CN110251232B

CN110251232B - Medical navigation guidance system

Info

Publication number: CN110251232B
Application number: CN201910642969.1A
Authority: CN
Inventors: 安德烈·诺沃米尔·赫拉迪奥; 理查德·泰勒·范森; 阿曼·加罗·巴克尔特齐亚; 埃里克·泰塔尔斯基
Original assignee: Intellijoint Surgical Inc
Current assignee: Intellijoint Surgical Inc
Priority date: 2013-03-15
Filing date: 2014-03-14
Publication date: 2022-09-09
Anticipated expiration: 2034-03-14
Also published as: EP2967439A4; CN105263409B; US11826113B2; AU2014231652B2; US20170224422A1; US20230200915A1; CN110251232A; US20150038836A1; AU2019272022B2; US20240216074A1; US10194996B2; AU2014231652A1; US9655749B2; CN105263409A; US11589930B2; US9247998B2; EP2967439A1; US9168103B2; AU2019272022A1; US20140275940A1

Abstract

The present disclosure provides a medical navigation guidance system. The medical navigation guidance system includes: an alignment mechanism comprising a lockable ball joint; a sensor for coupling to a bone and orienting using an alignment mechanism toward a site for a medical procedure; a sterile drape having an optically transparent window to cover the optical sensor in the sterile barrier; a target coupled to a target for tracking by a sensor; and a processing unit in communication with the sensor, the processing unit configured to direct alignment of the sensor with the target, the processing unit calculating and displaying directional instructions using position signals from the sensor to move the sensor and the target into alignment using the user interface.

Description

Medical navigation guidance system

The present application is a divisional application of the invention patent application having an application date of 2014, 3/14, application number of 201480028016.1, entitled "system and method for intraoperative leg position measurement".

Technical Field

The present disclosure relates generally to determining, monitoring, and presenting the relative positions of two bodies, such as the femur and pelvis, during a surgical procedure. In particular, the present disclosure relates to systems and methods for determining, monitoring, and presenting leg length and offset, such as in positioning a prosthesis between a pelvis and a femur.

Background

In many surgical procedures, including joint replacement such as Total Hip Arthroplasty (THA), achieving precise positioning of tools and implants relative to the patient's anatomy is critical to successful outcome. Fig. 1 shows a hip joint before 100 and after 102 surgery, and a coordinate system 104 defining a plurality of directions. The hip joint after surgery consists of a femoral component 106 and an acetabular component 108. In one THA technique, the hip joint is exposed and dislocated. Both the acetabulum and the femur are prepared to receive an implant. Typically, cup prostheses are implanted in the acetabulum, requiring alignment of the cup relative to the patient anatomy. A trial femoral prosthesis of various sizes may be selected to facilitate intraoperative adjustment may be implanted to assess the correct final femoral implant size. The fit and sizing of the joint may be iteratively evaluated, and the final prosthetic hip joint (106 and 108) implanted.

Positioning a prosthetic implant relative to a patient's anatomy involves a number of challenges, such as selecting the correct implant geometry, and altering the patient's skeletal anatomy (e.g., drilling, osteotomy, etc.), among others. Some important goals for successful THA include: proper alignment of the acetabular cup; recovery or correction of leg length and offset; hip center of rotation (COR) recovery; and stability of the new hip joint. The concept of leg length and offset variation initially appears simple; however, this is a complex clinical and geometric problem. Surgeons often need to make various accurate assessments of leg length and offset during surgery.

Disclosure of Invention

According to one aspect of the present disclosure, a medical navigation guidance system is provided. The medical navigation guidance system comprises: an alignment mechanism comprising a lockable ball joint; a sensor for coupling to a bone and orienting using an alignment mechanism toward a site for a medical procedure; a sterile drape having an optically transparent window to cover the optical sensor in the sterile barrier; a target coupled to a target for tracking by a sensor; and a processing unit in communication with the sensor, the processing unit configured to direct alignment of the sensor with the target, the processing unit calculating and displaying directional instructions using the position signals from the sensor to move the sensor and the target into alignment using the user interface.

According to another aspect of the present disclosure, a medical navigation guidance system is provided. The medical navigation guidance system includes: a sensor for orienting towards a site for a medical procedure to measure a position and orientation of a target coupled to a target; an alignment mechanism comprising a lockable ball joint to couple to the sensor and orient the sensor towards the site; a sterile drape having an optically transparent window to cover the sensor in the sterile barrier; a processing unit in communication with the sensor, the processing unit configured to guide alignment of the sensor with the site, the processing unit calculating using position signals from the sensor and displaying directional instructions using a user interface to move the sensor and the site into alignment.

Drawings

For a better understanding of the embodiments of the systems, methods, and devices described herein, and to show more clearly how they may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:

figure 1 is a diagram of a hip joint before and after THA comprising an anatomical reference frame according to the prior art;

FIG. 2 is an example of a system for determining and presenting intraoperative leg length and offset measurements;

fig. 3 is a flow chart illustrating operations for use of leg length and offset measurements according to an example;

fig. 4 and 5 are screen shots of a representative graphical user interface illustrating registration and measurement of leg length and offset according to an example;

FIG. 6 is a flow chart of operation of a workstation or other processing unit providing leg length and offset measurements according to an example;

FIG. 7 is a screenshot of a representative graphical user interface illustrating sensor and target alignment according to an example;

fig. 8A is an exploded view of a pelvic clamp assembly according to an example with a sterile drape employing an integrated optical window;

FIG. 8B is an end view of the pelvic clamp of FIG. 8A shown assembled with a sterile drape and sensors;

fig. 9 shows components of a pelvic platform according to an example;

fig. 10 shows a femoral platform with femoral screws according to an example;

11A and 11B illustrate an exemplary quick connect mechanism;

fig. 12 illustrates a beacon component according to an example;

13A and 13B show respective front and back faces of a planar target, such as for mounting on the beacon assembly of FIG. 12, according to an example; and

fig. 14 shows a sensor according to an example.

It will be appreciated that for simplicity and clarity of illustration, elements illustrated in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity.

Detailed Description

Referring to fig. 1, with respect to leg length and offset, leg length change is defined as a change in femoral position in the superior-inferior direction (i.e., as a result of surgery, a positive leg length change occurs if the femur translates in the inferior direction). Leg length variations may occur due to the arrangement of the acetabular component, the arrangement or sizing of the femoral component, or a combination of both. Note that in this figure, the femur and pelvis are aligned so that their relative flexion, rotation and abduction are zero. This relationship is considered "neutral". If the femur is not neutral relative to the pelvis, the coordinate system of the femur will not be aligned with the pelvis, but will rotate the same amount as the femur; for example, if the femur abducts 90 degrees, the downward direction of the femur will be the outward direction of the pelvis. In this case, it is clear that the total leg length variation is due to the leg length variation resulting from the acetabular component position (in the pelvic coordinate system) plus the leg length variation resulting from the femoral component position (in the femoral coordinate system). It is also clear that the two coordinate system alignment simplifies the problem when neutral.

Offset variations are similar to leg length variations; however, it is in the lateral-medial direction (i.e., as a result of surgery, if the femur translates laterally, a positive change in offset occurs). Occasionally in the hip arthroplasty technique, the offset is not purely defined in the medial-lateral direction (in the patient's coronal plane), but in a plane rotated about the patient's midline by the amount of femoral version (typically 10-15 degrees). The femoral prosthesis is not purely located on the medial-lateral plane; it is rotated slightly forward (see fig. 1) so that the sphere is more forward than the stem. This alternative to offset is defined as an internal rotation of the femur (about 10-15 degrees) such that the femoral prosthesis is purely in the coronal plane.

Some technical terms and definitions may be used throughout this document. Tracking techniques are primarily concerned with position and orientation. The terms "coordinate system," "reference system," and the like refer to a standard basis in which a position and an orientation may be described. The terms "pose" (position and orientation state evaluation), position, relative position, spatial orientation, etc., all refer to describing the position and/or orientation of a rigid body relative to some coordinate system.

The present invention provides systems, methods and computer program products for a navigational guidance system. In one example, intra-operative leg position measurements are provided during hip replacement surgery. An optical sensor for coupling to a pelvis and a target for coupling to a femur to align with the sensor are provided. The sensor provides a position signal to the processing unit to determine the relative position of the sensor and the target. The processing unit is configured to calculate and display in real time the position measurements using the baseline measurements and the maps of the leg positions. The map is defined by a registration range of motion (PROM) process in which instructions are presented to move the femur in at least two planes to generate signals to compute the map. The leg position may be the leg length and/or offset and/or the anterior-posterior position of the leg. The map is used to present leg position measurements in the anatomical structure rather than in the coordinate system of the sensor.

A system for providing intraoperative leg position measurements during hip arthroplasty of the pelvis and femur at a surgical site is disclosed. The system comprises: an optical sensor for coupling to a pelvis and for alignment with a surgical site; a target for coupling to a femur for alignment with a sensor, the sensor providing a signal in response to the target for determining a relative position of the sensor and the target; and a processing unit for communicating with the sensor, the processing unit configured to calculate and display in real time leg position measurements using baseline measurements of leg position and a map, wherein the map is defined by a registration range of motion (PROM) process. The processing unit may receive the first signal from the sensor and determine a relative position of the sensor and the target to determine a baseline measurement, determine a plurality of second signals generated by the PROM to define a map, and determine a plurality of third signals to display the leg position measurement in real time using the baseline measurement and the map. The processing unit may present instructions via the graphical user interface for moving the femur in at least two planes to generate a plurality of second signals during the PROM process. In one example, the leg positions are leg lengths and offsets. The processing unit may use the map to present leg position measurements in an anatomical coordinate system. The leg position measurement may be displayed independently of the orientation of the femur. In one example, the processing unit is further configured to detect hip dislocation in real time and alert based on the detection.

The present invention discloses a method for performing hip arthroplasty with intra-operative digital leg position guidance, comprising: determining and storing, by the processing unit, a pre-dislocation reference line femur position using a sensor and a target that provide signals for determining relative position; performing, by the processing unit, a registration range of motion (RROM) procedure after the prosthetic joint is repositioned to define the RROM map into an anatomical coordinate system for leg position measurements generated using the signals; and displaying the leg position measurement in real time on the display using the baseline femur position and the RROM map. The method may include receiving signals by a processing unit in response to intra-operative movement of the femur and calculating leg position measurements for intra-operative display. In one example, the method may include detecting and alerting of hip subluxation by the processing unit in response to the leg position measurement. The computer program product aspect is disclosed wherein there is a computer program product for performing hip arthroplasty with intra-operative digital leg position guidance, comprising a non-transitory medium storing instructions and data for configuring execution of a processing unit to perform such as according to the present method.

The present invention discloses a system to provide intraoperative guidance during a medical procedure, comprising: a single sensor for coupling to a bone and oriented toward a site for a medical procedure; a single target coupled to a target for tracking by a sensor; and a processing unit in communication with the sensor, the processing unit displaying the relative position of the target and the bone from the relative position of the target and the sensor calculated using the position signals from the sensor. The bone may be a pelvis. The target may be a femur. The processing unit may calculate the registration by causing movement of the object while collecting the pose data. The medical procedure may be a surgical procedure such as a hip replacement procedure. In one example, the bone is a pelvis and the target is a femur, and the processing unit calculates a measure of intraoperative leg length and offset variation.

The present invention discloses a method of providing intraoperative guidance during a medical procedure, comprising: receiving, at a processing unit, a plurality of position signals from a single sensor coupled to a bone and oriented toward a site for a medical procedure, the generated position signals for a single target coupled to a target, tracked by the sensor; calculating the relative position of the target object and the bone by the processing unit according to the position signal; and displaying the relative position on the display during the operation. The bone may be a pelvis. The target may be a femur. The method may include calculating, by the processing unit, a registration by causing motion of the target object while collecting the pose data. The medical procedure may be a surgical procedure such as a hip replacement procedure. In one example, the bone is a pelvis and the target is a femur, and the method further comprises calculating, by the processing unit, an intraoperative leg length and offset variation measurement.

A computer program product includes a non-transitory medium storing instructions and data for configuring execution of a processing unit to receive a plurality of position signals from a single sensor coupled to a bone and oriented toward a site for a medical procedure, the generated position signals for a single target coupled to a target tracked by the sensor; calculating the relative position of the target object and the bone according to the position signal; and displaying the relative position on the display during the operation.

The invention discloses a medical navigation guidance system, which comprises: a sensor for coupling to a bone and oriented toward a site for a medical procedure; a target coupled to a target for tracking by a sensor; and a processing unit in communication with the sensor, the processing unit configured to guide alignment of the sensor with the target, the processing unit calculating using position signals from the sensor and displaying directional instructions using the user interface to move the sensor and target into alignment. The system may include an alignment mechanism that facilitates two degrees of freedom orientation adjustment of the sensor relative to the bone. The alignment mechanism may be a locking mechanism that releasably secures the orientation of the sensor. The alignment mechanism is a lockable ball joint. The target may be used to define the location of the site. The processing unit may represent the pivotal orientation of the sensor as a cross-hair on a display screen and the position of the surgical site as a bull eye target. The system may include a releasable coupling for coupling the sensor to the bone.

The invention discloses a method for executing a medical procedure under navigation guidance, which comprises the following steps: the method includes guiding alignment of a sensor configured to track a target at a site for a procedure using a processing unit and a display, the processing unit receiving position signals from the sensor and calculating, and displaying directional instructions using a user interface to move the sensor and target into alignment. The sensor is coupleable to a bone and is capable of pivoting an orientation in at least two degrees of freedom, excluding pivoting about an optical axis of the sensor. The pivot orientation may be locked to maintain alignment. The processing unit sends a signal to lock the pivot orientation in response to the alignment. The target may be used to define a site. The method may include displaying the pivot orientation of the sensor in 2 degrees of freedom. The user interface may indicate the position of the surgical site in 2 degrees of freedom. In one example, the user interface represents the pivotal orientation of the sensor as a cross hair on the display screen and the position of the surgical site as a bull's eye target. The bone may be a pelvis. The target may be placed on the femur.

A computer program product includes a non-transitory medium storing instructions and data for configuring execution of a processing unit to guide alignment of a sensor configured to track a target at a site for a medical procedure using a display, the processing unit receiving position signals from the sensor and calculating and displaying directional instructions to move the sensor and target into alignment.

A system for rendering sterile a non-sterile sensor for navigation guidance during a surgical procedure is disclosed. The system comprises: a sterile drape having an optically transparent window for covering the sensor in a sterile barrier; a shield that, when engaged with the covered optical sensor, secures the sensor in alignment with the window through the drape without breaching the sterile barrier; and a clamp configured in its closed state to rigidly support the assembled shield, drape, and sensor while maintaining alignment of the optical sensor in the window. The shroud and the clamp may have corresponding mating surfaces that allow relative movement of the shroud and the clamp to adjust the orientation of the sensor when the sensor is in the shroud and the clamp is in the partially closed state. The respective mating surfaces may define portions of the respective spheres. The clamp is configured to couple to the bone, for example, using a releasable quick connect mechanism. A method is also disclosed for this purpose.

A Method And System For surgical tracking has been proposed in applicant's U.S. patent application No.13/328,997 entitled "Method And System For Aligning a procedure During Surgery" filed on 12/16/2011, published as 6/21/2012 And published as No.2012/0157887, the entire contents of which are incorporated herein. The method and apparatus avoids the need for stationary fixed fiducial line stereo cameras located outside the surgical field; in contrast, optical sensors incorporating targets are fixed directly to the patient's anatomy and surgical instruments within the surgical field. This architecture is well suited for measuring relative pose because the sensor is directly coupled to one of the tracked targets. It is also well suited for surgical applications, which typically have a relatively small surgical working volume. Such a method and apparatus for position tracking may be applied to various surgical (and in particular orthopedic) procedures. In particular, it may be used during THA to provide the surgeon with intra-operative guidance for leg length and offset.

Referring to fig. 2 herein, one exemplary system in which a sensor is directly coupled to one of the tracked targets is system 200, which provides the surgeon with intra-operative leg length and offset change measurements (e.g., determining relative position, monitoring changes, and presenting measurements). In this system 200, the goal is to measure leg length and offset (from references on the pelvis and femur) in real time. There is a sensor 202 coupled to the patient's pelvis 204 via a pelvic clamp 206 and a pelvic platform 208. The pelvic platform provides a mechanically rigid connection to the pelvis, for example using bone pins or screws. The pelvic clamp has three functional features: attaching a sensor to the pelvic platform; providing a means of aiming the sensor at the surgical site (when attached to the pelvic platform); and providing a repeatable, quick connection point between the pelvic platform and the pelvic clamp/sensor assembly (so that the surgeon can remove the assembly when it is not in use, or as a first point of failure in the event of an undesirable mechanical impact).

Referring again to fig. 2, there is a target 210 coupled to the femur 212 via a beacon 214 and a femoral platform 216. The femoral platform provides a mechanically rigid connection to the femur, for example using bone pins or bone screws. The beacon has two functional features: the target is attached to the femoral platform and provides a repeatable, quick connection point between the femoral platform and the beacon/target assembly (so that the surgeon can remove the assembly when it is not in use, or as a first point of failure in the event of an undesirable mechanical impact).

The system architecture has symmetry on the pelvic and femoral sides. The following system components are similar in that they provide substantially similar functionality: pelvic and femoral platforms for rigid connection to the bone; pelvic clamps and beacons are used to interface to their respective platforms, provide quick connection, and attach to sensors/targets; the sensor and target are components of a tracking system that are used simultaneously to measure their relative pose. It is advantageous to have such symmetry and structure in the device. It simplifies mechanical design, manufacturing and tolerance analysis (e.g. the same quick-connect mechanism can be used on both the pelvic and femoral sides). It also provides modularity and flexibility (e.g., different beacon designs can be implemented without changing the femoral platform or target design), which is very important when considering additional surgical applications (e.g., knee replacement).

In operation of the tracking system 200, the sensor 202 senses the target 210 and provides output (e.g., by any means of communication, such as USB) to a workstation 218 or other processing unit for processing by a processor or processors (not shown), e.g., configurable by one or more computer programs 220 (e.g., one or more applications, operating systems, etc., or other software, instructions and/or data) stored into a computer medium (not shown), such as a non-volatile medium, and processed by the processor or processors to determine a pose between the target 210 and the sensor 202 (and thus the pelvis and femur). It will be appreciated that the description of the workstation is simplified. In another exemplary embodiment, the method is implemented in hardware primarily using, for example, hardware components such as Application Specific Integrated Circuits (ASICs). Implementation of a hardware state machine to perform the functions and methods described herein will be apparent to those skilled in the relevant art. In yet another embodiment, the method is implemented using a combination of both hardware and software.

In particular, the sensor 202 is optical and the sensor output signal represents a 2-dimensional image. The target is visible to the optical sensor and has a recognizable pattern. By processing the image output of the sensors and employing a priori knowledge of the pattern geometry of the target, the workstation 218 is able to calculate the relative pose. In addition to calculating relative poses, the workstation 218 may display information to the surgeon in real-time via a Graphical User Interface (GUI), such as presenting information via the display 222. Representative screenshots according to examples are described below. This information can be displayed in any coordinate system; however, it is preferred to display the pose information to the surgeon in an anatomical coordinate system. The software workflow preferably coordinates with the surgical workflow and may: assisting the surgeon in performing certain actions, collecting certain data, verifying the integrity of the data, detecting errors, displaying data at a clinically appropriate time, logging the data, and the like.

In this example, the position guidance system relies on only one sensor and one target in order to provide intra-operative leg length/offset measurements. This is a reduction in complexity relative to existing computer navigation systems, which has fundamental requirements: multiple images are processed (stereo camera) and multiple objects are tracked simultaneously (pelvis, femur, stylus/other instruments).

Fig. 3 is a flow chart depicting a method of use of system 200 for intraoperatively measuring and displaying changes in leg length and offset to a surgeon during THA. During "setup" 302, the system is ready for use. This step 302 may occur just prior to the procedure, while the surgical personnel are performing their standard surgical preparations. In step 302, the workstation 218 is set in place and started. The sensor 202 is connected. Since this is a surgical device, the system components used within the sterile field are rendered sterile (whether terminally sterile, protected with a sterile drape, or reprocessed within the hospital). Additionally, in step 302, the beacon 214 and target 210 are assembled. At the end of this step, the system 200 is ready for use.

The goal of the next step 304 (referred to as the "baseline") is to determine and store the pre-operative leg length and offset references. This step 304 preferably occurs immediately after surgical exposure of the hip joint, prior to the native hip joint dislocation. The femoral platform 216 and the pelvic platform 208 are mounted to their respective bones so as to provide a rigid structure for the sensor 202 and the target 210 of the system 200. The beacon 214 (coupled to the target 210) is preferably mounted to the femoral platform 216. The sensor 202 is then placed within the pelvic clamp 206. Initially, the sensor 202 may have its orientation adjusted within the pelvic clamp 206. To align the sensor 202 with the surgical site, the software 220 (via a graphical user interface on the display 222) may guide the surgeon in aligning the orientation of the sensor 202 based on the pose of the target 210 (mounted on the femur, which represents the location of the surgical site). With proper alignment, the surgeon may lock the pelvic clamp 206 and sensor 202 in place so that the orientation is no longer adjustable. At this point, the system 200 is ready to determine and store the pre-operative leg length and offset references.

The required pre-operative leg length and offset references are used as a basis for calculating the changes in leg length and offset. This reference measurement is a gesture and may be triggered by the surgeon (e.g., by pressing a button located on sensor 202). Note that the reference measurements (poses) are not represented in anatomical coordinates (since the registration process has not yet taken place), but in the coordinate system of the sensor 202. The reference-line gesture is stored by software 220 for later use. The system 200 measures changes in leg length and offset; it relies on the surgeon and their preoperative plan for determining the expected values for leg length and offset changes, typically obtained by analyzing the left and right hip joints using preoperative radiographs. Note that during baseline measurements, it is necessary for the femur to be substantially "neutral" with respect to the pelvis; this means that the femoral coordinate system is aligned with the pelvic coordinate system, or in clinical terms, that the femur has zero flexion, zero adduction, and zero rotation (this requirement can be alleviated in the case where femoral registration is explicitly performed, and when pre-and post-operative COR is known).

After the baseline measurements of leg length and offset are recorded, the surgeon may proceed with hip replacement surgery. The beacon 214 (with the target 210) and the pelvic clamp 206 (with the sensor 202) can be removed using their respective quick connections so as not to clutter the surgical site (leaving the low profile pelvic 208 and femoral 216 platforms in place).

Typically, the surgeon performs a first trial reduction using a final acetabular shell having trial components (e.g., liner, broach neck (broach) head). It is useful when the function of the prosthetic hip joint is evaluated, including the changes in leg length and offset. Typically, surgeons who are not equipped with computer navigation use ad hoc techniques to assess changes in leg length and offset.

In order for the system 200 to provide the surgeon with meaningful real-time measurements of leg length and offset, registration must occur. Registration refers to the process in which a map between the coordinate system of the tracking system (i.e., sensor 202) and the anatomical coordinate system of the patient is determined. It is known to perform registration when using known fixed stereo camera based position navigation systems. This registration is typically accomplished with a tracked "probe" or "stylus" that contacts the anatomical landmarks and in this way reconstructs the patient's anatomical coordinate system. The systems (e.g., 200) and methods described herein may accommodate "probe" or "stylus" based registration; however, operation without the use of a probe or stylus may be preferred.

Referring to step 306 ("registration"), a registration process involving moving the femur (with the sensors 202 and targets 210 attached in their respective anatomical locations) in a predefined and known motion is used to map the patient's anatomy. This process will be referred to as registration range of motion (RROM). The RROM procedure may be advantageous for the following reasons:

it avoids the need for additional system components for registration (e.g., a tracked stylus);

the surgeon typically performs clinical range of motion tests simultaneously (i.e., the method of registration matches the existing surgical workflow);

predefined movements are well known in clinical terms and practice;

the RROM data is also used to calculate the hip COR (no additional data is required).

In particular, the RROM procedure may prompt the surgeon to move the femur in flexion/extension, internal/external rotation, and/or external/internal flexion, while the sensors 202 (coupled to the pelvis) in conjunction with the software 220 track the pose of the target 210 (coupled to the femur). For example, a GUI on display 222 may prompt the surgeon to move the femur in the flexion-extension directions; since the motion lies in a plane, the gesture tracking data may be further processed by software 220 to determine the equation for the plane in the sensor 202 coordinate system. To determine the patient's main anatomical reference frame (and thus decompose the measurements into leg length and offset coordinates), it is preferable to collect tracking system pose data for at least two planes (since the orthogonal reference frame can be determined from the two planes). An example of a workstation 218 (e.g., software) that prompts the surgeon during the RROM procedure is found in the GUI of fig. 4. At this point, the surgeon will be prompted to move the leg in a predetermined motion, as shown in instructional figure 402 (note that the instructional figure need not display the patient's anatomy, but rather a generic representation of the pelvis and femur, as well as the portions of system 200 intended to be taught). Motion is described in clinical terms 404. During the performance of the movement, workstation 218 accumulates gesture data until a sufficient amount is collected, as indicated by progress bar 406. The amount of pose data is considered sufficient when there is a high degree of confidence that the pose data associated with each motion will yield accurate anatomical features (i.e., planes); for example, to mitigate random noise and outliers, a minimum number of pose data points (including minimum differences in pose) may be required.

With further reference to the GUI of FIG. 4, a navigation panel 408 is shown which is intended to provide an indication of their current step to the surgeon in progress. Further, an additional instructional indicator 410 is shown. The indicators 410 correspond to user inputs (e.g., buttons on the sensors 202) with which the surgeon will interact, and the labels provide instructions regarding the actions resulting from each user input. For example, in such a case, one user input may return the system 200 to a previous step (as indicated in the navigation panel 408), while another user input may trigger an action (e.g., trigger collection of RROM gesture data) according to the current step in the process. The navigation panel 408 and tutorial indicators 410 may persist through multiple stages and GUIs of the software 220.

The RROM process 306 occurs after trial reduction, meaning that the acetabular cup or shell has been implanted. This is advantageous not only in that it matches existing surgical workflow, but also in that the prosthetic joint will facilitate smooth motion, whereas the native hip joint may not (e.g., due to flexion contractures, bony impingement, arthritic deformities, etc.).

At the end of the RROM procedure, the software has computed a map from the patient's coordinate system to the sensors 202, as well as the position of the hip COR (relative to the sensors 202). Both pieces of information may be used in the "real-time boot" step 308. In this step, real-time measurements of leg length and offset are provided to the surgeon via a GUI on display 222. For example, fig. 5 shows a graphical user interface including a display of leg length and offset changes 502 (real-time updates), and a snapshot of leg length and offset changes 504, which may be captured at the discretion of the surgeon (e.g., to help track numbers in several joint resets), for example, by pressing a "record" button on sensor 202. Surgeons may use real-time leg length and offset information to select trial and final implant sizes to meet their desired preoperatively planned leg length and offset changes. Note that the transition from the GUI of fig. 4 to the GUI of fig. 5 may be configured to occur automatically at the end of the registration step 306.

In the "real-time guidance" step 308, the measurement of leg length and offset changes is not affected by the orientation of the femur. This is important because other existing products are sensitive to returning the femur to the original baseline orientation in order to maintain accuracy. In this system and method, the RROM calculates the patient's anatomical coordinate system and hip COR, which facilitates "virtual" realignment of the femur, however it adopts a baseline measurement to orient. Briefly, the system and method automatically compares "apples" to "apples" when calculating leg length and offset changes.

In a "clean up" step 310, the device is removed from the patient, the single use component is discarded, and the other components are closed, cleaned, stored, etc. This step occurs after the surgeon is satisfied that the resulting leg length and offset changes have occurred, and/or after the final prosthetic hip joint has been implanted.

Fig. 6 is a flowchart of the operation of the workstation 218 for providing leg length and offset measurements according to an example. Software that is part of the system 200 executes on the workstation and provides the functionality and workflow as outlined in fig. 3 in conjunction with the clinical workflow. In step 602, the software is started and ready for use. For example, the surgeon or another user may choose to operate the hip joint (right or left) and ensure that the sensor 200 is plugged in and available for use. The surgeon may then advance (advance) the software.

After initial incision and installation of the femoral platform 216, beacon 214, target 210, pelvic platform 208, and pelvic clamp 206, the sensor 202 may be aligned and fixed. In step 604, software 220 guides the surgeon in aligning (and fixing) sensor 202 so that it is aimed at the surgical site. This may be accomplished via a GUI, as shown in fig. 7. The GUI uses a "bull's eye" graphic 702 and a real-time alignment indicator 704 displayed as a cross-hair, such that the surgeon is facilitated to hit the "bull's eye" 702 with the cross-hair 704 by adjusting the angle of the sensor 202, as shown by the instructional graphic 706. The angle of the sensor 202 is preferably adjustable in at least two rotational degrees of freedom, which helps the sensor 202 to align with the surgical site (i.e., rotating the sensor 202 about its optical axis would not help; the other two rotational degrees of freedom would require aligning the sensor 202 with the surgical site). The basis for alignment may be a pose of the target 210 coupled to the patient's femur, as shown in the instructional figure 706. The target 210 may be used in other ways to serve as a basis for alignment (e.g., manually holding the target 210 in the center of the surgical volume). Once the sensor 202 is properly aligned with the surgical site based on the pose of the target 210, the surgeon maintains this alignment by mechanically locking the sensor in place.

Once the sensors 202 are aligned (and the surgeon has advanced the software), and prior to hip dislocation, baseline posture measurements are taken, as indicated in step 606. During baseline measurements, the femur remains in a neutral position relative to the pelvis. The baseline gestures are stored in memory of the workstation 218, for example, for later access in the process. At this point, the surgeon may advance the software and remove the sensor 202 (along with the pelvic clamp 206, and the target 210 (along with the beacon 214), and continue the surgical procedure until they are ready to evaluate intraoperative leg length and offset, at which point the sensor 202 (along with the pelvic clamp 206) and the target 210 (along with the beacon 214) are replaced on the patient. By fitting the pose data to the geometric model). The anatomical coordinate system will then be used to represent the postural measurements with respect to leg length and offset, rather than the arbitrary coordinate system associated with the sensor 202. When calculating leg length and offset changes, the hip joint COR will then be used to compensate for the femur orientation.

After completion of the RROM, the software advances automatically, and the workstation 218 (via the GUI) begins displaying real-time and continuous leg length and offset change measurements to the surgeon (step 610), as previously shown in fig. 5. Compensating for the current orientation of the femur by taking into account the baseline femur orientation, and the hip joint COR as determined at step 608, the leg length and offset change measurements; the system 200 compares the baseline posture to the current (orientation compensated) posture and represents the difference in the patient's anatomical coordinate system, also determined in step 608. The surgeon may choose to capture the data manually (as in step 612), for example, via a user input associated with the "record" indicator 506. Once the surgeon is satisfied with the patient's leg length and offset, they may choose to end the procedure, as in step 614, which may trigger surgical data recording on the workstation. If there is a change in the hip COR due to a change in the acetabular side (e.g., changing the liner, changing the cup position, etc.), the surgeon will return to step 608 to repeat the RROM process (e.g., via a user input associated with the "back" indicator 508) in order to recalculate the hip COR. This is because the software compensates for the femur orientation by "virtually rotating" the femur orientation back to the baseline posture orientation and uses the acetabular hip joint COR as a pivot point for the virtual rotation. Instead of returning to step 608 to repeat the RROM process, an alternative method may include calculating only the new hip COR (e.g., by tracking the articulation of the reduction hip) since the patient's anatomical coordinate system does not experience changes due to changes in acetabular COR position. In another alternative embodiment, during step 610, if the hip COR position has changed, the software may continuously estimate the hip COR for automatic detection. This can be achieved by tracking the posture during the reduction and relying on the constraints during a given hip reduction, the leg length and offset change measurements should not change.

Since the system 200 is a surgical device, sterility of system components within the sterile field is important. Conventional methods for achieving sterility include: terminal sterilization (i.e., single use disposable, gamma radiation sterilized, ethylene oxide sterilized, etc.), re-sterilization (via a hospital treatment such as an autoclave), and barrier/drape (i.e., a protective sterile barrier covering non-sterile equipment). With respect to system 200, the following components are preferably either capable of being resterilized or terminally sterilized: beacon, femoral platform, pelvic clamp. Components and targets such as bone screws are well suited for terminal sterilization (to preserve their performance). The sensor may be terminally sterilized and used as a single use disposable item, or reused with a sterile drape. Some commercially available sterile drape products are intended for use with endoscopic cameras and provide an integrated optical "window". (an example of a commercially available drape is a closed system camera drape (PN96-5204) from Sklar Instruments, West Chester, PA, West of West Texas.). Such a drape may be preferred for use with non-sterile sensors 202 because the drape accommodates the entire wiring and facilitates optical sensing through the window while maintaining a sterile barrier.

In the case where a sterile drape is used to maintain the sterility of the sensor, the pelvic clamp may be configured to add another functional feature: the sensor optics are aligned with the drape window. In fig. 8A, an exploded view of the pelvic clamp assembly 800 with a sterile drape 804 is shown. The pelvic clamp assembly 800 includes the sensor 202 and the pelvic clamp 206, and optionally a shroud 806 and a sterile drape 804. The sterile drape 804 maintains a sterile barrier between the non-sterile sensor 202 and the surgical field. The shroud 806 clamps or secures the sensor 202 (sterile) with the sterile drape 804, and alignment features 810 (e.g., ring clamps) of the shroud 806 are used to align the optical elements 814 of the sensor with the drape window 812. The shroud 806 (shown in a simplified manner) has an outer surface 816 that mates with a mating surface on the inside of the clamp 818. Each of the mating surfaces may define a portion of a sphere such that the clamp/shield interface provides an alignment mechanism that is functionally lockable ball and socket joints. The clamp 206 (sterile) has a mechanism (e.g., screw/hinge combination) that applies a force to the shroud 806 (and thus to the sensor 202) and rigidly and releasably holds it in place. Thus, the shroud and clamp have corresponding mating surfaces that enable relative movement of the shroud and clamp to adjust the orientation of the sensor when the sensor is in the shroud and the clamp is in a partially closed state.

On the clamp 206, there is a quick-connect mechanism 820 for repeatedly coupling the sensor 202 with the pelvis 204 via the pelvic platform 208.

As a component of the system 200, the sensor 202 and the pelvic clamp 206 can be used as follows. Non-sterile sensors 202 are transferred into sterile drape 804 according to standard sterile draping techniques for which sterile drape 804 is used. Next, the sterile personnel manually align the sterile drape window 812 with the sensor optics 814. The shroud 806 is then coupled with the sensor 202 through the sterile drape 804 using the shroud alignment features 810, such that the shroud is coupled with the sensor 202 such that the drape window 812 is held in place relative to the sensor optics 814. The sterile personnel may insert the assembly including the shroud 806, the sensor 202, and the sterile drape 804 into the pelvic clamp 206 and perform the alignment or targeting process, as described in steps 304 and 604. Targeting may be performed manually by grasping the posterior portion of the sensor 202 (exposed when inserted into the pelvic clamp 206) and manipulating its orientation. The assembly of fig. 8 meets the following requirements: sterility, the ability to aim the sensor 202 (in 3 degrees of freedom due to mating spherical surfaces) and lock the sensor 202 in place, maintain optical performance, and provide a quick connection mechanism to the pelvis.

In fig. 8B, the pelvic clamp assembly 800 is shown in an assembled state. When assembled, the shield mates with the drape in a manner that facilitates wiping (e.g., if debris ends up on the drape window, this may obscure the optics and interfere with the operation of the system 200).

An exemplary pelvic platform 900 (an example of platform 208) is shown in fig. 9. There are three subassemblies: a screw 902, a wing nut 904, and a tubular hub 906. The operation of the device is as follows. The screw is driven into the pelvis and bone threads 908 engage the bone. The tubular hub slides the screw shaft down until the spikes 910 contact the bone (alternatively, the tubular portion can be used as an expander or guide for screw insertion). The wingnut is advanced down the machine threads 912 until it tightens the cannula spike 910 (or alternatively referred to as a tooth) into the bone. The device provides very rigid fixation, including torsional rigidity, using only a single stab incision. On top of the tubular hub, there is a repeatable quick connection 914 intended to mate with the pelvic clamp connection 820.

A femoral platform 1000 (an example of femoral platform 216) is shown in fig. 10. The femoral platform body 1002 is compressed into the femur (preferably the greater trochanter) and engaged via the spikes 1004. Next, the femoral screw 1006 is inserted through the femoral platform body to tighten the assembly down and provide a very rigid structure. The screw length is such that it will not damage the femoral intramedullary canal, which would interfere with the surgeon's broach procedure during THA. On the femoral platform body, there is a quick connect mechanism 1008 for connecting the femoral platform 1000 to the beacon 214, as described further below. The femoral platform is very similar in architecture to the pelvic platform, with bone screws that tighten down on the spikes to form a rigid structure with a quick-connect mechanism.

The quick connect mechanism (which connects with the pelvic clamp 206 and pelvic platform 208 and the beacon 214 and femoral platform 216) facilitates a clear, uncongested surgical site by allowing the respective components to be removed when not in use (left behind the inconspicuous pelvic and femoral platforms). Fig. 11A shows details of an exemplary quick connect mechanism in an isometric view, while fig. 11B shows details of the exemplary quick connect mechanism using a plan view. The exemplary mechanism comprises two mating components: a first side 1100 and a second side 1102. Both the first side 1100 and the second side 1102 cooperate via the combination of the bull-nose-pins 1104 and the guide rails 1106, which provide a highly repeatable contact surface.

The bull-nosed pin is a pin that terminates the hemisphere, and the guide rails provide two parallel contact surfaces that contact the pin on the hemispherical portion (i.e., the spacing between the rails is smaller than the diameter of the hemisphere). The guide track 1106 may be accomplished directly into the second side itself using locating pins or by machining grooves, preferably with undercuts. Three pairs of bull-nosed pins 1104 and guide rails 1106 may be used for repeatable connection; in practice, however, this arrangement may not provide sufficient stability, in which case four pairs (as shown) may be used while maintaining repeatability through tight manufacturing tolerances. In addition to providing a highly repeatable interface, the bull-nosed pin/rail combination provides a clearance distance between the first side 1100 and the second side 1102 of the quick-connect; this is important for surgical applications because debris (e.g., blood, soft tissue, bone debris) can foul the quick connect mechanism. By maintaining a gap between the sides, a repeatable attachment will maintain performance in the presence of debris that will typically be encountered during surgery. Also, the bull nose pin and rail design is debris tolerant because the pin and rail share a very small contact surface.

In addition to repeatable alignment of the sides, the quick connector requires a force to maintain engagement of the first side 1100 and the second side 1102. Many types of features can accomplish this; such as springs, mating threads, cam locks, etc. In fig. 11B, complementary magnets 1108 (on the first side 1100) and 1110 (on the second side 1102) are used to generate the coupling force. In the design shown, the magnetic polarities are such that the first side 1100 and the second side 1102 will automatically align when brought into proximity with each other. Additionally, the quick connect first side 1100 and second side 1102 (including the rail 1106 and male nosepin 1104, but not including the first side magnet 1108 and second side magnet 1110) are preferably made of a non-magnetic material. In this case, the first side 1100 and the second side 1102 will easily "snap" into place; this feature is very important for the surgeon user, who evaluates simplicity and confidence of use via positive tactile/audible feedback. It should be noted that the two halves may be positioned in only two orientations, 180 degrees from each other. This feature is important because it provides flexibility.

The beacon 214 with the mating quick connect mechanism is intended to engage with the femoral platform quick connect 1008 while rigidly holding the target 210. Referring to fig. 12, a beacon 1200 is shown (an example of beacon 214) having a quick connect mechanism 1202 (in this case, second side 1102), the quick connect mechanism 1202 engaging a femoral platform quick connect 1008 (in this case, first side 1100). The front surface 1204 is a support for the target 210, which by its shape (see fig. 13) indicates proper positioning of the target 210. The support 1204 has a support function 1206. The beacon 1200 provides a shaft 1208 that is easily grasped by the surgeon for attachment to and detachment from the femoral platform 216 without touching the target 210, and thus fouling the target 210. The top of the beacon 1210 includes a surface that can be impacted (e.g., hammered) that can be used to aid in the initial installation of the femoral platform 1000 (i.e., engaging the spikes 1004, but prior to the fixation of the screws 1006). In summary, the beacon 1200 supports the target 210 and can be repeatedly attached to and detached from the patient's femur by the surgeon (via the femoral platform 216) as required for the purpose of use of the system 200 for THA.

The target 210 provides an accurate and recognizable pattern for the pose tracked by the sensor during operation of the system 200. Due to the implementation of the pattern and the required precision, the target 210 is preferably a disposable system component. Fig. 13A and 13B show a front side 1300 and a back side 1320, respectively, of a planar target 210 according to an example. The rear of the planar target 210 includes a connection mechanism 1304 (e.g., a combination of a slot and a screw in this case) for securing the target to the beacon connection mechanism 1206. The front of the target 210 has a pattern of markers 1306. The marker pattern (which may include straight lines, circles, etc.) may employ redundancy so that if the target is partially obscured by debris (e.g., blood splatter), the tracking system may still function. The marker 1306 is identifiable by the sensor 202 and may include a light reflective material (where the sensor 202 provides a source of illumination). The labels are precisely positioned on the target substrate 1308. Due to the precision of laser cutting, positioning may be accomplished using a laser cutting process. During this manufacturing process, a light reflecting material is applied to cover the target substrate 1308. The laser cutter is used to kiss cut the desired pattern (e.g., it may be loaded into the laser cutter via a CAD file). Excess retroreflective material is removed leaving behind the desired pattern. The target substrate 1308 may be a black, diffuse material; in other words, the material is adapted to absorb and scatter light, particularly in the wavelengths of the tracking system (such as near infrared, for example), so that the mark 1306 signal is readily identifiable relative to the substrate 1308 (which does not cause specular reflection from the sensor illumination, for example).

An exemplary sensor 1400 (e.g., for use as sensor 202) is shown in fig. 14. It communicates with the workstation 218 via a cable 1402 or alternatively wirelessly. The sensor has an optical element 1404, which may include an infrared filter. Further, the sensor may comprise an integrated luminaire (not shown). The sensor comprises a user interface including a user input (i.e., button) 1406 and a user indicator (i.e., indicator LED) 1408. The user interface (both user input 1406 and user indicator 1408) retains its functionality through the sterile drape 804. Locating the user interface inside the sterile field has significant advantages, particularly over traditional passive computer navigation products; the surgeon can interact with the software 220 without the need for verbal communication with non-sterile personnel. On the sensor housing 1410, there are locating features 1412 (also on the bottom of the housing 1410) such as ridges that are used to locate or position the shroud 806 without risk of damaging the sterile drape 804 barrier. Note that housing 1410 also provides a locating feature (not shown) around optical element 1404 for shroud 806 to properly align optical element 1404 with sterile drape window 812. Internally, the sensor 1400 may store data in non-volatile memory, including calibration parameters, manufacturing information, and information to maintain data integrity.

Sensor 1400 comprises an optical sensor that includes a lens, an imager, and possibly an optical filter. Additionally, in the case of tracking the inactive target 210, the sensor 1400 may include an illuminator. Based on the sensor model (i.e., camera calibration), and based on the technique of monocular pose tracking, if the target 210 meets certain criteria (i.e., if the target 210 has at least three identifiable features), the sensor 1400 can provide the workstation 218 with sufficient sensor information to calculate the pose of the target 210.

The workstation component may be any computing platform that can facilitate the necessary calculations to translate the sensor output into a gesture, then further process the gesture, and provide a graphical user interface.

It may be advantageous to deviate from or supplement the software workflow, as outlined previously in fig. 6. The possible deviation will perform the RROM process simultaneously with the baseline measurement 606. This will facilitate: the preoperative hip COR is determined and the patient anatomical coordinate system prior to trial reduction is determined. Advantages of such a method may include one or more of the following:

the need for neutral positioning of the femur at the baseline stage is avoided;

facilitating acetabular cup positioning by tracking the impactor in the anatomical frame of reference (by coupling another target to the impactor);

the change in hip COR position was quantified (from post-operative to intra/post-operative).

Without performing RROM in synchronization with baseline measurements as suggested above, the acetabular cup may be positioned under tracking guidance by repositioning the cup after the RROM procedure (fig. 6, step 608). This can be done by: starting with a trial cup that is only loosely fixed to the acetabulum, then a final cup whose position is tracked via additional targets after initial trial cup reduction using sensor 202. Similarly, the position of the acetabular cup may be verified after the RROM procedure even if it is not feasible to change its position (e.g., if the final cup is affected before the RROM, its position may be verified). In any case, tracking the position of the acetabular cup may be performed by attaching an additional target (a second target, or using an existing target 210) to the acetabular cup impactor in a known orientation.

It may be clinically beneficial to detect subluxation of the hip joint (an undesirable partial dislocation that occurs in certain orientations within the range of reduction motion). In step 610, the software and related methods may be modified so that subluxation may be detected and visually or audibly delivered to the surgeon. This would allow the surgeon to identify the subluxation (which is often too subtle to detect with the eye), identify where the subluxation occurred within the range of motion, and then take corrective action. The premise is that by considering the positioning of the hip COR, the system 200 compensates for the femur orientation when calculating leg length and offset changes. As a result, in a given range of motion (i.e., without changing the size of the implant), the leg position will remain unchanged, regardless of how the femur is oriented; thus, if the system 200 detects a change in the leg position measurement, the cause would be joint subluxation (in other words, the ball is at least partially dislocated from the socket). The software 220 and method (step 610) can be modified to include a mode in which a significant change in position is interpreted as a subluxation of the joint and delivered to the surgeon since the position of the leg should not change. In one embodiment, the workstation 218 may be alerted in response to detection, for example, by emitting an audible signal, or beeping, when joint subluxation is detected during this mode. Using an audible signal will allow the surgeon to visually focus on the hip joint and obtain a clinical understanding of the nature of the joint subluxation.

In another embodiment, the systems and methods may be further modified to detect joint subluxation. For example, pre-dislocation baseline attitude measurements (in steps 304, 606) do not require detecting subluxation, meaning that these steps may be omitted or modified accordingly. Also, the calculation of a map to the patient's anatomical coordinate system (object of the RROM procedure) is not required to detect subluxation (although it may be useful to quantify where subluxation occurs within the range of motion of the replacement hip joint); however, it is preferred to calculate the hip COR. This is because the subluxation measurement essentially depends on whether the position of the examination target 210 to the radius of the hip COR (in 3D space) has changed within a given range of motion for a given reduction hip.

In step 610, a "stability cone" may be generated by tracking the orientation of the femur at its range of motion limits and detecting the posture at the location where the impact or subluxation occurred (as described above). This would allow the surgeon to assess whether the patient's range of motion is sufficient (e.g., young, active patients may desire a wide range of motion based on their daily activities, while elderly patients may not), and make clinical adjustments as needed. The "stability cone" may be generated and delivered to the surgeon graphically, numerically, or in any other suitable manner. Preferably, the "stability cone" is delivered relative to the patient's anatomical coordinate system. The software 220 and associated method (step 610) may be modified to include a "stability cone" mode in which tracking system pose data is used to evaluate a prosthetic joint, particularly at joint range of motion limits; further, this information may be displayed to the surgeon via display 222 in the patient's anatomical coordinate system.

It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it may be practiced with modification. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

It will be apparent to those skilled in the art upon reading this disclosure that each of the individual embodiments described and illustrated herein has discrete elements and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present invention. Any of the methods described may be performed in the order of events described or in any other order that is logically possible.

Claims

1. A medical navigation guidance system, comprising:

an alignment mechanism comprising a lockable ball joint;

a sensor for coupling to a bone and orienting towards a site for a medical procedure using the alignment mechanism;

a sterile drape having an optically transparent window to cover the sensor in a sterile barrier;

a target coupled to a target for tracking by the sensor; and

a processing unit in communication with the sensor, the processing unit configured to direct alignment of the sensor with the target, the processing unit calculating using position signals from the sensor and displaying directional instructions using a user interface to move the sensor and the target into alignment.

2. The system of claim 1, wherein the alignment mechanism facilitates at least two degrees of freedom orientation adjustment of the sensor relative to the bone.

3. The system of claim 1, wherein the alignment mechanism is a locking mechanism to releasably fix an orientation of the sensor.

4. The system of claim 1, wherein the target is used to define the location of the site.

5. The system of claim 1, wherein the processing unit is further configured to compute directional instructions in at least two degrees of freedom.

6. The system of claim 5, wherein the processing unit represents the pivotal orientation of the sensor as a cross-hair on a display screen and the location of the surgical site as a bull's eye target.

7. The system of claim 5, wherein the target is configured to provide a target location signal to the sensor to define a location of a surgical site.

8. The system of claim 1, wherein the sensor is an optical sensor.

9. The system of claim 1, wherein the target is a femur.

10. The system of claim 1, wherein the bone is a pelvis.

11. A medical navigation guidance system, comprising:

a sensor for orienting towards a site for a medical procedure to measure a position and orientation of a target coupled to a target;

an alignment mechanism comprising a lockable ball joint to couple to the sensor and orient the sensor toward the site;

a sterile drape having an optically transparent window to cover the sensor in a sterile barrier; and

a processing unit in communication with the sensor, the processing unit configured to direct alignment of the sensor with the site, the processing unit calculating using position signals from the sensor and displaying directional instructions using a user interface to move the sensor and the site into alignment.

12. The system of claim 11, wherein the alignment mechanism facilitates at least two degrees of freedom orientation adjustment of the sensor relative to the site.

13. The system of claim 11, wherein the alignment mechanism is a locking mechanism to releasably fix an orientation of the sensor.

14. The system of claim 11, wherein the sensor is attached to a bone of a patient.

15. The system of claim 11, wherein the target is used to define the location of the site.

16. The system of claim 11, wherein the processing unit is further configured to calculate the directional instructions in at least two degrees of freedom.

17. The system of claim 11, wherein the target is configured to provide a target location signal to the sensor to define a location of a surgical site.

18. The system of claim 17, comprising the target.