Abstract:
A process for creating a curved contour on or within a bone is provided, where the process includes positioning a bone of a patient in a fixed position in a coordinate system, generating scan data of the bone, creating a three-dimensional surface model of the bone based on the scan data, generating a cutting program to modify a surface of the bone based on the three-dimensional surface model and a prosthesis having a bone interface shape that is complementary to the curved contour, and modifying the bone with one or more curved blades or a curved drill bit that is robotically driven and positioned with the cutting program to form the curved contour. A system for creating a curved congruent contour on or within a bone for mounting a prosthesis is also described.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority benefit of U.S. Provisional Application Ser.No. 61/978,682 filed Apr. 11, 2014; the contents of which are hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates in general to orthopaedic procedures, and in particular to the creation of exact curved surfaces within, or on bones that replicates the curved surfaces of implants through resort to curved blades and drill bits with precise robotic control. 
       BACKGROUND OF THE INVENTION 
       [0003]    Throughout a subject&#39;s lifetime, bones and joints become damaged and worn through normal use and traumatic events. This degradation of the joints involving the articular cartilage and subchondral bone is common to degenerative diseases such as arthritis and results in symptoms including joint pain, tenderness, stiffness, and potential locking of the joint. 
         [0004]    Joint replacement arthroplasty is an orthopedic procedure in which the arthritic surface of the joint is replaced with a prosthetic component. It is considered the primary form of treatment to relieve joint pain or dysfunction that may limit mobility. During an arthroplasty procedure, the ends of the bone and articular cartilage are resurfaced (i.e., by cutting the bone) to match the backside of the implant. Current implants used in total knee arthroplasty have flat planar surfaces that connect to the patient&#39;s bone, because the current tools used for making the cuts are saws, which are only capable of making flat cuts. Typical femoral implants make use of 5 or 6 planar cuts that conform to the round nature of the condyles. However, in order to preserve the maximum amount of bone, a rounded or curved surface that more closely matches the natural geometry of the femoral condyles would be most effective, but accurately creating these rounded surfaces using conventional manual tools is nearly impossible. 
         [0005]    The accurate placement and alignment of an implant is a large factor in determining the success of a joint arthroplasty procedure. Even a slight misalignment there may result in poor wear characteristics, reduced functionality, decreased implant longevity, or a combination of these and other complications. 
         [0006]    In order to achieve accurate implant placement and alignment, one must accurately position the cutting tool vis-à-vis the bone prior to making any bone cuts. In some methods, a cutting jig may be used to accurately position and orient a cutting tool such as a saw, drill, or reamer. While in other methods, the cuts may be made using a surgical assist device (e.g., a surgical robot) that controls implements such as a saw, cutter, or reamer. When a surgical assist device is used to make the cuts, the position and orientation of the bone must be known precisely in three-dimensional space (and hence vis-à-vis the surgical assist device) to ensure that the cuts are made in the correct location. Conventional methods of determining spatial orientation and location of a bone require bone registration in a three-dimensional space, either using previously placed fiducial markers or by collecting or digitizing the locations of several points or a digitized matrix on the surface of the bone. The process using previously placed fiducial markers requires an additional surgical operation, and the process of digitizing points on the surface of the bone can be time consuming. 
         [0007]    The present applicant in PCT/IB2013/002311 entitled, “SYSTEM AND METHOD FOR REGISTRATION IN ORTHOPAEDIC APPLICATIONS”, which is incorporated herein by reference; provides more efficient methods for a surgeon to rapidly and accurately determine the spatial orientation and location of a bone during orthopedic surgery. 
         [0008]    While there have been many advancements in patient specific and personalized implants and orthopaedic surgery, there still exists a need for processes and surgical tools that provide bone surface contours that afford a precise, congruent and also improved fit for surgical implants. There further exists a need for a more precise fitting implant to improve implant acceptance and integration to the patient&#39;s bone. 
       SUMMARY OF THE INVENTION 
       [0009]    A process for creating a curved contour on or within a bone, where the process includes positioning a bone of a patient in a fixed position in a coordinate system, generating scan data of the bone, creating a three-dimensional surface model of the bone based on the scan data, generating a cutting program to modify a surface of the bone based on the three-dimensional surface model and a prosthesis having a bone interface shape that is complementary to the curved contour, and modifying the bone with one or more curved blades or a curved drill bit that is robotically driven and positioned with the cutting program to form the curved contour. 
         [0010]    A system for creating a curved congruent contour on or within a bone includes a processor configured to receive patient scan data and to generate a three-dimensional model and a cutting program to modify the surface of the bone based on the three-dimensional surface model and a prosthesis having a bone interface shape complementary to the curved contour, and a machine controlled by the processor and mechanically coupled to at least one curved blade or curved drill bit, the machine robotically driven and positioned with the cutting program to modify the bone to form the curved contour. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    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: 
           [0012]      FIG. 1  is a perspective view depicting a traditional femoral total knee arthroplasty (TKA) prosthesis (total knee replacement) with planar cuts and implant-bone interface; 
           [0013]      FIG. 2  is a perspective view depicting a femoral total knee arthroplasty (TKA) prosthesis (total knee replacement) with curved surfaces on the backside for which the bone can be prepared using the curved blades and robotic control according to an embodiment of the invention; 
           [0014]      FIG. 3  shows examples of surgical curved blades and drill bits that can be adapted for use with embodiments of the invention; 
           [0015]      FIG. 4  illustrates a system for intraoperatively determining the location of a patient&#39;s bone; and 
           [0016]      FIG. 5  is a flowchart depicting a process for the use of curved blades and drill bits with precise robotic control for the creation of exact curved surfaces within or on a patient&#39;s bones that replicate the curved surfaces of implants according to an embodiment of the invention. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0017]    The present invention has utility for the application of curved blades and drill bits with precise robotic control for the creation of exact curved surfaces or other congruent surfaces within or on bones that replicate the curved surfaces or any other non-linear surfaces of implants during orthopaedic procedures. A system and process is provided for a surgeon to rapidly and accurately use curved blades or drills with precise robotic control to create highly accurate curved surfaces on or within bone for joint arthroplasty. 
         [0018]    While rotatable curved blades and drill bits have been available and used for ear, nose, and throat (ENT) procedures, such as ethmoidectomy or urcinectomy, these surgical tools have never been applied to orthopaedic surgery. Furthermore, curved blades and drill bits have never been combined with software driven robotic control, and these surgical tools have been primarily designed for use with hand tools, which allows them to be used in the curved cavities present in ENT surgeries. The application of curved blades with precise robotic control in embodiments of the invention allows for rapid creation of exact curved surfaces that replicate the curved surfaces of implants such as those used in total hip and knee arthroplasty, in contrast to current implants used in total knee arthroplasty that have flat planar surfaces, since the current tools used for making the cuts are saws, which are only capable of making flat cuts. Currently, femoral implants make use of 5 or 6 planar cuts that conform to the round nature of the condyles. However, in order to preserve the maximum amount of bone, via bone conservation protocols, a rounded or curved surface that more closely matches the natural geometry of the femoral condyles would be most effective. Accurately creating these rounded surfaces using conventional manual tools is nearly impossible. In embodiments of the invention, the use of curved blades and drills with robotic control allows for the removal of a minimal amount of bone, and creates a matching surface to a curved backside of an implant. Furthermore, embodiments of the invention may be used in any application where curved cuts within bone might be advantageous. For example, embodiments of the inventive process may be universally used to prepare curved trajectories involving any bone drill cuts with the advantage of variable angled cutters, and the ability to precisely match the surgical pre planning and achieve exact trajectories to match the curved surfaces of implants such as total hip arthroplasty femoral components. Additionally, embodiments of the inventive process may be utilized in bone removal techniques by “layers” in which thin layers of bone are removed sequentially to achieve optimal bone preservation. 
         [0019]    The precise curved bone surface obtained with embodiments of the invention is advantageous for the allowance of potential bone ingrowth interface with the preservation of a “healthy” pool of osteoblastic cells with differentiative capabilities that can be triggered via “non impacted irritative processes of non thermal necrotic nature” due to the improved cutting of these surfaces when compared with other cutting techniques, and utilizing “bone layering” techniques to decrease the temperature gradient at the cutting site. Furthermore, compared to current robotic milling techniques, the use of robotic control results in removal of bone tissue in larger blocks instead of milling bone layer by layer and resulting in bone slurry. This would also decrease destabilization of the bony architecture via minimizing disruption of the interfaces between subchondral/cortical/cancellous bone. The larger blocks of bone also present an advantage to be saved for tissue banks or other clinical applications where bone tissue is needed. This justifies the ability to reintroduce patient specific bone tissue for regenerative processes or for pharmaceutical agent scaffold utilization. 
         [0020]    Referring now to the figures,  FIG. 1  is a perspective view depicting a traditional femoral total knee arthroplasty (TKA) prosthesis  14  (total knee replacement) with planar cuts  12  in a bone  10  that matches implant-bone interface  16  of the prosthesis  14 . 
         [0021]      FIG. 2  is a perspective view depicting a femoral total knee arthroplasty (TKA) prosthesis  24  (total knee replacement) with curved surfaces  26  on the backside for which the bone  10  may be prepared with a curved contour  22  using the curved blades and robotic control according to an embodiment of the invention. 
         [0022]      FIG. 3  shows examples of surgical curved blades and drill bits  30  that can be adapted for use with embodiments of the invention. 
         [0023]    In a specific embodiment, a system for creating a three-dimensional model of a patient&#39;s bone is provided, the system including a processor configured to receive patient scan data and to transform the patient scan data into a three-dimensional virtual model and create the adjustable model instructions based on the three-dimensional virtual model. A malleable registration guide blank is configured to couple to the adjustable model and to be shaped to fit the adjustable model to form a shaped custom registration guide that is configured to fit to the patient&#39;s bone in a unique way. 
         [0024]    A system for intraoperatively determining the location of a patient&#39;s bone is also provided, the system including a digitizer configured to determine intraoperatively the location of the fiducial markers, and a processor, coupled to the digitizer, and configured to determine the location of the registration guide with respect to the fiducial markers and to determine the location of the patient&#39;s bone with respect to the registration guide. 
         [0025]    An adjustable registration jig and systems for fitting such registration jigs to a bone using a preoperative planning software is provided. The registration jigs are adjustable such that the registration jigs may be placed on the bone surfaces of specific patients and the settings adjusted such that the registration jigs fit on the bone in a unique manner. The preoperative planning software determines the settings for the adjustable jig such that the jig fits precisely on the bone. The preoperative planning software uses medical images including but not limited to computed tomography (CT), magnetic resonance imaging (MRI), or X-ray scans of patients&#39; bones as input. The scan data may be used to create a three-dimensional model of the bone(s) involved in the procedure using the preoperative planning software. 
         [0026]    In a specific embodiment, each bone has a generic adjustable jig that may be placed on the bone and secured to the bone surface by adjusting some settings. The settings on these generic adjustable jigs may be changed to accommodate bones of a variety of sizes. The jigs may be made from polymer, ceramic, metal, or other suitable material, and sterilized, or alternatively jigs may be prefabricated via 3D printing processes with respect to the specific implant of the procedure. The preoperative planning software then determines the appropriate settings for the registration jig such that the jig will securely mate with the bone surface. The adjustable jigs have three or more fiducial markers that may be optical, mechanical, or electro-magnetic. The fiducial markers may be a part of the registration jig or they may be separate modular pieces that attach to the registration jig in a specific location, or that attach directly to the bone through an opening in the jig. The fiducial markers, whose positions relative to the registration jig are known and whose positions relative to the patient bone will be known once the registration jig is placed on the bone and adjusted to its unique position, may then be rapidly located intraoperatively to determine the spatial orientation of the bone in three-dimensions. 
         [0027]    In another embodiment, the preoperative planning software generates a three-dimensional model of an adjustable jig that consists of multiple pieces that mate with the surface of the bone. The jigs multiple pieces attach to each other using an adjustable mechanism, such as a rail. The preoperative planning software determines the appropriate settings for the registration jig such that the jig will securely mate with the bone surface. In this embodiment, the registration jig fits on the surface of the bone in a unique manner making use of the specific anatomy of the patient that may include distinguishing features such as worn bone surfaces or osteophytes. The software can determine three or more specific points on the registration jig that may be used to rapidly determine the spatial location and orientation of the adjustable jig. These specific registration points may serve as locations for fiducial markers that can be optical, mechanical, or electro-magnetic. The fiducial markers may be a part of the registration jig or the fiducial markers may be separate modular pieces that attach to the registration jig in a specific location or that attach directly to the bone through an opening in the jig. The fiducial markers, whose positions relative to the registration jig are known and whose positions relative to the patient bone will be known once the registration jig is placed on the bone in its unique position, may then be rapidly located intraoperatively to determine the spatial orientation of the bone in three-dimensions. 
         [0028]    In certain embodiments, the preoperative planning software generates instructions for computer-controlled tool paths to machine the patient-specific registration jigs in a tool path data file. The tool path can be provided as input to a CNC mill or other automated machining or rapid prototyping system, and the registration jigs may be machined from polymer, ceramic, metal, or other suitable material, and sterilized. The customized patient specific jigs are spatially registered to the bone surface in three-dimensional space. The parts of the registration jig may be made of varying thickness, but shall be made of a minimum thickness such that the guide can maintain its structural stiffness without deformation. Certain areas of the jig may be made thicker to provide this structural rigidity. 
         [0029]    During surgery, once the registration jig is applied to the bone intraoperatively, the jig can be adjusted such that it fits on the bone securely in a unique manner. The jig may be secured to the bone using fixation pins, fasteners, or another process of immobilizing the jig with respect to the bone. The fixation pins may or may not also serve as the fiducial markers. Once the location of the fiducial markers has been determined using a digitizer or other digital location device, the location and orientation of the underlying bone may be determined as there is a unique relationship between the orientation and location of the registration jig and that of the bone when the settings on the registration jig are adjusted according to the preoperative planning software. Prior to beginning the bone cutting, the registration jig may or may not be removed from the bone surface. If the registration jig is removed from the surface of the bone, the fiducial markers preferably remain attached to the bone during bone cutting. These fiducial markers may be used at any point during the surgery to rapidly determine the location and orientation of the bone. 
         [0030]    The registration jig may be modular in nature, consisting of multiple pieces. Once the registration jig is adjusted and is secured to the bone, part of the registration jig may be removed from the bone, leaving part of the jig fixed to the bone. The portion of the registration jig that remains fixed to the bone should contain on or within it, fiducial markers that may be used to determine the location and orientation of the registration jig. Once the location and orientation of these fiducial markers is known, the original location of the registration jig may be determined and the location and orientation of the underlying bone may be determined as there is a unique mating between the bone and the registration jig. 
         [0031]    The registration jig or guide may be customized to fit the contours of an individual patient bone surface. Depending on the embodiment, the registration guides are automatically planned and generated. The preoperative planning software uses medical images including CT, MRI, or X-ray scans of patients&#39; bones as input. The scan data can be used to create a three-dimensional model of the bone(s) involved in the procedure using the preoperative planning software. The software then generates a three-dimensional model of a registration guide that mates with the surface of the bone. Based on the three-dimensional model, the software generates instructions for computer-controlled tool paths to machine the patient-specific registration guide in a tool path data file. The tool path may be provided as input to a CNC mill or other automated machining or rapid prototyping system, and the registration guides may be machined from polymer, ceramic, metal, or other suitable material, and sterilized. The registration guide may be made of varying thickness, but is often made of a minimum thickness such that the guide can maintain a structural stiffness and bone interface integrity without deformation. Certain areas can be made thicker to provide this structural rigidity. 
         [0032]    The generated registration guide fits on the surface of the bone in a unique manner making use of the specific anatomy of the patient that may include distinguishing features such as worn bone surfaces or osteophytes. The software can determine three or more specific points on the registration guide that may be used to rapidly determine the spatial location and orientation of the registration guide. These specific registration points can serve as locations for fiducial markers that can be optical, mechanical, or electro-magnetic. The fiducial markers may be a part of the registration guide or they may be separate modular pieces that attach to the registration guide in a specific location or that attach directly to the bone through an opening in the registration guide. The fiducial markers, whose positions relative to the registration guide are known, and whose positions relative to the patient bone will be known once the registration guide is placed on the bone in its unique position, can then be rapidly located intraoperatively to determine the spatial orientation of the bone in three-dimensions. 
         [0033]    During surgery on the subject patient for which the customized guide was formed, once the registration guide is applied to the bone intraoperatively, the guide may be secured to the bone using fixation pins, fasteners, or another process of immobilizing the guide with respect to the bone. The fixation pins may or may not also serve as the fiducial markers. Once the location of the fiducial markers has been determined using a digitizer or other digital locating device, the location and orientation of the underlying bone can be determined as there is a unique mating between the registration guide and the bone. Prior to beginning the bone cutting, the registration guide may or may not be removed from the bone surface. If the registration guide is removed from the surface of the bone, the fiducial markers shall preferably remain attached to the bone during bone cutting. These fiducial markers may be used at any point during the surgery to rapidly determine the location and orientation of the bone. 
         [0034]    In a certain embodiment of the customized registration guide, the registration guide may be modular in nature, consisting of multiple pieces. Once the registration guide is secured to the bone, part of the registration guide may be removed from the bone, leaving part of the guide fixed to the bone. The part of the registration guide that remains fixed to the bone should contain on or within it, fiducial markers that may be used to determine the location and orientation of the registration guide. Once the location and orientation of these fiducial markers is known, the original location of the registration guide may be determined and the location and orientation of the underlying bone may be determined as there is a unique mating between the bone and the registration guide. 
         [0035]    The determination of the location and the position of a patient&#39;s bone in three-dimensional space enables a surgical procedure to be performed on the bone in its known location. For example, this may be particularly useful in robotic-assisted or computer-assisted surgery (e.g., computer navigation). For example, in a joint arthroplasty procedure in the orthopedic surgery field, accurate placement and alignment of an implant is a large factor in determining the success of the procedure. A slight misalignment may result in poor wear characteristics, reduced functionality, and a decreased longevity. Knowing the exact location of the bone in three-dimensional space prior to making any bone cuts enables accurate implant placement and alignment. 
         [0036]    For example, a joint arthroplasty procedure in the orthopedic surgery field may be performed knowing the exact location of the bone in three-dimensional space prior to making any bone cuts, thereby enabling accurate implant placement and alignment and improved likelihood of success of the procedure. Another example, an osteotomy procedure in the orthopedic surgery field may be performed knowing the orientation of the bone in three-dimensional space prior to making the bone cuts to increase the accuracy of making the bone cuts and congruent surfaces as desired. 
         [0037]    As shown in  FIG. 4 , a system for intraoperatively determining the location of a patient&#39;s bone includes a custom registration guide  44 , a digitizer  42  configured to determine intraoperatively the location of the fiducial markers  46 ; and a processor  40 , coupled to the digitizer  42 , and configured to determine the location of the registration guide with respect to the fiducial markers and to determine the location of the patient&#39;s bone with respect to the registration guide. The system preferably functions to precisely locate the position of a patient&#39;s bone in three-dimensional space to enable a surgical procedure to be performed on the bone in its known location. For example, this may be particularly useful in robotic-assisted or computer-assisted surgery (e.g., computer navigation). For example, in joint arthroplasty procedure in the orthopedic surgery field, accurate placement and alignment of an implant is a large factor in determining the success of the procedure. A slight misalignment may result in poor wear characteristics, reduced functionality, decreased longevity, or a combination of these and other complications. Knowing the exact location of the bone in three-dimensional space prior to making any bone cuts enables accurate implant placement and alignment. 
         [0038]    Continuing with  FIG. 4 , the custom registration guide  44  is coupled to the patient&#39;s bone. In certain embodiments, the guide  44  is fixed or immobilized with respect to the patient&#39;s bone. As described in detail above, the digitizer  42  in some inventive embodiments functions to determine intraoperatively the location of the fiducial markers  46 . Once the location of the fiducial markers is known, the processor  40  preferably functions to determine the location of the registration guide  44  with respect to the fiducial markers  46 , and to determine the location of the patient&#39;s bone with respect to the registration guide  44 . 
         [0039]    The processor  40  in some inventive embodiments functions to determine the location of the registration guide  44  with respect to the fiducial markers  46  based on the known spatial relationship between the fiducial markers  46  and the registration guide  44 , and to determine the location of the patient&#39;s bone with respect to the registration guide  44  based on the unique fit and known spatial relationship between the registration guide  44  and the patient&#39;s bone. Once the location of the fiducial markers  46  has been determined, the location and orientation of the underlying bone may be determined, as there is a unique mating between the registration guide  44  and the bone, and the position of the fiducial markers  46  with respect to the registration guide  44  is known by the design of the registration guide  44 . 
         [0040]      FIG. 5  is a flowchart depicting a process  50  for the use of curved blades and drill bits with precise robotic control for the creation of exact curved surfaces within or on a patient&#39;s bones that replicate the curved surfaces of implants according to an embodiment of the invention. The process starts with a scan of the patient&#39;s bone to be fitted with a prosthesis (step  52 ). Based on the scan a three dimensional model of the bone surface to be contoured is generated (step  54 ). Subsequently, a cutting program to contour the bone based on the three dimensional model and the shape of the bone interface of the prosthesis is generated (step  56 ). The patient is then immobilized and positioned in a coordinate system for surgery with jigs and fiducial markers fitted to the bone (step  58 ). Bone tissue is removed with the surgical curved blades and drill bits to produce a required contoured surface to fit the prosthesis (step  60 ). 
         [0041]    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.