WO2019215745A1

WO2019215745A1 - Robotically controlled ultrasonic scalpel

Info

Publication number: WO2019215745A1
Application number: PCT/IL2019/050531
Authority: WO
Inventors: Isador Lieberman; Eli Zehavi; Moshe Shoham
Original assignee: Mazor Robotics Ltd.
Priority date: 2018-05-09
Filing date: 2019-05-09
Publication date: 2019-11-14

Abstract

Robotic systems and methods for performing orthopaedic surgery using high power ultrasonic cutting tools, and having a higher degree of safety than prior art systems. Separate levels of safety are used to prevent damage to surrounding soft tissues such as nerves, organs or arteries. Firstly, the tool blade and its ultrasound operating mode are such that the effect on soft tissue is substantially less than on bone tissue. Furthermore, robotic guidance using preoperative images reduces the possibility of damage to soft tissue. Additionally, sensors are used to determine when the tool completes operation in bone, and reaches soft tissue, the sensors being either acoustic or based on the power drawn by the tool. Other implementations use the reflection from the bone regions of the ultrasound energy used to perform the procedure, to generate an image, providing direct viewing of the procedure without the need for preoperative image guidance.

Description

ROBOTICALLY CONTROLLED ULTRASONIC SCALPEL

FIELD OF THE INVENTION

The present invention relates to the field of the use of robotic guidance of ultrasonic scalpels and saws for performing orthopedic surgical procedures, especially for such procedures performed in the vicinity of soft tissue.

BACKGROUND

A recent development in the field of surgery relates to the use of high power ultrasonic power tools in order to perform routine cutting action in bone tissues, such as is described in US Patent Nos. 5,371,429 for“Electromechanical Transducer Device”, to R.R. Manna, 6,379,371 for“Ultrasonic Cutting Blade with Cooling” to T.A.D. Novak, et al, and 8,343,178 for“Method for Ultrasonic Tissue Excision with Tissue Selectivity” for“Method for Ultrasonic Tissue Excision with Tissue Selectivity”, also to T.A.D. Novak, et al, all of these patents being assigned to Misonix Incorporated of Farmingdale, NY, and further patents described in the Background sections of those patents. The advantage of this procedure, as described in some of the above references, is that provided the cutting blade has the correct predetermined dimensions and shape, and provided that it is operated under the correct ultrasound conditions, the scalpel is tissue selective, discriminating between the cutting action in hard bone tissue and softer surrounding tissue. Hard tissue (i.e., bone) is effectively cut as it is more rigid and less elastic than soft tissue. When rigid bone comes in contact with such an ultrasonically vibrated powered blade, it does not bend, deform or move away; rather it shears and breaks away. As a result, the bone absorbs a large portion of the blade’s energy and is cut at the point of contact with the blade.

On the other hand, under the correct scalpel dimensions and form, and under the correct operating conditions, soft tissue responds largely elastically when contacting the blade incidentally, that is, it moves, deforms and vibrates. This results in substantial dampening of the energy transferred from the blade to the tissue. The energy absorbed by the soft tissue at the point of contact is generally not sufficient to cut the tissue unless the blade makes contact with the soft tissue for a period of time.

These properties have great advantage during orthopedic procedures such as spinal surgery where bone segments are frequently removed in close vicinity to the spinal cord, nerve roots and major arteries. However, in active robotic surgical systems, where the robotic end effectors may be required not only to cut, but also to detract tissues, and where tactic feedback, such as is available when a surgeon uses an ultrasonic scalpel by hand, is not available, there still exists a danger that despite the greater safety of an ultrasonic scalpel with respect to soft tissue damage when compared with other surgical tools, there is need to provide positive safety features to prevent such damage.

There therefore exists a need for a robotically controlled ultrasonically driven surgical cutting system that overcomes at least some of the disadvantages of prior art systems and methods.

The disclosures of each of the publications mentioned in this section and in other sections of the specification, are hereby incorporated by reference, each in its entirety.

SUMMARY

The present disclosure describes new exemplary systems for performing orthopaedic surgery using high power ultrasonic cutting tools and having a higher degree of safety than prior art systems. Four separate levels of safety are used in the systems of the present disclosure. According to the first level, which is based on the use of a robotic system to guide the scalpel, a surgical plan is generated by the surgeon preoperatively on the basis of three dimensional image sets. This surgical plan is used to program the robotic system for execution, using such an ultrasonic cutting tool held in the robotically controlled end effector arm. The information input to the surgical plan includes the exact position in three dimensions of the orthopedic elements to be operated on, such that the robotic control should enable the cutting tool to avoid causing damage to soft tissue, such as nerves, organs or blood vessels in close proximity to the bone being cut or treated. The robotic control can be programmed to stop the tool from entering the dangerous region. Any such active robotic system must have a navigating monitoring system or a registration system based on some kind of marker element whose position is known in the preoperative three dimensional image sets, in order to relate the actual pose of the ultrasonic cutting tool with the elements of the subject’s anatomy which are to be operated on, or are situated adjacent thereto, as indicated in the surgical plan.

However, the position of any adjacent soft tissues, such as nerves, organs or blood vessels which must be avoided, are less clear on the commonly used CT imaging methods used for assessing such spinal operations, and may often be assessed by a knowledge of the anatomy rather than positively identified, such that the robotic guidance system may be less able than desired to provide an indication of the proximity of sensitive regions to be avoided, or even to provide control signals to prevent the ultrasonic cutting tool from entering the regions to be avoided. Consequently, although the information obtained from the preoperative images is used as the primary source of information for preparing the orthopaedic surgical plan itself, and for inputting instructions to the robot to execute the surgical plan as accurately as the system allows, a second layer of safety for the implementation of the surgical plan is provided by the selective cutting capability provided by the ultrasonic cutting tool, namely that incidental contact with soft tissue for a short time should not generally result in damage to the tissue.

The safety provided by the use of a robotic guidance system for implementing the orthopedic operation, and the inherent partial protection selectively applied to soft tissues by the ultrasonic cutting tool’s action, both depend on secondary effects, and are not direct indicators of inadvertent contact with soft tissue material. According to the novel methods and systems of the present application, additional layers of safety can be provided by the use of one or more sensor modalities, to determine directly when the tool approaches a forbidden region. Three different types of sensing systems may be used.

A first type of sensing can be implemented by using the ultrasound system itself to image the region being treated by the scalpel, in much the same way as a conventional ultrasound imaging system operates. In such a system, the piezoelectric crystal is used both to generate the ultrasound signal pulses, and to detect their reflection from the imaged tissues during the temporal time slots between transmission of the pulses. Since the form of a piezoelectric crystal and transmitter designed for generation of the ultrasound power levels for cutting use with a scalpel, may be different from those of crystals and transmitter heads for pure imaging applications, it may be necessary to use a separate detector to image the region being treated by the ultrasound scalpel, but the application is identical - imaging of the ultrasound waves generated by the scalpel, as reflected from the treatment region, to determine when the scalpel is cutting bone tissue, and when it is approaching soft tissue to which entry of the scalpel is not permitted. The surgeon can either view the ultrasound images produced directly on the monitor screen, or they may be image processed to provide automatic warning of impending entry into regions of nerves, blood vessels, and the like.

A second type of sensing may be based on the difference in sound, whether tone or intensity, emitted by the ultrasonic cutting blade when it exits the bone and reaches soft tissue. A sound detector such as a microphone may be provided to use this sensing method, if any automatic safety system is to be provided for the power control system. However, besides this possibility, the surgeon him/herself should be able to readily ascertain when the scalpel has concluded or is about to conclude the bone cutting operation, by the evident change in tone or intensity emanating from the procedure. It is to be understood that the tone heard during the cutting operation in hard tissue is that of the pulse rate of the ultrasound power, which is generally of the order of a few kHz, typically from 1 to 5kHz.

A third type of sensor is based on the electric power drawn by the ultrasonic blade, which should suddenly fall as the blade exits the bone. Current sensing circuitry in the control system can be used in order to provide a warning signal to the surgeon, or even to intervene in the provision of power to the scalpel.

A further sensing mechanism can be based on visual scans of the surgical region, though such visual scans may not be highly effective because of the difficulty of differentiating between different tissues in the region of an operation, where there may be considerable accumulations of blood and other bodily fluids. In any of the above mentioned safety methods for determining when a potential danger exists during the procedure, the warning output from the controller can be input to the robotic control to stop the tool from entering the dangerous region,

There is thus provided, in accordance with exemplary implementations of the systems described in this disclosure, a system for performing a robotic surgical procedure on a bone in close proximity to soft tissues of a subject, the system comprising:

(i) an ultrasound powered surgical tool, adapted to perform the surgical procedure on the bone,

(ii) a controller adapted to receive a surgical plan generated on a set of preoperative three dimensional images of the region of the bone, the surgical plan avoiding entry of a blade of the ultrasound powered surgical tool into the soft tissues of the subject, and

(iii) a robotic system for manipulating the ultrasound powered surgical tool, the robotic system being adapted to receive instructions from the controller to direct the motion of the blade to perform the surgical procedure on the bone, the co-ordinate system of the robotic system being registered with the features of the preoperative three dimensional images, such that the pose of the blade is known relative to features of the preoperative three dimensional images,

wherein the blade and its ultrasound operating mode are such that the cutting effect of the blade on soft tissue is substantially less than its cutting effect on bone tissue.

In such a system, the robotic system may be programmed to prevent the blade of the ultrasonic powered surgical tool from entering the region of the soft tissues by using the surgical plan to determine when the robotic actuation arm has reached a pose at which the ultrasonic cutting blade has completed cutting of the subject’s bone according to the surgical procedure. Any of such systems may further comprise a sensor for providing additional determination of when the ultrasonic cutting blade has completed the cutting of the subject’s bone. In such a case, the sensor may use the sound emitted by the ultrasonic cutting blade, the sound of bone cutting being different from that of soft tissue contact. The sensor may be a microphone adapted to input its output signal to the controller, the controller adapted to discriminate between changes in at least one of the tone or intensity of the sound. In another implementation, the sensor may use information regarding the power drawn by the ultrasonic cutting tool, the power decreasing when the ultrasonic cutting blade has completed the cutting of the subject’s bone.

There is further provided according to yet another implementation of the present disclosure, a system for performing a robotic surgical procedure on a bone structure in close proximity to soft tissues of a subject, the system comprising:

(i) an ultrasound powered surgical tool, adapted to input ultrasound power to a blade of the tool, such that the blade performs the surgical procedure on the bone structure,

(ii) an ultrasound detection probe, disposed on or in proximity to the ultrasound powered surgical tool, the probe adapted to receive reflections of the ultrasound power off the bone structure and its surrounding soft tissues, and to generate output signals containing information enabling an image of the bone structure and its surrounding soft tissues, and

(iii) a controller adapted to receive the output signals to generate an image delineating between the bone structure and its surrounding soft tissues.

In such a system, the image may be displayed on a monitor such that the position of the blade, the bone structure and the surrounding soft tissues can be observed. The controller may further be adapted to process the image information to detect the position of the blade relative to the bone structure and its surrounding soft tissue, and to use the position information to issue a warning if the blade moves into the region of the soft tissue. Additionally, the controller may be further adapted to process the image information to detect the position of the blade relative to the bone structure and its surrounding soft tissue, and to use the position information for real-time guidance of the robotic system, to ensure that the robot cannot move the blade into the region of soft tissue.

There is also provided in this application, a method of performing a robotic surgical procedure on a subject, on a bone in close proximity to soft tissues, the method comprising:

(i) providing a set of three dimensional preoperative images of the region of operation, the images showing the bone structure, (ii) using the images, preparing a surgical plan which enables cutting of the subject’s bone structure in close proximity to the soft tissues,

(iii) registering the pose of an ultrasonic cutting tool held in the activated arm of the robotic system, as determined by the robotic system, relative to the bone structure shown in the preoperative images, and

(iv) performing the cutting of the subject’s bone according to the surgical plan, the robotic system being programmed to prevent the blade of the ultrasonic cutting tool from entering the region of the soft tissues,

wherein the method uses the selective property of the ultrasonic cutting tool of having less likelihood of cutting a soft tissue in comparison with a bone tissue, in order to increase the safety of the method.

In such a method, the robotic system may be programmed to prevent the ultrasonic cutting blade from entering the region of the soft tissues by using the surgical plan to determine when the robotic arm has reached a pose at which the ultrasonic cutting blade has completed the cutting of the subject’s bone. The above described methods may also comprise the step of providing a sensor mechanism for determining when the ultrasonic cutting blade has completed the cutting of the subject’s bone, such that the safety of the method is further improved. In the latter case, the sensor may use the sound emitted by the ultrasonic cutting blade, or the the power drawn by the ultrasonic cutting tool.

A further method is also provided for performing a robotic surgical procedure on a bone structure in close proximity to soft tissues of a subject, the method comprising:

(i) inputting ultrasound power to an ultrasound powered surgical tool having a blade, to perform the surgical procedure on the bone structure,

(ii) receiving reflections of the ultrasound power off the bone structure and its surrounding soft tissues in an ultrasound detection probe, the probe being disposed on or in proximity to the ultrasound powered surgical tool, and generating output signals containing information to enable an image of the bone structure and its surrounding soft tissues, and

(iii) receiving the output signals and generating an image delineating between the bone structure and its surrounding soft tissues. Such a method may comprise the step of displaying the image on a monitor such that the position of the blade, the bone structure and the surrounding soft tissues can be observed. Alternatively, in such a method, the image information may be processed to detect the position of the blade relative to the bone structure and its surrounding soft tissue, and the position information used to issue a warning if the blade moves into the region of the soft tissue. Additionally, the image information may be further processed to detect the position of the blade relative to the bone structure and its surrounding soft tissue, and the position information used for real-time guidance of the robotic system, to ensure that the robot cannot move the blade into the region of soft tissue.

Finally, in any of the above described systems or methods, the soft tissue may comprise at least one of a nerve structure, a blood vessel or an organ.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which:

Fig.l shows a robotic surgical system, using an ultrasound cutting tool for performing an orthopedic action on an element of the subject’s anatomy; and

Fig. 2 is a schematic illustration of an ultrasound surgical scalpel system, showing the control functions used for the various implementations of the system described in the present application.

DETAILED DESCRIPTION

Reference is now made to Fig. 1, which illustrates schematically a robotic surgical system, using an ultrasound cutting tool 28 for performing an orthopedic bone excision action on an element of the subject’s spine. The robotic control system 40 has a display 30 for the surgeon 41 to follow the progress of the operation. However, the preloaded surgical plan can instruct the robotic system and its robotic arm 27 to execute the procedure without the need for the surgeon’s intervention. An acoustic pickup, such as a microphone 29 should be located in the region of the patient, or even on the robotic arm or the tool. The function of the microphone will be expounded hereinbelow. A location procedure must be used in order to ensure correct registry of the position of the ultrasonic cutting tool and the robotic arm, relative to the preoperatively imaged surgical site. This can be achieved, as is known in the art, by two commonly used methods: (i) either by use of a navigation system which can relate in real time, the position of the robotic actuating arm or the tool attached to it, to the patient’s anatomy, by means of markers attached to both and tracked by the navigation system,, or (ii) by means of a registration targeting procedure, such as using a three dimensional target attached to the subject in the region of the surgical site, and at least a part of which appears in the preoperative images, and to which the position and orientation of the robot can be related for the surgical procedure itself.

Reference is now made to Fig. 2, which is a schematic illustration of an ultrasound surgical scalpel system, with the control functions used for the various implementations of the system described in the present application.

The scalpel itself 50 is shown in this exemplary implementation, operating on a vertebra in the spine 54 of a subject. The spine is a region in which it is very important to provide close monitoring and control of the cutting position of the scalpel, because of the close proximity of sensitive tissues, such as the spinal cord, nerve roots and major arteries. The ultrasonic power for the scalpel is generated by a piezoelectric transducer 51 which transmits the ultrasonic power generated in the source down a rigid rod 52, to the scalpel blade 53, situated on the distal end of the rod 52. The power components of the ultrasonic head, including the scalpel itself, have to be cooled, most conveniently by a water cooling circuit (not shown in Fig. 2) The ultrasonic head 50 is held in the actuating arm of a robot 55, whose joints and arms are controlled by a controller 56, and which is programmed to move the scalpel blade to execute the surgeon’s surgical plan. The robotic control therefore has access to the preoperative images sets, and also to information regarding the robot’s exact pose, and hence the exact position and orientation of the tip of the scalpel, with respect to the vertebrae on which the scalpel is operating.

In an alternative implementation to using the surgical plan generated on the preoperative three dimensional image set of the region to be operated on, an intraoperative real-time image of the region being operated on may be obtained using an ultrasonic imaging probe 59, which generates an image from the ultrasound waves reflected off the anatomic details, and which should show the bone structure and the surrounding soft tissues. This image may be input to the control system 56, and displayed on the monitor 57 for the surgeon to be aware of where the blade of the surgical instrument completes its operation on the bone structure. Alternatively, the control system can perform image processing on the image data, to detect the scalpel blade, and the output used for real time guidance of the robotic system, ensuring that the robot is not allowed to move the scalpel into the region of soft tissue after completing the osteotomy or other bone processing operation. This may provide safer usage than generating a conventional ultrasound image which the surgeon can use to make his/her own decision about the possibility of danger to the soft tissues.

A microphone 29 may also be incorporated into the system for use in picking up the sound waves 58 of the interaction of the scalpel with the tissue on which it is working, and the resulting audio signal from the microphone is input to the controller.

Another safety feature involves measurement of the current drawn by the ultrasonic generator 51 using a current probe for input to the controller, or as determined at the power supply output for the ultrasonic power to be applied to the transducer 51. The current or power drawn is directly related to the energy expended by the scalpel, and provides an indication of when the scalpel blade completes a cut in a bone and passes out of the bone into the surrounding soft tissue, when the power consumption of the ultrasound scalpel should drop significantly.

A monitor 57 should be used both for monitoring images taken of the region of the operation, and for displaying information about the various parameters and characteristics being measured by the system.

The control unit 56 can be configured to oversee all or some of the operational parameters of the system, both power and control outputs and sensor inputs, and to control the operation of the robotically controlled motion of the scalpel blade. These control features shown in Fig. 2 include: 60 - ultrasonic current pulses for inputting to the ultrasound generator.

61 - a current sensor input to determine the ultrasound power being expended by the scalpel.

62 - output control commands to the robot to move the scalpel to execute the surgeons stored robotic plan.

63 - image information input from the ultrasonic probe at the operating site.

64 - output information for displaying on the monitor ultrasound images of the region of interest.

65 - signal input representing the audio information picked up by the microphone in the region of the scalpel’s action.

66 - an output signal to a warning lamp or an audible alarm to warn the surgeon of a potentially dangerous situation because of the position of the scalpel tip.

Other inputs or outputs may also be used depending on the configuration of the system and the various elements of information required for operation of the system in executing the surgical plan.

It is appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and subcombinations of various features described hereinabove as well as variations and modifications thereto which would occur to a person of skill in the art upon reading the above description and which are not in the prior art.

Claims

CLAIMS We claim:

1. A system for performing a robotic surgical procedure on a bone in close proximity to soft tissues of a subject, said system comprising:

an ultrasound powered surgical tool, adapted to perform said surgical procedure on said bone;

a controller adapted to receive a surgical plan generated on a set of preoperative three dimensional images of the region of said bone, said surgical plan avoiding entry of a blade of said ultrasound powered surgical tool into said soft tissues of said subject; and

a robotic system for manipulating said ultrasound powered surgical tool, said robotic system being adapted to receive instructions from said controller to direct the motion of said blade to perform said surgical procedure on said bone, the co ordinate system of said robotic system being registered with the features of said preoperative three dimensional images, such that the pose of said blade is known relative to features of said preoperative three dimensional images;

wherein said blade and its ultrasound operating mode are such that the cutting effect of said blade on soft tissue is substantially less than its cutting effect on bone tissue.

2. A system according to claim 1, wherein said robotic system is programmed to prevent said blade of said ultrasonic powered surgical tool from entering the region of said soft tissues by using said surgical plan to determine when said robotic actuation arm has reached a pose at which said ultrasonic cutting blade has completed cutting of said subject’s bone according to said surgical procedure.

3. A system according to either of claims 1 and 2, further comprising a sensor for providing additional determination of when said ultrasonic cutting blade has completed the cutting of said subject’s bone.

4. A system according to claim 3, wherein said sensor uses the sound emitted by said ultrasonic cutting blade, the sound of bone cutting being different from that of soft tissue contact.

5. A system according to claim 4, wherein said sensor is a microphone adapted to input its output signal to said controller, said controller adapted to discriminate between changes in at least one of the tone or intensity of said sound.

6. A system according to claim 3, wherein said sensor uses information regarding the power drawn by said ultrasonic cutting tool, said power decreasing when said ultrasonic cutting blade has completed the cutting of said subject’s bone.

7. A system according to any of the preceding claims, wherein said soft tissue comprises at least one of a nerve structure, a blood vessel or an organ.

8. A system for performing a robotic surgical procedure on a bone structure in close proximity to soft tissues of a subject, said system comprising:

an ultrasound powered surgical tool, adapted to input ultrasound power to a blade of said tool, such that said blade performs said surgical procedure on said bone structure;

an ultrasound detection probe, disposed on or in proximity to said ultrasound powered surgical tool, said probe adapted to receive reflections of said ultrasound power off said bone structure and its surrounding soft tissues, and to generate output signals containing information enabling an image of said bone structure and its surrounding soft tissues; and

a controller adapted to receive said output signals to generate an image delineating between said bone structure and its surrounding soft tissues.

9. A system according to claim 8, wherein said image is displayed on a monitor such that the position of said blade, said bone structure and said surrounding soft tissues can be observed.

10. A system according to claim 8, wherein said controller is further adapted to process said image information to detect the position of said blade relative to said bone structure and its surrounding soft tissue, and to use said position information to issue a warning if said blade moves into the region of said soft tissue.

11. A system according to claim 8, wherein said controller is further adapted to process said image information to detect the position of said blade relative to said bone structure and its surrounding soft tissue, and to use said position information for real time guidance of the robotic system, to ensure that the robot cannot move said blade into the region of soft tissue.

12. A system according to any of claims 8 to 11, wherein said soft tissue comprises at least one of a nerve structure, a blood vessel or an organ.

13. A method of performing a robotic surgical procedure on a subject, on a bone in close proximity to soft tissues, said method comprising:

providing a set of three dimensional preoperative images of the region of operation, said images showing the bone structure;

using said images, preparing a surgical plan which enables cutting of the subject’s bone structure in close proximity to said soft tissues;

registering the pose of an ultrasonic cutting tool held in the activated arm of said robotic system, as determined by the robotic system, relative to the bone structure shown in said preoperative images; and

performing the cutting of the subject’s bone according to the surgical plan, said robotic system being programmed to prevent the blade of said ultrasonic cutting tool from entering the region of said soft tissues,

wherein said method uses the selective property of said ultrasonic cutting tool of having less likelihood of cutting a soft tissue in comparison with a bone tissue, in order to increase the safety of said method.

14. A method according to claim 13 wherein said robotic system is programmed to prevent said ultrasonic cutting blade from entering the region of said soft tissues by using said surgical plan to determine when said robotic arm has reached a pose at which said ultrasonic cutting blade has completed the cutting of said subject’s bone.

15. A method according to claim 13, further comprising the step of providing a sensor mechanism for determining when said ultrasonic cutting blade has completed the cutting of said subject’s bone, such that the safety of said method is further improved.

16. A method according to claim 15, wherein said sensor uses the sound emitted by said ultrasonic cutting blade.

17. A method according to claim 15, wherein said sensor uses the power drawn by said ultrasonic cutting tool.

18. A method according to any of claims 13 to 17, wherein said soft tissue comprises at least one of a nerve structure and a blood vessel.

19. A method for performing a robotic surgical procedure on a bone structure in close proximity to soft tissues of a subject, said method comprising:

inputting ultrasound power to an ultrasound powered surgical tool having a blade, to perform said surgical procedure on said bone structure;

receiving reflections of said ultrasound power off said bone structure and its surrounding soft tissues in an ultrasound detection probe, said probe being disposed on or in proximity to said ultrasound powered surgical tool, and generating output signals containing information to enable an image of said bone structure and its surrounding soft tissues; and

receiving said output signals and generating an image delineating between said bone structure and its surrounding soft tissues.

20. A method according to claim 19, comprising the step of displaying said image on a monitor such that the position of said blade, said bone structure and said surrounding soft tissues can be observed.

21. A method according to claim 19, wherein said image information is processed to detect the position of said blade relative to said bone structure and its surrounding soft tissue, and said position information is used to issue a warning if said blade moves into the region of said soft tissue.

22. A method according to claim 19, wherein said image information is further processed to detect the position of said blade relative to said bone structure and its surrounding soft tissue, and said position information is used for real-time guidance of the robotic system, to ensure that the robot cannot move said blade into the region of soft tissue.

23. A method according to any of claims 19 to 22, wherein said soft tissue comprises at least one of a nerve structure, a blood vessel or an organ.