Abstract:
A veterinary precision fixation device for use in tibial plateau leveling osteotomy procedures includes a jig assembly having a center jig member having a first and second end, a first jig leg pivotally coupled to the first end, and a second jig leg pivotally coupled to the second end. The device also includes a saw guide assembly having a saw fixation member slidably coupled to at least one slide bar wherein the slide bar is coupled to the center jig member proximate the first end. A method for using the precision fixation device in a tibial plateau leveling osteotomy is also provided.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The most common condition causing either acute or chronic hind leg lameness in dogs is injury to the anterior cruciate ligament, and subsequent instability in the knee joint. This results in severe cartilage erosion and degenerative joint disease. This arthritic condition is progressive, and without surgery leads to permanent weight-bearing lameness. Once a cruciate ligament injury or tear occurs, the anatomic stability of the joint is permanently changed. 
         [0002]    The canine or feline stifle (knee) joint shares basic similarity to the human knee joint. The lower end of the femur rests on two doughnut-shaped cartilages (menisci) that sit on top of the tibia (tibial plateau). Two internal ligaments, the anterior and posterior cruciate ligaments, work to reduce shearing forces. The knee cap (patella) attaches to the tibia by the patellar ligament and acts to extend the stifle. The medial and lateral collateral ligaments stabilize the stifle joint side-to-side. Other internal ligaments stabilize the meniscal pads during flexing and extension. 
         [0003]    In both the canine and feline patient, the femur rest on a tibial plateau that slopes to the back of the stifle. This slope varies by the animal&#39;s breed, size, and by individual and can vary from 5 to 40 degrees. This posterior slope results in a constant backward or posterior sliding motion (thrust) of the lower femur on the menisci and tibial plateau. This posterior thrust by the femur is countered by the anterior cruciate ligament (ACL) inside the stifle joint. It is common for the ACL to partially or completely tear as a result of normal shearing forces within the joint brought on by aging, wear and tear, and athletic activity. The, incidence of injury is far more common than in humans, and the surgical repair is complex. Abnormal shearing forces tear the meniscal cartilages and ulcerate the femoral condyles and truchlear groove, as the patella moves upward with normal extension of the leg. 
         [0004]    A bone-cutting procedure that decreases the weight-bearing slope of the tibia to nearly 5° has been described by Barclay Slocum in U.S. Pat. No. 4,677,973 entitled “Proximal, tibial osteotomy for leveling a tibial plateau.” The procedure described therein hinges on accurately assessing the individual patient&#39;s joint pathology, surgically changing the slope without changing other forces within the joint, and assessing, and then correcting, any meniscal damage. The surgical procedure, as disclosed by the &#39;973 patent and its progeny, encompasses a specific surgical approach to the stifle joint and proximal tibia and then the attachment of a jig to the tibia. This is accomplished primarily by visualizing certain landmarks and making a freehand, curved, but ideally perpendicular, cut through the tibial plateau with a vibrating oscillating saw. The procedure described in the &#39;973 patent is open to severe error because the surgeon must simultaneously visually hold the saw in three dimensions as it cuts freehand through the tibia. 
         [0005]    Accordingly, there is a need in the art for a device that helps to control the freehand cut made by the oscillating curved saw blade. There is also a need in the art for a jig that is less subjectively applied to the tibia thereby reducing human error in placement. 
       SUMMARY OF THE INVENTION 
       [0006]    This invention relates generally to a veterinary surgical device and a method of using a veterinary surgical device. In particular, the present invention relates to a precision fixation device for use in tibial plateau leveling osteotomies that reduces surgical error, assists in providing a concise bone cut, and results in minimal bone and soft tissue destruction during surgery. The veterinary precision fixation device of the present invention generally includes a jig assembly having a center jig member having a first and second end, a first jig leg pivotally coupled to the first end, and a second jig leg pivotally coupled to the second end. The device also includes a saw guide assembly having a saw fixation member slidably coupled to at least one slide bar wherein the slide bar is coupled to the center jig member proximate the first end. 
     
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0007]    In the accompanying drawings that form a part of the specification and that are to be read in conjunction therewith and in which like reference numerals are used to indicate like parts in the various views: 
           [0008]      FIG. 1  is a top perspective view of the precision fixation device in accordance with one embodiment of the present invention; 
           [0009]      FIG. 2  is a top perspective exploded view of the precision fixation device in accordance with one embodiment of the present invention; 
           [0010]      FIG. 3  is a top perspective view of the precision fixation device shown in conjunction with an oscillating saw and an animal&#39;s tibia in phantom in accordance with one embodiment of the present invention; 
           [0011]      FIG. 4A  is a top perspective view of the second slide bar and second adjustment member in accordance with one embodiment of the present invention; 
           [0012]      FIG. 4B  is a top perspective view of the first slide bar in accordance with one embodiment of the present invention; 
           [0013]      FIG. 5  is a top perspective view of the center jig member  16  in accordance with one embodiment of the present invention; 
           [0014]      FIG. 6  is a top perspective view of the saw guide member in accordance with one embodiment of the present invention; 
           [0015]      FIG. 7A  is a top perspective view of one of the jig legs in accordance with one embodiment of the present invention; 
           [0016]      FIG. 7B  is a top plan view of the jig leg of  FIG. 7A  in accordance with one embodiment of the present invention; and 
           [0017]      FIG. 8  is a bottom perspective view of an adjustment member in accordance with one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    As shown in  FIGS. 1-3 , the precision fixation device  10  of the present invention includes a jig assembly  12  and a saw guide assembly  14 . Jig assembly is preferably formed from stainless steel, plastic, or any other material suitable for use in veterinary surgery. Jig assembly  12  includes a center jig member  16 , a first jig leg  18 , and a second jig leg  20 . Center jig member  16 , as shown in  FIG. 5 , is preferably from about 3.0-6.0 in length (L), from about 0.5-0.7 wide (W), and from about 0.3-0.6 inches high (H). However, it will be appreciated by one skilled in the art that the dimensions of center jib member may be altered to suit the size of the animal being operated upon or to meet any other desired application. Center jig member  16  includes a generally planar or flat top surface  22 , an opposing generally planar bottom surface  24 , a generally planar inner surface  26 , an opposing generally planar outer surface  28 , a generally rounded first end  30 , and an opposing generally rounded second end  32 . Each of first and second ends  30  and  32  includes a first and second aperture  34  and  36 , respectively, extending through center jig member  16  from top surface  22  to bottom surface  24 . First and second apertures  34  and  36  preferably have a diameter of from about 0.15-0.2 inches and are configured to receive a screw  104  or  118  of a first or second adjustment member  96  or  110  described hereinbelow. In one embodiment, apertures  34  and  36  may have a threaded interior surface configured for receiving a screw or other threaded coupling mechanism therethrough. However, it is within the scope of this invention that the interior surface of apertures  34  and  36  may be smooth or otherwise configured to receive any suitable coupling mechanism. Each of first and second ends  30  and  32  also include first and second cutout portions  38  and  40 , respectively, each having a height of from about 0.16 to 0.2 inches and extend inwardly from each of ends  30  and  32  about 0.3-0.7 inches toward the center of center jig member  16 . Cutout portions  38  and  40  are configured to receive a first end  50  of each of first and second jig legs  18  and  20  and are preferably disposed about 0.18-0.24 inches below top surface  22  and about 0.9-0.14 inches above bottom surface  24 . First and second apertures  34  and  36  are preferably spaced from about 0.2-0.4 inches from first and second ends  30  and  32 , respectively, with a distance between first and second apertures  34  and  36  of from about 2.0-6.0 inches such that apertures  34  and  36  are interrupted by cutout portions  38  and  40 . 
         [0019]    First and second jig legs  18  and  20 , shown in  FIGS. 7A and 7B , are each preferably from about 1.0-4.0 inches long (L), from about 0.3-0.7 inches wide (W), and include a generally planar top surface  42 , an opposed generally planer bottom surface  44 , a generally planar inner surface  46 , an opposed generally planar outer surface  48 , a generally rounded first end  50  and a generally rounded second end  52 . The height (H) of jig legs  18  and  20  at first end  50  is preferably from about 0.3-0.7 inches and tapers or reduces approximately hallway along length L to a height (H) of from about 0.16 to 0.2 inches at second end  52 . It will be appreciated that second end  52  is configured to be inserted into cutout portions  38  and  40 . Jig legs  18  and  20  each include an adjustment member aperture  54  extending from top surface  42  to bottom surface  44  and proximate second end such that, when second end  52  is inserted into a cutout portion  38 ,  40 , adjustment member aperture  54  lines up with first and second apertures  34  and  36  in center jig member  16  such that adjustment member  96  or  110  described hereinbelow may be inserted through center jig member  16  and second end  52  thereby enabling adjustable pivotal movement of jig leg  18  or  20  between anywhere between a 30-300 degree radius from center jig member  16 . An upper tibial positioning aperture  56  extending through first end  50  of first jig leg  18  from top surface  42  to bottom surface  44  is configured to receive an upper tibial pilot pin  58  therethrough as shown in  FIG. 3 . A first slide bar aperture  60  extending generally through the center of first jig leg  18  from top surface  42  to bottom surface  44  is configured to threadably receive a first slide bar  70  therein or therethrough. In one embodiment, slide bar aperture  60  may have a threaded interior surface configured for receiving a screw or other threaded coupling mechanism therein. However, it is within the scope of this invention that the interior surface of slide bar aperture  60  may be smooth or otherwise configured to receive any suitable coupling mechanism for coupling with first slide bar  70 . A lower tibial positioning aperture  62  extending through first end  50  of second jig leg  20  from top surface  42  to bottom surface  44  is configured to receive a lower tibial pilot pin  64  therethrough as shown in  FIG. 3 . Second jig leg  20  may be identical to first jig leg  18  for interchangeably and may also include a slide bar aperture  66  extending generally through the center of second jig leg  20  from top surface  42  to bottom surface  44  that is configured to receive a slide bar (not shown) therein or therethrough. 
         [0020]    Saw guide assembly  14  includes saw fixation member  68 , a first slide bar  70 , a second slide bar  72 , and an adjustment bar  74 . Saw guide assembly  14  is preferably formed from stainless steel, plastic, or any other material suitable for use in veterinary surgery. Saw fixation member  68  may be any shape having rounded edges for safety purposes. In one embodiment as shown in  FIG. 6 , saw fixation member  68  has a roughly triangular shape with rounded edges such that a first end  76  has a larger width than a second end  78 . For example, first end  76  is preferably from about 1.2 to 1.9 inches wide at its widest point whereas second end  78  is preferably from about 0.4-1.0 inches wide at its widest point. First end  76  includes a saw positioning aperture  80  extending therethrough configured for receiving and supporting a vibrating oscillating saw  82  therein and therethrough as shown in phantom in  FIG. 3 . First end  76  also includes opposing set screw apertures  77  for receiving set screws (not shown) for tightening and securing saw  82  within saw positioning aperture  80 . Second end  78  includes a second slide bar aperture  84  extending therethrough configured for receiving second slide bar  72  therethrough. Between saw positioning aperture  80  and second slide bar aperture  84 , saw fixation member  68  also includes a first slide bar aperture  86  extending therethrough configured for receiving first slide bar  70  therethrough. 
         [0021]    Second slide bar  72  as shown in  FIG. 4B  is generally cylindrical having a rounded first end  88  and a threaded second end  90  for threadably engaging first slide bar aperture  60  in first jig leg  18 . First slide bar  70  is generally cylindrical and preferably has a smaller or shorter length than that of second slide bar  72 . First slide bar  70  as shown in  FIG. 4A  includes a rounded first end  92  and a second end  94  having a first adjustment member  96  threadably coupled thereon or otherwise permanently affixed thereto. Adjustment member  96  includes a generally O-shaped shoulder  98  having a top surface  100  and a bottom surface  102  defining an optional aperture (not shown) therethrough. Aperture may include a threaded interior for threadably coupling with second end  94  of first slide bar  70 . In another embodiment, second end  94  of first slide bar  70  may be welded, soldered, or simply glued to top surface  100  or within aperture. Bottom surface  102  of adjustment member includes a screw  104  extending outwardly therefrom and configured to threadably couple with first slide bar aperture  60  on first end of center jig member  16 . In the preferred embodiment, screw  104  has a length sufficient to extend through first aperture  34  adjacent top surface  22  of center jig member  16 , through adjustment member aperture  54  of first jig leg  18  when second end  52  of first jig leg  18  is inserted into cutout portion  38  proximate first end  30  of center jig member  16 , and then through first aperture  34  adjacent bottom surface  24  of center jig member  16 . 
         [0022]    Adjustment bar  74  is generally cylindrical and may have a shorter length than that of either first or second slide bars  70  and  72 . Adjustment bar  74  includes a generally rounded first end  106  and an opposing second end  108  having a second adjustment member  110 , one embodiment of which is shown in  FIG. 8 , threadably coupled thereon or otherwise permanently affixed thereto. Adjustment member  110  includes a generally O-shaped shoulder  112  having a top surface  114  and a bottom surface  116  defining an optional aperture (not shown) therethrough. Aperture may include a threaded interior for threadably coupling with second end  108  of adjustment bar  74 . In another embodiment, second end  108  of adjustment bar  74  may be welded, soldered, or simply glued to top surface  114  or within aperture. Bottom surface  116  of adjustment member  110  includes a screw  118  extending outwardly therefrom and configured to threadably couple with second aperture  36  proximate second end  32  of center jig member  16 . In the preferred embodiment, screw  118  has a length sufficient to extend through second aperture  36  adjacent top surface  22  of center jig member  16 , through adjustment member aperture  54  of second jig leg  20  when second end  52  of second jig leg  20  is inserted into cutout portion  40  proximate second end  32  of center jig member  16 , and then through second aperture  36  adjacent bottom surface  24  of center jig member  16 . 
         [0023]    In use, an animal patient is maintained on isofluorane anesthesia with constant anesthetic monitoring in dorsal recumbency and with complete body drape and the surgery leg free in a vertical plane. Routine pre-operative betadyne preparation is performed prior to draping. The patient&#39;s leg is extended and flexed to evaluate pre-operative anatomy and to determine if any valgus or varus deviation or torsion of distal extremity exists. Pre-operative radiographs have identified a desired plateau slope change of from 5-40 degrees. The surgical blade chosen varies based on the anterior-posterior thickness of the tibia. The tibial plateau rotation is calculated based on the chosen blade, and the degree of rotation. 
         [0024]    The skin and subcutaneous fascia are incised down to the periosteum, from the tibial plateau to approximately 2 cm distal to the tibial crest in an anteromedial plane approximately 1.5 cm caudal to the palpable anterior midline edge of the tibial crest and distally parallel with the tibial shaft. The skin and subcutaneous incision is extended proximally and caudally in a slightly curved fashion to the level of the proximal patella. The periosteum starting at the tibial plateau is incised distally to the limits of the skin-subcutaneous incision. The periosteum is then reflected anteriorly to the edge of the tibial crest, with a periosteal elevator, and also posteriorly beneath the muscle attachments of the pes ansorimus group to the posterior edge of tibia  120  by a combination of sharp scalpel dissection and periosteal elevation. This landmark dissection reveals the 1) medical aspect of the stifle joint, 2) the medial collateral ligament, and 3) the muscle fiber attachment of the popliteus to the caudal femur. From the tibial plateau, the periosteal incision is carried proximal, deeper through fascial planes to the sartorius muscle attachment. Care should be taken to not enter the femorotibial joint space. Three 25 gauge needles are used to identify the tibial plateau, and the caudal aspect of the tibia  120 , just caudal to the medial collateral ligament. 
         [0025]    A 5 mm incision is made immediately caudal to the posterior edge of the medial collateral ligament, through the joint capsule with a #15 blade. Through this 5 mm incision, a #11 blade is inserted, pointed anterolateral at an imaginary point halfway between the tibial crest and the fibular head, and used to cut the medial meniscus, releasing it to fall posteriorly. The 5 mm incision is closed with cruciate 2-0 PDS. Three 25 gauge needles are placed in the knee joint as close to the tibial plateau as possible, the first caudal to the patellar ligament, the second approximately 5-8 mm caudal to the meniscal release incision, and the third at the posterior but most proximal point on tibia  120 . 
         [0026]    The popliteus muscle fibers, as attached to posterior tibia  120 , are cut close to tibia  120 , from approximately 2 cm distal to the caudal edge of the femorotibial joint (as previously found with a 25 gauge needle) for approximately 4 cm. Using a sharp periosteal elevator, all muscle fibers and soft tissue are separated from the posterior-lateral aspect of the femur. The pocket created is packed with 3-4 saline-soaked gauze sponges. The tibialis anterior muscle is separated from its tibial plateau attachment from 2 cm below the femoral tibial joint and distally 3-4 cm by using sharp periosteal elevator dissection. The pocket created is packed with saline-soaked gauze sponges. 
         [0027]    The patient&#39;s leg should be positioned accurately to pinpoint accurate placement of the upper and lower tibial positioning pins  58  and  64  that hold jig assembly  12  in place. The stifle and hock joints are flexed with the femur perpendicular thereto. That is, the femur is vertical to the table and the patient&#39;s foot/metatarsus is held or positioned against the surgeon&#39;s chest. Tibia  120  is held substantially parallel to the surgical table and substantially perpendicular to the femur. If a valgus or varus tibial deviation is present, the foot/metatarsus will not appear vertical or parallel with the femur. 
         [0028]    In another embodiment of the method of the present invention, the patient is positioned in lateral recumbency and the surgery leg placed on the table, in a substantially perfect horizontal plane with stifle and tibiotarsal joints partially flexed. After the patient is placed in lateral recumbency, a vacuum positioner bag is placed beneath the surgical leg. A horizontal laser beam is used to position the distal leg, from just above the patella, so that the horizontal beam of the laser lays center of the patellar ligament, center of the proximal to distal tibia, and to the center of the torsus. The vacuum positioner bag is deflated when the leg is parallel to the horizontal beam. 
         [0029]    A ⅛″ threaded pin is inserted through a small stab wound approximately 5 mm distal to the second 25 gauge needle and midway between the posterior edge of the medial collateral ligament and the third 25 gauge needle. The pin is started to make a small pilot hole and then removed. Prior to drilling the proximal pin, the laser horizontal beam is used to confirm that the lower leg is in a substantially perfect horizontal plane. If the leg is positioned correctly, the laser beam bisects the patella, the patellar ligament, the tibia, and the metatarsus. In general, if the leg is positioned correctly prior to surgery on the vacuum positioner bag and, if the leg has not been repositioned, then no adjustments in positioning of the leg should be necessary. 
         [0030]    Preplaced 25 gauge needles identify the posterior edge of the proximal tibia  120 , and the posterior edge of the femorotibial joint. A 25 gauge needle is placed just caudal to the medial collateral ligament in the joint. A second 25 gauge needle is “walked” off the posterior-proximal edge of tibia  120 . The tip of the proximal pin is placed 2-5 mm caudal to the medial collateral ligament, and 3-5 mm below the joint. In general the pin will be placed caudal of the medial collateral ligament, ⅔ of the distance between the medial collateral ligament and the posterior edge of tibia  120 . 
         [0031]    The proximal pin is verified to be substantially vertical to the plane of tibia  120  with the vertical laser beam and then it is seated through tibia  120 . The laser insures accuracy of the pin placement, that is, the pin is desirably substantially perpendicular to the horizontal plane of the tibia. 
         [0032]    Precision fixation device  10  is substantially preassembled for a left or right leg surgery by an assistant. Assembled device  10  is slid over upper tibial positioning pin  58  via upper tibial positioning aperture  56 . The lower tibial positioning pin  64  is positioned in the distal one-third of tibia  120  via lower tibial positioning aperture  62 . A 5 mm skin incision makes a window for pin  64  to enter the bone of tibia  120 . The laser is now used to verify that device  10  is in a substantially perfect horizontal plane and parallel to the plane of the tibia  120 . Device  10  is generally held tight against the proximal tibia  120  and the lower  64  pin is then set. The laser again is used to verify the absolute vertical position of the lower tibial pin  64  as it is seated through tibia  120 . 
         [0033]    The appropriate cutting blade is generally chosen prior to surgery. Any diameter blade may be used in connection with device  10 . Saw fixation member  68  is slid onto the first and second slide bars  70  and  72 , the blade of saw  82  is positioned on tibia  120  so that the proximal edge of the saw  82  will cut the proximal end tibia  120 . Set screws are tightened within screw apertures  77  to prevent saw  82  from rotating within saw fixation member  68 . At 90# of pressure, saw  82  is capable of guiding itself through the bone of tibia  120  thereby insuring a substantially perfect 90° cut in all planes relative to tibia  120 . 
         [0034]    Saw  82  should not move out of the precision plane when it is fixed in position by the saw fixation member  68  on slide bars  70  and  72 . Saw  82  is then activated and, with aggressive flushing, tibia  120  is cut approximately two-thirds of the way through. The saw blade is then retracted and chisel marks are made to accurately delineate the mm of rotation. The saw cut is completed with rigorous irrigation by inserting saw  82  into the previous saw cut and activating saw  82 . The saw blade is not rotated or twisted by the surgeon, but instead allowed to slowly cut by the actual blade vibration on tibia  120 . 
         [0035]    Once tibia  120  is cut, jig assembly  12  is checked to confirm that it is secure. The saline soaked gauze is removed from the lateral aspect of tibia  1420 . A threaded ⅛″ pin is drilled medial to lateral, obliquely, through the proximal cut fragment, close to the saw line. A second pin is then used to rotate the proximal cut segment so that the rotation is complete and the chisel lines meet. A 1/16″ threaded pin is inserted just lateral to the patellar ligament attachment to the tibial crest and is driven posterior into the proximal cut fragment. 
         [0036]    Prior to plating, the cut line is visualized for plate placement. The appropriate TPLO plate is contoured to fit the cut surface and proximal shaft of tibia  120 . Care is taken to get a perfect anatomical fit. The distal  3  holes are drilled, tapped, and screws placed in a neutral position. Holes  4  &amp;  5  are drilled and 4.0 mm cancellous screws are placed in a loading position, but are tightened together. Hole  6  is drilled parallel to the tibial plateau, and a 4.0 mm cancellous screw is tightened. 
         [0037]    A culture is taken prior to closure. O-PDS is used to close the periosteum and pes ansorinus group over the plate with simple interrupted sutures. The fascia and subcutaneous are closed with 2-0 PDS sutures. If possible, a subeuticular pattern is run with 2-0 vicryl. Stainless steel staples close the skin. A light pressure wrap over the incision and down tibia  120  to the hock joint is applied. Post-op x-rays are taken to evaluate the bone cut line, closure of the saw line, and final degrees of rotation. 
         [0038]    From the foregoing, it may be seen that the inventive precision fixation device and method of using the same is particularly well suited for the proposed usages thereof. Furthermore, since certain changes may be made in the above invention without departing from the scope hereof, it is intended that all matter contained in the above description or shown in the accompanying drawing be interpreted as illustrative and not in a limiting sense. It is also to be understood that the following claims are to cover certain generic and specific features described herein.