Patent Publication Number: US-9414940-B2

Title: Sensored head for a measurement tool for the muscular-skeletal system

Description:
FIELD 
     The present invention pertains generally to surgical electronics, and particularly to methods and devices for assessing alignment and surgical implant parameters during spine surgery and long-term implantation. 
     BACKGROUND 
     The spine is made up of many individual bones called vertebrae, joined together by muscles and ligaments. Soft intervertebral discs separate and cushion each vertebra from the next. Because the vertebrae are separate, the spine is flexible and able to bend. The vertebrae provide a conduit for the spinal cord neural bundle. Together the vertebrae, discs, nerves, muscles, and ligaments make up the vertebral column or spine. The spine varies in size and shape, with changes that can occur due to environmental factors, health, and aging. The healthy spine has front-to-back curves, but deformities from normal cervical lordosis, thoracic kyphosis, and lumbar lordosis conditions can cause pain, discomfort, and difficulty with movement. These conditions can be exacerbated by herniated discs, which can pinch nerves. 
     There are many different causes of abnormal spinal curves and various treatment options from therapy to surgery. The goal of the surgery is a usually a solid fusion of two or more vertebrae in the curved part of the spine. A fusion is achieved by operating on the spine and adding bone graft. The vertebral bones and bone graft heal together to form a solid mass of bone called a fusion. Alternatively, a spinal cage is commonly used that includes bone graft for spacing and fusing vertebrae together. The bone graft may come from a bone bank or the patient&#39;s own hipbone or other autologous site. The spine can be substantially straightened with metal rods and hooks, wires or screws via instrumented tools and techniques. The rods or sometimes a brace or cast hold the spine in place until the fusion has a chance to heal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various features of the system are set forth with particularity in the appended claims. The embodiments herein, can be understood by reference to the following description, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates a spine measurement system in accordance with an example embodiment; 
         FIG. 2  illustrates a spinal instrument in a non-limiting example; 
         FIG. 3  illustrates a spinal instrument having integrated electronics in a non-limiting example; 
         FIG. 4  illustrates an insert instrument with vertebral components in a non-limiting example; 
         FIG. 5  illustrates a lateral view of the spinal instrument positioned between vertebrae of the spine for sensing vertebral parameters in a non-limiting example; 
         FIG. 6  illustrates a graphical user interface (GUI) showing an axial view of the spinal instrument of  FIG. 5  in accordance with an example embodiment; 
         FIG. 7  illustrates the spinal instrument positioned between vertebra of the spine for intervertebral position and force sensing in accordance with an example embodiment; 
         FIG. 8  illustrates a user interface showing the spinal instrument of  FIG. 7  in accordance with an example embodiment; 
         FIG. 9  illustrates a lateral view of the spinal insert instrument for placement of the spine cage in accordance with an example embodiment; 
         FIG. 10  illustrates the graphical user interface showing the insert instrument of  FIG. 9  in a non-limiting example; 
         FIG. 11  is a block diagram of the components of the spinal instrument in accordance with an example embodiment; 
         FIG. 12  is a diagram of an exemplary communications system for short-range telemetry in accordance with an example embodiment; 
         FIG. 13  illustrates a communication network for measurement and reporting in accordance with an example embodiment; 
         FIG. 14  illustrates an exemplary diagrammatic representation of a machine in the form of a computer system within which a set of instructions, when executed, may cause the machine to perform any one or more of the methodologies disclosed herein; 
         FIG. 15  illustrates components of a spinal instrument in accordance with an example embodiment; 
         FIG. 16  illustrates a spine measurement system for providing intervertebral load and position of load data in accordance with an example embodiment; 
         FIG. 17  illustrates a spine measurement system for providing intervertebral load and position of load data in accordance with an example embodiment; 
         FIG. 18  illustrates an exploded view of the module and the handle in accordance with an example embodiment; 
         FIG. 19  illustrates a shaft for receiving a removable sensored head in accordance with an example embodiment; 
         FIG. 20  illustrates a cross-sectional view of a female coupling of the sensored head in accordance with an example embodiment; 
         FIG. 21  illustrates an exploded view of a spinal instrument in accordance with an example embodiment; 
         FIG. 22  illustrates a cross-sectional view a shaft region of the spinal instrument of  FIG. 21  in accordance with an example embodiment; 
         FIG. 23  illustrates a cross-sectional view of a sensored head region of the spinal instrument of  FIG. 21  in accordance with an example embodiment; 
         FIG. 24  illustrates an exploded view of the sensored head region of the spinal instrument of  FIG. 21 ; and 
         FIG. 25  illustrates a cross-sectional view of the sensored head region of the spinal instrument of  FIG. 21  in accordance with an example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     While the specification concludes with claims defining the features of the embodiments of the invention that are regarded as novel, it is believed that the method, system, and other embodiments will be better understood from a consideration of the following description in conjunction with the drawing figures, in which like reference numerals are carried forward. 
     As required, detailed embodiments of the present method and system are disclosed herein. However, it is to be understood that the disclosed embodiments are merely exemplary, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the embodiments of the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting but rather to provide an understandable description of the embodiment herein. 
     Broadly stated, embodiments of the invention are directed to a system and method for vertebral load and location sensing. A spine measurement system comprises a spinal instrument coupled to a remote display. The spine measurement system can measure load, balance, and alignment to assess load forces on the vertebra. The spinal instrument can be an active device having an electronic assembly and a sensorized head assembly that can articulate within a vertebral space. The sensorized head can be inserted between vertebra and report vertebral conditions such as force, pressure, orientation and edge loading. The spine measurement system further includes alignment circuitry. The alignment circuitry provides positional information for identifying an orientation and location of the spinal instrument. A GUI of the remote system can be used to show where the spine instrument is positioned relative to vertebral bodies as the instrument is placed in the inter-vertebral space during the surgical procedure. The system can report optimal prosthetic size and placement in view of the sensed load and location parameters including optional orientation, rotation and insertion angle along a determined insert trajectory. 
     An insert instrument is also provided herein with the load balance and alignment system for inserting a vertebral component such as a spine cage or pedicle screw. The system in view of previously captured parameter measurements can check and report if the instrument is edge loading during an insertion. It shows tracking of the insert instrument with the vertebral component and provides visual guidance and feedback based on positional and load sensing parameters. The system shows three-dimensional (3D) tracking of the insert instrument in relation to one or more vertebral bodies whose orientation and position are also modeled in 3D. 
       FIG. 1  illustrates a spine measurement system  100  in a non-limiting example. The system  100  comprises a spinal instrument  102  that can be communicatively coupled to a remote system  105 . The spine measurement system  100  can further include alignment circuitry  103  to determine positional information of at least one of an orientation, rotation, angle, and location. The positional information can relate to a tool, device, equipment, patient, or region of the muscular-skeletal system. In the example, alignment circuitry  103  can be part of spinal instrument  102  or comprise external components. In one embodiment, external components comprising alignment circuitry  103  can couple to spinal instrument  102  or to regions of the spine for determining positional information. In one embodiment, location and position can be determined via one or more accelerometers. Alternatively, location and position can be determined via a time of flight or differential time of flight of a signal. The positional information can include orientation and translation data used to assess an alignment of the spine  112 . The positional information can be measured in real-time during the procedure or provided to remote system  105 . 
     In the example, spinal instrument  102  can be used intra-operatively to measure a parameter of the spinal region. Spinal instrument  102  includes at least one sensor for measuring the parameter. Spinal instrument  102  can have more than one sensor for measuring different parameters and providing quantitative data to the surgeon in real-time. In one embodiment, spinal instrument  102  measures load, position of load, and alignment. Spinal instrument  102  is not limited to load and alignment measurement example. Other sensor types for measuring different parameters can be integrated into the device. The quantitative data generated by spinal instrument  102  can be used to determine a location for placing a prosthetic component such as a pedicle screw or a spine cage in the spine. Spinal instrument  102  can be used to distract the spinal region being measured. In general, spinal instrument  102  and alignment circuitry  103  may be used within a sterile field  109  of an operating room. The sterile field  109  can also be called a surgical field where a patient operation is performed. Typically, remote system  105  is outside the sterile field  109  of the operating room. The remote system  105  can be a laptop, mobile workstation, display or other device that presents a Graphical User Interface (GUI)  107 . In one embodiment, GUI  107  contains a workflow that shows the spine  112  and reports spinal instrument quantitative measurement data. For example, remote system can receive and display load, load position, and alignment data from spinal instrument  102  and alignment circuitry  103 . Alternatively, spinal instrument  102  can have an interface for displaying or indicating the quantitative measurement data. In the example, the spinal instrument  102  is a self-contained device for generating measurement data. 
     The GUI  107  is presented by way of the remote system  105  and spine measurement system  100 . In the example, the GUI  107  may have more than one window to show the quantitative measurement data provided by spinal instrument  102  and alignment circuitry  103 . GUI  107  is shown on the display of remote system  105  for providing real-time quantitative data from spinal instrument  107  and alignment circuitry  103 . In the example, spinal instrument  102  is being directed to a spinal region. More specifically, spinal instrument  102  is being directed between vertebrae of the spine. Sensors can be placed within a sensored head of spinal instrument  102 . The sensored head can be used to distract the vertebrae thereby generating a gap between vertebrae that is the height of the sensored head. Spinal instrument  102  can be wired or wirelessly coupled to remote system  105 . In the example, spinal instrument  102  is wirelessly coupled to remote system  105  for transmitting data. That transmitted data can include load, location, and position data. GUI  107  can display alignment data in real-time such as shaft angle and a rotation component corresponding to the direction of spinal instrument  102  in relation to the vertebrae of interest. Furthermore, GUI  107  can provide quantitative measurement data on the load and position of load applied by the vertebrae to the sensored head of spinal instrument  102  after insertion. Thus, measurement system  100  allows the surgeon and medical staff to visualize use of the spinal instrument  102  and the sensed parameters. 
     The spine measurement system  100  can be communicatively coupled to a database  123  system such as a server  125  to provide three-dimensional (3D) imaging (e.g., soft tissue) and 3D models (e.g., bone) captured prior to, or during, surgery. The 3D imaging and models can be used in conjunction with positional information measured during the procedure to establish relative location and orientation. The server  125  may be local in near vicinity or remotely accessed over the Internet  121 . As one example, the server  125  provides 3D spine and vertebra models. A CAT scanner (not shown) can be employed to produce a series of cross-sectional x-ray images of a selected part of the body. A computer operates the scanner, and the resulting picture represents a slice of the body. The server  125  produces a three-dimensional (3D) model from the slices. The server  125  can also provide 3D models generated from Magnetic Resonance Imaging (MRI) scanners (not shown). The server  125  may also support fluoroscopic imaging to provide real-time moving images of the internal structures of a patient with respect to the spine measurement system  100  devices through the use of X-ray source (not shown) and fluorescent screen. 
     In the example, the sensored head of spinal instrument  102  includes a sensor for measuring load. In one embodiment, the sensored head includes more than one sensor for measuring a location of an applied force, pressure, or load to the surfaces of the sensored head. Measuring the location of the applied force to surfaces of the sensored head of spinal instrument  102  provides information related to the spinal region and the distribution of the force. For example, an application may require an even distribution of force applied over a large area of the surfaces of the sensored head. Conversely, an application may require a peak force applied over a small area of the surface of the sensored head. In either example, spinal instrument  102  can provide measurement data related to force magnitude and location of the applied force whereby the surgeon uses the quantitative data in conjunction with subjective information for assessing the probed spinal region. 
     Many physical parameters of interest within physical systems or bodies can be measured by evaluating changes in the characteristics of energy waves or pulses. As one example, changes in the transit time or shape of an energy wave or pulse propagating through a changing medium can be measured to determine the forces acting on the medium and causing the changes. The propagation velocity of the energy waves or pulses in the medium can be affected by physical changes in of the medium. The physical parameter or parameters of interest can include, but are not limited to, measurement of load, force, pressure, displacement, density, viscosity, and localized temperature. These parameters can be evaluated by measuring changes in the propagation time of energy pulses or waves relative to orientation, alignment, direction, or position as well as movement, rotation, or acceleration along an axis or combination of axes by wireless sensing modules or devices positioned on or within a body, instrument, equipment, or other mechanical system. Alternatively, measurements of interest can be taken using film sensors, mechanical sensors, polymer sensors, mems devices, strain gauge, piezo-resistive structure, and capacitive structures to name but a few. 
       FIG. 2  illustrates a spinal instrument  400  in a non-limiting example. A side view and a top view are presented. Spinal instrument  400  is a more detailed illustration of a non-limiting example of spinal instrument  102  of  FIG. 1 . Spinal instrument  400  comprises a handle  409 , a shaft  430 , and a sensored head  407 . The handle  409  is coupled at a proximal end of the shaft  430 . Sensored head  407  is coupled to a distal end of the shaft  430 . A surgeon holds spinal instrument  400  by the handle  409  to direct shaft  430  and sensored head  407  to a spinal region. In one embodiment, handle  409 , shaft  430 , and sensored head  407  form a rigid structure that has little flex. Alternatively, one or more of handle  409 , shaft  430 , and sensored head  407  may have some flexibility. Spinal instrument  400  includes an electronic assembly  401  operatively coupled to one or more sensors. The sensors can be coupled to surfaces  403 / 406  on moving components  404 / 405  of sensored head  407 . Electronic assembly  401  can be located towards the proximal end of the shaft  407  or in handle  409 . As shown, the electronic assembly  401  is a module that is coupled to shaft  409 . Electronic assembly  401  comprises electronic circuitry that includes logic circuitry, an accelerometer, and communication circuitry. The electronic circuitry controls sensor measurement, receives measurement data, stores the data, and can send the data to an external device. 
     In one embodiment, surfaces  403  and  406  of sensored head  407  can have a convex shape. The convex shape of surfaces  403  and  406  support placement of sensored head  407  within the spinal region and more specifically between the contours of vertebrae. In one embodiment, sensored head  407  is height adjustable by way of the top component  404  and the bottom component  405  through a jack  402  that evenly distracts and closes according to handle  409  turning motion  411 . Jack  402  is coupled to interior surfaces of components  404  and  405  of sensored head  407 . Shaft  430  includes one or more lengthwise passages. For example, interconnect such as a flexible wire interconnect can couple through one lengthwise passage of shaft  430  such that electronic assembly  401  is operatively coupled to one or more sensors in sensored head  407 . Similarly, a threaded rod can couple through a second passage of shaft  430  for coupling handle  409  to jack  404  thereby allowing height adjustment of sensored head  407  via rotation of handle  409 . 
     Spine instrument  400  can also determine location and orientation by way of one or more embedded accelerometers. The sensored head  407  supports multiple functions that include the ability to determine a parameter of the procedure area (e.g., intervertebral space) including pressure, tension, shear, load, torque, bone density, and/or bearing weight. In one embodiment, more than one load sensor can be included within sensored head  407 . The more than one load sensors can be coupled to predetermined locations of surfaces  403  and  406 . Having more than one load sensor allows the sensored head  407  to measure load magnitude and the position of applied load to surfaces  403  and  406 . The sensored head  407  can be used to measure, adjust, and test a vertebral joint prior to installing a vertebral component. As will be seen ahead, measurement system  100  can evaluate the optimal insertion angle and position of spinal instrument  400  during intervertebral load sensing. The measurement system  100  can replicate insertion angle and position for instrument  400  or for another tool such as an insertion instrument. 
     In the present invention these parameters can be measured with an integrated wireless sensored head  407  or device comprising an i) encapsulating structure that supports sensors and contacting surfaces and ii) an electronic assemblage that integrates a power supply, sensing elements, ultrasound resonator or resonators or transducer or transducers and ultrasound waveguide or waveguides, biasing spring or springs or other form of elastic members, an accelerometer, antennas and electronic circuitry that processes measurement data as well as controls all operations of energy conversion, propagation, and detection and wireless communications. Sensored head  407  or instrument  400  can be positioned on or within, or engaged with, or attached or affixed to or within, a wide range of physical systems including, but not limited to instruments, appliances, vehicles, equipments, or other physical systems as well as animal and human bodies, for sensing and communicating parameters of interest in real time. 
     Spinal instrument  400  can be used in the installation of a spinal cage as a non-limiting example. The spinal cage is used to space vertebrae in replacement of a disc. The spinal cage is typically hollow and can be formed having external threads for fixation. Two or more cages are often installed between the vertebrae to provide sufficient support and distribution of loading over the range of motion. In one embodiment, the spinal cage may be made of titanium for supporting spinal load and spacing between vertebrae. A bone growth material can also be placed in the cage to initiate and promote bone growth thereby further strengthening the intervertebral area long-term. Spinal instrument  400  can be used to provide quantitative data such as load and position of load for a region between vertebrae that may be a candidate for a prosthetic component such as the spinal cage. Typically, spinal instrument  400  is inserted in a gap selected by the surgeon between vertebrae. Spinal instrument  400  measures load and position of load that can be viewed on an interface on the device or to a remote system such as that disclosed in  FIG. 1 . The position of load corresponds to the vertebral area surfaces applying the load on surfaces  403  or  406  of sensored head  407 . The angle and position of insertion of the sensored head  407  of spinal instrument  400  can also be measured. The load magnitude and position of load measurement are used by the surgeon to determine an implant location between the vertebrae and the size of the spinal cage for the implant location. Typically, the height and length of the selected spinal cage is approximately the height and length of sensored head  407 . Moreover, the area chosen for the spinal cage location may load the prosthetic component within a predetermined load range as measured by spinal instrument  400 . Conversely, quantitative measurements of vertebral loading outside the predetermined range may be found unsuitable for prosthetic component installation. The surgeon can modify the contact surfaces of the vertebrae to fall within the predetermined range as measured by spinal instrument  400 . The surgeon can also locate a different region between the vertebrae that is more suitable based on quantitative data provided by spinal instrument  400 . 
     In the example, a spinal cage is inserted in the measured region after removing the sensored head  407 . The spinal cage can be inserted in the same location measured by sensored head  407  using quantitative measurement data. The alignment data of spinal instrument  400  is generated and recorded during an insertion process and measurement of load and position of load. The loading on the implanted spinal cage when inserted in the same position and angle as sensored head  407  is approximately equal to the measurements made by spinal instrument  400 . The recorded angle and position measurements can be subsequently used to guide the spinal cage into the same location and more specifically by a similar insertion path as spinal instrument  400 . In one embodiment, spinal instrument  400  can be used to place the prosthetic component into the identified region. A separate instrument can also be used for insertion of the prosthetic component. 
       FIG. 3  illustrates a spinal instrument  410  having integrated electronics in a non-limiting example. Spinal instrument  410  is a more detailed illustration of a non-limiting example of spinal instrument  102  of  FIG. 1  and relates to spinal instrument  400 . Electronic assembly  401  is placed within handle  415  of spinal instrument  410 . Placing electronic assembly  401  in handle  415  provides the benefit of isolating the circuitry from the external environment. Handle  415  can further provide shock isolation for the electronic assembly  401  for reliability. In one embodiment, an external wireless energy source  414  can be placed in proximity to a charging unit within electronic assembly  401  to initiate a wireless power recharging operation. The wireless energy source  414  can include a power supply, a modulation circuit, and a data input. The power supply in energy source  414  can be a battery, a charging device, a capacitor, a power connection, or other energy source for generating wireless power signals that can transfer power to spinal instrument  410 . The external wireless energy source  414  can transmit energy in the form of, but not limited to, electromagnetic induction, or other electromagnetic or ultrasound emissions. In at least one exemplary embodiment, the wireless energy source includes a coil to electromagnetically couple and activate (e.g., power on) with an induction coil in sensing device when placed in close proximity. 
     Electronic assembly  401  operatively couples to sensors in sensored head  407  for measuring a parameter. Electronic assembly  401  includes communication circuitry for transmitting measured parameter data to a receiver via data communications circuitry. The received parameter data can be processed remotely to permit visualization of the level and distribution of the parameter at various points on the sensored head. Information can also be provided to electronic assembly  401  using external wireless energy source  414 . Data can be provided through an interface or port to external wireless energy source  414 . The information or data can be input from another data source, such as from a computer via a wired or wireless connection (e.g., USB, IEEE802.16, etc.). In one embodiment, external wireless energy source  414  includes a modulation circuitry that can modulate the input information onto the power signals for sourcing energy to electronic assembly  401 . In the example, electronic assembly  401  has demodulation circuitry coupled for removing and providing the information for use by spinal instrument  410  from the power signals. 
       FIG. 4  illustrates an insert instrument  420  with vertebral components in a non-limiting example. Electronic assembly  401  as described herein supports the generation of orientation and position data of insert instrument  420 . In one embodiment, electronic assembly  401  includes an accelerometer for providing orientation and position data. Referring to  FIG. 11  briefly, electronic assembly  401  of insert instrument  420  can have more or less circuitry than that disclosed for spinal instruments  400  and  410 . By way of measurement system  100 , the user can replicate the insertion angle, position and trajectory (path) to achieve proper or pre-planned placement of a vertebral component. Insert instrument  420  comprises a handle  432 , a shaft  434 , and a tip  451 . An attach/release mechanism  455  couples to the proximal end of shaft  434  for controlling tip  451 . Attach/release mechanism  455  allows a surgeon to retain or release vertebral components coupled to tip  451 . Attach/release mechanism  455  can mechanically couple through shaft  434  to control tip  451 . Alternatively, attach/release mechanism  455  can be an electronic control. In the example, handle  432  extends at an angle in proximity to a proximal end of shaft  434 . Positioning of handle  432  allows the surgeon to accurately direct tip  451  in a spinal region while allowing access to attach/release mechanism  455 . Electronic assembly can be housed in handle  432  or attached to insert instrument  420 . Referring to  FIG. 12  briefly, electronic assembly  401  includes communication circuitry to securely transmit and receive data from a remote system. Insert instrument  420  is a tool of spine measurement system  100 . Quantitative measurement data such as orientation and position data can be transmitted to remote system  105  of  FIG. 1  for real time and visualization of an insertion process. Electronic assembly  401  can also couple to one or more sensors of insert instrument  420 . In a first example, tip  451  can be coupled to a pressure sensor to determine a force, pressure, or load being applied by the spinal region to a prosthetic component coupled thereto. In a second example, tip  451  can be removable such that a sensored head can be coupled to insert instrument  420 . In a third example, the prosthetic component can include a sensor. The sensor of the prosthetic component includes an interface that couples to electronic assembly  401  for providing quantitative measurement data. 
     In the illustration, an example prosthetic component is a spine cage  475 . Spine cage  475  is a small hollow device, usually made of titanium, with perforated walls that can be inserted between the vertebrae of the spine during a surgery. In general, a distraction process spaces the vertebrae to a predetermined distance prior insertion of spine cage  475 . Spine cage  475  can increase stability, decrease vertebral compression, and reduce nerve impingement as a solution to improve patient comfort. Spine cage  475  can include surface threads that allow the cage to be self-tapping and provide further stability. Spine cage  475  can be porous to include bone graft material that supports bone growth between vertebral bodies through cage  475 . More than one spine cage can be placed between vertebrae to alleviate discomfort. Proper placement and positioning of spine cage  475  is important for successful long-term implantation and patient outcome. As mentioned above, the orientation and position of insert instrument  420  can be tracked in real-time in relation to the spinal region of interest. In one embodiment, the orientation and position being tracked is a prosthetic component retained by insert instrument  420 . In the example, the prosthetic component is spine cage  475 . Spine cage  475  can be tracked in 3D space because the location of the prosthetic component is known in relation to the spinal instrument  420  and the one or more measurement accelerometers therein. 
     In the illustration a second prosthetic component is a pedicle screw  478 . The pedicle screw  478  is a particular type of bone screw designed for implantation into a vertebral pedicle. There are two pedicles per vertebra that couple to other structures (e.g. lamina, vertebral arch). A polyaxial pedicle screw may be made of titanium to resist corrosion and increase component strength. The pedicle screw length ranges from 30 mm to 60 mm. The diameter ranges from 5.0 mm to 8.5 mm. It is not limited to these dimensions, which serve as dimensional examples. Pedicle screw  478  can be used in instrumentation procedures to affix rods and plates to the spine to correct deformity, and/or treat trauma. It can be used to immobilize part of the spine to assist fusion by holding bony structures together. By way of electronic assembly  401  (which may be internally or externally integrated), the insert instrument  420  can determine depth and angle for screw placement and guide the screw therein. In the example, one or more accelerometers are used to provide orientation, rotation, angle, or position information of tip  451  during an insertion process. 
     In one arrangement, the screw  478  is embedded with sensors. The sensors can transmit energy and obtain a density reading and monitor the change in density over time. As one example, the measurement system  100  can monitor and report healing of a fracture site. The sensors can detect the change in motion at the fracture site as well as the motion between the screw and bone. Such information aids in monitoring healing and gives the healthcare provider an ability to monitor vertebral weight bearing as indicated. The sensors can also be activated externally to send energy waves to the fracture itself to aid in healing. 
       FIG. 5  illustrates a lateral view of spinal instrument  400  positioned between vertebrae of the spine for sensing vertebral parameters in a non-limiting example. The illustration can also apply to spinal instrument  410  and insert instrument  420 . In general, a compressive force is applied to surfaces  403  and  406  when sensored head  407  is inserted into the spinal region. In one embodiment, sensored head  407  includes two or more load sensors that identify magnitude vectors of loading on surface  403 , surface  406 , or both associated with inter-vertebral force there between. In the example shown, the spinal instrument  400  is positioned between vertebra (L 5 ) and the Sacrum (S 1 ) such that a compressive force is applied to surfaces  403  and  406 . One approach for inserting the instrument  400  is from the posterior (back side) through a minilaparotomy as an endoscopic approach may be difficult to visualize or provide good exposure. Another approach is from the anterior (front side) which allows the surgeon to work through the abdomen to reach the spine. In this way spine muscles located in the back are not damaged or cut; avoiding muscle weakness and scarring. Spinal instrument  400  can be used with either the anterior or posterior spine approach. 
     Aspects of the sensorized components of the spine instrument  400  are disclosed in U.S. patent application Ser. No. 12/825,638 entitled “System and Method for Orthopedic Load Sensing Insert Device” filed Jun. 29, 2010, and U.S. patent application Ser. No. 12/825,724 entitled “Wireless Sensing Module for Sensing a Parameter of the Muscular-Skeletal System” filed Jun. 29, 2010 the entire contents of which are hereby incorporated by reference. Briefly, the sensored head  407  can measure forces (Fx, Fy, and Fz) with corresponding locations and torques (e.g. Tx, Ty, and Tz) and edge loading of vertebrae. The electronic circuitry  401  (not shown) controls operation and measurements of the sensors in sensored head  407 . The electronic circuitry  401  further includes communication circuitry for short-range data transmission. It can then transmit the measured data to the remote system to provide real-time visualization for assisting the surgeon in identifying any adjustments needed to achieve optimal joint balancing. 
     A method of installing a component in the muscular-skeletal system is disclosed below. The steps of the method can be performed in any order. An example of placing a cage between vertebrae is used to demonstrate the method but the method is applicable to other muscular-skeletal regions such as the knee, hip, ankle, spine, shoulder, hand, arm, and foot. In a first step, a sensored head of a predetermined width is placed in a region of the muscular-skeletal system. In the example, the insertion region is between vertebrae of the spine. A hammer can be used to tap an end of the handle to provide sufficient force to insert the sensored head between the vertebrae. The insertion process can also distract the vertebrae thereby increasing a separation distance. In a second step, the position of the load applied to the sensored head is measured. Thus, the load magnitude and the position of the loading on the surfaces of the sensored head are available. How the load applied by the muscular-skeletal system is positioned on the surfaces of the sensored head can aid in determining stability of the component once inserted. An irregular loading applied to sensored head can predict a scenario where the applied forces thrust the component away from the inserted position. In general, the sensored head is used to identify a suitable location for insertion of the component based on quantitative data. In a third step, the load and position of load data from the sensored head is displayed on a remote system in real-time. Similarly, in a fourth step, the at least one of orientation, rotation, angle, or position is displayed on the remote system in real-time. Changes made in positioning the sensored head are reflected in data on the remote system display. In a fifth step, a location between vertebrae having appropriate loading and position is identified and the corresponding quantitative measurement data is stored in memory. 
     In a sixth step, the sensored head is removed. In a seventh step, the component is inserted in the muscular-skeletal system. As an example, the stored quantitative measurement data is used to support the positioning of the component in the muscular-skeletal system. In the example, the insertion instrument can be used to direct the component into the muscular-skeletal system. The insertion instrument is an active device providing orientation, rotation, angle, or position of the component as it is being inserted. The previously measured direction and location of the insertion of the sensored head can be used to guide the insertion instrument. In one embodiment, the remote system display can aid in displaying relational alignment of the insertion instrument and component to the previously inserted sensored head. The insertion instrument in conjunction with the system can provide visual, vocal, haptic or other feedback to further aid in directing the placement of the component. In general, the component being inserted has substantially equal height and length as the sensored head. Ideally, the component is inserted identical in location and position to the previously inserted sensored head such that the loading and position of load on the component is similar to the quantitative measurements. In an eighth step, the component is positioned identically to the previously inserted sensored head and released. The insertion instrument can then be removed from the muscular-skeletal system. In a ninth step, at least the sensored head is disposed of. 
     Thus, the sensored head is used to identify a suitable location for insertion of the component. The insertion is supported by quantitative measurements that include position and location. Furthermore, the approximate loading and position of loading on the component is known after the procedure has been completed. In general, knowing the load applied by the muscular-skeletal system and the position on the surfaces of the component can aid in determining stability of the component long-term. An irregular loading applied on the component can result in the applied forces thrusting the component away from the inserted position. 
       FIG. 6  illustrates a graphical user interface (GUI)  500  showing a axial (top) view of the sensorized spinal instrument of  FIG. 5  in a non-limiting example. The graphical user interface  500  is presented by way of the remote system  105  and spine measurement system  100  of  FIG. 1 . Reference is made to spinal instrument  400  of  FIG. 2  and measurement system  100  of  FIG. 1 . The GUI  500  illustrates an example of how data can be presented. The GUI  500  includes a window  510  and a related window  520 . The window  520  shows the spine instrument  400  and sensor head  407  in relation to vertebrae  522  under evaluation. In this example, a axial (top) view of the vertebra is shown. It indicates a shaft angle  523  and a rotation component  524  which reveal the approach angle and rotation of the spine instrument  400 , for instance, as it is moved forward into the incision. The window  520  and corresponding GUI information is presented and updated in real-time during the procedure. It permits the surgeon to visualize use of spinal instrument  400  and the sensed parameters. The window  510  shows a sensing surface ( 403  or  406 ) of the sensored head  407 . A cross hair  512  is superimposed on the sensor head image to identify the maximal point of force and location. It can also lengthen to show vertebral edge loading. A window  513  reports the load force, for example, 20 lbs across the sensor head surface. This information is presented and updated in real-time during the procedure. 
     As previously noted, spine measurement system  100  can be used intra-operatively to aid in the implantation of the prosthesis, instrumentation, and hardware by way of parameter sensing (e.g., vertebral load, edge loading, compression, etc.). The spinal instrument  400  can include a power source that can provide power for only a single use or procedure. In one embodiment, components such as spinal instrument  400  can be disposed of after being used in a procedure. The remote system  105  can be placed outside the surgical field for use in different procedures and with different tools. 
     In the spine, the affects on the bony and soft tissue elements are evaluated by the measurement system  100 , as well as the soft tissue (e.g., cartilage, tendon, ligament) changes during surgery, including corrective spine surgery. The sensors of a tool, device, or implant used during the operation (and post-operatively) can support the evaluation and visualization of changes over time and report dynamic changes. The sensors can be activated intra-operatively when surgical parameter readings are stored. Immediately post-operatively, the sensor is activated and a baseline is known. 
     The measurement system  100  allows evaluation of the spine and connective tissue regarding, but not limited to bone density, fluid viscosity, temperature, strain, pressure, angular deformity, vibration, load, torque, distance, tilt, shape, elasticity, and motion. Because the sensors span a vertebral space, they can predict changes in the vertebral component function prior to their insertion. As previously noted, the measurement system  100  can be used to place spine instrument  400  in the inter-vertebral space, where it is shown positioned relative to the vertebral body  522 . Once it is placed and visually confirmed in the vertebral center, the system  100  reports any edge loading on the instrument which in turn is used to size a proper vertebral device and insertion plan (e.g., approach angle, rotation, depth, path trajectory). Examples of implant component function include bearing wear, subsidence, bone integration, normal and abnormal motion, heat, change in viscosity, particulate matter, kinematics, to name a few. 
       FIG. 7  illustrates spinal instrument  400  positioned between vertebra of the spine for intervertebral position and force sensing in accordance with an example embodiment. Reference is made to spinal instrument  400  of  FIG. 2  and measurement system  100  of  FIG. 1 . The illustration can also apply to spinal instrument  410  of  FIG. 3  and insert instrument  420  of  FIG. 4 . As shown, sensored head  407  of spinal instrument  400  is placed between vertebrae L 3  and vertebrae L 4 . The spinal instrument  400  distracts the L 3  and L 4  vertebrae the height of sensored head  407  and provides quantitative data on load magnitude and position of load. As mentioned previously, the spine measurement system  100  can include alignment circuitry  103 . The alignment circuitry  103  can comprise external devices such as a wand  510 A and a wand  520 A. Wands  510 A and  520 A can include accelerometers or circuitry to generate signals for time of flight and differential time of flight measurements. Wands  510 A and  520 A are coupled to different areas of the spinal region. In one embodiment, spinal instrument  400  includes circuitry that communicates with wand  510 A and a wand  520 A to determine position and alignment. Wands  510 A and  520 A are coupled to different vertebra of the spine with spinal instrument  400  positioned to be in line of sight with each wand. A long shaft  514  is provided on each wand to permit placement within vertebra of the spine and also line up with other wands and an electronic assembly  401  of the spine instrument  400 . Wand  510 A tracks an orientation and position of vertebra L 3 , while wand  520 A tracks an orientation and position of vertebra L 4 . This permits the spine measurement system  100  to track an orientation and movement of the spine instrument  400  relative to movement of the neighboring vertebra. Each wand can also be sensorized similar to spinal instrument  400 . Wands  510 A and wand  520 A respectively includes a sensor  512 A and a sensor  513 A. Sensors  512 A and  513 A can transmit and receive positional information. In the example, electronic assembly  401  in conjunction with wands  510 A and  520 A dually serves to resolve an orientation and position of spinal instrument  400  during the procedure. Thus, spine measurement system  100  can simultaneously provide quantitative measurement data such as load and position of load, position and alignment of spinal instrument  400 , and position and alignment of one or more regions of the spine. 
       FIG. 8  illustrates user interface  600  showing the spinal instrument  400  of  FIG. 7  in accordance with an example embodiment. Reference is made to spinal instrument  400  of  FIG. 2  and measurement system  100  of  FIG. 1 . The illustration can also apply to spinal instrument  410  of  FIG. 3  and insert instrument  420  of  FIG. 4 . User interface  600  is presented by way of the remote system  105  and spine measurement system  100  (see  FIG. 1 ). The GUI  600  includes a window  610  and a related window  620 . The window  620  shows spinal instrument  400  and sensored head  407  in relation to a vertebral component  622  under evaluation. In this example, a sagital view of the spine column is shown. It indicates a shaft angle  623  and a rotation component  624  which reveal the approach angle and rotation of spinal instrument  400  and sensored head  407 . The window  620  and corresponding GUI information is presented and updated in real-time during the procedure. It permits the surgeon to visualize sensored head  407  of the spinal instrument  400  and the sensed load force parameters. The window  610  shows sensing surfaces of the sensor head  407 . A cross hair  612  is superimposed on the image of sensored head  407  to identify the maximal point of force and location. It can also adjust in width and length to show vertebral edge loading. Another GUI window  613  reports the load force across the sensored head  407  surface. The GUI  600  is presented and updated in real-time during the procedure. 
       FIG. 9  illustrates a lateral view of spinal insert instrument  420  for placement of spine cage  475  in accordance with an example embodiment. The illustration can also apply to spinal instrument  400  of  FIG. 2  and spinal instrument  410  of  FIG. 3  when adapted to retain components for insert installation. Insert instrument  420  provides a surgical means for implanting vertebral component  475  (e.g. spine cage, pedicle screw, sensor) between the L 3  and L 4  vertebrae in the illustration. Mechanical assembly tip  451  at the distal end of shaft  434  permits attaching and releasing of the vertebral component by way of attach/release mechanism  455 . The vertebral component  475  can be placed in the back of the spine through a midline incision in the back, for example, via posterior lumbar interbody fusion (PLIF) as shown. The insert instrument  420  can similarly be used in anterior lumbar interbody fusion (ALIF) procedures. 
     In one method herein contemplated, the position of spine cage  475  prior to insertion is optimally defined for example, via 3D imaging or via ultrasonic navigation as described with alignment circuitry  103  of  FIG. 1  with spinal instrument  400  shown in  FIGS. 6 and 7 . The load sensor  407  (see  FIG. 7 ) is positioned between the vertebra to assess loading forces as described above where an optimal insertion path and trajectory is therein defined. The load forces and path of instrument insertion are recorded. Thereafter as shown in  FIG. 9 , insert instrument  420  inserts the final spinal cage  475  according to the recorded path of spinal instrument  400  and as based on the load forces. During the insertion, the GUI as shown in  FIG. 10  navigates the spinal instrument  420  to the recorded insertion point. Spinal insert instrument  420  can be equipped with one or more load sensors serving as a placeholder to a final spinal cage. After placement of spinal cage  475  between the vertebra, release of the spine cage from insert instrument  420 , and removal of the insert instrument  420 , the open space occupied around the spinal cage is then closed down via rods and pedicle screws on the neighboring vertebra. This compresses the surrounding vertebra onto the spinal cage, and provides stability for verterbral fusion. During this procedure, the GUI  700  of  FIG. 10  reports change in spinal anatomy, for example, Lordosis and Kyphosis, due to adjustment of the rods and tightening of the pedicle screws. Notably, the GUI  700  also provides visual feedback indicating which the amount and directions to achieve the planned spinal alignment by way of instrumented adjustments to the rods and screws. 
       FIG. 10  illustrates graphical user interface (GUI)  700  showing a lateral view of the insert instrument  420  of  FIG. 9  in a non-limiting example. GUI  700  can be presented by way of the remote system  105  and measurement system  100  of  FIG. 1 . GUI  700  includes a window  710  and a related window  720 . The window  720  shows insert instrument  420  and vertebral component  475  in relation to the L 4  and L 5  vertebrae under evaluation. In this example, a sagital (side) view of the spine column is shown. It indicates a shaft angle  723  and a rotation component  724  which reveal the approach angle and rotation of insert instrument  420  and vertebral component  475 . Window  720  and corresponding GUI information can be presented and updated in real-time during the procedure. The real-time display permits the surgeon to visualize the vertebral component  475  of the insert instrument  420  according to the previously sensed load force parameters. 
     Window  710  shows a target sensored head orientation  722  and a current instrument head orientation  767 . The target orientation  722  shows the approach angle, rotation and trajectory path previously determined when the spine instrument  400  was used for evaluating loading parameters. The current instrument head orientation  767  shows tracking of the insert instrument  420  currently used to insert the spine cage  475 . GUI  700  presents the target orientation model  722  in view of the current instrument head orientation  767  to provide visualization of the previously determined surgical plan. 
     Referring to  FIGS. 1, 5, 6, 7, and 8 , spinal instrument  400  is used to assess procedural parameters (e.g., angle, rotation, path) in view of determined sensing parameters (e.g., load, force, edge). Referring back to  FIG. 10 , once these procedural parameters were determined, measurement system  100  by way of GUI  700  now guides the surgeon with insert instrument  420  to insert the vertebral components  475  (e.g., spine cage, pedicle screw). In one arrangement, measurement system  100  provides haptic feedback to guide insert instrument  420  during the insertion procedure. For example, insert instrument  420  can vibrate when the current approach angle  713  deviates from the target approach angle, provides a visual cue (red/green indication), or when the orientation  767  is not aligned with the target trajectory path  722 . The amount of feedback (e.g. haptic or visual) can correspond to the amount of deviation. Alternatively, vocal feedback can be provided by system  100  to supplement the visual and haptic information being provided. The GUI  700  effectively recreates the position and target path of insert instrument  420  through visual and haptic feedback based on the previous instrumenting. It is contemplated herein that spinal instrument  420  can also be adapted for both load measurement and an insertion process. 
     The loading, balance, and position can be adjusted during surgery within predetermined quantitatively measured ranges through surgical techniques and adjustments using data from sensorized devices disclosed herein for alignment and parameter through measurement system  100 . Both the trial and final inserts (e.g., spine cage, pedicle screw, sensors, etc.) can include the sensing module to provide measured data to the remote system for display. A final insert can also be used to monitor the vertebral joint long term. The data can be used by the patient and health care providers to ensure that the vertebral joint or fused vertebrae is functioning properly during rehabilitation and as the patient returns to an active normal lifestyle. Conversely, the patient or health care provider can be notified when the measured parameters are out of specification. This provides early detection of a spine problem that can be resolved with minimal stress to the patient. The data from final insert can be displayed on a screen in real time using data from the embedded sensing module. In one embodiment, a handheld device is used to receive data from final insert. The handheld device can be held in proximity to the spine allowing a strong signal to be obtained for reception of the data. 
     A method is disclosed for inserting a prosthetic component in a spinal region in a non-limiting example. The method can be practiced with more or less than the number of steps shown and is not limited to the order shown. To describe the method, reference will be made to  FIGS. 1, 7, and 9  although it is understood that the method can be implemented in any other manner using other suitable components. In a first step, the spinal region is distracted to create a gap or spacing. The distraction process produces a suitable spacing for receiving a prosthetic component. As disclosed herein, the distraction process can also generate quantitative data such as load and position of load measurements applied by the spinal region to a measurement device of similar size to the prosthetic component. In a second step, the prosthetic component is directed to the spinal region. In the example, an insert instrument is used by a surgeon to direct the prosthetic component held by the tool at a tip of the device. In a third step, the insert instrument measures at least one of orientation, rotation, angle, or position of the prosthetic component. The insert instrument can track a trajectory of the insert instrument and prosthetic component in real-time during the insertion process. In a fourth step, the insert instrument transmits data related to one of orientation, rotation, angle, or position of the prosthetic component and insert instrument. In the example, the data is transmitted wirelessly local to the procedure. 
     In a fifth step, the transmitted data from the insert instrument is displayed on a remote system. In the example, the remote system can be in the operating room where the procedure is being performed in view of the surgeon. The at least one of orientation, rotation, angle, or position measurement data can be displayed in a manner that allows visualization of the trajectory of the prosthetic component to the spinal region. The visualization allows the surgeon to better direct the prosthetic component where visibility to the region is limited. Furthermore, the visualization provides the benefit of placing the prosthetic component in a previously identified area and at a similar trajectory of the spinal region using quantitative measurement data. In a sixth step, the trajectory of the insert instrument and prosthetic component being tracked can be compared with a trajectory previously measured. The compared trajectories can be displayed and visualized on the display of the remote system. 
     In a seventh step, the prosthetic component is inserted into the spinal region. In the example, the prosthetic component is placed in the gap or spacing from the prior distraction process. The prosthetic component can be placed in approximately the same location and alignment of a prior device such as the spinal instrument disclosed herein. In an eighth step, the prosthetic component is released in the spinal region. The surgeon can view the placement of the prosthetic component on the remote display. The location and alignment of the prosthetic component is supported by the measurement data provided by the insert instrument. The attach/release mechanism is used to release the prosthetic component from the insert instrument. In a ninth step, the insert instrument is removed from the spinal region. In a tenth step, the insert instrument can be disposed of after the procedure is completed. Alternatively, the insert instrument can be sterilized for use in another procedure. 
       FIG. 11  is a block diagram of the components of spinal instrument  400  in accordance with an example embodiment. The block diagram can also apply to spinal instrument  410  of  FIG. 3  and insert instrument  420  of  FIG. 4 . It should be noted that spinal instrument  400  could comprise more or less than the number of components shown. Spinal instrument  400  is a self-contained tool that can measure a parameter of the muscular-skeletal system. In the example, the spinal instrument  400  measures load and position of load when inserted in a spinal region. The active components of spinal instrument  400  include one or more sensors  1602 , a load plate  1606 , a power source  1608 , electronic circuitry  1610 , a transceiver  1612 , and an accelerometer  1614 . In a non-limiting example, an applied compressive force is applied to sensors  1602  by the spinal region and measured by the spinal instrument  400 . 
     The sensors  1602  can be positioned, engaged, attached, or affixed to the surfaces  403  and  406  of spinal instrument  400 . In general, a compressive force is applied by the spinal region to surfaces  403  and  406  when inserted therein. The surfaces  403  and  406  couple to sensors  1602  such that a compressive force is applied to each sensor. In one embodiment, the position of applied load to surfaces  403  and  406  can be measured. In the example, three load sensors are used in the sensored head to identify position of applied load. Each load sensor is coupled to a predetermined position on the load plate  1606 . The load plate  1606  couples to surface  403  to distribute a compressive force applied to the sensored head of spinal instrument  400  to each sensor. The load plate  1606  can be rigid and does not flex when distributing the force, pressure, or load to sensors  1602 . The force or load magnitude measured by each sensor can be correlated back to a location of applied load on the surface  403 . 
     In the example of intervertebral measurement, the sensored head having surfaces  403  and  406  can be positioned between the vertebrae of the spine. Surface  403  of the sensored head couples to a first vertebral surface and similarly the surface  406  couples to a second vertebral surface. Accelerometer  1614  or an external alignment system can be used to measure position and orientation of the sensored head as it is directed into the spinal region. The sensors  1602  couple to the electronic circuitry  1610 . The electronic circuitry  1610  comprises logic circuitry, input/output circuitry, clock circuitry, D/A, and A/D circuitry. In one embodiment, the electronic circuitry  1610  comprises an application specific integrated circuit that reduces form factor, lowers power, and increases performance. In general, the electronic circuitry  1610  controls a measurement process, receives the measurement signals, converts the measurement signals to a digital form, supports display on an interface, and initiates data transfer of measurement data. Electronic circuitry  1610  measures physical changes in the sensors  1602  to determine parameters of interest, for example a level, distribution and direction of forces acting on the surfaces  403  and  406 . The insert sensing device  400  can be powered by an internal power source  1608 . Thus, all the components required to measure parameters of the muscular-skeletal system reside in the spinal instrument  400 . 
     As one example, sensors  1602  can comprise an elastic or compressible propagation structure between a first transducer and a second transducer. The transducers can be an ultrasound (or ultrasonic) resonator, and the elastic or compressible propagation structure can be an ultrasound waveguide. The electronic circuitry  1610  is electrically coupled to the transducers to translate changes in the length (or compression or extension) of the compressible propagation structure to parameters of interest, such as force. The system measures a change in the length of the compressible propagation structure (e.g., waveguide) responsive to an applied force and converts this change into electrical signals, which can be transmitted via the transceiver  1612  to convey a level and a direction of the applied force. For example, the compressible propagation structure has known and repeatable characteristics of the applied force versus the length of the waveguide. Precise measurement of the length of the waveguide using ultrasonic signals can be converted to a force using the known characteristics. 
     Sensors  1602  are not limited to waveguide measurements of force, pressure, or load sensing. In yet other arrangements, sensors  1602  can include piezo-resistive, compressible polymers, capacitive, optical, mems, strain gauge, chemical, temperature, pH, and mechanical sensors for measuring parameters of the muscular-skeletal system. In an alternate embodiment, a piezo-resistive film sensor can be used for sensing load. The piezo-resistive film has a low profile thereby reducing the form factor required for the implementation. The piezo-resistive film changes resistance with applied pressure. A voltage or current can be applied to the piezo-resistive film to monitor changes in resistance. Electronic circuitry  1610  can be coupled to apply the voltage or current. Similarly, electronic circuitry  1610  can be coupled to measure the voltage and current corresponding to a resistance of the piezo-resistive film. The relation of piezo-resistive film resistance to an applied force, pressure, or load is known. Electronic circuitry  1610  can convert the measured voltage or current to a force, pressure, or load applied to the sensored head. Furthermore, electronic circuitry  1610  can convert the measurement to a digital format for display or transfer for real-time use or for being stored. Electronic circuitry  1610  can include converters, inputs, outputs, and input/outputs that allow serial and parallel data transfer whereby measurements and transmission of data can occur simultaneously. In one embodiment, an ASIC is included in electronic circuitry  1610  that incorporates digital control logic to manage control functions and the measurement process of spinal instrument  400  as directed by the user. 
     The accelerometer  1614  can measure acceleration and static gravitational pull. Accelerometer  1614  can be single-axis and multi-axis accelerometer structures that detect magnitude and direction of the acceleration as a vector quantity. Accelerometer  1614  can also be used to sense orientation, vibration, impact and shock. The electronic circuitry  1610  in conjunction with the accelerometer  1614  and sensors  1602  can measure parameters of interest (e.g., distributions of load, force, pressure, displacement, movement, rotation, torque, location, and acceleration) relative to orientations of spinal instrument  400 . In such an arrangement, spatial distributions of the measured parameters relative to a chosen frame of reference can be computed and presented for real-time display. 
     The transceiver  1612  comprises a transmitter  1622  and an antenna  1620  to permit wireless operation and telemetry functions. In various embodiments, the antenna  1620  can be configured by design as an integrated loop antenna. The integrated loop antenna is configured at various layers and locations on a printed circuit board having other electrical components mounted thereto. For example, electronic circuitry  1610 , power source  1608 , transceiver  1612 , and accelerometer  1614  can be mounted on a circuit board that is located on or in spinal instrument  400 . Once initiated the transceiver  1612  can broadcast the parameters of interest in real-time. The telemetry data can be received and decoded with various receivers, or with a custom receiver. The wireless operation can eliminate distortion of, or limitations on, measurements caused by the potential for physical interference by, or limitations imposed by, wiring and cables coupling the sensing module with a power source or with associated data collection, storage, display equipment, and data processing equipment. 
     The transceiver  1612  receives power from the power source  1608  and can operate at low power over various radio frequencies by way of efficient power management schemes, for example, incorporated within the electronic circuitry  1610  or the application specific integrated circuit. As one example, the transceiver  1612  can transmit data at selected frequencies in a chosen mode of emission by way of the antenna  1620 . The selected frequencies can include, but are not limited to, ISM bands recognized in International Telecommunication Union regions 1, 2 and 3. A chosen mode of emission can be, but is not limited to, Gaussian Frequency Shift Keying, (GFSK), Amplitude Shift Keying (ASK), Phase Shift Keying (PSK), Minimum Shift Keying (MSK), Frequency Modulation (FM), Amplitude Modulation (AM), or other versions of frequency or amplitude modulation (e.g., binary, coherent, quadrature, etc.). 
     The antenna  1620  can be integrated with components of the sensing module to provide the radio frequency transmission. The antenna  1620  and electronic circuitry  1610  are mounted and coupled to form a circuit using wire traces on a printed circuit board. The antenna  1620  can further include a matching network for efficient transfer of the signal. This level of integration of the antenna and electronics enables reductions in the size and cost of wireless equipment. Potential applications may include, but are not limited to any type of short-range handheld, wearable, or other portable communication equipment where compact antennas are commonly used. This includes disposable modules or devices as well as reusable modules or devices and modules or devices for long-term use. 
     The power source  1608  provides power to electronic components of the spinal instrument  400 . In one embodiment, power source  1608  can be charged by wired energy transfer, short-distance wireless energy transfer or a combination thereof. External power sources for providing wireless energy to power source  1608  can include, but are not limited to, a battery or batteries, an alternating current power supply, a radio frequency receiver, an electromagnetic induction coil, a photoelectric cell or cells, a thermocouple or thermocouples, or an ultrasound transducer or transducers. By way of power source  1608 , spinal instrument  400  can be operated with a single charge until the internal energy is drained. It can be recharged periodically to enable continuous operation. The power source  1608  can further utilize power management techniques for efficiently supplying and providing energy to the components of spinal instrument  400  to facilitate measurement and wireless operation. Power management circuitry can be incorporated on the ASIC to manage both the ASIC power consumption as well as other components of the system. 
     The power source  1608  minimizes additional sources of energy radiation required to power the sensing module during measurement operations. In one embodiment, as illustrated, the energy storage  1608  can include a capacitive energy storage device  1624  and an induction coil  1626 . The external source of charging power can be coupled wirelessly to the capacitive energy storage device  1624  through the electromagnetic induction coil or coils  1626  by way of inductive charging. The charging operation can be controlled by a power management system designed into, or with, the electronic circuitry  1610 . For example, during operation of electronic circuitry  1610 , power can be transferred from capacitive energy storage device  1624  by way of efficient step-up and step-down voltage conversion circuitry. This conserves operating power of circuit blocks at a minimum voltage level to support the required level of performance. Alternatively, power source  1608  can comprise one or more batteries that are housed within spinal instrument  400 . The batteries can power a single use of the spinal instrument  400  whereby the device is disposed after it has been used in a surgery. 
     In one configuration, the external power source can further serve to communicate downlink data to the transceiver  1612  during a recharging operation. For instance, downlink control data can be modulated onto the wireless energy source signal and thereafter demodulated from the induction coil  1626  by way of electronic circuitry  1610 . This can serve as a more efficient way for receiving downlink data instead of configuring the transceiver  1612  for both uplink and downlink operation. As one example, downlink data can include updated control parameters that the spinal instrument  400  uses when making a measurement, such as external positional information, or for recalibration purposes. It can also be used to download a serial number or other identification data. 
     The electronic circuitry  1610  manages and controls various operations of the components of the sensing module, such as sensing, power management, telemetry, and acceleration sensing. It can include analog circuits, digital circuits, integrated circuits, discrete components, or any combination thereof. In one arrangement, it can be partitioned among integrated circuits and discrete components to minimize power consumption without compromising performance. Partitioning functions between digital and analog circuit enhances design flexibility and facilitates minimizing power consumption without sacrificing functionality or performance. Accordingly, the electronic circuitry  1610  can comprise one or more integrated circuits or ASICs, for example, specific to a core signal-processing algorithm. 
     In another arrangement, the electronic circuitry  1610  can comprise a controller such as a programmable processor, a Digital Signal Processor (DSP), a microcontroller, or a microprocessor, with associated storage memory and logic. The controller can utilize computing technologies with associated storage memory such a Flash, ROM, RAM, SRAM, DRAM or other like technologies for controlling operations of the aforementioned components of the sensing module. In one arrangement, the storage memory may store one or more sets of instructions (e.g., software) embodying any one or more of the methodologies or functions described herein. The instructions may also reside, completely or at least partially, within other memory, and/or a processor during execution thereof by another processor or computer system. 
     The electronics assemblage also supports testability and calibration features that assure the quality, accuracy, and reliability of the completed wireless sensing module or device. A temporary bi-directional coupling can be used to assure a high level of electrical observability and controllability of the electronics. The test interconnect also provides a high level of electrical observability of the sensing subsystem, including the transducers, waveguides, and mechanical spring or elastic assembly. Carriers or fixtures emulate the final enclosure of the completed wireless sensing module or device during manufacturing processing thus enabling capture of accurate calibration data for the calibrated parameters of the finished wireless sensing module or device. These calibration parameters are stored within the on-board memory integrated into the electronics assemblage. 
     Applications for the electronic assembly comprising the sensors  1602  and electronic circuitry  1610  may include, but are not limited to, disposable modules or devices as well as reusable modules or devices and modules or devices for long-term use. In addition to non-medical applications, examples of a wide range of potential medical applications may include, but are not limited to, implantable devices, modules within implantable devices, intra-operative implants or modules within intra-operative implants or trial inserts, modules within inserted or ingested devices, modules within wearable devices, modules within handheld devices, modules within instruments, appliances, equipment, or accessories of all of these, or disposables within implants, trial inserts, inserted or ingested devices, wearable devices, handheld devices, instruments, appliances, equipment, or accessories to these devices, instruments, appliances, or equipment. 
       FIG. 12  is a diagram of an exemplary communications system  1700  for short-range telemetry in accordance with an exemplary embodiment. The illustration applies to spinal instrument  400  of  FIG. 2 , spinal instrument  410  of  FIG. 3 , insert instrument  420  of  FIG. 4 , and spine measurement system  100  of  FIG. 1 . It should be noted that communication system  1700  may comprise more or less than the number of components shown. As illustrated, the communications system  1700  comprises medical device communications components  1710  in a spinal instrument and receiving system communications in a processor based remote system. In one embodiment, the receiving remote system communications are in or coupled to a computer or laptop computer that can be viewed by the surgical team during a procedure. The remote system can be external to the sterile field of the operating room but within viewing range to assess measured quantitative data in real time. The medical device communications components  1710  are operatively coupled to include, but not limited to, the antenna  1712 , a matching network  1714 , a telemetry transceiver  1716 , a CRC circuit  1718 , a data packetizer  1722 , a data input  1724 , a power source  1726 , and an application specific integrated circuit (ASIC)  1720 . The medical device communications components  1710  may include more or less than the number of components shown and are not limited to those shown or the order of the components. 
     The receiving station communications components  1750  comprise an antenna  1752 , a matching network  1754 , a telemetry receiver  1756 , the CRC circuit  1758 , the data packetizer  1760 , and optionally a USB interface  1762 . Notably, other interface systems can be directly coupled to the data packetizer  1760  for processing and rendering sensor data. 
     Referring to  FIG. 11 , the electronic circuitry  1610  is operatively coupled to one or more sensors  602  of the spinal instrument  400 . In one embodiment, the data generated by the one or more sensors  602  can comprise a voltage, current, frequency, or count from a mems structure, piezo-resistive sensor, strain gauge, mechanical sensor, pulsed, continuous wave, or other sensor type that can be converted to the parameter being measured of the muscular-skeletal system. Referring back to  FIG. 12 , the data packetizer  1722  assembles the sensor data into packets; this includes sensor information received or processed by ASIC  1720 . The ASIC  1720  can comprise specific modules for efficiently performing core signal processing functions of the medical device communications components  1710 . A benefit of ASIC  1720  is in reducing a form factor of the tool. 
     The CRC circuit  1718  applies error code detection on the packet data. The cyclic redundancy check is based on an algorithm that computes a checksum for a data stream or packet of any length. These checksums can be used to detect interference or accidental alteration of data during transmission. Cyclic redundancy checks are especially good at detecting errors caused by electrical noise and therefore enable robust protection against improper processing of corrupted data in environments having high levels of electromagnetic activity. The telemetry transmitter  1716  then transmits the CRC encoded data packet through the matching network  1714  by way of the antenna  1712 . The matching networks  1714  and  1754  provide an impedance match for achieving optimal communication power efficiency. 
     The receiving system communications components  1750  receive transmissions sent by spinal instrument communications components  1710 . In one embodiment, telemetry transmitter  1716  is operated in conjunction with a dedicated telemetry receiver  1756  that is constrained to receive a data stream broadcast on the specified frequencies in the specified mode of emission. The telemetry receiver  1756  by way of the receiving station antenna  1752  detects incoming transmissions at the specified frequencies. The antenna  1752  can be a directional antenna that is directed to a directional antenna of components  1710 . Using at least one directional antenna can reduce data corruption while increasing data security by further limiting the data is radiation pattern. A matching network  1754  couples to antenna  1752  to provide an impedance match that efficiently transfers the signal from antenna  1752  to telemetry receiver  1756 . Telemetry receiver  1756  can reduce a carrier frequency in one or more steps and strip off the information or data sent by components  1710 . Telemetry receiver  1756  couples to CRC circuit  1758 . CRC circuit  1758  verifies the cyclic redundancy checksum for individual packets of data. CRC circuit  1758  is coupled to data packetizer  1760 . Data packetizer  1760  processes the individual packets of data. In general, the data that is verified by the CRC circuit  1758  is decoded (e.g., unpacked) and forwarded to an external data processing device, such as an external computer, for subsequent processing, display, or storage or some combination of these. 
     The telemetry receiver  1756  is designed and constructed to operate on very low power such as, but not limited to, the power available from the powered USB port  1762 , or a battery. In another embodiment, the telemetry receiver  1756  is designed for use with a minimum of controllable functions to limit opportunities for inadvertent corruption or malicious tampering with received data. The telemetry receiver  1756  can be designed and constructed to be compact, inexpensive, and easily manufactured with standard manufacturing processes while assuring consistently high levels of quality and reliability. 
     In one configuration, the communication system  1700  operates in a transmit-only operation with a broadcasting range on the order of a few meters to provide high security and protection against any form of unauthorized or accidental query. The transmission range can be controlled by the transmitted signal strength, antenna selection, or a combination of both. A high repetition rate of transmission can be used in conjunction with the Cyclic Redundancy Check (CRC) bits embedded in the transmitted packets of data during data capture operations thereby enabling the receiving system to discard corrupted data without materially affecting display of data or integrity of visual representation of data, including but not limited to measurements of load, force, pressure, displacement, flexion, attitude, and position within operating or static physical systems. 
     By limiting the operating range to distances on the order of a few meters the telemetry transmitter  1716  can be operated at very low power in the appropriate emission mode or modes for the chosen operating frequencies without compromising the repetition rate of the transmission of data. This mode of operation also supports operation with compact antennas, such as an integrated loop antenna. The combination of low power and compact antennas enables the construction of, but is not limited to, highly compact telemetry transmitters that can be used for a wide range of non-medical and medical applications. 
     The transmitter security as well as integrity of the transmitted data is assured by operating the telemetry system within predetermined conditions. The security of the transmitter cannot be compromised because it is operated in a transmit-only mode and there is no pathway to hack into medical device communications components. The integrity of the data is assured with the use of the CRC algorithm and the repetition rate of the measurements. Limiting the broadcast range of the device minimizes the risk of unauthorized reception of data. Even if unauthorized reception of the data packets should occur there are counter measures in place that further mitigate data access. A first measure is that the transmitted data packets contain only binary bits from a counter along with the CRC bits. A second measure is that no data is available or required to interpret the significance of the binary value broadcast at any time. A third measure that can be implemented is that no patient or device identification data is broadcast at any time. 
     The telemetry transmitter  1716  can also operate in accordance with some FCC regulations. According to section 18.301 of the FCC regulations the ISM bands within the USA include 6.78, 13.56, 27.12, 30.68, 915, 2450, and 5800 MHz as well as 24.125, 61.25, 122.50, and 245 GHz. Globally other ISM bands, including 433 MHz, are defined by the International Telecommunications Union in some geographic locations. The list of prohibited frequency bands defined in 18.303 are “the following safety, search and rescue frequency bands is prohibited: 490-510 kHz, 2170-2194 kHz, 8354-8374 kHz, 121.4-121.6 MHz, 156.7-156.9 MHz, and 242.8-243.2 MHz. 
     Section 18.305 stipulates the field strength and emission levels ISM equipment must not exceed when operated outside defined ISM bands. In summary, it may be concluded that ISM equipment may be operated worldwide within ISM bands as well as within most other frequency bands above 9 KHz given that the limits on field strengths and emission levels specified in section 18.305 are maintained by design or by active control. As an alternative, commercially available ISM transceivers, including commercially available integrated circuit ISM transceivers, may be designed to fulfill these field strengths and emission level requirements when used properly. 
     In one configuration, the telemetry transmitter  1716  can also operate in unlicensed ISM bands or in unlicensed operation of low power equipment, wherein the ISM equipment (e.g., telemetry transmitter  1716 ) may be operated on ANY frequency above 9 kHz except as indicated in Section 18.303 of the FCC code. 
     Wireless operation eliminates distortion of, or limitations on, measurements caused by the potential for physical interference by, or limitations imposed by, wiring and cables coupling the wireless sensing module or device with a power source or with data collection, storage, or display equipment. Power for the sensing components and electronic circuits is maintained within the wireless sensing module or device on an internal energy storage device. This energy storage device is charged with external power sources including, but not limited to, a battery or batteries, super capacitors, capacitors, an alternating current power supply, a radio frequency receiver, an electromagnetic induction coil, a photoelectric cell or cells, a thermocouple or thermocouples, or an ultrasound transducer or transducers. The wireless sensing module may be operated with a single charge until the internal energy source is drained or the energy source may be recharged periodically to enable continuous operation. The embedded power supply minimizes additional sources of energy radiation required to power the wireless sensing module or device during measurement operations. Telemetry functions are also integrated within the wireless sensing module or device. Once initiated the telemetry transmitter continuously broadcasts measurement data in real time. Telemetry data may be received and decoded with commercial receivers or with a simple, low cost custom receiver. 
       FIG. 13  illustrates a communication network  1800  for measurement and reporting in accordance with an example embodiment. Briefly, the communication network  1800  expands communication for spine measurement system  100  of  FIG. 1 , spinal instrument  400  of  FIG. 2 , spinal instrument  410  of  FIG. 3 , and insert instrument  420  to provide broad data connectivity to other devices or services. As illustrated, spinal alignment system  100 , spinal instrument  400 , and insert instrument  420  can be communicatively coupled to the communications network  1800  and any associated systems or services. It should be noted that communication network  1800  can comprise more or less than the number of communication networks and systems shown. 
     As one example, measurement system  100 , spinal instrument  400 , spinal instrument  410 , and insert instrument  420  can share its parameters of interest (e.g., distributions of load, force, pressure, displacement, movement, rotation, torque and acceleration) with remote services or providers, for instance, to analyze or report on surgical status or outcome. In the case that a sensor system is permanently implanted, the data from the sensor can be shared for example with a service provider to monitor progress or with plan administrators for surgical planning purposes or efficacy studies. The communication network  1800  can further be tied to an Electronic Medical Records (EMR) system to implement health information technology practices. In other embodiments, the communication network  1800  can be communicatively coupled to HIS Hospital Information System, HIT Hospital Information Technology and HIM Hospital Information Management, EHR Electronic Health Record, CPOE Computerized Physician Order Entry, and CDSS Computerized Decision Support Systems. This provides the ability of different information technology systems and software applications to communicate, to exchange data accurately, effectively, and consistently, and to use the exchanged data. 
     The communications network  1800  can provide wired or wireless connectivity over a Local Area Network (LAN)  1801 , a Wireless Local Area Network (WLAN)  1805 , a Cellular Network  1814 , and/or other radio frequency (RF) system. The LAN  1801  and WLAN  1805  can be communicatively coupled to the Internet  1820 , for example, through a central office. The central office can house common network switching equipment for distributing telecommunication services. Telecommunication services can include traditional POTS (Plain Old Telephone Service) and broadband services such as cable, HDTV, DSL, VoIP (Voice over Internet Protocol), IPTV (Internet Protocol Television), Internet services, and so on. 
     The communication network  1800  can utilize common computing and communications technologies to support circuit-switched and/or packet-switched communications. Each of the standards for Internet  1820  and other packet switched network transmission (e.g., TCP/IP, UDP/IP, HTML, HTTP, RTP, MMS, SMS) represent examples of the state of the art. Such standards are periodically superseded by faster or more efficient equivalents having essentially the same functions. Accordingly, replacement standards and protocols having the same functions are considered equivalent. 
     The cellular network  1814  can support voice and data services over a number of access technologies such as GSM-GPRS, EDGE, CDMA, UMTS, WiMAX, 2G, 3G, WAP, software defined radio (SDR), and other known technologies. The cellular network  1814  can be coupled to base receiver  1810  under a frequency-reuse plan for communicating with mobile devices  1802 . 
     The base receiver  1810 , in turn, can connect the mobile device  1802  to the Internet  1820  over a packet switched link. Internet  1820  can support application services and service layers for distributing data from spinal alignment system  100 , spinal instrument  400 , and insert instrument  420  to the mobile device  502 . The mobile device  1802  can also connect to other communication devices through the Internet  1820  using a wireless communication channel. 
     The mobile device  1802  can also connect to the Internet  1820  over the WLAN  1805 . Wireless Local Access Networks (WLANs) provide wireless access within a local geographical area. WLANs are typically composed of a cluster of Access Points (APs)  1804  also known as base stations. Spinal alignment system  100 , spinal instrument  400 , and insert instrument  420  can communicate with other WLAN stations such as laptop  1803  within the base station area. In typical WLAN implementations, the physical layer uses a variety of technologies such as 802.11b or 802.11g WLAN technologies. The physical layer may use infrared, frequency hopping spread spectrum in the 2.4 GHz Band, direct sequence spread spectrum in the 2.4 GHz Band, or other access technologies, for example, in the 5.8 GHz ISM band or higher ISM bands (e.g., 24 GHz, etc.). 
     By way of the communication network  1800 , spinal alignment system  100 , spinal instrument  400 , and insert instrument  420  can establish connections with a remote server  1830  on the network and with other mobile devices for exchanging data. The remote server  1830  can have access to a database  1840  that is stored locally or remotely and which can contain application specific data. The remote server  1830  can also host application services directly, or over the internet  1820 . 
       FIG. 14  depicts an exemplary diagrammatic representation of a machine in the form of a computer system  1900  within which a set of instructions, when executed, may cause the machine to perform any one or more of the methodologies discussed above. In some embodiments, the machine operates as a standalone device. In some embodiments, the machine may be connected (e.g., using a network) to other machines. In a networked deployment, the machine may operate in the capacity of a server or a client user machine in server-client user network environment, or as a peer machine in a peer-to-peer (or distributed) network environment. 
     The machine may comprise a server computer, a client user computer, a personal computer (PC), a tablet PC, a laptop computer, a desktop computer, a control system, a network router, switch or bridge, or any machine capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken by that machine. It will be understood that a device of the present disclosure includes broadly any electronic device that provides voice, video or data communication. Further, while a single machine is illustrated, the term “machine” shall also be taken to include any collection of machines that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein. 
     The computer system  1900  may include a processor  1902  (e.g., a central processing unit (CPU), a graphics processing unit (GPU, or both), a main memory  1904  and a static memory  1906 , which communicate with each other via a bus  1908 . The computer system  1900  may further include a video display unit  1910  (e.g., a liquid crystal display (LCD), a flat panel, a solid-state display, or a cathode ray tube (CRT)). The computer system  1900  may include an input device  1912  (e.g., a keyboard), a cursor control device  1914  (e.g., a mouse), a disk drive unit  1916 , a signal generation device  1918  (e.g., a speaker or remote control) and a network interface device  1920 . 
     The disk drive unit  1916  may include a machine-readable medium  1922  on which is stored one or more sets of instructions (e.g., software  1924 ) embodying any one or more of the methodologies or functions described herein, including those methods illustrated above. The instructions  1924  may also reside, completely or at least partially, within the main memory  1904 , the static memory  1906 , and/or within the processor  1902  during execution thereof by the computer system  1900 . The main memory  1904  and the processor  1902  also may constitute machine-readable media. 
     Dedicated hardware implementations including, but not limited to, application specific integrated circuits, programmable logic arrays and other hardware devices can likewise be constructed to implement the methods described herein. Applications that may include the apparatus and systems of various embodiments broadly include a variety of electronic and computer systems. Some embodiments implement functions in two or more specific interconnected hardware modules or devices with related control and data signals communicated between and through the modules, or as portions of an application-specific integrated circuit. Thus, the example system is applicable to software, firmware, and hardware implementations. 
     In accordance with various embodiments of the present disclosure, the methods described herein are intended for operation as software programs running on a processor, digital signal processor, or logic circuitry. Furthermore, software implementations can include, but not limited to, distributed processing or component/object distributed processing, parallel processing, or virtual machine processing can also be constructed to implement the methods described herein. 
     The present disclosure contemplates a machine readable medium containing instructions  1924 , or that which receives and executes instructions  1924  from a propagated signal so that a device connected to a network environment  1926  can send or receive voice, video or data, and to communicate over the network  1926  using the instructions  1924 . The instructions  1924  may further be transmitted or received over a network  1926  via the network interface device  1920 . 
     While the machine-readable medium  1922  is shown in an example embodiment to be a single medium, the term “machine-readable medium” should be taken to include a single medium or multiple media (e.g., a centralized or distributed database, and/or associated caches and servers) that store the one or more sets of instructions. The term “machine-readable medium” shall also be taken to include any medium that is capable of storing, encoding or carrying a set of instructions for execution by the machine and that cause the machine to perform any one or more of the methodologies of the present disclosure. 
     The term “machine-readable medium” shall accordingly be taken to include, but not be limited to: solid-state memories such as a memory card or other package that houses one or more read-only (non-volatile) memories, random access memories, or other re-writable (volatile) memories; magneto-optical or optical medium such as a disk or tape; and carrier wave signals such as a signal embodying computer instructions in a transmission medium; and/or a digital file attachment to e-mail or other self-contained information archive or set of archives is considered a distribution medium equivalent to a tangible storage medium. Accordingly, the disclosure is considered to include any one or more of a machine-readable medium or a distribution medium, as listed herein and including art-recognized equivalents and successor media, in which the software implementations herein are stored. 
     Although the present specification describes components and functions implemented in the embodiments with reference to particular standards and protocols, the disclosure is not limited to such standards and protocols. Each of the standards for Internet and other packet switched network transmission (e.g., TCP/IP, UDP/IP, HTML, HTTP) represent examples of the state of the art. Such standards are periodically superseded by faster or more efficient equivalents having essentially the same functions. Accordingly, replacement standards and protocols having the same functions are considered equivalents. 
     The illustrations of embodiments described herein are intended to provide a general understanding of the structure of various embodiments, and they are not intended to serve as a complete description of all the elements and features of apparatus and systems that might make use of the structures described herein. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. Other embodiments may be utilized and derived therefrom, such that structural and logical substitutions and changes may be made without departing from the scope of this disclosure. Figures are also merely representational and may not be drawn to scale. Certain proportions thereof may be exaggerated, while others may be minimized. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. 
     Such embodiments of the inventive subject matter may be referred to herein, individually and/or collectively, by the term “invention” merely for convenience and without intending to voluntarily limit the scope of this application to any single invention or inventive concept if more than one is in fact disclosed. Thus, although specific embodiments have been illustrated and described herein, it should be appreciated that any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. This disclosure is intended to cover any and all adaptations or variations of various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, will be apparent to those of skill in the art upon reviewing the above description. 
       FIG. 15  illustrates components of a spinal instrument  2000  in accordance with an example embodiment. Spinal instrument  2000  is a more detailed illustration of a non-limiting example of spinal instrument  102  of  FIG. 1 , spinal instrument  400  of  FIG. 2 , and spinal instrument  410  of  FIG. 3 . Spinal instrument  2000  is a measurement device having a sensored head  2002  that incorporates at least one sensor for measuring a parameter of the spine. Spinal instrument  2000  comprises sensored head  2002 , sensors  2008 , shaft  2010 , electronic assembly  2024 , interconnect  2028 , and handle  2030 . In one embodiment, handle  2030  is formed by coupling structures  2020  and  2022  together. A proximal end  2018  of shaft  2010  couples to a distal end of handle  2030 . A proximal end of sensored head  2002  couples to a distal end  2014  of shaft  2010 . Handle  2030  can be held by a surgeon to guide the instrument into the spine region of a patient to take one or more quantitative measurements. Sensored head  2002  can be inserted into the spine region such that the sensors  2008  can measure the parameters of interest. Electronic assembly  2024  operatively couples to sensors  2008  to receive, process, and provide quantitative measurement data. In general, spinal instrument  2000  can provide quantitative measurement data of a probed region by sensors  2008  mounted on or in sensored head  2002 . The quantitative data can also support the installation of a component into the muscular-skeletal region. Quantitative data or information related to the procedure can be displayed on an interface  2038  that may be included in spinal instrument  2000 . Alternatively, spinal instrument  2000  can provide quantitative data in support of a procedure through a remote system as disclosed herein. The remote system can be wired or wirelessly coupled to spinal instrument  2000 . The quantitative data can be provided in real-time with visualization of the procedure. 
     In the example, sensored head  2002  comprises a support structure  2004  and a support structure  2006 . Support structures  2004  and  2006  can move in relation to one another. For example, a compressive force can be applied to external surfaces of support structures  2004  and  2006 . Structures  2004  and  2006  can move under the compressive force resulting in a change of height of sensored head  2002 . In general, the external surfaces of support structures  2004  and  2006  would move closer together as the applied force or pressure increases. In one embodiment, the movement or change in distance between the external surfaces of support structures  2004  and  2006  is small in relation to the height of sensored head  2002  when no compressive force is applied. 
     Sensors  2008  are shown disassembled from sensored head  2002 . Sensors  2008  are placed within sensored head  2002  when assembled. Sensors  2008  couple between interior surfaces of support structures  2004  and  2006 . A compressive force, pressure, or load applied to exterior surfaces of support structures  2004  and  2006  couples to sensors  2008 . A measurable parameter of a sensor may directly or indirectly correspond to the force, pressure, or load applied thereto. In one embodiment sensors  2008  are film sensors having a low profile. An example of a film sensor is a piezo-resistive sensor or a polymer sensor. Piezo-resistive film sensors change resistance with an applied force, pressure, or load. Other sensor types can be used as disclosed herein. In general, each sensor is located at a predetermined position within sensored head  2002 . The predetermined position can couple to a predetermined location on the external surfaces of support structures  2004  and  2006 . Locating each sensor at a known predetermined position supports the determination of the location of applied load to exterior surfaces of support structures  2004  and  2006 . As shown, four sensors are placed within sensored head  2002 . Typically more than one sensor is used to determine location of applied load. The load measurements of sensors  2008  are assessed in relation with the corresponding location of each sensor. For example, the sensor nearest to the applied load will measure the highest load magnitude. Conversely, the sensor farthest from the applied load will measure the lowest load magnitude. Each sensor measurement can be used in the determination of the location where the load is applied to the exterior surfaces of support structures  2004  and  2006  and the magnitude of the applied load at the identified location. 
     The resistance of a piezo-resistive film sensor corresponds to the thickness of the film. An applied pressure to piezo-resistive film sensor reduces the thickness thereby lowering the resistance. The surface area of each piezo-resistive sensor is selected to fit within sensored head  2002  and relate to a predetermined location on the external surfaces of support structures  2004  and  2006  for location identification. The surface area of sensors  2008  corresponds to the range of resistance being measured over the measurable load range of spinal instrument  2000 . Typically, the magnitude and change in magnitude of the measurable parameter of sensors  2008  over the specified load range is known or measured. 
     A voltage or current is typically provided by electronic assembly  2024  to piezo-resistive film sensors. For example, providing a known current to the piezo-resistive film sensor generates a voltage that corresponds to the resistance. The voltage can be measured by electronic assembly  2024  and translated to a load measurement. Similarly, a known voltage can be applied to the piezo-resistive film sensor. The current conducted by the piezo-resistive film sensor corresponds to the resistance of the device. The current can be measured by electronic assembly  2024  and translated to the load measurement. Accuracy of the measurement can be improved by calibration of each sensor and providing the calibration data to electronic assembly  2024  for providing correction to the measured data. The calibration can compare sensor measurements to known loads applied to sensored head  2002 . Calibration can occur over different operating conditions such as temperature. In one embodiment, sensors  2008  may be calibrated as part of a final test of spinal instrument  2000 . 
     As mentioned previously, sensors  2008  comprise four sensors that support the measurement of the position of loading applied to at least one of the external surfaces of support structures  2004  and  2006 . In one embodiment, support structures  2004  and  2006  have convex shaped external surfaces that aid in the insertion of sensored head  2002  into the spinal region such as between vertebrae. The height of sensored head  2002  is a distance between the external surfaces of the support structures  2004  and  2006 . Sensored head can be used to distract and generate a gap between vertebrae. For example, the surgeon selects a sensored head of a predetermined height to produce a gap approximately equal to the sensored head height. 
     Shaft  2010  provides a separation distance between handle  2030  and sensored head  2002 . The shaft  2010  allows the surgeon to view and direct sensored head  2002  of spinal instrument  2000  into an exposed area of the spine. A distal end  2014  of the shaft  2010  fits into and fastens to a proximal end  2016  of sensored head  2002 . In one embodiment, shaft  2010  is cylindrical in shape and includes at least one lengthwise passage  2012 . Proximal end  2016  of sensored head  2002  can include an opening for receiving distal end  2014  of shaft  2010 . The shaft  2010  can be secured in the opening of sensored head  2002  by mechanical, adhesive, welding, bonding or other attaching method. In one embodiment, the attaching process permanently affixes sensored head  2002  to shaft  2010 . The lengthwise passage  2012  of shaft  2010  may be used to couple a component from handle  2030  to sensored head  2002 . For example, an interconnect  2028  can couple through the lengthwise passage  2012 . The interconnect  2028  extends out of the lengthwise passage  2012  on both distal end  2014  and proximal end  2018  of shaft  2010 . Interconnect  2028  couples sensors  2008  to electronic assembly  2024 . Similarly, a second lengthwise passage in shaft  2010  can support a threaded rod that couples to a scissor jack within sensor head  2002  for raising and lowering support structures  2004  and  2006  as disclosed herein. Although a cylindrical shape is disclosed, shaft  2010  can be formed having other shapes. In the example, shaft  2010  is rigid and does not bend or flex when used to insert sensored head  2002  into the spine region. In one embodiment, handle  2030 , shaft  2010 , support structure  2004 , and  2006  are formed of a polymer material such as polycarbonate. Alternatively, spinal instrument can comprise metal components or a combination of polymer and metal to form the structure. The metal components can comprise stainless steel. 
     Handle  2030  comprises a structure  2020  and a structure  2022 . The structures  2020  and  2022  can be formed to include one or more cavities, slots, or openings. A cavity  2026  is shaped to receive electronic assembly  2024  that is housed in handle  2030 . The cavity  2026  can include one or more features to support and retain electronic assembly  2024 . A slot  2032  can be used to guide and retain interconnect  2028  to electronic assembly  2024  for coupling. Structures  2020  and  2022  couple together to form handle  2030 . An opening  2034  on the distal end of handle  2030  receives proximal end  2018  of shaft  2010 . In one embodiment, structures  2020  and  2022  can be formed of a polymer or metal. In the example, sensored head  2002 , shaft  2010 , and structures  2020  and  2022  can be formed by a molding process using a polymer material such as polycarbonate. The structures  2020  and  2022  can be fastened together by mechanical, adhesive, welding, bonding or other attaching method. Similarly, proximal end  2018  of shaft  2010  can be coupled to opening  2034  on the distal end of handle  2030  by mechanical, adhesive, welding, bonding, or other attaching method. In general, the active circuitry within spinal instrument  2000  is isolated from the external environment and a rigid device is formed when sensored head  2002 , shaft  2010 , and handle  2030  are coupled together. In one embodiment, the sealing process is permanent and spinal instrument  2000  cannot be disassembled to replace components such as the power source (e.g. batteries) that can be included in electronic assembly  2024 . The handle  2030  can be formed having a shape that is ergonomic for positioning spinal instrument  2000 . The handle  2030  can include weights placed in interior cavities that improve the feel and balance of the device for the surgical procedure. Reinforcement structures can be added to stiffen spinal instrument  2000  thereby reducing device flex. The proximal end of handle  2030  includes a flange  2036  for being tapped by a hammer to aid in the insertion of sensored head  2002  into the spinal region. The flange is sized to accept a standard slap-hammer to aid in the removal of the sensor head from the spinal region. Flange  2036  and the proximal end of handle  2030  are reinforced to withstand hammer taps by the surgeon. 
     Electronic assembly  2024  controls a measurement process of spinal instrument  2000 . In the example, the components of the system are mounted to a printed circuit board. The printed circuit board can have multiple layers of interconnect. Components can be mounted on both sides of the printed circuit board. In one embodiment, the printed circuit board includes a connector  2040  for receiving and retaining interconnect  2028 . In the example, interconnect  2028  can be a flexible planar interconnect having copper traces thereon comprising five interconnects for coupling to sensors  2008 . A power source such as a battery can be mounted to the printed circuit board for powering electronic assembly  2024 . Communication circuitry of electronic assembly  2024  can wirelessly transmit measurement data to a remote system for viewing in real-time. Spinal instrument  2000  can also receive information or data through a wired or wireless connection. Spinal instrument  2000  can include display  2038  with a GUI to locally provide data to the surgeon. Spinal instrument  2000  can also be operatively coupled via a remote sensor system to allow control or feedback through vocal, visual, haptic, gestures, or other communicative means to simplify a workflow or reduce staff required for the procedure. 
       FIG. 16  illustrates a spine measurement system  2100  for providing intervertebral load and position of load data in accordance with an example embodiment. Spine measurement system  2100  is a more detailed illustration of a non-limiting example of spine measurement system  100  of  FIG. 1 . System  2100  can also include an insert instrument and external alignment devices. The system  2100  comprises spinal instruments  2102 A-F ( 2102 A,  2102 B,  2102 C,  2102 D,  2102 E, and  2102 F) that include active circuitry for measuring a parameter of the muscular-skeletal system. Spinal instruments  2102 A-F are a non-limiting example of spinal instrument  400  of  FIG. 2 , spinal instrument  410  of  FIG. 3 , and spinal instrument  2000 . In the example, spinal instruments  2102 A-F each include one or more sensors to measure load and position of load. 
     The system  2100  comprises a set of spinal instruments  2102 A-F where each tool has a different distraction height. Spinal instruments can also be provided having sensored heads of different lengths. As shown, the set of spinal instruments  2102 A-F have a sensored head length  2120 . An example of sensored heads having different head lengths is disclosed below and can be adapted to system  2100 . Each spinal instrument  2102 A,  2102 B,  2102 C,  2102 D,  2102 E, and  2102 F respectively has sensored heads  2104 A,  2104 B,  2104 C,  2104 D,  2104 E, and  2104 F. The surgeon selects the spinal instrument for an appropriate sensored head height that distracts a spinal region appropriate for a patient physiology. As shown, the six sensored heads  2104 A,  2104 B,  2104 C,  2104 D,  2104 E, and  2104 F respectively have heights A, B, C, D, E, and F. The six different heights A-F of sensored heads  2104 A-F are an example of what might be provided in a typical system. An example of a distraction height range for a set of sensored heads can be from 6 millimeters to 14 millimeters. An example range of the length of a sensored head can be from 22 millimeters to 36 millimeters. In general, the different height and lengths of sensored heads  2104 A-F of system  2100  are chosen to cover a statistically significant portion a patient population a surgeon is likely to see. The actual number of sensored heads having different height and lengths can vary depending on the application. In one embodiment, sensored head height and lengths that are out of the norm can be inventoried in the operating room but may not be part of the set provided initially during the procedure. The inventoried sensored heads can be made available to the surgeon in the event that the set does not provide a suitable sensored head height and length for the patient. 
     In general, spine measurement system  2100  measures a parameter of the spinal region. In the example, load and position of load are measured. Spinal instruments  2102 A-F can also measure the location and position in 3D space with one or more internal accelerometers within each tool. In one embodiment, an accelerometer identifies the trajectory, location and position of the sensored head in real-time. The accelerometer can be located in the handle of spinal instruments  2102 A-F with the electronic assembly. The one or more parameter measurements output by system  2100  provide quantitative data to support the procedure. For example, the surgeon exposes the spinal region and views the area of interest. The spinal instruments  2102 A-F is made available such that the surgeon can select and use at least one of the tools. Remote system  105  is typically placed outside the sterile field of the operating room. In one embodiment, each spinal instrument  2102 A-F may be stored in individual sterilized packaging that is not opened until the surgeon views the spinal region being repaired. The selection of a spinal instrument is patient specific due to variations in spine gap and patient physiology. In the example, the surgeon first determines the appropriate gap height and then opens a sterile package having the spinal instrument with the sensored head of the selected height. In one embodiment, the selected spinal instrument can be placed by a device that can initiate a power up sequence. The enabling process couples an internal power source of the tool to the electronic circuitry and sensors therein. Once powered up, the selected spinal instrument can be coupled to remote system  105 . Remote system  105  receives and displays data from the selected spinal instrument. Remote system  105  includes a GUI  107  for controlling user interaction and providing data on a display. The GUI  107  can provide different screens or windows at different steps of the procedure as a workflow that provides quantitative data to the surgeon in one or more formats such that the data supports the surgical outcome. 
     The surgeon holds the selected spinal instrument by the handle and directs the sensored head between the vertebrae. The enabled spinal instrument sends load, position of load, instrument position, and location data to the remote system  105  where it is displayed in real-time. As mentioned herein, the exterior surfaces of the sensored head are convex in shape such that the tip is narrowed allowing penetration between a separated space between vertebrae prior to distraction. The amount of force required to distract vertebrae can vary. A controlled force applied to the selected spinal instrument may be required to increase the opening between vertebrae. For example, a hammer can be used to tap the flange at the end of the handle of the selected spinal instrument to insert the sensored head between the vertebrae. 
     In the example, the final position of the sensored head corresponds to the location where a component such as a spinal cage can be placed in a subsequent step. The spinal cage would have a height and length substantially equal to the height and length of the sensored head of the selected spinal instrument. System  2100  measures and displays quantitative data from the selected spinal instrument such as trajectory, position, location, loading, and position of loading of the sensored head. The data supports the placement of the component in the location. More specifically, the loading and position of load on the component placed between the vertebrae can be substantial equal to the quantitative measurements from the selected spinal instrument when the component is placed and located in the final position of the sensored head when distracting the vertebrae. 
     The surgeon may find that the selected spinal instrument has a sensored head height that is larger or smaller than needed. The surgeon uses as many spinal instruments as required to distract the vertebrae to an appropriate height. This similarly applies to the selection of spinal instruments of different lengths. In one embodiment, the power source within each spinal instruments  2102 A-F can power the tool for only a single procedure. Moreover, spinal instruments  2102 A-F may not be capable of being sterilized for reuse without compromising the integrity of the device. The spinal instruments that have been removed from sterilized packaging can be disposed of after the surgical procedure is performed. The spinal instruments that remain in sterile packaging can be used in another procedure. The spinal instruments that are disposed of after being used can be replaced to complete the set. 
     An alternate approach can use a passive set of spinal instruments to do the initial distraction. The passive spinal instruments have no measurement capability. The surgeon identifies an appropriate distraction height between vertebrae with the passive spinal instruments. The set of passive spinal instruments have heads with equal heights as spinal instruments  2102 A-F. A spinal instrument is then selected from spinal instruments  2102 A-F having a height equal to the identified distraction height made by the passive spinal instrument. The selected spinal instrument is then inserted between the vertebrae. Quantitative data measurements are then taken by the selected spinal instrument in preparation for implanting a component between the vertebrae. The passive spinal instruments can also be low cost disposable or tools that can be sterilized after use. The alternate approach provides the benefit of minimizing the number of spinal instruments  2102 A-F used in the procedure. 
     A method of providing spinal instruments to an operating room is disclosed below. The steps of the method can be performed in any order. The example comprises a system that includes more than one spinal instruments having active circuitry for measurement of a spinal region. The non-limiting example is used to demonstrate a method that is applicable to other muscular-skeletal regions such as the knee, hip, ankle, spine, shoulder, hand, arm, and foot. In a first step, more than one spinal instrument is provided within the operating room. The spinal instruments are in individually sterilized packaging. In one embodiment, the spinal instruments each have a different distraction height and length. The surgeon exposes the spinal region and assesses the patient physiology. In a second step, one of the spinal instruments is selected. In the example, the spinal instrument is selected having an appropriate distraction height for the patient. The spinal instrument is used to measure a parameter of the spinal region such as load and position of load. In a third step, the selected spinal instrument is removed from the sterilized packaging. In a fourth step, the selected spinal instrument is enabled. In the example, the enabling process couples an internal power source to the circuitry in the selected spinal instrument thereby powering up the device for generating quantitative measurement data. 
     Powering up the selected spinal instrument enables communication circuitry within the device. In a fifth step, the selected spinal instrument couples to a remote system. In the example, the remote system is in the operating room within viewing range of the surgeon. The remote system includes a display for presenting the quantitative measured data from the selected spinal instrument. The remote system can indicate that the selected spinal instrument is enabled by audio, visual, or haptic feedback. 
     The distraction height can be determined using passive spinal distraction instruments prior to selecting the active spinal instrument. The surgeon selects a passive spinal instrument after the spine region is assessed or exposed. In a sixth step, the spinal region is distracted using the selected passive spinal instrument. The passive spinal instruments have no active circuitry for measurement. In the example, a set of passive spinal instruments has identical heights and lengths as the set of active spinal instruments. In a seventh step, the passive spinal instrument is removed from the spinal region after distraction with the selected passive spinal instrument. In an eighth step, the selected spinal instrument is inserted in the spinal region previously distracted by the selected passive spinal instrument. In the example, the selected spinal instrument has the same height and length as the selected passive spinal instrument. In a ninth step, the selected spinal instrument takes parameter measurements. The data can be wirelessly transmitted to a remote system for display or visualization of the procedure. 
     One or more of the active spinal instruments can be used during the procedure. In a tenth step, the active spinal instruments that were used to take measurements of the spinal region are disposed of after the procedure. In one embodiment, the passive spinal instruments can go through a sterilization process and are not disposed. Alternatively, the used passive spinal instruments can be disposed similar to the active spinal instruments. In an eleventh step, the spinal instruments that were used and disposed of are replaced. The replacements re-complete the set for a subsequent procedure. The remaining active spinal instruments that were not used are sterile as their sterilized packaging was not opened during the procedure and thus can be reused. 
       FIG. 17  illustrates a spine measurement system  2200  for providing intervertebral load and position of load data in accordance with an example embodiment. Spine measurement system  2200  is a more detailed illustration of a non-limiting example of spine measurement system  100  of  FIG. 1 . The system  2200  comprises a remote system  105  and a modular spinal instrument. System  2200  can also include an insert instrument and external alignment devices. The modular spinal instrument comprises a handle  2206 , a shaft  2208 , a plurality of removable sensored heads  2204 A-F, and a module  2210 . In general, the spinal instrument is a modular active device having components that can be coupled to handle  2206  and shaft  2208 . Three sets of removable sensored heads  2204 A-F ( 2204 A,  2204 B,  2204 C,  2204 D,  2204 E, and  2204 F),  2216 A-F ( 2216 A,  2216 B,  2216 C,  2216 D,  2216 E, and  2216 F), and  2218 A-F ( 2218 A,  2218 B,  2218 C,  2218 D,  2218 E, and  2218 F) are shown in system  2200 . There can be more or less than three sets of sensored heads provided in system  2200 . Sensored heads  2204 A-F,  2216 A-F, and  2218 A-F can be coupled to or removed from the distal end of shaft  2208 . Similarly, module  2210  can be coupled to or removed from a cavity  2214  of handle  2206 . An external surface of module  2210  can be shaped as part of an exterior surface of handle  2206  when attached. Module  2210  includes an electrical assembly  2212  comprising electronic circuitry for receiving, processing, and sending quantitative data from sensors in a sensored head. Module  2210  can also include a power source for powering spinal instrument  2202  during a procedure. Electrical interfaces and interconnect couple module  2210  to one of sensored heads  2204 A-F when respectively assembled to handle  2206  and shaft  2208 . 
     In general, sensored heads of different heights and different lengths are provided as part of the system for supporting spine measurements over a large statistical population of spine anatomy. The concept can be applied to the configuration disclosed in  FIG. 16  where additional sets of spinal instruments can be provided having different sensored head lengths. The modular spinal instrument is a measurement device and a distractor. Removable sensored heads  2204 A,  2204 B,  2204 C,  2204 D,  2204 E, and  2204 F respectively have a sensored head height of A, B, C, D, E, and F. Similarly, removable sensored heads  2216 A,  2216 B,  2216 C,  2216 D,  2216 E, and  2216 F and  2218 A,  2218 B,  2218 C,  2218 D,  2218 E, and  2218 F respectively have head height A, B, C, D, E, and F. The six different heights A-F of sensored heads  2204 A-F are an example of what might be provided in a typical system. Each set can set can have more or less than the number of heights show. As mentioned previously, an example range for sensored head heights can be 6 millimeters to 14 millimeters. Sensored heads  2204 A-F,  2216  A-F, and  2218 A-F respectively have a sensored head length of  2220 ,  2222 , and  2224 . The surgeon selects the appropriate sensored head length based on the patient spine anatomy. An example range for sensored head lengths can be from 22 millimeters to 36 millimeters. 
     The actual number of sensored heads having different heights can vary depending on the application. In one embodiment, sensored head height and length that are out of the norm can be inventoried in the operating room but may not be part of the set provided within the surgical field of the operating room. They can be made available to the surgeon in the event that the set does not provide a suitable sensored head height and length for the patient. The sensored head of spinal instrument  2202  is inserted in the spinal region thereby generating a gap or spacing approximately equal to the height of the sensored head. Spinal instrument  2202 A-F is a non-limiting example of spinal instrument  400  of  FIG. 2  and spinal instrument  410  of  FIG. 3 . In the example, spinal instruments  2202 A-F includes one or more sensors to measure load and position of load. 
     In general, system  2200  can be used in an operating room to provide quantitative measurements on the spinal region. A surgeon exposes and reviews the spinal region prior to distraction. The surgeon may select one of the sets of sensored heads  2204 A-F,  2216 A-F, and  2218 A-F respectively having the sensored head lengths  2220 ,  2222 , and  2224 . For example, the surgeon chooses the set of sensored heads  2204 A-F having the shortest head length  2220 . The surgeon can then select one of sensored heads  2204 A-F having a height that distracts the spinal region appropriate for a patient physiology. In one embodiment, sensored heads  2204 A-F are in individual sterilized packaging. The selected sensored head is removed from the individual sterilized packaging. The surgeon couples the selected sensored head to the distal end of shaft  2208 . Similarly, module  2210  is removed from sterilized packaging and installed in handle  2206 . System  2200  is then enabled for providing quantitative data from spinal instrument  2202 . The enabling process can couple an internal power source of the tool to the electronic circuitry and sensors therein. Once powered up, the selected spinal instrument can be coupled to remote system  105 . Remote system  105  will provide indication that spinal instrument  2202  is enabled and operating. Remote system  105  receives and displays data from the selected spinal instrument. Remote system  105  includes a GUI  107  for initiating a workflow, controlling user interaction, and providing data on a display. The GUI  107  can provide different screens or windows at different steps of the procedure as a workflow that provides quantitative data to the surgeon in or more formats such that the data supports the surgical outcome. 
     The surgeon during the procedure may find that the selected sensored head has a height that is larger or smaller than needed. Spinal instrument  2202  can be removed from the spinal region to replace the sensored head. The sensored head can be replaced as many times as necessary until an appropriate distraction height is achieved and the quantitative measurements of spinal instrument  2202  provide assessment of the spinal region. In one embodiment, the power source within module  2210  can power the tool for a single surgical application. Module  2210  can be sealed to prevent replacement of the power source. Furthermore, after a completed procedure, module  2210  and used sensored heads  2204 A-F are disposed of in a manner to prevent reuse. A complete set of sensored heads  2204 A-F can be made for a subsequent procedure by replacing the used sensored heads and combining with the unused remaining sensored heads  2204 A-F. Spinal instrument  2202  provides the benefit of lowering cost by replacing only a portion of the system. 
     A method of measuring a spinal region is disclosed below. The steps of the method can be performed in any order. The example comprises a spinal instrument having active circuitry for measuring a parameter, position, and trajectory. The spinal instrument can be used to distract the spinal region. The spinal instrument is modular allowing rapid changes during a procedure to change a distraction height. The non-limiting example is used to demonstrate a method that is applicable to other muscular-skeletal regions such as the knee, hip, ankle, spine, shoulder, hand, arm, and foot. 
     In a first step, one of a plurality of removable sensored heads is selected. The plurality of sensored heads comprises a set where each sensored head has a different height. One or more sets of sensored heads can be provided where the sensored heads of a set have a different head length than the other sets. In one embodiment, each sensored head is in an individual sterilized package. The selected sensored head is removed from the sterilized packaging. In a second step, a selected sensored head is coupled to a distal end of a shaft of the instrument. In one embodiment, the sensored head and the shaft respectively have a female and male coupling. The male coupling is inserted into the female coupling and locked into place. The locking step can be a rotation of the sensored head to a position that includes one or more retaining features. In a third step, a module is coupled to the spinal instrument. The module includes an electronic assembly for receiving data from sensors in the sensored head. In one embodiment, the module is placed in a cavity of the handle. The module includes a retaining feature that locks it into place in the handle but allows removal of the module. The electronic assembly operatively couples to the sensored head via electrical interfaces and interconnect in the instrument. The instrument can be enabled for taking measurements during the distraction process. 
     In a fourth step, the sensored head on the instrument is removed. In one embodiment, the active circuitry in the instrument is disabled prior to the sensored head removal process. In the example, the sensored head is rotated back from the locked position such that the shaft can be withdrawn. In a fifth step, a sensored head is selected from the remaining sensored heads. Typically, the previous sensored head is replaced to select a different distraction height based on the patient physiology. As before, the newly selected sensored head is removed from the individualized sterilized packaging. In a sixth step, the newly selected sensored head is coupled to the distal end of the shaft of the instrument as disclosed above. In a seventh step, the instrument is enabled for generating quantitative measurement data on the muscular-skeletal system. The process of enabling couples a power source within the module to the electronic assembly to power the instrument. In one embodiment, the power source is disconnected from the electronic assembly while in the sterilized packaging to prevent discharge and maximize life. In an eighth step, the used sensored heads and the module are disposed of after a procedure. The sensored head and the module are removed from the instrument and disposed of appropriately. In one embodiment, the main body of the instrument comprising the handle and shaft can be sterilized for a subsequent procedure. 
       FIG. 18  illustrates an exploded view of module  2210  and handle  2206  in accordance with an example embodiment. Module  2210  and handle  2206  are part of spinal instrument  2202  of  FIG. 17 . Reference can be made to components of  FIG. 17  and  FIG. 18 . A removable module  2210  is a non-limiting example that can be applied to instruments and tools described herein to lower system cost and provide a performance upgrade path. Module  2210  comprises an electronic assembly  2212  for receiving, processing, and sending measurement data from sensors in the sensored head of spinal instrument  2202 . Electronic assembly  2212  corresponds to electronic assembly  2024  of  FIG. 15  and includes at least some of the circuitry described in  FIG. 11  and  FIG. 12 . Electronic assembly  2212  is sealed within module  2210  and is isolated from an external environment. Module  2210  couples to and is removable from spinal instrument  2202 . In general, spinal instrument  2202  includes an electrical interface that couples to module  2210 . In the example, spinal instrument  2202  includes a cavity  2214  for receiving module  2210 . An electrical interface  2308  in cavity  2214  couples to and aligns with electrical interface  2302  when module  2210  is inserted. In one embodiment, electrical interfaces  2302  and  2308  are held together under pressure to ensure electrical coupling of each interface. For example, electrical interface  2308  can include spring contacts that compress under insertion of module  2210  to maintain coupling under force. A flexible interconnect  2310  couples to electrical interface  2308  in cavity  2214  of handle  2206 . Flexible interconnect  2310  extends through the shaft of spinal instrument  2202  for coupling to sensors in a sensored head region of the device. 
     In the example, module  2210  can be made from a polymer material such as polycarbonate. Module  2210  can be molded in two or more pieces and assemble together to form a housing or enclosure. Electronic assembly  2212  can be placed in a molded cavity that retains and orients the circuitry within module  2210 . Electronic assembly  2212  can be coupled to electrical interface  2302  using a flexible interconnect. Electronic assembly  2212  and electrical interface  2302  can include one or more connectors that couple to the flexible interconnect to simplify assembly. The remaining molded pieces can be attached to form the housing or enclosure using sealing methodologies such as adhesives, welding, mechanical fastening, or bonding. In one embodiment, wireless communication is used to send measurement data from spinal instrument  2202  to a remote system for display and visualization. A polymer material such as polycarbonate is transmissive to wireless signals allowing the measurement data to be transmitted from within module  2210  through the enclosure. 
     Module  2210  further includes a feature  2304  to align and retain the device when coupled to spinal instrument  2202 . Feature  2304  fits into opening  2312  when module  2210  is inserting into cavity  2214  of handle  2206 . A locking mechanism is shown in an opposing view of module  2210 . The locking mechanism comprises a flexible tab  2306  having a flange  2316  that extends from tab  2306 . Flange  2316  corresponds and fits into opening  2314  in cavity  2214  of handle  2206 . The features  2304  and  2316  respectively in openings  2312  and  2314  retain and prevent module  2210  from disengaging during use of spinal instrument  2202 . A removal process of module  2210  requires flexible tab  2306  to be flexed such that flange  2316  is removed from opening  2214 . Module  2210  can then be disengaged from cavity  2214  while bending flexible tab  2306  to prevent flange  2316  from coupling to opening  2314 . 
       FIG. 19  illustrates a shaft  2404  for receiving a removable sensored head  2402  in accordance with an example embodiment. The illustration shows a detailed view of sensored head  2402  and a distal end  2404  of shaft  2208  of  FIG. 17 . Reference can be made to components of  FIG. 17  and  FIG. 18 . Sensored head  2402  corresponds to sensored heads  2204 A-F of  FIG. 17  for providing an example of a removable sensored head from spinal instrument  2202 . In general, a proximal end of sensored head  2402  includes a coupling that mates with a coupling on the distal end  2404  of shaft  2208  of the tool. The couplings mate together to physically attach sensored head  2402  and shaft  2208  for a distraction and measurement process. The coupling on the proximal end of sensored head  2402  and the coupling on distal end  2404  of shaft  2208  when attached form a rigid structure that can be inserted in the spinal region and moved to position the device under load. Sensored head  2402  includes one or more sensors for measuring a parameter of the spinal region. The sensors can be coupled by a flexible interconnect within sensored head  2402  to an electrical interface in proximity to the coupling on sensored head  2402 . Similarly, an electronic assembly can be coupled to an electrical interface on the distal end  2404  of shaft  2208  by a flexible interconnect that extends through a lengthwise passage of shaft  2208 . The electrical interfaces of sensored head  2402  and distal end  2404  of shaft  2208  align and couple the electrical assembly to the sensors when attached together by the couplings. Thus, sensored head  2402  can be removed and replaced when required during the procedure. 
     A female coupling is accessible through an opening  2406  at a proximal end of the sensored head  2402  in the example attachment mechanism. A male coupling  2408  extends from distal end  2404  of shaft  2208 . The male coupling  2408  comprises a cylindrical extension  2414  having a retaining feature  2416 . The coupling types can be reversed such that the male coupling is on sensored head  2402  and the female coupling on distal end  2404  of shaft  2208 . An electrical interface  2410  can be formed on the distal end of shaft  2404 . Male coupling  2408  extends centrally from electrical interface  2410 . Electrical interface  2410  includes spring-loaded pins  2412  for electrical coupling and seals the distal end  2404  of shaft  2208 . Spring-loaded pins  2412  are located on a periphery of electrical interface  2410  around male coupling  2408 . Spring loaded pins  2412  couple to a flexible interconnect within shaft  2208 . Spring loaded pins  2412  can compress under pressure applied by the attaching process. The force applied by spring loaded pins  2412  to the corresponding electrical interface on sensored head  2402  ensures reliable electrical coupling from sensors to the electrical assembly when attached. Spring-loaded pins  2412  include a gasket or seal to isolate an interior of shaft  2208  from an external environment. In one embodiment, electrical interface  2410  can be sealed allowing sterilization of shaft  2404  and handle  2206  for reuse in a subsequent procedure. As shown, there are five spring-loaded pins  2412  on electrical interface  2410 . The five pins couple to four sensors in sensored head  2402  and ground. In the example, the four sensors measure load and position of load applied by the spinal region to the exterior surfaces of sensored head  2402 . 
       FIG. 20  illustrates a cross-sectional view of a female coupling  2502  of sensored head  2402  in accordance with an example embodiment. In general, male coupling  2408  couples to female coupling  2602  to retain sensored head  2402  to distal end  2404  of shaft  2208 . Reference may be made to  FIG. 17 ,  FIG. 18 , and  FIG. 19 . Opening  2406  of sensored head  2402  receives the distal end  2404  of shaft  2208 . Female coupling  2502  includes an electrical interface  2504  that corresponds to electrical interface  2410  on distal end  2404  of shaft  2208 . Electrical interface  2504  includes electrical contact points  2506  that align to spring loaded pins  2412  when sensored head  2502  is attached to distal end  2404  of shaft  2208 . Electrical interconnect  2508  couples electrical contact points  2506  to sensors in sensored head  2402 . Female coupling  2502  includes a keyed opening  2510  that is located centrally on the structure. Keyed opening  2510  has a single position that allows retaining feature  2416  to be inserted through female coupling  2502 . 
     In one embodiment, the outer diameter of electrical interface  2410  is approximately equal to or smaller than the inner diameter of opening  2406 . The fit of electrical interface  2410  to opening  2406  supports the rigid coupling of sensored head  2402  to shaft  2404 . Sensored head  2402  is rotated after retaining feature  2416  is inserted through keyed opening  2510 . A spring-loaded barrier  2512  is in a rotation path of retaining feature  2416 . Spring-loaded barrier  2512  can compress to approximately surface level of the surface of female coupling  2502 . The surface of spring-loaded barrier  2512  can be curved or spherical. Retaining feature  2416  when rotated compresses spring-loaded barrier  2512  and rotates over the structure during the attaching process. The spring in spring loaded barrier  2512  raises the structure back above the surface of female coupling  2502  after retaining feature rotates past. A rotation stop  2514  in the rotation path prevents further rotation of sensored head  2402  by blocking retaining feature  2416 . 
     In one embodiment, retaining feature  2416  is stopped between rotation stop  2514  and spring-loaded barrier  2512 . Rotation stop  2514  and spring loaded barrier  2512  form a barrier to prevent movement and rotation of sensored head  2402  when in use. Furthermore, rotation stop  2514  positions sensored head  2402  such that electrical interface  2504  and electrical interface  2410  are aligned for coupling sensors in sensored head  2402  to the electrical assembly for providing sensor measurement data. In general, retaining feature  2416  is held against the surface of female coupling  2502  under force. For example, the rotation path of retaining feature  2416  can be sloped to increase the force between retaining feature  2416  and the surface of female coupling  2502  as it approaches rotation stop  2514 . Spring loaded pins  2412  can also apply a force that presses retaining feature  2416  to the surface of female coupling  2502 . 
       FIG. 21  illustrates an exploded view of a spinal instrument  2600  in accordance with an example embodiment. Spinal instrument  2600  is a more detailed illustration of a non-limiting example of spinal instrument  102  of  FIG. 1 , spinal instrument  400  of  FIG. 2 , and spinal instrument  410  of  FIG. 3 . Spinal instrument  2600  is a measurement device having a sensored head  2002  that incorporates at least one sensor for measuring a parameter of a spinal region. Spinal instrument  2600  comprises a housing  2602 , housing  2604 , electronic assembly  2626 , interconnect  2630 , and sensors  2638 . In general, housings  2602  and  2604  couple together to isolate electronic assembly  2626 , interconnect  2630 , and sensors  2638  from an external environment. Housings  2602  and  2604  respectively include a support structure  2610  and a support structure  2616 . Sensors  2638  couple to support structures  2610  and  2616  to measure the parameter of the spinal region. In a surgical procedure, support structures  2610  and  2616  can come in contact with the spinal region. In one embodiment, support structures  2610  and  2616  comprise a sensored head of spinal instrument  2600  that can compress sensors  2638  when a compressive force is applied. 
     Housing  2602  comprises a handle portion  2606 , a shaft portion  2608 , and the support structure  2610 . Similarly, housing  2604  comprises a handle portion  2612 , a shaft portion  2614 , and the support structure  2616 . Housing  2604  further includes a flange  2644 , a cavity  2618 , and a lengthwise passage  2646 . Flange  2644  is a reinforced structure on a proximal end of the handle of spinal instrument  2600 . Flange  2644  can be struck with a hammer or mallet to provide an impact force to insert the sensored head of spinal instrument  2600  into the spinal region. Cavity  2618  supports and retains an electronic assembly  2626 . Electronic assembly  2626  receives, processes, and sends quantitative measurements from sensors  2638 . A power source  2628  couples to electronic assembly  2626 . In one embodiment, the power source can be one or more batteries that are mounted on a printed circuit board of electronic assembly  2626 . Electronic assembly  2626  can be coupled to sensors  2638  by a flexible interconnect  2630 . Flexible interconnect  2630  can comprise a flexible substrate having patterned electrically conductive metal traces. Electronic assembly  2626  can have one or more connectors that couple to flexible interconnect  2630  to simplify assembly. Flexible interconnect  2630  couples through a lengthwise passage in the shaft of spinal instrument  2600 . In one embodiment, lengthwise passage  2646  is used as a channel for flexible interconnect  2630  that couples cavity  2618  to a sensored head region. Retaining features  2640  can retain power source  2628 , electronic assembly  2626 , and flexible interconnect  2630  in place when assembling spinal instrument  2600 . Retaining features  2640  can comprise foam that can be coupled to components and compress without damaging active components as housing  2602  is coupled to housing  2604 . 
     The sensored head of spinal instrument  2600  comprises support structure  2610 , support structure  2616 , interconnect  2634 , sensor guide  2636 , and sensors  2638 . The exterior surfaces of support structures  2610  and  2616  may be shaped convex to support insertion into the spinal region. Interconnect  2634  is a portion of flexible interconnect  2630  that overlies an interior surface of support structure  2616 . Flexible interconnect  2634  includes conductive traces that couple to electrical contact regions of sensors  2638 . Sensor guide  2636  overlies interconnect  2634 . In one embodiment, interconnect  2634  and sensor guide  2636  can be aligned and retained within support structure  2616  by a peripheral sidewall. Sensor guide  2636  includes openings for retaining and positioning sensors  2638 . In the example, sensors  2638  are force, pressure, or load sensors. Interconnect  2634  can have electrical contact regions that align with the openings of sensor guide  2636 . The electrical contact regions are exposed for coupling to sensors  2638  through the openings of sensor guide  2636 . Sensor guide  2636  also retains and positions sensors  2638  such that the electrical interface of each sensor can couple to a corresponding electrical contact region of interconnect  2634 . The electrical interface of sensors  2638  can be coupled to the corresponding electrical contact region of interconnect  2634  by such means as solder, conductive epoxy, eutectic bond, ultrasonic bond, or mechanical coupling. Sensor guide  2636  also positions sensors to couple to support structure  2610  or  2616  at predetermined locations. In one embodiment, sensors  2638  contact an internal surface of support structure  2610  or  2616  that correspond to locations on the external surfaces. Positioning the sensors via sensor guide  2636  allows the position of the applied load on the external surface of support structure  2610  to be calculated. A load plate  2642  can be coupled between sensors  2638  and the interior surface of support structure  2610 . Load plate  2642  distributes loading from the interior surface of support structure  2610  to each sensor  2638 . 
     As mentioned previously, housings  2602  and  2604  when coupled together support compression of the sensored head of spinal instrument  2600 . A compressive force applied across the external surfaces of support structures  2610  and  2616  is directed to sensors  2638 . Other components such as support structure  2610 , support structure  2616 , load plate  2642 , and interconnect  2634  in the compression path do not deform under load. In one embodiment, load plate  2642  comprises a metal such as steel or stainless steel. A compressible adhesive  2624  can be used to couple the periphery of support structures  2610  and  2616  thereby allowing movement of the sensored head and sensors  2638  therein over the measurement range. The compressible adhesive  2624  can be an adhesive such as a silicone based adhesive. The adhesive  2624  is elastic such that the sensored head returns to an unloaded position or moves to a repeatable unloaded height after being compressed. In one embodiment, a second adhesive  2622  is used around a remaining periphery of housings  2602  and  2604  to seal and couple the structures together. Adhesives  2622  and  2624  are applied prior to coupling housings  2602  and  2604  together. Adhesive  2622  can be a bonding adhesive such as a glue or epoxy that mates the peripheral surfaces together. In other words, the bonded surfaces coupled by adhesive  2622  do not have a range of compression as the surfaces are held in contact to one another by adhesive  2622 . Alternatively, adhesive  2624  can be used around the entire periphery to couple housings  2602  and  2604  together. 
       FIG. 22  illustrates a cross-sectional view of a shaft region of spinal instrument  2600  in accordance with an example embodiment. The shaft region is a cross-sectional view comprising shaft  2608  and  2614  respectively of housing  2602  and housing  2604  coupled together. The illustration provides detail on the coupling of housings  2602  and  2604  that corresponds a portion of the shaft region and a handle region of spinal instrument  2600 . Reference can be made to components of  FIG. 21 . In general, a housing for the active components of spinal instrument  2600  is formed by coupling housing  2602  to housing  2604 . In one embodiment, peripheral surfaces of housing  2602  and housing  2604  are fastened together using more than one adhesive. The peripheral surfaces of housings  2602  and housing  2604  mate such that the structures align, form a barrier, and provide surface area for bonding. In the example, a peripheral surface  2702  of housing  2602  has a geometric shape such as a triangular extension. A peripheral surface  2704  of housing  2604  has a corresponding geometric shape such as a v-shaped groove for receiving the triangular extension. Other tongue and groove geometry can be used such as square, round, or other polygonal shapes. Joints such as a butt-joint or a lap joint can also be used. The profile of the peripheral surfaces of a sensored head region differs from peripheral surfaces  2702  and  2704  of the shaft and handle regions. In the example, surfaces of the triangular extension of peripheral surface  2702  contact surfaces of the v-shaped groove of peripheral surface  2704  when housings  2602  and  2604  are coupled together. 
     As mentioned previously, peripheral surfaces  2702  and  2704  respectively of housings  2602  and  2604  couple the handle portion and the shaft portion of spinal instrument  2600 . Peripheral surface  2702  fits into peripheral surface  2704  providing alignment feedback during assembly. Referring to  FIG. 21 , the handle portion and the shaft portion corresponds to the area where adhesive  2622  are applied. In the example, adhesive  2622  attaches or bonds peripheral surfaces  2702  and  2704  together with no play or gap between the surfaces other than the adhesive material. In one embodiment, the handle portion and the shaft portion coupled by peripheral surfaces  2702  and  2704  cannot be disassembled without damage to the housing due to the bond integrity of the joint. The shape of peripheral surfaces  2702  and adhesive  2622  seals and isolates an interior of spinal instrument  2600  from an external environment. As shown, a portion of the distal end of the shaft and the peripheral surfaces of support structures  2610  and  2616  can have a different profile as disclosed herein. Similarly, other geometric shaped surfaces or curved surfaces can be used for peripheral surfaces  2702  and  2704 . 
       FIG. 23  illustrates a cross-sectional view of a sensored head region of spinal instrument  2600  in accordance with an example embodiment. The illustration provides detail on the coupling of support structures  2610  and  2616  corresponding to the sensored head region and a distal portion of the shaft region. Reference can be made to components of  FIG. 21  and  FIG. 22 . In general, the sensored head region includes at least one sensor for measuring a parameter of the spinal region. In the example, sensors for measuring a force, pressure, or load are coupled between support structures  2610  and  2616 . The support structures  2610  and  2616  compress the sensors when inserted into the spinal region. The sensors output a signal corresponding to the compression. Thus, support structures  2610  and  2616  move in relation to one another allowing compression of the sensors. 
     As shown, the periphery of housing  2602  and housing  2604  corresponding to support structures  2610  and  2616  of the sensored head region couple together in a manner allowing movement. Support structure  2610  of housing  2602  includes a peripheral surface  2802  having a triangular shaped region. Support structure  2616  of housing  2604  includes a peripheral surface  2804  having a v-shaped groove. In one embodiment, a gap  2806  exists between peripheral surface  2802  and peripheral surface  2804  when housing  2602  is coupled to housing  2604 . More specifically, the surfaces of the triangular shaped region of peripheral surface  2802  do not contact the surfaces of the v-shaped groove of peripheral surface  2804  when peripheral surface  2702  of housing  2602  contacts peripheral surface  2704  of housing  2604  as shown in  FIG. 22 . Gap  2806  allows a compressive force applied to the external surfaces of support structures  2610  and  2616  to move such that the height of the sensored head region is reduced. Gap  2806  is larger than a change in height of the sensors over the measurement range of spinal instrument  2600 . Although surfaces are shown as triangular and v-groove shaped in the non-limiting example, surfaces  2802  and  2804  can take other shapes that support gap  2806  and movement of support structures  2610  and  2616 . 
     The sensored head region and the portion of the distal end of the shaft corresponds to the area where adhesive  2624  shown in  FIG. 21 . In the example, adhesive  2624  elastically attach peripheral surfaces  2802  and  2804  together. Adhesive  2624  fills gap  2806  between the peripheral surfaces  2802  and  2804 . Support structures  2610  and  2616  form a housing for the sensor assembly of spinal instrument  2600 . Adhesive  2624  can compress when a load is applied across support structures  2610  and  2616 . Adhesive  2624  rebounds elastically after compression of the support structures  2610  and  2616  thereby returning the sensored head region back to gap  2806  when unloaded. Filling gap  2806  with adhesive  2624  seals and isolates an interior of the sensored head region and the distal end of the shaft from an external environment. In one embodiment, adhesive  2622  and adhesive  2624  are applied at approximately the same time during the assembly process. Adhesive  2622  is applied to at least one of peripheral surfaces  2702  and  2704  of  FIG. 22 . Similarly, adhesive  2624  is applied to at least one of peripheral surfaces  2802  and  2804 . Housing  2602  and housing  2604  are then coupled together to form the housing for the active system of spinal instrument  2600 . 
     In one embodiment, support structure  2610  and support structure  2616  can be modified to make the exterior load bearing surfaces flexible. A peripheral groove  3006  is formed in the support structure  2610 . In general the groove is formed circumferentially such that the external load-bearing surface can flex. A force, pressure, or load is directed to sensors underlying the load bearing surface. The flexible support structure load-bearing surface minimizes load coupling that can cause measurement error. For example, grooves  3006  reduce load coupling from peripheral surface  2802  to  2804 . Loading applied to the load-bearing surface of support structure  2610  is coupled through interior surface  3004  to load sensors  2638 . Grooves  3006  can bound interior surface  3004 . A load plate can be used to distribute loading from internal surface  3004  to sensors  2636 . Similarly, a groove  3008  is formed circumferentially in support structure  2616  such that the external load-bearing surface of support structure  2616  can flex. A force, pressure, or load applied to the load-bearing surface of support structure  2616  is directed through interior surface  3002  to sensors  2638 . The load coupling through surface  2804  to surface  2802  is minimized by the flexible external load-bearing surface of support structure  2616 . Grooves  3008  can bound interior surface  3002 . 
       FIG. 24  illustrates an exploded view of a sensored head region of spinal instrument  2600  in accordance with an example embodiment. In general, support structure  2616  includes a sidewall  2904  having peripheral surface  2804 . As shown, the peripheral surface  2804  of sidewall  2904  is a v-groove. Interconnect  2634  of flexible interconnect  2634  couples sensors  2638  to electronic assembly  2626 . Flexible interconnect  2634  extends through the shaft of spinal instrument  2600  to the sensored head region. In one embodiment, interconnect  2634  can be shaped to fit in support structure  2616 . Interconnect  2634  overlies an interior surface of support structure  2616 . Interconnect  2634  is positioned, aligned, and retained on support structure  2616  by sidewalls  2904 . 
     As shown, sensor guide  2636  overlies interconnect  2634 . Sensor guide  2636  positions and holds sensors  2838 . In one embodiment, sensor guide includes openings  2906  for four sensors. The four sensors  2838  can determine a load magnitude applied to support structures  2610  and  2616  as well as position of the applied load. Electrical contacts of sensor  2638  couple to corresponding contact regions on interconnect  2634 . In one embodiment, each sensor  2638  has two contacts, one of which is a common ground. Openings  2906  of sensor guide  2636  align to and expose the underlying interconnect  2634 . Moreover, openings  2906  show contact regions of interconnect  2634  for coupling to a sensor. A load plate  2636  can overlie sensors  2638 . Load plate  2636  is an optional component for distributing an applied force, load, or pressure applied to support structures  2610  and  2616  to sensors  2638 . Load plate  2636  couples to an interior surface of support structure  2610 . Load plate  2636  can also be positioned and aligned in the sensored head region by sidewalls  2904  of support structure  2616 . Alternatively, support structure  2610  can have a retaining feature for load plate  2636 . 
       FIG. 25  illustrates a cross-sectional view of an assembled sensored head region of spinal instrument  2600  in accordance with an example embodiment. The illustration provides detail on the stacked assembly within support structures  2610  and  2616  corresponding to the sensored head region. Reference can be made to components of  FIG. 21 ,  FIG. 23 , and  FIG. 24 . Support structure  2616  includes sidewall  2904  that bounds interior surface  3002 . In the example, groove  3008  is adjacent to sidewall  2904  and bounds surface  3002  of support structure  2616 . Groove  3008  promotes support structure  2616  to flex under loading. Flexible interconnect  2630  couples electronic assembly  2626  to sensors  2638 . Flexible interconnect  2630  includes interconnect  2634  that is housed in the sensored head region of spinal instrument  2600 . Interconnect  2634  includes contact regions for coupling to sensors  2638 . Interconnect  2634  overlies interior surface  3002  of support structure  2616 . Interconnect  2634  is retained, aligned, and positioned within the sensored head region by sidewall  3002  of support structure  2616 . 
     Sensor guide  2636  overlies interconnect  2634 . Sensor guide  2636  is shaped similar to interconnect  2634 . Sensor guide  2636  is retained, aligned, and positioned within the sensored head region by sidewall  2904  of support structure  2616 . Sensor guide  2636  has openings that align with the contact regions of interconnect  2634 . Sensors  2638  are placed in the openings of sensor guide  2636  such that contacts of sensors  2638  couple to contact regions on interconnect  2634 . In one embodiment, sensor guide plate  2636  comprises a non-conductive polymer material. In the example, sensors  2638  extend above a surface of sensor guide  2636  for coupling to load plate  2642  or an interior surface of support structure  2610 . 
     A load plate  2642  is an optional component of the stacked assembly. Load plate  2642  distributes the force, pressure, or load applied to support structures  2610  and  2616  to sensors  2638 . In one embodiment, load plate  2642  can be shaped similarly to interconnect  2634  and sensor guide  2634 . Load plate  2642  overlies and couples to sensors  2638 . In the example, support structure  2610  includes a peripheral sidewall that positions load plate  2642  over sensors  2638 . In the example, groove  3006  is adjacent to the peripheral sidewall of support structure  2610  and bounds surface  3004  of support structure  2610 . Groove  3006  promotes support structure  2610  to flex under loading. An internal surface  3004  of support structure  2610  couples to load plate  2642 . Peripheral surface  2802  of support structure  2610  is coupled to peripheral surface  2804  of support structure  2616  in a manner to support movement under a compressive load. In particular, sensors  2638  can change in height under loading. As disclosed above, elastic adhesive  2624  fills a gap between peripheral surfaces  2802  and  2804 . Adhesive  2624  couples support structures  2610  and  2616  together. The adhesive  2624  seals and isolates the stacked assembly of the sensored head region from an external environment. Moreover, adhesive  2624  can compress such that a force, pressure, or load applied to support structures  2610  and  2616  translates from the external surfaces to sensors  2638  for measurement. 
     While the present invention has been described with reference to particular embodiments, those skilled in the art will recognize that many changes may be made thereto without departing from the spirit and scope of the present invention. Each of these embodiments and obvious variations thereof is contemplated as falling within the spirit and scope of the invention.