Patent Description:
Expandable implants need an accurate way to noninvasively monitor adjustment thereof. Current devices and methods of monitoring adjustment in expandable implants are insufficient because critical assumptions often introduce error into their measurements. Provided herein is a novel solution to the problem. <CIT> describes an expandable implant with landmarks which are identifiable by ultrasound.

This disclosure includes devices and methods for measuring an amount of adjustment of an expandable implant using ultrasound.

The present invention provides an expandable implant as set out in claim <NUM>. Further advantageous features are set out in the dependent claims. The invention also provides a method for measuring a change in dimension of an implant using ultrasound as set out in claim <NUM>.

These and other features may be further understood by those with skill in the art upon a review of the appended drawings, wherein:.

For purposes of explanation and not limitation, details and descriptions of certain preferred embodiments and methods are hereinafter provided such that one having ordinary skill in the art may be enabled to make and use the invention. These details and descriptions are representative only of certain preferred embodiments. However, a myriad of other embodiments which will not be expressly described will be readily understood by those having skill in the art upon a thorough review hereof.

In medical implants, transcutaneous transmission of information is particularly difficult at Radio Frequencies (RF) because of the attenuation characteristics in fluids and aqueous tissues experienced within the human body by RF transmission frequencies. Ultrasound frequencies however, have mitigated attenuation characteristics and superior transmission qualities when transmitted through fluids and aqueous tissues, especially as compared with RF.

Another benefit of ultrasound frequencies is their demonstrated and superior transmission characteristics through metal. This is particularly useful in medical implants, distraction rods for example, where metals like titanium are often included.

The frequency of ultrasound sound waves of the ultrasound signal chosen for transcutaneous communication should be generally greater than about <NUM> kilohertz (kHz). In some embodiments, the frequency of ultrasound sound waves may be between <NUM> and <NUM> or about <NUM>. In some embodiments, <NUM> may be used.

The benefits of utilizing ultrasound sound waves for transcutaneous communication using an ultrasound signal include: (<NUM>) that ultrasound sound waves have both favorable propagation and minimal attenuation characteristics through metal or solid mediums (e.g., metallic medical implants), and (<NUM>) that ultrasound sound waves have favorable propagation and minimal attenuation characteristics through various aqueous tissues in animals (e.g. human skin, muscle and bone).

One of the challenges with expandable implants, particularly implants that can be adjusted non-invasively, is that previously there existed no reliable in situ method of measuring an amount of adjustment of the expandable implant short of radiographic imaging the expandable implant, and for e.g. exposing the patient to an additional amounts of radiation.

In distraction rods for example, one can monitor adjustment of the distraction rod by taking advantage of the fact that rotation of the internal magnet of the distraction rod, has a direct relationship with a quantified amount of distraction of the distraction rod. Similarly, one can monitor adjustment of the distraction rod by taking advantage of the fact that movement of one surface relative to another will have a direct relationship with a quantified amount of distraction of the distraction rod.

The mechanism to distract the distraction rod may include coupling an internal magnet of the distraction rod with one or more external magnet of an External Adjustment Device sometimes referred to as an External Remote Controller (ERC). Thus, one might assume there should be a fixed correlation between rotation of the external magnet with rotation of the internal magnet. Therefore, by monitoring rotation of the external magnet one can approximate an amount of rotation of the internal magnet, and therefore deduce a total amount of distraction of the distraction rod.

Occasionally however, the one or more magnet of the ERC may become decoupled from the internal magnet of the expandable implant, at least temporarily, and while the one or more external magnet rotates the internal magnet of the distraction rod may not. This is sometimes referred to as slippage or stalling. As a result, monitoring the rotation of the external magnets alone may not necessarily provide a completely accurate measurement of the adjustment or distraction of the distraction rod.

In a general embodiment, an expandable implant configured to be measured using ultrasound includes a vibration element tuned for ultrasonic vibration, with the vibration element configured to produce an ultrasonic vibration upon an adjustment of the expandable implant, and each ultrasonic vibration corresponding to an amount of adjustment of the expandable implant.

Because ultrasound frequencies have favorable transmission characteristics in fluids, aqueous tissues and even metals, the resulting ultrasonic emissions may be observed locally at the expandable implant or by an external transceiver located outside of the patient. Similarly, in some embodiments one or more other implants may include one or more ultrasonic transducer configured to detect and report an amount of adjustment of the ultrasound implant.

Now, the one or more ultrasound transducer may include: piezoelectric transducers, ingle crystal ultrasonic transducers, lead zirconate titanate (PZT) ultrasound transducers, piezoelectric polyvinylidene fluoride (PVDF) ultrasound transducers, capacitive micro-machined ultrasound transducers (CMUT), piezoelectric micro-machined ultrasound transducers (PMUT), or any ultrasound transducer commonly known and used in the art.

In some embodiments, the ultrasound transducer may be disposed on and within the expandable implant, operably connected to one or more of: a controller, a memory, a power supply, or any other electronic component disposed on the expandable implant, with the ultrasound transducer configured to count a number of ultrasounds transmissions emitted by the vibration element.

In some embodiments, the resulting ultrasound transmissions are observed by an ultrasound transducer located outside of the patient. For external observation it may be favorable to use an array of ultrasound transducers to maximize an amount of signal observed at increased distances. The ultrasound transducer may be disposed on and within an external device, for example the External Remote Control (ERC), and operably connected to one or more of: a controller, a memory, a power supply, and any known electronic component, with the ultrasound transducer configured to count a number of ultrasound transmissions produced by the vibration element. In some embodiments the ultrasound transducer is provided in contact with the skin of the patient to minimize an amount of air gap, since ultrasound waves experience large amounts of reflection at interfaces such as air gaps.

The vibration element communicates with a surface of the expandable implant. That surface may be configured to move upon an adjustment of the expandable implant. The surface includes a plurality of agitation elements. The agitation elements include bumps. Upon a communication of the bumps with the vibration element the vibration element will produce an ultrasound transmission.

The shaft includes at least one agitation element configured to communicate with the vibration element upon a rotation of the shaft. A plurality of vibration elements tuned for ultrasound vibration and a plurality of agitation elements are disposed on the shaft, the plurality of agitation elements configured to communicate with the plurality of vibration elements to produce a plurality of ultrasound transmissions. An increased number of vibration elements will increase the magnitude of the transmissions produced, improving detection of the ultrasound transmissions. Improved signal strength is particularly useful when observing the ultrasound transmissions external to the patient.

In some embodiments, the vibration element communicates with a surface of a rotatable internal magnet of an expandable implant. That rotatable internal magnet may be configured to rotate upon an adjustment of the expandable implant. The surface of the rotatable internal magnet may include one or more agitation elements. Upon a communication of the agitation element with the vibration element, the vibration element will produce an ultrasound transmission.

Now, turning to the drawings <FIG> shows a patient <NUM> with scoliosis. The concave portion <NUM> of the spinal curve can be seen on the left side <NUM> of the patient <NUM>, and the convex portion <NUM> can be seen on the right side <NUM> of the patient <NUM>. Of course, in other patients, the concave portion <NUM> may appear on the right side <NUM> of the patient <NUM> while the convex portion <NUM> may be found on the left side <NUM> of the patient <NUM>. In addition, as seen in <FIG>, some rotation of the spine <NUM> is present, and unevenness between the left shoulder <NUM> and right shoulder <NUM> is seen.

<FIG> illustrates the Cobb angle <NUM> of a spine <NUM> of a patient with scoliosis. To determine the Cobb angle, lines <NUM> and <NUM> are drawn from vertebra <NUM> and <NUM>, respectively. Intersecting perpendicular lines <NUM> and <NUM> are drawn by creating <NUM>° angles <NUM> and <NUM> from lines <NUM> and <NUM>. The angle <NUM> created from the crossing of the perpendicular lines <NUM> and <NUM> is defined as the Cobb angle. In a perfectly straight spine, this angle is <NUM>°.

In patients with scoliosis, corrective surgery may be elected. The corrective surgery may include a placement of and adjustment of and expandable implant. Historically, adjustment required repeated surgeries each time adjustment of the expandable implant was required. Modernly, noninvasively expandable implants allow adjustment of these devices in situ. However, informational feedback from the expandable implants has proven difficult to receive.

<FIG> illustrates an external adjustment device for example ERC <NUM> that is configured for adjusting an expandable implant <NUM>. The expandable implant <NUM> may include any for example: number of distraction devices such as those disclosed in <CIT>, <CIT>, <CIT>, <CIT> (published as <CIT>, <CIT>, <CIT> and <CIT> respectively).

The distraction device <NUM> includes a housing <NUM> configured to be secured to a bone of a patient in a first location and a rod <NUM> configured for telescopic engagement with the housing <NUM>, the rod <NUM> configured to be secured to a bone of a patient in a second location.

The distraction device <NUM> also includes a rotationally mounted, internal magnet <NUM> that rotates in response to a magnetic field applied by the external adjustment device <NUM>. Rotation of the magnet <NUM> in one direction effectuates distraction while rotation of the magnet <NUM> in the opposing direction effectuates retraction. Distraction includes a measurable increase in a total length of the expandable implant <NUM>, while retraction includes a measurable decrease in a total length of the expandable implant <NUM>.

In some embodiments, the internal magnet <NUM> is operably coupled to a lead screw (<FIG>, <NUM>), with a rotation of the internal magnet <NUM> configured to rotate the lead screw <NUM>. The lead screw <NUM> includes a threaded surface configured to communicate with a threaded surface of the rod <NUM>. Allowing a rotation of the lead screw <NUM> to move the rod <NUM> relative to the housing <NUM>.

In some embodiments, the external adjustment device <NUM> may be powered by a rechargeable battery and by a power cord <NUM>. The external adjustment device <NUM> may include a first handle <NUM> and a second handle <NUM>. The second handle <NUM> is shown in a looped shape, and can be used to carry the external adjustment device <NUM>. The second handle <NUM> can also be used to steady the external adjustment device <NUM> during use. Generally, the first handle <NUM> of this embodiment extends linearly from a first end of the external adjustment device <NUM> while the second handle <NUM> is located at a second end of the external adjustment device <NUM> and extends substantially off axis or is angled with respect to the first handle <NUM>.

The first handle <NUM> contains the motor <NUM> that drives a first external magnet <NUM> and a second external magnet <NUM> as best seen in <FIG>, via gearing, belts and the like. On the first handle <NUM> is an optional orientation image <NUM> comprising a body outline <NUM> and an optional orientation arrow <NUM> that shows the correct direction to place the external adjustment device <NUM> on the patient's body, so that the expandable implant <NUM> is adjusted in the relative direction. While holding the first handle <NUM>, the operator presses with his thumb the distraction button <NUM>, which has a distraction symbol <NUM>, and is a first color, for example green. This distracts the expandable implant <NUM>. If the expandable implant <NUM> is over-distracted and it is desired to retract, or to lessen the distraction of the expandable implant <NUM>, the operator presses with his thumb the retraction button <NUM> which has a retraction symbol <NUM>.

Distraction turns the magnets <NUM>, <NUM> one direction and retraction turns the magnets <NUM>, <NUM> in the opposite direction. The magnets <NUM>, <NUM> include stripes <NUM> that can be seen in window <NUM>. This allows easy identification of whether the magnets <NUM>, <NUM> are stationary or turning, and in which direction they are turning. This allows quick trouble shooting by the operator. The operator can determine the point on the patient where the internal magnet <NUM> of the expandable implant <NUM> is located, and can then put the external adjustment device <NUM> in correct location with respect to the expandable implant <NUM>, by marking the corresponding portion of the skin of the patient, and then viewing this spot through the alignment window <NUM> of the external adjustment device <NUM>.

<FIG> illustrates the orientation of poles of the first and second external magnets <NUM>, <NUM> and the internal magnet <NUM> of the expandable implant <NUM> during a distraction procedure. For the sake of description, the orientations will be described in relation to the numbers on a clock. First external magnet <NUM> is turned (by gearing, belts, etc.) synchronously with second external magnet <NUM> so that north pole <NUM> of first external magnet <NUM> is pointing in the twelve o'clock position when the south pole <NUM> of the second external magnet <NUM> is pointing in the twelve o'clock position. At this orientation, therefore, the south pole <NUM> of the first external magnet <NUM> is pointing is pointing in the six o'clock position while the north pole <NUM> of the second external magnet <NUM> is pointing in the six o'clock position. Both first external magnet <NUM> and second external magnet <NUM> are turned in a first direction as illustrated by respective arrows <NUM>, <NUM>. The rotating magnetic fields apply a torque on the internal magnet <NUM> of the expandable implant <NUM>, causing it to rotate in a second direction as illustrated by arrow <NUM>. Exemplary orientation of the north pole <NUM> and south pole <NUM> of the internal magnet <NUM> during torque delivery are shown in <FIG>. When the first and second external magnets <NUM>, <NUM> are turned in the opposite direction from that shown, the internal magnet <NUM> will be turned in the opposite direction from that shown. The orientation of the first external magnet <NUM> and the second external magnet <NUM> in relation to each other serves to optimize the torque delivery to the implanted magnet <NUM>.

Now, it has been shown that monitoring the rotation of the external magnets <NUM>, <NUM> can give insight into an amount of rotation of the internal magnet <NUM> of the expandable implant <NUM>. However, the external magnets <NUM>, <NUM> may become decoupled from the internal magnet <NUM>, at least temporarily, and while the external magnets <NUM>, <NUM> rotate the internal magnet <NUM> of the expandable implant <NUM> may not. This is sometimes referred to as slippage or stalling, and may result in inaccurate monitoring of a total amount of adjustment of the expandable implant <NUM>.

<FIG> shows a schematic view of an expandable implant <NUM> implanted within a patient <NUM>, the expandable implant <NUM> having an ultrasound counter <NUM> disposed therein. The expandable implant <NUM> includes a housing <NUM> and a rod <NUM> configured to move telescopically relative to the housing <NUM>. The rod <NUM> includes a threaded surface configured to communicate with a lead screw <NUM>. As described above, upon a rotation of the lead screw <NUM> by the rotatable internal magnet <NUM>, the rod <NUM> will move relative to the housing <NUM>.

Adjacent to the internal magnet <NUM> is an ultrasound counter <NUM>. The ultrasound counter <NUM> is configured to generate at least one ultrasound transmission upon, for example, each rotation of the lead screw <NUM>. The expandable implant <NUM> also is shown including an ultrasound transducer <NUM> operably coupled to an electronics module <NUM>.

The ultrasound transducer <NUM> is configured to send and/or receive ultrasound transmissions A. Now, as described herein, in some embodiments the ultrasound counter <NUM> is configured to generate ultrasound transmissions A corresponding to an amount of adjustment of the expandable implant <NUM>. The ultrasound transmissions A may be observed locally at the expandable implant <NUM> by the ultrasound transducer <NUM>. The electronics module <NUM> operatively and electronically coupled to the ultrasound transducer <NUM> may include one or more of: a controller, a memory, a power supply, and any other electronic component, with the ultrasonic transducer <NUM> configured to count a number of ultrasonic transmissions A produced by the ultrasound counter <NUM>.

In some embodiments, the ultrasound transmissions A may be observed external to the patient <NUM> by an external ultrasound transducer <NUM>. The external ultrasound transducer <NUM> may be part of an external remote control (ERC) <NUM> of the expandable implant <NUM>, and may be a separate device <NUM>. The external ultrasound transducer <NUM> may be in communication with one or more various electronic devices, for e.g. a smart phone <NUM> across various communication bands B including: RF, WiFi, Bluetooth, Internet, ultrasound communication and any known communication method. One or more of the external ultrasound transducer <NUM>, the smart phone <NUM>, and any known electronic device may be connected to the internet <NUM> e.g. a cloud <NUM>. This allows a practitioner <NUM> to remotely receive distraction information from the expandable implant <NUM>, by remotely accessing and even adjusting the expandable implant <NUM>.

<FIG> shows an ultrasound counter <NUM> in accordance with a first embodiment. As one with skill in the art may appreciate, the ultrasound counter <NUM> is designed for integration with expandable implants <NUM> including those described above, at least a portion of the ultrasound counter <NUM> may be disposed for example in the housing <NUM> of the expandable implant <NUM> adjacent to the internal magnet <NUM>. The ultrasound counter <NUM> includes at least one vibration element <NUM> tuned for ultrasonic vibration. For convenience, a portion of the vibration element <NUM> is shown transparent to illustrate the communication between the vibration element <NUM> and an agitation element <NUM> disposed on the rotatable shaft <NUM>. The shaft <NUM> is shown in communication with the internal magnet <NUM> of an expandable implant <NUM> and is configured to rotate upon a rotation of the rotatable permanent magnet <NUM>.

The vibration element <NUM> is tuned to produce an ultrasonic transmission, e.g. a vibration at an ultrasonic frequency, upon an agitation by the agitation element <NUM>. A rotation of the internal permanent magnet <NUM>, which occurs upon activation by an external remote control <NUM> as described above, will be communicated to the rotatable shaft <NUM>, and the agitation element <NUM> will communicate with the vibration element <NUM> to produce a transmission at an ultrasonic frequency.

Each rotation of the shaft <NUM> will correlate to a rotation of the internal magnet <NUM>. Rotation of the internal magnet <NUM> will also correlate to some fixed amount of adjustment of the expandable implant <NUM>. Therefore, each ultrasonic transmission produced by the vibration element <NUM> will correspond to a quantified amount of adjustment of a total length of the expandable implant <NUM>.

<FIG> shows a cross-sectional view of the ultrasound counter <NUM> in accordance with the first embodiment. The rotatable shaft <NUM> is shown having a plurality of agitation elements <NUM> disposed thereon. The ultrasound counter <NUM> is also shown including a plurality of vibration elements <NUM>.

One distinct advantage of this design is that generation of the ultrasound transmissions is purely mechanical. This is advantageous in expandable implants because no power is required to produce the transmissions. The energy required can be harvested from the drive mechanism used to adjust the expandable implant. Energy harvesting, storage and depletion are notable problems in non--invasively expandable implants.

<FIG> shows a perspective view of an ultrasound counter <NUM> in accordance with a second embodiment, including an ultrasonic transducer <NUM>. As one with skill in the art may appreciate, the ultrasound counter <NUM> is designed for integration with expandable implants <NUM> including those described above. The ultrasound counter <NUM> includes at least one vibration element <NUM> tuned for ultrasonic vibration and at least one agitation element <NUM>. For convenience, a portion of the ultrasound counter <NUM> is shown transparent to illustrate the communication between the vibration element <NUM> and the agitation element <NUM>. The agitation element <NUM> is shown disposed on a rotatable shaft <NUM>. The rotatable shaft <NUM> is shown in communication with the internal magnet <NUM> of an expandable implant <NUM>.

The resulting ultrasonic transmissions of the vibration element <NUM> may be observed locally at the expandable implant <NUM> by the ultrasonic transducer <NUM>. The ultrasonic transducer <NUM> is shown disposed on the ultrasound counter <NUM>, but in some embodiments may be part of and disposed adjacent to the expandable implant <NUM>. The ultrasonic transducer <NUM> is operably connected to an electronics module <NUM> including one or more of: a controller, a memory, a power supply, or any other electronic component, with the ultrasonic transducer <NUM> configured to count a number of ultrasonic transmissions produced by the vibration element <NUM>.

<FIG> shows a cross-sectional view of an ultrasound counter <NUM> in accordance with a third embodiment. In this embodiment, the ultrasound counter <NUM> includes a plate <NUM> having a vibration element <NUM> and an anti-rotation element <NUM>. As illustrated in the exploded view of <FIG>, the plate <NUM> is configured to be telescopically received in a housing <NUM>. And the plate <NUM> is configured to receive at least a portion of a shaft <NUM> therethrough, with the shaft <NUM> shown including a plurality of agitation elements <NUM>. The plate <NUM> is configured to be moved telescopically within the resonator housing <NUM>.

The plate <NUM> can change configuration upon a rotation of the shaft <NUM>. For example in a first configuration configured to lock and prevent undesired rotation of the shaft <NUM>, the anti-rotation element <NUM> will be in contact with the agitation element <NUM>, with communication between the anti-rotation element <NUM> and the agitation element <NUM> configured to prevent a rotation of the shaft <NUM>. In a second configuration for monitoring adjustment of an expandable implant <NUM>, the vibration element <NUM> will be in communication with the agitation element <NUM>, and the anti-rotation element <NUM> will not be in communication with the agitation element <NUM>. The ultrasound counter <NUM> includes a bias element <NUM> configured to bias the plate <NUM> in the first configuration.

The shaft <NUM> is configured to be operably coupled to a drive system <NUM> of an expandable implant <NUM>, the drive system <NUM> including for example the rotatable permanent magnet <NUM> of the expandable implant <NUM> as shown above. In some embodiments the shaft <NUM> may be configured to prevent undesired rotation of the drive system when in the locked configuration. And in some embodiments the drive system may include: an electronic motor, a pneumatic motor, and any actuator known and used in implants.

Now, with the plate <NUM> in the first configuration, upon an application of sufficient torque a rotation of the permanent magnet <NUM> will induce a rotation of the shaft <NUM>. With the sufficient torque the bias element will yield and the plate will move from the first configuration into the second configuration. The vibration element <NUM> is configured to communicate with the plurality of agitation elements <NUM> to produce an ultrasonic transmission. As described above, these transmissions may be observed locally at the expandable implant <NUM> or may be observed outside of the patient by an external transceiver.

The ultrasound counter <NUM>, further includes a pair of thrust bearings <NUM> configured to minimize an amount of axial force place on ultrasound counter <NUM>. Mitigation of axial forces is helpful in maintaining a specific frequency of the ultrasonic transmissions produced by the vibration element <NUM>.

Now as one with skill in the art may appreciate, the vibration elements of the embodiments described above are tuned to a ultrasound frequency such that upon agitation by the agitation element, the vibration element will produce a vibration at an ultrasound frequency. Generally, this frequency is between <NUM> - <NUM> and above. The current embodiments have been tuned to approximately <NUM>.

When observing the signal produced by the vibration element at <NUM>, noise may be produced by every component of the expandable implant. In some embodiments, a load cell <NUM>,<NUM> may be included to measure axial forces on the expandable implant. Measuring the axial forces can help filter the noise floor when observing the ultrasound signal produced by the vibration element at <NUM>.

Also, in some embodiments the agitation elements can be disposed on a rotatable magnet and the vibration elements may be configured to communicate with the agitation elements disposed on the rotatable magnet upon a rotation of the rotatable magnet.

In some embodiments, the actuator may be a rotatable magnet, an electric motor, or any actuator known and used in the art to actuate expandable implants.

In some embodiments, adjustment of the expandable implant may result in motion of a surface of the expandable implant. The expandable implant may include one or more vibration element configured to vibrate upon an adjustment of the expandable implant. For example, if the motion is linear, one or more agitation element may be disposed on a first surface and one or more vibration elements may be disposed on a second surface. Upon, a movement of the first surface relative to the second surface, the one or more vibration element will communicate with the one or more agitation element to produce ultrasound vibrations. The vibration elements and/or agitation elements may be disposed such that each vibration corresponds to a given amount of displacement of the first surface relative to the second surface.

A method for measuring a change in dimension of an implant using ultrasound includes the steps: (i. ) Providing an expandable implant having an agitation element configured to move upon an adjustment of the expandable implant and a vibration element tuned for ultrasonic vibration, the vibration element configured to produce an ultrasonic vibration upon an agitation by the agitation element. ) Adjusting the expandable implant. ) Counting a total number of ultrasonic vibrations produced by the vibration element. ) Calculating a change in dimension from the total number of vibrations produced by the vibration element.

<FIG> is a schematic illustration of an ultrasound counter <NUM> in accordance with a third embodiment, the ultrasound counter <NUM> configured to produce an ultrasound transmission upon an adjustment of an expandable implant. The ultrasound counter <NUM> is configured to be integrated with an expandable implant. The ultrasound counter <NUM> includes a vibration element <NUM>. The vibration element <NUM> is configured to communicate with a surface of the internal magnet <NUM> of the expandable implant <NUM>. In some embodiments, the internal magnet <NUM> includes one or more agitation element <NUM> disposed on the surface thereof, the agitation elements <NUM> configured to agitate the vibration element <NUM> to produce an ultrasound transmission A. Each ultrasound transmission A will correlate with an amount of rotation of the internal magnet <NUM>. By counting a number of ultrasound transmissions A, either locally at the implant or remotely outside of the patient as described above, one can determine an amount of adjustment of the expandable implant <NUM>.

<FIG> is a schematic illustration of an ultrasound counter <NUM> in accordance with a fourth embodiment, the ultrasound counter <NUM> configured to produce an ultrasound transmission A upon linear movement of an adjacent surface <NUM> of an expandable implant <NUM>. In some embodiments of expandable implants, linear movement instead of rotation movement is used to adjust the expandable implants. The vibration element <NUM> will communicate with a moving surface <NUM> of the expandable implant <NUM> to produce an ultrasound transmission (ultrasound signal) A upon a movement of the surface <NUM>. The surface <NUM> may include one or more agitation elements to communicate with the vibration element <NUM>.

Each ultrasound transmission A will correlate with an amount of movement of the surface <NUM>. By counting a number of ultrasound transmissions A, either locally at the implant or remotely outside of the patient as described above, one can determine an amount of adjustment of the expandable implant <NUM>.

In some embodiments, expandable implants may include: expandable cages, expandable rods, expandable plates, and any medical implant known and used in the art of expandable medical devices.

Claim 1:
An expandable implant (<NUM>) comprising:
a plurality of vibration elements (<NUM>) tuned for ultrasonic vibration, the vibration elements configured to produce an ultrasonic vibration upon an adjustment of the expandable implant;
an agitation element (<NUM>) configured to communicate with the vibration elements to produce the ultrasonic vibration upon the adjustment of the expandable implant; and
a shaft (<NUM>);
characterized in that the expandable implant further comprises a plurality of bumps disposed on the shaft, the plurality of bumps configured to communicate with the plurality of vibration elements to produce a plurality of ultrasonic vibrations.