Safety mechanism for ultrasonically vibrating surgical tools

Abstract

An ultrasonically vibrating surgical tool for removing cement (7) in artificial joint revision surgery has an ultrasonic vibration source operationally coupled to a working tip (5) that acts on the cement (7) in the lumen (8) of a bone such as a femur (1). When acting on the cement (7), the tool vibrates at substantially a single resonant frequency. If the working tip (5) comes into contact with a hard material such as the bone wall (6) of the femur (1), additional supplemental vibrations are generated at other frequencies. The tool is equipped with a microphone or other vibration detector to pick up these supplemental vibrations, which may be in the audible or ultrasonic range. If supplemental vibrations are detected at a frequency characteristic of contact between the working tip (5) and bone, the user of the tool is warned and the operation of the tool is interrupted.

Description

Technical Field

[0001]

[0001] The present invention relates to an improvement of an ultrasonic vibratable surgical tool for removing surgical cement during replacement of an orthopedic implant (arthroplasty). More specifically, but not limited thereto, the present invention relates to a mechanism for warning a user that such a tool may contact a hard substance such as bone instead of cement, thereby potentially damaging the bone.

Background Art

[0002]

[0002] Orthopedic implants such as hip joints and other limb joint replacements are often held in place by at least one component of the implant having an elongated tapered shaft extending from the joint element of the implant into the lumen of the hollow bone. In the case of a hip joint prosthesis, one component of the implant is thus fixed in the lumen of the femur of the recipient. The shaft can be fixed in place by cancellous bone material growing internally from the inner wall of the lumen. However, 25 - 50% of the implant is often cemented in place within the lumen of the femur using a surgical cement based on thermoplastic poly(methyl methacrylate), often referred to as PMMA cement.

[0003]

[0003] Such implants can typically be estimated to have a lifespan of up to 20 years. However, today, the average remaining life of a recipient after surgery may be significantly longer than 20 years. As the average remaining life increases, the probability that the implant will break during use also increases, and its replacement becomes necessary. It is rare for such "breakage" to consist of metal fatigue and cracks in the implant itself. More often, this consists of local breakage of the cement holding the implant in place, resulting in the implant becoming loose.

[0004]

[0004] Furthermore, recipients of hip prostheses are more likely to reach an age where osteoporosis begins to appear, leading to weakened bones or even a decrease in bone mass. This, too, can cause the implant to loosen from the surrounding bone.

[0005]

[0005] Furthermore, infection at the interface between the implant and the bone may occur, in some cases, due to a loss of sterility during implant fixation, or due to the transfer of bacteria from some other infected site to the trauma zone of the implant, particularly at the interface between the bone and cement. This particular condition may occur as part of revision, all It will be necessary to completely remove the cement.

[0006]

[0006] During revision, the implant or a fragment thereof is first removed from the bone cavity. Next, some or all of the PMMA cement remaining in the cavity must be removed. Then, the new implant is installed using new cement in the same procedure. If there is an infection, all the cement must be removed, and a temporary spacer is installed, typically for 6 weeks, while the infection is cleared. Only then can the spacer be removed, and the new implant be installed in a two-step procedure.

[0007]

[0007] In many cases, old cement is firmly packed into any space between the implant and the adjacent wall of the bone cavity. Furthermore, when the original implantation procedure was performed well, the PMMA cement adheres firmly to the inner wall of the bone cavity. This cement backing is particularly difficult to remove towards the distal end of deep cavities. Sometimes, as long as there is no infection and the old cement is well fixed, some of the old cement can be left in place, allowing for "cement-in-cement" fixation. Nevertheless, old cement is more prone to forming localized defects from which fracture can spread than new cement, or it may fail to adhere immediately or over time. Typically, PMMA cement strengthens over the first four or five years, and then slowly weakens and deteriorates as it approaches 20 years, so the lifespan of such an implant is estimated to be nominally 20 years.

[0008]

[0008] Therefore, surgeons need to have the ability to conveniently remove old cement wherever and whenever it is deemed necessary, depending on its location and condition.

[0009]

[0009] Only when all the necessary PMMA cement has been removed should the transplantation of a new prosthesis using new cement be permitted.

[0010]

[0010] The conventional surgical approach to removing residual aged and hardened PMMA cement has literally involved hammering a chisel into the bone cavity to scrape the cement out in small pieces. This is a slow, inefficient, and tiring procedure for the surgeon, typically taking hours to complete.

[0011]

[0011] Although cement removal using high-energy drills and burs has also been employed, the tips of these tools can be difficult to control within the limited space of the lumen. In any case, there is a risk that the chisel or drill bit may come into contact with and damage the bone adjacent to the cement being removed. Both the risks and the resulting side effects increase with the patient's age, especially when there is osteoporosis or other causes of brittle bone. Furthermore, prolonged surgical procedures under general anesthesia represent a significant risk to the patient, especially when there are other health problems.

[0012]

[0012] In patients with advanced osteoporosis, resulting in thin femoral walls, surgeons may be compelled to perform an osteotomy. In this case, a "controlled" opening is cut laterally into the femoral wall to allow direct access to and removal of PMMA located distal to the implant. Recovery from such an osteotomy is time-consuming, adding stress and cost to the procedure and exacerbating patient trauma.

[0013]

[0013] A significant advance was made when methods for using ultrasound in this area were developed. The friction generated between the titanium probe, which vibrates above 20 kHz, and the low-temperature, hard PMMA cement in contact with the probe is sufficient to heat and soften the PMMA cement, bringing it to a soft, putty-like consistency within about 1 second.

[0014]

[0014] Because PMMA has poor thermal conductivity, this heating effect does not spread to adjacent tissues but rather remains relatively localized at the site of contact with the probe. PMMA cement has a relatively low melting point / glass transition temperature of about 85°C, so relatively little energy needs to be transferred to the cement to cause this softening.

[0015]

[0015] The softened cement thus produced can be easily "scooped out" from the bone cavity rather than requiring high-impact hammering or high-speed drilling.

[0016]

[0016] A suitably designed ultrasonic vibration system may be impedance-matched to the cement in particular, which makes energy deposition to the cement efficient, but transfer to the adjacent bone significantly less efficient. This further reduces the risk of bone damage.

[0017]

[0017] An early example of such an ultrasonically vibrating tool is disclosed in European Patent No. EP0599950.

[0018]

[0018] Ultrasonic revision has been widely adopted since its introduction in the 1990s. However, more recently, it has been discovered that there may be advantages to applying different vibration modes for this purpose.

[0019]

[0019] The preceding systems used longitudinal mode ultrasonic vibrations, which are easier to generate than other modes. Unfortunately, transferring longitudinal mode vibration energy to PMMA cement does not appear to be as efficient as expected. Furthermore, it appears that a portion of the vibration energy tends to be emitted in the form of a "beam" extending distally from the tip of the tool to adjacent tissue. Therefore, it was still possible to cause localized damage to the bone when the tool was operated with its distal working tip aligned towards the bone or especially when it was touching the bone.

[0020]

[0020] Subsequently, the advantages of tools operated by ultrasonic vibration in torsional mode, and tools vibrated in a combination of torsional and longitudinal modes, have been established.

[0021]

[0021] It has been suggested that such tools may be effective in removing cement. This is assumed to be at least in part due to the efficient transfer of vibrational energy by the cement. Research into the detailed mechanisms of these processes is ongoing.

[0022]

[0022] Nevertheless, with any of these tools, there is still a risk of damaging the structural bone material of the surrounding femur or other hollow bone, especially if the tool is activated while the distal working tip of the tool is touching the wall of a bone cavity. Even if the resonant ultrasonic vibrations occurring in the shaft and distal working tip of the surgical tool are substantially reflected by strong contact with the bone surface, there is still a possibility of some energy transfer from the tool to the bone. Thus, the working tip of the tool may locally fragment or cut into the bone, especially if the bone is already weakened. Also, the energy released into the bone may weaken the entire bone within a considerable amount of bone adjacent to the tool.

[0023]

[0023] Therefore, users of surgical tools need to be informed when the working tip comes into contact with bone or other solid material. Some surgeons can utilize the audible tone that may be produced when such contact occurs. However, as will be described in more detail below, this is not sufficiently reliable and is not suitable for all users. Therefore, a more reliable and widely applicable solution is needed. [Overview of the Initiative]

[0024]

[0024] Accordingly, an object of the present invention is to provide a device for operating an ultrasonically vibrating surgical tool, the device for detecting such unexpected contact between the operated tool and adjacent bone (or similar material) and for warning the user of the tool accordingly. Another object of the present invention is to provide a device in which the operation of the device and the associated surgical tool is altered upon such detection. A further object of the present invention is to provide a method for operating such a device.

[0025]

[0025] According to a first aspect of the present invention, an ultrasonically vibrable surgical tool is provided that is adapted for cement removal in artificial joint revision surgery, and this surgical tool is A source of ultrasonic vibrations, where the source of ultrasonic vibrations is operatively connected to an elongated shaft means having an operating tip located adjacent to its distal end, the elongated shaft means adapted to transmit the ultrasonic vibrations to the operating tip, comprising: The tool comprises vibration detector means adapted to detect supplementary vibrations, where the supplementary vibrations are generated as a result of contact between the operating tip and solid bone, metal, or other hard substances, The vibration detector means is operatively coupled to signaling means adapted to indicate to the user of the tool that such contact has occurred.

[0026]

[0026] Preferably, the vibration detector means is adapted to detect supplementary vibrations having a frequency below a certain ultrasonic range.

[0027]

[0027] Preferably, the vibration detector means is adapted to detect supplementary vibrations having a frequency below 20 kHz.

[0028]

[0028] The vibration detector means may be adapted to detect supplementary vibrations having a frequency below 15 kHz.

[0029]

[0029] Optionally, the vibration detector means is adapted to detect supplementary vibrations having a frequency of at least 10 kHz.

[0030]

[0030] Advantageously, the vibration detector means is adapted to detect supplementary vibrations having a frequency approximately one-third of the frequency of the ultrasonic vibrations generated by the source and transmitted to the operating tip.

[0031]

[0031] The vibration detector means may be adapted to detect supplementary vibrations in the region of 12 kHz.

[0032]

[0032] Preferably, the vibration detector means is adapted to detect supplemental vibrations having a frequency above 20 kHz.

[0033]

[0033] Advantageously, the vibration detector means is adapted to detect supplemental vibrations having a higher frequency than the ultrasonic vibrations generated by the ultrasonic vibration source and transmitted to the working tip.

[0034]

[0034] The vibration detector means may be adapted to detect supplemental vibrations having a frequency above 36 kHz.

[0035]

[0035] Preferably, the vibration detector means is adapted to detect supplemental vibrations having multiple frequencies.

[0036]

[0036] The vibration detector means may then activate the signaling means in response to the simultaneous detection of supplemental vibrations of two or more distinct frequencies.

[0037]

[0037] The vibration detector means may be adjustable to a preset frequency or one or more preset frequencies.

[0038]

[0038] In a preferred embodiment, the vibration detector means is adapted to detect any supplemental vibrations within a specific frequency range.

[0039]

[0039] Preferably, the signaling means is then activated only when supplemental vibrations are detected within one or more pre-selected frequency ranges within the particular frequency range.

[0040]

[0040] Preferably, the signaling means is activated only when the vibration detector means detects a supplemental vibration having an amplitude exceeding a certain threshold.

[0041]

[0041] Advantageously, the threshold is selectable.

[0042]

[0042] Preferably, the signaling means is activated only when the vibration detector means detects a supplemental vibration that lasts longer than a preset duration.

[0043]

[0043] Advantageously, the signaling means is activated only when the vibration detector means detects a specific supplemental vibration that lasts longer than a preset duration.

[0044]

[0044] Preferably, the vibration detector means includes data processing means or is operationally connected to data processing means.

[0045]

[0045] Advantageously, the data processing means is programmed to convert the waveform detected by the vibration detector into a frequency spectrum.

[0046]

[0046] The data processing means may be programmed to perform a Fast Fourier Transform on the waveform detected by the vibration detector means.

[0047]

[0047] The data processing means can be programmed to divide the frequency spectrum into a plurality of pre-selected frequency ranges and, at its discretion, record signals that fall within each of the plurality of pre-selected frequency ranges.

[0048]

[0048] The data processing means may be programmed to record only signals having an amplitude greater than the amplitude threshold.

[0049]

[0049] The data processing means may be programmed to activate the signaling means according to pre-selected criteria.

[0050]

[0050] In a preferred embodiment, the signaling means comprises audible, visible, and / or tactile signaling means.

[0051]

[0051] The vibration detector means can be operationally connected to the ultrasonic vibration source so as to interrupt or turn off the generation of ultrasonic vibration by the ultrasonic vibration source when the vibration detector means detects a captured vibration.

[0052]

[0052] Advantageously, when the vibration detector detects a supplemental vibration, the generation of ultrasonic vibrations by the ultrasonic vibration source is interrupted until the supplemental vibration stops.

[0053]

[0053] Alternatively, when a supplemental vibration is detected by the vibration detector means, the ultrasonic vibration generation by the ultrasonic vibration source is turned off until the user takes action to restart the generation.

[0054]

[0054] According to a second aspect of the present invention, a method is provided for detecting contact between an ultrasonically vibrating surgical tool and bone or other hard material, the method being provided with the surgical tool described in the first aspect above, Detecting supplementary vibrations resulting from contact between the tool's operating tip and solid bone, metal, or other hard material, The method includes the steps of: in response to the detection of the supplemental vibration, activating a signaling means to indicate to the user of the tool that contact has occurred.

[0055]

[0055] In a preferred embodiment, the generation of ultrasonic vibrations is interrupted or turned off in response to the detection of the supplemental vibrations.

[0056]

[0056] Next, embodiments of the present invention will be described more specifically as examples with reference to the figures in the attached drawings. [Brief explanation of the drawing]

[0057] [Figure 1] This is a cross-sectional elevation view of the upper portion of the femur, where an ultrasonic surgical tool is being used to remove residual PMMA cement from the femoral cavity. [Figure 2]Figure 1 is a cross-sectional elevation view of the upper portion of the femur, showing an ultrasonic surgical tool penetrating the remaining PMMA cement within the femoral cavity and making contact with the bone. [Figure 3A] This graph shows the vibration frequency of the detection signal as a ratio of the power ratio of the detection signal to the tool's drive signal for a tool operating normally in bulk cement. [Figure 3B] This shows a portion of the graph in Figure 3A after it has been rescaled with the power ratio axis limited to a maximum of 0.01. [Figure 4A] This is a graph of the vibration frequency of the detected signal against the power ratio of the detected signal, similar to Figure 3A, for when the tool first touches the bone. [Figure 4B] This shows a portion of the graph in Figure 4A after it has been rescaled with the power ratio axis limited to a maximum of 0.01. [Figure 5A] This is a graph of the vibration frequency of the detected signal against the power ratio of the detected signal, similar to Figure 3A, for when the tool is in full contact with the bone. [Figure 5B] This shows a portion of the graph in Figure 5A after it has been rescaled with the power ratio axis limited to a maximum of 0.01. [Modes for carrying out the invention]

[0058]

[0057] Next, referring to the figures, particularly Figure 1, the femur 1 has the shaft of the hip prosthesis removed from the cavity 8 of the femur 1, leaving a thick layer of PMMA cement 7 coating the inner surface of the bone wall 6 of the femur 1. This cement layer 7 may need to be completely or partially removed before the replacement prosthesis is implanted in the femur 1. The implantation uses new cement to ensure a secure bond between the replacement prosthesis and the bone wall 6 of the femur 1.

[0059]

[0058] A portion of an ultrasonically vibrating surgical tool is also shown. It comprises an elongated cylindrical titanium shaft 3, which has a handle (not visible in Figure 1) adjacent to its proximal end for the user to operate the tool. The shaft 3 is operationally connected to an ultrasonic generator (also not visible in Figure 1), also adjacent to its proximal end. The middle portion of the elongated shaft 3 comprises a conversion element 4, which has several spirally extending rows or chains of recesses or dimples formed on its outer surface. These have the effect of partially converting the longitudinal mode ultrasonic vibrations generated by the generator and transmitted to the elongated shaft 3 into torsional mode ultrasonic vibrations.

[0060]

[0059] The working head 5 of the tool is located at the distal end of the elongated shaft 3, distal to the conversion element 4. Thus, the working head 5 is actuated by ultrasonic vibrations in a compound torsional longitudinal mode.

[0061]

[0060] When the working head 5 comes into contact with the cement 7, the vibrations transmitted to the cement 7 cause rapid local heating and softening of the cement 7. This makes it possible to drive the substantially conical working head 5 into the bulk cement 7 and physically crush the cement 7 for subsequent removal.

[0062]

[0061] The entire details of this form of tool and its operation are disclosed in UK Patent Application GB2601592 and corresponding applications in other jurisdictions. Further ultrasonically vibrating tools that may be subsequently used to complete the removal of cement are also disclosed in said applications.

[0063]

[0062] The ultrasonic generator is programmed to vary the frequency of the ultrasonic vibrations it provides in order to find the resonant frequency within the tool. Once the resonant frequency of the tool is found, the amplitude of the vibration at the tip of the working head 5 is maximized, and therefore the vibration energy present in the working head 5 and transmitted from there to the cement 7 is maximized.

[0064]

[0063] The tool in question conventionally operates at frequencies in the 36kHz range. In context, the upper limit of human hearing has traditionally been considered to be around 20kHz, and therefore 20kHz has traditionally been used as the defined lower limit of vibrations considered to be "ultrasonic" vibrations. However, hearing damage and simply aging can significantly reduce this upper limit of human hearing. For example, the 20kHz limit generally applies to most people up to their late teens, but the upper limit of frequencies tends to drop thereafter to 18kHz, 15kHz, and may even be as low as 12kHz for older adults with no other hearing problems. Human hearing sensitivity also tends to decrease as it approaches both the upper and lower limits of frequencies. In context, speech generally ranges from 200Hz to 5kHz, and music generally ranges from 50Hz to 10kHz.

[0065]

[0064] Figure 2 shows the femur 2 in an alternative state, where the working head 5 of the tool penetrates deeper into the layer of cement 7 than in Figure 1. The tip of the working head 5 is in contact with the solid bone 6 of the wall of the femur 2. Vibrational energy is likely to be transmitted to the bone 6, and in practice, the working tip 5 cuts into the bone 6 or otherwise damages and weakens the bone 6. Damage to the bone 6 can extend to perforation of the bone, which requires complex repair procedures, increasing the duration, cost, and stress of the procedure and increasing patient trauma.

[0066]

[0065] In reality, the working head 5 is likely to bounce off or fly away from the bone 6 upon contact, but even a brief contact may be sufficient to cause damage to the bone 6.

[0067]

[0066] As described above, the ultrasonic vibrations occurring within the tool are adjusted to find a suitable resonant frequency for the tool. This resonant frequency is hardly affected by the contact between the working head 5 and the (rapidly softening) cement 7. However, while the working head 5 is in contact with a hard solid material such as bone 6, a vibration coupling effect is created between the tool and the bone 6, which results in various additional resonances of the composite system (for a short time), having a different frequency from the initial resonance occurring within the tool alone. In practice, typical additional resonances appear to be undertones of the original resonance, having about half the frequency (therefore, in the case of this tool, this additional resonance is about 18 kHz).

[0068]

[0067] 18kHz would be above the upper limit of hearing for almost all experienced surgeons. Therefore, these surgeons would not be able to tell when they have hit bone from the generation of lower harmonics. Even if they notice an increase in physical resistance to the movement of the working head 5 when it makes contact with bone, or notice the working head 5 "bouncing" off the bone 6, this is likely to be too late after the bone 6 has already been damaged.

[0069]

[0068] Some surgeons have come to recognize hearing other lower-frequency "squeals" or "screeches" as an indicator that they have touched bone 6 with a tool. However, it is unlikely that all surgeons are able to detect these sounds.

[0070]

[0069] In any case, the intensity of the additional resonance may be low or very low, depending, for example, on the exact hardness and stiffness of the cement and bone, and the strength of their bond. Therefore, although the additional resonance is theoretically within the audible range, it may be too quiet to hear, and surgeons accustomed to listening to these "squeaks" often do not consider them sufficiently reliable, even if they are in the middle of the audible range.

[0071]

[0070] It has also been found that as a result of contact between the tool and bone, additional resonances of overtones and other high frequencies may occur that are considerably beyond the audible range of any user. Here, the resonances are inaudible regardless of their intensity.

[0072]

[0071] Accordingly, in the present invention, the tool is provided with a vibration detector mechanism. In the first example, this vibration detector is tuned to pick up vibrations in the 18 kHz range. Conveniently, the vibration detector comprises an acoustic / ultrasonic microphone mounted inside the ultrasonic generator itself. Typically, due to the power cable connecting the ultrasonic generator to the tool itself, the generator is less than 3 meters from the tool, making it easy to detect the vibrations in question.

[0073]

[0072] The vibration detector mechanism is set to track the amplitude of vibrations from the tool at approximately 18 kHz. When this amplitude exceeds a preset threshold, this is treated as an indicator that the working head 5 has come into contact with the bone 6 or other solid material, and therefore the detector mechanism is triggered to emit an appropriate alarm signal.

[0074]

[0073] These detectors can be made far more sensitive than the best human hearing.

[0075]

[0074] This alarm signal may be used to activate an audible alarm that operates at a lower frequency, making it easier for all users to hear. Optionally, the audible alarm may have a distinctive tone or sound, rather than a substantially single-frequency pure tone of ultrasonic vibrations, their harmonics, and subharmonics. An alternative alarm tone may be provided that is selectable by the user.

[0076]

[0075] The alarm signal may be used to activate a visible alarm if the user deems it more useful. Additionally or alternatively, a tactile alarm, such as a vibrating element visible to the naked eye within the tool's grip, may be activated to send a tactile warning to the user's hand.

[0077]

[0076] In some examples of the present invention, the user can select which form of alarm to activate.

[0078]

[0077] In each case, the surgeon using the tool is quickly and reliably alerted when the working head 5 touches a solid material such as bone 6. The surgeon can then react by cutting off the supply of ultrasonic vibrations to the tool. Although the tool is made of titanium, in practice it is not particularly sharp at the level of the naked eye, and its shape is such that it can hardly damage bone when not being actuated with ultrasound.

[0079]

[0078] The ultrasonic vibrations sent to the tool are typically turned on by the surgeon pressing a finger-operated switch on the handpiece, or alternatively, by pressing a foot pedal switch. Therefore, it is generally easier and simpler to release the switch or pedal and cut off the ultrasonic vibrations than to react to an alarm by retracting the working head 5 from contact with the bone 6, and possibly with something else undesirable in the process.

[0080]

[0079] Some surgeons prefer to have complete personal control over the ultrasonic vibrations in this way, while others prefer more automated systems. In automated systems, along with sounding an alarm (or instead), the detector mechanism automatically cuts off the ultrasonic vibrations supplied to the tool when triggered.

[0081]

[0080] In one version, the ultrasonic generator then requires input from the user, for example, by tapping a foot pedal, to resume. In other versions, the ultrasonic vibrations are paused for a short period, perhaps one or two seconds, sufficient to give the surgeon time to controllly retract the (now inactive) tool and remove it from contact with the bone 6 before the vibrations automatically resume and the operation begins again.

[0082]

[0081] The present invention began by focusing on “downharmonic” vibrations of about 18 kHz, which very few users can hear, but it was found that vibrations of other frequencies occur as a result of contact between the tool and bone or other hard surfaces. Some of these are frequencies that are considered ultrasonic, including frequencies above the driving frequency (which was 36 kHz in this series of tests).

[0083]

[0082] These frequencies have never been picked up during the existing use of these tools, even by the most perceptive human hearing users, but a mechanism similar to that described above can be used if a microphone of the correct form optimized to detect the relevant frequency range is provided. Such microphones are readily available, for example, those specially manufactured for use in bat detectors, but standard microphones used in smartphones appear to be capable of picking up frequencies well above the audible range.

[0084]

[0083] A further example is the use of more than one diagnostic frequency. Thus, the system may be configured to monitor multiple frequencies and respond to a significant signal at any of the possible frequencies, or alternatively, to respond only if there is one signal at more than one diagnostic frequency, especially if these signals are relatively weak.

[0085]

[0084] As the present invention is further developed, it has become clear that such a system needs to exhibit the lowest possible false positive rate in order to avoid being excessively frustrating and inconvenient for the user, and at the same time, it needs to minimize false negatives in order to avoid damaging the contact between the tool and the bone.

[0086]

[0085] In this regard, one unexpected finding was that lower harmonics of about half the drive frequency, approximately 18 kHz in the above example, could occur even without contact between the tool and the bone, including when the tool was working properly with the balas cement 7. Therefore, if the system is targeting an 18 kHz signal, there is a risk of excessive false positives.

[0087]

[0086] Therefore, further examples of the present invention have been developed to prevent this problem.

[0088]

[0087] These have the same overall layout as the first example described above, but track different frequencies. The operation of these versions of the present invention will now be described with reference to Figures 3A to 5B.

[0089]

[0088] The sound intensity picked up by the vibration detector during the operation of the tool is processed electronically by a well-known Fast Fourier Transform (FFT) algorithm that acquires a time-domain sound waveform and converts it into frequency-domain data. This yields a sound with a frequency spectrum over a frequency range of 1 kHz to 100 kHz. The FFT can be performed 60 times per second, making it possible to track the entire frequency spectrum in real time. In the plots created shown in Figure 3A and subsequent figures, the vertical axis is the power ratio of the intensity of the signal detected at a particular frequency, which is normalized with respect to the intensity of the drive signal and gives a ratio between 0 and 1.0.

[0090]

[0089] The detected frequencies can be subdivided into a series of “frequency windows”. The selected frequency windows to be monitored are defined to avoid the tool drive signal / main resonance at approximately 36 kHz and the lower harmonics at approximately 18 kHz, which have been found to be unreliable indicators of tool-bone contact. The exact limits of these windows are now thought to depend on the exact tool morphology, and it may be necessary to establish different sets of windows for different tools. Figures 3A and following show examples of these for specific tools illustrated in Figures 1 and 2.

[0091]

[0090] Figure 3A shows the frequency spectrum of this tool operating in bulk cement. Four frequency windows 11, 12, 13, and 14 to be monitored are defined, which in this particular example range from 9600 to 13200 Hz, 14200 to 16700 Hz, 21000 to 26000 Hz, and 28000 to 35000 Hz, respectively (Note: these cover frequency ranges in both the “audible” range and the low ultrasonic range). In practice, each frequency window is divided into a series of “bins” that cover adjacent subdivisions of the window’s frequency range, each of which is monitored individually. The “bins” are sized according to the size of the FFT, and their size and number are a balance between accuracy and the processing power and speed of the processing unit performing the FFT.

[0092]

[0091] In the case of bulk cement, only the detection signal 15 visible in Figure 3A is the resonant frequency of the tool, which is slightly above 36 kHz. This has a power ratio of 0.94 and indicates that the vast majority of the input drive signal is emitted from the tool at a favorable frequency.

[0093]

[0092] Figure 3B shows the same plot as Figure 3A, but the y-axis covers only power ratios from 0 to 0.01. Therefore, signal 15 is extended far outside the scale. This figure also shows that in this example, the frequency windows 11, 12, 13, and 14 are set with an upper limit of 0.007 for the power ratio. Therefore, the detected signal must exceed an amplitude of 0.07 in order to be treated as significant (the exact useful value of this upper limit may also differ from that shown for different tools).

[0094]

[0093] In Figure 3B, no detectable signals are found in any of the frequency windows 11, 12, 13, and 14. Only signal 16 can be seen between the two windows 12 and 13, which represents a half-frequency lower harmonic of approximately 18 kHz. As mentioned above, this is thought to occur spontaneously at varying intensities under all operating conditions and is therefore not the best marker for bone contact. There are several other signals with very low amplitude, but none are near the defined upper limits for the frequency windows 11, 12, 13, and 14 being monitored.

[0095]

[0094] Figure 4A shows a typical frequency spectrum for when the tool just touches the bone. Signal 15, representing the tool's drive frequency / main resonance at approximately 36 kHz, drops to a power ratio of 0.32 in intensity. Signal 16, representing the half-frequency lower harmonic at approximately 18 kHz, increases significantly to a power ratio of 0.11. Both of these signals 15 and 16 are, in fact, very Although the frequencies are slightly varied, both remain outside the monitored frequency windows 11, 12, 13, and 14.

[0096]

[0095] Figure 4B shows the same plot as Figure 4A, but again the y-axis covers only power ratios from 0 to 0.01. Signals 15 and 16 are consequently extended out of scale. However, signals such as those labeled 17 and 18, which are within one of the frequency windows 11, 12, 13, and 14, appear at new frequencies. Here, signal 17 is approximately 12 kHz and signal 18 is approximately 24 kHz. These are thought to be due to contact between the tool and the bone for reasons explained below. Nevertheless, at this stage these signals 17 and 18 have amplitudes well below the threshold of a power ratio of 0.007 and are therefore not considered significant enough to confirm clear tool-to-bone contact.

[0097]

[0096] In Figure 4B, multiple signals 19 with frequencies higher than the drive frequency can also be seen, and their relationship will be explained below.

[0098]

[0097] Figure 5A shows a typical frequency spectrum when bone contact is sustained, showing a large change from Figures 3A and 4A. The main resonant signal 15 at approximately 36 kHz has a power ratio of approximately 0.54 here, but the lower harmonic signal 16 at approximately 18 kHz has disappeared, confirming its low reliability as a marker for bone contact. However, the signal 17 at approximately 12 kHz has increased significantly to a power ratio of approximately 0.1, and the signal 18 at approximately 24 kHz has increased even further to a power ratio of 0.46.

[0099]

[0098] Figure 5B shows the same plot as Figure 5A, where the y-axis also covers only power ratios from 0 to 0.01, and a threshold of 0.07 is shown for each of the monitored frequency windows 11, 12, 13, and 14 (for clarity, the frequency windows 11, 12, 13, and 14 are not labeled in Figure 5B). The signal 17 at approximately 12 kHz and the signal 18 at approximately 24 kHz clearly exceed the threshold power ratio values ​​for their respective frequency windows 11 and 13, and these also fall within one of the windows 11, 12, 13, and 14, with further signals exceeding these thresholds.

[0100]

[0099] Thus, in this example, within three of the four frequency windows 11, 12, and 13, there are detectable signals that exceed the threshold set for significance. This is a clear indicator of contact between the bone and the tool and can be used to trigger a contact warning signal and / or to trigger an interruption of the ultrasonic drive signal supplied to the tool, as described above for the first tool.

[0101]

[0100] Figure 5B also shows that when the tool is in full contact with the bone, several signals 19 above the drive frequency are also significantly amplified. In this example, they appear at frequencies such as approximately 48 kHz, 60 kHz, and 72 kHz, which suggests that they may be harmonics of the 12 kHz or 24 kHz signal. In this particular version of the invention, no frequency window for monitoring these frequencies is defined, but this is not considered an issue in current implementations, and further development for investigating this portion of the frequency spectrum is underway as of the filing date.

[0102]

[0101] With regard to other parts of the spectrum, frequencies far below 10 kHz have been found to be unsuitable for monitoring because (a) their actual amplitudes are typically far below the amplitudes of ultrasonic and near-ultrasonic signals monitored by the systems described above, and (b) this audible frequency range can be very "busy" even when the tool is simply working on the bulk cement.

[0103]

[0102] The threshold level of the defined frequency window can be set by referencing the intensity of the detected drive signal, as described above, or it can be set as an absolute value. Normalizing by referencing the drive signal has the advantage of eliminating the influence of the exact distance from the microphone to the tool, or the influence of the possibility that the surgeon may be standing in a straight line between the microphone and the tool. In either case, the set threshold is an empirical compromise between minimizing false positives and minimizing the time it takes to warn the user of bone contact.

[0104]

[0103] The system's sensitivity can be adjusted by controlling the number of consecutive "positives" (i.e., signals exceeding a threshold detected within a particular bin in consecutive FFT runs) required before a contact warning is generated. The conditions required to terminate a warning can also be adjusted so that the system generates a single consecutive warning rather than a series of rapidly repeating short warnings.

[0105]

[0104] In the currently preferred version of the present invention, the definition used for a “true sustained” bone contact worthy of a warning is that the contact signal in a particular bin exceeds a threshold over five consecutive cycles of the FFT calculation. Since the FFT is currently performed at 60 cycles per second, this still provides the user with a very quick alert. Currently, these positives can be in any one, two, three, or all four of the frequency windows 11, 12, 13, 14. The approach taken is to “accumulate” the positives for each bin until one or more reach five positives. If there are no values ​​above the threshold across the entire frequency range, all bins are reset to zero.

[0106]

[0105] Therefore, the required number of consecutive positives can be adjusted to match the sensitivity of the system. This may be chosen at the discretion of the surgeon, for example, by selecting high sensitivity when it is known that the patient's bone is very brittle or already damaged, or by selecting low sensitivity when it is known that it is very likely that the bone will be touched for a short time, or when the risk of bone perforation is low, such as when scraping cement out of the bone cavity proximal rather than drilling a hole in the cement distally, as in Figures 1 and 2.

[0107]

[0106] In order to ensure that the present invention works well for each tool, it is considered important to establish a standard for which it works for various tools. It is preferable that the frequency window being monitored covers the signals generated by the entire range of possible contacts, rather than requiring different settings for different tools, for example. The precise tool geometry is considered important, along with all the different degrees of tool contact that may result. Factors that influence this interaction are, a) contact force, b) contact angle, c) Bone decay due to cement, d) Bone characteristics, including density, thickness, and type (Note: Cancellous bone that may be growing around the implant is generally too soft to be detected by this approach, so only contact with cortical bone is recorded. This is actually beneficial, as the formed cancellous bone also, in principle, needs to be removed before implanting a new prosthesis).

[0108]

[0107] The aforementioned variability in the precise interaction between bone and tool is thought to be the reason behind the unreliability of the traditional approach in which surgeons listen for audible contact "squeaks."

[0109]

[0108] Thus, the present invention makes it possible to minimize undesirable contact between an ultrasonically operated tool and adjacent bone or other solid material in a more reliable and convenient way than existing approaches such as listening for specific squealing or screeching sounds that may or may not be produced at audible intensity.

Claims

1. An ultrasonically vibrating surgical tool adapted for cement removal in artificial joint revision surgery, An ultrasonic vibration source is provided, and here, the ultrasonic vibration source is operationally connected to an elongated shaft means having an operating tip located adjacent to its distal end. The elongated shaft means is adapted to transmit the ultrasonic vibrations to the working tip, Equipped with, The surgical tool comprises vibration detector means adapted to detect supplemental vibrations, wherein the supplemental vibrations are generated as a result of contact between the working tip and solid bone, metal, or other hard material. An ultrasonically vibrating surgical tool, wherein the vibration detector means is operationally coupled to a signaling means adapted to indicate to the user of the surgical tool that contact has occurred.

2. The ultrasonic vibrating surgical tool according to claim 1, wherein the vibration detector means is adapted to detect supplemental vibrations having a frequency below a certain ultrasonic range.

3. The ultrasonic vibrating surgical tool according to claim 1, wherein the vibration detector means is adapted to detect supplemental vibrations having a frequency below 20 kHz.

4. The ultrasonic vibrating surgical tool according to any one of claims 1 to 3, wherein the vibration detector means is adapted to detect supplemental vibrations having a frequency below 15 kHz.

5. The ultrasonic vibrating surgical tool according to any one of claims 1 to 4, wherein the vibration detector means is adapted to detect supplemental vibrations having a frequency greater than 10 kHz.

6. The ultrasonic vibrating surgical tool according to any one of claims 1 to 5, wherein the vibration detector means is adapted to detect supplemental vibrations having a frequency of about one-third of the frequency of ultrasonic vibrations generated by the source and transmitted to the working tip.

7. The ultrasonic vibrating surgical tool according to any one of claims 1 to 6, wherein the vibration detector means is adapted to detect supplemental vibrations in the 12 kHz range.

8. The ultrasonic vibrating surgical tool according to claim 1, wherein the vibration detector means is adapted to detect supplemental vibrations having a frequency above 20 kHz.

9. The ultrasonic vibrating surgical tool according to claim 8, wherein the vibration detector means is adapted to detect supplemental vibrations having a higher frequency than the ultrasonic vibrations generated by the ultrasonic vibration source and transmitted to the working tip.

10. The ultrasonic vibrating surgical tool according to claim 8, wherein the vibration detector means is adapted to detect supplemental vibrations having a frequency above 36 kHz.

11. The ultrasonic vibrating surgical tool according to any one of claims 1 to 10, wherein the vibration detector means is adapted to detect supplemental vibrations having multiple frequencies.

12. The ultrasonic vibrating surgical tool according to claim 11, wherein the vibration detector means activates the signaling means in response to the simultaneous detection of supplemental vibrations of two or more distinct frequencies.

13. The ultrasonic vibrating surgical tool according to any one of claims 1 to 12, wherein the vibration detector means is adjustable to a preset frequency or one or more preset frequencies.

14. The ultrasonic vibrating surgical tool according to any one of claims 1 to 13, wherein the vibration detector means is adapted to detect any supplemental vibration within a specific frequency range.

15. The ultrasonic vibrating surgical tool according to claim 14, wherein the signaling means is activated only when supplemental vibrations are detected within one or more pre-selected frequency ranges within the specific frequency range.

16. The ultrasonic vibrating surgical tool according to any one of claims 1 to 15, wherein the signaling means is activated only when the vibration detector means detects a supplemental vibration having an amplitude exceeding a certain threshold.

17. The ultrasonically vibrating surgical tool according to claim 16, wherein the threshold is selectable.

18. The ultrasonic vibrating surgical tool according to any one of claims 1 to 17, wherein the signaling means is activated only when the vibration detector means detects a supplemental vibration that lasts longer than a preset duration.

19. The ultrasonic vibrating surgical tool according to claim 18, wherein the signaling means is activated only when the vibration detector means detects a specific supplemental vibration that lasts longer than a preset duration.

20. The ultrasonic vibrating surgical tool according to any one of claims 1 to 19, wherein the vibration detector means comprises a data processing means or is operationally connected to a data processing means.

21. The ultrasonic vibrating surgical tool according to claim 20, wherein the data processing means is programmed to convert the waveform detected by the vibration detector means into a frequency spectrum.

22. The ultrasonic vibrating surgical tool according to claim 21, wherein the data processing means is programmed to perform a fast Fourier transform on the waveform detected by the vibration detector means.

23. The ultrasonic vibrating surgical tool according to claim 21 or 22, wherein the data processing means is programmed to divide the frequency spectrum into a plurality of pre-selected frequency ranges and record signals that fall within each of the plurality of pre-selected frequency ranges.

24. The ultrasonic vibrating surgical tool according to claim 23, wherein the data processing means is programmed to record only signals having an amplitude greater than an amplitude threshold.

25. The ultrasonic vibrating surgical tool according to any one of claims 20 to 24, wherein the data processing means is programmed to operate the signaling means according to a pre-selected criterion.

26. The ultrasonic vibrating surgical tool according to any one of claims 1 to 25, wherein the signaling means comprises audible, visible, and / or tactile signaling means.

27. The ultrasonic vibrating surgical tool according to any one of claims 1 to 26, wherein the vibration detector means is operationally connected to the ultrasonic vibration source such that when the vibration detector means detects a supplemental vibration, it interrupts or turns off the generation of ultrasonic vibration by the ultrasonic vibration source.

28. A method for detecting contact between an ultrasonically vibrating surgical tool and bone or other hard material, To provide a surgical tool according to any one of claims 1 to 27, To detect supplementary vibrations resulting from contact between the operating tip of the surgical tool and solid bone, metal, or other hard material, In response to the detection of the aforementioned supplemental vibration, the signaling means is activated to indicate to the user of the surgical tool that the contact has occurred. A method comprising the steps of performing a certain action.

29. The method according to claim 28, wherein the generation of ultrasonic vibrations is interrupted or turned off in response to the detection of the supplemental vibrations.

Images