WO2007038975A1

WO2007038975A1 - Method for cutting a biological tissue, and installation for cutting a biological tissue

Info

Publication number: WO2007038975A1
Application number: PCT/EP2005/011646
Authority: WO
Inventors: Alexandre Carpentier; Alban Pages
Original assignee: Alexandre Carpentier; Alban Pages
Priority date: 2005-10-05
Filing date: 2005-10-05
Publication date: 2007-04-12

Abstract

A LASER method of manually or robotically cutting a biological tissue with very low thermal effects and low cutting width under (150) micrometers comprising: (a) producing a pulsed light beam of a wavelength comprised between (150) nanometers and (3) micrometers, a repetition rate of over (1000) pulses per second, an on-state lapsing less than (100) nanoseconds, (b) applying said pulsed light beam on an application point of the cutting path of said biological tissue, (c) moving said pulsed light beam at a speed over 0.1 mm/second in order to cut said biological tissue, (d) controlling in depth by echography, optical coherence tomography, or feed back information from the LASER beam.

Description

Method for cutting a biological tissue, and installation for cutting a biological tissue

FIELD OF THE INVENTION The invention relates to methods of cutting a biological tissue, and installations for cutting a biological tissue.

BACKGROUND OF THE INVENTION

More particularly, the invention relates to a method of cutting a hard biological tissue such as bone by use of a LASER.

LASER interaction with organic and inorganic targets has been investigated over the past thirty-five years for applications as diverse as material processing and tissue ablation. Recent years have brought increased interest in the use of LASERS as a therapeutic and preventive tool in various dental applications such as removal of carious lesions (removal of tooth decay) , surgical treatment of oral malignancies and periodontal diseases, and preparation and sterilization of root canals.

In spite of these advances, LASERs remain limited to removing injured (soft, as opposed to hard) tooth structure since the LASERS currently in use for dental procedures generate unacceptable heat levels which cause collateral damage to the tooth surface and in the tooth pulp.

Early procedures for removal of hard dental substances involved optical drilling using CO₂, ruby and Nd: YAG (Neodymium doped Yttrium Aluminum Garnet) LASERS requiring high radiant exposure and resulting in considerable damage to surrounding tissue. As a consequence, it was generally concluded in the mid 1970s that lasers would not become a common drilling tool unless a new method was found to reduce collateral damage.

Optical dental drilling with Er:YAG (Erbium doped YAG) lasers yielded encouraging results in the early 1990s, and has shown capabilities to perform as an efficient drill without generating excessive damage to surrounding tissue.

Yet, in view of the time required for drilling a hole in a tooth using such a method, it was excluded to be able to produce a cut of sufficient cutting speed along the hard biological material to make the method compete with traditional sawing technologies used for bone cutting.

DE 101 33 341 contemplates the use of bone cutting using a CO₂ LASER. However, the cutting speed of this method is not described. Further, CO₂- LASERS operate at an infra-red wavelength of about 10 micrometers, at which LASER energy is highly absorbed by water or other translucent fluids. This might be problematic since, when cutting biological tissue, one is bound to expose the beam to water, or other translucent fluids, such as cerebrospinal fluid, into which one does not want the energy to be transferred. Further, in the above technique, it would not be possible to use water-cooling of the biological tissue, since most of the energy would be lost into the coolant water.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method for cutting bone which would enable a bone cutting speed at least comparable to those obtained by traditional sawing while minimizing collateral damage to the surrounding tissues.

To this end, the invention provides a method of cutting a biological tissue along a cutting path extending along an external surface of the biological tissue, the method comprising the following steps:

(a) producing a pulsed light beam of a wavelength comprised between 150 nanometers and 3 micrometers and exhibiting a plurality of pulses with a repetition rate of over 1000 pulses per second, each pulse comprising an on-state lapsing less than 100 nanoseconds, by operation of a pulsed laser,

(b) applying said pulsed light beam on an application point of the cutting path of said biological tissue in order to transfer sufficient energy to said biological tissue to remove at least some of the biological tissue at said application point, and

(c) moving said pulsed light beam so that the application point is displaced along said cutting path of said biological tissue at a speed over 0.1 mm/second in order to cut said biological tissue along said cutting path.

One will note that the displacement of the application point of the beam and the timing of the pulsed beam can be controlled independently of one another. The method makes it possible to obtain a quick cut with minimal collateral damage to the surrounding tissues.

Furthermore, the method makes it possible to use a YAG LASER which is suitable for use with optical transfer means such as optical fibers, which make it possible to use the LASER in a medical environment.

Previously known and used long pulse (over 1 microsecond on-state) LASER systems operating in the microsecond pulse duration regime have shown to be generally inefficient in their ability to remove substantial amounts of tissue without causing extensive collateral damage. In a conventional long pulse LASER system, much of the optical energy delivered to a material removal target site has not gone into disrupting the structural integrity of the target material, but is rather transferred to the surrounding tissue as thermal, acoustic or mechanical energy. This energy propagates through the surrounding tissue as both mechanical shock waves and heat which manifest as undesirable cracks, material charring, discoloration and surface melting. Different results are got, however, when material removal is performed with LASERS having pulse durations closer to the characteristic electron-lattice energy- transfer time for a particular tissue or material of interest. For the majority of hard, biologic materials, this characteristic energy transfer time is of the picosecond order. However, when pulsed LASER systems are operated in a parametric regime including pulse durations around this characteristic transfer time, the physical mechanism of material removal changes. Globally, two different regimes exist, depending on the pulse duration. If this duration is long compared to the characteristic electron-lattice energy transfer time, a big plasma is created. The energy of the beam at the end of the pulse is transferred mostly to the plasma, and not to the tissue to be cut. That will heat the surroundings of the treated zone. However, if the pulse duration is approximately equal to the characteristic electron-lattice energy transfer time, the plasma created is smaller and doesn't heat the tissue.

Yet, with such short on-states, it requires a LASER able to provide a high frequency of the pulsed beam in order not to heat the plasma too much and with a significant energy output in order to remove sufficient material with each pulse to obtain a satisfying cutting speed. Consequently, it is convenient to use longer on- states, up to 100 nanoseconds at an easily obtainable frequency in order to provide an optimized bone cutting speed with low collateral damage.

The thermal collateral damage is minimized with such a pulse duration. Because the mechanism for energy transfer from the LASER to the target material involves forming a localized, plasma from the target material rather than melting and boiling away the target material, little energy is transferred to the material bulk before the material is removed by ablation. As was described above, damage occurs only in an area irradiated by sufficient beam intensity to produce ionization. At the pulse durations according to the present method, there is insufficient time for lattice coupling and, therefore, negligible diffusion induced collateral damage. Consequently, short pulse width LASER systems offer a notable reduction in the amount of collateral damage caused in a material as a result of LASER-material interaction. The damaged area, when formed by short pulses, is typically several orders of magnitude smaller than when formed with long (microsecond) pulses.

The energy transferred to the bone is sufficient in order to obtain as high cutting speeds as the ones obtained with classical mechanical cutting, namely over 0,1 mm/s along the cutting path, at a width of a few tens of millimeters.

Since a wavelength of less than 3 micrometers is used for the light beam, the energy is almost entirely transferred to the bone to be cut, although the beam might have to cross translucent fluid, such as blood, cerebrospinal fluid or water (for example coolant water) to reach the bone. This provides minimal collateral damage and high cutting efficiency to the present method.

In particular embodiments of the method according to the invention, one might also use the following features : each pulse has an energy in the range between 0.01 mJ to 100 mJ, and a peak power in the range between 10⁸ W/cm² and 5.10¹⁴ W/cm² ; - the diameter of the focal spot of said beam on the biological tissue is less than 100 μm wide ; the pulsed light beam applies on the biological tissue an energy density per surface unit of above 10 j/cm², and preferably of above 50 J/cm² ; step (a) is performed remotely from said biological tissue, and the pulsed light beam produced during step (a) is conveyed by a light conveying device towards the operating field for being applied to said biological tissue ; during steps (b) and (c) , the biological tissue is cooled ;

- the biological tissue is cooled by water and/or pressurized gas; - the method further comprises a step (d) of monitoring a material characteristic of said biological tissue during step (c) ; said material characteristic is the thickness of the biological tissue at the application point ; - during step (d) , a plasma formed by interaction of the biological tissue and the pulsed light beam is observed, and said material characteristic is monitored from the observation of said plasma ;

- the method further comprises a step (e) of checking if the biological tissue is submitted to secure operation ; step (c) is interrupted if the check of step (e) is deemed unsecure ; said material characteristic is an amount of removed biological tissue ; said biological tissue is hard bone ; prior to step (a) , the following steps are performed:

(f) soft biological tissue covering. said application path is removed in order to expose said bone, and

(g) a guide is placed to keep a constant distance between said bone and an application head emitting said pulsed light beam toward said bone ; - prior to step (a) , the following steps are performed :

(d) a through hole is performed in said bone, away from said cutting path, and

(e) said guide is introduced through said through hole beneath said bone under said application point, and, during step (c) , said guide is moved together with said pulsed light beam ; during step (f) , a cavity is formed, the bottom of which being formed by said bone, and the cavity is filled with a coolant ; during step (a) , said pulsed laser is operated at an operation rate of over 5000 pulses per second, preferably over 10000 pulses per second ; during step (a) , said pulsed laser is operated at an on-state lapsing less than 10 nanoseconds, preferably less than 1 nanosecond ;

- said biological tissue includes an external surface oriented towards an application head for applying said pulsed light beam, and an internal surface opposed thereto, said biological tissue exhibiting a given thickness between said internal and external surfaces, and wherein cutting involves removing all biological tissue comprised between said internal and external surfaces ;

- said pulsed LASER is operated at an on-state lapsing over 100 picoseconds ;

- the application point is displaced back and forth along said cutting path and the average speed of the application point along said cutting path is over 0.1 mm/s ; - the bone exhibits a given thickness and during step (c) one varies a focal plane of said pulsed light beam along said thickness .

According to another aspect, the invention relates to an installation for cutting a biological tissue along a cutting path extending along an external surface of said biological tissue comprising:

(A) A pulsed LASER adapted to produce a pulsed light beam of a wavelength comprised between 150 nanometers and 3 micrometers, said beam comprising a plurality of pulses with a repetition rate of over 1000 pulses per second, each pulse comprising an on-state lapsing less than 100 nanoseconds,

(B) An application head for applying said pulsed light beam on an application point of the cutting path of said biological tissue in order to transfer sufficient energy to said biological tissue to remove at least some of the biological tissue at said application point, and

(C) A displacement device for moving said pulsed light beam so that the application point is displaced along said cutting path of said biological tissue at a speed over

0.1 mm/second in order to cut said biological tissue along said cutting path.

In particular embodiments of the installation, one might also use one or more of the following features : a removable optical wave guide adapted to convey said light beam produced by the LASER to the application means ; said optical wave guide comprises an optical fibre for conveying said light beam to the application means ; said optical wave guide comprise an articulated mirror adapted to convey said light beam to the application means ; said displacement device further comprise a sabot adapted to be inserted beneath said biological tissue, under said application point ; a cooling device adapted to provide coolant to said biological tissue during the operation of said laser ; said displacement device comprises a handle comprising a profiled grip for a surgeon's hand, and an attachment portion for attaching thereto said application head ; said application head is attached to said attachment portion. - said displacement device further comprise a sabot, adapted for insertion beneath said biological tissue, and adapted to protect deeper biological tissue from said laser beam impinging on said sabot through said biological tissue. According to another aspect, the invention relates to a displacement device for such an installation.

According to another aspect, the invention relates to a method of preparing an installation for cutting a biological tissue along a cutting path extending along an external surface of said biological tissue comprising:

(a' ) setting a pulsed LASER adapted to produce a pulsed light beam of a wavelength comprised between 150 nanometers and 3 micrometers, so that said beam comprises a plurality of pulses with a repetition rate of over 1000 pulses per second, each pulse comprising an on- state lapsing less than 100 nanoseconds,

(b' ) connecting said pulsed LASER to an application head for applying said pulsed light beam on an application point of a cutting path of a biological tissue in order to transfer sufficient energy to said biological tissue to remove at least some of the biological tissue at said application point, and

(c') providing a displacement device for moving said pulsed light beam so that the application point is displaced along said cutting path of said biological tissue at a speed over 0.1 mm/second in order to cut said biological tissue along said cutting path.

In particular embodiments of the method, one might also use one or more of the following features : - during step (a' ) , said laser is set to produce a pulsed light beam at an operation rate of over 5000 pulses per second, preferably over 10000 pulses per second ;

- during step (a' ) , said laser is set to produce a pulsed light beam at an on-state lapsing less than 10 nanosecond, preferably less than 1 nanosecond. BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will be apparent from the following description, drawings and claims. On the drawings :

- Fig. 1 is a schematic view of an installation for cutting biological tissue,

- Fig. 2 is a schematic side view of the displacement device of Fig. 1, - Fig. 3a is a schematic view of the top of the head of a patient,

- Fig. 3b is a schematic view corresponding to Fig. 2 when the installation is in use,

- Fig. 4 is a picture showing a bone cut according to the above method, where the long arrow is 1 millimeter long,

- Fig. 5a is a schematic perspective view of a long bone provided with a vise, and .

- Fig. 5b is a schematic view of an example of an application means cooperating with the vise of Fig. 5a.

On the drawings, corresponding or similar elements have the same reference numbers .

MORE DETAILED DESCRIPTION .

Fig. 1 shows a schematic view of an installation for performing cutting of a hard biological tissue, such as a skull bone of a patient. The patient 1 is for example lying on a table and is to receive brain surgery, from a neurosurgeon 3 who is standing close to table 2. For the brain surgery to be performed, it is necessary to first remove a part of the skull bone, in a so-called "craniotomy" , which aims at removing parts of the skull bone in order to gain access to the internal parts of the skull .

Such surgery, is usually performed on a hard bone tissue in order to access internal injured brain tissue. It, therefore, requires skull bone to be as little damaged as possible, in order for the patient 1 to recover from the surgery. Consequently, during craniotomy, some of the aims are to minimize the width of the cutting path, and to impart as little collateral damage as possible to surrounding tissue. This would make it possible, after surgery, when the removed part of the bone is reinstalled for closing the bone skull, that the removed part will link more efficiently with parts of the skull which had remained in place during the surgery.

The installation comprises a YAG laser 4 which is connected, through an optical waveguide 5 to an application head 6 (Fig. 2) which is carried by a displacement device 7 held by the neurosurgeon 3. The laser 4 is a laser able to provide a pulsed light beam exhibiting a wavelength comprised between 150 nanometers and three micrometers . The beam could be made visible by using a suitable frequency-doubling cristal. The produced light beam is a pulsed beam of repetition rate over 1 thousand pulses per second, preferably over 5 thousand pulses per second and more preferably over 10 thousand pulses per second. These pulses exhibit an on- state during which the light beam is emitted, and an off- state during which it is not emitted. The on-state lasts less than 1 hundred nanoseconds, preferably between 10 nanoseconds and 10 picoseconds, and more preferably between 1 nanosecond and 100 picoseconds.

Each pulse has an energy in the range between 0.01 mJ to 100 mJ, for a peak power in the range between 10⁸ watt per square centimer (W/cm²) and 5.10¹⁴ W/cm²" The light pulse is transferred along optical wave guide 5 which is conveniently an optical fiber, to an application head 6, which is adapted to deliver the light beam to patient 1. The convenience of the optical fibber 5 is well adapted to the present invention. However, other types of optical wave guides are contemplated within the scope of the invention, such as, in particular movable arms incorporating mirrors (not represented) . Yet the use of such a system as an optical wave guide would require precise guidance of the movable arms for transmission of the light beam to the moving application head.

The precise guidance can be performed by a robotic arm which is able to reproduce a route predefined manually by the surgeon on the bone itself, or predefined on a 3D- navigation computer system based on the patient CT scan.

In order to set the laser 4 to provide the suitable light beam, the laser 4 could be provided with a setting panel 8 comprising buttons 8a, 8b, 8c for setting the repetition rate, the time lapse of the on-state, and/or the level of delivered energy per pulse. Alternatively, this setting panel could be provided in a computer commanding operation of laser 4.

The displacement device 7 is represented in detail on Fig 2. It comprises a grip 9 shaped to be held by a neurosurgeon 3. The grip 9 rotatably supports a treatment applicator 10, the end 10a of which, which is opposed to the grip 9 comprises an attachment portion for releasable connection to the application head 6. For example, the application head 6 could be snap fitted, or screwed or else, on the end 10a of the treatment applicator 10.

The optical fiber 5 which runs from laser 4 to application head 6 could also be retained locally on the treatment applicator 10, for example by a series of hooks 11. The grip 9 also comprises an elongate member 12 which runs parallel to the treatment applicator 10 and is terminated by a guide 13 which is oriented towards the application head 6, so that a beam emitted by the application head 6 would impinge on the guide 13. The guide 13 might include or be made of an energy-absorbing material, such as porcelain, in order to protect the surrounding tissues from the heat generated by the beam impinging on the guide. The guide could be water-cooled, and could include a thermoelement adapted to measure its temperature and transmit it to a remote security system as a security measurement.

Referring back to Fig. 1, the installation might also provide a cooling system 14 for cooling the biological tissue submitted to the cutting. The cooling system would for example comprise a water-filled bottle 15 connected to an injection nozzle 16 adapted to be operated by the neurosurgeon 3 for delivering water contained in the water bottle 15 to the biological tissue during the cut. It is also contemplated that the cooling system could provide a continuous flow of air instead or in combination with the jet of water as previously described.

As shown on Fig 3a, the head of patient is presented for surgery. In a first step, the skin and flesh of the head 17 are removed by a retractor 25 in order to expose the external surface 18a of the skull bone to the surgeon .

Then, the surgeon will bore a hole 19 into the skull bone 18, for example by mechanical drilling. The hole 19 will be wide enough for the introduction of the elongate member 12 carrying the guide inside the hole 19, as shown on Fig. 3b.

In the next step, the elongate member 12 is inserted into the hole 19, and the application head is disposed facing an application point on the skull bone where biological material is to be removed.

The light beam 21 described before is applied to the application point 20 in order to apply about over 10 J/cm² in order to remove the biological tissue therefrom. Simultaneously, the coolant might be applied • to the application point 20, by spraying, or by forming a so- called "pool" of water above the external surface 18a of the skull bone 18.

In order to provide maximal cutting efficiency, the focal plan will for example be placed at about mid- thickness of the cortical bone 18.

The surgeon will then move the displacement device, for example by rotating around the hole 19 in order to displace the application point 20 of the light beam along a cutting path where the cut is to be effected. A transfixiant cut of a millimiter-thick bone is obtained even when moving the application point at speeds over 0.5 mm/s. along the cutting path. This might of course depend on the physiological strength of the individual bone of patient 1. During some experiments, cutting speeds about 1 mm/s were obtained. In any case, cutting speeds of over 0.1 mm/s are considered of interest for the invention.

It is to be noted that the cutting speed data provided herewith is the average speed of displacement of the application point. It is contemplated that the instantaneous speed might be faster, for example by moving the application point back and forth along the application path in combination with an average movement of the above- listed average speed. This could for example be performed by reciprocating a mirror at the application head in order to direct the subsequent pulses towards various application points of the application path.

A fast back and forth movement of the length about

1 centimeter could thus be applied to the application point, while the displacement device is moved at the slower speed corresponding to the average cutting speed.

If the beam does not exhibit a visible wavelength, it can be coupled with a visible beam emitted for example by He : Ne LASER and conveyed along the optical wave guide, in order to visualize the application point. During the application of the beam, it is also noted that the focal plan can be moved through the thickness of the bone.

Once a cut of the skull bone 18 has been performed, as shown in dotted lines on Fig. 3a, the central part 18b can be removed as shown on Fig. 3b, so that the neurosurgeon might access to the damaged brain tissue.

During cutting, the energy of the light beam will not reach the brain tissue thanks to the guide 13 provided beneath the bone 18 under the application head 6. It is contemplated that the guide 13 could be made of a magnetic material, in order to follow a metallic part of the optical head 6 with accuracy.

It is further contemplated to provide the installation with security means which would stop operation of the laser 4 in case of emergency.

As a suitable security system, it is contemplated to use a system able to monitor mechanical or biometrical characteristics of the biological tissue under cut. The security system could for example be provided as an echography or optical coherence tomography head 22, carried by elongate member 12 close to the sabot 13. Such an echography or optical coherence tomography head is suitable for performing ablated bone depth diagnostics of the bone 18. As the light beam is ablating material, the depth of the ablated bone is monitored continuously by the echography or optical coherence tomography head. Ablated bone characteristic is provided to the security system 23 which could for example be an internal module of laser 4 able to stop operation of the laser source, in case of emergency. In another embodiment, the echography or optical coherence tomography head could be placed on the guide 13, or close to the guide 13 and connected to the guide 13 to be moved along the guide 13. Transfer of the acoustic movement from the echography head to the bone could be performed by a locally applied gel.

It is to be noted that the laser 4 could conveniently be disposed in a room which is not the operation room where the surgery takes place, and could be connected by a sterilizable optical wave guide 5 and application head 6, which are releasably connected to a disposable displacement device 7. This would allow for low risk of contamination of patient 1 during a surgery, at the sole low cost of the disposable displacement device 7, and of the sterilization of the optical parts 5, 6. In addition, such a LASER could be shared by various operation rooms by simply connecting the LASER to a given operation room, provided two medical cutting operations are not performed simultaneously in two different rooms. It is contemplated that the application of the system will involve foot pedal 24 operation by the surgeon 3 who is able to start and stop operation of the laser 4 on the basis of visual examination of the target tissue and evaluation of the progress of the procedure. On experiment conducted on human bones, speeds of about 0.3 mm/sec, have been obtained with a cutting width as low as 50 μm for a 7 mm thick bone. For example, the short arrow on Fig. 4 represents a 100 μm wide cut obtained in a exemplary experiment . For a long bone, as shown on Fig. 5a, the skin and flesh are first removed (not shown) where the cut is to be performed. If necessary, the muscular insertions are also removed. A vise 26 is fixed on the bone by screws 31. The vise 26 exhibits a circular slit 27 for the insertion of a guiding sleeve 28 carrying the treatment applicator 10. The treatment applicator 10 can be frictionally translatable inside the guiding sleeve 28.

The application head 6 is located at the end of the treatment applicator as previously described, and delivers the optical beam to the bone to be cut. Cooling water can be applied through guiding grid 29 made of spaced arms 29a connected to an end ring 30 which is contacted to the bone.

The guiding sleeve is translated along the slit 27 and the treatment applicator is translated in order to keep the end ring 30 in contact with the bone during the cut.

If the femoral head is thus cut, it can then be removed for its replacement by a prothesis.

Claims

1. A method of cutting a biological tissue along a cutting path extending along an external surface of said biological tissue, the method comprising the following steps :

2. Method according to claim 1, wherein each pulse has an energy in the range between 0.01 mJ to 100 mJ, and a peak power in the range between 10⁸ W/cm² and 5.10¹⁴ W/cm².

3. Method according to claim 1 or claim 2 , wherein the diameter of the focal spot of said beam on the biological tissue is less than 100 μm wide.

4. Method according to any preceding claim, wherein the pulsed light beam applies on the biological tissue an energy density per surface unit of above 10 J/cm², and preferably of above 50 J/cm².

5. Method according to any of the preceding claims, wherein step (a) is performed remotely from said biological tissue, and wherein the pulsed light beam produced during step (a) is conveyed by a light conveying device towards the operating field for being applied to said biological tissue .

6. Method according to any of the preceding claims, wherein, during steps (b) and (c) , the biological tissue is cooled.

7. Method according to claim 6, wherein the biological tissue is cooled by water and/or pressurised gas.

8. Method according to any of the preceding claims, further comprising a step (d) of monitoring a material characteristic of said biological tissue during step (c) .

9. Method according to claim 8 , wherein said material characteristic is the thickness of the biological tissue at the application point.

10. Method according to claim 8 wherein, during step

(d) , a plasma formed by interaction of the biological tissue and the pulsed light beam is observed, and in which said material characteristic is monitored from the observation of said plasma.

11. Method according to any of claims 8 to 10, further comprising a step (e) of checking if the biological tissue is submitted to secure operation.

12. Method according to claim 11, wherein step (c) is interrupted if the check of step (e) is deemed unsecure.

13. Method according to any of claims 10 to 12, wherein said material characteristic is an amount of removed biological tissue.

14. Method according to any of the preceding claims, wherein said biological tissue is hard bone.

15. Method according to claim 14, wherein, prior to step (a) , the following steps are performed:

(f) soft biological tissue covering said application path is removed in order to expose said bone, and (g) a guide is placed to keep a constant distance between said bone and an application head emitting said pulsed light beam toward said bone.

16. Method according to claim 15, wherein, prior to step (a) , the following steps are performed:

(d) a through hole is performed in said bone, away from said cutting path, and

(e) said guide is introduced through said through hole beneath said bone under said application point, and wherein, during step (c) , said guide is moved together with said pulsed light beam.

17. Method according to claim 16 wherein, during step (f) , a cavity is formed, the bottom of which being formed by said bone, and wherein, the cavity is filled with a coolant .

18. Method according to any of the preceding claims, wherein, during step (a) , said pulsed laser is operated at an operation rate of over 5000 pulses per second, preferably over 10000 pulses per second.

19. Method according to any of the preceding claims, wherein, during step (a) , said pulsed laser is operated at an on-state lapsing less than 10 nanoseconds, preferably less than 1 nanosecond.

20. Method according to any of the preceding claims, wherein said biological tissue includes an external surface oriented towards an application head for applying said pulsed light beam, and an internal surface opposed thereto, said biological tissue exhibiting a given thickness between said internal and external surfaces, and wherein cutting involves removing all biological tissue comprised between said internal and external surfaces .

21. Method according to any of the preceding claims, wherein said pulsed LASER is operated at an on state lapsing over 100 picoseconds.

22. Method according to any of the preceding claims, wherein the application point is displaced back and forth along said cutting path, and wherein the average speed of the application point along said cutting path is over 0.1 mm/s .

23. Method according to any of the preceding claims, wherein the bone exhibits a given thickness, and wherein, during step (c) , one varies a focal plane of said pulsed beam along said thickness.

24.An installation for cutting a biological tissue along a cutting path extending along an external surface of said biological tissue comprising:

(C) A displacement device for moving said pulsed light beam so that the application point is displaced along said cutting path of said biological tissue at a speed over 0.1 mm/second in order to cut said biological tissue along said cutting path.

25. Installation according to claim 24, further comprising a removable optical wave guide adapted to convey said light beam produced by the LASER to the application means .

26. Installation according to claim 24 or 25 wherein said optical wave guide comprises an optical fibre for conveying said light beam to the application means.

27. Installation according to claim 24 or 25 wherein said optical wave guide comprise an articulated mirror adapted to convey said light beam to the application means.

28. Installation according to any of claims 24 to

27, wherein said displacement device further comprise a guide adapted to be inserted beneath said biological tissue, under said application point.

29. Installation according to any of claims 24 to

28, further comprising a cooling device adapted to provide coolant to said biological tissue during the operation of said laser.

30. Installation according to any of claims 24 to

29, wherein said displacement device comprises a handle comprising a profiled grip for a surgeon's hand, and an attachment portion for attaching thereto said application head.

31. Installation according to claim 30, wherein said application head is attached to said attachment portion.

32. Installation according to claim 30 or 31, wherein said displacement device further comprise a guide, adapted for insertion beneath said biological tissue, and adapted to protect deeper biological tissue from said laser beam impinging on said guide through said biological tissue.

33.A displacement device for an installation according to any of claims 30 to 32.

34.A method of preparing an installation for cutting a biological tissue along a cutting path extending along an external surface of said biological tissue comprising: (a' ) setting a pulsed LASER adapted to produce a pulsed light beam of a wavelength comprised between 150 nanometers and 3 micrometers, so that said beam comprises a plurality of pulses with a repetition rate of over 1000 pulses per second, each pulse comprising an on- state lapsing less than 100 nanoseconds, (b' ) connecting said pulsed LASER to an application head for applying said pulsed light beam on an application point of a cutting path of a biological tissue in order to transfer sufficient energy to said biological tissue to remove at least some of the biological tissue at said application point, and

(C) providing a displacement device for moving said pulsed light beam so that the application point is displaced along said cutting path of said biological tissue at a speed over 0.1 mm/second in order to cut said biological tissue along said cutting path.

35. Method according to claim 34, wherein, during step (a' ) , said laser is set to produce a pulsed light beam at an operation rate of over 5000 pulses per second, preferably over 10000 pulses per second.

36. Method according to claim 34 or 35, wherein, during step (a' ) , said laser is set to produce a pulsed light beam at an on-state lapsing less than 10 nanosecond, preferably less than 1 nanosecond.