Medical device for the treatment of biological tissue

The invention relates to a medical instrument for the treatment of biological tissue according to the preamble of claim 1.

Such instruments are used to accelerate the healing process by means of pressure waves or shock waves during bone fractures and bone defects, but also during periods of periodontal disease, or only to initiate them at all. Further fields of application are the treatment of chronic pain in tendon spine diseases and the resolution of myofascial trigger areas. It is assumed that with the help of the pressure waves micro-damage is generated in the biological tissue, which causes the body to regenerate.

For such applications so-called extracorporeal pressure or shockwave devices have so far been used. These devices produce an acoustic impulse and pass it over the skin surface to the target area within the body, where it then unfolds its effect. A simple device of this device class is described in the patent<patcit id="pcit0001" dnum="DE19725477A"><text>DE-A-197 25 477</text></patcit> Described. Here, the acoustic impulse is generated by the impact of a projectile and uncocussed into the body via a blunt transmission element. Other such medical devices focus the acoustic impulse on the target area. A typical example of such a device is given in the German laid-open application<patcit id="pcit0002" dnum="DE2351247A"><text>DE-A-23 51 247</text></patcit> to find. Here, a spark discharge serves as a source for the acoustic impulse, which is focused by an ellipsoid-shaped reflector. The generation of pressure waves now includes electromagnetic and piezoelectric sources (<patcit id="pcit0003" dnum="DE3502751A"><text>DE-A-35 02 751</text></patcit>) Of the prior art. Known alternative means of focusing are the use of acoustic liquid or solid lens (<patcit id="pcit0004" dnum="US5727875A"><text>US-A-5,727,875</text></patcit>), The formation of the acoustic source as a moving spherical cap surface (<patcit id="pcit0005" dnum="DE3312014C"><text>DE-C-33 12 014</text></patcit>) Or the arrangement of several sources on a spherical surface (<patcit id="pcit0006" dnum="DE19928491A"><text>DE-A-199 28 491</text></patcit>), As are frequently used in piezoelectric drives.

To operate all known focusing systems, a high-voltage power supply is necessary to generate the short, but violent, acoustic impulses. This makes the devices complicated, limits the maximum repetition frequency per unit of time in a still reasonable size, and requires safety measures to isolate the high voltage. With embodiments according to the<patcit id="pcit0007" dnum="DE19725477A"><text>DE-A-197 25 477</text></patcit> A focussing of the acoustic energy is not possible and applications are restricted to surface-area indications.

From the <patcit id="pcit0008" dnum="US20010014780A"><text>US 2001/0014780</text></patcit> A medical instrument is known which, by means of an ultrasound transducer, which has an inwardly curved concave exit boundary surface, a focused pressure wave is coupled in via an impedance matching means. The generation and focusing of the pressure waves is not effected at the outlet boundary surface of the impedance matching means.

From the <patcit id="pcit0009" dnum="US5160336A"><text>U.S. Patent 5,160,336</text></patcit> A ballistic pressure wave generator is known, as it is also known in principle from the <patcit id="pcit0010" dnum="DE19725477A"><text>DE-A-197 25 477</text></patcit> Is known.

From the <patcit id="pcit0011" dnum="US4315514A"><text>U.S. Patent 4,315,514</text></patcit> A method is known for selectively destroying cells in which ultrasonic waves are operated with a resonance frequency of the cells to be destroyed and are focused on the cells to be destroyed by means of a lens made of polystyrene.

The invention is therefore based on the object of designing a pressure or shock wave device in such a way that it generates pressure waves or shock waves in a simple and cost-effective manner and focuses these on a target area in the body. The features of claim 1 serve to achieve this object.

The invention advantageously consists of a primary pressure wave generator in which a striking part can be accelerated to a high final speed by means of a drive means and exerts a force impulse on a transmission element. As a result of this force impact, the striking part induces a pressure wave in the transmission element, which propagates in the latter in the direction of its exit boundary surface, in order to be coupled into the biological tissue from there. The exit boundary surface is designed in such a way that the emerging wave forms a focus in the biological tissue. This is achieved by a shaping of the transmission element in which, for each local individual wave, the running time is equal from the generation during the force impact to the focus. The entrance boundary surface of the transmission element is thereby smaller than the exit boundary surface. In a first approximation, a nearly spherical exit boundary surface would result for a straight transmission element made of steel. The exit boundary surface has a larger diameter than the entrance boundary surface or the transverse dimension of the impact part.

The transmission element is designed as an exponential funnel, which transfers the planar wave without losses from small to larger cross-sections.

A projectile consisting of metal or another high-strength material is preferably provided as the striking part, which projectile can be moved back and forth in a guide by means of a compressed air pulse. Due to its simplicity and the weight advantage, the pneumatic drive is particularly well suited for accelerating the striking part to a high end speed and associated high impulse energies. However, other drives by means of a spring mechanism or in an electromagnetic manner are also conceivable.

In particular in orthopedic applications, it is advantageous to couple a plurality of individual pulses into the biological tissue in order to achieve an optimal effect. The drive means is therefore preferably designed in such a way that a periodical reciprocating motion of the striking part is possible. The number of strokes is about 1 to 30 Hz, preferably 5 to 12 Hz. For an orthodontic application currently recommended pulse number of approximately 2000 per session, treatment times of less than five minutes are possible.

In a preferred embodiment, the transmission element is guided axially and linearly in a housing, a spring / damping element being arranged between the transmission element and the housing. In this way, a decoupling of the transmission element is realized. Moreover, a large deflection of the transmission element is not necessary and also not desired, since this is perceived as particularly painful by the patients. Rather, the wave transmission is effected by a compression or expansion of the transmission element and not by its displacement. Typical values ​​for the stroke of the transmission element are therefore also less than 0.5 mm.

Between the striking part and the transmission element, an intermediate element can be arranged, which transfers the force impulse from the striking part onto the transmission element. This intermediate piece can serve to provide better shielding of the drive means against the application area or also to redirect the direction of the pressure wave or to influence the pressure wave characteristic.

The transmission element preferably consists of a high-strength material, such as, for example, steel, in order to withstand the load by the impacting impact part. In a preferred embodiment, the beating surface of the striking part and the hit surface of the transmission element are planar and perpendicular to the direction of motion of the striking part. In such a case, the impact causes a plane wave in the transmission element, which propagates therein. If the transmission element consists of a bolt without a substantial change in the cross section, the shaft retains its shape and travels as a plane wave in the direction of its exit boundary surface. The preferred exit boundary surface of the transmission element is almost the shape of an inwardly curved spherical surface. In such a case, there is a point in the biological tissue in which all individual local waves arrive at the same time due to the different sound velocities in the transmission element and in the biological tissue and thus form a focus. The position of the focus in the biological tissue relative to the transmission element can be preset by selecting the radius of curvature of the exit boundary surface. The ideal geometry of the exit boundary surface differs somewhat from a spherical surface and can be determined by calculation.

In order to increase the radiated acoustic power of the transmission element, its exit boundary surface is to be selected as large as possible, but the diameter of the impact part must be kept as small as possible in order to make the moving masses and impulses manageable for a medical application. It has been found that, with the same diameter of the striking part and the exit area of ​​the transmission element, focusing is only conditionally possible.

For an optimal generation of the pressure wave in the transmission element, the striking surface of the striking part and the entrance surface of the transmission element must be of the same size. The exit diameter of the transmission element is larger than the transverse dimension of the impact part or its own entry diameter.

Neglecting the ideal forwarding, any other cross-sectional expansion of the transmission element from its entry point to the exit diameter is also conceivable. The geometry of the exit boundary surface of the transmission element must then be selected in such a way that the transit times of the wave form a focus in the biological tissue.

In the case of such transmission elements, the outer edges, which are formed by the inwardly arched exit boundary surface, are provided. Since the movement of the transfer element can not be completely avoided by the impact pulse, these projecting edges can damage or at least irritate the biological tissue. Therefore, in a preferred embodiment, these outer edges are formed atraumatically. Rounding off the edges or a protective coating are appropriate measures. It is also conceivable that the outer edges of the housing slightly protrude in the axial direction so that the transfer element does not come into direct contact with the biological tissue.

An impedance matching medium, which improves the coupling of the pressure wave into the biological tissue, can be arranged between the exit boundary surface of the transmission element and the coupling point on the biological tissue. If air inclusions are present between the exit boundary surface of the transfer element and the entrance surface of the biological tissue, a part of the pressure pulse is reflected at this acoustic discontinuity and the transferred portion is reduced. A suitable paste-shaped impedance matching medium is, for example, an ultrasonic gel or other paste-like masses with a similar impedance as the biological tissue (eg vaseline).

To avoid air inclusions, the cavity formed by the spherical surface can also be lined with a solid, acoustically good conducting material. One such suitable material is, for example, polystyrene.

Show it:<ul><li><figref idrefs="f0001"><b>FIG.</b> 1</figref> and <figref idrefs="f0002">2</figref> Illustrations of a mechanically operated medical instrument in cross - section, and </li><li><figref idrefs="f0003 f0004">FIGS. 3 to 6</figref> A series of different embodiments of a transmission element.</li></ul>

This in <figref idrefs="f0001"><b>FIG.</b> 1</figref> shown handpiece <b>1</b> Consists of a housing <b>4,</b> Which is a pneumatic internal cylinder <b>6</b> In which a striking part <b>10</b> With the help of pneumatic drives <b>14</b> In conjunction with a static pressure chamber <b>8th,</b> The inner cylinder <b>6</b> Coaxially annularly, is moved back and forth between two end positions. Alternatively, it is also possible to hit the striking part<b>10</b> Hydraulically, mechanically, electromagnetically or by other means of propulsion. Depending on the type of drive, a suitable length of the acceleration path can be selected. In the case of a pneumatically operated impact mechanism and a conventional compressed air pressure of approximately 0.3 MPa (3 bar), the acceleration distance is approximately 50 to 200 mm. The striking part<b>10</b> Can be selected in terms of its length, final speed and material composition for characterizing the pressure or impact wave. A power setting of the medical instrument is usually effected by regulating the compressed air by means of a pressure reducer.

In the proximal end position of the striking part <b>10</b> Is at the end of the inner cylinder <b>6</b> a magnetic holder <b>17</b> Which is the metallic striking part <b>10</b> In its proximal end position can hold up again one over the connector <b>13</b> Applied pneumatic pressure the striking part <b>10</b> In the direction toward the distal end of the inner cylinder <b>6</b> Accelerated. The movement direction of the striking part<b>10</b> Is connected to one at the distal end of the inner cylinder <b>6</b> located annular slots <b>16</b> To the Staudruckkammer <b>8th</b> . Acceleration of the striking part<b>10</b> This arrives at the distal end of the inner cylinder at a high final speed of, for example, 10 to 25 m / s <b>6</b> Arranged entry interface 20 of a transmission element <b>2</b> And induces therein a thrust or shock wave that extends as far as its exit boundary surface <b>19</b> Is propagated and then introduced into the biological tissue. The transmission element<b>2</b> Consists of a metallic material and is in a receptacle <b>18</b> Slidingly guided. An annular groove<b>3</b> Is in the transmission element <b>2</b> And in the recording <b>18</b> In which there is a resilient spring / damping element <b>15</b> Is located. This has the task of the transmission element<b>2</b> From the recording <b>18</b> To decouple, but also ensures that the transmission element <b>2</b> Is returned to its initial position after the beating process. At the same time, the spring / damping element seals<b>15</b> the pressure chamber <b>8th</b> Against the outer space and thus prevents the leakage of compressed air and the penetration of dirt. The exit boundary surface<b>19</b> of the transmission element <b>2</b> Is formed as part of a spherical surface. The focus<b>7</b> Of the exiting pressure or shock wave corresponds in a first approximation to the geometric center of the spherical surface.

Upon completion of the striking action, the spring / damping element moves <b>15</b> the transmission element <b>2</b> Back to its initial position. The striking part<b>10</b> Is determined by the pressure in the pressure chamber <b>8th</b> Overpressure by the backflow of the air through the annular slots <b>16</b> Into its rest position on the proximal end of the inner cylinder <b>6</b> And from the magnet holder <b>17</b> . The instrument is now ready for a new beat.

In the <figref idrefs="f0002"><b>FIG</b></figref> Is provided with an intermediate piece <b>9</b> With a seal <b>11,</b> Which is between striking part <b>10</b> and transmission element <b>2</b> Is arranged. This component has the task of the striking part<b>10</b> And the impact pulse on the transmission element <b>2</b> Forward. The recording<b>18a</b> and <b>18b</b> Is constructed secondarily here. By releasing the rotary connection 12, the transmission element can be<b>2</b> And the front recording <b>18a</b> Removed. The handpiece<b>1</b> Remains closed and can be simply cleaned, disinfected and sterilized without liquid or dirt entering the inside of the handpiece <b>1</b> Could penetrate.

By varying the radius of curvature of the exit boundary surface <b>19</b> of the transmission element <b>2</b> Can adjust the position of the focus <b>7</b> Can be set. In<figref idrefs="f0003"><b>FIG</b></figref> Is a transfer element <b>2</b> , Which has a large radius of curvature, whereby the focus <b>7</b> Further downstream of the exit boundary surface <b>19</b> To lie. <figref idrefs="f0003"><b>FIG</b></figref> Shows an embodiment with a small radius of curvature.

Due to the geometric shape of the exit boundary surface <b>19</b> of the transmission element <b>2</b> Sharp edges are formed, which can lead to injury or irritation of the biological tissue. For this reason, the outer edges of the transfer element<b>2</b> in <figref idrefs="f0004"><b>FIG</b></figref> rounded.

To avoid air inclusions and a flat surface of the transmission element <b>2</b> Is the spherical exit boundary surface <b>19</b> of the transmission element <b>2</b> in <figref idrefs="f0004"><b>FIG</b></figref> With an acoustically well conductive insert <b>5</b> Which has similar impedances as the biological tissue