Patent Publication Number: US-2023135541-A1

Title: Hip surgery systems and methods

Description:
INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS 
     Any and all applications for which a foreign or domestic priority claim is identified in the Application Data Sheet as filed with the present application are hereby incorporated by reference under 37 CFR 1.57. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present application is directed to systems and methods for joint replacement, in particular to systems and methods for hip joint replacement which utilize a surgical orientation device or devices. 
     Description of the Related Art 
     Joint replacement procedures, including hip joint replacement procedures, are commonly used to replace a patient’s joint with a prosthetic joint component or components. Specifically, the hip joint often requires replacement in the form of prosthetic components due to strain, stress, wear, deformation, misalignment, and/or other conditions in the joint. Prosthetic hip joint components can be designed to replace, for example, an acetabular prosthetic socket in the hip and/or a femoral head. 
     Current systems and methods often use expensive, complex, bulky, and/or massive computer navigation systems which require a computer or computers, as well as three dimensional imaging, to track a spatial location and/or movement of a surgical instrument or landmark in the human body. These systems are used generally to assist a user to determine where in space a tool or landmark is located, and often require extensive training, cost, and room. 
     Where such complex and costly systems are not used, simple methods are used, such as “eyeballing” the alignment of a prosthetic acetabular cup or femoral broach. These simple methods are not sufficiently accurate to reliably align and place implant components and the bones to which such components are attached. 
     Correct positioning of surgical instruments and implants, as used in a surgical procedure with respect to the patient’s anatomy, is therefore often an important factor in achieving a successful outcome. In certain orthopedic implant procedures, such as total hip replacement (THR) or arthroplasty, total knee arthroplasty (TKA), high tibial osteotomy (HTO), and total shoulder replacement (TSR), for example, the optimal orientation of the surgical implant can enhance initial function and long term operability of the implant. A misaligned acetabular prosthetic cup can lead to complications such as dislocation of the hip joint, decreased joint motion, joint pain, and hastened failure of the implant. 
     SUMMARY OF THE INVENTIONS 
     Accordingly, there is a lack of devices, systems and methods that can be used to accurately position components of prosthetic joints without overly complicating the procedures, crowding the medical personnel, and/or burdening the physician or health-care facility with the great cost of complex navigation systems. Thus, there is a need in the art for improved systems and methods for obtaining accurate orientation of surgical instruments and implants during various orthopedic repair and replacement procedures, including total hip replacement (“THR”). Furthermore, there is a need for such devices and methods to be simple and easy to operate. 
     In accordance with at least one embodiment, an apparatus for preparing a hip joint can comprise a reference post having a distal end adapted to be driven into a portion of a pelvic bone, a proximal end, and a reference post body extending along a longitudinal axis between the proximal and distal ends, a coupling device disposed adjacent to the proximal end of the reference post adapted for connecting the reference post body to a second surgical component, and an orientation sensor coupled with the reference post. 
     In accordance with another embodiment, an apparatus for preparing a hip joint can comprise a mounting structure having a first end adapted to secure to a patient’s anatomy and a second end disposed away from the first end, an elongate member having a first end and a second end, the first end of the elongate member adapted to connect to the second end of the mounting structure, a marking device coupled with the second end of the elongate member for visually indicating the position of an anatomical landmark during a procedure, and a surgical orientation device coupled with the elongate member for movement therealong for measuring at least one of position and orientation along the elongate member. 
     In accordance with another embodiment, an apparatus for assessing the orientation of an acetabular landmark or an acetabular implant can comprise a handling device comprising a proximal end with a handle, a distal end, and an elongate member extending therebetween, an acetabular landmark contacting device coupled with the distal end of the handling device, and a surgical orientation device for detecting and recording an orientation of the acetabular landmark or the acetabular implant. 
     In accordance with another embodiment, an acetabular surface preparation apparatus can comprise a handling device comprising a proximal end with a handle, a distal end, and a rotatable shaft extending therebetween, a surface preparation device coupled with the distal end and adapted to remove bone from the acetabulum to create a surface suitable for receiving an acetabular implant, a sleeve disposed around the rotatable shaft and adapted to remain stationary while the shaft is rotating, and a surgical orientation device coupled with the sleeve such that the orientation device can remain stationary while the rotatable shaft is rotated. 
     In accordance with another embodiment, an acetabular implant placement device can comprise a handling device comprising a proximal end with a handle, a distal end, and an elongate member extending therebetween, wherein the distal end comprises an implant contacting structure adapted to couple with an acetabular implant, and a surgical orientation device coupled with the handling device such that the orientation of at least one of the handling device and the surgical orientation device can be monitored as the acetabular implant is advanced into the acetabulum. 
     In accordance with another embodiment, a method for preparing a patient’s hip for receiving an implant can comprise providing a first orthopedic system comprising a reference post comprising an orientation sensor, an impactor coupled with the reference post, a first angle assessment guide, and a portable surgical orientation device attached to the angle assessment guide, attaching the reference post to a hip bone of the patient, measuring and recording a reference distance from the reference post to an anatomical landmark using the portable surgical orientation device, removing the angle assessment guide, impactor, and portable surgical orientation device from the reference post, providing a second orthopedic system comprising an alignment guide, a second angle assessment guide attached to the alignment guide, and the portable surgical orientation device attached to the alignment guide, measuring an orientation of an anatomical plane using the second angle assessment guide, orienting an implant relative to the anatomical plane and inserting the implant into the acetabulum using the second orthopedic system, attaching a femoral broach to the patient’s femur, the femoral broach including a head, positioning the head in the implant, providing the first orthopedic system a second time, and measuring changes in the reference distance. 
     In accordance with another embodiment, a method for preparing a patient’s hip for receiving an implant can comprise attaching a first orthopedic system to the patient’s hip with a reference device, the first orthopedic system comprising a portable surgical orientation device, measuring and recording a reference distance from the reference device to an anatomical landmark using the portable surgical orientation device, measuring an orientation of an anatomical plane on the patient’s hip using a second orthopedic system, the second orthopedic system comprising the portable surgical orientation device, orienting an implant relative to the anatomical plane using the second orthopedic system, inserting the implant into the acetabulum, inserting a prosthetic femoral head into the implant, and measuring changes in the reference distance using the first orthopedic system. 
     In accordance with another embodiment, a method for positioning a patient in a hip procedure can comprise advancing a reference device into a patient’s pelvic bone, coupling a surgical orientation device with the reference device such that the orientation device is not moveable relative to the pelvic bone, measuring at least one of the position or orientation of at least a portion of the patient’s hip joint using the surgical orientation device, and moving the patient’s hip joint to selected position the patient relative to a fixed reference frame based on the measurement on the surgical orientation device. 
     In accordance with another embodiment, a method for assessing relative position of portions of a hip joint can comprise coupling a surgical orientation device to a first bone of a patient’s hip at a first location with a reference device, measuring a reference distance from the reference device to an anatomical landmark of a second bone using the surgical orientation device, performing a hip procedure, and after performing the hip procedure, confirming the position of the anatomical landmark relative to the first location. 
     In accordance with another embodiment, a method of placing an acetabular implant can comprise providing an orientation apparatus comprising an elongate member having a handle disposed at a proximal end, an angle assessment device disposed at a distal end, and a surgical orientation device, advancing the angle assessment device into contact with an anatomical landmark of the acetabulum while measuring orientation of the landmark, preparing the acetabulum for receiving the acetabular implant, placing the acetabular implant within the acetabulum, and advancing the angle assessment device into contact with the acetabular implant to confirm the orientation of the implant. 
     In accordance with another embodiment, a method of preparing an acetabular surface for receiving an acetabular implant can comprise providing a handle, a shaft rotatably coupled with the handle, a reamer coupled a distal end of the shaft, and an orientation device coupled in a fixed position relative to the handle, providing contact between the reamer and an acetabular surface while rotating the shaft and reamer to remove bone within the acetabulum, and measuring the orientation of the reamer while providing contact between the reamer and an acetabular surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    shows a representation of a human anatomy, identifying generally the femur, pelvis, iliac spine, and lesser trochanter; 
         FIG.  2 A  is a side view of a orthopedic system according to one embodiment for establishing a reference location on a patient’s anatomy; 
         FIG.  2 B  is a front view of the orthopedic system of  FIG.  2 A ; 
         FIG.  2 C  is a perspective view of the orthopedic system of  FIG.  2 A ; 
         FIG.  2 D  is a front view of a reference post according to one embodiment; 
         FIG.  3 A  is a side view of an orthopedic system according to one embodiment for measuring distances in and around a joint; 
         FIG.  3 B  is a top view of the orthopedic system of  FIG.  3 A ; 
         FIG.  4    is an exploded perspective view of a orthopedic system according to one embodiment for determining an orientation of a plane in a patient’s anatomy; 
         FIG.  5    is a perspective view of a orthopedic system according to one embodiment for preparing a portion of a patient’s anatomy to receive an implant; 
         FIG.  6    is a perspective view of a orthopedic system according to one embodiment for orienting a prosthetic component; 
         FIG.  7    is a perspective view of a surgical orientation device according to one embodiment that can be used in conjunction with one or more of the orthopedic systems described herein; 
         FIG.  8    is a back view of the surgical orientation device of  FIG.  7   ; 
         FIG.  9    is a perspective view of the surgical orientation device of  FIG.  7   ; 
         FIG.  10 A  is a top view of the surgical orientation device of  FIG.  7   ; 
         FIG.  10 B  is a bottom view of the surgical orientation device of  FIG.  7   ; 
         FIG.  11    is a block diagram of an electrical system of the surgical orientation device of  FIG.  7   ; 
         FIGS.  12 A-C  illustrate operation of accelerometers according to embodiments that can be used as sensors in the electrical system of  FIG.  11   ; 
         FIG.  12 D  is a perspective view of interior components of the surgical orientation device of  FIG.  7   ; 
         FIG.  12 E  is a flow chart of an embodiment of an orientation measurement process performed by the surgical orientation device of  FIG.  7   ; 
         FIG.  13    illustrates a method in which the patient’s hip is generally parallel to an operating table and a reference post of the orthopedic system of  FIGS.  2 A-C  is inserted into the patient’s anatomy; 
         FIG.  13 A  illustrates a method in which the patient’s hip is generally parallel to an operating table and a fixture is provided for coupling a reference post of the orthopedic system of  FIGS.  2 A-C  with the patient’s anatomy; 
         FIG.  13 B  illustrates a technique for coupling a reference post with the fixture shown in  FIG.  13 A ; 
         FIG.  14    illustrates a method in which the orthopedic system of  FIGS.  3 A-B  is being used to measure a distance between the fixed reference post and a reference location on the patient’s anatomy; 
         FIG.  14 A  illustrates a method in which the orthopedic system of  FIGS.  3 A-B  is used to measure a distance between the fixed reference post and a reference location on the patient’s anatomy; 
         FIGS.  15 - 18    illustrate techniques for resecting a femoral head and cleaning of osteophytes around the acetabular rim; 
         FIG.  19    is a perspective view of the orthopedic system of  FIG.  4    being used to determine the orientation of a plane defined by landmarks on the patient’s acetabular rim; 
         FIG.  20    is a perspective view of the orthopedic system of  FIG.  5    being used to ream out a portion or portions of the patient’s acetabular socket; 
         FIGS.  21  and  22    are perspective views of the orthopedic system of  FIG.  6    being used to orient a prosthetic acetabular cup; 
         FIG.  23    is a perspective view of a polymer insert being placed in the prosthetic acetabular cup; 
         FIGS.  24 - 26    are perspective views of a preparation of femoral canal, broach, and prosthetic femoral head; 
         FIG.  27    is a perspective view of the patient’s hip joint being reduced back into place, with the prosthetic femoral head inserted into the prosthetic acetabular cup; 
         FIG.  28    is a perspective view of the orthopedic system of  FIGS.  3 A-B  being used again to measure a distance between the fixed reference post and a reference location on the patient’s anatomy; and 
         FIGS.  29 A and B  are schematic illustrations of a change in leg length (LL) and leg offset (OS) as measured prior to and after a hip preparation procedure according to one embodiment. 
         FIGS.  30 A-W  show various embodiments of user interface screens that can be displayed during an orthopedic procedure or procedures. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Although certain preferred embodiments and examples are disclosed below, it will be understood by those skilled in the art that the inventive subject matter extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the inventions, and to obvious modifications and equivalents thereof. Thus it is intended that the scope of the inventions herein disclosed should not be limited by the particular disclosed embodiments described below. Thus, for example, in any method or process disclosed herein, the acts or operations making up the method/process may be performed in any suitable sequence, and are not necessarily limited to any particular disclosed sequence. For purposes of contrasting various embodiments with the prior art, certain aspects and advantages of these embodiments are described where appropriate herein. Of course, it is to be understood that not necessarily all such aspects or advantages may be achieved in accordance with any particular embodiment. Thus, for example, it should be recognized that the various embodiments may be carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other aspects or advantages as may be taught or suggested herein. 
     I. Overview of Systems and Methods 
     The following sections describe in detail systems and methods for a hip replacement procedure. The orthopedic systems described herein include orthopedic systems and orthopedic devices for preparing the hip to receive prosthetic components. The systems include but are not limited to orthopedic systems  10 ,  110 ,  210 ,  310 , and  410  described herein, each of which can be used during various stages of an orthopedic procedure or procedures, such as for example a total hip replacement procedure. These orthopedic systems and devices can be used to perform minimally invasive, cost-efficient, successful orthopedic procedures. 
     II. Orthopedic Systems 
     A number of different orthopedic systems are discussed below. These systems are useful, for example, for modifying the natural hip joint to enable the hip joint to have a prosthetic component or components, such components including but not limited to a prosthetic acetabular cup. 
       FIG.  1    illustrates a pelvis, femur, iliac spine, and lesser and greater trochanter regions. As will be described further herein, these and/or other anatomical locations and landmarks can be referenced and used throughout an orthopedic procedure or procedures in conjunction with the systems described herein. 
     A. Orthopedic System For Establishing a Reference Location on the Patient’s Anatomy 
     With reference to  FIGS.  2 A-D , an orthopedic system  10  can be used to provide a fixed reference on a patient’s anatomy, as well as to provide an anchor and/or support for other orthopedic systems. As illustrated in  FIG.  2 A , the orthopedic system  10  can comprise a surgical orientation device  12 , reference device  14 , impactor  16 , and angle assessment guide  18 . 
     1. Device For Use As a Reference in the Patient’s Anatomy 
     The system  10  can comprise a device or component that serves as a reference for other systems or devices. For example, and as illustrated in  FIG.  2 A , the reference device  14  can comprise a reference post  14 , and can serve as a reference for other systems or devices. The reference post  14  can comprise a thin, metallic pin that can be at least partially driven (e.g. hammered with a slap hammer) into a bony area on the patient’s anatomy. As will be described further herein, the reference post  14  can be partially driven, for example, into the iliac spine on a patient’s pelvis. Other types of reference posts can also be used. The reference post  14  can also be used to hold back tissue that would otherwise cover the surgical field, e.g., skin and muscle and other sub-dermal tissues. In a preferred arrangement, the reference post  14  also can serve as an anchor or otherwise mechanically support other joint preparation systems, as discussed below. The reference post  14  can comprise a mounting structure. For example, the reference post  14  can support the system  310  in one technique. The reference post  14  also can be coupled with an orientation sensor or sensors  15 , which can be disposed on the reference post’s surface or inside the reference post  14 . The sensor or sensors  15  can detect orientation (e.g.position) and/or relative movement of the reference post  14 . By detecting movement of the sensor(s)  15 , movement of anatomy with which the reference post is coupled (e.g. surrounding bony area) can also be detected. 
     In one technique, the impactor  16  is used to assist in placement of the reference post  14 . With continued reference to  FIGS.  2 A-C , the impactor  16  can be releasably coupled to the reference post  14 . The impactor  16  can drive the reference post  14  into a bony area on the patient’s anatomy, and the impactor  16  can then be removed. The impactor  16  can include, for example, an elongate rod  20  with one end  22  for pounding or striking with a hammer, and an opposite end  24  for releasably connecting to the impactor  14 . 
       FIG.  2 D  shows another embodiment of a reference post  14 ′ which can be used with system  10 . The reference post  14 ′ can comprise a proximal portion  30 , an elongate body  32 , and a distal portion  34 . The proximal portion  30  can comprise a coupling structure comprising an annular recess  36  defined between a proximally facing shoulder  38  and a distally facing shoulder  40 . Other coupling structures are also possible. As described above, the impactor  16  can comprise a coupling structure  24  for releasable attachment to the reference post  14 ′. In some embodiments, the end  24  of impactor  16  can comprise be fork-shaped as shown in  FIG.  2 C , and adapted to be received within the annular recess  36  of the reference post  14 . The fork-shaped structure  24  can abut at least one of the proximal end  30  of the reference post  14  and the proximally facing shoulder  38  to transfer a force to the body  32  of the reference post  14  and drive distal end  34  into the bone. Thus, the impactor  16  can enable the force of blows of the hammer to be transferred to the reference post  14  such that the distal end  34  of reference post  14  can be advanced into the bone. 
     2. Device For Angle Assessment Relative to Operating Table 
     The system  10  can further comprise a device which can be used to orient the patient’s pelvis relative to the operating table. For example, and as described further herein, the angle assessment guide  18  can be used to orient the patient’s pelvis. The angle assessment guide  18  can comprise a member  19 , an attachment structures  26 , and an end member  28 . The attachment structure  26  can couple (e.g. attach, releasably attach) the angle assessment guide  18  to the impactor  16  and/or reference post  14  at a certain angle “a”. The angle “a” can be any of a number of angles, and preferably 45 degrees.  FIG.  2 A  shows “a” at an angle of approximately 45 degrees. The angle assessment guide  18  can comprise any of a number of sizes and shapes. For example, the angle assessment guide can comprise a first elongate member, a second elongate member, and a third elongate member. The first elongate member can couple with the proximate end of the reference post  14 ,  14 ′, and can comprise the elongate rod  20  of the impactor. The second elongate member can couple with the first elongate member at an angle relative to the first elongate member (e.g. an acute angle), and can comprise member  19 . The third elongate member can be mounted to the second elongate member, and can comprise the cross-bar-shaped member  28  as illustrated in  FIG.  2 A . The surgical orientation device  12  can be releasably coupled to the angle assessment guide  18 , such that movement of the angle assessment guide  18  causes identical movement of the surgical orientation device  12 . The surgical orientation device can alternatively or additionally be releasably coupled to the reference post  14 . In some embodiments, the surgical orientation device can be coupled to the cross-bar member  28  with a coupling device such as that disclosed in U.S. Pat. Application No. 12/509,388, filed Jul. 24, 2009, the contents of which are incorporated in their entirety by reference herein. 
     3. Surgical Orientation Device 
     With continued reference to  FIGS.  2 A-C , the surgical orientation device  12  can be can be used for verifying an alignment and/or measuring distances. “Surgical orientation device” is a broad term as used herein, and includes, without limitation, devices which can be used alone or in conjunction with an orthopedic device or devices to identify or track a relative position of one or more orthopedic devices or anatomical structures, and can encompass any of the embodiments shown in the drawings and as described herein, as well as any of the embodiments shown or described in U.S. Pat. Application No. 12/509,388, filed Jul. 24, 2009, the contents of which are incorporated in their entirety by reference herein. 
     For example,  FIG.  7    shows an embodiment of a surgical orientation device  12 . The surgical orientation device  12  can comprise a compact device for use in orienting a cutting guide or other surgical tool in a joint replacement procedure. In some techniques, the surgical orientation device  12  can be configured for being hand-held during a procedure. Preferably the surgical orientation device  12  is portable. 
     The surgical orientation device  12  can be used, for example, to identify an orientation of an anatomical plane, such as for example a plane defined by landmarks on a patient’s acetabular rim. The surgical orientation device  12  can be used, for example, to measure distances, such as for example a distance between the reference post  14  and an anatomical landmark or landmarks on the patient’s anatomy. Other uses are also possible. Furthermore, the surgical orientation device  12 , as described herein, can be used alone or in conjunction with other devices, components, and/or systems, including but not limited to the sensor(s)  15  on the reference post  14 , if included. 
     In a preferred arrangement, the surgical orientation device  12  can comprise a generally rectangular-shaped structure having an outer housing  30 . The outer housing  30 , as well as its contents can be portable. The outer housing  30  can be comprised, at least in part, of plastic including but not limited to ABS, polycarbonate, or other suitable material. The surgical orientation device  12  can be configured for hand-held use. The surgical orientation device  12  can be configured for mounting to other surgical devices, as discussed below. 
     With continued reference to  FIG.  7   , a front side  32 , or a portion of the front side  32 , of the surgical orientation device  12  can comprise a display  34 . The display  34  can be a separate component from the outer housing  30  or can be integrated on or within the outer housing  30 . The display  34  can comprise an output device. For example, the display  34  can comprise a liquid crystal display (“LCD”) or Ferroelectric Liquid Crystal on Silicon (“FLCOS”) display screen. The display screen can be sized such that a user can readily read numbers, lettering, and/or symbols displayed on the display screen while performing a medical procedure. In an embodiment, the display  34  comprises a Quarter Video Graphics Array (“QVGA”) Thin Film Transistor (“TFT”) LCD screen. Other types of display screens can also be used, as can other shapes, sizes, and locations for the display  24  on the surgical orientation device  12 . 
     The surgical orientation device  12  can further comprise at least one user input device  36 . The at least one user input device  36  can comprise a plurality of buttons located adjacent the display  34 . The buttons can be activated, for example, by a finger, hand, and/or instrument to select a mode or modes of operation of the device  12 , as discussed further below. In a preferred arrangement, the at least one user input comprises three buttons located underneath the display  34  as illustrated in  FIG.  7   . In other embodiments, the user input device  36  is a separate component from the housing  30 . For example, the user input device  36  can comprise a remote input device coupled to the surgical orientation device  12  via a wired or wireless connection. In yet other embodiments, the user input device  36   comprises a microphone operating in conjunction with a speech recognition module configured to receive and process verbal instructions received from a user. 
     As discussed below, the surgical orientation device  12  can include a user interface with which a clinician can interact during a procedure. In one embodiment, the display  34  and at least one user input  36  can form a user interface. The user interface can allow a surgeon, medical personnel, and/or other user to operate the surgical orientation device  12  with ease, efficiency, and accuracy. Specific examples and illustrations of how the user interface can operate in conjunction with specific methods are disclosed further herein. 
       FIGS.  8  and  9    show a back side  37  of the surgical orientation device  12 . The back side  37  can include an attachment structure or structures  38 , as well as a gripping feature or features  39  for facilitating handling of the surgical orientation device  12 . The attachment structures  38  can facilitate attachment of the surgical orientation device  12  to another device, such as for example a coupling device (not shown). In a preferred arrangement, the attachment structures  38  comprise grooves, or channels  40 , along a portion of the back side of the surgical orientation device  12 . 
     The attachment structures  38  can be formed, for example, from protruding portions of the back side of the surgical orientation device  12 , and can extend partially, or entirely, along the back side of the surgical orientation device  12 . The attachment structures  38  can receive corresponding, or mating, structures from the coupling device  14 , so as to couple, or lock, the coupling device to the surgical orientation device  12 .  FIGS.  10 A and  10 B  show top and bottom sides  41   a ,  41   b  of the surgical orientation device  12 . The surgical orientation device  12  can comprise optical components  42  that can be located on the top side  41   a , the bottom side  41   b , or the top and bottom sides  41   a ,  41   b  of the surgical orientation device  12 . The optical components  42  can comprise transparent windows  44  integrated into the surgical orientation device  12 . The optical components  42  can be windows that permit visible light (e.g. laser light) to emit from the top side  31   a , the bottom side  31   b , or both the top and bottom sides  41   a ,  41   b  of the surgical orientation device  12 . While the embodiment illustrated in  FIGS.  10   a  and  10   b    shows two windows  44  for transmitting light, other numbers are also possible. Additionally, while the optical components  42  are shown located on the top and bottom of the surgical orientation device  12 , in other embodiments the optical components  42  can be located in other positions and/or on other portions of the surgical orientation device  12 . 
       FIG.  11    illustrates a high-level block diagram of an electrical system  1100  of the surgical orientation device  12 . The electrical system  1100  comprises an electronic control unit  1102  that communicates with one or more sensor(s)  1104 , one or more visible alignment indicators  1106 , a power supply  1108 , a display  1110 , external memory  1112 , one or more user input devices  1114 , other output devices  1116  and/or one or more input/output (“I/O”) ports  1118 . 
     In general, the electronic control unit  1102  can receive input from the sensor(s), the external memory  1112 , the user input devices  1114  and/or the I/O ports  1118  and controls and/or transmits output to the visible alignment indicators  1106 , the display  1110 , the external memory  1112 , the other output devices  1116  and/or the I/O ports  1118 . The electronic control unit  1102  can be configured to receive and send electronic data, as well as perform calculations based on received electronic data. In certain embodiments, the electronic control unit  1102  can be configured to convert the electronic data from a machine-readable format to a human readable format for presentation on the display  1110 . The electronic control unit  1102  can comprise, by way of example, one or more processors, program logic, or other substrate configurations representing data and instructions, which can operate as described herein. In other embodiments, the electronic control unit  1102  can comprise controller circuitry, processor circuitry, processors, general purpose single-chip or multi-chip microprocessors, digital signal processors, embedded microprocessors, microcontrollers and/or the like. The electronic control unit  1102  can have conventional address lines, conventional data lines, and one or more conventional control lines. In yet other embodiments, the electronic control unit  1102  can comprise an application-specific integrated circuit (ASIC) or one or more modules configured to execute on one or more processors. In certain embodiments, the electronic control unit  1102  can comprise an AT91SAM7SE microcontroller available from Atmel Corporation. 
     The electronic control unit  1102  can communicate with internal memory and/or the external memory  1112  to retrieve and/or store data and/or program instructions for software and/or hardware. The internal memory and the external memory  1112  can include random access memory (“RAM”), such as static RAM, for temporary storage of information and/or read only memory (“ROM”), such as flash memory, for more permanent storage of information. In some embodiments, the external memory  1112  includes an AT49BV160D-70TU Flash device available from Atmel Corporation and a CY62136EV30LL-45ZSXI SRAM device available from Cypress Semiconductor Corporation. The electronic control unit  1102  can communicate with the external memory  1112  via an external memory bus. 
     In general, the sensor(s)  1104  can be configured to provide continuous real-time data to the surgical orientation device  12 . The electronic control unit  1102  can be configured to receive the real-time data from the sensor(s)  1104  and to use the sensor data to determine, estimate, and/or calculate an orientation (e.g. position) of the surgical orientation device  12 . The orientation information can be used to provide feedback to a user during the performance of a surgical procedure, such as a total hip replacement surgery, as described in more detail herein. 
     In some arrangements, the one or more sensors  1104  can comprise at least one orientation sensor configured to provide real-time data to the electronic control unit  1102  related to the motion, orientation (e.g. position)of the surgical orientation device  12 . For example, a sensor module  1104  can comprise at least one gyroscopic sensor, accelerometer sensor, tilt sensor, magnetometer and/or other similar device or devices configured to measure, and/or facilitate determination of, an orientation of the surgical orientation device  12 . The term “module” as used herein can include, but is not limited to, software or hardware components which perform certain tasks. Thus, a module can include object-oriented software components, class components, procedures, subroutines, data structures, segments of program code, drivers, firmware, microcode, circuitry, data, tables, arrays, etc. Those with ordinary skill in the art will also recognize that a module can be implemented using a wide variety of different software and hardware techniques. 
     In some embodiments, the sensors  1104  can be configured to provide measurements relative to a reference point(s), line(s), plane(s), and/or gravitational zero. Gravitational zero, as referred to herein, refers generally to an orientation in which an axis of the sensor  1104  is perpendicular to the force of gravity, and thereby experiences no angular offset, for example tilt, pitch, roll, or yaw, relative to a gravitational force vector. In other embodiments, the sensor(s)  1104  can be configured to provide measurements for use in dead reckoning or inertial navigation systems. 
     In various embodiments, the sensor(s)  1104  comprise one or more accelerometers that measure the orientation of the surgical orientation device  12  relative to gravity. For example, the accelerometers can be used as tilt sensors to detect rotation of the surgical orientation device  12  about one or more of its axes. For example, the one or more accelerometers can comprise a dual axis accelerometer (which can measure rotation about two axes of rotation). The changes in orientation about the axes of the accelerometers can be determined relative to gravitational zero and/or to a reference plane registered during a tibial or femoral preparation procedure as described herein. 
     In certain embodiments, a multi-axis accelerometer (such as the ADXL203CE MEMS accelerometer available from Analog Devices, Inc. or the LIS331DLH accelerometer available from ST Microelectronics.) detects changes in orientation about two axes of rotation. For example, the multi-axis accelerometer can detect changes in angular position from a horizontal plane (e.g., anterior/posterior rotation) of the surgical orientation device  12  and changes in angular position from a vertical plane (e.g., roll rotation) of the surgical orientation device  12 . The changes in angular position from the horizontal and vertical planes of the surgical orientation device  12  as measured by the sensor  1104  can be used to determine changes in orientation of the surgical orientation device  12 . 
     In some arrangements, the sensors  1104  can comprise at least one single-or multi-axis gyroscope sensor and at least one single- or multi-axis accelerometer sensor. For example, a sensor module  1104  can comprise a three-axis gyroscope sensor (or three gyroscope sensors) and a three-axis accelerometer (or three accelerometer sensors) to provide orientational measurements for all six degrees of freedom of the surgical orientation device  12 . In some embodiments, the sensors provide an inertial navigation or dead reckoning system to continuously calculate the orientation and velocity of the surgical orientation device  12  without the need for external references 
     In some embodiments, the sensors  1104  comprise one or more accelerometers and at least one magnetometer. The magnetometer can be configured to measure a strength and/or direction of one or more magnetic fields in the vicinity of the surgical orientation device  12 . The magnetometer can advantageously be configured to detect changes in angular position about a vertical axis. In other embodiments, the sensors  1104  comprise one or more sensors capable of determining distance measurements. For example a sensor located in the surgical orientation device  12  can be in electrical communication (wired or wireless) with an emitter element mounted at the end of a measurement probe. For example, sensor  15  in reference post  14  can comprise an emitter element. In certain embodiments, the electrical control unit can be configured to determine the distance between the sensor and emitter (for example, an axial length of a measurement probe corresponding to a distance to an anatomical landmark, such as a bony eminence of the pelvis or femur, such as the greater or lesser trochanter). 
     In other embodiments, the one or more sensors  1104  can comprise a temperature sensor to monitor system temperature of the electrical system  1100 . Operation of some of the electrical components can be affected by changes in temperature. The temperature sensor can be configured to transmit signals to the electronic control unit  1102  to take appropriate action. In addition, monitoring the system temperature can be used to prevent overheating. In some embodiments, the temperature sensor comprises a NCP21WV103J03RA thermistor available from Murata Manufacturing Co. The electrical system  1100  can further include temperature, ultrasonic and/or pressure sensors for measuring properties of biological tissue and other materials used in the practice of medicine or surgery, including determining the hardness, rigidity, and/or density of materials, and/or determining the flow and/or viscosity of substances in the materials, and/or determining the temperature of tissues or substances within materials. 
     In certain embodiments, the sensors  1104  can facilitate determination of an orientation of the surgical orientation device  12  relative to a reference orientation established during a preparation and alignment procedure performed during orthopedic surgery. Further details regarding the operation of the sensors in conjunction with a total hip replacement surgery are described herein. 
     The one or more sensors  1104  can form a component of a sensor module that comprises at least one sensor, signal conditioning circuitry, and an analog-to-digital converter (“ADC”). In certain embodiments, the components of the sensor module  1104  are mounted on a stand-alone circuit board that is physically separate from, but in electrical communication with, the circuit board(s) containing the other electrical components described herein. In other embodiments, the sensor module is physically integrated on the circuit board(s) with the other electrical components. The signal conditioning circuitry of the sensor module can comprise one or more circuit components configured to condition, or manipulate, the output signals from the sensor(s)  1104 . In certain embodiments, the signal conditioning circuitry comprises filtering circuitry and gain circuitry. The filtering circuitry can comprise one more filters, such as a low pass filter. For example, a 10 Hz single pole low pass filter can be used to remove vibrational noise or other low frequency components of the sensor output signals. The gain circuitry can comprise one or more operational amplifier circuits that can be used to amplify the sensor output signals to increase the resolution potential of the sensor. For example, the operational amplifier circuit can provide gain such that a 0 g output results in a midrange (e.g., 1.65 V signal), a +1 g output results in a full scale (e.g., 3.3 V) signal and a -1 g output results in a minimum (0 V) signal to the ADC input. 
     In general, the ADC of the sensor module can be configured to convert the analog output voltage signals of the sensor(s)  1104  to digital data samples. In certain embodiments, the digital data samples comprise voltage counts. The ADC can be mounted in close proximity to the sensor to enhance signal to noise performance. In certain embodiments, the ADC comprises an AD7921 two channel, 12-bit, 250 Kiloseconds per Sample ADC. In an arrangement having a 12-bit ADC can generate  4096  voltage counts. The ADC can be configured to interface with the electronic control unit  1102  via a serial peripheral interface port of the electronic control unit  1102 . In other embodiments, the electronic control unit  1102  can comprise an on-board ADC that can be used to convert the sensor output signals into digital data counts. 
     With continued reference to  FIG.  11   , the visible alignment indicators  1106  can comprise one or more lasers, which can be configured to project laser light through the optical component or components  32  described above. For example, the visible alignment indicators  1106  can comprise a forward laser and an aft laser. The laser light can be used to project a point, a plane, and or a cross-hair onto a target or targets, including but not limited to an anatomical feature or landmark, to provide alternative or additional orientation information to a surgeon regarding the orientation of the orientation device  12 . For example, laser light can be used to project a plane on a portion of bone to indicate a resection line and a cross-hair laser pattern can be used to ensure alignment along two perpendicular axes. In certain embodiments, the laser light or other type of probe (e.g. a mechanical probe such as an elongate rod) can be used to mark or identify landmarks on the patient’s hip area, such as the lesser trochanter and/or iliac spine. In certain embodiments, the laser light or other type of probe can be used to constrain a degree of freedom, such as rotation about a vertical axis, of an instrument relative to anatomy or one instrument relative to another. The probe can be used, for example, to return an instrument to a specific rotational orientation. In certain embodiments, the visible alignment indicators  1106  can be used to determine a distance to an anatomical feature or landmark (for example, a laser distance measurement system). For example, the electronic control unit  1102  can project laser light to a target and a sensor  1104  within the surgical orientation device can sense the laser light reflected back from the target and communicate the information to the electronic control unit. The electronic control unit  1102  can then be configured to determine the distance to the target. The lasers can be controlled by the electronic control unit  1102  via pulse width modulation (“PWM”) outputs. In certain embodiments, the visible alignment indicators  1106  comprise Class 2M lasers. In other embodiments, the visible alignment indicators  1106  comprises other types of lasers or light sources. 
     The power supply  1108  can comprise one or more power sources configured to supply DC power to the electronic system  1100  of the surgical orientation device  12 . In certain embodiments, the power supply  1108  comprises one or more rechargeable or replaceable batteries and/or one or more capacitive storage devices (for example, one or more capacitors or ultracapacitors). In other embodiments, power can be supplied by other wired and/or wireless power sources. In preferred arrangements, the power supply  1108  comprises two AA alkaline, lithium, or rechargeable NiMH batteries. The surgical orientation device  12  can also include a DC/DC converter to boost the DC power from the power supply to a fixed, constant DC voltage output (e.g., 3.3 volts) to the electronic control unit  1102 . In some embodiments, the DC/DC converter comprises a TPS61201DRC synchronous boost converter available from Texas Instruments. The electronic control unit  1106  can be configured to monitor the battery level if a battery is used for the power supply  1108 . Monitoring the battery level can advantageously provide advance notice of power loss. In certain embodiments, the surgical orientation device  12  can comprise a timer configured to cause the surgical orientation device  12  to temporarily power off after a predetermined period of inactivity and/or to permanently power off after a predetermined time-out period. 
     As discussed above, the display  1110  can comprise an LCD or other type screen display. The electronic control unit  1102  communicates with the display via the external memory bus. In certain embodiments, the electronic system  1100  comprises a display controller and/or an LED driver and one or more LEDs to provide backlighting for the display  1110 . For example, the display controller can comprise an LCD controller integrated circuit (“IC”) and the LED driver can comprise a FAN5613 LED driver available from Fairchild Semiconductor International, Inc. The electronic control unit  1102  can be configured to control the LED driver via a pulse width modulation port to control the brightness of the LED display. For example, the LED driver can drive four LEDs spaced around the display screen to provide adequate backlighting to enhance visibility. The display can be configured to display one or more on-screen graphics. The on-screen graphics can comprise graphical user interface (“GUI”) images or icons. The GUI images can include instructive images, such as illustrated surgical procedure steps, or visual indicators of the orientation information received from the sensor(s)  1104 . For example, the display can be configured to display degrees and either a positive or negative sign to indicate direction of rotation from a reference plane and/or a bubble level indicator to aid a user in maintaining a particular orientation. The display can also be configured to display alphanumeric text, symbols, and/or arrows. For example, the display can indicate whether a laser is on or off and/or include an arrow to a user input button with instructions related to the result of pressing a particular button. 
     With continued reference to  FIG.  11   , the user input device(s)  1114  can comprise buttons, switches, a touchscreen display, a keyboard, a joystick, a scroll wheel, a trackball, a remote control, a microphone, and the like. The user input devices  1114  can allow the user to enter data, make selections, input instructions or commands to the surgical orientation device  12 , verify a position of the surgical orientation device  12 , turn the visible alignment indicators  1106  on and off, and/or turn the entire surgical orientation device  12  on and off. The other user output devices  1116  (i.e.. other than the display  1110 ) can comprise an audio output, such as a speaker, a buzzer, an alarm, or the like. For example, the audio output can provide a warning to the user when a particular condition occurs. The output devices  1116  can also comprise a visible output, such as one or more LED status or notification lights (for example, to indicate low battery level, an error condition, etc.). The audio output can comprise different patterns, tones, cadences, durations, and/or frequencies to signify different conditions or events. In other embodiments, output from the electronic control unit  1102  can be sent to external display devices, data storage devices, servers, and/or other computing devices (e.g., via a wireless network communication link). 
     The I/O ports  1118  of the electronic control unit  1102  can comprise a JTAG port and one or more serial communication ports. The JTAG port can be used to debug software installed on the electronic control unit  1102  during testing and manufacturing phases. The JTAG port can be configured such that it is not externally accessible post-manufacture. The serial communication ports can include a Universal Serial Bus (“USB”) port and/or one or more universal asynchronous receiver/transmitters (“UART”) ports. At least one of the UART ports can be accessible externally post-manufacture. The external UART port can be an infrared (“IR”) serial port in communication with an infrared (“IR”) transceiver. The IR serial port can be used to update the software installed on the electronic control unit  1102  post-manufacture and/or to test the operation of the electronic control unit  1102  by outputting data from the electronic control unit  1102  to an external computing device via an external wireless connection. Other types of I/O ports are also possible. 
     As described above, the sensor(s)  1104  can comprise one or more accelerometers. Accelerometers can measure the static acceleration of gravity in one or more axes to measure changes in tilt orientation. For example, a three-axis accelerometer can measure the static acceleration due to gravity along three orthogonal axes, as illustrated in  FIG.  12 A . A two-axis accelerometer can measure the static acceleration due to gravity along two orthogonal axes (for example, the x and y axes of  FIG.  12 A ). The output signals of an accelerometer can comprise analog voltage signals. The output voltage signals for each axis can fluctuate based on the fluctuation in static acceleration as the accelerometer changes its orientation with respect to the gravitational force vector. In certain embodiments, an accelerometer experiences static acceleration in the range from -1 g to +1 g through 180 degrees of tilt (with -1 g corresponding to a -90 degree tilt, 0 g corresponding to a zero degree tilt, and +1 g corresponding to a +90 degree tilt. The acceleration along each axis can be independent of the acceleration along the other axis or axes. 
       FIG.  12 B  illustrates a measured acceleration along each of the three axes of a three-axis accelerometer in six different orientation positions. TOP and BOTTOM labels, as well as a circle indicating Pin 1 of the accelerometer, have been included to aid in determining the various orientations. A gravitational force reference vector is illustrated as pointing straight down toward the Earth’s surface. At positions A and B, the x-axis and the y-axis of the accelerometer are perpendicular to the force of gravity and the z-axis of the accelerometer is parallel to the force of gravity; therefore, the x and y acceleration components of static acceleration due to gravity at positions A and B are 0 g and the z component of static acceleration due to gravity at positions A and B is +1 g and -1 g, respectively. At positions C and E, the x-axis and the z-axis of the accelerometer are perpendicular to the force of gravity and the y-axis is parallel to the force of gravity; therefore, the x and z acceleration components of static acceleration due to gravity at positions C and E are 0 g and the y component of static acceleration due to gravity at positions C and E is +1 g and -1 g, respectively. At positions D and F, the y-axis and z-axis are perpendicular to the force of gravity and the x-axis is parallel to the force of gravity; therefore, the y and z acceleration components of static acceleration due to gravity at positions D and F are 0 g and the x component of static acceleration due to gravity at positions D and F is +1 g and -1 g, respectively. A dual-axis accelerometer operates in the same manner but without the z component. In certain arrangements, a three-axis accelerometer can be used as a tiltmeter to measure changes in orientation about two axes. 
     Multi-axis accelerometers can be conceptualized as having a separate accelerometer sensor for each of its axes of measurement, with each sensor responding to changes in static acceleration in one plane. In certain embodiments, each accelerometer sensor is most responsive to changes in tilt (i.e., operates with maximum or optimum accuracy and/or resolution) when its sensitive axis is substantially perpendicular to the force of gravity (i.e., when the longitudinal plane of the accelerometer sensor is parallel to the force of gravity) and least responsive when the sensitive axis is parallel to the force of gravity (i.e., when the longitudinal plane of the accelerometer sensor is perpendicular to the force of gravity).  FIG.  12 C  illustrates the output of the accelerometer in g’s as it tilts from -90 degrees to +90 degrees. As shown, the tilt sensitivity diminishes between -90 degrees and -45 degrees and between +45 degrees and +90 degrees (as shown by the decrease in slope). This resolution problem at the outer ranges of tilt motion makes the measurements much less accurate for tilt measurements over 45 degrees. In certain embodiments, when the mounting angle of the surgical orientation device  12  is known, the sensor(s)  1104  can be mounted to be offset at an angle such that the accelerometer sensors can operate in their more accurate, steeper slope regions. For example, for use during the knee surgery preparation procedures described herein, the sensor(s)  1104  can be mounted at approximately a 22-degree angle relative to the anterior-posterior axis of the surgical orientation device  12  to account for a predetermined range of motion of the surgical orientation device  12  about the flexion/extension axis during the procedures. It should be appreciated by one of ordinary skill in the art that the accelerometer can be mounted at acute angles other than approximately 22 degrees. In other arrangements, the sensor(s)  1104  can be mounted to be offset to account for a predetermined range of motion about other axes of rotation as well. In yet other arrangements, for example, when a three-axis accelerometer is used, the accelerometer sensor(s) can be mounted in parallel with the anterior-posterior axis of the surgical orientation device  12 . In one three-axis accelerometer arrangement, a handoff system can be incorporated to ensure that the accelerometer sensors with the most accurate reading (e.g., &lt; 45 degrees) are being used at each orientation position. The handoff system can employ hysteresis to avoid “bouncing” phenomena during the handoffs between the accelerometer sensors. 
       FIG.  12 D  illustrates the inside of the surgical orientation device  12  according to at least one embodiment. The surgical orientation device  12  can comprise one or more circuit boards and/or other circuitry capable of installation within the surgical orientation device  12 . As illustrated, the surgical orientation device  12  can comprise a sensor board  46 A and a main board  46 B. The components of the sensor module (including the sensor(s)  1104 ) can be mounted on the sensor board  46 A and the other components of the electrical system  1100  are mounted on the main board  46 B. The sensor board  46 A can comprise one or more sensors  50  (e.g., sensor(s)  1104  as described above). In alternative embodiments, the sensor board  46 A and the main board  46 B can be combined into a single circuit board. The sensor board  46 A and the main board  46 B can comprise rigid or flexible circuit boards. The sensor board  46 A and the main board  46 B can be fixedly or removably coupled to the outer housing  20 . 
     As illustrated, the sensor board  46 A is mounted at an approximately 22-degree angle relative to a plane extending longitudinally through the housing  30 , which can be parallel to or correspond to an anterior-posterior axis of the main board  46 B. As described above, mounting the sensor board  46 A at an offset angle can enable the one or more sensors to operate in the regions of maximum or optimum sensitivity, accuracy and/or resolution. The particular mounting offset angle can be selected based on a range of motion of the surgical orientation device  12  during a particular orthopedic procedure. As shown in  FIG.  12 D , the surgical orientation device  12  can include two AA batteries  38  as the power supply  1110  for providing power to the surgical orientation device  12 . The surgical orientation device  12  also can include lasers  42  as the visible alignment indicators  1106  described above. 
       FIG.  12 E  is a high-level flowchart of an exemplary conversion process for converting an analog voltage output signal of a multi-axis accelerometer into an angle degree measurement for presentation on the display  34 . Although the steps are described as being implemented with hardware and/or software, each of the steps illustrated in  FIG.  12 E  can be implemented using hardware and/or software. It should be appreciated that a similar conversion process can be performed for any other type of sensor or for multiple separate sensors without departing from the spirit and/or scope of the disclosure. 
     For each axis of rotation measured (e.g., pitch and roll), the multi-axis accelerometer can continuously output an analog voltage signal. At Block  1205 , the signal conditioning circuitry of the sensor module can filter the analog output voltage signal (e.g., with a low pass filter) to remove noise from the signal that may be present due to the high sensitivity of the multi-axis accelerometer. At Block  1210 , the signal conditioning circuitry amplifies, or boosts, the output voltage signal, for example, via the gain circuitry described above. 
     At Block  1215 , the ADC can convert the continuous analog voltage signal into a discrete digital sequence of data samples, or voltage counts. In certain embodiments, the ADC can sample the analog voltage signal once every two milliseconds; however, other sampling rates are possible. In certain embodiments, the analog voltage signal is oversampled. At Block  1220 , the electronic control unit  1102  can generate a stable data point to be converted to an angle measurement. The electronic control unit  1102  can apply a median filter to the sampled data to eliminate outliers (e.g., spikes) in the data. For example, the electronic unit  1102  can use an 11-sample median filter to generate the middle value from the last 11 samples taken. The output of the median filter can then be fed into a rolling average filter (for example, a  128  sample rolling average filter). The rolling average filter can be used to smoothe or stabilize the data that is actually converted to an angle measurement. The electronic control unit  1102  can implement Blocks  1215  and  1220  using a finite impulse response (“FIR”) or an infinite impulse response (“IIR”) filter implemented in a software module. 
     At Block  1225 , the electronic control unit  1102  can convert the voltage count data to an angle measurement in degrees. In performing the conversion, the electronic control unit  1102  can be configured to apply a calibration conversion algorithm based on a calibration routine performed during a testing phase prior to sale of the surgical orientation device  12 . The calibration conversion can be configured to account for unit-to-unit variations in components and sensor placement. The calibration routine can be performed for each axis being monitored by the multi-axis accelerometer. The calibration conversion can comprise removing any mechanical or electrical offsets and applying an appropriate gain calibration for a positive or negative tilt. 
     As described above, the ADC can comprise an ADC with 12-bit resolution, which provides 4096 distinct voltage counts, wherein a -90 degree tilt corresponds to 0 counts (-2048 signed counts), a zero degree tilt corresponds to 2048 counts (0 signed counts), and a +90 degree tilt corresponds to 4096 counts (+2048 signed counts). The tilt angle for each axis (e.g., pitch and roll) of the multi-axis accelerometer can be calculated from the voltage count data based on standard trigonometric relationships as the arcsin of the acceleration component in each particular axis. In arrangements in which the electronic control unit  1102  applies the calibration conversion, the tilt angle for each axis can be calculated as follows: 
     
       
         
           
             
               
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      where OFFSET corresponds with a zero offset of the surgical orientation device  12  determined during the calibration routine and GAIN corresponds with a ratiometric value determined during the calibration routine, with one GAIN value being used for negative tilt angles and a different GAIN value being used for positive tilt angles. 
     Also at Block  1225 , in arrangements where a dual-axis accelerometer is used, the electronic control unit  1102  can be configured to adjust the pitch angle (x axis) calculation to account for the mounting offset angle (described above) of the dual-axis accelerometer relative to the outer housing  20  of the surgical orientation device  20 . The result of Block  1225  is an absolute angle for each axis of rotation (e.g., pitch, roll) being monitored by the dual-axis accelerometer. The absolute pitch and roll angles can be used to calculate orientation measurements of the surgical orientation device  12 . 
     Orientation measurements for the surgical orientation device  12  can be determined based on a wide variety of reference frames in conjunction with any of a variety of surgical procedures. 
     In certain embodiments, calculations can be performed by software modules executed by the electronic control unit  1102 . In other embodiments, the electronic control unit  1102  can generate measurements using data stored in one or more look-up tables (“LUT”s). In other embodiments, other calculations can be derived based on the type of sensor or sensors used, the procedure being performed, and/or the reference frame being employed. Specific calculations in accordance with other procedures are described, for example, in U.S. Pat. Application No. 12/509,388, filed Jul. 24, 2009, the contents of which are incorporated in their entirety by reference herein. 
     In certain embodiments, the electronic control unit  1102  can perform a stabilization routine, process, or algorithm to assess or determine the stability, or reliability, of the calculated angle measurements. For example, the electronic control unit  1102  can keep a history of the last 100 ms of calibrated sample data for each axis being monitored by the sensor(s)  40 . Each time a new sample is added to the 100-sample history, a maximum and minimum value is determined for the 100-sample data set. The electronic control unit  1102  can then determine a delta difference between the maximum and minimum values. The electronic control unit  1102  can then compare the delta difference between the maximum and minimum values to a threshold. If the delta difference is lower than the threshold, then the data is considered to be stable and it is stored in memory (e.g., external memory  1112 ) and time-stamped. If the delta difference is greater than the threshold, then the data is considered to be unstable. When retrieving an angle reading to display to the user, the electronic control unit  1102  can be configured to transmit the last stable data reading (assuming it is not too old) to the display  1110  instead of the current unstable reading. If the last stable angle exceeds a time threshold, the unstable angle reading can be displayed along with a visual indication notifying the user that the angle reading is unstable. For example, a red “shaky hand” icon or graphical user interface image can be displayed on the display screen. 
     B. Orthopedic System For Measuring Distances in a Joint 
     With reference to  FIGS.  3 A and  3 B , a orthopedic system  110  can be used to measure distances in a joint. These distances can be measured between, for example, a reference (e.g. reference post  14 ) and an anatomical landmark (e.g. a predetermined landmark such as the lesser trochanter). The distances can be measured both before a procedure as well as after a procedure to determine whether the procedure has been successful. The orthopedic system  110  can comprise the surgical orientation device  12  described above, the reference post  14  described above (including, for example, sensor  15 ), a measuring device  112  and a marking device  118 . 
     1. Device For Measuring Distances in a Joint 
     With continued reference to  FIGS.  3 A and  3 B , the measuring device  112  can comprise a structure or structures (e.g. an elongate structure) which facilitate measurement of a distance between the fixed reference post  14  and an anatomical reference or references. The measuring device  112  can comprise an angle assessment guide. The measuring device  112  can be releasably coupled to the reference post  14 . For example, the measuring device  112  can comprise a coupling device  113  or other structure which connects the measuring device  112  to the proximal end  30  of the reference post  14 ′. The measuring device  112  can include a marking or markings  114  along at least one side or portion. The markings  114  can provide the user with visual evidence of the distance between the fixed reference post  14  and the marking device  118 . 
     The measuring device  112  can further include a hinge  115 . The hinge  115  can allow the measuring device  112 , or a portion of the measuring device  112 , to be pivotably rotated relative to the reference post  14 . In some embodiments, the measuring device  12  and marking device  118  can be both pivotably rotated about the hinge  115 , as well as rotated about the coupling device  113 . For example, the hinge  115  and coupling device  113  can allow for rotational movement of the marking device  118  in both a first plane, as well as a second plane orthogonal to the first plane. Thus, the measuring device  18  can be moved in at least two degrees of rotational freedom. 
     In some embodiments, the marking device  118  can comprise a laser device. For example, a laser can be emitted from a marking device  118  and/or measuring device  112 . The laser can contact and/or reference an anatomical location, and such location can be used to obtain a measurement or measurements as described herein. 
     The measuring device  112  can further comprise an attachment structure  116 . The attachment structure  116  can releasably attach the surgical orientation device  12  to the measuring device  112 . The attachment structure  116  can comprise a coupling device or devices that allows the surgical orientation device  12  and/or marking device  118  to move relative to the measuring device  112 . For example, in a preferred arrangement, when the reference post  14  is fixed into the patient’s bony anatomy, the surgical orientation device  12  and marking device  118  can slide longitudinally along a length of the measuring device  112 , thereby changing the relative distance between the reference post  14  and the marking device  118 . The attachment device  116  can further allow the marking device  118  to be moved generally through a range of elevations so as to bring the marking device closer to or in contact with an anatomical landmark. As described above, the surgical orientation device  12  can be configured to detect translational changes. Thus, both the markings  114  and surgical orientation device itself can facilitate an accurate measurement of a distance between the proximal end  30  of reference post  14  and the marking device  118 . 
     2. Device For Marking An Anatomical Landmark 
     With continued reference to  FIG.  3 B , the marking device  118  can comprise a pin or other structure which can be used to physically pinpoint and/or contact an anatomical landmark. For example, and as described further herein, an end  120  of the marking device  118  can be brought into contact with and/or placed adjacent the lesser trochanter, and the location on the lesser trochanter can be marked with an ink or some other marking agent, such as for example a methylene blue marker. The marking device  118  can be releasably coupled to the surgical orientation device  12 , such that any movement of the surgical orientation device  12  causes identical movement of the marking device  118 . The marking device  118  can visually indicate a position of an anatomical landmark during a procedure. In certain embodiments, the marking device  118  can be a laser which projects a point of light down onto the anatomy without making physical contact or impairing access to or visualization of the joint space. In certain embodiments a fan-style laser can be incorporated into the system to be substantially in alignment with the measuring device  112 . The laser can be used as an aid to align an axis of the measuring device  112  (e.g. the “leg length” axis) with an axis of the leg by orienting the measuring device  112  such that the laser line passes through the center of the knee, ankle or other appropriate landmark. 
     C. Orthopedic System For Determining an Orientation of a Plane in a Patient’s Anatomy 
     With reference to  FIG.  4   , an orthopedic system  210  can be used to determine the orientation of an anatomical plane in the human anatomy, such as for example an anatomical plane defined by a landmark or landmarks along the acetabular rim in a patient’s pelvic area. The orthopedic system  210  can comprise the surgical orientation device  12  described above, and an anatomical contact device  214 . 
     1. Anatomical Contact Device For Contacting a Landmark or Landmarks 
     With continued reference to  FIG.  4   , the anatomical contact device  214  can comprise a hand-held and/or portable orthopedic device which comprises at least one component that contacts at least one anatomical landmark on the patient’s anatomy. For example, the anatomical contact device  214  can comprise an alignment handle  216  which is releasably coupled to the surgical orientation device  12 . The alignment handle  216  can comprise a proximal end  217  with a handle, a distal end  219 , and an elongate member  221  extending therebetween. The alignment handle  216  can be gripped by a user’s hand and moved, such that the handle  216  and surgical orientation device  12  generally move together. 
     The anatomical contact device  214  can further comprise an anatomical contact component  218 . The anatomical contact component  218  can comprise an acetabular landmark contacting device, and can be releasably coupled to the alignment handle  216 , or can be integrally formed with the alignment handle  216 . In a preferred arrangement, the component  218  can comprise a tripod-like structure, with three arms  220  extending radially outwardly from a center portion  222  of the component  218 . Each of the three arms  220  can be spaced radially equally from one another at 120 degrees, although other arrangements are also possible, as are other numbers of arms  220 . Each of the arms  220  can further be angled such that no one plane contains any two of the arms  220 . Each of the arms  220  can comprise a tip  224 . As described further herein, the tips  224  can be used to contact landmarks on the acetabular rim of the patient. 
     D. Orthopedic System For Preparing an Acetabular Surface 
     With reference to  FIG.  5   , an orthopedic system  310  can be used to prepare a portion of a patient’s anatomy, such as for example an acetabular socket area in a patient’s pelvis. The orthopedic system  310  can be used, for example, to ream at a specified angle or orientation relative to a reference and/or anatomical landmark. The orthopedic system  310  can comprise the surgical orientation device  12  described above, a protective mounting device  312 , and a surface preparation tool  314 . 
     1. Stationary Mount for the Surgical Orientation Device 
     With continued reference to  FIG.  5   , the mounting device  312  can comprise a structure which releasably attaches to the surgical orientation device  12  and allows the surgical orientation device  12  to generally remain still while reaming takes place. For example, the protective mounting device  312  can comprise an elongate tubular structure and/or bearing which permits relative rotational movement of a structure within its inner surfaces. The protective mounting device  312  can be made of plastic, metal, or other suitable material. The mounting device  312  can comprise lubricant applied to its inner surfaces, and/or can comprise a bearing or bearings which inhibit the mounting device  312  from rotating when reaming is taking place. 
     2. Acetabular Surface Preparation Device 
     With continued reference to  FIG.  5   , the surface preparation tool  314  can comprise a device which can prepare a portion of a patient’s anatomy. For example, the surface preparation tool  314  can ream out a portion of a patient’s acetabular socket. The surface preparation tool  314  can comprise a reamer handle  316 . The reamer handle  316 , or a portion of the reamer handle  316 , can extend through the mounting device  312 , and at least a portion of the reamer handle  316  can rotate relative to the mounting device  312  while at least a portion of the surface preparation tool  314  is rotating. In some embodiments, the reamer handle  316  can comprise a proximal end  317  that comprises a handle, a distal end  319 , and a rotatable shaft portion  321  extending therebetween, the rotatable shaft portion  321  being rotatably coupled with the proximal end  317 . 
     The surface preparation tool  314  can further comprise a surface preparation device  318 . The surface preparation device  318  can be releasably coupled or integrally formed with the reamer handle  316 , and can comprise a cutting tool or element which digs into and reams out bony matter and/or tissue in the patient’s anatomy. For example, the surface preparation device  318  can comprise a generally spherical-shaped cutting tool which is configured to ream out an acetabular socket. 
     E. Orthopedic System For Orienting a Prosthetic Hip Component 
     With reference to  FIG.  6   , a orthopedic system  410  can be used to orient a prosthetic component, such as for example a prosthetic acetabular cup. The orthopedic system  410  can be used to orient the prosthetic component at a specified angle or orientation relative to a reference and/or anatomical landmark. The orthopedic system  410  can comprise, for example, the surgical orientation device  12  described above, a guide device  412 , and a prosthetic component  414  (e.g. prosthetic acetabular cup). 
     1. Device For Guiding a Prosthetic Component 
     With continued reference to  FIG.  6   , the guide device  412  can comprise a proximal end  416 , a distal end  418 , and an elongate portion  419  extending therebetween. The proximal end  416  can comprise a handle that can be gripped by a user. The elongate portion  419  can comprise an elongate rod or structure which can be releasably coupled to the surgical orientation device  12 , such that the guide device  412  and surgical orientation device  12  generally move together. 
     The distal end  418  can comprise a implant contacting structure which releasably couples the guide device  412  to the prosthetic component  414 . While coupled, the prosthetic component  414  can move with the guide device  412 . Once oriented, the prosthetic component  414  can be released from the guide device  412 . 
     2. Prosthetic Component for Insertion in the Patient’s Anatomy 
     The prosthetic component  414  can comprise any of a number of commonly available prosthetics, including but not limited to prosthetic acetabular cups. The acetabular cup size can vary depending upon the patient. The prosthetic component  414  can be sized and shaped so as to fit into the area reamed out by orthopedic system  310 . 
     III. Hip Preparation Methods 
     A number of different hip preparation methods are discussed below. These methods can be used in conjunction with the systems described above, and are useful for modifying the natural hip joint to enable the hip joint to have a prosthetic component or components, such components including but not limited to a prosthetic acetabular cup. 
     A. Pre-Operative Planning 
     Prior to any hip procedure, a surgeon or other medical personnel can create templates of a patient’s anatomy, and use these templates to determine ideal post-procedure conditions within the patient’s anatomy. For example, in a hip replacement procedure, the surgeon can first obtain x-ray images of the patient’s pelvis. Based on the images, the surgeon can look at a diseased side of the hip, as well as the healthy side, and determine goals for joint offset and leg length. 
       FIG.  29 A  illustrates a joint offset prior to incising the capsule joint in the hip. As illustrated in  FIG.  29 A , joint offset (represented for example by the arrows labeled “OS”) generally represents a medial/ lateral component of the distance between two landmarks, one of which is generally fixed. For example, during a hip replacement procedure utilizing one or more of the systems described above, the reference post  14  can remain fixed. Thus, joint offset can be represented by a distance “OS” between the fixed reference post  14  and a specified landmark “A” on the femur, taken in a generally medial/lateral direction. 
     Similarly, leg length can be represented by the arrows “LL” in  FIG.  29 A . With reference again to  FIG.  29 A , the leg length “LL” can be the component of the distance between the fixed reference post  14  and the specified landmark “A” on the femur, taken in a generally proximal/distal direction perpendicular to that of the medial/lateral direction. 
     When viewing the pre-operative x-rays, the surgeon can get an idea of what changes in joint offset and leg length will be necessary on the diseased side of the hip to bring the hip into symmetry (e.g. both sides of the hip having the same leg length and joint offset). If both sides of the hip are not brought into symmetry, the joint offset on the diseased side of the hip can cause wear and deterioration of the surrounding ligaments. 
     B. Establishing a Reference For Hip Replacement Using an Orthopedic System 
     With reference to  FIG.  13   , the orthopedic system  10  described above can be used to establish a reference in the patient’s anatomy. The reference can be established prior to incising a joint capsule in the hip. For example, once the hip anatomy has been exposed by pulling back surrounding tissue, the reference post  14  can be driven into a specified landmark on the patient’s anatomy. In one embodiment, such landmark remains immobile throughout the rest of a hip replacement procedure. Thus, a landmark such as the iliac spine can be used, although other landmarks are also possible. For example, in some embodiments, as discussed in greater detail below, the reference post  14  can be driven into a portion the femur, or other parts of the human anatomy. In some embodiments, the reference post  14  can be clamped and/or otherwise anchored to a portion of the femur, and the pelvis can be referenced relative to the femur. 
     Once a landmark is chosen, the surgeon can use a slap hammer or other device to pound the impactor  16  and drive the reference post  14  into the patient’s anatomy as desired, until the reference post  14  is firmly in place. If the reference post  14  has a sensor  15  on or embedded within or otherwise coupled to the reference post  14 , the sensor  15  can be at least partially within the bony mass of the pelvis (or other bony area), or can still be exterior of the anatomy after insertion of the reference post  14 . In some embodiments, the reference post  14  can comprise a retractor. For example, with the surrounding tissue pulled back, the reference post  14  can be configured as an anchor or as a retractor to at least partially hold back the tissue that would normally be disposed above or around the surgical site. 
     With reference to  FIGS.  2 A and  13   , prior to the hip replacement procedure, and prior to driving the reference post  14  into the iliac spine, the surgical orientation device  12  can be registered in a position parallel to the operating table and floor. For example, data about the orientation of the surgical orientation device  12  can be obtained through the sensor or sensors  50  in the surgical orientation device  12  while the surgical orientation device is held parallel to the operating table. 
     Once the surgical orientation device  12  is registered, and the reference post  14  has been driven into the iliac spine, the pelvis can be adjusted and moved relative to a fixed reference frame. Because the angle α described above and shown in  FIG.  2 A  can remain fixed relative to the reference post  14 , movement of the system  10  and surgical orientation device  12  can be monitored. For example, in some embodiments the surgical orientation device  12  can be positioned at a known angle, such as an acute angle (e.g. 45 degrees), relative to a medial-lateral plane of the pelvic bone. In some embodiments, the surgical orientation device  12  can be positioned at about 45 degrees relative to a longitudinal axis of the reference post  14 . In some embodiments, the hip (with the reference post  14  inserted) can be adjusted until the surgical orientation device  12  indicates an angle 90°-α, at which point the reference post  14  is positioned generally perpendicular to the floor, and the patient’s pelvis is positioned generally parallel to the floor. Such positioning of the pelvis can be helpful, for example, in proper positioning of the prosthetic component  414  described above. In some embodiments, the reference post  14  can be driven vertically into the iliac spine while the patient is in a supine position. A probe, such as for example a laser or mechanical rod, can be used to align the surgical orientation device  12  with an axis of the leg to establish a reference rotation about a vertical axis and a direction for leg length measurement(s). 
     As described above, the reference post  14  can contain a sensor or sensors  15  that evaluate the orientation (e.g. position or angle) of the pelvis or other bony area. For example, once the pelvis has been positioned generally parallel to the operating table and floor, the sensor or sensors  15  can be zeroed and/or registered by the surgical orientation device  12  or other device. In a preferred arrangement, the sensor  15  can communicate with the surgical orientation device  12 , giving the surgical orientation device  12  information about the orientation of the iliac spine and/or pelvis. If the pelvis moves during the hip procedure, the surgical orientation device  12  can account for such movement since it has information about such movement from sensor  15 . Furthermore, the surgical orientation device  12  can additionally obtain information about the spatial location of the reference post  14  based on the sensor or sensors  15 , and can use that information to obtain and record measurements of distance between the reference post  14  and surgical orientation device  12 . In some embodiments, the sensor  15  can comprise a satellite sensor which communicates with the surgical orientation device  12 , and is separately read by the surgical orientation device  12 . In some embodiments, the surgical orientation device  12  and reference post  14  can each comprise a sensor or sensors. In some embodiments the surgical orientation device  12  can be configured to only receive information from the sensor  15 , and does not itself have an orientation sensor. Furthermore, in some embodiments, more than one sensor can be used. For example, the systems described herein can comprise two or more sensors  15  located on the pelvis, greater trochanter, and/or other anatomical landmarks. 
     In one embodiment, a first satellite sensor is the sensor  15  coupled with the reference post  14 , a second satellite sensor is coupled with another surgical device, and both satellite sensors provide sensor data to a variation of the surgical orientation device  12 . Where two satellite sensors are provided, one can be coupled with a first bone adjacent to a joint and a second can be coupled with a second bone adjacent to a joint. With two satellite sensors, the position, orientation, or movement of these bones and the joint to which they are adjacent can be monitored. 
     With the reference post  14  thus positioned, the impactor  16 , angle assessment guide  18 , and surgical orientation device  12  can be removed, leaving only the reference post  14  behind. The reference post  14  can then serve as a reference as described above, and can be used as an anchoring point for attachment of the orthopedic system  110 . 
       FIGS.  13 A and  13 B  show a technique in which the reference post  14  can be coupled with the patient’s anatomy without being attached to any bony structure. Rather, as shown in these figures, a fixture  510  is provided for indirectly coupling the reference post  14  to the patient’s anatomy. Although shown as providing for indirect coupling with a femur, the fixture  510  can be configured for attachment to other anatomy such that the reference post  14  does not need to be directly connected to bony structure. This arrangement is useful where the clinician prefers not to disrupt the bony structure, such as where the bony structure is delicate or would be unduly weakened by such interaction. 
     In one embodiment, the fixture  510  includes a bone engagement portion  514  that is configured to engage the bone in a static manner. For example, the bone engagement portion  514  can comprise a clamping structure that generates sufficient normal force to provide secure frictional engagement with the femur or other anatomy. In some embodiments, the clamping structure is spring loaded or includes a ratchet design to allow for quick attachment with sufficient force for immobilizing the fixture  510 . 
     The fixture  510  preferably also is configured to securely receive the reference post  14 . For example, a mounting structure  518  can be coupled with the bone engagement portion  514  and disposed laterally. The bone engagement portion  514  provides a surface area into which the reference post  14  can be driven using a slap hammer or other device for transmitting a force to the distal end of the reference post  14 . For example, the impactor  16  can be coupled with the reference post  14 , as described herein, prior to driving the distal end of the reference post  14  into the mounting structure  518 . In other techniques, the distal end of the reference post  14  can be coupled with the mounting structure  518  by clamping or other techniques that do not require applying a driving force, as with a slap hammer. 
     In the technique of  FIGS.  13 A,  13 B, and  14 A , the other orthopedic systems described herein can be used during further aspects of procedures. For example, the angle assessment guide  18  can be used with the surgical orientation device  12  in applying the reference post  14 . This technique can be used in placing the reference post  14  when the femur is positioned parallel to a surgical table. In some techniques, the femur is placed such that it is disposed generally perpendicular to the direction of gravity prior to placement of the reference post  14 , as shown in  FIG.  13 B . 
       FIG.  14 A  illustrates that after the reference post  14  has been placed, the measuring device  112  can be used to acquire information about the location of one or more anatomical landmarks. For example, the measuring device  112  can be used to locate a probe (e.g., a laser or mechanical probe or rod) above a landmark on the hip while the reference post  14  is coupled with the femur. In particular, the measuring device  112  can be coupled with the reference post to provide for multiple degrees of freedom. For example, the measuring device  112  can be pivoted about a longitudinal axis of the reference post  14 . In some embodiments, the measuring device  112  is also tiltable about a second axis that is disposed generally perpendicular to the longitudinal axis of the reference post  14 , as described in connection with  FIGS.  3 A and  3 B . Such tilting may facilitate engagement with a wide variety of anatomical landmarks on the hip by the marking device  118 . 
     C. Measuring Joint Distances Using an Orthopedic System 
     With reference to  FIGS.  3 A-B and  14   , prior to incising the joint capsule, the orthopedic system  110  can be used to measure at least one distance in the hip joint area . For example, the attachment structure  116  of the measuring device  112  can be releasably coupled to the surgical orientation device  12 , and the measuring device  112  can be coupled to the fixed reference post  14 . The measuring device  112  can be aligned with the axis of the leg so that measuring device  112  measures the leg-length component. The user can slide surgical orientation device  12  and/or marking device  118  along the measuring device  112  until the end  120  of the marking device  118  is contacting a selected location or locations on the femur (e.g., the superior aspect of the lesser trochanter), which location can then be marked with a suitable biocompatible marker or other marking agent. The surgical orientation device  12 , in a linear measurement mode, can then be zeroed, and can record a distance between the fixed reference post  14  and the anatomical landmark or landmarks. In a preferred arrangement, the measurement of distance between the reference post  14  and marked location on the anatomical landmark can be obtained via communication between the surgical orientation device  12  and the sensor  15  in reference post  14 . The marking or markings  114  can provide an additional indication, of the measured distance. 
     The surgical orientation device  12  can have two linear measurement components, one which responds to leg length and one which responds to offset. While the lesser trochanter is described in terms of an anatomical landmark, a different anatomical landmark or landmarks can be used instead, including but not limited to the greater trochanter. In another embodiment, a satellite tiltmeter can be attached to the femur on a location such as the greater trochanter which allows the angle of the femur to be zeroed and later reproduced when these measurements are repeated at the trial reduction phase. This can eliminate small errors in leg-length and offset which can be caused movement of the femur. If attached to the greater trochanter, this could be designed so that it is not in the way during the procedure. 
     The distance between the reference post  14  and the superior aspect of the lesser trochanter can be correlated, or related to, anatomical distances such as leg length and joint offset as described above. For example, and as described above, such distance can be assessed by the medical provider in a pre-operative x-ray assessment. With reference to again to  FIG.  29 A , end points of lines connecting the references points described above can roughly correspond to a hypotenuse indicative of an anatomical distance, such that zeroing the surgical orientation device  12  can result in the surgical orientation device registering this first anatomical distance or distances as a reference distance(s). As used herein “zeroing” is not limited by setting the SOD display to read “0”, but also includes, for example, recording a position in three dimensional space relative to a selected reference frame. 
     D. Determining the Orientation of an Anatomical Plane Using an Orthopedic System 
     With reference to  FIGS.  15 - 18   , once the orthopedic system  110  has been used to measure a first reference distance or distances, the components of the system  110  other than the reference post  14  can be removed. The joint capsule can then be incised, and the proximal femur can be removed. Once the proximal femur is removed, osteophytes surrounding the acetabular rim of the patient can also be removed according to known procedures. 
     With reference to  FIGS.  4  and  19   , the orthopedic system  210  can be used to determine the orientation of an anatomical plane in the patient. For example, once the joint capsule has been incised and osteophytes have been removed, the alignment handle  216  can be releasably coupled to the surgical orientation device  12 . The alignment handle  216  can then be gripped by the surgeon, and the anatomical contact component  218  can be moved into contact with the acetabular rim. For example, the tripod-like structure with arms  220 , as shown in  FIGS.  4  and  19   , can be placed against the acetabular rim, and the tips  224  of the contact component  218  can contact three landmarks on the acetabular rim. These three landmarks can be determined by the surgeon or other user. Once three landmarks have been contacted, the contact component  218  can be referencing a plane extending across the acetabular rim. At this point, the surgeon can register the orientation of this plane with the surgical orientation device  12 . In some embodiments, a planar laser can project a line onto the pelvis of the patient. The surgeon can make a mark somewhere on this line which can be referenced in later steps. This can serve the purpose of establishing a reference rotational position of the orthopedic system about a vertical line. If rotation about a vertical axis is not constrained in some form, then there can be an infinite number of orientations that satisfy a tiltmeter reading, since their locus can form a cone. Also, the surgical orientation device  12  can incorporate the orientation of the reference pin  14  in its calculations so that the surgical orientation device  12  can compensate for any subsequent movement of the pelvis. 
     In some embodiments, and as described herein, the surgical orientation device  12  can include a light indicator, such as a laser or lasers. The lasers can be emitted from optical components  42  of the surgical orientation device. Thus, in some embodiments of the orthopedic system  110 , the surgical orientation device, or other component, can emit a laser or lasers towards a landmark or landmarks in order to obtain an orientation of the acetabular rim. For example, the lasers can be emitted from the surgical orientation device such that they pinpoint an area or areas along the acetabular rim, and provide an indication to the surgical orientation device  12  of the orientation of a plane extending across the rim. In other embodiments, different landmarks can be used. 
     E. Preparing a Portion of the Patient’s Anatomy Using an Orthopedic System 
     With reference to  FIGS.  5  and  20   , the orthopedic system  310  can be used to prepare a portion of the patient’s anatomy. For example, the orthopedic system  310  can be used to ream out an acetabular socket at a defined angle and/or orientation. 
     Once the orthopedic system  210  has established a reference plane, such as for example the plane defined by the three reference landmarks on the acetabular rim, the reamer  318  can be moved into the area bounded by the acetabular rim. The surgeon can hold the reamer handle  316 , and the reamer  318  and/or a portion or portions of the reamer handle  316  can spin and rotate. As the reamer  318  spins and digs into the bony area in the acetabulum, the surgical orientation device  12  can remain generally still while coupled to the mounting device  312 . The surgeon can use the surgical orientation device  12  to monitor the orientation of the reamer  318 . Thus, the surgeon can ream at a defined angle relative to the aforementioned reference plane, with the surgical orientation device  12  providing an indication or indications on its display as to whether the reamer  318  is reaming perpendicular to such plane, or at an some angle relative to the plane. In some embodiments, the surgeon can choose an appropriate angle based on pre-operative templates and/or a desired range of angles and movement for the implant  414 . 
     F. Orienting a Prosthetic Component Using an Orthopedic System 
     With reference to  FIGS.  6  and  21   , the orthopedic system  410  can be used to orient a prosthetic component, such as for example a prosthetic acetabular cup. For example, the orthopedic system  410  can be used to orient a prosthetic component  414 . 
     Once the orthopedic system  310  has been used to ream out an acetabular socket, the orthopedic system  410  can be assembled. For example, the surgical orientation device  12  can be releasably coupled to the handle  416 , and a prosthetic component  414  can be releasably coupled to the handle  416 . The surgeon can then hold onto the handle  416  and move the prosthetic component  414  (e.g. prosthetic acetabular cup) towards the reamed out acetabular socket. The surgical orientation device  12  can be used to monitor the orientation of the prosthetic component  414  as it is moved and adjusted within the acetabulum. One can use a laser line (or other probe, such as for example a mechanical probe) to illuminate or otherwise reference a mark made earlier to control the rotation of the surgical orientation device  12  about a vertical axis. One can also use the orientation of the reference post  14  to compensate for movement of the pelvis. Once the prosthetic component  414  is positioned as desired (e.g. based on a pre-operative determination), the handle  416  and surgical orientation device  12  can be removed. 
     In some embodiments, the orthopedic system  210  can then be used again to assess the orientation of the prosthetic component, as illustrated in  FIG.  22   . The anatomical contact component  218  can be placed against the prosthetic component  414 , and the surgical orientation device  12  can indicate whether the prosthetic component  414  is oriented in the same plane as that previously registered by the surgical orientation device, or whether there is some angular offset or offsets. For example, the surgical orientation device  12  can indicate the prosthetic component  414  is tilted at a five degree angle in one frame of reference relative to the orientation of the reference plane previously registered by the surgical orientation device and orthopedic system  210 . As described above, such an offset may be advantageous or desired, depending on how the surgeon wishes to orient the prosthetic. The system  210  can allow the prosthetic component  414  to be aligned with the rim of the acetabulum as described above, or relative to the plane of the pelvis, whichever is preferred. In the latter case it can be unnecessary to register the rim of the acetabulum. 
     G. Measuring Joint Distances Again Using an Orthopedic System 
     With reference to  FIGS.  24 - 27   , once a prosthetic component  414  has been positioned, joint distance(s) can be measured again. For example, once the prosthetic acetabular cup has been positioned, a femoral canal can be formed, and a prosthetic femoral broach and head can be coupled to the femur. Once the broach and head are coupled, the hip joint can be reduced and put back in place, with the prosthetic femoral head resting inside the prosthetic cup (e.g. prosthetic component  414 ). 
     With reference to  FIG.  28   , once the hip joint is reduced, the orthopedic system  110  can again be used to measure a distance from the fixed reference post  14  to an anatomical landmark (e.g. the same marked location on the superior aspect of the lesser trochanter). 
     With reference to  FIG.  29 B , this second reading can be compared with the first reading (e.g. the reading shown in  FIG.  29 A ). Thus, a measurement or measurements can be taken both prior to joint capsule incision and after joint reduction to determine whether there has been any change in joint offset “OS” and leg length “LL” in the patient’s anatomy. If the measurements are satisfactory for the surgeon, the prosthetic implant can be left in. If not, the surgeon can remove the implant  414  and/or adjust the implant  414  using one or more of the systems described above, until desired measurements are obtained. In some embodiments the surgical orientation device  12  can be programmed with a database of geometries of prosthetic components. The surgeon can input the configuration of components used in trial reduction plus his goals for adjusting offset and leg-length. The surgical orientation device  12  can then perform calculations based on three-dimensional geometry to determine a combination of components which should achieve his goals and recommend them to the surgeon. This can take much of the trial and error out of the process. 
     IV. Additional Sensors for Relative Movement 
     While the embodiments of the orthopedic systems and methods described above are described as having and using a sensor or sensors  50  located within the surgical orientation device  12 , in some embodiments the orthopedic systems or other systems used for joint replacement can include an additional sensor or sensors  50  or  15 . For example, and as described above, the reference post  14  can include a sensor  15 . These additional sensors can be located on other surgical components and/or anatomical landmarks. U.S. Pat. No. 7,559,931 discloses examples of sensors on multiple surgical components and/or anatomical landmarks, and is herein expressly incorporated by reference in its entirety. In some embodiments, the orthopedic systems can include an additional sensor or sensors on the femur, hip, or other anatomical locations. The additional sensor can include a microcontroller and/or communication device (e.g. infrared or other wireless technology (e.g. Bluetooth™)) which can relay information from the additional sensor to the electronic control unit  1102  of the surgical orientation device  12 . This additional sensor or sensors can detect changes in movement of the patient’s anatomy during an orthopedic procedure, so as to verify whether the patient’s anatomy has moved or changed position during the procedure. In some embodiments, the sensor or sensors described herein (e.g. sensor  15 ) can be part of a variable capacitance system similar to that used in digital calipers. 
     The electronic control unit  1102  can be configured to receive the information from this additional sensor or sensors, and/or the sensor’s communications device, and combine that information with information from the sensor or sensors  50  located within the surgical orientation device  12  to calculate an overall, or aggregate, movement and orientation of the surgical orientation device  12  relative to, for example, an axial line or plane. The electronic control unit  1102  can correct for changes in position of the surgical orientation device  12 . 
     Additionally, the additional sensor or sensors can be located in a device. The device can be constructed such that the device is autoclavable and reusable, and can allow insertion and removal of a disposable battery. The additional sensor or sensors can be incorporated with any of the systems and/or methods described herein, and can be placed on any of the components of the systems described herein. 
     V. User Interfaces 
     The systems and methods described above can each incorporate the use of a measuring device, such as for example the surgical orientation device  12 . As described above, the surgical orientation device  12  can comprise at least one user input, a display and an electronic control unit. The user inputs and display, and/or the combination of the inputs, display, and electronic control unit can together form part of an interactive user interface. For example, the interactive user interface can comprise a housing (e.g., housing  30  described above), a coupling member formed on or within the housing configured to removably couple the user interface to an orthopedic device (e.g., handle  416 ), a sensor (e.g., sensor  50  described above), an electronic control unit (e.g., electronic control unit  1102  described above), a user input (e.g., user input  36  described above, which can transmit input commands to the electronic control unit), and a display (e.g., display  34  described above). 
     The interactive user interface can comprise a graphical user interface having an interactive window displaying on-screen graphics. For example, the interactive user interface can provide the user with a plurality of screen displays. The screen displays can illustrate the steps to be performed in a surgical procedure and can guide the user through the performance of the steps. Each screen display can comprise one or more on-screen graphics. The on-screen graphics can comprise one or more visual cues or indicators to prompt the user as to what step or steps to take next during one of the procedural methods described above. The visual cues referenced herein can comprise instructive images, diagrams, pictoral representations, icons, animations, visual cues, charts, numerical readings, measurements, textual instructions, warnings (visual and/or audible), or other data. The interactive user interface can be configured to alter attributes (e.g., color) of the on-screen graphics according to one or more data protocols. The interactive user interface can provide visual feedback to the user during performance of one or more surgical procedures. In certain embodiments, the interactive user interface can be configured to generate graphical user interface (“GUI”) images to be displayed to the user. As described above, the user can interact with the surgical orientation device  12  via one or more user input devices  1114  (e.g., buttons, switches, touchscreen displays, scroll wheel, track ball, keyboard, remote controls, a microphone in conjunction with speech recognition software). The interactive user interface further can allow the user to confirm that a step has been completed (for example, by pressing a user input button). The interactive user interface can allow the user to enter data (e.g., a numerical value, such as a distance, an angle, and/or the like), verify a position of the surgical orientation device  12 , turn a visible alignment indication system on and off, and/or turn the entire surgical orientation device on and off. In certain embodiments, the interactive user interface provides one or more drop-down lists or menus from which a user can make selections. For example, the user can make selections from a drop-down list using a scroll wheel, trackball, and/or a series of button presses. In some embodiments, the user interface provides a drop-down list of predicates that dynamically updates based on user input. 
     In at least one embodiment, a module for creating an interactive user interface can comprise a computer readable medium having computer readable program code embodied therein. The computer readable program code can comprise a computer readable program code configured to display one or more of a plurality of GUI images on a user interface of a surgical orientation device, the GUI images comprising instructive images related to the performance of a surgical procedure. The computer readable program code can be configured to receive instructions from a user identifying the surgical procedure to be performed (e.g., which joint and/or right or left). The computer readable program code can be configured to show the user steps to be performed in the identified process for the identified surgical procedure. The computer readable program code can be configured to guide the user in performance of the steps. For example, the computer readable program code can be configured to receive from the user an instruction to continue to the next step in the procedure, to receive orientation data from a sensor mounted within the surgical orientation device, and to display the orientation data on the user interface of the surgical orientation device. 
     In at least one embodiment, the surgical orientation device  12  described above can comprise a display module configured to display information and a sensor module configured to monitor the orientation of the surgical orientation device  12  in a three-dimensional coordinate reference system, and to generate orientation data corresponding to the monitored orientation of the surgical orientation device. The surgical orientation device  12  can further comprise a control module configured to receive the orientation data from the sensor module and convert it to objective signals for presentation on the display module, the control module also configured to display a set of GUI images or other on-screen graphics on the display module, the GUI images or on-screen graphics representing the orientation data received from the sensor module and also representing instructive images related to the performance of the joint replacement surgery. 
     In at least one embodiment, the surgical orientation device  12  can receive orientation data from a sensor module, receive input commands from a user input module to store orientation data from a user input module, convert the orientation data to a human readable format for presentation on a display device, and display on the display device on-screen graphics or GUI images for communicating information to a user based on the input commands and the orientation data, the information comprising instructive images for performing a joint replacement surgery and one or more visual indicators of a current orientation of the display device with respect to a fiducial, or reference, orientation. 
     In at least one embodiment, the surgical orientation device  12  described herein can comprise a sensor module coupled to an alignment jig and configured to measure and record a fiducial orientation and to continuously collect orientation data of the surgical orientation device, a display module configured to display at least one visual indicator of the orientation of the surgical orientation device with respect to the fiducial, or reference, orientation, the display module further configured to display instructive images of one or more steps to be performed by the surgeon during the joint replacement surgery, and a control module configured to receive the orientation data and to convert the orientation data to objective signals for presentation on the display module. 
       FIGS.  30 A-W  show various screen shots which can form part of the interactive user interface or interfaces described above. The screen shots can be seen, for example, on a display of the surgical orientation device  12 . 
     As shown in  FIG.  30 A , an interface screen can illuminate requesting the user to press a user input, e.g., a center button on the surgical orientation device  12 . Thereafter, a message can be displayed indicating to the user that the surgical orientation device  12  is preparing for operation. The message can be a display of text on a screen, as illustrated in  FIG.  30 A , an audible sound, or other signal to the user to wait for the device to confirm a proper operational state. For example, a variety of self-tests can be performed. In one embodiment, information about the operating system, such as its version, can be displayed for review. 
       FIG.  30 B  shows a user interface screen which indicates that a range of potential cup size templates are available. For example, the user interface screen can indicate a “52” size. 
       FIG.  30 C  shows a user interface screen requesting the user to scroll through template options. For example, the user can press a side toggle button to scroll through cup size template options. 
       FIG.  30 D  shows a user interface screen in which a user has selected a “48” size cup implant. The selection can be made by pressing a middle button below the display screen on the surgical orientation device  12 . This selection of cup size can be based on a user’s pre-operative assessment of a patient. 
       FIGS.  30 E-G  show user interface screens similar to those of  FIGS.  30 B-D , in which a user can scroll through and select an appropriate stem size template. 
       FIG.  30 H  shows a user interface screen providing input to a user to attach the surgical orientation device  12  to the angle assessment guide  18 . The user can press a user input (e.g. an enter button) on the surgical orientation device  12  to indicate completion of this step. 
       FIG.  30 I  shows a user interface screen providing input to a user to attach the reference post  14  to the impactor  16 . The user can press a user input (e.g. an enter button) on the surgical orientation device  12  to indicate completion of this step. 
       FIG.  30 J  shows a user interface screen providing information on the orientation of the system  10  to guide the user in proper orientation while the reference post  14  is impacted into patient. 
       FIG.  30 K  shows a user interface screen providing instructions to a user to attach the surgical orientation device  12  to the system  110 . The user can press a user input (e.g. an enter button) to indicate completion of this step. 
       FIG.  30 L  shows a user interface screen providing instructions to a user to attach the marking device  118  to the system  110 . The user can press a user input (e.g. an enter button) to indicate completion of this step. 
       FIG.  30 M  shows a user interface screen providing instructions to establish the position of the marking device  118  in system  110 , with the marking device  118  referencing an anatomical landmark determined by the user. Once the user has contacted the anatomical landmark, the user can press a button (e.g. an enter button) to record an orientation of the system  110  with respect to that landmark. 
       FIG.  30 N  shows a user interface screen providing instructions to a user to prepare the acetabulum for cup implantation. The user can press a user input (e.g. an enter button) to indicate completion of this step. 
       FIG.  30 O  shows a user interface screen providing instructions to a user to attach the surgical orientation device  12  to the system  210 . The user can press a user input (e.g. an enter button) to indicate completion of this step. 
       FIG.  30 P  shows a user interface screen providing instructions to a user to assess a plane of the acetabulum. The user can press a user input (e.g. an enter button) to indicate completion of this step. 
       FIG.  30 Q  shows a user interface screen providing instructions to a user to ream the acetabulum using system  310 , as well as providing feedback to the user on the orientation of the reamer (with the surgical orientation device  12  attached) so that user can use the reamer in accordance with the plane established by acetabular lip assessment guide. The user can press a user input (e.g. an enter button) to indicate completion of this step. 
       FIG.  30 R  shows a user interface screen providing instructions to a user to position a prosthetic cup  414  in the acetabulum. The user can press a user input (e.g. an enter button) to indicate completion of this step. 
       FIG.  30 S  shows a user interface screen providing instructions to a user to impact the prosthetic cup into the acetabulum using the system  410 , as well as providing feedback to the user on the orientation of the prosthetic cup (with the surgical orientation device  12  attached) so that the user can impact the cup in accordance with the plane established by the system  210 . The user can press a user input (e.g. an enter button) to indicate completion of this step. 
       FIG.  30 T  shows a user interface screen providing instructions to the user to fit a trial hip implant. The user can press a user input (e.g. an enter button) to indicate completion of this step. 
       FIGS.  30 U,  30 V  show a user interface screen providing instructions to the user to assess the orientation of the system  110  with respect to the anatomical landmark that was previously assessed by the marking device  118  on the system  110 . The user can measure the distance again from the reference post  14  to the landmark measure previously. 
       FIG.  30 W  shows a user interface screen displaying leg length and joint off-set changes based on orientation changes of jigging system from initial assessment of anatomical landmark in  FIG.  13    and final assessment in  FIG.  22   . 
     Although these inventions have been disclosed in the context of certain preferred embodiments and examples, it will be understood by those skilled in the art that the present inventions extend beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the inventions and obvious modifications and equivalents thereof. In addition, while several variations of the inventions have been shown and described in detail, other modifications, which are within the scope of these inventions, will be readily apparent to those of skill in the art based upon this disclosure. It is also contemplated that various combinations or sub-combinations of the specific features and aspects of the embodiments can be made and still fall within the scope of the inventions. It should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the disclosed inventions. Thus, it is intended that the scope of at least some of the present inventions herein disclosed should not be limited by the particular disclosed embodiments described above.