Patent Publication Number: US-8977332-B1

Title: Retractor device with oximeter sensor and force sensor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is a continuation of U.S. patent application Ser. No. 12/689,053, filed Jan. 18, 2010, issued as U.S. Pat. No. 8,688,186 on Apr. 1, 2014, which claims the benefit of U.S. provisional patent application 61/149,916, filed Feb. 4, 2009, which are incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to the field of medical devices and more specifically to a retractor device with an oximeter sensor and force sensor. 
     Retractors play an important role in medicine. Retractors typically retract or hold aside tissue so that a physician (e.g., surgeon) can gain access to an area for operation or observation. It is important to not damage the tissue when retracting the tissue. 
     One area of medicine that retractors are commonly used is during spinal surgery. Tens of thousands of spinal surgeries are performed each year. The number of spinal surgeries is continuing to increase due, in part, to an aging population, active lifestyles, and a better understanding of what causes back pain. Back pain may be due to disc herniation, degenerative disc disease, spinal trauma, and osteoarthritis just to name a few examples. 
     The spinal cord is the main pathway through which the brain sends and receives signals. The nerve fibers in the spinal cord branch off to form pairs of nerve roots that travel through small openings between the vertebrae. These nerves control the body&#39;s function including the vital organs, sensation, and movement. 
     During spinal surgery, it is often necessary to retract, or hold, the nerve root aside so that the surgeon can access the surgical site. With current medical devices, however, it is difficult if not impossible, to tell whether the nerve root is being damaged during the retraction. Damage to the nerve root or any nerve is undesirable—leading to loss of sensation, numbness, or pain to patient. 
     There is, then, a continuing demand for medical devices that provide patient feedback, provide more features, are easier to use, and generally address the needs of patients, doctors, and others in the medical community. 
     Therefore, there is a need to provide improved devices and techniques for retractors. 
     BRIEF SUMMARY OF THE INVENTION 
     A retractor device has a retractor including a shaft, a handle connected to a proximal end of the shaft, and a tip connected to a distal end of the shaft, where the tip has a retractor portion and an oximeter sensor. The retractor device further includes a force sensor that is operatively connected to the retractor. 
     The oximeter sensor in the device measures oxygen saturation of a tissue being retracted by the retractor device. The force sensor measures an amount of force applied to a retracted tissue by the tip of the retractor device. Thus, the retractor device can simultaneously measure two parameters of a retracted tissue—oxygen saturation level of the retracted tissue contacting the tip of the retractor device and an amount of force applied to the retracted tissue by the tip. 
     In one implementation, the retractor device is a nerve root retractor device for retracting a nerve. The tissue oxygen saturation sensing capability can potentially prevent nerve root hypoxia during spinal surgical retraction. In addition, force sensor measurements allow a surgeon to monitor and adjust an amount of force applied to a retracted tissue during surgery. Thus, the use of an excessive amount of force, which can potentially damage a tissue, can be avoided during retraction. By having both oximeter sensor and force sensor, the retractor device can better assist determining the effect of surgical manipulation on the health of nerve roots and other tissues. 
     In another implementation, the retractor device has a force sensor that is an integral part of a retractor, and the force sensor can be located at any suitable location between a handle and a tip of the retractor. For instance, the force sensor has a first end and a second end, the first end and the second end being on opposite side of each other along the axis of the force sensor. The first end of the force sensor can be attached to the handle of the retractor, and the second end of the force sensor can be attached to a proximal end of a shaft of the retractor. 
     In yet another embodiment, the retractor device can have a force sensor as a separate attachment to the retractor. For instance, the first end of the force sensor is attached to the handle of the retractor by a clamp. The second end of the force sensor is attached to a separate handgrip element or second handle. A surgeon can hold the handgrip element or second handle (not the handle on the retractor itself) to retract a tissue, and an amount of force that is applied to the tissue by the tip of the retractor device is measured by the force sensor. 
     In yet another implementation, the retractor device has an oximeter sensor including a first sensor opening and a second sensor opening on a bottom side of the tip. There is a first optical fiber and a second optical fiber. The first optical fiber passes through a channel in the shaft and a distal end of the first optical fiber is connected to the first sensor opening of the tip. The second optical fiber passes through the channel in the shaft and a distal end of the second optical fiber is connected to the second sensor opening of the tip. 
     Other objects, features, and advantages of the present invention will become apparent upon consideration of the following detailed description and the accompanying drawings, in which like reference designations represent like features throughout the figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a block diagram of a retractor device with an oximeter sensor and a load cell, and other components. 
         FIG. 2  shows details of an embodiment of a retractor device. 
         FIG. 3  shows a photograph of mechanical parts of a retractor device. 
         FIG. 4A  shows a calibration setup of a load cell, with the axis of the load cell being vertical. 
         FIG. 4B  shows a calibration setup of a retractor device having a load cell, with the axis of the load cell being vertical. 
         FIG. 5  shows a calibration setup of a retractor device having a load cell, with the axis of the load cell being horizontal. 
         FIG. 6A  shows a side view of a retractor device and a direction of force applied. 
         FIG. 6B  shows a top view of the retractor device shown in  FIG. 6A . 
         FIG. 7  shows a perspective view of a first implementation of a tip. 
         FIG. 8  shows a bottom view of the first implementation of a tip. 
         FIG. 9  shows a perspective view of a second implementation of a tip. 
         FIG. 10  shows a bottom view of the second implementation of a tip. 
         FIG. 11  shows a perspective view of a third implementation of a tip. 
         FIG. 12  shows a bottom view of the third implementation of a tip. 
         FIG. 13  shows a side view of the third implementation of a tip. 
         FIG. 14  shows a perspective view of the third implementation of the tip attached to a nerve retractor. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a block diagram of a retractor device  100  that is used for retracting a tissue, such as a nerve root. Retractor device  100  can also be used to measure oxygen saturation of the retracted tissue and an amount of force applied to the tissue during retraction.  FIG. 1  also shows an oximeter console  133  and a load cell interface  129  which are connected to components of retractor device  100 . 
     Retractor device  100  has an oximeter retractor tip  103  which is connected to a force sensor or load cell  106 , which is in turn connected to a handle  109 . Oximeter retractor tip  103  includes a retractor portion which is used to retract a tissue and an oximeter sensor which is used to measure oxygen saturation level of the tissue contacting the tip. The retractor device is used by placing the oximeter sensor at the retractor tip in contact with a tissue such as a nerve, and the tissue is pulled aside by the retractor tip. 
     Load cell  106  in the retractor device measures an amount of force that is applied to the tissue by oximeter retractor tip  103  when a surgeon holds handle  109  and retracts or pulls aside the tissue. Load cell  106  is a transducer that converts a force or load acting on it into an electrical signal. When there are changes in the force or load, there will be a change in the electrical signal produced by the load cell. The load cell can be located at any suitable location between oximeter retractor tip  103  and handle  109 . 
     Oximeter console  133  is connected to an oximeter sensor located at oximeter retractor tip  103  by a cable. Light is transmitted from oximeter console  133 , through optical fiber in the cable, out a sensor opening on the tip and into the nerve. The reflected light from the nerve is then received by another sensor opening at the tip, transmitted back to the oximeter console via optical fiber. The oximeter console processes and analyzes light information or signals using algorithms and converts the signals into oxygen saturation values in terms of percentage. The oximeter console can include a screen to display the oxygen saturation measurement and the timing of measurement. The measurements can also be stored in the oximeter console. 
     Load cell interface  129  is connected to load cell  106  of the retractor device by a cable. The signal from load cell  106  is transmitted to load cell interface  129  directly or via circuitry. The load cell interface transforms the electrical signals from the load cell into a force or other measurement or reading, which can be shown on a display. 
     While oximeter console  133  and load cell console  129  are shown as separate blocks in  FIG. 1 , these components can be enclosed in a single housing (e.g., a console or computer), or in separate housings. For example, the load cell interface may be incorporated within oximeter console  133 . Alternatively, some subcomponents of oximeter console  133  and load cell interface  129  can be combined into a single housing while other subcomponents are housed separately. 
       FIG. 2  shows one embodiment of a retractor device. A retractor device  210  includes a retractor that has a first handle  213 , a shaft  216  connected at its proximal end  219  to the first handle, and a tip  222  connected to a distal end  225  of the shaft. The shaft can be made of steel. The tip includes a retractor portion or retractor blade  228  and an oximeter sensor  231 . Oximeter sensor  231  has one or more sensor openings  230  on a bottom surface of the oximeter sensor, adjacent to retractor blade  228 . 
     The shaft can include an internal channel or passageway. Optical fibers can pass from sensor openings on the tip, through the channel, through the handle, and into a cable jacket or cable insulation. Alternatively, the fibers can be run along the shaft and secured by, for example, shrink wrap. The optical fibers that travel inside or along the shaft are exposed through sensor opening  230  on a bottom surface of tip  222 . Cable  276  that includes optical fibers is configured to be connected to a system unit or oximeter console (not shown). 
     Retractor device  210  also includes a force sensor  255 . Force sensor  255  has a first end  257  and a second end  259  on the opposite side of the first end along the axis of force sensor  255 . Force sensor  255  measures an amount of force that is applied in a horizontal direction along its axis. First end  257  of force sensor  255  is connected to an L-shaped clamp element  243 . L-shaped clamp element  243 , together with linear clamp element  241 , is clamped to first handle  213  of the retractor by a fastener  215 . Second end  259  of force sensor  255  is connected to a second handle  265 . Force sensor  255  also has a cable  275  which transmits a signal measured by force sensor  255  to a system unit or force sensor console (not shown). 
     Retractor device  210  can be used by placing oximeter sensor  231  in contact with a nerve. Light is transmitted from a system unit or console (not shown in  FIG. 2 ), through optical fiber in cable  276 , out a sensor opening  230  on tip  222  and into the nerve. The reflected light from the nerve is then received by another sensor opening on the tip, transmitted back to the console via optical fiber, and then processed. The console can display oxygen saturation measurement. The same or separate console can also display an amount of force that is applied by the retractor tip to retract the nerve. 
     Retractor device  210  has two handles—first handle  213  and second handle  265 . When first handle  213  is used to retract a tissue, there is no change in load or force for load cell  255  as it is not being pulled upon. When the tissue is retracted using first handle  213 , oxygen saturation measurements of a retracted tissue can be made. However, a force applied to a retracted tissue will not be measured. 
     When second handle  265  is used to retract a tissue, since the handle is connected to load cell  255 , a strain gauge in load cell  255  becomes deformed as the surgeon pulls second handle  265  to retract a tissue. The load or force measured by load cell  255  is converted into an electrical signal which is transmitted to a system unit (not shown) via cable  275 . When the tissue is retracted using second handle  265 , both oxygen saturation and force measurements can be made. 
     While  FIG. 2  illustrates an embodiment of the invention where the force sensor is attached to a retractor as a separate unit and is pulled upon by a second handle, the force sensor can be an integral part of the retractor itself. For example, the force sensor can be located between first handle  213  and proximal end  219  of the shaft of the retractor. In another example, the force sensor can be located in the middle of shaft  216 . In yet another example, the force sensor can be located between distal end  225  of the shaft and retractor tip  222 . When the force sensor is integrated as part of a retractor, second handle  265  can be omitted in the device, and first handle  213  can be used to retract or pull aside a tissue. 
       FIG. 3  shows a photograph of mechanics of a retractor device  300 . Retractor device  300  has a retractor  310  that has a tip with an oximeter sensor at a distal end. A handle of retractor  310  is attached to one end of a load cell  355  by a clamp  342 . The opposite side of load cell  355  is attached to an aluminum handle  365 . The load cell can sense a load ranging between zero to ten pounds. A cable  315  connects load cell  355  to a system unit (not shown). A cable  313  connects the oximeter sensor at the tip of retractor  310  to a system unit (not shown). 
       FIGS. 4A ,  4 B, and  5  illustrate various setups for calibrating a load cell. Shown in  FIGS. 4A ,  4 B, and  5  is a load cell, such as from Cooper Instruments &amp; Systems, Model LPM 530-HW10 (Warrenton, Va.). The data sheet and users&#39; guide for this load cell is incorporated by reference along with all other references cited in this application. According to the factory calibration, the load cell and amplifier provide one volt of output per one pound of force. The factory calibration is verified by using the setups shown in  FIGS. 4A ,  4 B, and  5 . 
     In  FIG. 4A , a poise is attached to one end of the axis of the load cell, and a handle is attached to the other end of the axis of the load cell. As shown in  FIG. 4A , the axis of the load cell is vertical. A cable from the load cell is connected to an amplifier, which is then connected to a voltmeter. Therefore, an LCD reading on the voltmeter represents the weight of the poise that is hung vertically on the load cell. 
     In a first calibration, no poise was attached to the load cell. In a second calibration, a poise weighing 200 grams was attached. In a third calibration, a poise weighing 400 grams was attached. The results are shown in table A. 
     In the first calibration for the setup shown in  FIG. 4A , the voltmeter reading was 0.04 volt. Since no poise was attached in this setup, 0.04 volt represents an offset that is subtracted from the voltmeter reading when weights are attached to the load cell. Accordingly, the calibration equation for the setup shown in  FIG. 4A  is as follows:
 
[force used on the load cell]=([LCD reading]−0.04 volt)*4.9 Newton.
 
     This equation agrees with the factory calibration with an error of about 5 percent. It is noted that one kilogram of force equals 2.205 pound of force, which equals 9.8 Newton. 
     In  FIG. 4B , a retractor device shown in  FIG. 3  was used to calibrate a poise. As shown in  FIG. 4B , the retractor device is held by a second handle attached to a load cell so that the axis of the load cell is vertical. A poise is hung at the tip of the retractor device. Again, voltage measurements were made with zero weight, with a poise weighing 200 grams, and with a poise weighing 400 grams. The results are shown in table A. 
     When no weight was attached for the setup shown in  FIG. 4B , the voltmeter reading was 0.22 volt. Since no poise is attached in this setup, 0.22 volt represents a force due to the weight of the retractor device. Therefore, if the retractor device is to be used as shown in  FIG. 4B  (i.e., with a force on the retractor device tip being vertical), then the calibration equation is as follows:
 
[Vertical force used on the retractor tip]=([LCD reading]−0.22 Volt)*4.9 Newton.
 
       FIG. 5  shows how a retractor device is used in retracting a tissue. In this figure, the second handle pulls on a load cell horizontally to the left to retract a tissue. The voltmeter reading without hanging any poise is 0.1 volt as shown in the last column of table A. Therefore, the calibration equation for the setup shown in  FIG. 5  is as follows:
 
[horizontal force on the retractor tip]=([LCD reading]−0.1 volt)*4.9 Newton.
 
     For example, when a retracting force of two Newton is executed onto the retractor device tip along the horizontal direction in  FIG. 5 , the voltmeter reading should be about 0.51 volt. 
     
       
         
           
               
             
               
                 TABLE A 
               
             
            
               
                   
               
               
                 Calibration Results 
               
            
           
           
               
               
               
            
               
                   
                 Weight  
                 LCD reading (Volt) 
               
            
           
           
               
               
               
               
               
            
               
                   
                 (gram) 
                 Figure 4A 
                 Figure 4B 
                 Figure 5 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 0 
                 0.04 
                 0.22 
                 0.1 
               
               
                   
                 200 
                 0.47 
                 0.62 
                   
               
               
                   
                 400 
                 0.97 
                 1.04 
               
               
                   
                   
               
            
           
         
       
     
       FIG. 6A  illustrates a side view of a retractor device. As shown in  FIG. 6A , the retractor device has a force sensor  615  that is connected between an oximeter retractor  610  and a handle  618 . Force sensor  615  measures an amount of force applied to a tissue  630  by a retractor tip  622  when handle  618  is pulled to the right to retract the tissue. A retractor portion  612  cradles tissue  630  so that the tissue is ready to be pulled, and oximeter sensor  613  measures an oxygen saturation level of tissue  630  at the point of contact. 
     Typically, oximeter retractor  610  has a shaft that is angled to assist a surgeon in viewing or retracting a tissue. For example, the shaft may be bent at an angle  627  of about 105 degrees as shown in  FIG. 6A . Angle  627  shown in  FIG. 6A  is merely exemplary, and the shaft may be bent at any suitable angle ranging between 90 and 179 degrees. However, in an embodiment, the shaft can be straight with angle  627  of 180 degrees, and the retractor device is a straight puller. 
       FIG. 6B  illustrates a top view of the same retractor device shown in  FIG. 6A . As shown, the retractor device includes force sensor  615  which is connected between a tip of oximeter retractor  610  and handle  618 , ready to pull nerve  630  resting near tip  622  of the retractor device. 
     In  FIGS. 6A and 6B , when the retractor device is pulled by handle  618  in a horizontal direction to the right, nerve  630  is pulled away from its original, resting position to the right. The distance that nerve  630  travels at the point of contact is referred to as a “retraction distance,” shown as d r  in  FIG. 6A . When handle  618  pulls the retractor device to the right, then a retraction distance of nerve  630  increases. When the retractor device is returned back to the left, then a retraction distance decreases to a point where the retraction distance equals zero as shown in  FIGS. 6A and 6B . 
       FIG. 7  shows a perspective view of a first implementation of a tip  705 . The tip includes a retractor blade and an oximeter sensor  710  attached to a top surface  715  of the tip. The tip attaches to a shaft  720 . The tip also includes a retractor portion  723 . Optical fibers are encased in a cable jacket  725 , travel along the shaft, into the oximeter sensor, and are exposed through an opening on a bottom surface  730  of the tip. Cable jacket  725  and shaft are wrapped with a tubing  735 . Such tubing may be heat-shrink tubing. 
     In a specific implementation of  FIG. 7 , the tip of the retractor has a length of about 17.5 millimeters, width of about 8 millimeters, and a thickness (not including the retractor blade) of about 5 millimeters. 
       FIG. 8  shows a bottom view of the first implementation of a tip  805 . The tip has a retractor blade and slot  810 , within which there are sensor openings. There are four sensor openings for ends of fiber optic cables. The openings  815   a ,  815   b ,  820   a , and  820   b  are for source and detector fibers. 
       FIG. 9  shows a perspective view of a second implementation of a tip  905  with an encasement  910  which contains optical fiber attached to the tip. 
     In a specific implementation of  FIG. 9 , the tip of the retractor has a length of about 17.5 millimeters, width of about 8 millimeters, and a thickness (not including the retractor blade) of about 3 millimeters. 
       FIG. 10  shows a bottom view of the second implementation of a tip  1005 . The tip includes a retractor blade and four sensor openings on a bottom surface  1010  of the tip. The sensor openings include openings  1015   a ,  1015   b ,  1015   c , and  1015   d . Optical fiber is connected to each of the sensor openings. The sensor openings can include sources and detectors. 
       FIG. 11  shows a perspective view of a third implementation of a tip  1105 . 
       FIG. 12  shows a bottom view of the third implementation of a tip  1205 . The tip includes two sensor openings on a bottom surface  1210  of the tip. The two sensor openings include an opening  1215  and an opening  1220 . The openings include a source and detector. 
       FIG. 13  shows a side view of the third implementation of a tip  1305 . A retractor portion or retractor blade  1310  is at an angle  1315  to a shaft  1320  onto which the tip is attached. In an implementation, the angle is about 90 degrees. Angle  1315  ranges from about 90 degrees to about 179 degrees. 
     In a specific implementation of  FIG. 13 , the tip of the retractor has a length of about 5 millimeters, width of about 3 millimeters, and a thickness (not including the retractor blade) of about 2 millimeters. 
       FIG. 14  shows a side view of the third implementation of the tip  1405  connected to a nerve retractor  1410 . This figure shows the handle of the retractor, which connects to the shaft and the tip. 
     This description of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form described, and many modifications and variations are possible in light of the teaching above. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications. This description will enable others skilled in the art to best utilize and practice the invention in various embodiments and with various modifications as are suited to a particular use. The scope of the invention is defined by the following claims.