50  itself is a one piece “snake” like design that allows the reaming blades to be assembled to the crankshaft  50  by sliding them over either one of the ends of the crankshaft  50  and placing them in their respective journals  74 . The journals  74  of the crankshaft  50  and internal grooves located internally to the anterior portion of the housing. Power can either be applied directly to the crankshaft or can be applied to drive gears that mesh with the crankshaft. 
         [0065]    Turning now to  FIG. 7 ,  FIG. 7  is an example of a partial view of the reamer blades of  FIG. 5  mounted on the crankshaft of  FIG. 6 . As the crankshaft  50  is rotated, blades  42  reciprocate forward and backward. As the crankshaft  50  rotates, the journals rotate within the crankshaft slot to allow for the reciprocating motion to only move in one direction. Thus the length of the crankshaft slot is approximately equal to the diameter of the journals as the crankshaft is rotated. 
         [0066]    Turning now to  FIG. 8 ,  FIG. 8  is an example of a partially assembled modular reamer  100  according to an aspect of the invention. Cross bars  102  in a housing  104  support blades  110 . The bars  102  extend laterally through slots  116  in the blades  110 . The cross bars  102  are supported by transverse holes  118  located in the side of the reamer housing  104  and several supports  120  located inferior and internal to the reaming blades  110 . The blades  110  are raised above the sides of the housing so that the housing sides do not act as a depth stop. If a depth stop is desired in reaming, the height of the blades can be a specific height above the side of the housings. The distance from the top of the blades to the top of the sides of the housing will determine the depth of reaming allowed by the reamer. 
         [0067]    While this embodiment includes a housing that has a bottom portion, other embodiments may not have a bottom portion and the blades may be supported from the housing sides. The blades may include cutting teeth on both the top and bottom of the reamer. In such an embodiment, the blades may cut both above and below the reamer. Thus, when put in a joint like the knee, the reamer may be configured to cut cartilage and bone on both sides of the reamer, thereby cutting both the femur and the tibia at the same time. Such an embodiment may better align the cutting surfaces between the two bones and may also be used to effectively gauge the depth of the resurfacing of the bone on both sides of the implant. 
         [0068]    Turning now to  FIG. 9 ,  FIG. 9  is an example of an embodiment of a cartridge of a modular reamer  130 . While the embodiment shows four supports for each crossbar for four cutting blades, fewer or additional supports may be added. Additionally, the embodiments are not limited to only four blades. 
         [0069]    Turning now to  FIG. 10 ,  FIG. 10  is an example of parts of an embodiment of a modular housing  140 . The housing includes a lavage port  144  and a crankshaft guide  146 . The housing supports the lavage ports  144  and the crankshaft for the blades. Bone and cartilage, when cut free, may flow under the blades through the lavage ports  144  and out of the joint. 
         [0070]    Turning now to  FIG. 11 ,  FIG. 11  is an example of an embodiment of a pair of reamers  180  attached to a motor  184  mounted on a leg  190 . The motor may be attached with Velcro  190  or other fixation means. Drive shafts may be connected from the motor  184  to the reamers  180 . 
         [0071]    When performing various surgical procedures where the instrument(s) require energy from an external source (motor), many times surgeons require the use of both hands to manipulate the patient or the instrument. By including the power source (battery(s) or transformer), motor controls (I.e trigger for speed and/or motor control) and motor in a hands free device with or without gearing onto a patients leg, the surgeon is free to use both hands to manipulate the patients anatomy or the instrumentation in the desired manor. While power sources (and possibly controls) have been isolated from the instrument and delivered to the motor and the instrument previously by cables, the motor has generally remained attached to the instrument. The motor may be heavy (limiting agility and responsiveness of the instrument) and may limit access to the surgical site for instruments based upon size of the motor and instrument. Thus, being able to isolate the motor, control and power source from the instrument may increase access and increase surgeon agility as well as increase instrument tactile instrument proprioception. An appendage attached surgical instrument motor, gearing, power supply, motor control and housing may address some of these issues. 
         [0072]    In one embodiment, the complete appendage assembly is comprised of a battery(s), one or two DC motors, motor control circuitry, a speed control device (potentiometer or like) a housing contoured to fit the anatomy of a human leg or other appendage, a gel pad and Velcro securing straps. The assembled device would be strapped to the patient&#39;s leg and attached to the surgical instrument via flexible or rigid drive shafts. Once the motor is energized it would power the surgical instrument at various speeds and torques depending on the input of the surgeon via the speed control device that in integral to the leg assembly. 
         [0073]    The device would be mounted mid-shaft of the proximal or distal portion of the entire appendage directly below or above the joint that the instrument in involved in. It would be connected the appendage by Velcro straps or similar types of devices as well as padding between the housing and the patient to protect the patient from impact and heat from the motor as well as to dampen an vibration caused by the motor or instrument. The device would be connected to the instrument requiring power by either a flexible or rigid drive shaft. Devices that could take advantage of this type of device would include but not be limited to reamers, drills, burrs, saws and power distraction or reduction devices. 
         [0074]    The assembly could be attached to the thigh or any appendage of the patient. The device could be strapped to the surgeon. The device could pull power from an AC outlet or pneumatic system instead of the battery. The device could be divided into modules and only the motor and possibly the speed control is attached to the patient&#39;s leg with the other modules being compact and located on the table with the patient or on a side table. This would require the motor and control to be attached via a cable. A final possibility is that motor and control circuitry is attached to the leg and either powered by a battery or power cord. The difference being the speed control is located in the surgeon&#39;s hand and sends the control signals via Blue Tooth or similar technology. The instrument could be handheld and the controls and power source could be located on the patient&#39;s or doctor&#39;s appendage or body. 
         [0075]    Turning now to  FIGS. 12 through 18 ,  FIGS. 12 through 18  are embodiments of reamers and power sources.  FIG. 12  is an example of an embodiment of a pair of reamers  200  driven through a single drive shaft  204  and motor  210 . A coupling  216  couples the reamers  200  to each other. The reamers  200  are placed within the joint over a tibia  220 . The coupling  216  allows for energy to transfer between the reamers  200  while maintaining the middle portions of the tibia where the cruciate ligaments cross. A single power supply  210  and single flexible shaft allow for minimal amounts of power devices within the joint. This may be beneficial for MIS approaches where minimal incisions are made. However, chatter from one reamer may adversely effect the other reamer. 
         [0076]    Turning now to  FIG. 13 ,  FIG. 13  is an example of an embodiment of a pair of reamers  200  being driven through a pair of flexible drive shafts  230  from a motor  232 . The embodiment requires an additional flexible drive shaft through the incision, but may help to eliminate chatter between the reamers. Additionally, the set of shafts  230  may allow for independent shimming of the different compartments. 
         [0077]    Turning now to  FIG. 14 ,  FIG. 14  is an example of an embodiment of a pair of reamers  200  being driven by a single motor through a pair of drive shafts  250  and  252  each extending through different incisions. The drive shaft  250  may extend through a lateral incision while the drive shaft  252  may extend through a lateral incision. The embodiment may allow for better clearance through the primary medial incision while making a small lateral incision. However, an additional incision is required. 
         [0078]    Turning now to  FIG. 15 ,  FIG. 15  is an example of an embodiment of a pair of reamers  200  being driven by a pair of motors  260  through a pair of drive shafts  270 .  FIG. 17  is an example of an embodiment of a pair of reamers  200  being driven by a pair of motors  260  through a pair of drive shafts  260  each extending through different incisions, similar to the embodiment of  FIG. 14 . 
         [0079]    Turning now to  FIGS. 18 and 19 , the figures are an example of an embodiment of a single reamer  300  being used serially to prepare the lateral and medial sides of a tibia  310 . A single drive shaft  320  may extend through the medial incision or through a lateral incision in order to prepare the lateral side. Inserts  330  may be used to support the other compartment when one compartment is being reamed. Control for each condyle may be better, but additional time would be needed to prepare both condyles. 
         [0080]    In view of the foregoing, it will be seen that several advantages of the invention may be achieved and attained. 
         [0081]    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. 
         [0082]    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.