Patent Publication Number: US-2021177621-A1

Title: Registration tools, systems, and methods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation application of U.S. application Ser. No. 16/970,493, filed Aug. 17, 2020, which application is a national stage application of PCT/US2019/019633, filed Feb. 26, 2019, which claims the benefit of and priority to U.S. Provisional Patent Application No. 62/636,045, filed Feb. 27, 2018. All of the aforementioned applications are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to surgical systems for orthopedic joint replacement surgery and, more particularly, to methods of intra-operative pelvic registration. 
     BACKGROUND 
     Robotic systems are often used in applications that require a high degree of accuracy and/or precision, such as surgical procedures or other complex tasks. Such systems may include various types of robots, such as autonomous, teleoperated, and interactive. 
     Interactive robotic systems may be preferred for some types of surgery, such as joint replacement surgery, because they enable a surgeon to maintain direct, hands-on control of the surgical procedure while still achieving a high degree of accuracy and/or precision. For example, in knee replacement surgery, a surgeon can use an interactive, haptically guided robotic arm in a passive manner to sculpt bone to receive a joint implant, such as a knee implant. To sculpt bone, the surgeon manually grasps and manipulates the robotic arm to move a cutting tool (e.g., a rotating burr) that is coupled to the robotic arm to cut a pocket in the bone. As long as the surgeon maintains a tip of the burr within a predefined virtual cutting boundary or haptic boundary defined, for example, by a haptic object, the robotic arm moves freely with low friction and low inertia such that the surgeon perceives the robotic arm as essentially weightless and can move the robotic arm as desired. If the surgeon attempts to move the tip of the burr to cut outside the virtual cutting boundary, however, the robotic arm provides haptic feedback (e.g., forced resistance) that prevents or inhibits the surgeon from moving the tip of the burr beyond the virtual cutting boundary. In this manner, the robotic arm enables highly accurate, repeatable bone cuts. When the surgeon manually implants a knee implant (e.g., a patellofemoral component) on a corresponding bone cut the implant will generally be accurately aligned due to the configuration of and interface between the cut bone and the knee implant. 
     The above-described interactive robotic system may also be used in hip replacement surgery, which may require the use of multiple surgical tools having different functions (e.g., reaming, impacting), different configurations (e.g., straight, offset), and different weights. A system designed to accommodate a variety of tools is described in U.S. patent application Ser. No. 12/894,071, filed Sep. 29, 2010, entitled “SURGICAL SYSTEM FOR POSITIONING PROSTHETIC COMPONENT AND/OR FOR CONSTRAINING MOVEMENT OF SURGICAL TOOL”, which is hereby incorporated by reference in its entirety. 
     During a hip replacement surgery, as well as other robotically assisted or fully autonomous surgical procedures, the patient bone is intra-operatively registered with a corresponding virtual or computer bone model to correlate the pose (i.e., position and rotational orientation) of the actual, physical bone with the virtual bone model. The patient bone (physical space) is also tracked relative to the surgical robot, haptic device, or surgical tool with at least one degree of freedom (e.g., rotating burr). In this way, the virtual cutting or haptic boundaries controlled and defined on the virtual bone model via a computer can be applied to the patient bone (physical space) such that the haptic device is constrained in its physical movement (e.g., burring) when working on the patient bone (physical space). 
     Intra-operative registration of the pelvis can be challenging because of the complex geometry of the pelvis and, in particular, the concave nature of the acetabulum. While certain methods exist in the art for registration of a patient pelvis, there is need in the art for registration methods that increase accuracy while decreasing registration time. 
     BRIEF SUMMARY 
     Aspects of the present disclosure may involve a system for registering patient data gathered intra-operatively of a first bone with a computer model of the first bone in a coordinate system. The first bone may include a concave portion and forming a joint with a second bone may include a convex portion. The system may include a) a surgical navigation system may include a tracking device and at least one tool configured to be tracked in its movement by the tracking device. The system may further include b) at least one computing device in communication with the surgical navigation system, the at least one computing device storing the computer model of the first bone in the coordinate system. The at least one computing device may perform the following steps: i) receiving first data points of the patient data from first intra-operatively collected points on an articular surface of the concave portion, the first data points collected using the at least one tool, the first data points corresponding in location to a first articular region on the computer model; ii) receiving a second data point from a second intra-operatively collected point on the first bone, the second data point collected using the at least one tool, the second data point corresponding in location to a second virtual data point on the computer model; iii) determining an intra-operative center of rotation from the first data points, the intra-operative center of rotation corresponding to a physical center of rotation of the second bone relative to the first bone; iv) aligning the intra-operative center of rotation with a virtual center of rotation of the computer model in the coordinate system; v) comparing a first distance between the virtual center of rotation and the second virtual data point and a second distance between the intra-operative center of rotation and the second data point; and vi) running a transformation with the patient data and the computer model so as to have them correspond with respect to position and orientation. 
     Aspects of the present disclosure may involve one or more tangible computer-readable storage media storing computer-executable instructions for performing a computer process on a computing system. The computer process may include a) receiving a plurality of first data points of patient data points captured on a first patient bone in a first location using a tracking device of a navigation system, the first patient bone may include a concave portion forming a joint with a convex portion of a second patient bone, the plurality of first data points representing a first virtual surface profile of the first patient bone at the first location. The computer process may further include b) receiving a second data point of patient data points captured on the first patient bone in a second location using the tracking device, the second location being different than the first location. The computer process may further include c) determining a first center of rotation from the plurality of first data points, the first center of rotation being representative of a physical center of rotation of the second patient bone relative to the first patient bone. The computer process may further include d) locationally matching the first center of rotation with a virtual center of rotation of a computer model of the first patient bone, wherein the plurality of first data points, the second data point, the first center of in the coordinate system, the computer model, and the virtual center of rotation being in a common coordinate system. The computer process may further include e) locationally matching the second data point and a second virtual data point of the computer model to register the patient data points with the computer model with respect to position and orientation, the second virtual data point located on the computer model in a location corresponding to the second location on the first patient bone. 
     Aspects of the present disclosure may involve a computerized method of intra-operatively registering patient data associated with a first bone with a computer model of the first bone in a coordinate system. The first bone may include a concave portion and forming a joint with a second bone may include a convex portion. The computerized method may include a) receiving first data points of the patient data from first intra-operatively collected points on an articular surface of the concave portion of the first bone, the first data points collected with a tracking device of a navigation system. The computerized method may further include b) receiving a second data point of the patient data from a second intra-operatively collected point on the first bone, the second data point collected with the tracking device, the second data point corresponding in location to a second virtual data point on the computer model. The computerized method may further include c) determining an intra-operative center of rotation of the second bone relative to the first bone from the first data points. The computerized method may further include d) locationally matching the intra-operative center of rotation with a virtual center of rotation of the computer model in the coordinate system. The computerized method may further include e) comparing a first distance between the virtual center of rotation and the second virtual data point and a second distance between the intra-operative center of rotation and the second data point. 
     In certain instances, the computerized method may further include: f) receiving a third data point of the patient data from a third intra-operatively collected point on the first bone, the third data point collected with the tracking device, the third data point being in a different location on the first bone than the second data point and corresponding in location to a third virtual data point on the computer model; and g) comparing a third distance between the virtual center of rotation and the third virtual data point and a fourth distance between the intra-operative center of rotation and the third data point. 
     Aspects of the present disclosure may involve a computerized method of registering first patient data associated with a first patient bone and a computer model of the first patient bone in a coordinate system with respect to translation and rotation. The first patient bone may include a concave portion forming a joint with a convex portion of a second patient bone. The computerized method may include a) locking the translation between the first patient data and the computer model of the first patient bone by: i) receiving a plurality of first data points of the first patient data, the plurality of first data points corresponding to first points collected on the first patient bone in a first location, the first points collected with a tracking device of a navigation system; ii) determining an intra-operative center of rotation of the convex portion of the second patient bone relative to the concave portion of the first patient bone from the plurality of first data points; and iii) aligning the intra-operative center of rotation with a virtual center of rotation of the computer model of the first patient bone in the coordinate system. 
     In certain instances, the computerized method may further include: b) locking the rotation between the first data points and the computer model of the first patient bone by: i) capturing a second data point of the first data points on the first patient bone using the tracking device, the second data point being in a different location than the plurality of first data points and corresponding in location to a second virtual data point on the computer model; and ii) using information associated with the second data point and the second virtual data point to lock the rotation of the first data points with the computer model. 
     Aspects of the present disclosure may involve a system for guided landmark capture during a registration procedure involving registering intra-operative data associated with a first bone of a patient with a computer model of the first bone. The system may include a) a surgical navigation system may include a tracking device and at least one tool configured to be tracked in its movement by the tracking device. The system may further include b) a display device. The system may further include c) at least one computing device in electrical communication with the display device and the surgical navigation system, the at least one computing device may include: an input; an output; a memory; and a central processing unit (“CPU”) in electrical communication with the input, the output and the memory, the memory may include software for operating a graphical user interface (“GUI”), the at least one computing device configured to: i) display the GUI, and the computer model of the first bone on the display device, the GUI may include a virtual point displayed on the computer model of the first bone, the virtual point corresponding to a physical point on the first bone for intra-operatively capturing with the at least one tool, the GUI may further include a graphic at least partially surrounding the virtual point, the graphic being spaced apart from the virtual point by a radius. The GUI may further be configured to ii) adjust a size of the radius of the graphic based on a change in distance between the at least one tool and the physical point on the first bone. 
     Aspects of the present disclosure may involve a registration system that includes a bone pin guide and a bone pin clamp. The bone pin guide may include a guide body, a first guide may include a first guide through-hole having a first longitudinal axis, and a second guide may include a second guide through-hole having a second longitudinal axis. The first and second guide through-holes being spaced apart a distance, the first and second longitudinal axes being parallel to each other, and the bone pin guide may guide first and second bone pins into a bone via the first and second guides. The bone pin clamp may include a clamp body, first, second, and third clamp through-holes extending through the clamp body, a plurality of registration indents defined on the clamp body, and a clamping mechanism that may include at least one adjustable fastener. The first and third clamp through-holes being spaced apart the distance, the second clamp through-hole positioned between the first and third clamp through-holes, and the bone pin clamp may receive the first and second bone pins in the first and third clamp through-holes and guide a third bone pin into the bone via the second clamp through-hole. 
     In certain instances, the bone pin clamp further may include a sleeve coupled to the clamp body and extending distally therefrom, the second clamp through-hole extending through the sleeve. 
     In certain instances, the plurality of registration indents may include three registration indents positioned on a proximal surface of the clamp body. 
     In certain instances, the clamping mechanism may include a center lock body and a main lock body positioned within an inner volume of the clamp body. 
     In certain instances, the main lock body may be biased in position within the inner volume via a plurality of springs. 
     In certain instances, the clamp body further may include first, second, and third threaded through-holes extending into the clamp body and extending into the first, second, and third clamp through-holes, respectively, and wherein the at least one adjustable fastener may include first, second, and third threaded fasteners may be received within the first, second, and third threaded-through-holes, respectively, so as to extend into the first, second, and third threaded through-holes, respectively. 
     In certain instances, the registration system further may include a tracker array and a tracker coupling may couple to the tracker array and the bone pin clamp. 
     In certain instances, the first guide may include a first barrel extending distally from the guide body, the first guide through-hole defined within the first barrel, the second guide may include a second barrel extending distally from the guide body, the second guide through-hole defined within the second barrel. 
     In certain instances, opposite sides of the guide body each include planar tool engaging surfaces. 
     Aspects of the present disclosure may involve a registration system that may include at least one bone pin, a clamp, and a sleeve. The at least one bone pin may include a first pin having a pin longitudinal axis. The clamp may include at least one through-bore extending there through, the clamp may receive the at least one bone pin though the at least one through-bore. The sleeve may include a body having a sleeve longitudinal axis, a distal bore extending partially through a distal end of the body, and a proximal bore extending partially through a proximal end of the body. The distal bore may receive a portion of a proximal end of the first bone pin, the proximal bore may receive a distal end of a tracking device that may be tracked in its movement. The tracking device may include a device longitudinal axis, wherein, when the distal bore of the sleeve receives the portion of the proximal end of the first bone pin and when the proximal bore of the sleeve receives the distal end of the tracking device, the sleeve longitudinal axis, the pin longitudinal axis, and the device longitudinal axis are coaxial with each other. 
     Aspects of the present disclosure may involve a method of surgical registration that may include positioning a bone pin guide adjacent a patient bone. The bone pin guide may include a guide body, a first guide may include a first guide through-hole having a first longitudinal axis, and a second guide may include a second guide through-hole having a second longitudinal axis. The first and second guide through-holes being spaced apart a distance, and the first and second longitudinal axes being parallel to each other. The method may also include delivering a first bone pin into the bone via guidance by the first guide of the bone pin guide. The method may also include delivering a second bone pin into the bone via guidance by the second guide of the bone pin guide. The method may also include removing the bone pin guide from the first and second bone pins. The method may also include positioning a bone pin clamp adjacent the bone such that the first bone pin may be received within a first clamp through-hole of the bone pin clamp, and such that the second bone pin may be received within a third clamp through-hole of the bone pin clamp. The bone pin clamp may include a clamp body, the first clamp through-hole, a second clamp through-hole, and the third clamp through-hole, a plurality of registration indents defined on the clamp body, and a clamping mechanism that may include at least one adjustable fastener. The first and third clamp through-holes being spaced apart the distance, and the second clamp through-hole positioned between the first and third clamp through-holes. The method may also include delivering a third bone pin into the bone via guidance by the second through-hole of the bone pin clamp. The method may also include securing a position of the first, second, and third bone pins relative to the bone pin clamp via actuation of the clamping mechanism. The method may also include attaching a tracker array to the bone pin clamp. And the method may also include contacting at least one of the plurality of registration indents with a navigated instrument in a registration procedure. 
     In certain instances, the bone pin clamp further may include a sleeve coupled to the clamp body and extending distally therefrom, the second clamp through-hole extending through the sleeve. 
     In certain instances, the clamping mechanism may include a center lock body and a main lock body positioned within an inner volume of the clamp body. 
     In certain instances, the main lock body may be biased in position within the inner volume via a plurality of springs. 
     In certain instances, the clamp body further may include first, second, and third threaded through-holes extending into the clamp body and extending into the first, second, and third clamp through-holes, respectively, and wherein the at least one adjustable fastener may include first, second, and third threaded fasteners may be received within the first, second, and third threaded-through-holes, respectively, so as to extend into the first, second, and third threaded through-holes, respectively. 
     Aspects of the present disclosure may involve a computer-implemented method of registration that may include receiving first data points in a point-cloud corresponding to points on a patient bone in a first location that are registered with a navigated instrument. The method may also include receiving second data points in the point-cloud corresponding to points on a bone pin clamp that may be secured to the patient bone in a second location via a plurality of bone pins, the bone pin clamp may include a plurality of registration indent defining a plane, the plane being a known distance from the patient bone. The method may also include determining a bone surface point at the second location from the defined plane and known distance. And the method may also include registering the first and second data points in the point cloud with image data of the patient bone. 
     In certain instances, the bone surface point may be a point where one of the plurality of bone pins extends into the bone. 
     In certain instances, the first location may be an articular region of the acetabulum. 
     In certain instances, the first data points are fit to a sphere. 
     In certain instances, the first bone may be an ilium, the first location may be an acetabulum, and the second location may be an iliac crest. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a perspective view of a femur and a pelvis. 
         FIG. 1B  is a perspective view of a hip joint formed by the femur and pelvis of  FIG. 1A . 
         FIG. 2A  is an exploded perspective view of a femoral component and an acetabular component for a total hip replacement procedure. 
         FIG. 2B  is a perspective view illustrating placement of the femoral component and acetabular component of  FIG. 2A  in relation to the femur and pelvis of  FIG. 1A , respectively. 
         FIG. 3A  is a perspective view of an embodiment of a surgical system. 
         FIG. 3B  is a perspective view of an embodiment of a robotic arm of the surgical system of  FIG. 3A . 
         FIG. 4  illustrates an embodiment of a computer display for use during a surgical procedure. 
         FIG. 5  illustrates an embodiment of steps of a hip replacement procedure. 
         FIGS. 6 and 7  illustrate an embodiment of a pelvic registration method shown on a display screen. 
         FIG. 8A  illustrates an embodiment of steps of a pelvic registration method. 
         FIG. 8B  illustrates a table showing various characteristics of many of the steps of the pelvic registration method of  FIG. 8A . 
         FIG. 9A  is a lateral view of a three dimensional bone model of the patient pelvis showing a highlighted band along the articular surface of the acetabulum. 
         FIG. 9B  is a lateral view of the patient pelvis intra-operatively with a distal tip of a navigational probe contacting a point on the articular surface of the acetabulum. 
         FIG. 9C  depicts, on the left, a sphere generated by captured points on the articular surface of the acetabulum, and, on the right, a  3 / 4  segment of the sphere in order to show the radius of the sphere. 
         FIG. 9D  depicts a later view of the three dimensional bone model with a point of center of rotation determined pre-operatively from medical imaging of the patient pelvis. 
         FIG. 10A  is an antero-lateral view of the three dimensional bone model with a point highlighted on the anterior acetabular rim. 
         FIG. 10B  is a lateral view of the patient pelvis intra-operatively with a distal tip of a navigational probe contacting a point on the anterior acetabular rim. 
         FIG. 10C  is an antero-lateral view of the three dimensional bone model with a point highlighted on the posterior articular surface of the acetabulum. 
         FIG. 10D  is a lateral view of the patient pelvis intra-operatively with a distal tip of a navigational probe contacting a point on the posterior articular surface of the acetabulum. 
         FIG. 10E  is a postero-lateral view of the three dimensional bone model with a point highlighted on the posterior acetabular rim. 
         FIG. 10F  is a lateral view of the patient pelvis intra-operatively with a distal tip of a navigational probe contacting a point on the posterior acetabular rim. 
         FIG. 10G  is a postero-lateral view of the three dimensional bone model with a point highlighted on the anterior articular surface of the acetabulum. 
         FIG. 10H  is a lateral view of the patient pelvis intra-operatively with a distal tip of a navigational probe contacting a point on the anterior articular surface of the acetabulum. 
         FIG. 11A  is an antero-lateral view of the three dimensional bone model with a point highlighted on the anterior superior iliac spine. 
         FIG. 11B  is a lateral view of the patient pelvis intra-operatively with a distal tip of a navigational probe contacting a point on the ASIS. 
         FIG. 11C  is a lateral view of the three dimensional bone model depicting a pair of vectors in order to measure angular orientation relative to an acetabular plane. 
         FIG. 12A  is lateral view of the three dimensional bone model of the patient pelvis with a highlighted band on the anterior and superior aspect of the acetabular rim. 
         FIG. 12B  is a lateral view of the patient pelvis intra-operatively with a distal tip of a navigational probe contacting a point on the anterior aspect of the acetabular rim. 
         FIG. 12C  is lateral view of the three dimensional bone model of the patient pelvis with a highlighted band on the posterior and superior aspect of the acetabular rim. 
         FIG. 12D  is a lateral view of the patient pelvis intra-operatively with a distal tip of a navigational probe contacting a point on the posterior aspect of the acetabular rim. 
         FIG. 13A  is an anterior view of the three dimensional bone model depicting a pair of vectors in order to measure inclination about a plane that is perpendicular to the acetabular plane. 
         FIG. 13B  is a postero-lateral view of the three dimensional bone model with a point highlighted on the posterior acetabular rim, and a first embodiment of graphic surrounding the point, where the graphic is spaced apart from the point by a first radius. 
         FIG. 13C  is a postero-lateral view of the three dimensional bone model with a point highlighted on the posterior acetabular rim, and a first embodiment of graphic surrounding the point, where the graphic is spaced apart from the point by a second radius. 
         FIG. 13D  is a postero-lateral view of the three dimensional bone model with a point highlighted on the posterior acetabular rim, and a second embodiment of graphic surrounding the point, where the graphic is spaced apart from the point by a first radius. 
         FIG. 13E  is a postero-lateral view of the three dimensional bone model with a point highlighted on the posterior acetabular rim, and a second embodiment of graphic surrounding the point, where the graphic is spaced apart from the point by a second radius. 
         FIG. 14  is an example computing system having one or more computing units that may implement various systems and methods discussed herein is provided. 
         FIG. 15A  is a posterior view of a knee joint. 
         FIG. 15B  is an anterolateral view of a shoulder joint. 
         FIG. 15C  is an anterolateral view of an elbow joint. 
         FIG. 15D  is a medial view of an ankle joint. 
         FIG. 16A  is a posterior view of the pelvis showing the geometric relationship between the posterior superior iilac spines and a distal sacrum. 
         FIG. 16B  is a posterior view of the spinal column showing the geometric relationship between the distal most joints and the proximal most joints. 
         FIG. 17A  illustrates bone pins, a clamping device, and a navigated probe for use on a patient&#39;s iliac crest in a registration procedure. 
         FIG. 17B  illustrates bone pins, a clamping device, and a navigated probe for use on a patient&#39;s iliac crest in a registration procedure. 
         FIG. 17C  illustrates a bone pin and a navigated probe for use on a patient&#39;s iliac crest in a registration procedure. 
         FIG. 17D  illustrates bone pins, a clamping device, and a navigated probe for use on a patient&#39;s iliac crest in a registration procedure. 
         FIG. 17E  illustrates bone pins, a clamping device, a navigated probe, and a sleeved registration tool for use on a patient&#39;s iliac crest in a registration procedure. 
         FIG. 18A  is an isometric, exploded front view of a bone pin clamp. 
         FIG. 18B  is an isometric front view of a bone pin clamp. 
         FIG. 18C  is a first side view of the bone pin clamp. 
         FIG. 18D  is a second side view, opposite the first side view, of the bone pin clamp. 
         FIG. 18E  is a top view of the bone pin clamp. 
         FIG. 18F  is a bottom view of the bone pin clamp. 
         FIG. 18G  is a front view of the bone pin clamp. 
         FIG. 18H  is a back view of the bone pin clamp. 
         FIG. 19A  is an isometric front view of a bone pin guide. 
         FIG. 19B  is a first side view of the bone pin guide. 
         FIG. 19C  is a second side view, opposite the first side view, of the bone pin guide. 
         FIG. 19D  is a top view of the bone pin guide. 
         FIG. 19E  is a bottom view of the bone pin guide. 
         FIG. 19F  is a front view of the bone pin guide. 
         FIG. 19G  is a back view of the bone pin guide. 
         FIG. 20A  is an anterolateral view of a pelvis. 
         FIG. 20B  is an anterolateral view of a pelvis with the bone pin guide positioned against the iliac crest of the ilium. 
         FIG. 20C  is an anterolateral view of a pelvis with the bone pin guide positioned against the iliac crest of the ilium, and with a first bone pin positioned through a first guide of the bone pin guide. 
         FIG. 20D  is an anterolateral view of a pelvis with the bone pin guide positioned against the iliac crest of the ilium, and with the second bone pin positioned through a second guide of the bone pin guide. 
         FIG. 20E  is an anterolateral view of a pelvis with the two bone pins positioned in the iliac crest of the ilium, and with the bone pin guide removed. 
         FIG. 20F  is an anterolateral view of a pelvis with the two bone pins positioned in the iliac crest of the ilium, and with the bone pin clamp being positioned over the two bone pins. 
         FIG. 20G  is an anterolateral view of a pelvis with the two bone pins positioned in the iliac crest of the ilium, and with the bone pin clamp positioned over the two bone pins. 
         FIG. 20H  is an anterolateral view of a pelvis with the bone pin clamp positioned over the two bone pins, and with a third bone pin delivered through the third guide of the bone pin guide. 
         FIG. 20I  is a close-up view of the bone pin clamp positioned over the three bone pins. 
         FIG. 20J  is a close-up view of the bone pin clamp positioned over the three bone pins with a tracker arrary coupled to the clamp via a tracker coupling. 
         FIG. 20K  is a close-up view of the bone pin clamp positioned over the three bone pins with a tracker arrary coupled to the clamp via a tracker coupling, and with a navigated probe contacting a registration indent of the clamp. 
         FIG. 21A  is a flowchart of a method of registration using the bone pin guide and bone pin clamp. 
         FIG. 21B  is a flowchart of a computer-implemented method of registration using the bone pin clamp. 
         FIG. 22A  is an isometric view of a bone pin guide and a bone pin clamp positioned on an iliac crest. 
         FIG. 22B  is an isometric view of a bone pin guide positioned on an iliac crest. 
     
    
    
     DETAILED DESCRIPTION 
     The present application incorporates by reference the following applications in their entireties: U.S. patent application Ser. No. 12/894,071, filed Sep. 29, 2010, entitled “SURGICAL SYSTEM FOR POSITIONING PROSTHETIC COMPONENT AND/OR FOR CONSTRAINING MOVEMENT OF SURGICAL TOOL”; U.S. patent application Ser. No. 13/234,190, filed Sep. 16, 2011, entitled “SYSTEMS AND METHOD FOR MEASURING PARAMETERS IN JOINT REPLACEMENT SURGERY”; U.S. patent application Ser. No. 11/357,197, filed Feb. 21, 2006, entitled “HAPTIC GUIDANCE SYSTEM AND METHOD”; U.S. patent application Ser. No. 12/654,519, filed Dec. 22, 2009, entitled “TRANSMISSION WITH FIRST AND SECOND TRANSMISSION ELEMENTS”; U.S. patent application Ser. No. 12/644,964, filed Dece. 22, 2009, entitled “DEVICE THAT CAN BE ASSEMBLED BY COUPLING”; and U.S. patent application Ser. No. 11/750,807, filed May 18, 2007, entitled “SYSTEM AND METHOD FOR VERIFYING CALIBRATION OF A SURGICAL DEVICE”. 
     I. Overview 
     The hip joint is the joint between the femur and the pelvis and primarily functions to support the weight of the body in static (e.g., standing) and dynamic (e.g., walking) postures.  FIG. 1A  illustrates the bones of an operative side of a hip joint  10 , which include a left pelvis or ilium  12  and a proximal end of a left femur  14 . While a right pelvis and proximal end of a right femur is not shown in  FIG. 1A , such a discussion herein is applicable to both the right and the left femur and pelvis without limitation. Continuing on, the proximal end of the femur  14  includes a femoral head  16  disposed on a femoral neck  18 . The femoral neck  18  connects the femoral head  16  to a femoral shaft  20 . As shown in  FIG. 1B , the femoral head  16  fits into a concave socket in the pelvis  12  called the acetabulum  22 , thereby forming the hip joint  10 . The acetabulum  22  and femoral head  16  are both covered by articular cartilage that absorbs shock and promotes articulation of the joint  10 . 
     Over time, the hip joint  10  may degenerate (e.g., due to osteoarthritis) resulting in pain and diminished functionality. As a result, a hip replacement procedure, such as total hip arthroplasty or hip resurfacing, may be necessary. During hip replacement, a surgeon replaces portions of a patient&#39;s hip joint  10  with artificial components. In total hip arthroplasty, the surgeon removes the femoral head  16  and neck  18  and replaces the native bone with a prosthetic femoral component  26  comprising a head  26   a,  a neck  26   b,  and a stem  26   c  (shown in  FIG. 2A ). As shown in  FIG. 2B , the stem  26   c  of the femoral component  26  is anchored in a cavity the surgeon creates in the intramedullary canal of the femur  14 . Alternatively, if disease is confined to the surface of the femoral head  16 , the surgeon may opt for a less invasive approach in which the femoral head is resurfaced (e.g., using a cylindrical reamer) and then mated with a prosthetic femoral head cup (not shown). Similarly, if the natural acetabulum  22  of the pelvis  12  is worn or diseased, the surgeon resurfaces the acetabulum  22  using a reamer and replaces the natural surface with a prosthetic acetabular component  28  comprising a hemispherical shaped cup  28   a  (shown in  FIG. 2A ) that may include a liner  28   b.  To install the acetabular component  28 , the surgeon connects the cup  28   a  to a distal end of an impactor tool and implants the cup  28   a  into the reamed acetabulum  22  by repeatedly striking a proximal end of the impactor tool with a mallet. If the acetabular component  28  includes a liner  28   b,  the surgeon snaps the liner  28   b  into the cup  28   a  after implanting the cup  28   a.  Depending on the position in which the surgeon places the patient for surgery, the surgeon may use a straight or offset reamer to ream the acetabulum  22  and a straight or offset impactor to implant the acetabular cup  28   a.  For example, a surgeon that uses a postero-lateral approach may prefer straight reaming and impaction whereas a surgeon that uses an antero-lateral approach may prefer offset reaming and impaction. 
     II. Exemplary Robotic System 
     A surgical system described herein may be utilized to perform hip replacement, as well as other surgical procedures. As shown in  FIG. 3A , an embodiment of a surgical system  5  for surgical applications according to the present disclosure includes a computer assisted navigation system  7 , a tracking device  8 , a computer  15 , a display device  9  (or multiple display devices  9 ), and a robotic arm  30 . 
     The robotic arm  30  can be used in an interactive manner by a surgeon to perform a surgical procedure on a patient, such as a hip replacement procedure. As shown in  FIG. 3B , the robotic arm  30  includes a base  32 , an articulated arm  34 , a force system (not shown), and a controller (not shown). A surgical tool  58  (e.g., a rotary burring device as seen in  FIG. 3A , an end effector  40  having an operating member as seen in  FIG. 3B ) is coupled to an end of the articulated arm  34 , and the surgeon manipulates the surgical tool  58  by grasping and manually moving the articulated arm  34  and/or the surgical tool. 
     The force system and controller are configured to provide control or guidance to the surgeon during manipulation of the surgical tool. The force system is configured to provide at least some force to the surgical tool via the articulated arm  34 , and the controller is programmed to generate control signals for controlling the force system. In one embodiment, the force system includes actuators and a backdriveable transmission that provide haptic (or force) feedback to constrain or inhibit the surgeon from manually moving the surgical tool beyond predefined virtual boundaries defined by haptic objects as described, for example, in U.S. patent application Ser. No. 11/357,197 (Pub. No. US 2006/0142657), filed Feb. 21, 2006, and/or U.S. patent application Ser. No. 12/654,519, filed Dec. 22, 2009, each of which is hereby incorporated by reference herein in its entirety. In a certain embodiment the surgical system is the RIO™. Robotic Arm Interactive Orthopedic System manufactured by MAKO Surgical Corp. of Fort Lauderdale, Fla. The force system and controller are preferably housed within the robotic arm  30 . 
     The tracking device  8  is configured to track the relative locations of the surgical tool  58  (coupled to the robotic arm  30 ) and the patient&#39;s anatomy. The surgical tool  58  can be tracked directly by the tracking device  8 . Alternatively, the pose of the surgical tool can be determined by tracking the location of the base  32  of the robotic arm  30  and calculating the pose of the surgical tool  58  based on joint encoder data from joints of the robotic arm  30  and a known geometric relationship between the surgical tool and the robotic arm  30 . In particular, the tracking device  8  (e.g., an optical, mechanical, electromagnetic, or other known tracking system) tracks (or enables determination of) the pose (i.e., position and orientation) of the surgical tool and the patient&#39;s anatomy so the navigation system  7  knows the relative relationship between the tool and the anatomy. 
     In operation, a user (e.g., a surgeon) manually moves the robotic arm  30  to manipulate the surgical tool  58  (e.g., the rotary burring device, the end effector  40  having an operating member) to perform a surgical task on the patient, such as bone cutting or implant installation. As the surgeon manipulates the tool  58 , the tracking device  8  tracks the location of the surgical tool and the robotic arm  30  provides haptic (or force) feedback to limit the surgeon&#39;s ability to move the tool  58  beyond a predefined virtual boundary that is registered (or mapped) to the patient&#39;s anatomy, which results in highly accurate and repeatable bone cuts and/or implant placement. The robotic arm  30  operates in a passive manner and provides haptic feedback when the surgeon attempts to move the surgical tool  58  beyond the virtual boundary. The haptic feedback is generated by one or more actuators (e.g., motors) in the robotic arm  30  and transmitted to the surgeon via a flexible transmission, such as a cable drive transmission. When the robotic arm  30  is not providing haptic feedback, the robotic arm  30  is freely moveable by the surgeon and preferably includes a virtual brake that can be activated as desired by the surgeon. During the surgical procedure, the navigation system  7  displays images related to the surgical procedure on one or both of the display devices  9 . 
     To aid in tracking the various pieces of equipment within the system, the robotic arm  30  may include a device marker  48  to track a global or gross position of the robotic arm  30 , a tool end marker  54  to track the distal end of the articulating arm  34 , and a free-hand navigation probe  56  for use in the registration process. Each of these markers  48 ,  54 ,  56  (among others such as navigation markers positioned in the patient&#39;s bone) is trackable by the tracking device  8  with optical cameras, for example. 
     The navigation system  7  described herein may be any type of navigation system  7  known in the art without limitation. For example, the navigation system  7  may be an optical navigation system that optically tracks elements on a tracker array, an electromagnetic navigation system that uses magnetic fields and sensors to detect position, an ultrasound navigation system that scans bone surfaces and tool positions, fiber optic navigation systems utilizing fiber optic cables attached to components of the system, and mechanical arm navigation systems with arm encoders through the linkage. 
     The computer  15  may include a display and an input device (e.g., keyboard, mouse) and is configured to communicate with the navigation system  7 , the tracking device  8 , the various display devices  9  in the system, and the robotic arm  30 . Furthermore, the computer  15  may receive information related to a particular surgical procedure and perform various functions related to performance of the surgical procedure. For example, the computer  15  may have software as necessary to perform functions related to image analysis, surgical planning, registration, navigation, image guidance, and haptic guidance. A more detailed analysis of an example computing system having one or more computing units that may implement various systems and methods discussed herein, is described subsequently in reference to  FIG. 14 . 
       FIG. 3B  depicts an end effector  40  particularly suited for use in robotic assisted hip arthroplasty. The end effector  40  is configured to be mounted to an end of the robotic arm  30 . The end effector  40  includes a mounting portion  50 , a housing, a coupling device, and a release member. The end effector  40  is configured to individually and interchangeably support and accurately position multiple operating members relative to the robotic arm  30 . As seen in  FIG. 3B , the end effector  40  is coupled to an operating member  100 . The end effector  40  and related tools, systems, and methods are described in U.S. patent application Ser. No. 12/894,071, filed Sep. 29, 2010, which is hereby incorporated by reference in its entirety. 
     The mounting portion (or mount)  50  preferably couples the end effector  40  to the robotic arm  30 . In particular, the mounting portion  50  extends from the housing and is configured to couple the end effector  40  to a corresponding mounting portion  35  of the robotic arm  30  using, for example, mechanical fasteners, such that the mounting portions are fixed relative to one another. The mounting portion  50  can be attached to the housing or formed integrally with the housing and is configured to accurately and repeatably position the end effector  40  relative to the robotic arm  30 . In one embodiment, the mounting portion  50  is a semi-kinematic mount as described in U.S. patent application Ser. No. 12/644,964, filed Dec. 22, 2009, and hereby incorporated by reference herein in its entirety. 
     The end effector  40  in  FIG. 3B  is one example of a surgical tool that can be tracked and used by the surgical robotic arm  30 . Other tools (e.g., drills, burrs) as known in the art can be attached to the robotic arm for a given surgical procedure. 
     III. Pre-operative Planning a Surgical Procedure 
     Prior to the surgical procedure, a preoperative CT (computed tomography) scan of the patient&#39;s pelvis  12  and femur  14  is generated with a medical imaging device. While the discussion will focus on CT scans, other imaging modalities (e.g., MRI) may be similarly be employed. Additionally and alternatively, X-ray images derived from the CT scan and/or the three dimensional models  512 ,  514  can be used for surgical planning, which may be helpful to surgeons who are accustomed to planning implant placement using actual X-ray images as opposed to CT based models. The CT scan may be performed by the surgeon or at an independent imaging facility. Additionally or alternatively, intra-operative imaging methods may be employed to generate a patient model of the bone. For example, various boney surfaces of interest may be probed with a tracked probe to generate a surface profile of the surface of interest. The surface profile may be used as the patient bone model. Accordingly, the present disclosure is applicable to all methods of generating a patient bone model or a portion thereof. 
     As shown in  FIG. 4 , the CT scan or data from the CT scan is segmented and to obtain a three dimensional model  512  of the pelvis  12  and a three dimensional model  514  of the femur  14 . The three dimensional models  512 ,  514  are used by the surgeon to construct a surgical plan. The surgeon generates a surgical plan by designating a desired pose (i.e., position and orientation) of the acetabular component and the femoral component relative to the models  512 ,  514  of the patient&#39;s anatomy. For example, a planned pose  500  of the acetabular cup can be designated and displayed on a computer display, such as the display device  9 . During the surgical procedure, motion of the patient&#39;s anatomy and the surgical tool in physical space are tracked by the tracking device  8 , and these tracked objects are registered to corresponding models in the navigation system  7  (image space). As a result, objects in physical space are correlated to corresponding models in image space. Therefore, the surgical system  5  knows the actual position of the surgical tool relative to the patient&#39;s anatomy and the planned pose  500 , and this information is graphically displayed on the display device  9  during the surgical procedure. 
     In certain embodiments, the models  512 ,  514  may be of the full bone surfaces  12 ,  14  respectively. In certain embodiments, the models  512 ,  514  may be trimmed three dimensional models providing only critical regions of interest such as the acetabulum  22  and femoral head  16 . That is, the trimmed three dimensional models represent only a portion of the full bone models  512 ,  514 . In certain embodiments, the models  512 ,  514  may be the combination of multiple models. For example, model  512  may be the combination of individual three dimensional models of the operative pelvis, non-operative pelvis, and spine. 
     IV. Intra-operative Procedures 
     A. 
       FIG. 5  illustrates an embodiment of intra-operative steps of performing a total hip replacement. In this embodiment, steps S 1 -S 7 , S 9 , S 11 , and S 12  can be performed with or without robotic assistance. In other embodiments, S 1 -S 2  may not be required, S 3 -S 5  could be done before S 1 -S 2 , and S 7  could be done at any point before S 8 . Steps S 8  and S 10  are preferably performed using the robotic arm  30 . For example, step S 8  (reaming) can be performed using the robotic arm  30  of  FIG. 3  with the end effector  40  coupled to the operating member  100 , and step S 10  (impacting) can be performed using the robotic arm  30  with the end effector  40  coupled to another operating member. 
     In step S 1  of the surgical procedure, a tracking array is attached to the femur  14  to enable the tracking device  8  to track motion of the femur  14 . In step S 2 , the femur  14  is registered (using any known registration technique) to correlate the pose of the femur  14  (physical space) with the three dimensional model  514  of the femur  14  in the navigation system  7  (image space). Additionally, the femur checkpoint is attached. In step S 3 , the femur  14  is prepared to receive a femoral implant (e.g., the femoral component  26 ) using a navigated femoral broach. 
     B. Tracking and Registration of Pelvis 
     1. Overview 
     In step S 4  of  FIG. 5 , an acetabular tracking array is attached to the pelvis  12  to enable the tracking device  8  to track motion of the pelvis  12 . In step S 5 , a checkpoint is attached to the pelvis  12  for use during the surgical procedure to verify that the acetabular tracking array has not moved in relation to the pelvis  12 . The checkpoint can be, for example, a checkpoint as described in U.S. patent application Ser. No. 11/750,807 (Pub. No. US 2008/0004633), filed May 18, 2007, and hereby incorporated by reference herein in its entirety. 
     In step S 6 , the pelvis  12  is registered to correlate the pose of the pelvis  12  (physical space) with the three dimensional model  512  of the pelvis  12  in the navigation system  7  (image space). In certain embodiments, as shown in  FIG. 6 , registration is accomplished using the tracked navigation probe  56  to collect points on the pelvis  12  (physical space) that are then matched to corresponding points on the three dimensional model  512  of the pelvis  12  (image space). In certain embodiments, registration may be accomplished using a tool that is coupled to the end effector  40  of the robotic arm  30 . In certain embodiments, registration may be accomplished with any tool or device that is tracked with the navigation system  7 . Two methods of registering the three dimensional model  512  of the pelvis (image space) and the pelvis  12  (physical space) are described in the subsequent sections of this application. 
     2. First Pelvic Registration Method 
     As shown in  FIG. 6 , the display device  9  may show the representation  512  of the pelvis  12 , including one or more registration points  516 . The registration points  516  help the surgeon understand where on the actual anatomy to collect points with the tracked probe. The registration points  516  can be color coded to further aid the surgeon. For example, a registration point  516  on the pelvis  12  to be collected next with the tracked probe can be colored yellow, while registration points  516  that have already been collected can be colored green and registration points  516  that will be subsequently collected can be colored red. After registration, the display device  9  can show the surgeon how well the registration algorithm fit the physically collected points to the representation  512  of the pelvis  12 . 
     For example, as shown in  FIG. 7 , error points  518  can be displayed to illustrate how much error exists in the registration between the surface of the representation  512  and the corresponding surface of the physical pelvis  12 . In one embodiment, the error points  518  can be color coded, for example, with error points  518  representing minimal error displayed in green and error points  518  representing increasing amounts of error displayed in blue, yellow, and red. As an alternative to color coding, error points  518  representing different degrees of error could have different shapes or sizes. Verification points  519  can also be displayed. The verification points  519  illustrate to the surgeon where to collect points with the tracked probe to verify the registration. When a registration point  519  is collected, the software of the navigation system  7  displays the error (e.g., numerically in millimeters) between the actual point collected on the anatomy and the registered location of the representation  512  in physical space. If the registration error is too high, the surgeon re-registers the pelvis  12  by repeating the registration process of step S 6 . 
     This type of registration method requires the surgeon to continually switch his or her focus from the display device  9  showing the representation  512  of the pelvis  12 , including one or more registration points  516 , to the patient&#39;s physical pelvis  12  in order to collect accurate points. Switching focus takes time, and accurately estimating where the registration points  516  are on the patient&#39;s physical pelvis  12  takes even more time. In such a registration method described in this section, it may take at least forty-three points to complete an accurate registration. 
     3. Second Pelvic Registration Method 
     This section describes another registration method for registering the patient pelvis  12  (physical space) with the three dimensional model  512  (image space) of the pelvis  12  using a tracked probe  56  or other tool (e.g., end of robotic arm  30 ). The method described in this section may reduce the total number of collected points as compared with the previously described registration method. For example, with the method described in this section, a surgeon may complete an accurate registration with thirty-two points or less. Additionally, much of the registration described in this section is a region-based point collection, as opposed to a point-based point collection. In a region-based point collection, the surgeon is permitted to collect points within a region of the patient&#39;s bone, as opposed to an exact point as identified on the three dimensional bone model  512 . This permits the surgeon to focus on the patient&#39;s anatomy, and collect points within the permitted region on the bone without having to switch his or her focus to the display screen  9  and back to the patient&#39;s physical pelvis  12 . Collecting points within a permitted region increases accuracy as it is easier for the surgeon to collect points within a region encompassing many possible locations of permissible points, as compared with a single permissible point. 
     The patient pelvis  12  is referred to as in the “physical space” because the surgeon is physically using the tracked probe  56  to contact the patient pelvis  12  intra-operatively where the position and orientation of the probe  56  is known and tracked by the tracking device  8  and the navigation system  7 . The three dimensional model  512  of the pelvis  12  is referred to as in the “image space” because the model  512  is a computerized representation of the pelvis  12 , which, in certain implementations, may be taken from pre-operative medical images (e.g., CT, MRI) of the patient pelvis  12 . As stated previously, in certain implementations, the model  512  of the pelvis may be generated other ways, such as via intra-operatively tracking the pelvis over the bone surface to generate a bone surface profile, and in some embodiments a generic pelvis model may be presented. 
     In sum, use of the terms “physical space” and “image space” are utilized herein to clarify when reference is made to the patient&#39;s physical pelvis  12  or a three dimensional bone model  512 , which is a representation of the patient pelvis  12  provided as a three dimensional image, respectively. 
     Reference is made to  FIG. 8A , which shows a flowchart of the pelvic registration method  800 . The method  800  may include an initial registration  802  to provide an initial mapping of the patient pelvis  12  (physical space) with the three dimensional model  512  (image space) with respect to position and orientation. The method  800  may also include a fine registration  816  for fine tuning of the position and orientation. 
     i. Initial Registration 
     As seen in  FIG. 8A , the initial registration  802  includes a step of capturing the center of rotation  804 , capturing acetabular landmarks  808 , and capturing a distant reference point  814 . Capturing the acetabular landmarks  808  may include a step of capturing points on the acetabular rim  810 , and a step of capturing points on the surface of the acetabulum  812 . 
     In discussing each step in the registration method  800 , reference will be made to  FIG. 8B , which is a chart depicting the steps of the initial and fine registration  802 ,  816 , along with an overview of characteristics associated with each step. The Landmark/Region column indicates the portion of the pelvis that is at issue in each step of the method  800 . The Capture Method column indicates whether the method of capturing points or data is a point-based collection method or a region-based collection method. The difference between the two methods will be discussed subsequently. The Used By column indicates whether the particular step of the method  800  may be used in initial or fine registration  802 ,  816 . The Approach Dependent column indicates whether or not the system  5  will vary the procedure based on the particular surgical approach. For example, step  810  indicates that capturing points on the acetabular rim is approach dependent. Thus, the system  5  may indicate points for capturing during initial registration that are specific for the chosen surgical approach (e.g., direct anterior, antero-lateral, postero-lateral). In a direct anterior approach, for instance, the system  5  may identify points for capturing on the anterior acetabular rim since this particular area of the acetabulum is more accessible than others, such as the posterior acetabular rim. 
     Lastly, the Captured In column indicates where and when the points are captured. Each row indicates “Pre-Op/Intra-Op Registration”. While all steps of the method  800  occur during intra-operative registration on the patient pelvis (physical space), the points captured during the intra-operative registration must be compared with pre-operatively identified landmarks that correspond with the intra-operatively captured points in order to orient or register the patient pelvis  12  (physical space) with the three dimensional bone model  512  of the patient pelvis  12  (image space). Thus, each of the landmarks in the Landmark/Region column are identified in the three dimensional bone model  512  which is generated based on pre-operatively images (e.g., CT, MRI) of the patient pelvis  12 . These locations of pre-operative landmarks, relative to each other, are compared with the locations of the intra-operatively registered points to determine the accuracy of the registration process. 
     The discussion will now focus on the steps of the initial registration  802  and, in particular, the step of registering the center of rotation  804 . For this, reference is made to  FIGS. 9A-9B , which depict, respectively, a lateral view of the three dimensional model  512  of the pelvis  12  and a lateral view of the pelvis  12  (physical space). As seen in  FIG. 9A , the three dimensional model  512  of the pelvis  12 , as viewed on a display screen  9 , includes a highlighted band  824  on the articular or lunate surface  826  of the acetabulum  22 . The articular surface  826  is crescent-shaped and is typically covered by articular cartilage, which is not shown in the three dimensional model  512 . The non-articular area of the acetabulum  22  is the acetabular fossa  828 . The articular surface  826  of the acetabulum  22  is hemispherical in shape and abuts the femoral head (not shown) and allows it to rotate within the acetabulum  22 . 
     To register the center of rotation  804 , as seen in  FIG. 8 , a surgeon may use the navigational probe  56  to capture, collect, or record data points (referred to as patient data) on the patient pelvis  12  (physical space), as seen in  FIG. 9B , at multiple points along the articular surface  826  of the acetabulum  22  that corresponds to the highlighted band  824  on the three dimensional model  512  of the pelvis  12 . An alternative embodiment could use a navigational probe  56  or the tracked femur  14  that allows a surgeon to rotate within the acetabulum  22  thereby establishing a dataset representing the center of rotation  804 . Capturing, collecting, or recording data points means that the system  5  (e.g., computer  15 ) stores the location of the points relative to each other in a common coordinate system. An algorithm is then used to integrate the captured points into the coordinate system of the three dimensional bone model  512  to register or align the patient pelvis  12  (physical space) with the model  512 . In this way and upon completion of registration, a representation of the distal end a surgical tool  58  of the robotic arm  30  of the surgical system  5  may be displayed on the display  9  relative to the three dimensional bone model  512  in a way that appropriately corresponds with the physical location and orientation of the distal end of the surgical tool  58  with respect to the actual patient pelvis  12  (physical space). 
     Capturing data points or patient data within the highlighted band  824  may be referred to as a region-based point collection as opposed to a point-based collection because acceptable points may be captured throughout the articular surface  826  corresponding to the highlighted band  824 . In a point-based collection system, a specific point may be depicted on the three dimensional model  512  of the pelvis  12  and the surgeon may be queried to capture a data point at the specific point on the patient pelvis  12  (physical space) that corresponds to the specific point on the three dimensional model  512 . 
     In a certain embodiment, the system  5  may require the distance between any two points  830  to be spaced apart from each other a certain amount. The system  5  may require the distance between any two points  830  to be greater than 5 mm. The system  5  may require the distance between any two points  830  to be less than 80 mm. The system  5  may have an algorithm that defines a required distance between any two points  830  based on other inputs (e.g. acetabulum  22  or acetabular component  28 ). The system  5  may vary the distance between any two points  830  during point capture. Such a requirement may facilitate the dispersion of captured points  830  so that all points  830  are not captured in one region of the articular surface  826 , for example. In certain embodiments, the system  5  may not require a defined distance spacing between points  830 . In certain embodiments, the collected point  830  that is not satisfied the minimum spacing distance requirement may be rejected as an outlier or still be used for the point-to-model surface matching in fine registration  816 . 
     In a certain embodiment, the system  5  may require a maximum and/or a minimum number of points  830  to be collected on the articular surface  826 . The system  5  may require at least ten points  830  be captured. Additionally or alternatively, the system  5  may require less than twenty points  830  be captured. 
     Referring to  FIG. 9C , the system  5  can use the captured points  830  on the highlighted band  824  to define a sphere  832  with a center point  840  and a radius  834  since the articular surface  826  of the acetabulum  22  is spherical. Stated differently, the system  5  can generate a sphere  832  using the location of the captured points  830  because their locations relative to each other along with a best-fit calculation of the points  830  can be fitted to a sphere  832 . From the size of the sphere  832 , the radius  834  (or diameter, volume, etc.) can be determined. 
     It is noted that the sphere  832  on the left in  FIG. 9C  illustrates the highlighted band  824  and the points  830  on a spherical surface of the sphere  832 . The sphere  832  on the right illustrates a 3/4 segment of the sphere  832  in order to depict the radius  834 . 
     In a certain embodiment, the system  5  may optimize the number of points  830  by stopping point  830  collection when points  830  are more than the minimum number of points  830  but less than the maximum number of points  830 . The system  5  may use an algorithm such as convergence metrics to determine the stopping criterion/criteria. In a certain embodiment, a convergence metric can be the difference between the radius  834  calculated using N collected points  830  and the radius  834  calculated using a subset of collected points  830 , such as N- 1  collected points  830 . If the difference between the two radii  834  is smaller than a predefined threshold, the system  5  ends the point  830  collection early before the points  830  reach the maximum number of points  830 . In a certain embodiment, the convergence metrics can be calculated every time when a new point  830  is collected. 
     As seen in  FIG. 9D , a center of rotation point  836  may be pre-operatively determined based on the three dimensional bone model  512  of the pelvis  12 . A radius  838  may then be determined from the center of rotation point  836  to the articular surface  826  of the acetabulum. The center of rotation point  836  may be determined based on pre-operative scans of the patient pelvis  12  and femoral head  16 . 
     The size of the sphere  832  or, more particular, the radius  834  of the sphere  832  as determined from the intra-operative capturing of the points  830 , or patient data (physical space), as in  FIG. 9C , may be compared with the radius  838  from the center of rotation point  836  as determined from the three-dimensional bone model  512  (image space), as seen in  FIG. 9D . That is, the intra-operatively collected patient data (e.g., sphere  832  and radius  834  in  FIG. 9C ) may be compared with the pre-operatively determined values (e.g., radius  838  of  FIG. 9D ) to determine the variation there between. 
     More particularly, the system  5  may require a certain minimum difference between the two radii  834 ,  838  before the user of the system  5  may continue beyond step  804  of the initial registration  802 . In certain embodiments, the system  5  may require the radii  834 ,  838  to be less than 5 mm different from each other. In certain embodiments, the system  5  may require the radii  834 ,  838  to be less than 4 mm different from each other. In certain embodiments, the system  5  may require the radii  834 ,  838  to be less than 3 mm different from each other. In certain embodiments, the system  5  may require the radii  834 ,  838  to be less than 2 mm different from each other. In certain embodiments, the system  5  may require the radii  834 ,  838  to be less than 1 mm different from each other. 
     If the difference between the radii  834 ,  838  is within allowable tolerances, the system  5  (e.g., computer  15 ) may merge the location of the center point  840  of the sphere  832  as determined from the intra-operative capturing of the points  830  with the center of rotation point  836  as determined from the three dimensional bone model  512 . In this way, the translational orientation or aspect of registering the patient pelvis  12  (physical space) with the three dimensional bone model  512  of the pelvis  12 (image space) into a common coordinate system is fixed or locked into place. Stated differently, three degrees of freedom (i.e., translation in x, y, and z directions) may be fixed or preliminarily determined upon merging the center point  840  of the sphere  832  with the center of rotation point  836 ; thus, three degrees of freedom (i.e., rotation about the x, y, and z directions) are yet unknown. 
     In general, the system  5  is able to simplify the anatomy based on the CT scans to a patient specific geometrical feature. And then it generates a similar geometry based on the patient data from the captured points. The CT-based patient specific geometric feature is then compared with the intra-operatively captured geometric feature. The result of the comparison reflects the quality of points capturing and bone registration. 
     The subsequent steps of the registration process determine the rotational orientation of the patient pelvis  12  (physical space) with respect to the three dimensional bone model  512  of the pelvis (image space) such the robotic arm  30  of the system  5  will be oriented similarly in the image space and the physical space with respect to the bone model  512  of the pelvis and the patient pelvis, respectively. 
     Once the center of rotation  804  is calculated or captured, various other points of patient data such as acetabular landmarks may be captured  808 , as shown in  FIG. 8 . As stated previously, the capturing of the acetabular landmarks  808  may be used to determine the rotational orientation of the pelvis  12  (physical space) with the three dimensional bone model  512  of the pelvis  12  (image space). And since the translational relationship between the physical space and the image space is known by being fixed at the center of rotation point  836 , the various acetabular landmarks captured at step  808  may be used to check the distances between the landmarks and the center of rotation point  836 . 
     Capturing patient data as points on the acetabular landmarks at step  808  are point-based and may be approach dependent. As described previously, point-based data capture means that a point is identified (e.g., highlighted with a dot) on the three dimensional bone model  512  of the pelvis  12  (image space) and the surgeon is queried to select the corresponding point on the patient pelvis (physical space) with the navigational probe  56 . The system  5  (e.g., computer  15 ) can then compare the distances between, for example, the center of rotation point  836  and the highlighted point on the three dimensional bone model  512 , and the center  840  of the sphere  832  and the intra-operatively captured point. 
     To begin the discussion of capturing acetabular landmarks at step  808 , first is a description of antero-lateral and direct anterior approaches for capturing points on the acetabulum rim and articular surface at steps  810  and  812 , at  FIGS. 10A-10D . Second, is a description of postero-lateral approaches for capturing points on the acetabulum rim and articular surfaces at steps  810  and  812 , illustrated in  FIGS. 10E-10H . Though not described, the methods herein may be applied to other hip surgical approaches (e.g. direct superior) or to the capture of landmarks for registering other joints (e.g. shoulder, elbow, knee, ankle), as shown in  FIGS. 15A-15D . 
     Reference is made to  FIGS. 10A and 10B , which are, respectively, an antero-lateral view of the three dimensional bone model  512  of the patient pelvis  12  (image space) and a lateral view of the patient pelvis  12  (physical space). As seen in  FIG. 10A , the system  5  may identify (e.g., highlight) one or more points  842  on the anterior aspect of the acetabular rim  844  that forms the outer edge of the acetabulum  22  on the three dimensional bone model  512  of the patient pelvis (image space). The system  5  may then query the surgeon, as seen in  FIG. 10B , to capture the corresponding point(s)  842  on the patient pelvis  12  (physical space) by touching the distal end of the navigational probe  56  against the point  842  and logging, collecting, or capturing the position of the point  842  as patient data within the system  5 . As seen in  FIG. 10B , the point  842  on the anterior aspect of the acetabular rim  844  is accessible by the surgeon from a direct anterior approach or an antero-lateral approach. 
     For each point  842  identified by the system  5  and captured by the surgeon, the system  5  may then compare the distance between the identified point  842  and the center of rotation point  836  (image space), as seen in  FIG. 9D and 10A , with the intra-operatively gathered distance between the captured point  842  and the center point  840  of the sphere  832 , of  FIG. 9C and 10B . 
     In certain embodiments, the system  5  may identify and query the surgeon to capture a single point  842  on the anterior aspect of the acetabular rim  844 . In certain embodiments, the system  5  may identify and query the surgeon to capture two points  842  on the anterior aspect of the acetabular rim  844 . In certain embodiments, the system  5  may identify and query the surgeon to capture five points  842  on the anterior aspect of the acetabular rim  844 . In certain embodiments, the system  5  may identify and query the surgeon to capture ten points  842  on the anterior aspect of the acetabular rim  844 . In certain embodiments, the system  5  may identify and query the surgeon to capture fifteen points  842  on the anterior aspect of the acetabular rim  844 . In certain embodiments, the system  5  may identify and query the surgeon to capture another number of points  842  on the anterior aspect of the acetabular rim  844 . 
     In certain embodiments, the system  5  may display one point  842  at a time on the three dimensional bone model  512  and require the surgeon to capture the corresponding point  842  on the patient pelvis  12  (physical space) before the system  5  displays another point  842  on the three dimensional bone model  512 . In other embodiments, the system  5  may display all points  842  (e.g., 1, 2, 5, 10, 15) on the three dimensional bone model  512  of the pelvis and allow the surgeon to capture the corresponding points in any order he or she chooses. 
     Continuing on with capturing the acetabular landmarks, the surgeon may also capture one or more points on the acetabular articular surface, at step  812  of  FIG. 8 . As seen in  FIG. 10C , which is an antero-lateral view of the three dimensional bone model  512  of the patient pelvis  12  (image space), one or more points  846  may be identified (e.g., highlighted) on a posterior aspect of the articular surface  826  of the acetabulum  22  of the three dimensional bone model  512  of the patient pelvis (image space). The system  5  may query the surgeon, as seen in  FIG. 10D , which is a lateral view of the patient pelvis  12  (physical space), to capture the corresponding point(s)  846  on the posterior aspect of the patient pelvis  12  (physical space) by touching the distal end of the navigational probe  56  against the point(s)  846  and logging, collecting, or capturing the position of the point(s)  846  as patient data within the system  5 . As seen in  FIG. 10D , the point  846  on the posterior aspect of the acetabulum  22  is accessible by the surgeon from a direct anterior approach or an antero-lateral approach. 
     For each point  846  identified by the system  5  and captured by the surgeon, the system  5  may then compare the distance between the identified point  846  and the center of rotation point  836  (image space), as seen in  FIG. 9D and 10C , with the intra-operatively gathered distance between the captured point  846  and the center point  840  of the sphere  832 , of  FIG. 9C and 10D . 
     In certain embodiments, the system  5  may identify and query the surgeon to capture a single point  846  on the posterior aspect of the acetabulum  22 . In certain embodiments, the system  5  may identify and query the surgeon to capture two points  846  on the posterior aspect of the acetabulum  22 . In certain embodiments, the system  5  may identify and query the surgeon to capture five points  846  on the posterior aspect of the acetabulum  22 . In certain embodiments, the system  5  may identify and query the surgeon to capture ten points  846  on the posterior aspect of the acetabulum  22 . In certain embodiments, the system  5  may identify and query the surgeon to capture fifteen points  846  on the posterior aspect of the acetabulum  22 . In certain embodiments, the system  5  may identify and query the surgeon to capture another number of points  846  on the posterior aspect of the acetabulum  22 . 
     In certain embodiments, the system  5  may display one point  846  at a time on the three dimensional bone model  512  and require the surgeon to capture the corresponding point  846  on the patient pelvis  12  (physical space) before the system  5  displays another point  846  on the three dimensional bone model  512 . In other embodiments, the system  5  may display all points  846  (e.g., 1, 2, 5, 10, 15) on the three dimensional bone model  512  of the pelvis and allow the surgeon to capture the corresponding points in any order he or she chooses. 
     The following is a discussion of postero-lateral approaches for capturing points on the acetabulum rim and articular surfaces at steps  810  and  812 . Reference is made to  FIGS. 10E-10F  for capturing points on the acetabular rim  844  and to  FIGS. 10G-10H  for capturing points on the articular surface  826  of the acetabulum  22 . 
     As seen in  FIG. 10E , which is a postero-lateral view of the three dimensional bone model  512  of the pelvis  12  (image space) displayed on a display screen  9 , one or more points  848  may be identified (e.g., highlighted) on a posterior aspect of the acetabular rim  844  of the acetabulum  22  of the three dimensional bone model  512  of the patient pelvis (image space). The system  5  may query the surgeon, as seen in  FIG. 10F , which is a lateral view of the patient pelvis  12  (physical space), to capture the corresponding point(s)  848  on the posterior aspect of the acetabular rim  844  of the patient pelvis  12  (physical space) by touching the distal end of the navigational probe  56  against the point(s)  848  and logging, collecting, or capturing the position of the point(s)  848  as patient data within the system  5 . As seen in  FIG. 10F , the point  848  on the posterior aspect of the acetabulum rim  844  is accessible by the surgeon from a postero-lateral approach. 
     For each point  848  identified by the system  5  and captured by the surgeon, the system  5  may then compare the distance between the identified point  848  and the center of rotation point  836  (image space), as seen in  FIG. 9D and 10E , with the intra-operatively gathered distance between the captured point  848  and the center point  840  of the sphere  832 , of  FIG. 9C and 10F . 
     In certain embodiments, the system  5  may identify and query the surgeon to capture a single point  848  on a posterior aspect of the acetabular rim  844 . In certain embodiments, the system  5  may identify and query the surgeon to capture two points  848  on a posterior aspect of the acetabular rim  844 . In certain embodiments, the system  5  may identify and query the surgeon to capture five points  848  on a posterior aspect of the acetabular rim  844 . In certain embodiments, the system  5  may identify and query the surgeon to capture ten points  848  on a posterior aspect of the acetabular rim  844 . In certain embodiments, the system  5  may identify and query the surgeon to capture fifteen points  848  on a posterior aspect of the acetabular rim  844 . In certain embodiments, the system  5  may identify and query the surgeon to capture another number of points  848  on a posterior aspect of the acetabular rim  844 . 
     In certain embodiments, the system  5  may display one point  848  at a time on the three dimensional bone model  512  and require the surgeon to capture the corresponding point  848  on the patient pelvis  12  (physical space) before the system  5  displays another point  848  on the three dimensional bone model  512 . In other embodiments, the system  5  may display all points  848  (e.g., 1, 2, 5, 10, 15) on the three dimensional bone model  512  of the pelvis and allow the surgeon to capture the corresponding points in any order he or she chooses. 
     Now the discussion will focus on capturing anterior acetabular landmarks, at step  812  of  FIG. 8 . As seen in  FIG. 10G , which is a postero-lateral view of the three dimensional bone model  512  of the pelvis  12  (image space) displayed on a display screen  9 , one or more points  850  may be identified (e.g., highlighted) on an anterior aspect of the articular surface  826  of the acetabulum  22  of the three dimensional bone model  512  of the patient pelvis  12  (image space). The system  5  may query the surgeon, as seen in  FIG. 10H , which is a lateral view of the patient pelvis  12  (physical space), to capture the corresponding point(s)  850  on the anterior aspect of the articular surface  826  of the acetabulum  22  of the patient pelvis  12  (physical space) by touching the distal end of the navigational probe  56  against the point(s)  850  and logging, collecting, or capturing the position of the point(s)  850  as patient data within the system  5 . As seen in  FIG. 10H , the point  850  on the anterior aspect of the articular surface  826  of the acetabulum  22  is accessible by the surgeon from a postero-lateral approach. 
     For each point  850  identified by the system  5  and captured by the surgeon, the system  5  may then compare the distance between the identified point  850  and the center of rotation point  836  (image space), as seen in  FIG. 9D and 10G , with the intra-operatively gathered distance between the captured point  850  and the center point  840  of the sphere  832 , of  FIG. 9C and 10H . 
     In certain embodiments, the system  5  may identify and query the surgeon to capture a single point  850  on an anterior aspect of the articular surface  826 . In certain embodiments, the system  5  may identify and query the surgeon to capture two points  850  on an anterior aspect of the articular surface  826 . In certain embodiments, the system  5  may identify and query the surgeon to capture five points  850  on an anterior aspect of the articular surface  826 . In certain embodiments, the system  5  may identify and query the surgeon to capture ten points  850  on an anterior aspect of the articular surface  826 . In certain embodiments, the system  5  may identify and query the surgeon to capture fifteen points  850  on an anterior aspect of the articular surface  826 . In certain embodiments, the system  5  may identify and query the surgeon to capture another number of points  850  on an anterior aspect of the articular surface  826 . 
     In certain embodiments, the system  5  may display one point  850  at a time on the three dimensional bone model  512  and require the surgeon to capture the corresponding point  850  on the patient pelvis  12  (physical space) before the system  5  displays another point  850  on the three dimensional bone model  512 . In other embodiments, the system  5  may display all points  850  (e.g., 1, 2, 5, 10, 15) on the three dimensional bone model  512  of the pelvis and allow the surgeon to capture the corresponding points in any order he or she chooses. 
     It is noted that the surgeon may select the type of surgical approach within the system  5  so that the steps of capturing acetabular landmarks, at step  808  in  FIG. 8 , are only displayed for the selected surgical approach. In this way, for a direct anterior or an antero-lateral surgical approach, as seen in  FIGS. 10A-D , the system  5  may only display anterior acetabular rim  844  points  842  and posterior articular surface  826  points  846  on the acetabulum  22 . Similarly, for a postero-lateral approach, as seen in  FIGS. 10E-10H , the system  5  may only display posterior acetabular rim  844  points  848  and anterior articular surface  826  points  850  on the acetabulum  22 . 
     The next step in the initial registration  802 , according to  FIG. 8 , is to capture a distant reference point  814 . For this step  814 , reference is made to  FIGS. 11A-11C . As seen in  FIG. 11A , which is an antero-lateral view of the three dimensional bone model  512  of the patient pelvis  12  (image space) as displayed on a display screen  9 , a point  852  may be identified (e.g., highlighted) on a distant reference point or marker such as the anterior superior iliac spine (“ASIS”)  854 . In certain embodiments, the distant reference point may be the iliac spine crest or other landmarks that are spaced apart from the acetabulum  22 . In certain embodiments, the distant reference point may be another landmark within the incision. In certain embodiments, the distant reference point may be the ASIS on the non-operative side of the pelvis  12 , or another landmark on the non-operative side of the patient. 
     As seen in  FIG. 11B , which is a lateral view of the patient pelvis  12  (physical space), the system  5  may query the surgeon to capture the corresponding point  852  on the ASIS  854  of the patient pelvis  12  (physical space) by touching the distal end of the navigational probe  56  against the point(s)  852  and logging, collecting, or capturing the position of the point(s)  852  as patient data within the system  5 . As seen in  FIG. 11B , the point  852  on the ASIS  854  of the pelvis  12  is accessible by the surgeon from a multitude of surgical approaches since the ASIS may be identified (e.g., palpated) without an incision into the patient body. In the case of the system  5  using the iliac spine crest, a bone pin incision may be made in order to capture the point  852  on the iliac spine crest. In certain instances, the surgeon may utilize the bone pin guide  1900  and bone pin clamp  1800  as shown in  FIGS. 18A-19G , and as described in the flowchart of  FIG. 21A . And in certain instances, the surgeon may utilize the tools and methods described and shown in reference to  FIGS. 17A-17E . 
     In certain embodiments, the system  5  may identify and query the surgeon to capture a single point  852  (e.g., ASIS). In certain embodiments, the system  5  may identify and query the surgeon to capture two points  852  (e.g., ASIS, iliac spine crest). In certain embodiments, the system  5  may identify and query the surgeon to capture five points  852 . In certain embodiments, the system  5  may identify and query the surgeon to capture ten points  852 . In certain embodiments, the system  5  may identify and query the surgeon to capture fifteen points  852 . In certain embodiments, the system  5  may identify and query the surgeon to capture another number of points  852 . 
     In certain embodiments, the system  5  may display one point  852  at a time on the three dimensional bone model  512  and require the surgeon to capture the corresponding point  852  on the patient pelvis  12  (physical space) before the system  5  displays another point  850  on the three dimensional bone model  512 . In other embodiments, the system  5  may display all points  852  (e.g., 1, 2, 5, 10, 15) on the three dimensional bone model  512  of the pelvis and allow the surgeon to capture the corresponding points in any order he or she chooses. 
     For each point  852  identified by the system  5  and captured by the surgeon, the system  5  may then compare the distance between the identified point  852  and the center of rotation point  836  (image space), as seen in  FIG. 9D AND 11A , with the intra-operatively gathered distance between the captured point  852  and the center point  840  of the sphere  832 , of  FIG. 9C and 11B . 
     As seen in  FIG. 11C , which is an antero-lateral view of the three dimensional bone model  512  of the patient pelvis  12  (image space) as displayed on a display screen  9 , an intra-operatively determined vector V 1  is compared with a pre-operatively determined vector V 2 . The intra-operatively determined vector V 1  may extend from the center point  840 , which is coextensive with the center of rotation point  836 , to the intra-operatively captured point  852 ′, which corresponds to the ASIS  854  of the patient pelvis (physical space). The pre-operatively determined vector V 2  may extend from the center of rotation point  836  to the point  852  on the ASIS  854  as determined from the pre-operative image scans (e.g., CT, MRI) of the pelvis  12  (image space). 
     The vectors V 1 , V 2  may extend from an acetabular plane  856  which is coextensive with the acetabular rim  844 . From this plane  856 , a normal line centered at the center of rotation  836  may be identified. The angular difference A 1  between the vectors V 1 , V 2  may be used to lock the rotational alignment or orientation of the intra-operatively captured points (physical space) with the three dimensional bone model  512  (image space). 
     The system  5  may use the corresponding pre-operatively captured landmark points (image space), stored as patient data, as reference and give guidance to the user for capturing the intra-operatively captured landmark points (physical space). In certain embodiments, the system  5  may provide guidance based on the three dimensional geometry of pre-operatively captured landmark points (image space), and expect the same three dimensional geometry for the corresponding intra-operatively captured landmark points (physical space). In certain embodiments, the system  5  may use the Euclidean distance of landmark points to provide guidance. In certain embodiments, the system  5  may use the three dimensional angle between the vectors calculated from the landmark points to provide guidance. In certain embodiments, the system  5  may use the paired-point registration algorithm to best fit the pre-operatively captured landmark points (image space) and the corresponding intra-operatively captured landmark points (physical space), and use a fitting error to provide guidance. The guidance may be visual, audio, or tactile feedback or a combination of each. 
     Upon the completion of intra-operatively captured landmark points, the system  5  may use an algorithm to calculate the initial registration  802  transform using the intra-operatively captured landmark points (physical space) and the corresponding pre-operatively captured landmark points (image space). In certain embodiments, the system  5  may use a paired-point registration algorithm to compute the initial registration  802  transform. In certain embodiments, the system  5  may use intra-operatively captured landmark points  836 ,  842 ,  846 ,  848 ,  850 ,  852  (physical space), stored as patient data, and the corresponding pre-operatively captured landmark points (image space) to compute the initial registration  802  transform. In certain embodiments, the system  5  may only use a subset of the intra-operatively captured landmark points and the corresponding pre-operatively captured landmark points to find the best initial registration  802  transform. 
     ii. Fine Registration 
     Referring back to  FIG. 8A , fine registration  816  includes a region-based point collection or capture of acetabular landmarks  818 . Within this step, points are captured at the acetabular rim  820  and at the articular surface of the acetabulum  822 . As seen in  FIG. 8B , the region-based capture in the fine registration is approach dependent.  FIGS. 12A-12B  illustrate an antero-lateral and direct anterior approach to point capture on the acetabular rim  844 , and  FIGS. 12C-12D  illustrate a postero-lateral approach to point capture on the acetabular rim  844 . In certain embodiments, registration may be complete without the fine registration  816 . 
     To begin, reference is made to  FIGS. 12A and 12B , which are, respectively, a lateral view of the three dimensional bone model  512  of the patient pelvis  12  (image space) and a lateral view of the patient pelvis  12  (physical space). As seen in  FIG. 12A , the system  5  may identify a band  858 , which may be highlighted, on the anterior and superior aspect of the acetabular rim  844  that forms the outer edge of the acetabulum  22  on the three dimensional bone model  512  of the patient pelvis (image space). The band  858  may extend outward a certain amount from the acetabular rim  844 . The band  858  may indicate an allowable location for a region-based point collection or capture for a direct anterior or antero-lateral surgical approach. 
     As seen in  FIG. 12B , the system  5  may query the surgeon to capture points  860  on the patient pelvis  12  (physical space), using the navigational probe  56 , that correspond with the location of the band  858  on the three dimensional bone model  512  of the pelvis  12  (image space). Accordingly, the surgeon may contact the distal tip of the navigational probe  56  against various points  860  on the anterior and superior aspect of the acetabular rim  844  and capture, log, collect, or store data associated with the location of each point  860  as patient data within the system  5  (e.g., computer). 
     For fine registration of the acetabular rim  844  via a postero-lateral approach, as seen in  FIG. 12C , which is a lateral view of the three dimensional bone model  512  of the patient pelvis  12  (image space), the system may identify a band  862 , which may be highlighted, on the posterior and superior aspect of the acetabular rim  844  that forms the outer edge of the acetabulum  22  on the three dimensional bone model  512  of the patient pelvis  12  (image space). The band  862  may indicate an allowable location for a region-based point collection or capture for a postero-lateral surgical approach. 
     As seen in  FIG. 12D , the system  5  may query the surgeon to capture points  864  on the patient pelvis  12  (physical space), using the navigational probe  56 , that correspond with the location of the band  862  on the three dimensional bone model  512  of the pelvis  12  (image space). Accordingly, the surgeon may contact the distal tip of the navigational probe  56  against various points  864  on the posterior and superior aspect of the acetabular rim  844  and capture, log, collect, or store data associated with the location of each point  864  as patient data within the system  5  (e.g., computer). 
     During the step  820  of collecting points along the acetabular rim  844 , the system  5  may require the distance between any two captured points  860  (for anterior and antero-lateral approaches),  864  (for postero-lateral approaches) to be a minimum distance apart from each other. In certain embodiments, the system  5  may require a minimum spacing between two captured points  860 ,  864  to be at least 1 mm. In certain embodiments, the system  5  may require a minimum spacing between two captured points  860 ,  864  to be at least 2 mm. In certain embodiments, the system  5  may require a minimum spacing between two captured points  860 ,  864  to be at least 3 mm. In certain embodiments, the system  5  may require a minimum spacing between two captured points  860 ,  864  to be at least 4 mm. In certain embodiments, the system  5  may require a minimum spacing between two captured points  860 ,  864  to be at least 5 mm. In certain embodiments, the system  5  may require a minimum spacing between two captured points  860 ,  864  to be at least 6 mm. In certain embodiments, the system  5  may require a minimum spacing between two captured points  860 ,  864  to be at least 7 mm. In certain embodiments, the system  5  may require a different minimum spacing between two captured points  860 ,  864 . In certain embodiments, the system  5  may have an algorithm that defines a required distance between any two points  860 ,  864  based on other inputs (e.g. acetabulum  22  or acetabular component  28 ). In certain embodiments, the system  5  may vary the distance between any two points  860 ,  864  during point capture. Such a requirement may facilitate the dispersion of captured points  860 ,  864  so that all points  860 ,  864  are not captured in one region of the acetabular rim  844 , for example. In certain embodiments, the system  5  may not require a defined distance spacing between points  860 ,  864 . In certain embodiments, the collected point  860 ,  864  that is not satisfied the minimum spacing requirement may be rejected as an outlier or still be used for the point-to-model surface matching in fine registration  816 . 
     In certain embodiments, the system  5  may require the surgeon to capture a maximum and/or a minimum number of points  860 ,  864  for a given surgical approach before proceeding to a subsequent step of the registration process. For example, in certain embodiments the system  5  may require a minimum of twenty points be captured. In certain embodiments the system  5  may require a minimum of fifteen points be captured. In certain embodiments the system  5  may require a minimum of ten points be captured. In certain embodiments the system  5  may require a minimum of five points be captured. In certain embodiments the system  5  may require between ten and twenty points be captured. 
     In a certain embodiment, the system  5  may optimize the number of points  860 ,  864  by stopping point  860 ,  864  collection when points  860 ,  864  are more than the minimum number of points  860 ,  864  but less than the maximum number of points  860 ,  864 . The system  5  may use an algorithm such as convergence metrics to determine the stopping criterion/criteria. In a certain embodiment, a convergence metric can be the difference between 1) the root-mean-square error of point-to-model surface matching calculated using N collected acetabular rim points  860 ,  864  plus the articular surface points  830  and landmark points  842 ,  846 ,  848 ,  850 , and 2) the root-mean-square error of point-to-model surface matching calculated using a subset of collected acetabular rim points  860 ,  864  such as N−1 collected points  860 ,  864  plus the articular surface points  830  and landmark points  842 ,  846 ,  848 ,  850 . If the difference between the two root-mean-square errors is smaller than a predefined threshold, the system  5  ends the point  860 ,  864  collection early before the points  860 ,  864  reach the maximum number of points  860 ,  864 . In a certain embodiment, the convergence metrics can be calculated every time when a new point  860 ,  864  is collected. 
     Referring back the fine registration  816  of  FIG. 8A , the acetabulum articular surface is captured  822  and stored as patient data. This step  822  is similar to the methods described in reference to  FIGS. 9A and 9B  and, thus, the following discussion will be made with reference to those figures. Also, the discussion in reference to  FIGS. 9A and 9B  is also applicable to the discussion of step  822 . For example, while the minimum distance between the points  830  was discussed in reference to  FIGS. 9A and 9B , the system  5  may use the same parameters in the fine registration of the acetabulum articular surface capture  822 . For the fine registration at step  822 , as seen in  FIG. 9A , the system  5  may display on a display screen  9  a highlighted band  824  on the articular surface  826  of the acetabulum  22  on the three dimensional bone model  512  of the patient pelvis  12  (image space). As discussed previously, this is a region-based point capture where the surgeon may capture points  830  on the patient pelvis  12  (physical space) on any area of the pelvis  12  that corresponds with the highlighted band  824  (i.e., articular surface  826 ). 
     As with the methods described in reference to  FIGS. 9A-9B , the system  5  may require a certain number of points  830  be captured before moving on to other steps in the registration  800 . In certain embodiments, the system  5  may require a minimum of twenty points be captured. In certain embodiments the system  5  may require a minimum of fifteen points be captured. In certain embodiments the system  5  may require a minimum of ten points be captured. In certain embodiments the system  5  may require a minimum of five points be captured. In certain embodiments the system  5  may require between ten and twenty points be captured. 
     Once all the acetabular rim points  860 ,  864  are collected, an algorithm may be used to determine the registration transform for fine registration  816 . In a certain embodiment, the system  5  may use Iterative Closest Point (ICP) (P. J. Besl, H. D. McKay, A method for registration of 3-D shapes, IEEE Transactions on Pattern Analysis and Machine Intelligence, 1992), a point-to-surface matching algorithm that best fits the intra-operatively captured points (physical space) with the three dimensional bone model  512  (image space). In certain embodiments, the intra-operatively captured points might be a collection of previously mentioned articular surface points  830 , acetabular rim points  860 ,  864 , and landmark points  842 ,  846 ,  848 ,  850 . In certain embodiments, the intra-operatively captured points might be a collection of articular surface points  830 , acetabular rim points  860 ,  864 , and landmark points  842 ,  846 ,  848 ,  850  with certain points removed (e.g., statistical outliers). In certain embodiments, the intra-operatively captured points might be used for both initial registration  802  and fine registration  816 . In certain embodiments, the ICP algorithm may use the initial registration  802  transform as the initial guess to improve fine registration  816 . 
     Using the information from the fine registration  816 , quality metrics may be employed to determine the accuracy of registration. 
     Within the fine registration  816 , quality metrics may be employed for checking and verifying the accuracy of the rotational orientation around the acetabular normal, as similarly described with reference to  FIG. 11C . As seen in  FIG. 11C , an intra-operatively determined vector V 1  is compared with a pre-operatively determined vector V 2  to determine the difference in rotational orientation between the intra-operatively captured points and the pre-operatively determined points. The intra-operatively determined vector V 1  may extend from the center point  840 , which is coextensive with the center of rotation point  836 , to the intra-operatively captured point  852 ′, which corresponds to the ASIS  854  of the patient pelvis (physical space). The pre-operatively determined vector V 2  may extend from the center of rotation point  836  to the point  852  on the ASIS  854  as determined from the pre-operative image scans (e.g., CT, MRI) of the pelvis  12 . 
     The vectors V 1 , V 2  may extend from an acetabular plane  856 , defined in a lateral view, which is coextensive with the acetabular rim  844 . From this plane  856 , a normal line centered at the center of rotation  836  may be identified. The angular difference A 1  between the vectors V 1 , V 2  may be used to lock the rotational alignment or orientation of the intra-operatively captured points (physical space) with the three dimensional bone model  512  (image space). 
     Another quality metric, as seen in  FIG. 13A , which is an antero-lateral view of the three dimensional bone model  512  of the patient pelvis  12  (image space) displayed on a display screen  9  of the system  5 , may be employed for checking inclination or rotation about a plane  866  perpendicular to the acetabular plane  856  as described in reference to  FIG. 11C . As seen in  FIG. 13A , vectors V 1 , V 2  are the same vectors as shown and described in reference to  FIG. 11C .  FIG. 13A  simply displays the vectors V 1 , V 2  with respect to a plane  866  that is perpendicular to the acetabular plane  856  so as to measure an angular difference A 2  between the vectors V 1 , V 2  in the plane  866 . The angle A 2  may be used to measure an inclination or angular difference between the three dimensional bone model  512  of the pelvis  12  (image space) and the patient pelvis  12  (physical space). 
     Additionally or alternatively, the system  5  may include a quality metric by instructing the user to collect additional points on the patient&#39;s anatomy at different locations, and then the system  5  measures the distance between the captured point and the corresponding surface of the three dimensional bone model  512  to ensure registration accuracy is acceptable. In certain instances, the system  5  may queue the user to collect one verification point. In certain instances, the system  5  may queue the user to collect two verification points. In certain instances, the system  5  may queue the user to collect three verification points. In certain instances, the system  5  may queue the user to collect six verification points. In certain instances, the system  5  may queue the user to collect eight verification points. In certain instances, the system  5  may queue the user to collect up to ten verification points. 
     The location of the verification points may be locations corresponding to low confidence of registration (e.g., point-to-surface mapping is above a certain threshold). This way, areas of low confidence can identified and additional points can be captured in these areas to determine if registration can result in a higher confidence in the area. Once the user captures the verification points, the captured points may be added to the original point cloud, and all points may be used in the registration algorithm to refine the registration transform. 
     In certain instances, the location of the verification points may be approach dependent (e.g., direct anterior) so that the points are within the opening of the incision. In certain instances, the location of the verification points may be spaced apart from previously captured points so as to ensure a minimum distance between each of the captured points, or to ensure a balanced distribution of the captured points. 
     Upon completion of the fine registration  816 , the system  5  may indicate that the registration process  800  is complete, and the surgical procedure may commence. 
     The following discussion focuses on a graphical user interface (“GUI”)  1000  associated with guiding the capture of landmarks on the patient&#39;s anatomy during a registration procedure of a robotic surgery. Such guidance may be useful for the surgeon as he or she may be attempting to locate a physical point on the patient&#39;s pelvis  12  while also looking at a corresponding virtual point on the three dimensional bone model  512  displayed on a display screen  9 . In this way, the GUI  1000  may provide guidance to the surgeon that he or she is nearing the physical point on the pelvis  12  that corresponds to the virtual point on the bone model  512 . 
       FIGS. 13B-13C  depict a first embodiment of a GUI  1000  that guides a user in capturing a point  1002 .  FIGS. 13D-13E  depict a second embodiment of a GUI  1000  that guides a user in capturing a point  1002 . 
     Referring to  FIG. 13B , the GUI  1000  is displayed on a display screen  9 , which shows the three dimensional bone model  512  of the patient pelvis  12  on a portion of the screen  9 . A virtual point  1002  is displayed on the bone model  512  for which the user is instructed to capture or collect with the system  5  on the patient&#39;s pelvis (physical space) with the navigation probe or other tracked tool (not shown). In certain instances, a radius of the virtual point  1002  (being relative to the patient&#39;s anatomy as replicated in the bone model  512 ) may be about 4 millimeters (mm). In certain instances, the radius of the virtual point  1002  may be other distances such as, for example, 2 mm, 6 mm, or 10 mm, among others. 
     In the first embodiment, directional arrows or triangles  1004  will appear and surround point  1002  in a generally circular fashion when the tip of the navigation probe or other tracked tool is within a certain radius or distance to the physical point on the patient&#39;s pelvis  12  that corresponds with the location of the virtual point  1002  on the bone model  512 . In certain instances, the directional arrows  1004  will not be displayed until the tip of the navigation probe is within a 100 mm radius of the physical point that corresponds with the virtual point  1002 . In this way, the arrows  1004  may appear and disappear, respectively, as the tip of the navigation probe moves within the 100 mm radius, and moves outside of the 100 mm radius. The radius of 100 mm is exemplary, and may be other distances such as, for example, 50 mm, 150 mm, or 200 mm, among others. 
     When the tip of the probe approaches and enters a certain radius or distance away from the point on the patient&#39;s pelvis  12  corresponding to the point  1002  on the bone model  512  (e.g., 100 mm), the arrows  1004  may appear and be spaced apart from the point  1002  a first radius. As the user moves the tip of the probe closer to the point on the patient&#39;s pelvis  12  corresponding to the point  1002  on the bone model  512 , the arrows  1004  may move closer to the point  1002 , as seen in  FIG. 13C . Stated differently, as the user moves the tip of the probe closer to the point on the patient&#39;s pelvis  12  corresponding to the point  1002  on the bone model  512 , the first radius decreases to a second radius. In certain instances, as the tip of the probe gets progressively closer to the physical point on the patient&#39;s pelvis  12  corresponding to the point  1002  on the bone model  512 , the arrows  1004  corresponding move progressively closer to the point  1002 , and the radius of the arrows  1004  progressively decreases indicating the tip of the probe is near the point  1002  to be captured. In certain instances, the point  1002  and/or the arrows  1004  may change color when the point is captured and/or when the tip of the probe is in a location accurately corresponding to the point  1002 . 
     In this way, the GUI  1000  includes the directional arrows  1004  sequentially transitioning from a first state, as seen in  FIG. 13B , where the arrows  1004  are further away from the point  1002 , to a second state, as seen in  FIG. 13C , where the arrows  1004  are closer to the point  1002 . In certain instances, the color of the arrows and/or point  1002  may change when sequentially transitioning from the first state to the second state. For example, the colors may change from red, to yellow, and to green as the tip of the navigation probe progressively moves closer to the point  1002 . 
     Referring to  FIGS. 13D , the graphical user interface (“GUI”)  1000  is displayed on a display screen  9 , which shows the three dimensional bone model  512  of the patient pelvis  12  on a portion of the screen  9 . A virtual point  1002  is displayed on the bone model  512  for which the user is instructed to capture with the system  5  on the patient&#39;s pelvis (physical space) with the navigation probe or other tracked tool (not shown). In certain instances, a radius of the virtual point  1002  (being relative to the patient&#39;s anatomy as replicated in the bone model  512 ) may be about 4 mm. In certain instances, the radius of the virtual point  1002  may be other distances such as, for example, 2 mm, 6 mm, or 10 mm, among others. 
     In the second embodiment, a reticle  1004  having a circle with partial vertical and horizontal alignment indicators may appear and surround point  1002  when the tip of the navigation probe or other tracked tool is within a certain radius or distance to the physical point on the patient&#39;s pelvis  12  that corresponds with the location of the virtual point  1002  on the bone model  512 . In certain instances, the reticle  1004  will not be displayed until the tip of the navigation probe is within a 100 mm radius of the physical point that corresponds with the virtual point  1002 . In this way, the reticle  1004  may appear and disappear, respectively, as the tip of the navigation probe moves within the 100 mm radius, and moves outside of the 100 mm radius. The radius of 100 mm is exemplary, and may be other distances such as, for example, 50 mm, 150 mm, or 200 mm, among others. 
     When the tip of the probe approaches and enters a certain radius or distance away from the physical point on the patient&#39;s pelvis  12  corresponding to the virtual point  1002  on the bone model  512 , the circle of the reticle  1004  may appear and be spaced apart from the point  1002  a first radius. As the user moves the tip of the probe closer to the point on the patient&#39;s pelvis  12  corresponding to the point  1002  on the bone model  512 , the radius gets smaller such that the circle of the reticle  1004  moves closer to the point  1002 , as seen in  FIG. 13E . Stated differently, as the user moves the tip of the probe closer to the point on the patient&#39;s pelvis  12  corresponding to the point  1002  on the bone model  512 , the first radius decreases to a second radius. In certain instances, as the tip of the probe gets progressively closer to the point on the patient&#39;s pelvis  12  corresponding to the point  1002  on the bone model  512 , the size of the circle (e.g., the radius) of the reticle  1004  corresponding gets progressively smaller and closer to the point  1002  indicating that the tip of the probe is near the point  1002  to be captured. In certain instances, the point  1002  and/or the circle of the reticle  1004  may change color when the point is captured and/or when the tip of the probe is in a location accurately corresponding to the point  1002 . 
     In this way, the GUI  1000  includes the a reticle  1004  sequentially transitioning from a first state, as seen in  FIG. 13D , where a perimeter of the circle of the reticle  1004  is farther away from the point  1002 , to a second state, as seen in  FIG. 13E , where the perimeter of the circle of the reticle  1004  is closer to the point  1002 . In certain instances, the color of the reticle  1004  and/or point  1002  may change when sequentially transitioning from the first state to the second state. For example, the colors may change from red, to yellow, and to green as the tip of the navigation probe progressively moves closer to the point  1002 . 
     The directional arrows and reticle  1004  may be substituted for other graphics including, but not limited to a bulls eye, a pointer, a transparent circle or sphere, or destination pin, among others. Additionally, or alternatively, the graphic may blink, rotate, enlarge, or shrink to indicate a change in distance of the tip of the probe to the point  1002 . In certain instances, any graphic may be used that generally identifies the point  1002  on the bone model  512  in a first way when the tip of the probe is a first distance from the point on the patient&#39;s pelvis  12  that corresponds with the point  1002 , and generally identifies the point  1002  on the bone model  512  in a second way when the tip of the probe is a second distance from the patient&#39;s pelvis  12  that corresponds with the point  1002 . In this example, the first distance may be further away from the point  1002  than the second distance, and the first way may be the graphic with a first diameter that is larger than a second diameter of the graphic in the second way. 
     It is noted that the GUI described in reference to  FIGS. 13B-E  may be utilized at any step in the methods described herein without limitation (e.g., initial registration, fine registration, verification). 
     While the former sections of this application focus on registration of the pelvis  12 , the systems and methods described herein are applicable to intra-operative registration of other bones and joints.  FIGS. 15A-15D  depict example joints for intra-operative registration including a knee joint  600 , a shoulder joint  700 , an elbow joint  800 , and an ankle joint  900 , respectively. 
     As seen in  FIG. 15A , the knee joint  600  includes a distal end of a femur  602  and a proximal end of a tibia  604 . The distal end of the femur  602  includes medial and lateral condyles  606 . The proximal end of the tibia  604  includes a tibial plateau  608  including medial and lateral portions configured to mate with the corresponding condyles  606  of the femur  602 . As the knee joint  600  is articulated, the condyles  606  rotate relative to the tibial plateau  608 . A thin layer of cartilage may be positioned between the condyles  606  and the tibial plateau  608 . As seen in the figure, the condyles  606  may include a rounded or convex profile, whereas the tibial plateau  608  includes a concave profile. A total knee replacement may replace the distal end of the femur  602  including the condyles  606  with a femoral component of an implant, as well as a tibial component of an implant to replace the tibial plateau  608 . During surgical registration of the tibia  604  and femur  602  for the knee arthroplasty, as with the systems and methods described with reference to the pelvis  12 , a center of rotation could be calculated for the knee joint  600  based, for example, on a shape of the tibial plateau  608 , or otherwise. Similarly, portions of the tibia  604  or femur  602  surrounding the tibial plateau  608  and condyles  606  may be registered, as well as a long point on one or both bones. 
     As seen in  FIG. 15B , the shoulder joint  700  includes a lateral portion of a scapula  702  and a proximal end of a humerus  704 . The scapula  702  includes a glenoid cavity  706  which is a shallow pyriform articular surface on a lateral end of the scapula  702 . A humeral head  708 , which is nearly hemispherical in shape, articulates within the glenoid cavity  706 . A conventional total shoulder replacement surgery may replace the humeral head  708  and glenoid cavity  706  with an implant having a stem that fits within the humerus  704  and an implant ball that fits within a glenoid socket component that is fitted to the scapula in place of the glenoid cavity  706 . Generally, the humeral head  708  may be considered to include a convex bone portion, while the scapula  702  may be considered to include a concave bone portion. During surgical registration of the scapula  702  and humerus  704  in preparation for a shoulder arthroplasty, as with the systems and methods described with reference to the pelvis  12 , a center of rotation could be calculated for the shoulder joint  700  based, for example, on a shape of the glenoid cavity  706 , or otherwise. Similarly, portions of the scapula  702  surrounding the glenoid cavity  706  (e.g., a rim of the glenoid cavity  706 ) may be registered, as well as a long point (e.g., posterior spine of scapula  702 , clavicle, acrom ion). 
     As seen in  FIG. 15C , the elbow joint  800  includes a distal end of a humerus  802 , and a proximal end of an ulna  804 . The distal end of the humerus  802  includes a trochlea  806  that articulates with a trochlear notch  808  of the ulna  804 . The trochlea  806  is convex from anterior to posterior, and concave medial to lateral. The trochlear notch  808  of the ulna  804  is concave anterior to posterior, and convex medial to lateral. The distal end of the humerus  802  also includes a capitulum that articulates with a head of a radius (not shown). Generally, the distal end of the humerus  802  may be considered to include a convex bone portion, while the ulna  804  may be considered to include a concave bone portion. A conventional elbow replacement includes replacing the distal end of the humerus  802  and the proximal end of the ulna  804  with an implant component having a humeral metal stem component, a fixed hinge, and an ulna metal stem component. During surgical registration of the humerus  802  and the ulna  804 , as with the systems and methods described with reference to the pelvis  12 , a center of rotation could be calculated for the elbow joint  800  based, for example, on a shape of the trochlear notch  808 , or otherwise. Similarly, portions of the trochlear notch  808  (e.g., surrounding the notch  808 , radial notch) may be registered, as well a long point on the ulna  804 . 
     As seen in  FIG. 15D , the ankle joint  900  includes a distal end of the tibia  902  and a talus  904 . The fibula is not shown. The distal end of the tibia  902  includes an inferior articular surface or plafond. A superior surface of the talus  904  includes an articular surface or trochlea tali, which is semi-cylindrical, and which mates with the distal end of the tibia  902 . Generally, the distal end of the tibia  902  may be considered to include a concave bone portion, while the talus may be considered to include a convex bone portion. In a conventional ankle replacement surgery, the distal end of the tibia  902  and a proximal portion of the talus  904  are replaced with a tibial component and a talar component, respectively. The talar component is typically convex, and mates with the tibial component, which is concave. During surgical registration of an ankle replacement surgery, as with the system and methods described with reference to the pelvis  12 , a center of rotation could be calculated for the ankle joint  900  based, for example, on a shape of the distal end of the tibia  902  or plafond, or otherwise. Similarly portions of the distal end of the tibia  902  or plafond (e.g., surrounding area) may be registered, as well as a long point on the tibia  902  (e.g., tibial tuberosity). 
       FIGS. 16A and 16B  depict additional or alternative registration methods for other portions of the body that utilizes pattern geometry to reduce the number of registrations points needed for an accurate registration process.  FIG. 16A  depicts a posterior view of a pelvis  12  including a left and right ilium  1100 , and a sacrum  1102  between the left and right ilium  1100 .  FIG. 16B  depicts a posterior view of a spinal column  1104 . 
     As seen in  FIG. 16A , there is a geometric relationship between the right and left posterior superior iliac spine (“PSIS”)  1106  and the distal sacrum  1108 . The distal sacrum  1108  may be any point at a medial-lateral midline of the sacrum  110  including, but not limited to, the apex of the sacrum at its connection with the base of the coccyx. The right and left PSIS  1106  and the distal sacrum  1108  define an isosceles triangle with two equal length sides  1110  and two equal angles  1112 . Thus, the geometric information can be used in the registration process in a similar manner as the center of rotation calculation described previously. For example, a surgeon may capture the location of the right and left PSIS  1106  and the system  5  may guide the surgeon in capturing the location of the distal sacrum  1108  given that the lengths  1110  to the distal sacrum  1108  from each of the PSIS  1106  must be equal. Knowing the geometric relationship between the boney landmarks may provide guidance to the surgeon by ensuring the location for capturing of the distal sacrum  1108  is taken when the lengths  1110  are equal. 
     As seen in  FIG. 16B , there is a geometric relationship between the most proximal joints  1114  of the spine  1104  and the most distal joints  1116  of the spine  1104 . More particularly, the proximal joints  1114  and the distal joints  1116  may define an isosceles trapezoid with parallel bases  1118 ,  1120  and equal angles  1122  between the distal base  1118  and the legs  1124 . Thus, the geometric information can be used in the registration process in a similar manner as the center of rotation calculation described previously to ensure that the surgeon captures accurate points. 
     V. Pelvic Registration Tools and Methods of Use 
     The following description of tools, systems, and methods for use in registration procedures reference certain anatomy (e.g., iliac crest) as specific instances of use; however, it is foreseen that the tools, systems, and methods described herein may be used on different anatomical landmarks without limitation. The specific anatomical landmarks, such as the iliac crest, are merely exemplary of a location used in a hip procedure. As such, the tools, systems, and methods described herein may be used on bones associated with surgical procedures on other joints (e.g., knee, ankle elbow, shoulder, spine). 
       FIGS. 17A-17E  depict example tools and methods for use in capturing one or more points on the iliac crest  1700  of the ilium  1702  of the patient. One challenge with locating and capturing a point on the iliac crest  1700  in a hip registration procedure is that such an area may not be easily accessible to the surgeon within the incision opening for the hip procedure. While a separate stab incision may be utilized at the iliac crest  1700  to access and log a data point, it is generally desirable to make as few incisions into the body as possible. The following embodiments involve using a tracker  1704  that is ultimately attached to the patient, for example at the iliac crest  1700 , and obtaining the landmark crest point (as illustrated in  FIGS. 11A and 11B , and described in the corresponding section of the application, and described in reference to step  814  of  FIG. 8A ) in or around the incision for the attachment of the tracker  1704 . In this example, the iliac crest  1700  is used for tracking purposes in addition to the registration process  1200  defined previously. 
       FIG. 17A  depicts a first embodiment of a device  1706  and method for accessing and capturing one or more data points on the patient&#39;s iliac crest  1700 . The device  1706  includes three bone pins  1710  and a clamp  1708 . The clamp  1706  may include three equally spaced-apart through-bores  1712  for receiving the bone pins  1710  therein in a known orientation relative to each other. The clamp  1706  may include a locking feature (e.g., thumb-screw to compress against the pins  1710 ) so movement of the pins  1710  relative to the clamp  1706  is restrained once the locking feature is engaged. A tracker  1704  (e.g., optical, electromagnetic, ultrasound, fiber optic, mechanical arm linkage) may be attached or integrated with the clamp. The tracker  1704  may be monitored via a tracking device (e.g., camera)  8  of the navigation system  7 . In the first embodiment, a surgeon may access the patient&#39;s iliac crest  1700  for landmark acquisition by inserting a probe tip of a tracked probe  56  through one of the pin incisions and contacting the iliac crest  1700  at a point  1714  where the pin  1710  extends into the bone  1702 . While the device  1706  depicts three through-bores  1712 , the device may include a different number of through-bores  1712  without departing from the teachings of the present disclosure. Additionally or alternatively, the through-bores  1712  are described as being equally-spaced apart, but in certain instances the through-bores  1712  may be un-evenly spaced apart from each other. 
       FIG. 17B  depicts a second embodiment of a device  1706  and method for accessing and capturing one or more data points on the patient&#39;s body, for example at the iliac crest  1700 . The device  1706  includes three bone pins  1710  and a clamp  1708 . The clamp  1708  may include three equally spaced-apart through-bores  1712  for receiving the bone pins  1710  therein in a known orientation relative to each other. The clamp  1708  may include a locking feature (e.g., thumb-screw to compress against the pins  1710 ) so movement of the pins  1710  relative to the clamp  1708  is restrained once the locking feature is engaged. A tracker  1704  (e.g., optical, electromagnetic, ultrasound, fiber optic, mechanical arm linkage) may be attached or integrated with the clamp  1708 . The tracker  1704  may be monitored via a tracking device (e.g., camera)  8  of the navigation system  7 . In the second embodiment, a surgeon may access the patient&#39;s iliac crest  1700  for landmark acquisition by inserting a probe tip of a tracked probe  56  through a fourth stab incision to contact the iliac crest  1700  at a point  1714  either anterior or posterior side of the pins  1710 . 
     While the device  1706  depicts three through-bores  1712 , the device may include a different number of through-bores  1712  without departing from the teachings of the present disclosure. Additionally or alternatively, the through-bores  1712  are described as being equally-spaced apart, but in certain instances the through-bores  1712  may be un-evenly spaced apart from each other. 
       FIGS. 17C-17E  depict a third embodiment of a device  1706  and method for accessing and capturing one or more data points on the patient&#39;s body, for example at the iliac crest  1700 . The device  1706  includes bone pins  1710 , and a clamp  1708 . The clamp  1708  may include three equally spaced-apart through-bores  1712  for receiving the bone pins  1710  therein in a known orientation relative to each other. The clamp  1708  may include a locking feature (e.g., thumb-screw to compress against the pins  1710 ) so movement of the pins  1710  relative to the clamp  1708  is restrained once the locking feature is engaged. A tracker  1704  (e.g., optical, electromagnetic, ultrasound, fiber optic, mechanical arm linkage) may be attached or integrated with the clamp  1708 . The tracker  1704  may be monitored via a tracking device (e.g., camera)  8  of the navigation system  7 . 
     While the device  1706  depicts three through-bores  1712 , the device may include a different number of through-bores  1712  without departing from the teachings of the present disclosure. Additionally or alternatively, the through-bores  1712  are described as being equally-spaced apart, but in certain instances the through-bores  1712  may be un-evenly spaced apart from each other. 
     As seen in  FIG. 17C , a first bone pin  1710   a  may be inserted into the iliac crest  1700  of a patient. Using a tracked probe  56 , the surgeon may capture one or more points  1714  approximately where the bone pin  1710   a  extends into the bone  1702 . The exact point of entry into the bone  1702  cannot be probed since it is occupied by the bone pin  1710   a.  The surgeon may additionally capture a point  1716  at the proximal end of the bone pin  1710   a.  Then, the system  5  may calculate the length L of the pin calculating the distance between the captured points  1714 ,  1716 . 
     As seen in  FIGS. 17D , the first bone pin  1710   a  may be received within a first through-bore  1712   a  of the clamp  1708 . And two additional bone pins  1710   b,    1710   c  may be inserted into the iliac crest  1700  while being guided by the respective second and third through-bores  1712   b,    1712   c  of the clamp  1708 . The clamp  1708  may be distally advanced relative to the pins  1710   a,    1710   b,    1710   c,  and secured in position via the locking feature. A tracker  1704  may be attached to the clamp  1708 . The tracked probe  56  may be used to capture a data point  1716  at the proximal end of the first bone pin  1710   a  (as in  FIG. 17C ), and the tracked probe  56  may be used to find the longitudinal axis LA of the first bone pin  1710   a,  as seen in  FIG. 17D . The tracked probe  56  may, for example, be placed vertically next to the first bone pin  1710   a  and the longitudinal axis LAP may be captured. Once the axis LAP is captured, the axis LAP can be moved to intersect the proximal tip of the bone pin  1716  to define the bone pin axis LA. Then, extending the length L of the bone pin  1710   a  along the axis LA will yield the exact point  1718  where the bone pin  1710   a  extends into the ilium  1702 . 
     The tracked probe  56  can also be used to measure the distance the clamp  1708  is positioned relative to the proximal end of the bone pin  1710   a,  as seen in  FIG. 17D . This may contribute to orienting the tracker  1704  in its orientation relative to the clamp  1708  and the bone  1702 . 
       FIG. 17E  depicts an additional or alternative embodiment to that shown in  FIG. 17D . As with  FIG. 17D , the first bone pin  1710   a  may be received within a first through-bore  1712   a  of the clamp  1708 . And two additional bone pins  1710   b,    1710   c  may be inserted into the iliac crest  1700  while being guided by the respective second and third through-bores  1712   b,    1712   c  of the clamp  1708 . The clamp  1708  may be distally advanced relative to the pins  1710   a,    1710   b,    1710   c.  A tracker  1704  may be attached to the clamp  1708 . Next, a sleeve  1720  may be used to measure the proximal end  1716  of the bone pin  1710   a,  and the axis LA associated with the bone pin  1710   a  to ultimately determine a point  1718  on the iliac crest  1700  in which the bone pin  1710  intersects. The sleeve  1720  includes a distal bore  1722  for receiving the proximal end of the bone pin  1710   a,  and a proximal bore  1724  for receiving the distal end of a tracked probe  56 . The sleeve  1720  includes a longitudinal axis LAS that is coaxial with the longitudinal axes LAP, LA of the tracked probe  56  and the bone pin  1710   a,  respectively, when received in their respective bores  1724 ,  1722  of the sleeve  1720 . In this way, a surgeon may install the sleeve  1720  on the bone pin(s), and insert a tracked probe  56  into the proximal bore  1724  of the sleeve  1720 . A data point may be captured with the tracked probe  56  positioned within the sleeve  1720 , and the system  5  may determine the point  1718  on the iliac crest  1700  that the bone pin  1710   a  intersects, knowing the axis of the bone pin LA and the distance from the bone surface  1718  to the probe tip  1726  (through the bone pin, and sleeve). 
     While the sleeve  1720  is depicted in  FIG. 17E  as being used in conjunction with a particular bone pin  1710   a,  the sleeve  1720  may be used with any of the bone pins  1710   a,    1710   b,    1710   c  without limitation. 
       FIGS. 18A-18H and 19A-19G  depict additional or alternative embodiments of registration tools for computer assisted surgical procedures.  FIGS. 20A-20I  depict the tools in use on a patient&#39;s iliac crest. In general, the tools described hereinafter are designed to guide bone pins into a patient&#39;s bone during a registration procedure. And while the procedure described is a hip procedure with the tool used on the iliac crest, the tools are applicable to use on any bone and/or joint associated with a registration procedure. That is, discussion of a hip procedure is merely an exemplary discussion of the tool and one contemplated use. As described herein, the tools guide bone pins into the iliac crest during a hip registration procedure, secure the pins in position relative to the tool, and provide registration points on the tool for capturing with a navigated probe in the registration procedure. 
     More particular, FIG. 18 A depicts an isometric exploded view of a bone pin clamp  1800 . As seen in the figure, the bone pin clamp  1800  may include a clamp body  1802  and a barrel, or sleeve  1804  coupled to the clamp body  1802 . The clamp body  1802  may form a housing that supports a center lock body  1806 , a main lock body  1808 , and springs  1816  positioned within the clamp body  1802 . The center lock body  1806  and the main lock body  1808  may be adjustably positioned within the clamp body  1802  via engagement with a thumb screw  1810 . A back plate  1818  may be coupled to the clamp body  1802  (e.g., welded) so as to enclose the center lock body  1806 , main lock body  1808 , and springs  1816  within the clamp body  1802 . 
     As seen in  FIG. 18A , among others, the clamp body  1802  includes a proximal end  1820  and a distal end  1822 . The clamp body  1802  may additionally include three through-holes  1812   a,    1812   b,    1812   c  extending in a distal-proximal direction for receiving bone pins there through. The sleeve  1804  extends distally from the distal end  1822  of the clamp body  1802 , and terminates at a distal tip  1824 , which includes a conical taper in this instance. The central through-hole  1812   b  is coaxial with a lumen of the sleeve  1804 . 
     The bone pin clamp  1800  may also include registration indents  1826  on a proximal outer surface  1814  of the clamp body  1802  in known positions for receiving a tip of a navigated probe during the registration process. As seen in  FIG. 18A , there are three registration indents  1826 ; two registration indents  1826  are positioned in corners of the proximal outer surface  1814 , and one registration indent  1826  is positioned between two of the through-holes  1812   a,    1812   b.  The position and number of the indents  1826  may vary. In certain instances, the bone pin clamp  1800  may include a single registration indent  1826 . In certain instances, the bone pin clamp  1800  may include a two registration indent  1826 . In certain instances, the bone pin clamp  1800  may include a more than three registration indents  1826 . 
     The proximal outer surface  1814  may also include a window  1828  extending into an inner volume  1830  of the clamp body  1802 . The window  1828  may be used to couple the center lock body  1806  with a pair of dowels  1832  during the assembly process. The clamp body  1802  may include a front side  1834 , a back side  1836 , and a pair of lateral sides  1838 ,  1840 . The back side  1836  includes a rectangular opening  1842  that is enclosed by the back plate  1818 , which may be welded to the clamp body  1802  upon completion of the manufacturing of the bone pin clamp  1800 . 
     A front side  1834  of the clamp body  1802  may include a front threaded opening  1844  for receiving the thumb screw  1810  therein. Each of the pair of lateral sides  1838 ,  1840  includes a side threaded opening  1846 ,  1848  for receiving a thumb screw. 
     The bone pin clamp  1800  may additionally include a tracker coupling (not shown) that engages one of the thumb-screws  1810  for securing a tracking member (e.g., optical tracker, electromagnetic tracker, ultrasound tracker, fiber optic tracker, mechanical arm tracker) that is capable of being tracked by the navigation system  7 . 
     As seen in  FIG. 18A  ,the center lock body  1806  may include a pair of through-holes  1850  extending in a distal-proximal direction for receiving the pair of dowels  1832 , and a threaded through-hole  1852  extending front a front-back direction for receiving the thumb-screw  1810  therein. The pair of dowels  1832  may extend partially within the window  1828  so the center lock body  1806  is limited in its movement in a front-back direction. When the thumb-screw  1810  is received within the threaded through-hole  1852  of the center lock body  1806 , the distal tip of the thumb-screw  1810  may extend beyond the center lock body  1806  and into the opening defined by the center bone pin through-hole  1812   b.  When this happens, the thumb-screw  1810  may contact a bone pin positioned within the bone pin through-hole  1812   b  so as to secure a position of the bone pin relative to the bone pin clamp  1800 . 
     The main lock body  1808  may include a central recess  1854  for receiving the center lock body  1806  therein. The main lock body  1808  may also include a pair of outer bodies  1856 , each including a ledge  1858  on an outer end thereof. Each of the ledges include a partial cylindrical recess for receiving a portion of a thumb-screw (like  1810 ) extending inward relative to the main lock body  1808 . The central recess  1854  may also include a partial cylindrical recess for receiving a portion of a bone pin positioned through the central bone pin through-hole  1812   b.  A bone pin positioned in the bone pin through hole  1812   c  fits behind the ledge  1858  of the main lock body  1808 , and a thumb-screw engaged with the side threaded opening  1846  may contact the bone pin and secure a position of the bone pin relative to the bone pin clamp  1800 . Similarly, a bone pin positioned in the bone pin through hole  1812   a  fits behind the ledge  1858  of the main lock body  1808 , and a thumb-screw engaged with the side threaded opening  1848  may contact the bone pin and secure a position of the bone pin relative to the bone pin clamp  1800 . 
     The bone pin clamp  1800  may include four springs  1816  keeping the main lock body  1808  generally centrally positioned within the inner volume  1830  of the clamp  1800 . The springs  1816  may, for example, slightly bias the main lock body  1808  in a position within the inner volume  1830  so the ledges  1858  slightly occupy a space within the through-holes  1812   a,    1812   c.  In this way, the clamp  1800  may apply an amount of pressure against the bone pins positioned within the through-holes  1812   a,    1812   c.    
     The back plate  1818  may include a central through-hole  1860  and a pair of nubs or protrusion  1862  for supporting an end of the springs  1816  and keeping them in a position. 
     The bone pin clamp  1800  may be part of a registration system that may also include a bone pin guide  1900 , as seen in  FIGS. 19A-19G .  FIG. 19A  is an isometric view of the bone pin guide  1900 .  FIG. 19B  is a first side view of the bone pin guide  1900 .  FIG. 19C  is a second side view, opposite the first side view, of the bone pin guide  1900 .  FIG. 19D  is a top view of the bone pin guide  1900 .  FIG. 19E  is a bottom view of the bone pin guide 1900 .  FIG. 19F  is a front view of the bone pin guide  1900 . And  FIG. 19G  is a back view of the bone pin guide  1900 . 
     As seen in  FIG. 19A , among others, the bone pin guide  1900  may include a guide body  1902  at a proximal end  1904  and a pair of barrels, tubes, or sleeves  1906  extending distally from the buide body  1902 . The guide body  1902  may include a pair of through-holes  1908  spaced apart from each other that lead into an inner volume of the barrels  1906 . The guide body  1902  may additionally include a rectangular through-hole  1912  extending transverse to the pair of through-holes  1908  in a front-back direction. The guide body  1902  also may include planar surfaces  1914  on the outer sides  1916  thereof. In certain instances, the planar surfaces  1914  on the outer sides  1916  may be engaged by a tool when using the bone pin guide  1900  to guide bone pins into the bone. 
     The pair of barrels  1906  are coaxial with the pair of through-holes  1908  of the guide body  1902  and extend distally from a distal surface  1918  of the guide body  1902 , and terminate at a distal tip  1920 , which may include a conical taper. Opposite the distal surface  1918  is a proimal surface  1922  of the guide body  1902 . 
     The pair of through-holes  1908  of the guide body  1902  of the bone pin guide  1900  are spaced apart from each other the same distance as the outer bone pin through-holes  1812   a,    1812   c.  In this way, the bone pin guide  1900  may be used first to guide first and second bone pins into the patient bone (e.g., iliac crest) at predetermined trajectories (e.g., parallel trajectories) and predetermined spacing. 
       FIGS. 20A-20I  illustrate steps in a surgical registration procedure utilizing the bone pin guide  1900  and bone pin clamp  1800  described herein.  FIG. 21A  is a flowchart showing the steps of the surgical registration procedure  2100 . 
     To begin, reference is made to  FIG. 21A . As seen in the flowchart, the method  2100  may include, at step  2102 , making an incision (e.g., stab incision)  1924  at the iliac crest  1700 . As seen in  FIG. 20A , which is an anterolateral view of a patient pelvis, an incision  1924  is made at the iliac crest  1700  of the ilium  1702 . Step  2104  of  FIG. 21A , as illustrated in  FIG. 20B , may include positioning the bone pin guide  1900  up to the iliac crest  1700  such that the distal tips  1920  of the barrels  1906  contact the iliac crest  1700 . Step  2106  of  FIG. 21A , as illustrated in  FIG. 20C , may include inserting or delivering a first bone pin  1710   a  though a first through-hole  1908  of the guide body  1902  of the bone pin guide  1900  and into the iliac crest  1700 . Delivery of the bone pin may be via a drill or by hand. 
     Step  2108  of  FIG. 21A , as illustrated in  FIG. 20D , may include delivering a second bone pin  1710   c  though a second through-hole  1908  of the guide body  1902  of the bone pin guide  1900  and into the iliac crest  1700 . Step  2110  of  FIG. 21A , as illustrated in  FIG. 20E , may include removing the bone pin guide  1900  from the pair of bone pins  1710   a,    1710   c  such that the bone pins remain positioned in the iliac crest  1700  of the patient. Step  2112  of  FIG. 21A , as illustrated in  FIGS. 20F and 20G , may include sliding the outer through-holes  1812   a,    1812   c  of the bone pin clamp  1800  over the first and second bone pins  1710   a,    1710   c  until the distal tip  1824  of the sleeve  1804  contacts the iliac crest  1700 . Step  2114  of  FIG. 21A , as illustrated in  FIG. 20H , may include inserting or delivering a third bone pin  1710   b  through the central through-hole  1812   b  of the bone pin clamp  1800  and into the iliac crest  1700 . 
     Step  2116  of  FIG. 21A , as illustrated in  FIG. 201 , may include tightening the three thumb-screws  1810  so as to secure the bone pins  1710   a,    1710   b,    1710   c  in relation to the bone pin clamp  1800 . Step  2118  of  FIG. 21A , as illustrated in  FIG. 20J , may include attaching a tracker coupling  1926  to the bone pin clamp  1800 , and attaching a tracker array  1704  to the tracker coupling  1926 . 
     Step  2120  of  FIG. 21A , as illustrated in  FIG. 20K , may include contacting a distal tip of a tracked navigation probe  56  to one or more of the registration indents  1826  on the bone pin clamp  1800  and capturing the position of the probe  56  via the navigation system  7 . This step may include calculating a point  1928  the position on the bone  1700  through which the center bone pin  1710  extends through. The point  1928  may be calculated based on the following: the three registration indents  1826  may define a plane that is determined by the surgical system upon being contacted by the navigated probe  56 ; and, a distance (extending along a longitudinal axis of the sleeve  1804 ) from the plane (distance being normal to the plane) defined by the three registration indents  1826  to the distal tip  1824  of the sleeve  1804  is known. Therefore, once the plane defined by the three registration indents  1826  is determined, the point  1928  is the distance (from plane to distal tip  1824 ) normal to the plane. Step  2120  may include using the position on the iliac crest  1700  through which the bone pin  1710  extends into as a reference point in the hip registration algorithm (as the far point). It is noted, that while the longitudinal axis of the sleeve  1804  (the distance described previously) is normal to plane defined by the three registration indents  1826 , in certain instances, the sleeve  1804  may be designed to be at an angle other than normal to the plane. In such an instance, the distance (while not being normal to the plane) is still known as it is a known angle relative to the plane. While the bone pin clamp  1800  is described as including three registration indents  1826 , the device may include more or fewer indents  1826  without departing from the scope of the present disclosure. 
     As seen in  FIG. 21B , a computer-implemented method  2150  of registration using the bone pin clamp  1800  may include the following. At step  2152 , the method  2150  may include receiving first data points  830  in a point-cloud corresponding to points on a patient bone  1702  in a first location that are registered with a navigated instrument. In certain instances, the first location may be an articular region  826  of the acetabulum  22  as described in reference to  FIGS. 9A-9B . In certain instances, the first data points  830  are fit to a sphere  832  as described in reference to  FIG. 9C . In certain instances, the first bone may be an ilium  1702 , the first location may be an acetabulum  22 , and the second location may be an iliac crest  1700 . 
     Still referring to  FIG. 21B , the method  2150  may include, at step  2154 , receiving second data points in the point-cloud corresponding to points on a bone pin clamp  1800  that may be secured to the patient bone  1702  in a second location  1700  via a plurality of bone pins  1710   a,    1710   b,    1710   c,  the bone pin clamp  1800  may include a plurality of registration indents  1826  defining a plane, the plane being a known distance from an end of the clamp  1800 , which contacts the patient bone  1702 . The method  2150 , at step  2156 , may also include determining a bone surface point  1928  at the second location  1700  from the defined plane and known distance. And, step  2158  of the method  2150  may include registering the first and second data points in the point cloud with image data of the patient bone. In certain instances, the bone surface point may be a point  1928  where one of the plurality of bone pins extends into the bone  1702 . 
       FIGS. 22A and 22B  depict additional or alternative registration tools for collecting a far point, for example, on a patient&#39;s iliac crest.  FIG. 22A  depicts an isometric view of a bone pin guide  2200  and a bone pin clamp  2202  secured to bone pins  1710  that extend into the iliac crest  1700  of the ilium  1702 .  FIG. 22B  depicts an isometric view of an alternative bone pin guide  2200   a  capable of use with the bone pin clamp  2202  shown in  FIG. 22A . 
     The bone pin guide  2200  of  FIG. 22A  includes a platform  2204 , registration indents  2206  defined on corner projections of the platform  2204 , first, second, and third guide through-holes extending through the platform  2204  in a distal-proximal direction, a central sleeve  2208  extending distally from the second (middle) guide through-hole, and outer sleeves (shorter than the central sleeve  2208 )  2210  extending distally from the first and third guide through-holes. The registration indents  2206  may define a plane, that once identified, can be used in conjunction with the distance from the plane to the distal tip of the central sleeve  2208  to determine a point at which a bone pin positioned within the second guide through-hole extends into the bone. 
     The bone pin guide  2200   a  of  FIG. 22B  includes a platform  2204 , first, second, and third guide through-holes extending through the platform  2204  in a distal-proximal direction, a central sleeve  2208  extending distally from the second (middle) guide through-hole, and outer sleeves (shorter than the central sleeve  2208 )  2210  extending distally from the first and third guide through-holes. The bone pin guide  2200   a  also includes a registration barrel  2212  extending proximally from a back side of the guide  2200   a.  The barrel  2212  includes a partial through-hole  2214  that does not daylight into an opening on a distal end thereof. The barrel  2212  includes an axis  2216  extending longitudinally through the barrel that intersects an axis extending through the second guide through-hole. In this way, a navigated probe  56  positioned within the barrel  2212  will be aligned with the axis of a bone pin positioned within the second guide-through hole such that the point of intersection of the bone and the second bone pin can be determined and used in the registration process. 
     The bone pin clamp  2202  of  FIG. 22A  includes many features of the bone pin clamp  1800  shown in  FIGS. 18A-18H  except for a distally extending sleeve  1804 . The bone pin clamp  2202  may be slid on the platform  2204  of the bone pin guide  2200 ,  2200   a,  and secured in position relative to the guide  2200 ,  2200   a  via the thumb screw  1810 . A tracker coupling  2218  may be coupled with the bone pin clamp  2202 ,  2202   a  and a tracker array (not shown in  FIGS. 22A-22B ) may be coupled to the tracker coupling  2218 . 
     The aforementioned steps of the methods may be performed by a computer or computing system. Additionally or alternatively, the aforementioned steps of the methods may be in the form of instructions for performing a computer process on a computing system, where the instructions are stored in one or more tangible computer-readable storage media. 
     While various designs are shown and described for the bone pin clamp and bone pin guides, features from the various designs may be combined without limitation. 
     C. Registering of Robotic Arm 
     Referring back to  FIG. 5 , after registering the pelvis at step S 6 , the robotic arm  30  may be registered at step S 7 . In this step, the robotic arm  30  is registered to correlate the pose of the robotic arm  30  (physical space) with the navigation system  7  (image space). The robotic arm  30  can be registered, for example, as described in U.S. patent application Ser. No. 11/357,197 (Pub. No. US 2006/0142657), filed Feb. 21, 2006, and hereby incorporated by reference herein in its entirety. 
     D. Preparation of the Acetabulum and Performance of the Surgical Procedure 
     In operation, the surgeon can use the robotic arm  30  of  FIG. 3B  to facilitate a joint replacement procedure, such as reaming bone and implanting an acetabular cup for a total hip replacement or hip resurfacing procedure. As explained above, the robotic arm  30  includes a surgical tool configured to be coupled to a cutting element (for reaming) and to engage a prosthetic component (for impacting). For example, as seen in  FIG. 3B , for reaming, the end effector  40  can couple to the operating member  100 , which couples to a cutting element. Similarly, for impacting, the end effector  40  can couple to another operating member, which engages the prosthetic component. The robotic arm  30  can be used to ensure proper positioning during reaming and impacting. 
     In step S 8  of  FIG. 5 , the surgeon resurfaces the acetabulum  22  using a reamer, such as the operating member  100 , coupled to the robotic arm  30  of  FIG. 3B . As described above in connection with the operating member  100 , the surgeon couples the appropriate operating member (e.g., a straight or offset reamer) to the end effector  40 , connects the cutting element to the received operating member, and manually manipulates the robotic arm  30  to ream the acetabulum  22 . During reaming, the robotic arm  30  provides haptic (force feedback) guidance to the surgeon. The haptic guidance constrains the surgeon&#39;s ability to manually move the surgical tool to ensure that the actual bone cuts correspond in shape and location to planned bone cuts (i.e., cuts consistent with the surgical plan). 
     In step S 9  of  FIG. 5 , the surgeon verifies that the registration (i.e., the geometric relationship) between the acetabular tracking array and the pelvis  12  is still valid by contacting the pelvis checkpoint with a tracked probe as described, for example, in U.S. patent application Ser. No. 11/750,807 (Pub. No. US 2008/0004633), filed May 18, 2007, and hereby incorporated by reference herein in its entirety. If registration has degraded (e.g., because the acetabular tracking array was bumped during reaming), the pelvis  12  is re-registered. Registration verification can be performed any time the surgeon wants to check the integrity of the acetabular registration. 
     In step S 10  of  FIG. 5 , the prosthetic component  316  is implanted on the reamed acetabulum  22  using an impactor tool. In a manner identical to that described above in connection with step S 8  (reaming), during the impaction step S 10 , the display device  9  can show the planned pose  500 , the activation region  510 , the representations  512 ,  514  of the anatomy, and a representation of the surgical tool, as seen in  FIG. 4 . Also as described above in connection with step S 8 , if the surgeon moves the end effector  40  to override the haptic feedback, the controller can initiate automatic control of the surgical tool to substantially align at least one aspect of the actual pose with the corresponding desired aspect of the target pose. 
     In step S 11  of  FIG. 5 , the surgeon installs the femoral component on the femur  14 , and in step S 12 , the surgeon determines leg length and femoral offset. At any time during the surgical procedure, the display device  9  can show data related to progress and/or outcome. For example, after reaming in step S 8  and/or impacting in step S 10 ), data relating to the actual position of the reamed acetabulum  22  (or the implanted acetabular cup) can include, for example, numerical data representing error between the actual and planned locations in the three orthogonal planes of the patient&#39;s anatomy (i.e., medial/lateral, superior/inferior, and anterior/posterior). 
     V. Example Computing System 
     Referring to  FIG. 14 , a detailed description of an example computing system  1300  having one or more computing units that may implement various systems and methods discussed herein is provided. The computing system  1300  may be applicable to any of the computers or systems utilized in the preoperative or intra-operative planning of the arthroplasty procedure (e.g., registration), and other computing or network devices. It will be appreciated that specific implementations of these devices may be of differing possible specific computing architectures not all of which are specifically discussed herein but will be understood by those of ordinary skill in the art. 
     The computer system  1300  may be a computing system that is capable of executing a computer program product to execute a computer process. Data and program files may be input to the computer system  1300 , which reads the files and executes the programs therein. Some of the elements of the computer system  1300  are shown in  FIG. 14 , including one or more hardware processors  1302 , one or more data storage devices  1304 , one or more memory devices  1308 , and/or one or more ports  1308 - 1310 . Additionally, other elements that will be recognized by those skilled in the art may be included in the computing system  1300  but are not explicitly depicted in  FIG. 14  or discussed further herein. Various elements of the computer system  1300  may communicate with one another by way of one or more communication buses, point-to-point communication paths, or other communication means not explicitly depicted in  FIG. 14 . 
     The processor  1302  may include, for example, a central processing unit (CPU), a microprocessor, a microcontroller, a digital signal processor (DSP), and/or one or more internal levels of cache. There may be one or more processors  1302 , such that the processor  1302  comprises a single central-processing unit, or a plurality of processing units capable of executing instructions and performing operations in parallel with each other, commonly referred to as a parallel processing environment. 
     The computer system  1300  may be a conventional computer, a distributed computer, or any other type of computer, such as one or more external computers made available via a cloud computing architecture. The presently described technology is optionally implemented in software stored on the data stored device(s)  1304 , stored on the memory device(s)  1306 , and/or communicated via one or more of the ports  1308 - 1310 , thereby transforming the computer system  1300  in  FIG. 14  to a special purpose machine for implementing the operations described herein. Examples of the computer system  1300  include personal computers, terminals, workstations, mobile phones, tablets, laptops, personal computers, multimedia consoles, gaming consoles, set top boxes, and the like. 
     The one or more data storage devices  1304  may include any non-volatile data storage device capable of storing data generated or employed within the computing system  1300 , such as computer executable instructions for performing a computer process, which may include instructions of both application programs and an operating system (OS) that manages the various components of the computing system  1300 . The data storage devices  1304  may include, without limitation, magnetic disk drives, optical disk drives, solid state drives (SSDs), flash drives, and the like. The data storage devices  1304  may include removable data storage media, non-removable data storage media, and/or external storage devices made available via a wired or wireless network architecture with such computer program products, including one or more database management products, web server products, application server products, and/or other additional software components. Examples of removable data storage media include Compact Disc Read-Only Memory (CD-ROM), Digital Versatile Disc Read-Only Memory (DVD-ROM), magneto-optical disks, flash drives, and the like. Examples of non-removable data storage media include internal magnetic hard disks, SSDs, and the like. The one or more memory devices  1306  may include volatile memory (e.g., dynamic random access memory (DRAM), static random access memory (SRAM), etc.) and/or non-volatile memory (e.g., read-only memory (ROM), flash memory, etc.). 
     Computer program products containing mechanisms to effectuate the systems and methods in accordance with the presently described technology may reside in the data storage devices  1304  and/or the memory devices  1306 , which may be referred to as machine-readable media. It will be appreciated that machine-readable media may include any tangible non-transitory medium that is capable of storing or encoding instructions to perform any one or more of the operations of the present disclosure for execution by a machine or that is capable of storing or encoding data structures and/or modules utilized by or associated with such instructions. Machine-readable media may include a single medium or multiple media (e.g., a centralized or distributed database, and/or associated caches and servers) that store the one or more executable instructions or data structures. 
     In some implementations, the computer system  1300  includes one or more ports, such as an input/output (I/O) port  1308  and a communication port  1310 , for communicating with other computing, network, navigation, or robotic devices. It will be appreciated that the ports  1308 - 1310  may be combined or separate and that more or fewer ports may be included in the computer system  1300 . 
     The I/O port  1308  may be connected to an I/O device, or other device, by which information is input to or output from the computing system  1300 . Such I/O devices may include, without limitation, one or more input devices, or output devices, such as, for example, robotic arms, and navigation and tracking systems. 
     In one implementation, the input devices convert a human-generated signal, such as, human voice, physical movement, physical touch or pressure, and/or the like, into electrical signals as input data into the computing system  1300  via the I/O port  1308 . Similarly, the output devices may convert electrical signals received from computing system  1300  via the I/O port  1308  into signals that may be sensed as output by a human, such as sound, light, and/or touch. The input device may be an alphanumeric input device, including alphanumeric and other keys for communicating information and/or command selections to the processor  1302  via the I/O port  1308 . The input device may be another type of user input device including, but not limited to: direction and selection control devices, such as a mouse, a trackball, cursor direction keys, a joystick, and/or a wheel; one or more sensors, such as a camera, a microphone, a positional sensor, an orientation sensor, a gravitational sensor, an inertial sensor, and/or an accelerometer; and/or a touch-sensitive display screen (“touchscreen”), and/or tracking/probe devices associated with the navigation and tracking systems. The output devices may include, without limitation, a display, a touchscreen, a speaker, a tactile and/or haptic output device, and/or the like. In some implementations, the input device and the output device may be the same device, for example, in the case of a touchscreen. 
     In one implementation, a communication port  1310  is connected to a network by way of which the computer system  1300  may receive network data useful in executing the methods and systems set out herein as well as transmitting information and network configuration changes determined thereby. Stated differently, the communication port  1310  connects the computer system  1300  to one or more communication interface devices configured to transmit and/or receive information between the computing system  1300  and other devices by way of one or more wired or wireless communication networks or connections. Examples of such networks or connections include, without limitation, Universal Serial Bus (USB), Ethernet, Wi-Fi, Bluetooth®, Near Field Communication (NFC), Long-Term Evolution (LTE), and so on. One or more such communication interface devices may be utilized via the communication port  1310  to communicate one or more other machines, either directly over a point-to-point communication path, over a wide area network (WAN) (e.g., the Internet), over a local area network (LAN), over a cellular (e.g., third generation (3G) or fourth generation (4G)) network, or over another communication means. Further, the communication port  1310  may communicate with an antenna or other link for electromagnetic signal transmission and/or reception. 
     In an example implementation, patient data, bone models (e.g., generic, patient specific), transformation software, tracking and navigation software, registration software, and other software and other modules and services may be embodied by instructions stored on the data storage devices  1304  and/or the memory devices  1306  and executed by the processor  1302 . The computer system  1300  may be integrated with or otherwise form part of the surgical system  100 . The system may be configured for registering patient data gathered intra-operatively from a first bone with a computer model of the first bone in a common coordinate system. The first bone may joint a second bone to form a joint such as, for example, a hip joint, a knee joint, a shoulder joint, an elbow joint, or ankle joint, among others. The system may include a surgical navigations ystem including a tracking device and a tool (e.g., navigation probe, end of a surgical robotic arm) to be tracked in its movement by the tracking device. Additionally, the system may include a computing device (one or more) in communication with the navigation system. The computing device may perform the following steps: 1) receive first data points of the patient data from first intra-operatively collected points on an articular surface of the concave portion of the bone. The first data points may be collected using the at least one tool. The first data points may correspond in location to a first articular region on the computer model. 2) receive a second data point from a second intra-operatively collected point on the first bone. The second data point may be collected using the at least one tool. The second data point may correspond in location to a second virtual data point on the computer model. 3) determine an intra-operative center of rotation from the first data points. The intra-operative center of rotation may correspond to a physical center of rotation of the second bone relative to the first bone. 4) compare a first distance between the virtual center of rotation and the second virtual data point and a second distance between the intra-operative center of rotation and the second data point. And, 5) run a transformation with the patient data and the computer model so as to have them correspond with respect to position and orientation. 
     Another implementation carried out on an exemplary computing device may include the following steps: receiving first data points in a point-cloud corresponding to points on a patient bone in a first location that are registered with a navigated instrument; receiving second data points in the point-cloud corresponding to points on a bone pin clamp that may be secured to the patient bone in a second location via a plurality of bone pins, the bone pin clamp may include a plurality of registration indents defining a plane, the plane being a known distance from the patient bone; determining a bone surface point at the second location from the defined plane and known distance; and, registering the first and second data points in the point cloud with image data of the patient bone. In certain instances, the bone surface point may be a point where one of the plurality of bone pins extends into the bone. In certain instances, the first location may be an articular region of the acetabulum as described in reference to  FIGS. 9A-9B . In certain instances, the first data points are fit to a sphere as described in reference to  FIG. 9C . In certain instances, the first bone may be an ilium, the first location may be an acetabulum, and the second location may be an iliac crest. 
     The system set forth in  FIG. 14  is but one possible example of a computer system that may employ or be configured in accordance with aspects of the present disclosure. It will be appreciated that other non-transitory tangible computer-readable storage media storing computer-executable instructions for implementing the presently disclosed technology on a computing system may be utilized. 
     In the present disclosure, the methods disclosed herein, for example, those shown in  FIGS. 5 and 8A-8B , among others, may be implemented as sets of instructions or software readable by a device. Further, it is understood that the specific order or hierarchy of steps in the methods disclosed are instances of example approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the method can be rearranged while remaining within the disclosed subject matter. The accompanying method claims present elements of the various steps in a sample order, and are not necessarily meant to be limited to the specific order or hierarchy presented. 
     The described disclosure including any of the methods described herein may be provided as a computer program product, software, or computerized method that may include a non-transitory machine-readable medium having stored thereon instructions, which may be used to program a computer system (or other electronic devices) to perform a process according to the present disclosure. A machine-readable medium includes any mechanism for storing information in a form (e.g., software, processing application) readable by a machine (e.g., a computer). The machine-readable medium may include, but is not limited to, magnetic storage medium, optical storage medium; magneto-optical storage medium, read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g., EPROM and EEPROM); flash memory; or other types of medium suitable for storing electronic instructions. 
     While the present disclosure has been described with reference to various implementations, it will be understood that these implementations are illustrative and that the scope of the present disclosure is not limited to them. Many variations, modifications, additions, and improvements are possible. More generally, embodiments in accordance with the present disclosure have been described in the context of particular implementations. Functionality may be separated or combined in blocks differently in various embodiments of the disclosure or described with different terminology. These and other variations, modifications, additions, and improvements may fall within the scope of the disclosure as defined in the claims that follow. For example, while the description discusses methods involving the hip, the disclosure is similarly applicable to other joints including the shoulder, ankle, and spine, among others. 
     In general, while the embodiments described herein have been described with reference to particular embodiments, modifications can be made thereto without departing from the spirit and scope of the disclosure. Note also that the term “including” as used herein is intended to be inclusive, i.e. “including but not limited to.” 
     The construction and arrangement of the systems and methods as shown in the various exemplary embodiments are illustrative only. Although only a few embodiments have been described in detail in this disclosure, many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.). For example, the position of elements may be reversed or otherwise varied and the nature or number of discrete elements or positions may be altered or varied. Accordingly, all such modifications are intended to be included within the scope of the present disclosure. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes, and omissions may be made in the design, operating conditions and arrangement of the exemplary embodiments without departing from the scope of the present disclosure.