Abstract:
A system for removing osteal cement and prosthetic joint components in connection with a prosthetic joint revision includes a controller connected to and controlling operation of a transducer, such as a surgical saw or drill. A tool mounted on the transducer is adapted for engaging the prosthetic joint cement mantel and melting an engagement portion of same. The cement in the engagement portion is resolidified with the tool tip embedded therein. The tool thus bonds to the cement mantel, and is used for vibrating softening and breaking up same when operation of the transducer resumes. An osteal cement and prosthetic device removal method includes the steps of melting an engagement portion of the osteal cement mantel, bonding a transducer-mounted tool to the cement mantel by resolidifying the cement engagement portion and reactivating the transducer for vibrating, softening and breaking up the cement mantel whereby it can be removed from the patient.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of and claims priority in U.S. patent application Ser. No. 10/724,459, filed Nov. 28, 2003, now U.S. Pat. No. 7,326,217. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to implant systems and methods for orthopedic and dental applications. More specifically, the present invention relates to implant insertion and extraction with couplings for attachment to manual and power force transducers with control over force variables. 
     2. Description of the Related Art 
     Many orthopedic procedures involve implants for replacing damaged and dysfunctional joints. For example, total joint replacement (TJR) and hemi arthroplasty (replacing one-half of the joint) procedures have been developed. Hips, knees, elbows, shoulders and wrists are commonly reconstructed with implants, such as prosthetic joints that are designed for optimal wear, comfort, biocompatibility and performance. Such replacement joint implants have benefited many patients by restoring their mobility and other functions. 
     Reconstructive dental procedures include installing implants such as prosthetic teeth, bridges, mandibles, temporomandibular (TMJ) joints and other dental prostheses. Significant improvements in dental function can be achieved for many patients using such procedures. 
     An important objective in designing orthopedic and dental implants and in performing implant procedures relates to effectively and permanently bonding the prosthetic components to patients&#39; existing, viable bone and dental structure. For example, TJR orthopedic surgery typically involves removing damaged and degenerated existing joints and adjacent bone structure for replacement with prostheses. The remaining bone structure is preferably sound, dense and capable of withstanding dynamic loads in order to maximize patient function and mobility. A general objective of orthopedic and orthodontic surgery is to retain as much original, healthy bone structure as possible. 
     Orthopedic and orthodontic revision procedures are necessitated by prosthetic failures from various causes. For example, further deterioration and trauma can lead to prosthetic joint failures. Another problem relates to loosening and disengagement of the components. For example, orthopedic cement, which is commonly used to bond prosthetic components to bone, can loosen and disengage. Looseness and “play” in implants, such as prosthetic joints, can cause significant problems. These include patient discomfort and immobility. Moreover, such looseness can increase under dynamic loading, and can ultimately lead to complications associated with implant failure. 
     When revision procedures are indicated by such conditions, extracting existing implants and the cement mantels bonding same can present significant difficulties. Extracting prostheses that have been permanently bonded in place with high-strength adhesives can require substantial force, with resulting trauma and collateral damage. For example, perforated and cracked existing bone structures can result from forces associated with extracting failed prostheses. 
     Moreover, implants can become stuck during installation. For example, if the cavity formed for the implant shaft is too small, a test fit can result in immobility with resistance to both insertion and extraction. Extracting a stuck implant can require breaking the surrounding bone structure, with resulting complications. 
     The prior art has attempted to address some of the problems associated with orthopedic implant extractions. For example, the Engelbrecht et al. U.S. Pat. No. 4,248,232 discloses the use of a vibrating tool to soften the cement between nested components bonded together. The Hood et al. U.S. Pat. No. 5,045,054 discloses an ultrasound power generator adapted for coupling to endoprostheses and vibrating same to soften their adhesive bonds. Hood et al. disclose an ultrasonic tool for attachment to and removal of surgical components in U.S. Pat. No. 5,318,570. Vandewalle et al. U.S. Pat. No. 6,190,392 disclose an auger tool connected to an ultrasonic transducer/handpiece for extracting an osteal cement mantel. 
     Heretofore there has not been available an orthopedic and dental implant system and method with the advantages and features of the present invention. 
     SUMMARY OF THE INVENTION 
     In the practice of the present invention, systems and methods are provided for installing and extracting orthopedic and dental implants. In one aspect of the invention, a manual or power force transducer is coupled to an implant for imparting installation or extraction forces, ranging from low-amplitude vibrations to impact blows through a range of frequencies. The forces can act in either direction. i.e. insertion or extraction, or both in an alternating operational mode. The amplitudes of the forces can be varied, including amplitude differentials on insertion/extraction strokes. The forces can be linear reciprocating, rotorary reciprocating, oscillatory (side-to-side) or orbital. 
     In another aspect of the invention, a power source connects to a working tip adapted for melting an engagement portion of a cement mantel. Discontinuing the application of power to the working tip causes the cement to resolidify on and capture same. A second power application vibrates the entire homogenous portion of the cement loose for extraction. 
     In another aspect of the invention, the controller scans predetermined frequency, amplitude and other variable ranges and selects optimum values for such operating parameters based on feedback received from sensors connected to vibrating tools or patients. The sensors can detect current loading as a function of variable patient and system conditions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof. 
         FIG. 1  is a schematic, block diagram of an implant system embodying the present invention. 
         FIG. 1A  is a perspective view of a hip femoral implant. 
         FIGS. 2-9  are fragmentary views of the coupling in the process of attachment to the implant. 
         FIGS. 10-12  are fragmentary views of a coupling embodying another aspect of the invention, showing the process of attachment to the implant stem. 
         FIG. 13  is a top plan view of the coupling and the implant, taken generally along line  13 - 13  in  FIG. 12 . 
         FIG. 14  is a top plan view of the coupling and the implant, with the coupling compressed onto the implant stem. 
         FIG. 15  is a block diagram of an automated system embodying another aspect of the present invention. 
         FIG. 16  is a flowchart showing an aspect of the method of the present invention. 
         FIGS. 17-18  are cross-sectional views of a femur, showing an aspect of the method of the present invention for removing an orthopedic cement mantel from the intramedullary canal. 
         FIGS. 19-22  are vertical, cross-sectional views of a femur, showing the removal of a femoral implant and the cement mantel associated therewith according to an aspect of the method of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     1. Introduction and Environment 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. 
     Referring to  FIG. 1 , the reference numeral  2  generally designates an orthopedic and dental implant system embodying an aspect of the present invention. The system  2  generally includes an external subsystem  3  including a force transducer  4 , which can comprise a manual device, such as a slaphammer, or an electrical, pneumatic or hydraulic power device. The transducer  4  is adapted for variable operation, including such variable operating parameters as frequency, amplitude, direction (i.e. in or out with respect to the patient) and insertion and/or extraction. The transducer  4  can apply linear reciprocating, rotary reciprocating, oscillatory (side-to-side) or orbital force. A coupling  6  is connected to the force transducer  4 . The coupling  6  and its ancillary components can be disposable for one-time usage in conjunction with a TMJ or other procedure, or they can be adapted for sterilization and reuse. 
     A patient subsystem  5  includes an orthopedic or dental implant  8 , which is adapted for placement in a patient  12  with an interspace  10  therebetween, which can receive suitable orthopedic cement for bonding the implant  8  in place. 
       FIG. 1A  shows a femoral implant  15 , which can be used in a hip joint replacement procedure. The implant  15  includes an intramedullary canal shaft  17  integrally formed with a head  19  including a transverse passage  20 . The shaft  17  can be finished with a scratch fit texture or engraving to facilitate bonding to bone. A stem  22  projects upwardly at an oblique angle from the head  19  and mounts a spherical cap  24  on a Morse taper  25 . The cap  24  is pivotably received in an acetabular cup (not shown) to form a ball-and-socket type hip joint. Various configurations and designs of femoral and other implants can be used with the system of the present invention. 
     2. Transducer-to-Implant Couplings 
       FIG. 2  shows a distal end  26  of the coupling  6  with a clevis configuration including a pair of receivers  28  with hexagonal recesses  30 , which are adapted for alignment with the passage  20  ( FIG. 3 ).  FIG. 4  shows a guide wire  32  forming a loop  34  extending through the implant passage  20  and the coupling receivers  28 . The loop  34  can be captured with a suture  36 , which can be inserted into the patient from an entry location spaced from the entry location for the guide wire  32 .  FIGS. 5 and 5A  show a flexible guide extension member  38 , which tapers from a maximum diameter at a female-threaded base  40  to a minimum diameter at a pointed tip  42  with an eyelet  44 . The guide member  38  is adapted for pulling a fastener, such as a bolt  46 , through the aligned implant passage  20  and the clevis end receivers  28 . The bolt  46  is threadably received in the guide member base  40  and the guide member eyelet  44  receives the guide wire  32 , which is adapted for pulling the guide member  38  ( FIG. 5 ). The flexibility of the guide member  38  enables it to approach the passage  20  and the receivers  28  from oblique angles. 
       FIG. 6  shows the bolt  46  in place with the guide member  38  extending therefrom. The bolt  46  includes a bolt loop  48  extending from its threaded end and adapted to capture the guide wire  32  or a suture to provide an alternative or auxiliary technique for installing the bolt  46 . A nut  50  is threadably received on the end of the bolt  46  and can be drawn into the hexagonal recesses  30  ( FIGS. 7 and 8 ), or surface-mounted on the clevis  26  ( FIG. 9 ) with a washer  52 . 
     The coupling distal, clevis end  26  transmits force from the force transducer  4  to the implant  8 , as shown by the double-ended force arrow  54  ( FIG. 8 ), which represents the application of linear, reciprocating “in” strokes  14 , “out” strokes  16 , or both ( FIG. 1 ). As noted above, such forces can also be rotary reciprocating, oscillatory (side-to-side) or orbital. In operation such forces can be applied as necessary by the physician installing or extracting the implant  8 . Moreover, test fitting same is facilitated with reduced risk of the implant becoming irretrievably stuck in an overly-tight intramedullary canal. 
       FIGS. 10-14  show an alternative configuration coupling distal end  60  comprising another aspect of the invention. The coupling end  60  has a clevis configuration with a shaft  62  extending at an oblique angle therefrom and connected to the force transducer  4 . The coupling end  60  receives the implant stem  22  below a frusto-conical cap thereof and is clamped thereon ( FIGS. 13-14 ) by a fastener, which can comprise a bolt received in coupling end receivers  66  and including hexagonal recesses for the bolt head  70  and a nut  72  ( FIGS. 11 and 12 ), as required. A washer  74  can also be provided on either or both sides of the coupling end  60 . As shown in  FIG. 14 , the coupling end  60  is deformable in order to securely clamp the implant stem  22 . 
     3. Orthopedic Cement Extraction System and Method 
     A system  102  and a corresponding method comprising an alternative aspect of the present invention are shown in  FIGS. 15-22  and are adapted for installing and removing orthopedic and dental implants  103  and orthopedic cement  104 . Implants are commonly bonded in place with orthopedic cement, which may require removal in connection with revision procedures. For example, femoral implants are inserted into intramedullary canals and secured therein by cement. 
     Orthopedic cement  104  is placed in an interspace  130  around the implant  103  within the intramedullary canal of a bone  105  in a patient  107 . Although an exemplary application of the invention is described in connection with a hip TJR, applications for same are virtually unlimited and include other replacement joints, such as knees, shoulders, etc. 
     The system  102  generally includes a controller  116  including a programmable microprocessor  118 . The controller  116  can include various components, such as input and output devices, memory storage, etc. A foot pedal switch assembly  120  is connected to the controller  116  for providing input thereto and includes frequency and amplitude control switches  122 ,  124 , which are adapted for hands-free operation by an operator pressing same with his or her feet, for example in a sterile operating environment. 
     A transducer  126  is controlled by the controller  116  and is operably connected to a tool  127  for imparting mechanical energy to the implant  103  and/or the cement  104 . For example, the transducer  126  can provide rotorary reciprocating linear reciprocating, oscillatory (side-to-side), orbital and other types of motion. The tool  127  can comprise a coupling, as described above, or various reciprocating and oscillatory saws, which are suitable for use with the system  102 . Other types of tools include drills, vibrators and reciprocating chisels. The tool  127  is preferably designed for engaging the implant  103  or cutting, forming or shaping the cement  104 , and can be used for dynamically coupling the transducer  126  to the implant  103  and/or the cement  104 . A power source  128  provides power to the transducer  126  and can be controlled by the controller  116 . The power source  128  can comprise electrical power, compressed air, compressed nitrogen, hydraulic fluid, etc. 
     The microprocessor  118  receives input signals from sensors  109 ,  111 ,  113 ,  115 ,  117  and  119  connected to the system components as shown in  FIG. 1 . For example, sensors  109 ,  111  provide feedback from the transducer  126  and the tool  127  respectively. The sensors  113 ,  115 ,  117  and  119  provide feedback from the implant  103 , the cement  104 , the bone  105  and the patient  107  respectively. It will be appreciated that fewer or more sensors can be utilized with the present invention, and can monitor and provide feedback with respect to the operation of various system components and the operating parameters associated with same. For example, the power load on the transducer  126  can be sensed for reaction by the controller  116 , if necessary. Similarly, patient conditions such as temperature, blood pressure, stress indicators, etc. can be monitored and the microprocessor  118  can be preprogrammed to react to particular patient conditions and control the appropriate operating parameters of the system  102  whereby the primary functions thereof can be automated. 
     One or more of the sensors can comprise an energy-sensing device, such as an infrared thermal sensor. The controller  116  can be configured for thermally mapping the joint area whereby the temperature changes in the prosthetic joint  106 , the patient  107  and the cement mantel  104  can be monitored in real-time. Such a thermal map can be displayed on a monitor  125  connected to the controller  116 , which processes the thermal characteristics detected by the infrared thermal sensor as input for automatic control functions by the controller  116  and/or visual observation by means of the monitor  125 . 
     4. Orthopedic Cement and Implant Extraction Method 
       FIG. 16  is a flowchart of a method embodying the present invention. From start  132  a patient  107  is prepared at  134  and the controller  116  is initialized at  136 . Initializing the controller can include preprogramming certain operating parameters and conditions. For example, various common prostheses can be accommodated by preprogramming the controller to operate the transducer  126  at presumed optimum conditions, subject to varying the output signals to correspond to the actual conditions encountered. The existing joint  6  is accessed at  138  and the existing mass or mantel of cement  4  is exposed at  140 . Polymethylmethacrylate (PMMA) cement is commonly used for implant attachment, particularly in medullary canals. Such cement is susceptible to softening when vibrated in the ultrasonic range, and tends to reform and reharden when the energy application is discontinued. The transducer  126  is activated at  141  and operates at a first frequency f 1  and a first amplitude A 1 . 
     Accordingly, an engagement portion of the cement mantel  104  is melted at  142  and the tool  127  is embedded therein at  144 . The melted engagement portion resolidifies at  146 , thereby bonding the tool  127  to the cement mantel  104 . The transducer  126  operates at a second frequency t 2  and a second amplitude A 2  at  148 . For example, low-frequency vibration can be utilized to extract the cement. Feedback is received at  150 . Such feedback can be derived from the various sensors  109 ,  111 ,  113 ,  115 ,  117 ,  119  and can correspond to such conditions as temperature and transducer current flow (corresponding to load conditions). For example, greater cement resistance to vibration can cause a greater load on the transducer  126 , which in turn causes the current flow to increase. Such changing conditions can be sensed and predicted and can cause the controller  116  to respond accordingly. For example, upon encountering lessening resistance due to the cement mantel  104  softening, the controller  116  can reduce the amplitude of the energy applied to the transducer  126 . Moreover, the resonant frequency of the components can be monitored. Frequency and amplitude changes can thus be detected and reacted to, for example by reducing or discontinuing the application of power. 
     It will be appreciated that the microprocessor  118  can be programmed to provide appropriate reactions to accommodate various operational parameters. For example, it is generally desirable to avoid excessive heat, which can damage both bone and soft tissue thereby prolonging patient recovery. The microprocessor  118  can thus be programmed to reduce or cut off transducer power upon detecting certain conditions at any of several locations in the prosthetic joint or the patient. Moreover, manual inputs from the foot pedal switches  122 ,  124  or other operator-controlled inputs can be coordinated with automatic control features. For example, the operator can manually adjust such operating parameters as amplitude and frequency within predetermined operating ranges, beyond which automatic controls take over to avoid potential harm or discomfort to the patient. 
     If a frequency adjustment is indicated at decision box  152 , the controller provides another frequency (f n+1 ) at  154 , and returns to the feedback step  150 . When no further frequency adjustment is needed (negative branch from decision box  152 ), the method proceeds to lock in frequency at  156 . Another feedback step occurs at  158  and leads to an amplitude adjustment decision box at  160  from which a positive decision leads to the next amplitude (A n+1 ) being generated at  162 . The negative branch from the decision box  160  leads to a lock in amplitude step at  164 . Extraction occurs at  166 , the joint is revised at  168  and the method terminates at  170 . 
       FIGS. 17-18  show applications of the cement removal system  102  and the method described above in connection with removing a cement mantel  170  from the intramedullary canal  172  in a femur  174 . The mantel  170  is segmented with cuts  176 . The blade  178  forms an engagement portion  180  whereat the liquefied cement  170  is permitted to solidify on the blade  178 . The respective segments  182  can thus be extracted with the controlled application of force, such as low-frequency vibration, as shown in  FIG. 18 . 
       FIG. 19  shows a femur  210  and a femoral implant  208 , which are separated by an interspace  230  filled with orthopedic cement  204 .  FIG. 20  shows the implant  208  removed, leaving the cement  204  within the intramedullary canal  206 . As shown in  FIG. 21 , the tool  227  has penetrated an engagement portion  232  of the cement  204 , which resolidifies to capture same.  FIG. 22  shows a chunk  234  of cement  204  being removed from the intramedullary canal  206 . By properly adjusting the frequency and amplitude of the transducer  126 , substantial portions of the cement  204  can be removed. Upon completion of the extraction procedure, the walls of the intramedullary canal  206  are preferably free of cement  204 , as shown in  FIG. 22 . The treating physician can then proceed with the revision procedure, including installation of replacement prosthetic components. 
     Although the system  102  and its methods of use have been described in connection with computer-controlled automation, the methods of the present invention can be practiced manually. 
     It is to be understood that while certain embodiments and/or aspects of the invention have been shown and described, the invention is not limited thereto and encompasses various other embodiments and aspects.