This application claims the benefit of U.S. Provisional Application Serial No. 60/600,168 filed August 10, 2004, the teaching of which is incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to devices for the removal of a prosthetic implant from a prosthetic implant interface, as well as methods of use thereof. Such methods and devices are particularly useful in revision surgeries.

BACKGROUND OF THE INVENTION

It has been over seventy-five years since the first use of replacement parts for hip joints. There have been many advances in the prosthetic components, materials, surgical techniques and the like, so that today, total hip joint replacements are relatively commonplace. Approximately 168,000 hip joint replacement operations or arthroplasties are performed each year in the United States. In addition, related techniques have also been developed for replacing knee and shoulder joints.

The human hip, like the shoulder, is a ball and socket joint, in which the ball of femur fits into the socket of the pelvic bone. The normal hip can move backwards and forwards, from side-to-side, and can perform twisting motions. The hip contains a liquid, which lubricates the joint, and is held together with ligaments. Full function of the hip joint depends on the successful coordination of interrelated parts, including bones, muscles, tendons, ligaments, and nerves. When the hip is not able to function properly, hip replacement surgery may be an option.

There are two principal components to a hip joint replacement prosthesis. The first of these two components is an acetabular cup that is implanted in the acetabulum. The acetabular cup provides a spherical socket that is the bearing surface for the replacement joint. The second component of a hip joint replacement prosthesis comprises a femoral stem prosthesis that is fitted into the medullary canal of the femur and a femoral head on the stem having a spherical surface that meets with the acetabular socket. The femoral stem component is referred to as the prosthetic implant for the purposes of this invention.

During an arthroplasty procedure in the operating room, the femoral portion of the prosthetic implant is inserted by cutting off the old or diseased femoral neck with or without removing the greater trochanter. The medullary canal is then prepared using drills, reamers and successively larger rasps to produce a cavity that closely conforms to the femoral stem. After cleaning, the femoral stem is driven into place in the canal where a non-cemented prosthetic implant is inserted to establish a press fit. In the case of a non-cemented prosthetic implant, the femoral stem prosthesis contains some type of porous surface to which bone may adhere and infiltrate, thus anchoring the prosthetic implant over time. Alternatively, the prosthetic implant may be anchored in place by polymethylmethacrylate (PMMA) cement applied during placement of the prosthetic implant. In either case, preparing the cavity to fit the femoral stem prosthesis is tedious and prolongs the period during which the patient must be kept under general anesthesia.

Roughly one percent of the total hip replacements performed each year fail. due to complications and need to be revised. Reasons for this failure rate include local loosening of the prosthetic implant, prosthetic implant stem failure, fracture of the prosthetic implant, infection around the prosthetic implant or pain caused by loosening of the prosthetic implant.

Other joints of the body, such as the knee and the shoulder, undergo similar replacement arthroplasties and suffer from failures as noted above for hip replacements. Knee arthroplasties are conducted at rates similar to that of hip arthroplasties, whereas shoulder arthroplasties are not as common.

Revision arthroplasty surgery requires removal of the embedded prosthetic implant. The revision procedure is traumatic for the patient, tedious for the surgeon, and quite time consuming for the surgical staff and facilities. In addition, it is more expensive than the original arthroplasty procedure and is accompanied by a higher rate of morbidity and mortality. Often, there is less bone for the surgeon to work with, or more bone grafting may be needed to secure the second implant.

In performing the revision surgery, if possible, the surgeon will attempt to use the same surgical incision site used in the primary surgery. Once the implant is exposed, the surgeon will separate the thighbone component from the socket (acetabular component.) This is called dislocating the implant. The bone/cement/prosthetic implant interfaces typically become a solid cohesive unit inside the patient's body that is able to withstand the forces caused by the activities of daily living. Even in cases of prosthesis loosening, the loosening is often local and there remain areas of the bone/cement/prosthetic implant interfaces that are well fixed. Thus, the bone/cement/prosthetic implant interfaces must be disrupted to remove the failed prosthetic implant.

The current method of disrupting this interface consists of applying repetitive manual impacts to the prosthetic implant by means of a sliding hammer. This is a time- consuming process, both for the orthopedic surgeon and for the patient who is under general anesthesia for the duration of this procedure. There are currently no tools commercially available that easily and quickly separate the cement or bone from the prosthetic implant to allow for less traumatic removal of the prosthetic implant from the surgical site.

Removal of a prosthetic implant often requires very invasive surgery that is frequently destructive to the bone and surrounding soft tissues primarily due to the, * level of adherence of prosthetic implant to the bone and cement interfaces. As an . example of this, a well-fixed implant may require broad surgical exposure of the proximal femur in order to visualize and access the prosthetic implant during removal. In a revision surgery of this type, trauma to the patient can be severe. Inadvertent damage, including fracture of the femur, is not unusual.

Thus, there is a need for a less destructive, less invasive device and method for removing a prosthetic implant. Such advances for revision arthroplasties would reduce the procedure duration time for removal of a prosthetic implant, decrease the patient's exposure to general anesthesia and decrease the associated trauma and destruction of the surrounding tissue during these procedures. Such a device and method is expected to result in a significant decrease in patient morbidity and mortality as well as a reduction in procedure cost for healthcare providers, third party payors, and patients. On average, revision arthroplasty is typically two to three times more expensive than the original arthroplasty surgery.

SUMMARY OF THE INVENTION

The present invention provides a device for removing a prosthetic implant from a prosthetic implant interface. In particular, the device applies force to the prosthetic implant interface thereby disrupting the cement/implant or bone/implant interface. The invention further provides methods of using the device for the removal of a prosthetic implant from the bone implant interface once the cement/implant or bone/implant interface has been disrupted.

In one embodiment, the invention features a device for the disruption of a prosthetic implant comprising a body having a proximal end and a distal end, an impact rod having a proximal end and a distal end wherein the impact rod is disposed within the body and extends out of the distal end of the body in connection with the prosthetic implant directly or indirectly and an actuation mechanism, wherein the actuation mechanism and impact rod are disposed such that actuation causes the impact rod to transmit impacts to the implant. The device can further include a handle at the proximal end of the device. In preferred embodiments, the impact rod transmits repetitive impacts to the implant. The impact rod is preferably disposed so as to provide, impacts in a direction along the length of the impact rod and can provide : impacts in a direction away from the implant and/or towards the implant. Preferably, the impact rod is disposed so as to provide impacts that transmit force along the long axis of the implant. .

In one embodiment, the device further includes a mechanism for applying a gradual application of force to the implant. This mechanism can comprise the impact rod which would, thus, apply both impacts and gradual application(s) of force. The mechanism can be disposed so as to provide a gradual application of force in a direction away from the implant and/or towards the implant. In certain embodiments, the device further includes a mechanism for applying torque to the implant. This mechanism may comprise the impact rod which would, thus, apply both impacts and torque and, in some embodiments gradual application(s) of force as well.

In an exemplary embodiment, one or more mass is housed within the body and is in connection with the actuation mechanism. One or more flange is further positioned along the length of the impact rod such the mass is actuated to move towards the one or more flange. The mass contacts the one or more flange, which transmits force to the impact rod, which, in turn, transmits an impact to the interface. The one or more mass can be located distal the one or more flange such that contact between the mass and one or more flange results in an impact away from the interface. One or more mass could also or alternatively be located proximal the one or more flange such that contact between the mass and one or more flange results in an impact towards the interface. In some embodiments, a plurality of masses are positioned within the body and are individually actuatable so as to provide varying amounts of force. For example, larger weights can be actuated so as to provide larger forces and/or multiple weights could be actuated so as to provide larger forces.

In an exemplary embodiment, the mass is actuated by air/gas flow through the device. For example, one or more channels may be positioned within the body, through which pressurized air is circulated. The one or more channels are situated so as to provide pressurized air against the one or more mass, thereby propelling mass towards the one or more flanges.

In some embodiments, one or more dampers are in connection with the impact rod so as to modify the frequency and/or amplitude of the impacts as desired.

In some embodiments, the impact rod has a threaded distal end for direct connection to the implant via a threaded extraction hole or for connection to an intermediate connection mechanism. In other embodiments, the impact rod has a distal end having clamping portion, curved portion, or opening for direct connection to the implant, for example, where the threaded extraction hole is not present on the implant or is otherwise unusable, or for connection to an intermediate connection mechanism. The impact rod can be provided with multiple connection mechanisms, e.g. one or more threaded portions, clamping portions, curved portions and openings. In one embodiment, the multiple connection mechanisms are housed within the impact rod and are individually deployable outside the impact rod. In another embodiment, the impact rod has removable and interchangeable distal ends selected from threaded distal ends, clamping distal ends, curved distal ends and distal ends having openings. In yet another embodiment, the device includes a plurality of removable and interchangeable impact rods selected from impact rods having threaded distal ends, clamping distal ends, curved distal ends and distal ends having openings.

In some embodiments, the impact rod is connected to the implant via an intermediate connection mechanism. In one exemplary embodiment, a swivel connector extends from the distal end of impact rod and is in direct or indirect connection with the implant. In another embodiment, a hypothermia unit extends from the distal end of impact rod and is in direct or indirect contact with the implant. For example, in one embodiment, the hypothermia unit extends from the impact rod and a swivel connector further extends from the hypothermia unit to the implant. In one embodiment, the distal end of hypothermia unit has a hemispherical contact surface adapted to allow for rotation of the hypothermia unit relative to the implant. In yet another embodiment, the device includes a connector rod extending from the distal end of impact rod, swivel connector or hypothermia unit. The connector rod can have a hemispherical contact surface adapted to allow for rotation of the connector rod relative to the implant. As with the impact rod, the swivel connector, hypothermia unit and connector rod can have multiple connection mechanisms, e.g. one or more threaded portions, clamping portions, curved portions and openings, for connection to the implant as necessary.

The present invention further provides methods for disrupting a prosthetic implant interface (a) comprising providing a device comprising a body having a proximal end and a distal end, an impact rod disposed within the body and extending out of the distal end of the body, and an actuation mechanism in connection with the impact rod, (b) connecting the impact rod directly or indirectly to the implant such that the impact for is held under tension or compression within* the body, and (c) actuating 1I the device so as to cause the impact rod to transmit one or more impacts to the implant thereby disrupting the implant interface. In preferred embodiments, the impact rod transmits repetitive impacts to the implant.

In one embodiment, the impact rod is held under tension within the body and the device and is actuated so as to cause the impact rod to transmit one or more impacts in a direction away from the implant. In another embodiment, the impact rod is held under compression within the body and the device is actuated so as to cause the impact rod to transmit one or more impacts in a direction towards the implant.

In one embodiment, prior to actuating the device, the impact rod is positioned relative to the implant so as to provide impacts that transmit a force along the long axis of the implant.

In some embodiments, the methods further comprise, in addition to applying impacts to the implant, applying a gradual force to the implant. The gradual force can be applied in a direction away from and/or towards the implant.

In some embodiments, the methods further comprise, in addition to applying impacts to the implant, applying a torque to the implant. In some embodiments, frequency and/or the amplitude of impacts are modified before and/or after actuating the device.

In preferred methods, the device is actuated so as to cause the impact rod to transmit one or more impacts at a frequency ranging from about IHz to about 500 Hz, more preferably from about IHz to about 100 Hz, more preferably from about 1 Hz to about 50 Hz, and more preferably from about 1 Hz to about 10 Hz.

In preferred methods, the device is actuated so as to cause the impact rod to transmit one or more impacts at an amplitude less than about 5 times body weight, more preferably less than about 4 times body weight, more preferably less than about 3 times body weight, more preferably than about 2 times body weight, and more preferably is less than body weight.

In one embodiment, as the procedure progresses and the implant interface becomes disrupted and loosened, ^he amplitude is decreased.

A hypothermia unit may further be provided in' the device and the method can further include adjusting the temperature of the implant via the hypothermia unit prior to actuating the device and/or after actuation of the device. "In preferred embodiments, the hypothermia unit cools the implant .

After the interface has been disrupted, the device can be pulled or withdrawn away from the interface so as to remove the implant from the interface.

In a preferred embodiment, the device includes one or more mass located along the length of the impact rod and the impact rod includes one or more flange along its length. The mass is caused to contact the one or more flange thereby transmitting a force to the impact rod, which, in turn transmits a force to the implant. Preferably the mass is caused to contact the one or more flange by the application of pressurized air to the mass via one or more channels within the device. The pressurized air is preferably applied to the mass at intervals such that each contact between the mass and the flange(s) results in an impact transmitted by the impact rod to the implant.

Other aspects, embodiments and advantages of the present invention will become readily apparent to those skilled in the art are discussed below. As will be realized, the present invention is capable of other and different embodiments without departing from the present invention. Thus the following description as well as any drawings appended hereto shall be regarded as being illustrative in nature and not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the invention will be appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Figure 1 is a schematic view of a device for removing a prosthetic implant.

Figure 2 is a cross-sectional view of a device for removing a prosthetic implant.

Figure 3 A is a cross-sectional view of one embodiment of a swivel connector shown in Figure 3B with its various components.

Figure 3C is a schematic view of a swivel connector and a hypothermia unit as these two components may interact.

Figure 3D is a cross-sectional view of a hypothermia unit.

Figure 3E is a schematic view of a swivel connector arid hypothermia unit interaction wherein a temperature sensor is positioned in the swivel connector and a signal lead runs from the temperature sensor to the signal conditioner positioned externally away from the hypothermia unit.

Figure 3F is a schematic view of a swivel connector and the hypothermia unit interaction wherein a temperature sensor is positioned in the swivel connector and a signal lead runs from the temperature sensor to the signal conditioner positioned on the surface of the hypothermia unit.

Figure 3G is a schematic view of a swivel connector and hypothermia unit interaction wherein a temperature sensor is positioned in the hypothermia unit and the signal lead runs from the temperature sensor to the signal conditioner positioned externally the hypothermia unit.

Figure 4 shows an implant-extractor connector rod. The implant-extractor connector rod may be attached to the device and a swivel connector.

Figure 5 shows a view of a prosthetic implant within the medullary canal. In this embodiment, cement is used to attach the implant. The device is shown in this embodiment as connected to the implant directly via the impact rod. Also shown in this embodiment, the impacts are applied away from the implant in a direction described herein as generally perpendicular to the implant/surface of the implant at which the device is connected, so as to apply a shear along the cement or interface.

DETAILED DESCRIPTION

The present invention provides a device for the disruption of prosthetic implants and also provides methods for the disruption of prosthetic implants. More particularly, the devices and methods of the present invention disrupt the bone/implant or cement/implant interface. Also, such device and methods are useable to remove the implant from the surgical site after disruption if desired. Such devices and methods of the present invention overcome many limitations of current devices and methods for the removal of prosthetic implants.

Although the devices and methods of the present invention are primarily illustrated and described herein by means of devices which have been adapted for removal of hip prosthesis, it will be appreciated by those skilled in the art that such devices and methods also are adaptable for use on prosthetic implants in other areas of the body such as, for example, the shoulders, the knees and various other limb and extremity prosthetic implants. Further, the devices of the present invention are useable in the removal of either cemented or non-cemented prosthetic implants.

In one embodiment, the device provides or applies a repetitive force to the prosthetic implant interface. The repetitive force applied by the device is in the form of an impact. As used herein, an "impact" refers to a force impulse, i.e. a high force magnitude applied over a short time duration. The impulses may be repetitive. Furthermore, as used herein, an "impact" refers to both a force or hit against or towards the implant and away from the implant, or a combination of forces or hits against or towards the implant and away from the implant. In one preferred embodiment, the device provides repetitive impacts away from the implant. This repetitive impact is provided mechanically by the device rather than manually by the user of the device.

In other embodiments, in addition to the repetitive impacts, additional forces are applied either mechanically by the device or manually by the user. For example, in some embodiments, a withdrawal force and/or pushing force is applied or provided in addition to the impacts. In general, while the impacts provide relatively fast or sharp impulses (large magnitude and short duration), the withdrawal and pushing forces provide more gradual and/or constant applications of pressure or force over time. The pushing and/or withdrawing forces are either manually applied or mechanically applied by the device.

Further, in some embodiments, a twisting force or torque is applied to the implant either manually or mechanically. Thus, in one embodiment, as the impacts are applied to the implant, the user manually twists the device. In another embodiment, as the impacts are applied to the implant, the device further includes a rotating component that mechanically applies torque to the implant. For example, the device is operably coupled or connected with the implant via an impact rod that applies the impacts to the implant and, further, that can be adapted to apply torque impulses to the surface of the implant along the axis of the implant. A mechanical twisting force can be accomplished using any conventional type of rotational or twisting assembly such as, for example, that used in an impact wrench. Preferably, the rotation or twisting of the device, e.g. impact rod, is applied as a single or repetitive torque. In other words, the impact rod preferably does not rotate continuously as the impacts are applied because the impact rod is in connection with the implant and, thus, would likely cause damage. Rather, the rotation would be limited to a certain distance, less than a complete revolution of the impact rod, preferably less than a half revolution of the impact rod, and more preferably less than a quarter of a revolution of the impact rod.

In one embodiment, the device provides repetitive impacts and, further, the user gradually pulls or pushes on the device or on a portion of the device so as to provide a manual withdrawal and/or pushing force to the implant. In other embodiments, the repetitive impacts are provided continuously and the withdrawal and/or pushing force is applied. In yet other embodiments, the repetitive impacts are stopped while the withdrawal and/or pushing force is applied. In yet another embodiment, the withdrawal and/or pushing force can be applied between one or more repetitions of the impacts.

In another embodiment, the device is adapted to mechanically provide a withdrawal and/or pushing force. Thus, for example, the device includes an impact rod in connection with the implant that provides both impacts and a withdrawal and/or pushing force. The withdrawal and/or pushing force is actuated at any time by, for example, a trigger, button or other type of actuation mechanism that is in connection with the impact rod. Further, withdrawal and/or pushing forces are mechanically and automatically applied at set intervals during the procedure and more particularly are applied at specific times based on the frequency of the repetitive impacts. In one embodiment, the device is connected and attached to the implant via a movable extension mechanism, e.g. an impact rod, that provides impacts and that further moves away from or towards the implant so as to provide a withdrawal and/or pushing force. For example, the movable extension/impact rod is movably mounted within the device using any conventional assembly that gradually moves the extension/impact rod towards or away from the implant. Such assemblies are driven, for example, by an energy source, for example, hydraulics, pneumatics, electrical/mechanical (e.g. gears), magnetic fields and the like so that actuation causes the assembly to gradually move the extension/impact rod away from or towards the implant, thereby providing a withdrawal or pushing force.

In preferred embodiments, the repetitive impacts are in the form of vibrations or oscillations. Applicants note that the terms "vibrations" and "oscillations", as used herein, do not necessarily apply to very rapid motions. Rather, "vibrations" and "oscillations" are understood to refer to mechanically/automatically applied repetitive impacts. Such repetitive impacts are generally applied at regular intervals but can be applied at irregular intervals if desired. The frequency of the vibrations and oscillations can be modified prior to use to address specifics of each implant interface encountered, and/or during a procedure as the device is being used. In the second case, the procedure could be continued (e.g. the repetitive impacts applied) as the frequency is modified or it could be stopped (e.g. the repetitive impacts stopped) as the frequency is modified. The amplitude of the repetitive impacts also can be modified as desired prior to use to address specifics of each implant interface encountered, and/or during a procedure as the device is being used. In the second case, the procedure could be continued (e.g. the repetitive impacts applied) as the amplitude is modified or it could be stopped (e.g. the repetitive impacts stopped) as the amplitude is modified. In other embodiments, only the frequency (or the amplitude) is modified independently while the amplitude (or frequency) is maintained. In yet other embodiments, both the frequency and amplitude are modified.

As used herein, the term "frequency" is defined as the number of cycles or impacts that are applied in a certain amount of time. The unit of measurement for vibration frequency is typically expressed in Hertz (Hz), but is often also expressed as cycles per minute or second. For purposes of defining frequency herein, both Hz and applications of force per minute or second will be used. As used herein, the "amplitude" of the force is the magnitude of force or the measurement of how hard or strong the impact is.

In further embodiments, the frequency is increased to provide a faster disruption, while the amplitude is maintained or adjusted as desired. In other embodiments, for example, where there may be a fracture present and it is desirable to prevent further fracture or, for example where the procedure is on an elderly patient with more fragile bones, the amplitude would be decreased to provide more delicate handling of the implant while the frequency is maintained or adjusted as desired. It also is contemplated that the frequency and amplitude are maintained at constant levels throughout a procedure or are varied as the procedure progresses either manually or automatically. For example, as the procedure progresses and the interface becomes disrupted and loose; the amplitude is decreased to provide a smaller force as required. In some embodiments, as the amplitude is decreased, the frequency is increased to provide delicate handling at the interface without unnecessarily extending the « disruption. In other embodiments, the frequency is maintained or decreased. Further, the amplitude and/or frequency of the repetitive force can be customized to suit various implant geometries and specific factors present for each revision procedure. Thus, the repeated force delivered by the device can be optimized to disrupt the bone/implant or cement/ implant interfaces, which allows for easier, quicker, less traumatic removal of the prosthetic implant and minimal destruction of the surrounding tissue, primarily the bone into which the prosthetic implant was inserted.

The following provides some general guidelines for selecting an appropriate amplitude (magnitude) of repetitive force and frequency (for example, applications of force per minute or second), however, such guidelines are not limited to the following. High amplitude vibrations can be heard or felt or both depending on the frequency of the vibration. Ultrasonic waves are those sound waves that are of every high frequency with short wavelengths. The amplitude of a device according to the present invention is established or set high enough to be felt, but not so high that it will completely disrupt the interface in a single application of force, which often will lead to fracture at the interface and damage to the femur. The amplitude is preferably set or established so it will allow for disruption in more than one application of force. Without being bound by any particular theory, it is believed that disruption of an implant interface in a single impact, when applied to a normal and healthy non-elderly individual, wherein there is no fracture present and/or there is no excessive loosening, will often lead to fracture, which is undesirable. Thus, the amplitude is set or established so as to be preferably less that the amplitude required to disrupt a cement/implant or bone/implant interface in a single impact. Of course, where the patient is elderly, has weakened bones, or if the interface is fractured or loose, lower amplitudes would be applied accordingly based on these factors.

In general, when applied to a normal and healthy non-elderly individual, wherein the interface is not fractured and/or does not have more than ordinary loosening, the force being applied should generally be less than about twelve times body weight. Without being bound by theory, applications of force greater than about twelve times body weight will typically result in damage to the implant and/or femur and possibly other body parts. Further, when device is a hand-held, applications of high forces can make handling of the device difficult to manage. In preferred embodiments, the force being applied is less than about ten times body weight, more preferably less than six times body weight, more preferably less than five times body ■..- weight, more preferably less than four times body weight, more preferably less, than sthree' times body weight, more preferably less than two times body weight, and more preferably less than the body weight. Preferably, the force being applied is the lowest possible force that will provide disruption of the interface while not causing damage to the implant, femur or other body parts and while not unnecessarily extending the length of the procedure. When the patient is elderly, has weakened bones, or if the interface is fractured or loose, lower amplitudes are applied accordingly.

The frequency of the vibrations in the device of the present invention is preferably greater than 1 Hz and can be as high as ultrasound. In embodiments, when applied to a normal and healthy non-elderly individual, wherein the interface is not fractured and/or does not have more than ordinary loosening, the frequency is no greater than about 20 kHz, more preferably no greater than about 10 kHz, more preferably no greater than about 5 kHz, more preferably no greater than about IkHz, more preferably no greater than about 500 Hz, more preferably no greater than about 400 Hz, more preferably no greater than about 300 Hz, more preferably no greater than about 200 Hz, more preferably no greater than about 100 Hz, more preferably no greater than about 50 Hz, more preferably no greater than about 40 Hz. In a particular embodiments, in a typical hip revision surgery wherein the implant interface has no significant abnormal weakening or fracture (when applied to a normal and healthy non- elderly individual) the frequency of the vibrations ranges from about IHz to about 500 Hz, preferably from about 1 Hz to about 100 Hz, more preferably from about 1 Hz to 50 Hz, and more preferably from about 1 Hz to about 10 Hz, while the amplitude less than about 5 times body weight, preferably less than about 4 times body weight, more preferably less than about 3 times body weight, more preferably less than about 2 times body weight, and more preferably less than body weight. The frequency and amplitude are appropriately be adjusted for other situations and implant locations based on these guidelines.

Thus, by achieving a proper balance between the amplitude and frequency being provided the length of the procedure is not unnecessarily long and the potential of fracture or damage due to the application of force is reduced and minimized. It is to be noted that in some cases, the interface may be weakened prior to revision surgery and/or may already contain a fracture or damage. In such circumstances, the amplitude and/or frequency for would be adjusted accordingly. In particular, for such weakened/fractured states,' a lower amplitude woud be generally applied, with or without a modified frequency.

It also is within the scope of the present invention to also vary the direction(s) of the repetitive impacts. In one embodiment, the direction of impact travels along the linear axis of the device. Preferably!, when applied to the implant, the direction of the repetitive impact is preferably approximately perpendicular to the implant surface to which the impact is applied. This would generally correspond to a force that is being applied along the long axis of the implant. It is noted that the surface of the implant to which the device is generally applied is curved, as shown in Figure 5.

In other embodiments, it is desirable to provide an impact or force at non- perpendicular angles to the surface to which the impact is applied. This could be accomplished, for example, by providing a device with a linear pathway along the length of the device and holding the device at the desired angle, e.g. holding the device such that impact rod 6 (or the connection mechanism through which the impact rod is in connection with the implant) is angled away from the position shown in Figure 5. This also could be accomplished by providing a device that has adjustable angles of motion in relation to the length of the device. In further embodiments, the repetitive impacts are in the form of vibrations or oscillations that travel along multiple random, including non-linear, pathways. Thus, for example, the device could provide an impact rod or portion of the device providing impact that has multiple degrees of freedom. In some embodiments, it may be desirable to provide a combination of one or more types of motion. Thus, for example, in one embodiment, the device applies impacts that travel along the length of the device perpendicular to the implant surface as well as at angles non-perpendicular to the implant surface. In a preferred embodiment, the force is applied generally perpendicularly to the implant surface, which corresponds to a direction generally along the long axis of the implant (as shown in figure 5). Without being bound by any particular theory, it is believed that such a force would result in a sheer stress along the implant interface that would approach maximal sheer stress. In further embodiments, the direction and application of force and sheer stress that will provide the most efficient disruption varies because the shape of the femur (or other type of implant that the procedure is performed on), the medullary canal, as well as the particular implant geometry encountered typically varies to at least some degree.

In an exemplary embodiment, the device comprises a body having a distal portion that is in connection with the prosthetic implant and a means for actuating the device to provide repeated mechanical impacts or vibrations to the prosthetic implant via the distal portion. In one embodiment, the distal portion is directly in connection with the implant. In other embodiments, the distal portion is in connection with the implant via an intermediate portion. The distal portion is also in connection with an actuation mechanism such that actuation results in the distal portion transmitting a force to the implant.

Referring now to the various figures of the drawing wherein like reference characters refer to like parts, there is shown in Figure 1 shows one embodiment of a device 100 according to the present invention that can disrupt prosthetic implants such as that herein described. Such a device 100 includes a body 2 having a proximal end 2a and a distal end 2b. Although the body 2 is shown as having a tubular shape with a circular cross-section this shall not be construed as limiting the body to such as shape. It is within the scope of the present invention for other geometric shapes to be used for the body 2 such as, for example, an oval, square, triangular, hexagon or other shape. Also, it is generally preferred that the body e include a smooth outer surface so as to thereby prevent or minimize damage that may result if the body contacts tissues or other internal and external structures.

The device 100 also includes an impact rod 6 that is located at the distal end 2b of the body 2. The impact rod 6 is operably coupled to or in connection with an actuation mechanism 20, such as a trigger or button. Upon manipulation of the actuation mechanism, the device 100 is actuated so as to provide repetitive force via the impact rod 6. When the device is actuated, the impact rod 6 provides repetitive forces to the implant either directly or via one or more intermediate portions. In the illustrated embodiment, the actuation mechanism 20 is located at the proximal portion of the body 2 and may be located on, for example, a handle 19 as shown in Figure 1. The actuation mechanism 20, in some embodiments, is such that the frequency and/or amplitude of the repetitive force can be adjusted as desired. For example, in one embodiment, the actuation mechanism 20 includes a dial that can be turned in one direction to increase frequency and/or amplitude and in the other direction to decrease frequency and/or amplitude. Also, the actuation mechanism 20 can comprise separate dials, one for frequency and one for amplitude. The dials also can further include marked settings to provide set frequencies and amplitudes at certain positions of the dial. In another embodiment, the actuation mechanism 20 is,a sliding lever or similar mechanism that can be pushed in one direction (e.g. distally along the length of device) so as to increase frequency and/or amplitude and in the other direction (e.g. proximally along the length of the device) so as to decrease frequency and/or .amplitude. Separate sliding levers or similar mechanisms can be used for frequency and amplitude. Marked settings along the lever position may also be provided to apply certain frequencies and amplitudes at certain positions of the lever.

The device 100 also includes a handle 19, that can be located at the proximal end 2a of the body 2, which handle also can be used for assistance in holding and manipulating the device. Although the handle 19 is shown as T-like in shape, other conventional handle shapes can be used with the device of the present invention. In some embodiments, the handle 19 is the actuation mechanism that actuates the device 100. For example, the handle 19 may be pulled, depressed, rotated, or otherwise manipulated so as to cause the impacts. In another embodiment, and as described herein, the handle 19 conveniently includes a separate actuation mechanism 20. In further embodiments, the handle 19 is pulled, depressed or rotated so as to provide a withdrawal force, a pulling force and/or a twisting force/torque in addition to or alternatively to the impacts. Thus, for example, during operation of the device 100, the device is actuated to provide repetitive impacts. Further, a manual force along the length of the device is further be manually applied at the handle 19 to withdraw the prosthetic implant after it has been sufficiently disrupted or to assist in disruption. In further embodiments,, the handle is suitably provided with grooves, rubber coating or the like to assist the user in securely gripping the device. The device can further include a connector means or butt plate 10 located between the body 2 and the handle 19, by which the handle 19 is connected to the body 2.

Figure 2 shows a cross section of the interior of one embodiment of the device 100a. It is noted that while this embodiment shows a device 100a that operates or provides energy via air flow through the device, other mechanisms can be used so as to provide energy or impulses to the impact rod 6. For example, conventional mechanical mechanisms, which include gears, cams, and the like (such as those used in impact hammers and impact drills, both electrically and hydraulically actuated), and magnetic forces, can be used to provide energy or impulses to the impact rod 6. Thus, the description herein is understood to extend not only to energy application via air flow, but also to energy application via mechanical mechanisms (powered by electrical or hydraulic means) and magnetic" forces.

As shown in Figure 2, the impact rod 6 is housed within a hollow portion of the body 2. The impact rod 6 is disposed within the body 2 in a manner that allows it to move some distance, preferably no more than about 5 mm, preferably between about 0.5 to 4 mm, more preferably between about 1 to 3mm, along the length of the body 2. In particular embodiments, the impact rod 6, when in connection with the implant, is held within the body 2 under tension (particularly for impacts in a direction away from the implant) and/or in compression (particularly for impacts in a direction towards the implant) such that it will transmit a force along its length to the implant. As such, the impacts/impulses are generally not applied to the implant by a swinging or sliding motion of the rod 6 against or away from the implant, but, rather, by a small range of motion that transmits the impact/impulse to the implant. Such transmission of force, as discussed, is provided in a generally linear direction, perpendicular to and/or at an angle to the implant surface, and/or in random and non-linear directions.

The distance traveled by the impact/pull rod 6 is controlled by, for example, providing a lip 7 located along the length of the impact rod 6 that comes into contact with end cap 1 to prevent further motion of the impact rod 6 in the distal direction. Further, the proximal portion of the impact rod 6 (e.g. flange 15) may come into contact with a stop mechanism to prevent the impact rod 6 from withdrawing into the body 2 past a certain distance. In one embodiment, the repetitive impacts are caused by a mass 5 located within the device. Upon actuation of the device, the mass 5 contacts the impact rod 6, thereby transmitting a force or energy to the impact rod 6. The force is then transmitted from the impact rod 6, which is in connection with the implant (either directly or indirectly) and under tension or compression, to the implant.

Figure 2 shows one preferred embodiment, wherein the mass 5 is located within the body 2. The mass 5 can be a single mass defining an opening through which the impact rod 6 fits such that the mass 5 can slide along the impact rod 6. The mass 5 also can comprise one or more portions located on one or more sides of the impact/pull rod 6. The mass also can be a single mass or one or more portions located distal to the distal end of the impact rod 6. As shown, the impact rod 6 extends through an opening 18 of the device and its distal end 2b is placed in connection with the implant (either directly of indirectly). The sliding mass 5 is set into motion such that it contacts the impact rod 6. When the mass 5 contacts or strikes the impact rod 6, the mass transmits an impulse to the impact rod 6, which, in turn, transmits the impulse to the implant either directly or indirectly. For example, when the mass 5 is located along the length of the impact rod 6, the impact rod 6 can have, for example, one or more portions along its length with an increased diameter so as to provide a portion that the mass 5 contacts. In one embodiment, the mass 5 is located distal to the distal end of the impact rod 6 and the mass contacts the distal end or a portion of the distal end of the impact rod to provide an impulse or impact in the distal direction and, thus, an impact towards the implant. Preferably, the impulses or impacts are applied or transmitted along a linear pathway forwards (distally) and/or backwards (proximally) along the length of the body. To promote linearly transmitted impacts or impulses, the device 100a can be sized, shaped, and/or provided with an opening in the form of a pneumatic bearing 18 that assists in transmitting the impacts in a given direction.

As shown in Figure 2, the impact rod 6 can include a flange 15 at a proximal portion and a lip 7 at a distal portion. The mass 5 can be situated between the flange 15 and lip 7 and can be movable between the flange 15 and lip 7. If a repetitive pulling impact on the implant is desired, the mass is set into motion so as to repeatedly contact the flange 15, which will cause the impact rod 6, which is under tension and in connection with the implant, to transmit pulling impacts or impulses at the interface. In another embodiment, where a repetitive impact towards or against the implant is desired, the mass 5 is made to repeatedly contact the impact rod 6 in a distal direction (e.g. along lip 7 or a similar portion of impact rod 6), which will cause the impact rod 6, which would then be in compression and in connection with the implant, to transmit impacts or impulses towards the implant. In further embodiments, the mass 5 is made to provide impacts in both a proximal and distal direction by, for example, contacting both the flange 15 and lip 7, so as to transmit impacts or impulses to the implant both towards and away from the implant, in any order, amplitude and frequency.

The device 100a can be actuated so as to provide impacts or impulses in a number of ways. In one embodiment, the device is actuated by any conventional mechanical assembly, which may include gears, cams, and the like. Such mechanical assemblies could be electrically or hydraulically powered. Examples of such assemblies could include impact hammers and drills. In another embodiment, the device is actuated by use of magnetic force. The device preferably provides impacts or impulses via a moving mass 5, which can be set in motion.in a number of ways, including mechanical and magnetic assemblies..

In one embodiment, the device is actuated using air/gas flow. For example, as shown in Figure 2, the device includes one or more channels through which a material or fluid, preferably gas (e.g. air), can travel. As shown in Figs. 1 and 2, the air could ' enter through a coupling mechanism 21 or inlet port 12 that allows the device to be connected to a supply source, preferably an air supply source, so that air is circulated through the device. The pressurized gas can be sent to an inlet port 12 by actuation of, for example, an external trigger. A gas hose connected to the device at hose coupling 21 can supply the pressurized gas. The impact rod 6 transmits an impulse created by mass 5 as it slides/moves and hits the impact rod 6, for example at the flange 15 and/or the lip 7. The mass 5 slides/moves along the impact rod 6 and within body 2, for example, within a chamber 16. The device can also include pneumatic bearings/opening 18, end cap 1, and/or body breach 17 which further guide the range of motion of the impact rod 6.

The mass 5 is driven along the impact rod 6 and within the body 2 or chamber 16 by gas pressure transmitted along two or more supply passages 3 within the walls of the body 2. Pressurized gas is sent to supply passages 3 from the inlet 12. In one embodiment, the gas is sent from the inlet 12, which is located within butt plate 10 by means of a valve washer 13. As pressurized gas is supplied to the inlet 12 and the impact rod 6 is provided at the end cap 1, such that the lip 7 contacts the end cap 1, compressed gas pushes the valve washer 13 distally against one or more exhaust passages 9, thus opening the path from the inlet 12 to the one or more supply passages 3, and thereby closing gas flow to the proximal part of the body 2 or chamber 16 and pressurizing the distal part of the body 2 or chamber 16. As the mass 5 travels away from the end cap 1 , gas in the body 2 or chamber 16 is exhausted through two or more exhaust ports 4. As the mass 5 impacts the flange 15, the gas proximal to the mass 5 is exhausted through one or more exhaust passages 8,9 onto the distal surface of the valve washer 13, moving the value washer 13 and closing the gas flow to the supply passages 3 and the distal portion of body/chamber 16. Furthermore, the proximal end 2a of the impact rod 6 slides proximally due to impact from the mass 5 and occludes the gas supply from inlet 12. In one embodiment, manifold 11, which is a passageway that allows air to travel to the chamber 16, is provided in the butt plate 10.

The pressure behind the mass 5 in a distal portion of chamber 16 exhausts to ambient air via one or more exhaust ports 4, which may or may not be connected to hoses (not shown) that exhaust the supply gas remote from the surgical field. As the proximal end of the impact rod 6 slides proximally, the return passage 14 communicates with the inlet 12, sending pressurized gas into the proximal portion of chamber 16 through return passage 14 and out through the exhaust passages 8, propelling the mass 5 distally within chamber 16. Upon occlusion of return passage 14, valve washer 13 is pushed distally, for example in a valve chamber 39, by the pressurized gas in the inlet 12. Thus, the sequence starts all over again.

Preferably, the mass 5 contacts the flange 15 and/or lip 7 with an adequate force to provide amplitude in accordance with the amplitudes described herein. The size of the mass and/or the speed at which the mass contacts the flange can be adjusted so as to increase or decrease the amplitude as desired. In other embodiments, a plurality of masses could be located within the body 2. In such embodiments, if a greater amplitude is desired, two or more masses could be activated to contact the flange 15 and/or lip 7. If a smaller amplitude is desired, only one or fewer masses could be activated as desired. The masses could also be provided in varying sizes such that each size, upon contact with the impact/pull rod 6, will provide a certain amplitude of force. One or more of the masses could then be activated based on the desired amplitude desired. In yet other embodiments, a plurality of interchangeable and removable masses is provided. In further embodiments, wherein air is circulated through the device to actuate the mass, the rate of air flow is used to control the speed at which the mass 5 moves and, thus, is utilized to control force of contact between the mass 5 and impact rod 6. This can be accomplished by, for example, pumping in a greater flow of air via hose connector 21 or inlet 12 or, for example, by altering the mass 5, the diameter and number of the supply passages 3, the diameter and number of the exhaust passages 8, 9, the placement and number of the exhaust ports 4, the length and diameter of the chamber 16 and the pressure and flow of the supply gas. In certain preferred embodiments, up to six supply passages, up to six exhaust passages and up to six exhaust ports are present.

The frequency of repetitive force applied at the implant also can be controlled, at least in part, by the frequency and/or force of contacts between the mass 5 and the impact rod 6. Thus, for example, for each contact by the mass 5, the impact rod 6 can apply an impact to the implant

The period and/or frequency between contacts by the mass 5 can be adjusted to provide the desired frequency of impacts or impulses transmitted by the impact rod 6 to ■ the implant. In a preferred embodiment, wherein the mass movement is actuated by^air flow, the frequency of repetitive force applied at the implant is adjusted by altering any ■ one or more of the mass 5 size/mass, the diameter and number of air supply passages 3, the diameter and number of air exhaust passages 8,9, the placement and number of air exhaust ports 4, the length and diameter of the chamber 16 and the pressure and flow of the supply gas. In one preferred embodiment, up to six supply passages, up to six exhaust passages and up to six exhaust ports are disposed in the device. In embodiments where the device is a mechanical assembly (electrically or hydraulically powered) or actuated by the use of magnetic force, the frequency is adjusted, for example, by altering the length of travel by the mass between impacts (e.g. the length of chamber 16) and the force by which mass impacts the impact rod 6 (e.g. a greater force applied by mass to impact rod will result in a greater/faster recoil and, thus, a faster frequency) and my any other mechanism by which impact hammers and drills are adjusted.

In further embodiments, the frequency of repetitive force is alternatively or further modified by providing one or more dampers (not shown), that dampen or slow down the frequency or motion. In other embodiments, the portion of the device that provides the repetitive force is mechanically moved at desired frequency that may be adjusted accordingly. The impact rod 6 is designed to provide repetitive force to the implant either directly or indirectly. In one embodiment, the impact rod 6 is adapted for direct connection with the implant. For example, most prosthetic implants in use today are manufactured with a threaded extraction hole, typically at the proximal end of the prosthetic implant, for the purpose of attaching means for removing the prosthetic implant, such as an implant extractor handle or a slide hammer. Thus, the impact rod 6 can have one or more threaded portions, preferably a threaded distal end, that mates with the threaded extraction hole.

In some circumstances, where the threaded extraction hole on the existing indwelling prosthetic implant is absent or unusable because of thread damage or because it has become occluded by or embedded with tissue ingrowth, the impact rod 6 can have an additional or alternate connection mechanism. In one embodiment, the impact rod 6 has a clamping portion, curved portion, and/or opening that fits or can be fitted about a portion of the implant. Preferably, the clamping portion, curved portion or opening has a profile that corresponds to a portion of the implant and can further be adjustable so as to securely grasp the implant. Any conventional clamping means can be adapted for use. In other embodiments, the clamping means, curved portion or opening provides a better grip about the implant by, for example, providing a rubberized or resilient portion on the clamping means, curved portion or opening in contact with the implant or, for example, by providing grooves and/or teeth that grip the implant. Actuation of the device causes the impact rod 6 to apply impacts or impulses towards and/or away from the implant (while in connection with the implant) so as to apply impacts in a direction towards and/or away from the implant.

In other embodiments, because varying implant geometries and connection possibilities may be encountered, the impact rod 6 can include multiple connection mechanisms. For example, the impact rod 6 can have a threaded portion as well as a clamping portion, curved portion or opening all situated along its length. The impact rod 6 also can have multiple connection mechanisms that can be housed within the impact rod 6 and individually deployed as desired, for example, much like a Swiss Army knife. In yet other embodiments, the impact rod 6 has removable and interchangeable connection mechanisms, for example, a variety of removable interchangeable distal ends or extensions. Thus, for example, a threaded distal end/extension, clamping portion, curved portion and opening would be attached as desired. Further, because it is possible to encounter varying thread series in extraction holes, in some embodiments, a plurality of different threaded connection mechanisms could be included having various thread series.

In another embodiment, the impact rod 6 is in connection with the implant via one or more intermediate portions. Thus, the impacts would be applied to the implant by the impact rod 6 indirectly via the one or more intermediate portions. For example, as shown in Figure 3C, the impact rod 6 is in connection with the implant via a swivel connector 25. The swivel connector 25 provides additional distance between the distal end of the device and the implant, which can make it easier to connect the device to the implant and easier to perform the surgery in a limited surgical area. Further, a variety of swivel connectors could be provided with various connection mechanisms, for example, various thread series, various clamping portion(s), and openings for fitting about a portion of the implant. Thus the impact rod 6 can be in connection with the implant via the swivel connector 25, which provides the appropriate connection mechanism for the particular surgery. The swivel connector 25 is mounted on the impact rod 6 using any conventional connection means such as, for example, mating threaded portions, interlocking portions, mating tabs, and the like. Thus, for example, a device can include an impact rod 6, having a distal threaded end having conventional* thread series. In the event that the thread series on the impact rod 6 does not match the thread series of the extraction hole or if the hole is absent or unusable, and/or if the user wishes to have additional space between the device and the implant, an appropriate swivel connector 25 can be attached to the impact rod 6 via mating threaded portions.

In another embodiment, the impact rod 6 is in connection with the implant via a hypothermia unit 33, for example, as shown in Figs. 3C-D. In such embodiments, the device provides both impacts to the implant as well as temperature adjustment.

The hypothermia unit 33 is in direct or indirect connection with the implant. In one embodiment, the hypothermia unit 33 has a distal portion 22 that is placed in direct connection with the implant. As such, the distal portion 22 is sized and shaped so as to connect to a desired location of the implant via, for example, threaded portions, one or more clamping portions, or a curved or shaped portion as discussed above. The distal portion 22 of the hypothermia unit 33 also can be in indirect connection with the implant via an intermediate portion such as, for example, swivel connector 25 as discussed above. In one embodiment, the distal portion 22 has a hemispherical contact surface, as shown in Figure 3D, which contacts with a spherical inside surface 28 of the swivel connector 25. It is within the scope of the present invention for other connection mechanisms to be used to connect the distal portion 22 to the swivel connector 25 such as, for example, threaded portions, one or more clamping portions, or mating curved or shaped portions. In one embodiment, the hemispherical contact surface at distal end 22, as shown Figure 3D, is adapted to allow for rotation of the hypothermia unit 33 relative to the swivel connector 25 and/or the implant. The hypothermia unit 33 can, thus, allow for minor off-axis adjustments while still transmitting the impacts from the device.

In one embodiment, the swivel connector 25 is first attached to the proximal threaded extraction hole (not shown) found on most prosthetic implants. The distal end 22 of the hypothermia unit 33 with the hemispherical surface is then passed through an opening 29 of the swivel connector 25 and slid proximally until the hemispherical surface of the distal end 22 contacts the spherical inner surface 28 of the swivel connector 25. The hypothermia unit 33 is then allowed to rotate relative to the swivel -connector 25. Shaft 30 of hypothermia unit 33 can be disposed so as to contact a shoulder 27 of the swivel connector 25 to limit rotation. ..

The hypothermia unit 33 is mounted on the device via the impact rod 6 either directly or indirectly. In one embodiment, the hypothermia unit 33 proximal portion 31 is directly connected to the impact rod 6 using any conventional fastening means such as, for example, mating threaded portions. In another embodiment, the hypothermia unit proximal portion 31 is in contact with the impact rod 6 via an intermediate connecting portion

In further embodiments, the device further includes a connector rod 38, such as that shown in Figure 4. For example, in one embodiment, wherein the device does not utilize a hypothermia unit 33, the connector rod is used as an intermediate connection mechanism. In other embodiments, the connector rod 38 is used together with the hypothermia unit 33 if desired. In further embodiments, the connector rod 38 includes a hemispherical contact surface 37 or distal portion that is used together with swivel connector 25 as discussed with relation to the hypothermia unit 33 distal portion 22. Connector rod 38 has a proximal end or portion 36 that is mounted on impact rod 6 either directly or indirectly.

In this manner, heat from the prosthetic implant is transferred from the prosthetic implant, travels through the swivel connector 25 (if present) and through the hypothermia unit 33. In preferred embodiments, a hypothermic medium is circulated through the hypothermia unit 33. For example, as shown in Figure 3D, a hypothermic medium enters through medium inlet 32 and travels through one or more cooling channels 23, allowing heat to transfer into the hypothermic medium from the hypothermia unit 33, and exit through exit port 26. The hypothermic medium is provided to the hypothermia unit through tubing or the like and can further be driven and circulated by an external pump.

In further embodiments, the hypothermia unit 33 is actuated so as to cool the implant. Reducing the temperature of the prosthetic implant by the transfer of heat from it will generally make polymethylmethacrylate (PMMA) cement or other adhesive more brittle and more susceptible to disruption; thus, making separation of the prosthetic implant/cement interface more efficient. Furthermore, reducing the temperature of the prosthetic implant can cause the prosthetic implant to contract, thus establishing tensile stresses normal to the prosthetic implant/cement interface or prosthetic implant/bone interface,>thereby making the prosthetic implant interface more susceptible, to disruption. The hypothermia -unit 33 also can benefit in the removal of uncemented prosthetic implants, as the heat transfer from the prosthetic implant can cause the prosthetic implant to shrink sufficiently to place the prosthetic implant/bone interface under tension, even in the absence of PMMA, such that the prosthetic implant is more susceptible to the repetitive forces. In other embodiments, thermal cycling is used to assist in disruption of the implant interface. For example, cycling between applications of increased temperature and decreased temperature may further disrupt the implant interface by causing repetitive expansion and contraction. In some embodiments, temperature manipulation via the hypothermia unit 33 is provided prior to application of the repetitive force so as to provide the benefits prior to application of force. The temperature also can or alternatively be manipulated during the application of repetitive force. However, to provide optimal advantages from the temperature manipulation, the temperature should be manipulated at least for some time period before the application of force. The hypothermia unit 33 is in connection with a temperature actuating mechanism that causes the hypothermia unit to adjust the temperature accordingly. The temperature actuating mechanism can be adapted to provide certain temperatures by, for example, providing a mechanism in the form of a dial, lever, or the like that increases or decreases temperature depending on the direction the dial is turned or the lever moved and may include marked settings at certain positions of the dial or lever corresponding to certain temperatures. In general, the implant interface is not cooled to temperatures below 00C as such temperatures may cause tissue damage, and is not be heated to temperatures greater than body temperature (37°C).

In further embodiments, the temperature of the prosthetic implant is monitored by one or more temperature sensors 34, for example, as shown in Figure 3C, located internally in the hypothermia unit 33, and can be processed by a signal conditioner 35 via a signal lead 40. The temperature sensor(s) 34 or a thermocouple also can be positioned internally in the hypothermia unit 33, e.g. in a hole in the hypothermia unit 33 that is sealed so that it is embedded in the hypothermia unit 33. The signal lead 40 and the signal conditioner 35 can be externally attached to the outer surface of the hypothermia unit 33 and can be positioned for ease of use. The signal lead 40 and the signal conditioner 35 in this embodiment also can be positioned external to the hypothermia unit 33, either on the operating table or within the sterile field as seen in Figure 3G. The amount of signal lead wire from the sensor 34 is variable, but is preferably sufficiently long enough to reach outside the sterile field on the operating table or within the sterile field while the operator is working with the device.

In another embodiment, a temperature sensor 34 located on or within the swivel connector 25, if included monitors the temperature of the prosthetic implant. The temperature sensor 34 also can be positioned internally in the swivel connector 25, e.g. in a hole in the swivel connector that is then sealed so that it is embedded in the swivel connector 25. In this embodiment, a signal lead wire 40 extends from the temperature sensor to a signal conditioner 35 and the signal conditioner can be positioned external to the device as seen in Figure 3E. The amount of signal lead wire from the sensor is variable yet is preferably sufficiently long enough to reach the outside the sterile field on the operating table or within the sterile field while the operator is working with the device. When this particular embodiment is used with the hypothermia unit 33, the hypothermia unit 33 need not be configured with means for detecting, signaling or reading the temperature of the prosthetic implant. In addition, the signal conditioner from the temperature sensor of this embodiment can be positioned on the surface of the hypothermia unit 33 as seen in Figure 3F for ease in viewing the temperature of the prosthetic implant as cooling occurs. In this embodiment, the signal lead wire may cross the swivel connector 25 and plug into the signal conditioner 35. The signal conditioner is any commercially available standard signal conditioner. Such conditioners can have both analog and digital components and produce a digital signal read-out. As size of commercially available signal conditioners vary, the signal conditioner of these embodiments can be sized to fit the intended use in the present invention. As an example of this, a signal conditioner that is external to the hypothermia unit 33 is not necessarily the same size as a signal conditioner that is external to the operating room table or sterile field. The signal conditioner is preferably also large enough with its digital signal read-out so that the operator is apprised of the temperature status of the prosthetic implant before and while using the device concurrently with maintaining the temperature of the prosthetic implant to facilitate the removal of the prosthetic implant.

The hypothermia unit 33, impact rod 6 and the swivel connector 25 also can be used in connection with a universal extractor .with adaptor (not shown) to attach the hypothermia unit 33 or swivel connector. to the implant, for example, in the event that a prosthetic implant without a threaded extraction hole or with an occluded threaded extraction hole is encountered.

It is anticipated and thus with in the scope of the present invention for the device 100 to be commercially packaged and sold as a kit comprising a body with impact rod (for example, as shown in Figures 1 and 2), a universal extractor, adaptors of different thread series that will match the threads of various swivel connectors, adaptors with various connection mechanisms such as clamps and openings to connect with the implant, swivel connectors of different thread series that will match the threads of an adaptor to the universal extractor if needed (e.g. due to an absent or non¬ functional threaded extraction hole), a hypothermia unit, and a connector rod. Such an assembled kit also can contain instructions for assembly of the device without the hypothermia unit or with the hypothermia unit as it attaches to the device, as well as instructions for use of the device without the hypothermia unit and with the hypothermia unit. An assembled kit for the device for intra-institutional use also comprises the same components as above that are assembled and packaged by operating room staff between revision procedures that is subject to sterilization appropriate to minimize contamination of the sterile field during a revision procedure and subsequent development of infection by the patient. Alternatively, the hypothermia unit can be packaged and sold as a kit for replacement of this unit as needed with instructions for connecting to the implant extractor and its use. Other component parts such as the swivel connector with an embedded temperature sensor and the like can be individually sold as replacement parts as well.

EXAMPLES

EXAMPLE 1

A study was completed using a device that generated a pushing mechanical impact.

In this prosthetic implant study, a well-fixed, non-cemented femoral stem prosthetic implant was obtained from a female cadaveric specimen. The cadaver femur was transected below the level of the distal-most end of the prosthetic implant. Approximately 20 mm of bone was removed from the distal end of the transected femur in order to expose the distal end of the prosthetic implant. The proximal end of the femur was gripped in a vise. The flat end of a chisel with a. sawed off tip to provide a blunt end was attached to the device and was placed.on the distal end of the prosthetic implant. The device was then activated at which time the device applied repetitive impacts to the prosthetic implant such that after approximately 30 impacts applied within one minute, the prosthetic implant became dislodged from the femur. This study established approximate impact parameters needed to dislodge the prosthetic implant using the device.

EXAMPLE 2

In this study, a cemented femoral stem prosthetic implant was implanted post¬ mortem into a cadaveric femur. The cadaver femur was transected below the level of the distal-most end of the prosthetic implant. Approximately 20 mm of bone was removed from the distal end of the transected femur in order to expose the distal end of the prosthetic implant. The proximal end of the femur was gripped in a vise and the device as discussed in EXAMPLE 1 was placed on the distal end of the prosthetic implant. The device was then activated at which time repetitive impacts were applied to the prosthetic implant such that the femoral stem became dislodged with approximately 16-20 impacts at the distal end of the prosthetic implant within a minute. The prosthetic implant/cement interface had been disrupted to such an extent that the prosthetic implant was removed easily by hand. This study established that a pushing impact mass coupled with the frequency information obtained from EXAMPLE 1 was sufficient to dislodge a cemented prosthetic implant.

EXAMPLE 3

A study was conducted to develop and understand the relationship between temperature and PMMA fracture toughness in order to determine optimum hypothermic temperature ranges for dislodging a prosthetic implant. In this study, notched PMMA specimens were molded and impacted using a standard impact tester. Groups of 10 notched PMMA specimens in each group were tested at ambient temperatures of- 20°C, 0 0C, 20 0C, and 37 0C. It was demonstrated that the cement was weakened most effectively at temperatures of approximately 00C.

Although limited embodiments have been described and illustrated herein, it will be readily appreciated by those skilled in the art that there may be many modifications and variations of practice of this invention. Further, although described in the context of a hip joint replacement, it will be apparent that similar techniques may be used with prosthetic implants of shoulder joints, knees and the like, either cemented or non cemented. It is, therefore, to be understood that within the scope of the appended claims, this invention may be practiced otherwise than as specifically described. Although the invention has been described using specific terms herein, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.