Patent Publication Number: US-2009222019-A1

Title: Implant insertion device

Description:
FIELD OF THE INVENTION 
     The present invention relates to methods and devices for inserting an implant, and in particular to methods and devices for measuring and/or controlling an amount of force applied to an implant or other element during insertion. 
     BACKGROUND OF THE INVENTION 
     Many patients have enjoyed the benefits of joint replacement surgery where an artificial joint is substituted for a degenerate or damaged biological joint. This type of surgery is particularly prevalent in the hip joint, where often the preoperative patient experiences substantial pain in even the routine task of walking. The hip joint replacement operation is typical of joint replacement operations in that the existing joint is removed and a hip replacement system including a femoral component and an acetabular cup (together with a friction-resistant insert) are substituted. In particular, before the surgeon can begin the process of implanting the replacement components, he or she must first make a posteriorlateral incision, retract or dissect the covering musculature, dislocate the hip, and remove the femoral head. The acetabulum must also be reamed out to receive the acetabular cup, and the femur drilled and reamed to receive the femoral component. Once the femur cavity is sufficiently prepared, the surgeon can then insert the femoral component of the prosthesis by applying a force to the femoral component to wedge it into the cavity. Typically this force is applied by hammering the prosthesis into the femur cavity. The surgeon determines the amount of force to apply based upon experience and tactile feedback. 
     While tactile feedback can be effective, it can sometimes result in the application of too little or too much force to the femoral component. If too little force is applied to the femoral component, the femoral component will not be fully implanted within the femoral cavity potentially resulting in movement of the femoral component which can cause the patient pain. If too great a force is applied to the femoral component, the femur can fracture. When a fracture occurs wider surgical exposure is required to fix the fracture, rendering increased pain and recovery time for the patient. 
     Accordingly, there is a need for improved methods and devices for measuring and/or controlling an amount of force applied to an implant or other element. 
     SUMMARY OF THE INVENTION 
     The present invention provides methods and devices for measuring and/or controlling an amount of force applied to an implant or other element. In one embodiment, an implant inserter tool is provided that includes a shaft having a proximal end that is adapted to receive a force and a distal end that is adapted to contact an implant. The inserter tool also includes a force controlling element coupled to the shaft. In use, the distal end of the tool can be placed in contact with an implant or other element, and a force can be applied to the proximal end of the tool to drive the implant or other element into bone. The force controlling element can measure the amount of force applied to the inserter tool, thereby measuring the force applied to the implant or other element. 
     The force controlling element can have a variety of configurations. In one embodiment, the force controlling element can be a sensor, such as a piezoelectric sensor. In another embodiment, the force controlling element can be a dampening element such as a piston, a spring, or a compressible member. In yet another embodiment, the force controlling element can be adapted to collapse upon the application of a threshold level of force. For example, the force controlling element can be a torque limiter that is configured to collapse upon application of a threshold level of force thereto to prevent an excess amount of force from being applied to the implant or other element being impacted. 
     In another embodiment, the inserter tool can be part of a system that includes a driver that can apply force to the inserter tool, and means for controlling an amount of force applied to an implant being inserted into bone using the inserter and driver. The means for controlling an amount of force can be, for example, a sensor, a dampening element, or a torque limiter. The system can also include a variety of other features. For example, the system can include a processor that is adapted to receive patient data and to calculate a threshold force, based on the patient data, that can be applied to an implant without fracturing bone. The system can also optionally include a display element that is adapted to display an amount of force applied to the implant to provide real-time monitoring thereof. 
     Methods for inserting an implant are also disclosed herein, and in one embodiment, an implant can be positioned adjacent to bone, and an inserter tool can be positioned in contact with the implant. A force can be applied to the inserter tool to drive the implant into bone, and a measurement device coupled to the inserter tool or the implant can provide feedback relating to an amount of force applied to the inserter tool, and consequently the implant. The amount of force can be displayed to provide real-time monitoring. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a perspective view of one exemplary embodiment of an inserter that includes a sensor; 
         FIG. 2  is a perspective view of an exemplary embodiment of an implant insertion system that includes an inserter having a dampening element and an implant; 
         FIG. 3A  is a perspective view of another exemplary embodiment of an implant insertion system that includes an inserter after the application of a predetermined level of force; and 
         FIG. 3B  is a perspective view of the device of  FIG. 3A  after the application of an amount of force that exceeds the predetermined level. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Certain exemplary embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the devices and methods disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the devices and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments and that the scope of the present invention is defined solely by the claims. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. Such modifications and variations are intended to be included within the scope of the present invention. 
     In general, methods and devices are provided for measuring and/or controlling an amount of force applied to an implant, driver, broach, rasp, bone, or other elements. For example, the methods and devices disclosed herein can be used to measure and/or control the forces applied to an implant being driven into bone, thereby reducing or eliminating the risk of fracture to the bone. In certain exemplary embodiments, the various methods and devices can be incorporated into an inserter tool, an implant, a driver, or other devices that are used in procedures which require the application of force. A person skilled in the art will appreciate that, while the present invention is described in connection with driving implants into bone, the methods and devices can be used in a variety of medical procedures and for applying force to a variety of objects. 
       FIG. 1  illustrates one embodiment of an inserter tool  10  that can be used to measure and/or control force applied thereto. This force can be used, for example, to determine the amount of force transferred from the inserter tool  10  to an implant being driven into bone. As shown, the inserter tool  10  generally includes a shaft  12  having proximal and distal ends  12   a ,  12   b , and a force controlling element  14  coupled thereto or formed thereon. The shaft  12  can have virtually any shape or size, but in the illustrated exemplary embodiment it has a generally elongate rigid shape. The proximal end of the shaft  12   a  can vary in shape and size, but it is preferably adapted to receive a force from a driver, such as a hammer or mallet. In the illustrated embodiment, the proximal end of the shaft  12   a  includes a flange  17  formed thereon with a planar surface for receiving a force. The distal end of the shaft  12   b  can also vary in shape and size, and the particular configuration can vary depending upon the intended use. In the embodiment shown in  FIG. 1 , the distal end  12   b  is configured to contact an implant to drive the implant into bone. Thus, the distal end  12   b  has a pointed tip  15  that is configured to fit within a corresponding bore formed in an implant. In other embodiments, the distal end can be round, flat, or have various other geometries to complement the shape of an implant or other element. 
     As previously mentioned, the inserter tool  10  can also include a force controlling element  14  for measuring and/or controlling an amount of force applied to the shaft  12  of the inserter tool  10 , thereby measuring and/or controlling the amount of force transferred from the inserter tool to an implant being driven into bone. While the force controlling element can have a variety of configurations, in one embodiment, the force controlling element can be a sensor  14 . The sensor  14  can be located anywhere on the shaft  12  of the tool  10 . As shown in  FIG. 1 , the sensor  14  is located at a mid-portion of the shaft  12  between the proximal and distal ends  12   a ,  12   b . In particular, the sensor  14  is in the form of a housing that is disposed between and separates the shaft into proximal and distal portions  12   a ,  12   b . This allows the force to be transferred from the proximal portion  12   a , through the sensor  14 , to the distal portion  12   b  of the shaft  12 . The sensor  14  can be mated to the shaft  12  using a variety of techniques known in the art. For example, the sensor can be mated to the proximal and distal portions of the shaft  12  using an adhesive, welding, or other bonding techniques, or in other embodiments it can be integrally formed with the shaft  12 . A person skilled in the art will appreciate that, while  FIG. 1  illustrates a sensor  14  that is located at a mid-portion of the shaft  12 , the sensor can be located anywhere on the shaft or on other devices used in conjunction with the inserter tool  10  to apply or transfer a force. 
     While virtually any sensor can be used, one exemplary sensor for use with the present invention is a piezoelectric sensor. One suitable piezoelectric sensor is manufactured by PCB Piezoelectrics of Depew, NY (USA) and sold as model number 208c05. The sensor has a range of about 0.05 Newtons to 5000 Newtons, a sensitivity of about 0.22 mV/N, and a resolution of about 0.022 N/rms. Another exemplary sensor for use with the present invention is an accelerometer, which measures the acceleration of the inserter tool as a force is applied to it. When little or no acceleration is measured by the accelerometer after the application of a force, the implant will have been substantially secured in position and application of additional force may lead to fracture of the bone. 
     The sensor  14  can also be configured to communicate with a display, such as a monitor or a screen, for displaying the force measured by the sensor  14 .  FIG. 1  illustrates wires  19  extending from the sensor  14  and coupled to an external display  16 . The display  16  can include or be coupled to a processor, such as a computer, for converting the signal received from the wires into a signal indicative of the force. The signal can be, for example, a visual signal such as a numerical value, a graph, a chart, or a light, and/or an audible signal. While  FIG. 1  illustrates an external display  16 , the display can be coupled to or formed on the inserter tool, a driver, an implant, or on other devices used to apply or transfer a force. In other embodiments, the display can be worn by a user, such as in the form of a watch. 
     In another embodiment, the processor can be configured to analyze the measured force received from the sensor  14 . For example, the processor can be configured to receive patient data that can be used to calculate a threshold force, or a range of force, that can be applied to an implant being driven into bone without fracturing the bone. The patient data can include, by way of non-limiting example, bone density and strength, sex, age, shape and size of the implant, and other characteristics that may be relevant to determining the threshold force, or a range of force, that can be applied to an implant to drive the implant into bone without fracturing the bone. The threshold force, or the range of force, that is determined based on the patient data can be compared to the measured force received by the sensor and communicated to the processor. The display can indicate whether the measured force is within the predetermined range of force or below the predetermined threshold force, thereby allowing the user to adjust the amount of force applied to the implant as needed. This is particularly advantageous for minimally invasive procedures, where risk of bone fracture is increased. 
     In use, the distal end  12   b  of the inserter tool  10  can be placed in contact with an implant, and a force can applied to a proximal end  12   a  of the tool  10  using a driver, such as a hammer or mallet, to drive the implant into bone. As the force is transferred through the inserter tool  10 , the sensor  14  will emit a signal that corresponds to the amount of force applied to the shaft  12 , and thus the amount of force transferred to the implant. The signal can then be converted into a value indicative of the force which can be displayed to the user. As previously described, the measured force can also be compared to a predetermined threshold force or a predetermined range of force to prevent fracture of the bone. The surgeon can adjust the applied force when the measured force exceeds the predetermined threshold force. 
     While the force controlling element in  FIG. 1  is a sensor, in other embodiments the force controlling element can be a dampening element that is configured to dampen or decrease an amount of force applied to the shaft of the inserter tool, thereby decreasing the amount of force transferred from the inserter tool to an implant being driven into bone.  FIG. 2  illustrates one embodiment of an inserter tool  110  having a dampening element  114  formed thereon. In general, the inserter tool  110  includes a shaft  112  that is similar to the shaft discussed in  FIG. 1 , and a dampening element  114  coupled thereto. 
     The dampening element  114  can have any configuration, but in an exemplary embodiment it is preferably effective to decrease an amount of force transferred through the shaft  112 . As illustrated in  FIG. 2 , the dampening element  114  is in the form of a piston  114  having a small cylinder  122  that fits within a larger cylinder  120  to displace or compress fluid or air  124  disposed therebetween. A person skilled in the art will appreciate that, while  FIG. 2  illustrates a dampening element in the form of a piston  114 , the dampening element can have a variety of other configurations. For example, the dampening element can be in the form of a spring, a compressible member, or other structures that absorb or limit force. The dampening element  114  can also include other features to aid in controlling and/or limiting an amount of force transferred from the inserter tool  110  to an implant or other element. For example, the dampening element  114  can be adjustable to allow a user to vary the amount force absorbed by the dampening element  114 . Where the dampening element is a piston  114 , as shown in  FIG. 2 , this can be achieved by varying the amount of air or liquid  124  contained between the cylinders  120 ,  122 . Such a configuration will essentially allow a user to select a predetermined threshold force that is applied to an implant  140  or other element being impacted using the inserter tool  110 . The dampening element can also include other features, such as a sensor as previously discussed with respect to  FIG. 1 . 
       FIG. 2  illustrates the inserter tool  110  in use positioned in contact with a femoral implant  140 . The femoral implant  140  can be inserted into a patient&#39;s femur by applying a force to the proximal portion of the shaft  112   a . As the force is transferred from the proximal portion of the shaft  112   a , through the dampening element  114 , to the distal portion of the shaft  112   b , the dampening element  114  will absorb some of the force. As a result, the amount of force that is transferred to the distal portion of the shaft  112   b , and ultimately to the implant  140 , is decreased. This is particularly advantageous as the dampening element  114  will prevent too much force from being applied to the implant  140 , thereby reducing or preventing the risk of fracture of the bone. As noted above, a user can optionally adjust the threshold force, as may be necessary. 
     In another embodiment, the force controlling element can be a mechanical torque limiter that allows a portion of the inserter tool to collapse when a threshold force is applied thereto, thereby preventing excess force from being applied to an implant being driven into bone using the inserter tool.  FIGS. 3A-3B  illustrate one embodiment of an inserter tool  210  having a mechanical torque limiter  214  formed thereon. In general, the inserter tool  210  includes a shaft  212  that is similar to the shaft discussed in  FIG. 1 , and a mechanical torque limiter  214  coupled thereto between proximal and distal portions of the shaft  212 . The torque limiter  214  can have any configuration, but in an exemplary embodiment it is adapted to allow the inserter tool  210  to move from a linear configuration to a non-linear configuration when a threshold force is applied to the inserter tool  210 . As shown in  FIGS. 3A-3B , the torque limiter  214  has a first arm  232   a  mated to the proximal portion  212   a  of the shaft  212 , and a second arm  232   b  mated to the distal portion  212   b  of the shaft  212 . A spring-loaded housing  234  is coupled between the first and second arms  232   a ,  232   b . The spring-loaded housing  234  is adapted to remain in a locked position to hold the arms  232   a ,  232   b , and thus the proximal and distal portions  212   a ,  212   b  of the shaft  212 , in a linear configuration. When a threshold force is applied to the proximal portion  212   a  of the inserter tool, the spring-loaded housing  234  will unlock and collapse. As a result, the arms  232   a ,  232   b  are free to pivot relative to one another, thereby causing the proximal portion  212   a  to pivot relative to the distal portion  212   b  of the shaft  212  such that the proximal and distal portions  212   a ,  212   b  are held at an angle with respect to one another. This prevents an excess amount of force from being transferred through the inserter tool  210  to an implant. 
     A person skilled in the art will appreciate that the torque limiter  214  can also include other features to aid in controlling and/or limiting an amount of force transferred from the inserter tool  210  to an implant or other element. For example, the torque limiter can be adjustable to allow a user to vary the threshold force. While the adjustment techniques can vary, in the embodiment shown in  FIGS. 3A-3B  the torque limiter  214  can be adjusted by varying the tension of the spring. The mechanical torque limiter can also include a sensor, a processor, a display, and/or a dampening element, as previously discussed with respect to  FIGS. 1 and 2 . 
     In use, the distal end of the inserter tool  210  can be placed into contact with an implant (not shown). The force limiter remains in a locked configuration and the threshold force can be set as desired. A driver  270  can be used to apply a force to the proximal end of the shaft  212 . As shown in  FIG. 3A , when the force is at or below the threshold level, the force is transferred through the shaft  212  and applied to the implant. When the force exceeds the threshold, the torque limiter  214  will unlock and collapse. As a result the proximal portion  212   a  of the shaft  212  can pivot relative to the distal portion  212   b  of the shaft  212 , as shown in  FIG. 3B , to prevent the application of excess force to the implant. 
     One skilled in the art will appreciate further features and advantages of the invention based on the above-described embodiments. Accordingly, the invention is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety.