Abstract:
A process and system for performing orthopaedic surgery to create a series of channels with a subject&#39;s bone to allow a reduced pressure system to be applied directly to the bone-implant interface to enhance bone healing is provided. The process for to promote healing of a bone of a subject includes creating a three-dimensional model of the bone; preoperatively planning a location of an implant relative to the model; creating a plan for the location of precision channels that reach the bone-implant interface based on the model and the implant; resurfacing the bone to fit the implant into or onto the bone based on the preoperative plan; and milling the precision channels into the bone in the location to promote healing of the bone and/or bone implant interface; and applying a pressure reduction system at the bone-implant interface to promote bone healing.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority of U.S. Provisional Patent Application Ser. No. 61/787,616 filed Mar. 15, 2013, which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates generally to the field of orthopaedic surgery for the repair and replacement of damaged articular cartilage, and more specifically to a new and useful system and process for creating specific three-dimensional (3D) shapes in bone. 
       BACKGROUND OF THE INVENTION 
       [0003]    Articular cartilage is an avascular tissue that is found on the surfaces of joints and serves to provide a smooth interface upon which bones can articulate with each other. Defects in the articular cartilage can be caused by traumatic lesions or by osteochondritis dissecans or in accordance with other joint/ligament injuries. Lesions of this type in articular cartilage typically do not heal on their own, and are associated with symptoms such as joint pain, joint locking, and reduced or disturbed function. Due to the lack of vasculature in cartilage, these types of defects are known to progress to more severe forms of osteoarthritis, which may eventually require joint arthroplasty to restore joint function. Repair of these defects prior to the spreading of this articular damage may delay the need for a joint arthroplasty, especially in younger individuals. It is desirable to delay a joint replacement procedure as long as possible, especially in younger individuals, since their remaining lifespan may be longer than the lifetime of the implant. If the implant fails, the subject may require a revision procedure which is complicated and poses additional risk, inconvenience, and cost to the subject. 
         [0004]    There are various methods that currently exist to repair cartilage. One such exemplary method is the use of osteochondral plugs. In this method, which is typically used in the knee joint, healthy osteochondral plug(s) formed of both bone and cartilage are used to replace the site of the cartilage defect. This procedure allows the chance for the cartilage surface to repair itself with healthy tissue. Larger osteochondral defects are typically filled with multiple smaller osteochondral plugs to recreate as much of the cartilage surface as possible. These osteochondral plugs may be autografts, which are taken from the same individual receiving the plug, or they may be allografts, which are taken from other individuals, living or deceased. 
         [0005]    Another conventional method that has been described is the fabrication of custom-shaped grafts for cartilage regeneration. In this procedure, an MRI scan is used to reconstruct the 3D surface of the articular cartilage including the defect. A 3D computer model is then generated to fill the cartilage defect and recreate a smooth articular cartilage surface. From this 3D computer model, a custom-shaped graft is then fabricated using synthetic or natural materials using rapid prototyping or other techniques. This custom-shaped graft is then placed into the joint to recreate a smooth surface of the articular cartilage that restores the natural surface of the joint. 
         [0006]    Another conventional method that has been described is the fabrication of synthetic scaffolds that are designed to behave mechanically like natural articular cartilage. These scaffolds are often bio-absorbable and seeded with cells that will resorb the scaffold as new cartilage matrix is created to restore healthy cartilage. These scaffolds generally consist of two components, one of which is designed to integrate with the native bone and the other that is designed to integrate with the native cartilage. Both components of the scaffold are often made of bio-absorbable or biologically active materials such that natural tissue will eventually replace them. 
         [0007]    A common attribute of all the conventional cartilage repair techniques is that there must be a method of anchoring the cartilage replacement to the subchondral bone. There have been methods developed to remove bone plugs in the area of the cartilage defect (see U.S. Pat. Nos. 5,782,835 and 6,017,348). However, these methods lack precision in locating the cartilage defect and cannot create accurate shapes that will securely fix the cartilage replacement to the bone. Additionally, it is important to minimize the amount of healthy cartilage that needs to be removed and the current methods do not provide an easy method to create a specific shape based on the individual&#39;s particular cartilage defect. Finally, it is important to achieve joint surface congruity of the articular cartilage after the cartilage replacement has been implanted to ensure normal joint contact (Koh et al. Am J Sports Med, March 2004; 32, 2 pgs. 317-320). 
         [0008]    Thus, there exists a need for a more effective process to create a precise cavity for a particular cartilage replacement implant to the subchondral bone that can allow for seamless integration of the implant into the subject&#39;s body. 
       SUMMARY OF THE INVENTION 
       [0009]    A process and system for performing orthopaedic surgery to securely fasten an articular cartilage replacement to underlying bone is provided. The process for forming a pre-made cartilage implant intended for repair of a cartilage defect in a bone of a subject cartilage defect in a bone of a subject includes receiving scan data of the bone; creating a virtual three-dimensional model of the bone and the cartilage defect; creating a three-dimensional custom shape around the cartilage defect; and shaping a pre-made cartilage replacement implant to match the custom shape in three-dimensions. The repair of cartilage of knee joints and to other joints within the body and any other bones found within the body illustratively include the hip joint, shoulder joint, ankle joint, wrist joint, finger joint, toe joint, or other joint. The inventive orthopaedic surgery can be performed on humans or an animal of a non-human primate, a horse, a cow, a sheep, a goat, a dog, a cat, a rodent, and a bird. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The subject matter that is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0011]      FIG. 1  is a flowchart depicting a specific embodiment of the present invention for creating a custom shaped cavity for a cartilage replacement implant based on a three-dimensional virtual model of the subject&#39;s bone and cartilage using a robotic milling system; 
           [0012]      FIG. 2  is a schematic block diagram of an inventive system for creating a three-dimensional model of a subject&#39;s bone and cartilage including a cartilage defect and a plan for creating a cavity that encompasses the cartilage defect; 
           [0013]      FIGS. 3A and 3B  illustrate a robotic milling tip creating a customized cavity within the articular surface of a bone, and a custom shaped cartilage implant to be placed within the cavity; 
           [0014]      FIG. 4  illustrates a cartilage replacement implant that includes both a cartilage type layer and a bone type layer; 
           [0015]      FIG. 5  illustrates a customized cartilage replacement implant, as shown in  FIG. 3B , after it has been placed within the subject&#39;s bone, as shown in  FIG. 3A , resulting in a smooth surface; and 
           [0016]      FIG. 6  illustrates an example of a subject&#39;s bone with multiple cartilage defects in different locations 
       
    
    
       [0017]    The detailed description explains the preferred embodiments of the invention. 
       DESCRIPTION OF THE INVENTION 
       [0018]    The present invention has utility as a system and process for performing orthopaedic surgery to repair a cartilage defect. The following description of various embodiments of the invention is not intended to limit the invention to these specific embodiments, but rather to enable any person skilled in the art to make and use this invention through exemplary aspects thereof. Disclosed herein is a process to securely fasten an articular cartilage replacement to underlying bone. Reference will be made herein to the repair of cartilage of knee joints and it should be understood that the present invention may be applied to other joints within the body and any other bones found within the body. These other joints that are repaired through resort to the present invention illustratively include the hip joint, shoulder joint, ankle joint, wrist joint, finger joint, toe joint, or other joint. As used herein, a subject is defined as a human; or an animal of a non-human primate, a horse, a cow, a sheep, a goat, a dog, a cat, a rodent, and a bird. 
         [0019]    With reference to  FIG. 1 , an embodiment of an inventive process is detailed for creating a three-dimensional model of a subject&#39;s bone and cartilage and includes the steps of receiving scan data of a subject&#39;s bone and creating a virtual three-dimensional model of the subject&#39;s bone and cartilage including the cartilage defect in block S 110 ; creating a custom shape around the cartilage defect to be removed based on the virtual model in block S 120 ; creating or shaping a pre-made cartilage replacement implant to match the custom shape in block S 130 ; registering the location of the actual bone during the surgery such that the precise position and orientation of the bone is known by the robot in block S 140 ; robotically milling the custom shape into the bone in the location predetermined in the virtual model in block S 150 ; and finally placing the graft into the bone. 
         [0020]    Scan data of a subject&#39;s bone and cartilage for creating a virtual three-dimensional model of the subject&#39;s bone and cartilage of block S 110  is readily provided from conventional sources such as CT, MRI, X-ray scans of subjects&#39; bones, or a combination thereof. Modelling software such as VSG Amira or Medviso Segment is readily used to convert imaging scans into a model of bone of interest. The scan data may be collected by a system and process described herein or may alternatively, be collected prior to the creation of the custom milled bone shape by a systems and process specific to the bone imaging technique. It is appreciated that a physical model of the bone is readily formed with a conventional three dimensional printer or transferring the virtual model data to a computer-aided design (CAD) operated milling machine. 
         [0021]    The design of a custom shape for integration of a cartilage replacement implant on the virtual model is performed at block S 120 . The custom shape in certain embodiments of the present invention thereby minimizes the amount of healthy cartilage margin around the defect that will need to be removed. Block S 120  in other embodiments functions to create a model of the subject&#39;s bone and cartilage using surgical preoperative planning software. Additionally, block S 120  in still other embodiments also functions to create instructions for a robotic system to mill out the surface of the bone to create a cavity that accurately matches the custom shape that is created. One such robotic system is the ROBODOC System, manufactured by Curexo Technology Corporation of Fremont, Calif. 
         [0022]    The creation of a cartilage replacement implant to match the custom shape planned on the virtual model is provided at block S 130 . In some embodiments, this pre-made cartilage replacement implant is created of synthetic materials. Synthetic materials suitable for the formation of such an implant illustratively include polyglycolic acid, polylactic acid, hydrogels, agarose, and fibrin. In still other embodiments, this pre-made cartilage replacement implant is created using healthy autologous osteochondral plugs removed from a donor site within the subject, from another subject, from cadaver tissue, or tissue from another species. It is appreciated that sterilization techniques for non-autologous tissues are conventional to the art. In certain inventive embodiments, it has been found that an inventive cartilage replacement implant that contains both cartilage tissue and subchondral bone tissue promotes more rapid healing and implant integration (Grayson et al. 2008) due to bone tissue&#39;s vascular nature. In still other embodiments a physical model is used to evaluate the fit of the pre-made cartilage replacement implant. 
         [0023]    The registration of the location of the bone intraoperatively within the workspace of the robot is provided at block S 140 . This serves to determine the precise location and orientation of the bone within the workspace of the robot. In some embodiments, this may be accomplished using fiducial markers placed into or on the subject bone or at a fixed position remote from the bone. 
         [0024]    A fiducial marker is appreciated to be a material with an opacity that is different than that of surround subject tissue such that it can be identified in an image and used as a point of reference or measure, an active device such as a radio frequency identification (RFID) tag, or a combination thereof. In still other inventive embodiments, a registration guide is applied that fits on the bone, a surface matching algorithm, or any other method to determine the orientation of the subject bone. The usage of such techniques are further detailed in: PCT/IB2013/002311 entitled SYSTEM AND METHOD FOR REGISTRATION IN ORTHOPAEDIC APPLICATIONS. S. Cohan, “ROBODOC achieves pinless registration”  The Industrial Robot;  2001; 28, 5; pg. 381. P. J. Besl, “A Method for Registration of 3-D Shapes” IEEE Transactions on Pattern Analysis and Machine intelligence, 1992; 14, pgs. 239-256. 
         [0025]    The robotic custom shape milling into the bone is provided at block S 150 . In certain inventive embodiments, the milling functions to create a matching cavity to the cartilage replacement implant to be placed within the matching cavity. It is appreciated that by milling with a slight undersize in the pre-made cartilage replacement implant, the milled custom shape placed into the bone forms a press-fit interaction with a cartilage replacement implant placed therein. It is also appreciated that any gap formed by the undersizing is readily filled with adhesive materials, bone fragment packing, bone growth promoters, or combinations thereof. Milling is readily performed with a rotary bit engaging subject bone tissue. 
         [0026]    The placement of a cartilage replacement implant into the bone is provided at block S 160 . In certain inventive embodiments, the cartilage replacement implant is formed from both a cartilage layer and bone layer such that when the implant is placed into the bone, the bone layer of the implant more rapidly integrates into the subject bone as the implant begins to heal, as compared to an implant devoid of a bone layer. 
         [0027]    As shown in  FIG. 6 , one embodiment of the inventive system may involve a bone with multiple cartilage defects in different locations on the bone. In this embodiment, an inventive system functions to automatically create individual customized shapes,  30 ,  32 , and  34  for each of the defects. It is appreciated that there may be any number of individual defects so produced. The inventive system in certain embodiments has information about the orientations of each of the cartilage defects and customized shapes with respect to each other on the bone. The robot mills custom shaped cavities  30 ,  32 , and  34  into the bone, as shown in  FIG. 1 , block S 150 , all automatically as the robot knows how each cavity is oriented and located with respect to each other and with respect to the bone. 
         [0028]    As shown in  FIG. 2 , a system for creating a three-dimensional model of a subject&#39;s bone of a preferred embodiment preferably includes a processor  10  configured to receive subject scan data  12  and to transform the subject scan data into a three-dimensional virtual model and allows the user to create a customized shape  14  that includes the entire cartilage defect. In some embodiments, the processor  10  may automatically create the planned customized shape  14  to include the cartilage defect and minimize the amount of healthy cartilage tissue included. The system in certain inventive embodiments functions to create a three-dimensional model of a subject&#39;s bone based on the subject scan data input. The system functions to create a three-dimensional model of a subject&#39;s bone and cartilage in sufficient detail that the subject&#39;s real bone can be registered accurately to the three-dimensional model. The processor  10  in some embodiments automatically creates a suggested customized shape  14  that includes the cartilage defect. The processor  10  in some embodiments allows the user to modify the customized shape as they choose. The processor  10  in some embodiments creates instructions for a robotic milling tip  20 , as shown in  FIG. 3A , to precisely mill out the cavity in the bone. The system can be used for cartilage replacement or repair for orthopaedic surgery, but may alternatively be used for any suitable applications, clinical or otherwise. 
         [0029]    As shown in  FIG. 2 , the processor  10  is configured to receive subject scan data  12  and to transform the subject scan data into a planned customized shape  14  that includes the entire cartilage defect. The processor  10  in some embodiments functions to create instructions for the creation of a three dimensional surface model based on the subject scan data. In some embodiments, the processor may run preoperative surgical planning software. In some embodiments, the scan data may be in the form of CT, MRI, or X-ray scans of subjects&#39; bones. The scan data may be collected by the systems and methods described herein or may alternatively, be collected prior to the creation of the custom milled bone shape by systems and methods specific to imaging. 
         [0030]    As shown in  FIG. 2 , the processor  10  in some embodiments functions to create instructions for a robot to precisely mill the customized shape  14 . In some embodiments, there may be multiple customized shapes  30 ,  32 , and  34 , as shown in  FIG. 6 . In the case of multiple customized shapes, the processor  10  in some embodiments, functions to create instructions for a robot to precisely mill all of the customized shapes in an efficient matter based on the fact that all of the customized shapes will be in known positions relative to each other and relative to the bone. 
         [0031]    As shown in  FIG. 3A , the robot  20  precisely mills out a cavity  16  that matches exactly with a cartilage replacement implant  18 , shown in  FIG. 3B . In some embodiments, a slightly undersize the milled custom shape placed into the bone such that when the cartilage replacement implant  18  is placed into the bone, it will fit tightly in a press-fit. 
         [0032]    As shown in  FIG. 4 , the cartilage replacement implant includes a layer of cartilage  24  and a layer of bone  26 . In some embodiments the layer of cartilage  24  and layer of bone  26  may be synthetic or natural. In some embodiments, the cartilage replacement implant will only has a layer of cartilage and not include a layer of bone. 
         [0033]    As shown in  FIG. 5 , the cartilage replacement implant  18  is placed into the cavity  16  such that it creates a smooth surface  28  that matches with the healthy cartilage on the bone. A layer of bone  26 , as shown in  FIG. 4 , will be of the same thickness as the removed native bone and the layer of cartilage  24 , shown in  FIG. 4 , will be of the same thickness as the surrounding cartilage. 
         [0034]    In some embodiments of the system, there may be a reason during the surgical procedure or during another surgical procedure to return to the precise location where the customized shape has been created. If the bone location is still registered or re-registered within the workspace of the robot, the robot will be able to precisely guide its tip to the location of the customized shape for an additional procedure or any other reason. 
         [0035]    References recited herein are indicative of a level of skill in the art to which the invention pertains. These references are hereby incorporated by reference to the same extent as if each individual reference was explicitly and individually incorporated herein by reference. 
         [0036]    As a person skilled in the art will recognize from the previous detailed description and from the figures and claims, modifications and changes can be made to the preferred embodiments of the invention without departing from the scope of this invention defined in the following claims.