Lower extremities leg length calculation method

A method of calculating leg length discrepancy of a patient including: receiving patient bone data associated with a lower body of the patient; identifying anatomical landmarks in the patient bone data; orienting a first proximal landmark and a second proximal landmark relative to each other and an origin in a coordinate system; aligning a first axis associated with a first femur and a second axis associated with a second femur with a longitudinal axis extending in a distal-proximal direction, wherein the first and second distal landmarks are adjusted according to the alignment of the first and second axes; calculating a distance between the first and second distal landmarks in the distal-proximal direction along the longitudinal axis; and displaying at least one of the distance or a portion of the patient bone data on a display screen.

TECHNICAL FIELD

The present disclosure relates generally to surgical methods used in orthopedic joint replacement surgery and, more particularly, to methods of lower extremities leg length calculations.

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).

During a hip replacement procedure, a surgeon may attempt to correct a patient's leg length discrepancy (LLD), which is a difference in the length of the right and left leg, either caused by a true length discrepancy of one or more bones or a misalignment of one or more joints. The use of an accurate and reliable algorithm to assess LLD before and during surgery is important for planning and executing precision total hip replacement. Conventional imaging methods for measuring LLD involve measuring the distance between a pelvic reference (e.g., inter-ischial, tear drop line) and another reference on the proximal or distal femurs. Other conventional methods involve using tape measures and standing blocks to asses LLD pre or post-operatively. Intra-operatively, LLD is typically measured manually by palpating the distal femurs or malleoli with the patient supine and the legs in line with the shoulders. Most of these methods have limitations and may not provide reliable measurements of LLD. Thus, there is an opportunity to use pre-operative imaging such as but not limited to computed tomography (CT) data from the pelvis, knees and lower extremities to develop a reliable, repeatable algorithm for LLD measurement that accounts for the full length of the leg.

SUMMARY

Aspects of the present disclosure involve a method of calculating leg length discrepancy of a patient. In certain instances, the method may include receiving patient bone data associated with a lower body of the patient, the lower body includes a first side and a second side, the first side includes a first portion of a pelvis, a first femur, a first tibia, and a first distal extremity, the second side includes a second portion of the pelvis, a second femur, a second tibia, and a second distal extremity. In certain instances, the method may further include identifying anatomical landmarks in the patient bone data, the anatomical landmarks includes a first proximal landmark and a first distal landmark associated with the first side and a second proximal landmark and a second distal landmark associated with the second side. In certain instances, the method may further include orienting the first proximal landmark and the second proximal landmark relative to each other and an origin in a coordinate system. In certain instances, the method may further include aligning a first axis associated with the first femur and a second axis associated with the second femur with a longitudinal axis extending in a distal-proximal direction, the first and second distal landmarks may be adjusted according to the alignment of the first and second axes. In certain instances, the method may further include calculating the leg length discrepancy based on a first distance between the first proximal landmark and the first distal landmark and a second distance between the second proximal landmark and the second distal landmark. In certain instances, the method may further include displaying at least one of the leg length discrepancy or a portion of the patient bone data on a display screen.

In certain instances, the first axis may include a first femoral mechanical axis, and the second axis may include a second femoral mechanical axis.

In certain instances, the first axis and the second axis may be aligned parallel to the longitudinal axis.

In certain instances, the first and second proximal landmarks remain in an unchanged orientation relative to the origin when the first and second axes are aligned relative to the longitudinal axis.

In certain instances, the longitudinal axis may be defined as a normal vector to a pelvic axis extending through the first and second proximal landmarks.

In certain instances, the first proximal landmark may be associated with a first location on the first portion of the pelvis, and the second proximal landmark may be associated with a second location on the second portion of the pelvis.

In certain instances, the first tibia and the first distal extremity have a first alignment relative to the first femur that may be unchanged when the first and second axes may be aligned, the second tibia and the second distal extremity have a second alignment relative to the second femur that may be unchanged when the first and second axes may be aligned.

In certain instances, further includes adjusting at least one of the first alignment or the second alignment so as to adjust a condition at a knee joint.

In certain instances, the condition may be a valgus or valrus deformity.

In certain instances, the condition may be a flexed or extended knee joint.

In certain instances, further includes generating a three dimensional bone model of the first side and the second side from the patient bone data.

In certain instances, the patient bone data may include medical images of the lower body of the patient.

In certain instances, the medical images were generated from a medical imaging machine includes at least one of a CT scanner, MRI machine, ultrasound scanner, or X-ray machine.

In certain instances, the patient bone data may be captured via at least one of an intra-operative bone scanner, a digitizer, or a navigated ultrasound probe.

In certain instances, the first distal extremity may be a first talus bone, and the second distal extremity may be a second talus bone.

In certain instances, calculating the leg length discrepancy may include determining a difference between the first and second distances in the distal-proximal direction.

In certain instances, calculating the leg length discrepancy may include determining a distance between the first and second distal landmarks in the distal-proximal direction.

Aspects of the present disclosure involve a method of calculating leg length discrepancy of a patient body including a first side and a second side, the first side including a first portion of a pelvis, a first femur, a first tibia, and a first foot region, the second side including a second portion of the pelvis, a second femur, a second tibia, and a second foot region. In certain instances, the method may include receiving patient bone data associated with the first and a second sides of the patient body, one of the first or second sides including a degenerate or deformed condition, the patient bone data having been generated by a medical imaging device. In certain instances, the method may further include generating a computer model of the first and second sides of the patient body from the patient bone data. In certain instances, the method may further include identifying anatomical landmarks in the patient bone data or the computer model, the anatomical landmarks includes: a first proximal point and a first distal point on the first side; and a second proximal point and a second distal point on the second side. In certain instances, the method may further include orienting the first and second sides of the computer model relative to each other in a coordinate system such that: a pelvic axis extending through the first and second proximal points may be generally perpendicular to a longitudinal axis of the first and second sides of the computer model; and a first axis associated with the first femur and a second axis associated with the second femur may be generally parallel to the longitudinal axis. In certain instances, the method may further include calculating the leg length discrepancy based on the first and second sides of the computer model after orienting the first and second sides of the computer model relative to each other. In certain instances, the method may further include displaying at least one of the leg length discrepancy or a portion of the computer model on a display screen.

In certain instances, the first proximal point corresponds to a femoral head center of the first femur, and the second proximal point corresponds to a femoral head center of the second femur.

In certain instances, the first distal point corresponds to a first point in or on a first bone in the first foot region, and the second distal point corresponds to a second point in or on a second bone in the second foot region.

In certain instance, further includes: adjusting an orientation of at least one of a first knee joint of the computer model defined between the first femur and the first tibia or a second knee joint of the computer model defined between the second femur and the second tibia.

In certain instances, the patient bone data may include at least one of CT images, MR images, or X-ray images.

In certain instances, the leg length discrepancy may include determining a distance between the first and second distal points in a direction of the longitudinal axis.

In certain instances, the leg length discrepancy may include determining a difference between a first distance and a second distance, the first distance defined between the first proximal point and the first distal point on the first side, the second distance defined between the second proximal point and the second distal point on the second side.

Aspects of the present disclosure involve a method of calculating leg length discrepancy of a lower body of a patient includes a pelvic region, femurs, tibias, and feet. In certain instances, the method may include receiving patient bone data representative of at least a portion of the lower body of the patient including the pelvic region, femurs, tibias, and feet, the patient bone data having been generated via a medical imaging device. In certain instances, the method may further include generating computer models of the lower body from the patient bone data, the computer models including first and second side pelvic models, first and second femur models, first and second tibia models, and first and second foot models. In certain instances, the method may further include orienting the first and second side pelvic models relative to an origin in a coordinate system. In certain instances, the method may further include orienting the first and second femur models, first and second tibia models, and first and second foot models relative to the first and second side pelvic models. In certain instances, the method may further include adjusting an orientation of one of the first and second femur models, first and second tibia models, or first and second foot models with respect to an anteroposterior or mediolateral axis. In certain instances, the method may further include calculating the leg length discrepancy based upon a difference in length between a first landmark in the first foot model and a second landmark in the second foot model in a direction of a longitudinal axis extending from the first and second foot models to the first and second side pelvic models. In certain instances, the method may further include displaying at least one of the difference or a portion of the computer models on a display screen.

In certain instances, the patient bone data may include at least one of CT images, MR images, or X-ray images.

In certain instances, the first landmark may be a first point in or on a talus bone of the first foot model, and the second landmark may be a second point in or on a talus bone of the second foot model.

In certain instances, the patient bone data may include information associated with a statistical bone model.

DETAILED DESCRIPTION

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. 1Aillustrates the bones of a hip joint10, which include a left pelvis12and a proximal end of a left femur14. The proximal end of the femur14includes a femoral head16disposed on a femoral neck18. The femoral neck18connects the femoral head16to a femoral shaft20.

As shown inFIG. 1B, the femoral head16fits into a concave socket in the pelvis12called the acetabulum22, thereby forming the hip joint10. The acetabulum22and femoral head16are both covered by articular cartilage that absorbs shock and promotes articulation of the joint10. Over time, the hip joint10may 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's hip joint10with artificial components. In total hip arthroplasty, the surgeon removes the femoral head16and neck18and replaces the natural bone with a prosthetic femoral component26comprising a head26a, a neck26b, and a stem26c(shown inFIG. 2A). As shown inFIG. 2B, the stem26cof the femoral component26is anchored in a cavity the surgeon creates in the intramedullary canal of the femur14. Alternatively, if disease is confined to the surface of the femoral head16, 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 acetabulum22of the pelvis12is worn or diseased, the surgeon resurfaces the acetabulum22using a reamer and replaces the natural surface with a prosthetic acetabular component28comprising a hemispherical shaped cup28a(shown inFIG. 2A) that may include a liner28b. To install the acetabular component28, the surgeon connects the cup28ato a distal end of an impactor tool and implants the cup28ainto the reamed acetabulum22by repeatedly striking a proximal end of the impactor tool with a mallet. If the acetabular component28includes a liner28b, the surgeon snaps the liner28binto the cup28aafter implanting the cup28a. 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 acetabulum22and a straight or offset impactor to implant the acetabular cup28a. 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 inFIG. 3A, an embodiment of a surgical system5for surgical applications according to the present disclosure includes a computer assisted navigation system7, a tracking device8, a computer15, a display device9(or multiple display devices9), and a robotic arm30.

The robotic arm30can 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 inFIG. 3B, the robotic arm30includes a base32, an articulated arm34, a force system (not shown), and a controller (not shown). A surgical tool58(e.g., a rotary burring device as seen inFIG. 3A, an end effector40having an operating member as seen inFIG. 3B) is coupled to an end of the articulated arm34, and the surgeon manipulates the surgical tool58by grasping and manually moving the articulated arm34and/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 arm34, 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 arm30.

The tracking device8is configured to track the relative locations of the surgical tool58(coupled to the robotic arm30) and the patient's anatomy. The surgical tool58can be tracked directly by the tracking device8. Alternatively, the pose of the surgical tool can be determined by tracking the location of the base32of the robotic arm30and calculating the pose of the surgical tool58based on joint encoder data from joints of the robotic arm30and a known geometric relationship between the surgical tool and the robotic arm30. In particular, the tracking device8(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's anatomy so the navigation system7knows the relative relationship between the tool and the anatomy.

In operation, a user (e.g., a surgeon) manually moves the robotic arm30to manipulate the surgical tool58(e.g., the rotary burring device, the end effector40having an operating member) to perform a surgical task on the patient, such as bone cutting or implant installation. As the surgeon manipulates the tool58, the tracking device8tracks the location of the surgical tool and the robotic arm30provides haptic (or force) feedback to limit the surgeon's ability to move the tool58beyond a predefined virtual boundary that is registered (or mapped) to the patient's anatomy, which results in highly accurate and repeatable bone cuts and/or implant placement. The robotic arm30operates in a passive manner and provides haptic feedback when the surgeon attempts to move the surgical tool58beyond the virtual boundary. The haptic feedback is generated by one or more actuators (e.g., motors) in the robotic arm30and transmitted to the surgeon via a flexible transmission, such as a cable drive transmission. When the robotic arm30is not providing haptic feedback, the robotic arm30is 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 system7displays images related to the surgical procedure on one or both of the display devices9.

To aid in tracking the various pieces of equipment within the system, the robotic arm30may include a device marker48to track a global or gross position of the robotic arm30, a tool end marker54to track the distal end of the articulating arm34, and a free-hand navigation probe56for use in the registration process. Each of these markers48,54,56(among others such as navigation markers positioned in the patient's bone) is trackable by the tracking device8with optical cameras, for example.

The computer15may include a display and an input device (e.g., keyboard, mouse) and is configured to communicate with the navigation system7, the tracking device8, the various display devices9in the system, and the robotic arm30. Furthermore, the computer15may receive information related to a particular surgical procedure and perform various functions related to performance of the surgical procedure. For example, the computer15may 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 toFIG. 14.

FIG. 3Bdepicts an end effector40particularly suited for use in robotic assisted hip arthroplasty. The end effector40is configured to be mounted to an end of the robotic arm30. The end effector40includes a mounting portion50, a housing, a coupling device, and a release member. The end effector40is configured to individually and interchangeably support and accurately position multiple operating members relative to the robotic arm30. As seen inFIG. 3B, the end effector40is coupled to an operating member100. The end effector40and 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)50preferably couples the end effector40to the robotic arm30. In particular, the mounting portion50extends from the housing and is configured to couple the end effector40to a corresponding mounting portion35of the robotic arm30using, for example, mechanical fasteners, such that the mounting portions are fixed relative to one another. The mounting portion50can be attached to the housing or formed integrally with the housing and is configured to accurately and repeatably position the end effector40relative to the robotic arm30. In one embodiment, the mounting portion50is 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 effector40inFIG. 3Bis one example of a surgical tool that can be tracked and used by the surgical robotic arm30. 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

Referring toFIGS. 4 and 5A, a preoperative CT (computed tomography) scan of the patient's pelvis12and femur14is generated or obtained at step R1. The scan image may be generally described as “patient data” or “patient bone data.” Such patient data may be generated with a medical imaging device (e.g., CT scanner) prior to the surgical procedure. 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 models512,514can 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. Additionally and alternatively, generic bone data or models (e.g., based on statistical averages of a sample population) that are at least partially representative of the patient's bone shape and lengths, among other characteristics, may be used in place of or in addition to patient data that is sampled from the actual patient bone. In such an instance, a representative bone data set or model may be selected or generated that approximates the lengths and conditions of the actual patient bone. Accordingly, the present disclosure is applicable to all methods of obtaining or generating patient bone data and a patient bone model or a portion thereof.

As shown inFIG. 4and at step R2ofFIG. 5A, the CT scan or data from the CT scan is segmented and to obtain a three dimensional model512of the pelvis12and a three dimensional model514of the femur14. At step R3, leg length discrepancy (LLD) is determined prior to the surgery. Determining LLD pre-operatively is described more fully in the subsequent paragraphs.

At steps R4and R5ofFIG. 5A, the three dimensional models512,514are used by the surgeon to construct a surgical plan at least in part to correct LLD. The surgeon selects an implant at step R4ofFIG. 5Aand selects a desired pose (i.e., position and orientation) of the acetabular component and the femoral component relative to the models512,514of the patient's anatomy. For example and as seen inFIG. 4, a planned pose500of the acetabular cup can be designated and displayed on a computer display, such as the display device9. At step R5ofFIG. 5A, the various bone cuts or resections may be determined based upon the desired pose of the implant, among other possible factors.

It is noted that the pre-operatively planning may include a plan for a knee arthroplasty procedure in addition to a hip arthroplasty procedure. The knee arthroplasty procedure may be at the same time as the hip procedure or at a later time. Either way, correction of the LLD, among other deformities, may be in part due to the hip arthroplasty procedure and in part from the knee arthroplasty procedure. For example, the pre-operative planning may include a present correction of a shorter femur in a hip arthroplasty procedure while also planning for an eventual correction to a varus/valgus knee deformity in a knee arthroplasty occurring subsequent to the hip arthroplasty procedure.

A. Leg Length Calculation

In certain instances, LLD may be pre-operatively determined and then compared with an intra-operative determination of LLD, which will be discussed in subsequent sections of this application. In certain instances, step R3of determining pre-operative LLD may be based on using anatomical information between the proximal femurs and the lower extremities. Through imaging of the pelvis, knees, ankles and feet, the method of determining LLD described herein can be used to acquire information on the mechanical axes and use a distal landmark such as, for example, the calcaneus or talus, among other landmarks, to calculate LLD using the full length of the legs. While conventional (manual surgical) methods typically rely on subjective visual assessments of the knee positions, and conventional computer-assisted surgical methods focus only on “hip length” at the level of the greater or lesser trochanter or above, the method described herein utilizes computer assisted surgical systems and provides an LLD measurement that accounts for the full length of the legs.

Referring back to step R1ofFIG. 5Aand to step T1ofFIG. 8, which depicts a flow diagram of a method of calculating and correcting LLD, patient bone data or medical images of the pelvis, proximal femur, knee, ankle, and foot may be pre-operatively generated or obtained for both the affected and non-affected legs. As stated previously, various imaging modalities may be utilized to generate the patient bone data such as, for example, CT, MRI, X-ray, or the like. The patient bone data may provide various anatomical landmarks for calculating LLD pre- and intra-operatively.

As shown in step R2ofFIG. 5Aand step T2ofFIG. 8, a three-dimensional patient bone model is generated from the patient bone data via a segmentation process or otherwise. In certain instances, a segmentation process may include outlining or segmenting a boundary of a particular bone on each of a plurality of image scans or slices in a certain plane (e.g., sagittal, transverse, coronal). The segmenting of the image scans provides an outline of points on the bone at discrete increments. The plurality of image scans may be positioned adjacent to each other such that there is a gap between each image scan that is equal to the scan spacing (e.g., 2 mm) of the imaging machine. Generating the bone model entails extrapolating a surface in the gap area between the adjacent image slices so as to make a solid or surface model from the plurality of spaced-apart and segmented image scans. While a segmentation process is described herein, any known method of generating the bone models may be used for the purposes of this discussion.

At step T3ofFIG. 8, landmarks are selected in either the medical images or the three dimensional patient bone models. More particularly, the following anatomical landmarks may be selected or identified for each leg: anterior-superior iliac spine (ASIS), femoral head center, knee center, talus centroid. The list of landmarks is not exhaustive and may include additional or different landmarks without departing from the scope of the present disclosure.

An illustrative example of identifying and selecting the talus centroid can be seen inFIGS. 9 and 10. As seen inFIG. 9, which is a display screen9illustrating patient bone data600in the form of two dimensional images of a patient's foot602in various planes, the talus bone604is segmented in the top-right image along a bone boundary line606that separates the bone604from the surrounding tissue608. A user may segment the individual slices of the talus bone604, for example, in this view. The views of the talus bone604on the top-left, bottom-left, and bottom-right illustrate coronal, transverse, and sagittal views, respectively, and each view illustrates a user selecting a center point610of the talus bone604with cross-hairs movable via a cursor, for example. Since the talus bone604is three-dimensional in physical space, the centroid or center of mass612, as seen inFIG. 10, may be determined by identifying the center point610in the coronal, transverse, and sagittal views of the two dimensional images602, as shown inFIG. 9.

Upon completing the segmentation process for the talus bone604as shown inFIG. 9, the system5may generate the three dimensional bone model614of the talus bone604, as well as other segmented bones of the foot, as seen in the top-right ofFIG. 10. As seen in the top-left, bottom-right, and bottom-left views ofFIG. 10, the illustrations are the same as those shown inFIG. 9. Locational information pertaining to the position of the centroid612may be stored within the three dimensional bone model614.

In certain instances, calculating LLD may be done without generating three dimensional bone models of the various bones described herein. That is, the anatomical landmarks may be identified in the image data (e.g., CT, MRI, X-ray), and coordinates (e.g., x, y, z) associated with the identified landmarks may be used for calculating LLD without generating a 3D surface model of the bones.

And while the talus bone604is referenced herein as a distal or lower extremity landmark, other bones at or near the foot (e.g., navicular, calcaneus) or other landmarks of the talus (e.g., most distal aspect of the talus) may be used for purposes of calculating LLD without departing from the teachings of the present disclosure.

While segmentation and identification of landmarks is only shown for the talus bone604, segmentation and three dimensional bone model generation may continue for the each of the two dimensional images of the pelvis12, femur14, and tibia13, as described in any of the applications incorporated by reference. In certain embodiments, the anatomical landmarks may be selected or identified in the two dimensional medical images or the three dimensional bone model for the femur head centers and knee centers, as shown at step T3ofFIG. 8, in a similar manner as described with reference to the talus bone604inFIGS. 9 and 10.

At step T4ofFIG. 8, the three dimensional bone models of the femur, tibia, and talus514,513,614, together referred to as a patient bone model in an unadjusted state650and an adjusted state652, are displayed on a display screen9and the femoral models514of the patient bone models650,652are aligned relative to a longitudinal or vertical axis VA of the pelvis, as seen inFIG. 11A. In certain instances, as seen inFIG. 11D, the three dimensional bone model of the pelvis624may be used in the calculation and may be used to define a pelvic axis PA, for example, as extending medial-lateral across opposite points on the pelvis. The pelvic axis PA may be used to define the longitudinal or vertical axis VA of the pelvis as being a normal vector of the pelvic axis PA.

In certain instances, the femoral head centers616of the right and left femurs of the patient bone models650,652may be parallel to the pelvic axis PA (extending in a medial-lateral direction). In this case, the proximal femurs of the right and left legs are fixed relative to each other such that LLD may be determined at a distal anatomical landmark such as the talus bone, which provides an LLD calculation that encompasses the entire lengths of the legs.

In certain instances, the femoral models514may be aligned relative to the vertical axis VA, but not otherwise fixed or “zeroed” relative to each other at the pelvic axis PA (i.e., the right and left femoral head centers may be at different elevations on along the vertical axis VA). While right and left proximal femurs whose femoral head centers616are parallel with the pelvic axis PA allows for a length measurement to be determined only by the difference at the distal extremities (as noted by the distance D1inFIGS. 11B and 11C), the distance D1may also be found by measuring the entire length of each leg from a proximal landmark (e.g., ASIS, tear-drop, inferior ischial, femoral head center) to a distal landmark (e.g., talus centroid, distal aspect of talus or tibia), and determining the difference in length D1between the right and left legs. In this way, the proximal landmarks may be at different elevations on the vertical axis VA (i.e., not parallel to the pelvic axis) and a measure of LLD may be found. While the disclosure includes reference to a determination of leg length between the distal landmarks of a right and left leg, other measurements may be used, such as those described in this paragraph and others, to measure the difference in leg length between the right and left legs.

In certain instances and as seen inFIG. 11D, the pelvic model624may be used to define the coordinate system of the pelvic axis PA and the longitudinal or vertical axis VA, and the other bone models (e.g., femur, tibia, talus) may be oriented relative to the pelvic model624. In such instances, the pelvic axis PA may be defined by identifying and selecting opposite points on the pelvic model624and defining an axis through the points. For example and as shown inFIG. 11D, the ASIS625may be selected (at step T3ofFIG. 8) on a right and left side of the pelvic model624, and a line (the pelvic axis PA) may extend through the right and left ASIS625. Once the pelvic axis PA is defined from the pelvic model624, the longitudinal or vertical axis VA may be defined as a normal vector of the pelvic axis PA.

Once the vertical axis VA is defined, the femoral mechanical axes FMA of the femur models514may be aligned with the vertical axis VA of the pelvis, at step T4ofFIG. 8. It is noted, the femur and pelvic models514,624may be joined together such that aligning of the pelvic model624with the pelvic axis PA may cause the femur models514to move accordingly within the coordinate system. For example, the center of the acetabulum may be used as a common point between the pelvic and femur models624,514to join the models relative to each other, while allowing the femur model514to rotate about the center of acetabulum. In this way, once the pelvic model624is aligned relative to the pelvic axis PA, the femur model514is free to rotate about the center of acetabulum, but is restricted from translating within the coordinate system.

Aligning the pelvic model624in the medial-lateral direction via the selected points on, for example, the ASIS and defining the pelvic axis PA in this way allows for consideration of cartilage degeneration, and other factors, at the hip joint that may cause a perceived discrepancy in leg length even if the length of the right and left legs are the same. For example, a right hip joint of a patient may be normal with a healthy amount of cartilage at the joint and a left hip joint may be diseased with very little cartilage present in the joint. The patient may perceive a shorter left leg because of the difference in cartilage at the left hip joint despite the right and left legs being the same length. In such an instance, if femoral points were used to define the pelvic axis PA, as opposed to points on the pelvic model624, the right and left legs may measure as equal when, in this example, there is degeneration at the joint that causes a perception of leg length discrepancy.

Referring back toFIGS. 11A-11C, while the pelvic model624is not displayed, the femoral head centers616are shown relative to a pelvic axis PA that may be defined based on selected points (e.g., ASIS) on the pelvic model624. As seen inFIG. 11A, other deformities, such as those at the knee (e.g., varus/valgus deformities), may remain unadjusted at this point. Adjustment of the knee deformities, for example via a knee arthroplasty and its effect on LLD, will be addressed subsequently.

Upon defining the pelvic axis PA and longitudinal or vertical axis VA, described previously, the mechanical axes of the femur models514of the affected (right side) and unaffected side (left side) are aligned to be parallel with the vertical axis VA, as described in step T4ofFIG. 8and as seen inFIGS. 11A and 11B. Adjustment of the femoral and tibial mechanical axes can be seen inFIG. 11B, which illustrates a display screen9showing an adjusted bone model652, with adjustments made at the hip and knee region. The bone models650,652both include the femur, tibia, and talus bone models514,513,614and the identified femoral head centers616, knee centers618, and talus centroids612. The femoral mechanical axis FMA is defined between the femoral head center616and the knee center618. The tibial mechanical axis TMA is defined between the knee center618and the talus centroid612.

As seen inFIG. 11A, the un-adjusted bone model650represents a valgus knee620on the right and a normal knee622on the left. The mechanical axes FMA, TMA of the valgus knee620are offset and non-parallel to each other and to the vertical axis VA, whereas the mechanical axes FMA, TMA of the normal knee622are generally parallel to each other and the vertical axis VA. Upon aligning the femoral mechanical axes FMA with the vertical axis, the bone model652will appear as shown inFIG. 11B(which also shows a correction of the valgus knee joint).

In certain instances, the system5may use the identified anatomical landmarks as end points associated with the femoral and tibial mechanical axes FMA, TMA, and the system5may display the bone models of the femur, tibia, and talus bones514,513,614in the same orientation as the patient was positioned during an image scan (e.g., CT). In certain instances, an adjustment of the right and left femur models may cause the tibia and talus models to move accordingly while maintaining their original orientation relative to the femur models. In this way, a knee deformity may not be corrected by the initial adjustment of the right and left femur models to be parallel to the vertical axis. In certain instances, the system or surgeon may correct or adjust the orientation of the tibia and talus models relative to the femur so as to correct or adjust a knee or ankle deformity.

At steps T5and T6ofFIG. 8, the femoral and tibial mechanical axes FMA, TMA, among other parameters including varus/valgus deformities, flexion/extension angles of the knee, among others, can be identified, and adjusted or fixed by the system5and displayed on the display screen9.

The surgeon may view the bone model650inFIG. 11Ain various views to calculate knee deformities, as seen in step T5ofFIG. 8. For example, varus/valgus deformities may be seen in a coronal view, as depicted inFIG. 11A, whereas flexion/extension angles may be seen in a sagittal view (not shown).

At step T6and as seen inFIG. 11B, the system5may allow a user (e.g., surgeon) to set values for the femoral and tibial mechanical axes FMA, TMA relative to each other or the vertical axis VA to correct varus/valgus deformities, flexion/extension of the knee, and other parameters, such that the three dimensional bone models of the femur, tibia, and talus514,513,614will be moved according to the inputted values. In this way, the surgeon may virtually align both the affected (right side inFIG. 11A) and non-affected (left side inFIG. 11A) sides of the patient's body in a similar manner (e.g., with both affected and non-affected sides having zero degrees mechanical axis) so LLD may be pre-operatively determined or calculated, regardless of the orientation of the patient's body during the acquisition of two dimensional images.

Thus, as seen inFIG. 11B, the system5has adjusted the formerly valgus knee620by aligning the femoral and tibial mechanical axes FMA, TMA to be generally parallel with each other and the vertical axis VA. In this way, both knees620,622match each other with regard to femoral and tibial mechanical axes FMA, TMA. Adjustment of the valgus knee may be in anticipation of a knee arthroplasty procedure at the same time as the hip procedure or at another time as part of an effort to correct LLD at the hip and knee.

In certain instances, as seen inFIG. 11C, which is a coronal view of an adjusted bone model652displayed on a display screen9, a surgeon may not adjust the valgus knee on the right, but, upon adjusting the mechanical axis FMA of the femur model514to be parallel with the vertical axis VA, the surgeon may leave the orientation of the femur relative to the tibia unadjusted.

In certain instances, as seen in step T7ofFIG. 8, the system5may pre-operatively calculate LLD as the distance D1between the talus centroids612as measured relative to the vertical axis VA. More particularly and as seen inFIGS. 11B and 11C, LLD may be measured as the distance D1, along the vertical axis VA, between a first perpendicular line P1intersecting a first talus centroid612and a second perpendicular line P2intersecting a second talus centroid612. As discussed previously, the distance D1may be calculated by measuring the length of the entire right and left legs and calculating the difference. For example, each of the right and left legs may be measured from the pelvic axis (e.g., right and left ASIS) to the talus centroid612, and the difference between the right and left legs will yield the distance D1.

In this way, an LLD calculation is made by virtually aligning the bone models650,652that will be representative of the patient's physical body following a hip and/or a knee arthroplasty procedure. Using a distal anatomical landmark such as the talus bone provides an LLD calculation that encompasses the entire lengths of the legs as opposed to conventional methods, which focus on only the proximal femur. And by including information from the pelvis, such as using the pelvic axis PA as defined through points (e.g., ASIS) on the pelvis, allows for an LLD calculation that captures potential degeneration at the joint as well as other deformities of the leg(s).

It is also noted that while the embodiment inFIGS. 11A-11Cdo not show the pelvic model624, in certain instances, as seen inFIG. 11D, a three dimensional bone model624of the pelvis12may be depicted on the display screen9along with the bone models of the femur, tibia, and talus514,513,614. As seen inFIG. 11D, which is a front view of a display screen9showing the bone models514,513,614, a surgeon may set values for varus deformities626and extension628at the knee. Upon setting the values, the hip length or LLD is displayed630accordingly. In the embodiment inFIG. 11D, the un-adjusted bone model650and adjusted bone model652may be combined to show only a single bone model650,652that is adjusted according to the set values or not adjusted if the values are unmodified.

At step T9ofFIG. 8, the surgeon pre-operatively plans the hip replacement procedure to correct the LLD as determined from step T7. During this step, the surgeon may select an implant and determine the position and orientation of the implant to correct the LLD, as seen in step R4ofFIG. 5A. Selection of the implant and determination of the pose of the implant may influence the determination of the bone cuts or resections to perform on the bones (e.g., proximal femur, acetabulum), as seen in step R5ofFIG. 5A. For example, implant stem length may be a factor to consider to lengthen or shorten the length of the femur to compensate for a particular LLD deformity.

It is noted that in certain instances, patient data may be captured via a localizer tool (e.g., digitizer, navigated ultrasound probe) by a surgeon just prior to or during the surgical procedure. In such instances, the patient data obtained from the localizer tool may take the place of obtaining pre-operative images (e.g., CT, MRI, X-ray) at step T1, ofFIG. 8, and generating a 3D bone model at step T2, also ofFIG. 8. The localizer tool may gather information about a particular bone such as surface contour information, rotational information (e.g., center of rotation), or location data associated with certain anatomical landmarks. The gathered information may be used by the system5to calculate mechanical axes (e.g., FMA, TMA) and develop a model with which to calculate and adjust deformities, at step T5and T6ofFIG. 8.

The remaining portions of the intra-operative procedure will be discussed in the following sections.

During the surgical procedure and referring back toFIG. 3A, motion of the patient's anatomy and the surgical tool in physical space are tracked by the tracking device8, and these tracked objects are registered to corresponding models in the navigation system7(image space). As a result, objects in physical space are correlated to corresponding models in image space. Therefore, the surgical system5knows the actual position of the surgical tool relative to the patient's anatomy and the planned pose500(as seen inFIG. 4), and this information is graphically displayed on the display device9during the surgical procedure.

A. Tracking and Registration of Femur

FIG. 5Billustrates an embodiment of intra-operative steps of performing a total hip replacement. In this embodiment, steps S1-S12may be performed with or without the robotic arm30. For example, step S8(reaming) can be performed using robotic arm30with the end effector40coupled to the operating member100or the operating member200, and step S10(impacting) can be performed using the robotic arm30with the end effector40coupled to the operating member300or the operating member400.

In step S1of the surgical procedure, as seen inFIG. 12A, which is a coronal view of a patient's skeletal structure to undergo a hip arthroplasty procedure, a cortical tracking array632is attached to the femur14to enable the tracking device8to track motion of the femur14. In step S2, the femur14is registered (using any known registration technique) to correlate the pose of the femur14(physical space) with the three dimensional model514of the femur14in the navigation system7(image space). Additionally, the femur checkpoint is attached. In step S3, the femur14is prepared to receive a femoral implant (e.g., the femoral component26) using a navigated femoral broach.

B. Tracking and Registration of Pelvis

In step S4ofFIG. 5B, a pelvic tracking array634is attached to the pelvis12to enable the tracking device8to track motion of the pelvis12, as seen inFIG. 12A. In step S5, a checkpoint is attached to the pelvis12for use during the surgical procedure to verify that the pelvic tracking array has not moved in relation to the pelvis12. 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 S6, the pelvis12is registered to correlate the pose of the pelvis12(physical space) with the three dimensional model512of the pelvis12in the navigation system7(image space). In certain embodiments, as shown inFIG. 6, registration is accomplished using the tracked navigation probe56to collect points on the pelvis12(physical space) that are then matched to corresponding points on the three dimensional model512of the pelvis12(image space). Two methods of registering the three dimensional model512of the pelvis (image space) and the pelvis12(physical space) are described in the subsequent sections of this application.

As shown inFIG. 6, the display device9may show the representation512of the pelvis12, including one or more registration points516. The registration points516help the surgeon understand where on the actual anatomy to collect points with the tracked probe. The registration points516can be color coded to further aid the surgeon. For example, a registration point516on the pelvis12to be collected next with the tracked probe can be colored yellow, while registration points516that have already been collected can be colored green and registration points516that will be subsequently collected can be colored red. After registration, the display device9can show the surgeon how well the registration algorithm fit the physically collected points to the representation512of the pelvis12.

For example, as shown inFIG. 7, error points518can be displayed to illustrate how much error exists in the registration between the surface of the representation512and the corresponding surface of the physical pelvis12. In one embodiment, the error points518can be color coded, for example, with error points518representing minimal error displayed in green and error points518representing increasing amounts of error displayed in blue, yellow, and red. As an alternative to color coding, error points518representing different degrees of error could have different shapes or sizes. Verification points519can also be displayed. The verification points519illustrate to the surgeon where to collect points with the tracked probe to verify the registration. When a registration point519is collected, the software of the navigation system7displays the error (e.g., numerically in millimeters) between the actual point collected on the anatomy and the registered location of the representation512in physical space. If the registration error is too high, the surgeon re-registers the pelvis12by repeating the registration process of step S6.

C. Registering of Robotic Arm

Referring back toFIG. 5B, after registering the pelvis at step S6, the robotic arm30may be registered at step S7. In this step, the robotic arm30is registered to correlate the pose of the robotic arm30(physical space) with the navigation system7(image space). The robotic arm30can 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 arm30to 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 arm30includes a surgical tool configured to be coupled to a cutting element (for reaming) and to engage a prosthetic component (for impacting). For example, for reaming, the end effector40can couple to the operating member100or the operating member, each of which couples to the cutting element. Similarly, for impacting, the end effector40can couple to the operating member or the operating member, each of which engages the prosthetic component. The robotic arm30can be used to ensure proper positioning during reaming and impacting.

In step S8ofFIG. 5B, the surgeon resurfaces the acetabulum22using a reamer, such as the operating member100, coupled to the robotic arm30. As described above in connection with the operating member100, the surgeon couples the appropriate operating member (e.g., a straight or offset reamer) to the end effector40, connects the cutting element to the received operating member, and manually manipulates the robotic arm30to ream the acetabulum22. During reaming, the robotic arm30provides haptic (force feedback) guidance to the surgeon. The haptic guidance constrains the surgeon'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 S9ofFIG. 5B, the surgeon verifies that the registration (i.e., the geometric relationship) between the acetabular tracking array and the pelvis12is 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 pelvis12is re-registered. Registration verification can be performed any time the surgeon wants to check the integrity of the acetabular registration.

In step S10ofFIG. 5B, the prosthetic component316is implanted on the reamed acetabulum22using an impactor tool. In a manner identical to that described above in connection with step S8(reaming), during the impaction step S10, the display device9can show the planned pose500, the activation region510, the representations512,514of the anatomy, and a representation of the surgical tool. Also as described above in connection with step S8, if the surgeon moves the end effector40to 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.

E. Leg Length Calculation

In step S11ofFIG. 5B, the surgeon installs the femoral component on the femur14. Next, in step S12ofFIG. 5Band step T11ofFIG. 8, the surgeon determines leg length and femoral offset. At any time during the surgical procedure, the display device9can show data related to progress and/or outcome. For example, after reaming in step S8and/or impacting in step S10), data relating to the actual position of the reamed acetabulum22(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's anatomy (i.e., medial/lateral, superior/inferior, and anterior/posterior).

In certain instances, step S12ofFIG. 5Band step T11ofFIG. 8for determining leg length discrepancy (LLD) may include comparing the pre-operatively determined LLD with an intra-operative measurement of LLD.

In certain instances, intra-operative LLD may be determined by based on the position of the femoral and pelvic tracking arrays634,632, as seen inFIGS. 12A and 12B.FIG. 12Adepicts a coronal view of a patient's skeletal structure including the pelvis12, femur14, and knee joint10with a pelvic tracking array634positioned in the pelvis12and a femoral tracking array632positioned in the femur14prior to the resection of the proximal femur including the femoral neck and head18,16.FIG. 12Bdepicts a coronal view of a patient's skeletal structure including the pelvis12, femur14, and knee joint10with a pelvic tracking array634positioned in the pelvis12and a femoral tracking array632positioned in the femur14following the resection of the proximal femur and implantation of femoral and acetabular components of a hip implant system636.

Upon registering the pelvis12and the femur14via the pelvic tracking array634and the femoral tracking array632, the system5may calculate a first value or distance D10between the tracking arrays634,632in a given pose(s) (i.e., position and orientation) of the femur14relative to the pelvis12. For example, the surgeon may position the patient's femur14such that the femoral mechanical axis (not shown inFIG. 12A) is parallel to the vertical axis (not shown inFIG. 12A). In certain instances, the surgeon may use the tracking ability of the system5to verify that the femur14is positioned in the correct pose relative to the pelvis12for determining the distance D20.

Following the hip replacement procedure where the proximal femur is resected and replaced with a femoral component that is positioned within an acetabular component, as seen inFIG. 12B, the surgeon may calculate a second value or distance D20between the tracking arrays634,632in a given pose(s) of the femur14relative to the pelvis12. In certain instances, the pose may be the same for determining the distances D10, D20.

The difference between the pre-resection distance D10and the post-resection distance D20is given by distance D30, as seen inFIG. 12B. The distance D30represents the change in leg length that resulted from the actual hip replacement procedure. This distance D30may then be compared with the pre-operatively calculated LLD. In certain instances, where a hip replacement procedure was the only planned procedure (i.e., a knee arthroplasty was not planned for), the post-operative distance D30may be compared with the pre-operative value of LLD. If, for example, a surgeon desired to correct a knee deformity that pre-operatively showed a 3 mm shorter leg, a post-operative distance D30change of 3 mm longer, for example, may indicate that the hip replacement procedure was successful in correcting LLD.

In certain instances, where a knee arthroplasty procedure is to take place at a given time after the hip replacement procedure, the distance D30associated with a change in the proximal femur may be one component of the overall LLD to be fixed. That is, the surgeon may calculate or determine that the hip replacement procedure will fix total LLD by a factor of X, and a subsequent knee replacement procedure (e.g., to fix varus/valgus deformity) will fix total LLD by a factor of Y, where X plus Y equals the total LLD.

In certain instances, a pre- and post-resection determination of leg length may be determined without the aid of a femoral tracking array. For example, as seen inFIG. 12C, which is a front view of a right side of a pelvis12, hip joint10, femur14, knee joint17, patella19, fibula21, and talus604prior to a hip replacement surgery, a surgeon may calculate a pre-resection LLD as a distance D40between the pelvic tracking array634and a distal landmark such as a distal aspect of the talus638or a distal aspect of the tibia640. As seen inFIG. 12D, which is a front view of a right side of a pelvis12, hip joint10, femur14, knee joint17, patella19, fibula21, and talus604following a hip replacement surgery, the surgeon may calculate a post-resection LLD as a distance D50between the pelvic tracking array634and a distal landmark such as a distal aspect of the talus638or a distal aspect of the tibia640.

The difference between the pre-resection distance D40and the post-resection distance D50is given by distance D60, as seen inFIG. 12D. The distance D60represents the change in leg length that resulted from the actual hip replacement procedure. This distance D60may then be compared with the pre-operatively calculated LLD. In certain instances, where a hip replacement procedure was the only planned procedure (i.e., a knee arthroplasty was not planned for), the post-operative distance D60may be compared with the pre-operative value of LLD. If, for example, a surgeon desired to correct a knee deformity that pre-operatively showed a 3 mm shorter leg, a post-operative distance D60change of 3 mm longer, for example, may indicate that the hip replacement procedure was successful in correcting LLD.

In certain instances, where a knee arthroplasty procedure is to take place at a given time after the hip replacement procedure, the distance D60associated with a change in the proximal femur may be one component of the overall LLD to be fixed. That is, the surgeon may calculate or determine that the hip replacement procedure will fix total LLD by a factor of X, and a subsequent knee replacement procedure (e.g., to fix varus/valgus deformity) will fix total LLD by a factor of Y, where X plus Y equals the total LLD.

Instead of using the femoral tracking array (shown inFIGS. 12A-12B) the distal landmarks may be captured by the surgeon via a digitizer or tracked navigation probe. For example, the surgeon may place the distal tip of a tracked probe against a distal landmark (e.g., distal aspect of tibia640or talus638) and the location of the landmark may be stored by the system5. In this way, the surgeon may capture or log the location of the distal landmark on the patient's distal extremity pre- and post-hip replacement, and the difference in the distance between the distal extremity and the pelvic tracking array634may provide a difference in LLD as a result of the surgical procedure. It is noted that the distal aspects of the tibia and talus640,638are exemplary and other distal landmarks may be similarly employed without departing from the scope of the present disclosure.

V. Example Computing System

Referring toFIG. 13, a detailed description of an example computing system1300having one or more computing units that may implement various systems and methods discussed herein is provided. The computing system1300may be applicable to any of the computers or systems utilized in the preoperative or intra-operative planning of the arthroplasty procedure (e.g., registration, leg length discrepancy), 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 system1300may 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 system1300, which reads the files and executes the programs therein. Some of the elements of the computer system1300are shown inFIG. 13, including one or more hardware processors1302, one or more data storage devices1304, one or more memory devices1308, and/or one or more ports1308-1310. Additionally, other elements that will be recognized by those skilled in the art may be included in the computing system1300but are not explicitly depicted in FIG.13or discussed further herein. Various elements of the computer system1300may communicate with one another by way of one or more communication buses, point-to-point communication paths, or other communication means not explicitly depicted inFIG. 13.

The processor1302may 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 processors1302, such that the processor1302comprises 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 system1300may 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 ports1308-1310, thereby transforming the computer system1300inFIG. 13to a special purpose machine for implementing the operations described herein. Examples of the computer system1300include 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 devices1304may include any non-volatile data storage device capable of storing data generated or employed within the computing system1300, 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 system1300. The data storage devices1304may include, without limitation, magnetic disk drives, optical disk drives, solid state drives (SSDs), flash drives, and the like. The data storage devices1304may 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 devices1306may 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.).

In some implementations, the computer system1300includes one or more ports, such as an input/output (I/O) port1308and a communication port1310, for communicating with other computing, network, or vehicle devices. It will be appreciated that the ports1308-1310may be combined or separate and that more or fewer ports may be included in the computer system1300.

The I/O port1308may be connected to an I/O device, or other device, by which information is input to or output from the computing system1300. Such I/O devices may include, without limitation, one or more input devices, output devices, and/or environment transducer devices.

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 system1300via the I/O port1308. Similarly, the output devices may convert electrical signals received from computing system1300via the I/O port1308into 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 processor1302via the I/O port1308. 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”). 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 port1310is connected to a network by way of which the computer system1300may 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 port1310connects the computer system1300to one or more communication interface devices configured to transmit and/or receive information between the computing system1300and 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 port1310to 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 port1310may 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 devices1304and/or the memory devices1306and executed by the processor1302. The computer system1300may be integrated with or otherwise form part of the surgical system100.

The system set forth inFIG. 13is 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.

The described disclosure including any of the methods described herein may be provided as a computer program product, or software, 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.

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.”