Patent Publication Number: US-2003236472-A1

Title: Systems and methods for moving anatomical elements

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
     [0001] This application claims the benefit of the filing date of Provisional Application No. 60/390,131 filed on Jun. 19, 2002. 
    
    
     
       BACKGROUND  
       [0002] Anatomical elements can be moved or separated in surgical procedures to increase the working space available to access the space between, around and/or through the anatomical elements. For example, anatomical elements can include tissues of the patient that require separation to access a location in the patient&#39;s body. In another example, anatomical elements can include adjacent bony portions that require separation for insertion of an implant or the like between the bony portions.  
       [0003] Under-separation of the anatomical elements may not provide the desired or maximum access to the space between, around and/or through the elements. Under-separation can also result in additional wear and/or stress on an implant positioned between the anatomical elements. Over-separation of the anatomical elements can result in cutting or tearing of the tissue connecting the anatomical elements. Other complications can result depending on the location of tissue separation, such as dysphasia in anterior cervical approaches. Over-separation can also hyperextend the space between the anatomical elements. For example, if the anatomical elements were adjacent bony portions, a loose implant fit in the space between the elements may result with over-separation.  
       [0004] Over and under-separation of anatomical elements can be a surgical result stemming from the surgeon having to use subjective judgements, tactile feedback, and visual observations of the anatomical elements to determine the separation employed on the anatomical elements during the surgical procedure. Furthermore, differing separations of the same anatomical elements may be desirable for different types of implants and procedures. The lack of objective information regarding the anatomical elements can prevent the surgeon from achieving an optimal separation result for the surgical procedure.  
       SUMMARY  
       [0005] There is provided systems and methods for moving at least one anatomical element relative to another and providing objective feedback of one or more separation characteristics of the separated anatomical elements. The separation characteristic(s) can provide an objective indication to the surgeon of the condition of the anatomical elements, which can then be employed to obtain a surgical result.  
       [0006] According to one aspect, there is a system and method for moving anatomical elements having a feedback system that determines a separation characteristic from the anatomical elements.  
       [0007] According another aspect, there is a system and method for moving anatomical elements having a feedback system that determines a separation characteristic from the anatomical elements. The separation characteristic is compared to a desired separation characteristic. When the desired separation characteristic is obtained, a construct is positioned in the space between or adjacent the anatomical elements.  
       [0008] According another aspect, there is a system and method for moving anatomical elements having a feedback system that determines a separation characteristic from the anatomical elements. The separation characteristic is compared to a threshold separation characteristic. When a threshold characteristic is obtained, further surgical steps can be undertaken. For example, a device can be inserted in the space between the anatomical elements, or engaged to the anatomical elements. In another example, steps can be taken to bring the separation characteristic below the threshold by, for example, moving the anatomical elements toward one another or increasing an incision size.  
       [0009] In one aspect, the system includes a first member having a feedback system associated therewith that is contactable with a first anatomical element. The feedback system determines a separation characteristic of the first anatomical element and a second anatomical element as the first anatomical element is moved relative the second anatomical element.  
       [0010] In one aspect, the system includes a first member having a feedback system associated therewith contactable with a first soft tissue element. The feedback system determines a separation characteristic of the first soft tissue element and a second soft tissue element as the first soft tissue element is moved relative to the second soft tissue element.  
       [0011] In another aspect, a surgical tool for moving soft tissue elements includes a first member contactable with a first soft tissue element. The first soft tissue element is spaced from a second soft tissue element. A feedback system associated with the surgical tool is operable to determine a separation characteristic of the first and second soft tissue elements.  
       [0012] In a further aspect, a system for moving soft tissue elements is provided. The system comprises a first member contactable with a first soft tissue element that is spaced from a second soft tissue element. A second member is contactable with the second soft tissue element. A feedback system associated with at least one of the first and second members is operable to determine a separation characteristic of the first and second soft tissue elements.  
       [0013] In one aspect, a system for moving a first soft tissue element and a second soft tissue element is provided. The system comprises a member contactable with the first soft tissue element and the second soft tissue element. The member maintains the first soft tissue element in a spaced apart relationship with respect to the second soft tissue element. A feedback system associated with the member determines a separation characteristic of the first and second soft tissue elements.  
       [0014] In another aspect, a system includes an instrument for moving a first soft tissue element and a second soft tissue element is provided. The instrument is contactable with the first soft tissue element and the second soft tissue element. A feedback system associated with the instrument is operable to determine a separation characteristic of the first soft tissue element and the second soft tissue element.  
       [0015] One aspect includes a system for moving first and second soft tissue elements. The system comprises a first member contactable with the first soft tissue element, and a second member contactable with the second soft tissue element. A third member, connectable with the first member and the second member, maintains the first soft tissue element in a spaced apart relationship with respect to the second soft tissue element. A feedback system is associated with the first member for determining a separation characteristic of the first and second soft tissue elements.  
       [0016] Another aspect includes a method for moving soft tissue elements. The method includes coupling a tissue separation system with soft tissue elements to be moved, moving the soft tissue elements, and determining a separation characteristic of the soft tissue elements.  
       [0017] In another aspect a tissue separation system is provided. The system includes a connector having first and second ends with a portion therebetween. A stationary arm is affixed to the first end and a movable arm is affixed to the second end. The movable arm is movable along the connector with respect to the stationary arm. A feedback system associated with the system is operable to determine a separation characteristic associated with the tissue during and/or after the movable arm and the stationary arm are moved relative to one another.  
       [0018] In a further aspect, a system for moving vertebral bodies is provided. The system comprises a connector having an engageable portion extending between opposite ends. A first member extends from one end of the connector and is connectable with a first vertebral body. A second member is movably engaged to the connector, and extends therefrom and is connectable with a second vertebral body. The second arm is movable along the connector with respect to the first arm. A system associated with at least one of the first arm and the second arm determines an actual separation characteristic, which is comparable to a desired or predetermined separation characteristic. Feedback is provided to the surgeon regarding the same. The actual separation characteristic can be adjusted based on the feedback to obtain a desired or predetermined separation characteristic.  
       [0019] In another aspect, a method for moving vertebral bodies includes coupling a vertebral body separator to the vertebral bodies to be moved, separating the vertebral bodies, and determining a separation characteristic of the vertebral bodies. The separation characteristic can be compared to desired or predetermined separation characteristics to determine if separation of the vertebral bodies is appropriate and/or should be increased or decreased for insertion of an interbody device or engagement of a plate or rod construct to the vertebrae.  
       [0020] In another aspect, a method for moving vertebral bodies includes coupling a vertebral body separator to the vertebral bodies to be moved, separating the vertebral bodies, and determining a separation characteristic of the vertebral bodies. If the determined separation characteristic corresponds to a desired separation characteristic, a construct is inserted in the space between or adjacent the vertebral bodies.  
       [0021] These and other aspects will also be apparent from the following description of the illustrated embodiments.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0022]FIG. 1 is a block diagram of one embodiment of a system for separating anatomical elements and providing feedback regarding the same.  
     [0023]FIG. 2 is a block diagram of another embodiment system for separating anatomical elements and providing feedback regarding the same.  
     [0024]FIG. 3 is a block diagram of another embodiment system for separating anatomical elements and providing feedback regarding the same.  
     [0025]FIG. 4 is a block diagram of another embodiment system for separating anatomical elements and providing feedback regarding the same.  
     [0026]FIG. 5 is a block diagram of another embodiment system for separating anatomical elements and providing feedback regarding the same.  
     [0027]FIG. 6 is a block diagram of another embodiment system for separating anatomical elements and providing feedback regarding the same.  
     [0028]FIG. 7 is a chart for a method of separating soft tissue elements.  
     [0029]FIG. 8 is a chart for a method of separating vertebral elements.  
     [0030]FIG. 9 is a perspective view of one embodiment instrument for separating and providing feedback regarding the separation of anatomical elements.  
     [0031]FIG. 10 is an elevation view of another embodiment instrument for separating and providing feedback regarding the separation of anatomical elements.  
     [0032]FIG. 11 is a view of a portion of the instrument of FIG. 10 having an alternate embodiment feedback.  
    
    
     DETAILED DESCRIPTION  
     [0033] For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is hereby intended. Any such alterations and further modifications in the illustrated devices, and any such further applications of the principles of the invention as illustrated herein are contemplated as would normally occur to one skilled in the art to which the invention relates.  
     [0034] Referring to FIG. 1, there is shown a system  10  for moving at least a first anatomical element  12  relative to a second anatomical element  14 . Anatomical elements  12  and  14  are located in a patient undergoing surgery, and require separation from one another or reducing the separation from one another as a result of a surgical procedure being performed on a patient. System  10  includes a member  16  contactable with first anatomical element  12 . Member  16  can be manipulated by the surgeon to move first anatomical element  12  and second anatomical element  14  relative to one another. A feedback system  18  is associated with member  16  and provides immediate, real-time, and/or requested information to the surgeon regarding one or more separation characteristics associated with first and second anatomical elements  12 ,  14 . Feedback system  18  can also provide the surgeon an indication when a desired or predetermined separation characteristic is obtained, and/or when certain threshold separation characteristics are obtained and/or approached.  
     [0035] Anatomical elements  12  and  14  may include any relatively soft or relatively hard organic tissue which can be moveable relative to one another either in their pre-surgical state or in an altered state provided during surgery. Suitable examples of anatomical elements include epithelial tissue, including the dermal layers of skin and body cavities; connective tissue, including loose connective tissue, dense connective tissue, adipose tissue, cartilage, blood, and bone; muscle tissue, including smooth muscle tissue, skeletal muscle tissue, and cardiac muscle tissue; adipose tissue; nervous tissue; vascular tissue, including blood vessels, veins, arteries, and capillaries; cartilage tissue, including hyaline cartilage tissue, elastic cartilage tissue, and fibrocartilage tissue; and bone, including spongy bone tissue, compact bone tissue, cortical bone tissue, and cancellous bone tissue.  
     [0036] Although the first and second anatomical elements can be organic tissues, they do not have to be the same type of organic tissue. It is contemplated, for example, first and second anatomical elements  12 ,  14  include opposing, interrupted tissue masses on opposite sides of a surgical incision. It is also contemplated first and second anatomical elements  12 ,  14  can be, for example, opposing endplates of adjacent vertebrae. It is further contemplated that first and second anatomical elements  12 ,  14  can be, for example, endplates of vertebrae separated by one or more in place or removed vertebrae. Also contemplated are first and second anatomical elements that are first and second vertebral bodies, which may be adjacent to one another or include one or more additional vertebrae therebetween. The first and second anatomical elements may each be either the anterior portion of a vertebra, or one or more of the posterior elements of a vertebra, such the spinous or transverse processes, the facets, pedicles or lamina, for example.  
     [0037] A member can include any device, mechanism or body capable of moving first anatomical element  12  and second anatomical element  14  relative to one another. A member may be placed in direct contact with the anatomical element, or contactable with the anatomical element with one or more fasteners, connecting elements or the like engaged to the anatomical element. Examples of members include tissue retractors, tissue spreaders, tissue forceps, vertebral body distractors, and disc space spreaders. Further examples of members include one or more retractor elements such as blades, arms, pins, scoops, valves, bodies, shafts, flanges, bodies, fingers, extensions, and tips or the like capable of contacting and moving one or more anatomical elements. The member can be configured to contact soft tissue anatomical elements. Additional examples of members include one or more distractor elements such as bodies, fingers, extensions, tips or the like that can be inserted along, adjacent, against or into and anatomical element. For example, the member can be configured to contact an endplate of a vertebral body, a connector engaged to a vertebrae, connected to an anterior or posterior element of a vertebral body, or otherwise configured to contact and move a hard or bony tissue element.  
     [0038] As used herein, feedback system includes any system associated with member  16  and capable of determining one or more separation characteristics associated with moving first anatomical element  12  relative to second anatomical element  14 . The one or more separation characteristics may include a distance an anatomical element is moved, a force or load exerted on an anatomical element, a strain associated with moving anatomical elements  12 ,  14  relative to one another, relative angles between anatomical elements or angle of one of the anatomical elements, distance between the anatomical elements, pressure exerted on one or both anatomical elements, or any other quality capable of objectively representing or characterizing separation of the anatomical elements. The feedback system may receive an input representative of the separation characteristic from an input system and may further include one or more output systems such as a visual display, audio, haptic, graphical, voice or other communication/response to communicate the one or more separation characteristics to the surgeon. In one particular embodiment, for example, the feedback system includes indicia visible to the surgeon, such as an analog scale, digital readout, or the like.  
     [0039] Further, feedback systems may include a processing system having appropriate hardware and/or software for converting input data into representative objective separation characteristics. Additionally, the processing system may include appropriate hardware, software, and predetermined separation characteristic values for outputting an adjustment signal representing a change in position required to achieve a predetermined or desired separation characteristic. Suitable examples of feedback systems include any one or combination of a distance-measuring system, a force-measuring system, a strain-measuring system, a degree-measuring system, an angle-measuring system, and a pressure measuring system.  
     [0040] Referring to FIG. 2, there is shown another embodiment system  20  for moving at least first anatomical element  12  relative to second anatomical element  14 . System  20  includes a first member  22  contactable with first anatomical element  12  and a second member  24  contactable with second anatomical element  14 . First and second members  22 ,  24  can be manipulated by the surgeon to move first anatomical element  12  and second anatomical element  14  relative to one another. A feedback system  26  is associated with one or both of the first and second members  22 ,  24  to provide immediate, real-time, and/or requested objective information to the surgeon regarding one or more separation characteristics associated with the first and second anatomical elements  12 ,  14 . Feedback system  26  can also provide the surgeon an indication when a desired or predetermined separation characteristic is obtained, when certain threshold separation characteristics are obtained, and/or as threshold separation characteristics are approached.  
     [0041] There is further provided an adjustment mechanism  28  associated with first and second members  22 ,  24  which is operable to move one or both of first and second members  22 ,  24  toward one another or away from one another. Adjustment mechanism  28  can be removably coupled to one or both of first and second members  22 ,  24 , or permanently coupled to one or both of the first and second members  22 ,  24 . Adjustment mechanism  28  can be associated with feedback system  26  so that the one or more separation characteristics can be determined in response to manipulation of the adjustment mechanism. Adjustment mechanism  28  can be provided with any of the separation systems discussed herein.  
     [0042] Referring to FIG. 3, there is shown another embodiment system  30  for moving at least first anatomical element  12  relative to second anatomical element  14 . System  30  includes a member  32  contactable with each of the first anatomical element  12  and the second anatomical element  14 . Member  32  can be manipulated by the surgeon to move at least one of the first anatomical element  12  and the second anatomical element  14  relative to the other. A feedback system  34  is associated member  32  to provide immediate, real-time information, and/or requested information to the surgeon, either directly or through input/output system  36 , regarding one or more separation characteristics associated with the first and second anatomical elements  12 ,  14 .  
     [0043] Feedback system  34  can also provide the surgeon, either directly or through input/output system  36 , an indication when a desired or predetermined separation characteristic is obtained, and/or when certain threshold separation characteristics are obtained or approached. It is further contemplated that input/output system  36  can be used to provide information to feedback system  34  regarding pre-determined separation characteristic limits or desired separation characteristic results. These limits and/or results can be compared to one ore more actual separation characteristics determined by feedback system  34  and a signal provided to the surgeon indicative of the same through input/output system  36 . Input/output system  36  can be provided with any of the separation systems discussed herein.  
     [0044] Referring to FIG. 4, there is shown another embodiment system  40  for moving at least first anatomical element  12  and second anatomical element  14 . System  40  includes a first member  42  contactable with first anatomical element  12  and second member  44  contactable with second anatomical element  14 . First and second members  42 ,  44  can be manipulated by the surgeon to move or separate first anatomical element  12  and second anatomical element  14  away from one another. Second member  44  is connected with a portion of first member  42  extending between first and second members  42 ,  44 . Second member  44  is movable relative to first member  42  to separate first and second anatomical elements  12 ,  14 .  
     [0045] A feedback system  46  can be associated with movable second member  44  to provide immediate or real-time information to the surgeon regarding one or more separation characteristics associated with moving the first and second anatomical elements  12 ,  14 . Feedback system  46 , either directly or through input/output system  48 , can also provide the surgeon an indication when a desired or predetermined separation characteristic is obtained, and/or when certain threshold separation characteristics are obtained. It is further contemplated that input/output system  48  can be provided with information regarding pre-determined separation characteristic limits or desired separation characteristic results. These limits and/or results can be compared to actual separation characteristic determined by feedback system  46  and a signal provided to the surgeon indicative of the same through input/output system  48 .  
     [0046] Referring to FIG. 5, another embodiment separation system  100  is shown. Separation system  100  includes a first member  130  that contacts first anatomical element  12 , and creates or alters a spaced apart relationship between first anatomical element  12  and second anatomical element  14 , from a first position, as indicated in dashed lines, and a second position, as indicated in solid lines for first member  130  and first anatomical element  12 . Feedback system  140  is associated with first member  130 , and receives feedback  142  representative of separation characteristic  144  of the first and second anatomical elements  12 ,  14 . Further, feedback system  140  may include an output  146  that communicates one or more separation characteristics  144  to an attendant or surgeon. Thus, through first member  130  and feedback system  140 , system  100  can measure separation characteristic  144  and thereby allow the attendant or surgeon to monitor, adjust and/or control the separation between first anatomical element  12  and second anatomical element  14  and/or to achieve a desired or predetermined separation characteristic.  
     [0047] An adjustment mechanism  132  can be associated with first member  130  and operable to further move apart or together first and second anatomical elements  12 ,  14 . Feedback system  140  and/or processor  160  can be linked to provide a signal  133  to adjustment mechanism  132  in response to an input or measured separation characteristic. A locking mechanism  134  can lock adjustment mechanism  132  to maintain first and second anatomical elements  12 ,  14  in a separated or spaced position. Processor  160  can be provided with feedback system  140  and include hardware and/or software for converting inputs into representative separation characteristics. Additionally, the processing system may include appropriate hardware, software, and predetermined separation characteristic values for outputting an adjustment signal representing a change in position required to achieve a predetermined separation characteristic. Input/output system  150  can communicate via link  146  with feedback system  140  and/or processor  160  to provide input signals of desired or threshold separation characteristics and to receive output signals from feedback system  140  and/or processor  160 .  
     [0048] Referring to FIG. 6, another embodiment separation system  300  is shown. Separation system  300  includes a first member  330  that contacts first anatomical element  12  and a second member  332  that contacts second anatomical element  14 . A connector  334  extends between and mechanically links first member  330  and second member  332 . First and second members  330 ,  332  are moveable relative to one another to provide or alter a spaced apart relationship between first anatomical element  12  and second anatomical element  14  from a first position, as indicated in dashed lines, and a second position, as indicated in solid lines.  
     [0049] Feedback system  340  is associated with first and second members  330 ,  332  and receives feedback  342  representative of separation characteristic  344  of the first and second anatomical elements  12 ,  14 . Further, feedback system  340  may include an input/output system  350  that communicates one or more separation characteristics  344  to an attendant or surgeon. Thus, through first member  330 , second member  332  and feedback system  340 , system  300  can measure separation characteristic  344  and thereby allow the attendant or surgeon to monitor, adjust and/or control the separation between first anatomical element  12  and second anatomical element  14 , and/or to achieve a desired or predetermined separation characteristic.  
     [0050] An adjustment mechanism  338  can be associated with first member  330  and operable to further separate or release first and second anatomical elements  12 ,  14 . Feedback system  340  and/or processor  360  can be linked to provide a signal  339  to adjustment mechanism  338  in response to an input or measured separation characteristic. A locking mechanism  336  can lock adjustment mechanism  338  to maintain first and second anatomical elements  12 ,  14  in a separated or spaced position. Processor  360  can be provided with feedback system  340  and include hardware and/or software for converting inputs into representative separation characteristics. Additionally, the processing system may include appropriate hardware, software, and predetermined separation characteristic values for outputting an adjustment signal representing a change in position required to achieve a predetermined separation characteristic. Input/output system  350  can communication via link with feedback system  340  and/or processor  360  to provide input signals of desired or threshold separation characteristics and to receive output signals from feedback system  340  and/or processor  360 .  
     [0051] Referring to FIG. 7, a method  200  for moving first and second soft tissue anatomical elements is shown in block diagram form. At  210  the separation system is placed into contact with at least one of the two tissue elements be moved. For example, in methods employing separation system  100  of FIG. 5, first member  130  may be brought into contact with first tissue element, or brought into contact with an element or device in contact with first tissue element. Method  200  continues at  220  in which the two tissue elements are moved by moving at least one of the tissue elements away from the other tissue element. For example, in methods employing separation system  100  of FIG. 5, first member  130  may be moved from a first position to a second position, thereby creating or adjusting a space between first tissue element and the second tissue element.  
     [0052] At  230 , a separation characteristic associated with moving the first and second tissue elements is determined. The separation characteristic can be determined during movement or after movement is complete. For example, in methods employing separation system  100 , feedback system  140  may receive feedback  142  from first member  130  representative of a separation characteristic  144 . Feedback system  140  may then provide, either directly or through an input/output system, an indication to the attendant or surgeon that is representative of separation characteristic  144 .  
     [0053] Method  200  may further include at  240  adjusting the separation system and the spacing of the anatomical elements. For example, in methods employing separation system  100 , first member  130  may be coupled to an adjustment mechanism  132 , where adjustment mechanism  132  adjusts first member  130  to further separate or reduce separation of the tissue elements. The tissue elements can also be locked at  250  to maintain a separation characteristic associated with the anatomical elements. For example, with reference to separation system  100 , first member  130  may further include locking mechanism  134  that is operable to lock first member  130  in a desired position for maintaining a separation characteristic  144  associated with the first and second tissue elements. It is further contemplated at  260  that the tissue can be released or moved toward one another by, for example, unlocking locking mechanism  134  or manipulating adjustment mechanism  132 . The first and second tissue elements can be moved in closer proximity to one another and maintained in this closer proximity, or can be completely released to return toward their pre-separation position.  
     [0054] In one application of a method of moving soft tissue elements, an incision is made to access a surgical site on or near the spinal column. One specific application includes accessing the spinal column from an anterior approach to the cervical spine. Other applications contemplate other approaches, including posterior, postero-lateral, antero-lateral and lateral approaches to the spine, and accessing other regions of the spine, including the thoracic, lumbar and/or sacral portions of the spine. The first and second members of the separation instrument are inserted in the incision in contact with first and second tissue elements. The separation instrument is then manipulated to separate the tissue elements, and the feedback system measures one or more separation characteristics associated with the tissue elements.  
     [0055] A desired or threshold separation characteristic can be provided to or known to the surgeon prior to moving the tissue elements. For example, the desired separation characteristic can correspond to a maximum pressure or tension on the tissue elements determined through pre-operative planning or anatomical studies. The surgeon can maintain the actual separation characteristic measured during surgery at or below the desired or threshold separation characteristic. The feedback system can further be programmed to provide, either directly or through an input/output system, a warning, indication or comparison that the actual separation characteristic is approaching, the same as, or exceeding the desired or threshold separation characteristic. The surgeon can then select an appropriate course of action to maintain the actual separation characteristic within a desired limit or below a threshold separation characteristic. For example, the surgeon can stop tissue separation, reduce tissue separation, or increase the size of the incision. In this manner, the size of the incision can be optimized and made as small as possible in view of the tissue spacing required and the allowable separation characteristics.  
     [0056] Referring to FIG. 8, a method  400  for moving first and second vertebral elements is shown in block diagram form. One application of method  400  is to increase a disc space height of a collapsed disc space between a pair of vertebrae. At  410  the separation system is coupled to at least one of the two vertebral elements be moved. Method  400  continues at  420  in which the two vertebral elements are separated by moving at least one of the vertebral elements relative to the other to increase a disc space height. The vertebrae can be locked in the separated position, or the separated position can be adjusted to increase the disc space height or decrease the disc space height with an adjustment mechanism.  
     [0057] At  430 , a separation characteristic associated with moving the first and second vertebrae is determined. The separation characteristic can be determined during movement of the vertebrae or after movement is complete. For example, the load, pressure or force required to increase the disc space height can be determined during separation. The size of the space between the vertebral elements and/or the angulation between the vertebral elements can also be determined. The feedback system measures the separation characteristic and an indication of the same can be provided to the surgeon.  
     [0058] At  440 , the determined separation characteristic is compared to a desired, predetermined or threshold separation characteristic, which can be developed through pre-operative planning, anatomical studies, and/or during surgery. For example, the predetermined or threshold separation characteristic can correspond to a maximum pressure or tension to be exerted by the members of the instrument on anatomical features of the vertebrae. The surgeon can maintain the actual separation characteristic measured during surgery to a level at or below the predetermined or threshold separation characteristic. The feedback system can further be programmed to provide, either directly or through an input/output system, a warning, indication or comparison that the actual separation characteristic is approaching, the same as, or exceeded the predetermined or threshold separation characteristic. The surgeon can then select an appropriate course of action to maintain or adjust the actual separation characteristic.  
     [0059] One example of a separation instrument is shown in FIG. 9. Separation instrument  500  includes a first member  502  and a second member  504 . A connector  506  extends between first member  502  and second member  504 . A feedback system  508  is operable to provide to the attendant or surgeon an indication of at least one separation characteristic of the anatomical elements in response to movement of at least one of the first and second members  502 ,  504  relative to the other. An adjustment mechanism  532  can be provided and manipulated by the attendant or surgeon to facilitate movement of first and second members  502 ,  504  relative to one another.  
     [0060] First member  502  includes a first end  510  and an opposite second end  516 . Second end  516  is connected with connector  506 . In the illustrated embodiment, second end  516  includes a ring extending about and immovably engaged to or formed with one end of connector  506 . An extension  518  extends from second end  516  to an intermediate portion  514 . A contacting portion  512  extends from intermediate portion  514  to first end  510 . Second member  504  includes a first end  520  and an opposite second end  526 . Second end  526  is connected with connector  506 . In the illustrated embodiment, second end  526  includes a ring extending about and movably engaged to the body of connector  506 . Accordingly, connector  506  and first member  502  can be moved relative second member  504 . An extension  528  extends from second end  526  to an intermediate portion  524 . A contacting portion  522  extends from intermediate portion  524  to first end  520 .  
     [0061] Contacting portions  512 ,  522  can be, for example, a retractor element if instrument  500  were employed in a tissue retraction procedure, or a distractor element if separation instrument  500  were employed in a procedure moving bony portions. It is further contemplated that the entire length of contacting portions of first and second members  502 ,  504  can contact the anatomical element, only a portion of the length can contact the anatomical element, or the contacting portion can be engaged to a member or coupling element engaged to or in contact with the anatomical element. Contacting portions  512 ,  522  can be angled away from the remaining portions of instrument  500  so that instrument  500  can be maintained out of the way of the approach to the surgical site.  
     [0062] Connector  506  can be provided with engagement teeth  530  therealong for engagement with adjustment mechanism  532 . Adjustment mechanism  532  is engaged or coupled with second member  504 . In the illustrated embodiment, adjustment mechanism  532  is a thumbwheel coupled to a pinion member (not shown) having teeth that interdigitate with teeth  530  to move connector  506  and thus first member  502  relative to second member  504 . Adjustment mechanism  532  can be manipulated to modify or adjust the separation characteristic to obtain a desired separation characteristic. Adjustment mechanism  532  may comprise manual thumbscrew, a deflection beam torque wrench, a spring ratchet, or similar mechanism. A locking mechanism can also be provided to prevent adjustment mechanism  532  and/or connector  506  from being moved so that a separation characteristic can be maintained during the surgical procedure.  
     [0063] Feedback system  508  may comprise a distance-measuring system, an angle measuring system, a force-measuring system, a change in force per change in distance measuring system, a pressure measuring system, and/or a strain measuring system. It is contemplated that feedback system  508  can be coupled to an output system to provide the surgeon an indication of the separation characteristic measured by feedback system  508 . For example, a scale could be provided along or adjacent connector  506  to provide an indication of the separation characteristic. Feedback system  508  can also be coupled to other output systems, such as an oscilloscope, which can be operable to chart one or more of the separation characteristics.  
     [0064] In one embodiment, feedback system  508  measures the force applied to the anatomical elements versus the distance the anatomical elements are moved relative to one another. This separation characteristic is plotted along a chart, and when the applied force results in little or no change in distance between the anatomical elements, the increase in the separation force is stopped. The chart can provide a visual indication to stop separation of the anatomical elements since the distance component of the chart will not change as the distraction force increases.  
     [0065] Another example of a separation instrument is shown in FIG. 10. Separation instrument  600  includes a first member  602  and a second member  604 . A connector  606  extends between first member  602  and second member  604 . A feedback system  608  is operable to provide to the attendant or surgeon an indication of at least one separation characteristic of the anatomical elements in response to movement of at least one of the first and second members  602 ,  604  relative to the other. An adjustment mechanism  632  can be provided and manipulated by the attendant or surgeon to facilitate movement of first and second members  602 ,  604  relative to one another.  
     [0066] First member  602  includes a first end  610  and an opposite second end  616 . Second end  616  is connected with connector  606 . In the illustrated embodiment, second end  616  includes a ring extending about and immovably engaged to or formed with one end of connector  606 . An extension  618  extends from second end  616  to an intermediate tapered portion  614 . A contacting portion  612  extends from intermediate portion  614  to first end  610 . Contacting portion  612  can be angled relative to extension  618  to position the remaining portion of the instrument away from the approach to the surgical site.  
     [0067] Second member  604  includes a first end  620  and an opposite second end  626 . Second end  626  is connected with connector  606 . In the illustrated embodiment, second end  626  includes a ring-like element extending about and movably engaged to the body of connector  606 . Accordingly, second member  604  can be moved relative first member  602 . An extension  628  extends from second end  626  to an intermediate tapered portion  624 . A contacting portion  622  extends from intermediate tapered portion  624  to first end  620 . Intermediate portion  624  can extend along connector  606  to position contacting portion  622  adjacent contacting portion  612 . Contacting portion  622  can be angled relative to extension  628  to position the remaining portion of the instrument away from the approach to the surgical site.  
     [0068] Contacting portions  612 ,  622  can be, for example, a retractor element if instrument  600  were employed in a tissue separation procedure, or a distractor element if separation instrument  600  were employed in a procedure moving bony portions. It is further contemplated that the entire length of contacting portions of first and second members  602 ,  604  can contact the anatomical element, only a portion of the length can contact the anatomical element, or the contacting portion can be engaged to a member or coupling element engaged to or in contact with the anatomical element.  
     [0069] Connector  606  can be provided with engagement teeth  630  therealong for engagement with adjustment mechanism  632 . Adjustment mechanism  632  can be positioned in housing  631  extending about second member  604 . In the illustrated embodiment, adjustment mechanism  632  is a pinion wheel that is rotatable along and in interdigitating engagement with one or more of the teeth  630  to move second member  604  along connector  606 . Adjustment mechanism  632  can be manipulated with a thumbwheel or tool engagement device (not shown) to modify or adjust first and second members  602 ,  604  to obtain a desired or adjusted separation characteristic.  
     [0070] A locking mechanism  634  can also be provided to prevent adjustment mechanism  632  and/or second member  604  from being moved relative to connector  606 . In the locked condition the separation characteristic can be maintained during the surgical procedure. In the illustrated embodiment, locking mechanism  634  includes a lever  635  having an end  636  selectively engageable and biased into engagement with teeth  630  of connector  606 . Lever  635  is pivotally coupled at  638  to housing  631  adjacent second end  626  of second member  604 . End  636  can be rotated in the direction indicated by arrow P to move out of engagement with teeth  630  and allow adjustment mechanism  632  to be used to adjust the separation characteristic. Furthermore, when unlocked, first and second members  602 ,  604  can be moved toward one another to release the anatomical elements or reduce the separation between the anatomical elements. When the desired separation characteristic is obtained, lever  635  of locking mechanism  634  can be rotated or biased in the direction opposite arrow P to engage teeth  630 .  
     [0071] Feedback system  608  may comprise a distance-measuring system, an angle measuring system, a force-measuring system, a change in force per change in distance measuring system, a pressure measuring system, and/or a strain measuring system. It is contemplated that feedback system  608  can be coupled to an output system  650  to provide the surgeon an indication of the separation characteristic measured by feedback system  608 . For example, a scale could be provided along or adjacent connector  606  to provide an indication of the separation characteristic. Feedback system  608  can also be coupled to other output systems, such as an oscilloscope, which can be operable to chart, plot, or provide a display indicative of one or more of the separation characteristics.  
     [0072] In the illustrated embodiment, feedback mechanism  608  can be a strain gauge coupled to extension  628  of first member  604  adjacent connector  606 . The strain gauge can be positioned to measure the shear forces in extension  628  created by the distraction forces exerted on first member  604 . It is further contemplated that the strain gage could be alternatively or additionally positioned on extension  618  to measure the tensile bending forces and/or the compression bending forces. Feedback system  608  could additionally or alternatively be coupled to first member  602 , coupled to adjustment mechanism  632 , and/or connector  606 .  
     [0073] In FIG. 11 there is shown an alternate embodiment feedback system  660  with separation instrument  600 , it being understood that feedback mechanism  660  could be employed with the other separation instrument embodiments. Feedback mechanism  660  includes a housing  666  in which spring  662  is positioned. Spring  662  is coupled to or in communication with extension  628  via a coupling member  664 , and is responsive to loads exerted on second member  604  to provide a signal indicative of a separation characteristic to input/output system  650 .  
     [0074] Although instruments  500  and  600  are shown with gear and rack or ratcheting type connectors between the first and second members of the separation instruments, other means for moving first and second members, or for moving a member of the separation instrument, are also contemplated. For example, such means may include a scissors-type connector between the first and second members, one or more resilient hinges or pivot pins between first and second members, ratchet mechanisms, motor and drive shaft, or linkages. For instruments employing a single contacting member, the member may be coupled to a proximal portion with a scissors-type connector, one or more resilient hinges or pivot pins, a ratchet mechanism, motor and drive shaft, or linkage, for example.  
     [0075] In one example of a surgical technique employing the separation instrument of the present invention will be discussed with reference to FIG. 10. An interbody construct  700 , such as an intradiscal fusion device or corpectomy device, is to be inserted in the disc space between adjacent vertebrae  702 ,  704 . It has been found that the force required to distract the vertebrae  702 ,  704  is approximately linearly related to the compressive force exerted on the interbody fusion or corpectomy device  700  when the distraction force is released. In one specific example, the residual compressive force can be in the range from 5% to 15% of the applied distractive load. Accordingly, the surgeon can distract the vertebrae  702 ,  704  to achieve a desired separation characteristic which corresponds to a desired compressive force that will be exerted on the interbody construct  700  inserted between the vertebrae  702 ,  704  when the separation instrument is removed. The compression loading of the interbody construct  700  facilitates the fusion of the adjacent vertebrae and helps retain the interbody construct  700  in the space between the vertebrae  702 ,  704 . Accordingly, the separation instrument can provide the surgeon an objective indication of the compression loading that will be applied to the inserted interbody construct  700 , and distraction of the vertebra can be optimized and/or adjusted accordingly to achieve a desired separation characteristic.  
     [0076] In another example employing the separation instrument, a construct  700  in the form of an artificial disc device is to be inserted in the disc space between adjacent vertebrae  702 ,  704 . It can be desirable to provide a separation characteristic for an artificial disc device that would differ for an interbody fusion device. For example, greater post-operative compression loading is desirable for an interbody fusion device to facilitate fusion and maintain implant positioning before and during fusion. Lesser post-operative compression loading is desirable for an artificial disc since fusion between the vertebrae is not sought, and reduced compression forces will reduce wear of the artificial disc components. The surgeon can obtain a separation characteristic corresponding to a distraction force applied to the adjacent vertebrae, which corresponds to a desired compressive force that will be exerted on the artificial disc when the separation instrument is released. Accordingly, the separation instrument can provide the surgeon an objective indication of the compression loading that will be applied to the artificial disc to be inserted, and distraction of the vertebra  702 ,  704  can be adjusted accordingly to achieve a desired separation characteristic prior to or after insertion of the artificial disc device.  
     [0077] According to the present invention, it is contemplated that an interbody construct  700  can be inserted in the disc space between adjacent vertebrae  702 ,  704 . The distractive force applied to separate vertebral bodies can be used to predict compressive forces that will be post-operatively exerted on the interbody construct  700  when the distraction force is released. In addition, a compression load between the vertebrae  702 ,  704  can be applied to provide additional compression loading to the interbody construct  700 . The separation characteristic between the vertebrae  702 ,  704  supplied by the pre-insertion distraction forces and/or applied post-construct insertion can be post-operatively maintained by securing an extra-vertebral construct  706  to the vertebrae to maintain the compression loading against the inserted interbody construct  700 . The separation instrument of the present invention can be employed for any one or all of pre-insertion distraction, post-insertion compression and to determine separation characteristics associated therewith.  
     [0078] The measured separation characteristic can be compared to a desired separation characteristic, adjusted if necessary, and when acceptable, the extra-vertebral construct  706  can be secured to the adjacent vertebrae  702 ,  704  with bone engaging fasteners  708 ,  710 , respectively, to maintain the desired compressive load on the interbody construct  700 . For example, the pre-insertion distraction force indicated by the separation instrument may indicate that that the post-insertion compression loading of the interbody construct  700  will not be sufficient. Accordingly, the distraction force can be increased.  
     [0079] The distraction force may not be able to be increased due to, for example, a maximum force limitation or threshold. In such cases, and in other cases where desired or necessary after insertion of the interbody construct  700 , a compressive load can be applied with the separation instrument. The separation instrument measures the compression loading and when a desired compression loading is obtained, the extravertebral construct  706  can be secured to the vertebrae  702 ,  704  to maintain the compression loading. Engagement of the extra-vertebral construct  706  to the adjacent vertebrae can prevent or resist subsidence of the interbody construct  700  into the vertebral endplates, thus enabling higher compression loading of the interbody construct  700  to facilitate, for example, bony incorporation or anchorage of the interbody construct  700  to the vertebral endplates. It is contemplated that the extra-vertebral construct  706  can be a plating system, rod system, tethering system or other suitable system for engaging vertebrae  702 ,  704  extra-vertebrally. It is further contemplated the interbody construct  700  can be a fusion device, spacer, or artificial disc, for example.  
     [0080] While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered illustrative and not restrictive in character. All changes and modifications that come within the spirit of the invention are desired to be protected.