Probe, sleeve, system, method and kit for performing percutaneous thermotherapy

A cryosurgical probe that is operative to bring target nerve tissue to a temperature below about −140° C. so as to reduce or eliminate regeneration of the nerve tissue by growing an ice ball. The probe comprises a thermally conductive body, a thermally insulating body and a temperature sensor. The thermally conductive body has a conductive portion adapted to contact the tissue and form an ice ball thereat during use. The thermally insulating body is adjacent to the conductive portion onto which the ice ball forms during use. The temperature sensor is positioned at a predetermined position on the thermally insulating body with respect to the conductive portion. The predetermined position corresponds to a predetermined size of the ice ball grown in the tissue when the sensor reads a predetermined temperature. The insulating body provides sufficient thermal insulation between the conductive body and the surrounding tissue so that the sensor detects freezing of. The surrounding tissue is in contact with the sensor by growth of the ice ball from the conductive portion onto the insulating body. A sleeve for fitting to a probe and a kit comprising at least two sleeves or two probes, each having one sensor but positioned at different locations is also disclosed. Furthermore, a system using a controller for shutting down a cooling of the probe and methods for performing percutaneous thermotherapy by fitting a sleeve on a probe or by shutting down the cooling of the probe are also disclosed.

FIELD OF THE INVENTION

The present invention relates generally to the field of systems for percutaneous thermotherapy. More particularly, the invention relates to an improved cryoprobe used in cryosurgery.

BACKGROUND OF THE INVENTION

The treatment of back pains still remains a challenge for many reasons. One of such reasons is the difficulty to permanently and exclusively cure the cause of such pains without affecting surrounding tissues in an area of a human body that is a main channel of nerve impulse.

Different causes of back pain exist. Of all chronic low back pain problems, about 20% can be attributed to the facet joints. This cause is also known as the chronic lumbar facet joint syndrome. Among patients, 90% are successfully treated through conservative procedures such as active physiotherapy and NSAIDS. For the remaining 10%, further investigation as well as a more aggressive therapeutic approach must be considered. Once the diagnosis of the facet joint syndrome is clinically made, percutaneous thermotherapy procedures may be considered, seeking a minimally invasive treatment with low morbidity and satisfactory clinical efficiency.

Discogenic back pain, another cause of back pain, is responsible for close to 60% of chronic low back pain in the general population. Once conservative treatment has been fully used, 5% of the patients remain with back pain that can be considerably invalidating. Usual treatment of this invalidating condition is spinal fusion or disc arthroplasty, both associated with considerable morbidity, off-work time, and social cost. Clinically discogenic pain patients have constant back pain that is amplified in the vertical disc loading positions, with a sitting being even worse or equal to the standing position pain. Disc pain is reproduced by pain provocation procedures such as discograms or discometry. Denervation of a portion of the disc, to relieve some if not most of the pain by a percutaneous procedure, is a known advantageous alternative with a reduction of the cited disadvantages of the more aggressive procedures.

Cryotherapy exists as therapy of discogenic back pain or facet joint syndrome since 1961. However, this technique originally used liquid nitrogen as coolant, reaching a treatment temperature of approximately −80 C.°., while the trocar was placed under fluoroscopic guidance. Limited control of the cryoanalgesia process with this combination of technology has resulted in only temporarily pain relief. Studies even showed that there does not exist statistical differences between patients who had such a treatment and patients treated with a placebo pr probe. On the other hand, a study showed that irreversible damage to the nervous structures is obtained only when temperatures reach below −140 C.°. Temperatures above −140 C.° only temporarily affect the nerve tissue.

It is therefore possible to divide thermotherapy in two types: moderate and extreme temperature thermotherapy. Moderate temperature thermotherapy only temporarily affects nerve tissues and therefore does not cause permanent damages. Consequently, pain relief is only temporary. Monitoring of such treatments is not as critical as it is with extreme temperature thermotherapy. Should the probe affect tissues that should not have been affected, the effects would only be temporary. Extreme temperature thermotherapy (either extremely high or extremely low temperatures), on the other hand, causes permanent damages to tissues. Destroying tissue with this type of treatment is desirable in order to permanently remove pain generators in a body by destroying the nerves in tissues of any nature, or to treat tumors of any kind in a minimally invasive fashion, such as percutaneously. Because of its permanent effects on the body, careful monitoring of the effects of a probe used for extreme temperature treatment is mandatory. Furthermore, cold, whose propagation is far more predictable in the human body than heat, is more often used for extreme temperature treatment. It follows that careful monitoring of a growth of an ice ball of treated tissues created by a cryoprobe is necessary, especially when treating chronic lumbar facet joint syndrome, where inadequate propagation of the ice ball could affect spinal tissues and permanently paralyze a patient. Up to now, monitoring the size of the ice ball was realized either by imagery or by temperature monitoring. Temperature monitoring is accomplished by positioning a temperature sensor that will detect a variation in a temperature of the surrounding tissues and, consequently, the presence of the ice ball. Doing so requires separately inserting in the patient's body the cryoprobe and at least one temperature sensor. Then, X-ray, or another imaging method, must be used to verify a position of the temperature sensor with respect to the cryoprobe.

Imagery monitoring typically uses technologies such as MRI, CT scanning, or ultrasound. However, simultaneously using such imagery systems while operating adds to the complexity of the operation.

Different types of cryoprobes have been suggested. For example, U.S. Pat. No. 6,551,309 describes a cryoprobe comprising, at its tip, several sensors used to monitor that the tip is cooled. However, these sensors are laid out on a thermally and electrically conductive surface and are therefore only adapted to measure the temperature of the tip of the cryoprobe but not that of the surrounding tissues. Consequently, this cryosurgery system requires the use of an MRI imaging system.

US patent application No. 20040024391 describes an apparatus and a method to protect certain tissues during a cryosurgery. This document describes a probe provided with a temperature sensor laid out on a portion remote from its tip. The temperature sensor is used to follow a change of the induced temperature to treated tissues. However, this document does not disclose placing the temperature sensor at a specific distance from the tip such as to monitor the growth of an ice ball and control the cooling by the probe accordingly. Consequently, the apparatus and method described in this document still requires the use of an imagery method such as X rays, ultrasounds, CT or MRI.

There is therefore a need for an improved system for percutaneous thermotherapy that does not require constant visual monitoring of the surgery so that such treatment may be conducted without resorting to imagery systems, which may not be available in all health facilities, and that does not require the use of an additional external temperature sensor.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a system for percutaneous thermotherapy that overcomes the above drawbacks.

It is another object of the present invention to provide a system for percutaneous thermotherapy that does not necessarily require special imagery systems.

It is another object of the present invention to provide a system for percutaneous thermotherapy that automatically stops the cooling of a conductive portion of the probe when an ice ball of treated tissues has reached a predetermined size.

It is another object of an aspect of the present invention to provide an insulated portion having one or more sensors that is capable of being accurately positioned on an existing probe for thermotherapy.

According to one aspect of the invention, there is provided a cryosurgical probe that is operative to bring target nerve tissue to a temperature below about −140° C. so as to reduce or eliminate regeneration of the nerve tissue by growing an ice ball. The probe comprises a thermally conductive body, a thermally insulating body and a temperature sensor. The thermally conductive body has a conductive portion adapted to contact the tissue and form an ice ball thereat during use. The thermally insulating body is adjacent to the conductive portion onto which the ice ball forms during use. The temperature sensor is positioned at a predetermined position on the thermally insulating body with respect to the conductive portion. The predetermined position corresponds to a predetermined size of the ice ball grown in the tissue when the sensor reads a predetermined temperature. The insulating body provides sufficient thermal insulation between the conductive body and the surrounding tissue so that the sensor detects freezing of the surrounding tissue in contact with the sensor by growth of the ice ball from the conductive portion onto the insulating body.

In a variation of this aspect of the invention, the conductive body is located at a distal tip of the probe opposed to a grabbing end. Such a probe may be used for treating lumbar discs pain.

In another variation of this aspect of the invention, the insulating body is located at the distal tip of the probe opposed to the grabbing end. Such a probe may be used for treating spinal facet joint syndrome.

In another aspect of the invention, there is provided a method of manufacturing a cryosurgical probe as defined here above. The method comprises the step of determining the predetermined position as a function of a desired ice ball size and thermal characteristics of the surrounding tissue.

In yet another aspect of the invention, there is provided a sleeve for fitting to a cryosurgical probe having a conductive portion. The sleeve is operative to bring target nerve tissue to a temperature below about −140° C. so as to reduce or eliminate regeneration of the nerve tissue by growing an ice ball. The sleeve comprises a thermally insulating body and a temperature sensor. The temperature sensor is positioned on the thermally insulating body so that when the sleeve is installed on the cryosurgical probe, the temperature sensor is at a predetermined position with respect to the conductive portion of the cryosurgical probe. The predetermined position corresponds to a predetermined size of the ice ball grown in the tissue when the sensor reads a predetermined temperature. The insulating body provides sufficient thermal insulation between the conductive body and surrounding tissue that the sensor detects freezing of the surrounding tissue being in contact with the sensor by growth of the ice ball from the conductive portion onto the insulating body.

In a variation of this aspect of the invention, the sleeve has a closed ended tip and the conducting body is located at the tip. This type of sleeve may be used for treating lumbar discs pain.

In another variation of this aspect of the invention, the sleeve has a closed ended tip and the insulating body is located at the tip. This type of sleeve may be used for treating spinal facet joint syndrome.

In yet another aspect of the invention, there is provided a method of manufacturing a sleeve as defined here above. The method comprises the step of determining the predetermined position as a function of a desired ice ball size and thermal characteristics of the surrounding tissue.

In a further aspect of the invention, there is provided a system for percutaneous thermotherapy for use with a cryosurgical probe having a conductive portion. The system comprises a controller and a sleeve as defined here above. The sleeve is adapted to be placed on the probe so that the sensor is at a predetermined longitudinal position from the conductive portion. The sensor is operative to send a signal to the controller. The controller is operative to control a cooling of the conductive portion based on the signal sent by the sensor.

In another aspect of the invention, there is provided a method of manufacturing such a system for percutaneous thermotherapy. The method comprises the step of determining the predetermined position as a function of a desired ice ball size and thermal characteristics of the surrounding tissue.

In yet a further aspect of the invention, there is provided a system for percutaneous thermotherapy comprising a controller and a probe as defined here above. The sensor of the probe is operative to send a signal to the controller. The controller is operative to control a cooling of the conductive portion based on the signal sent by the sensor.

In another aspect of the invention, there is provided a method of manufacturing such a system for percutaneous thermotherapy. The method comprises the step of determining the predetermined position as a function of a desired ice ball size and thermal characteristics of the surrounding tissue.

In yet another aspect of the invention, there is provided a method for performing percutaneous cryotherapy using a cryosurgical probe. The method comprises the step of selecting an insulating body having a temperature sensor adapted to be placed at a predetermined distance from a conductive portion of the probe, based on a desired size of an ice ball of tissues surrounding the conductive portion.

In yet another aspect of the invention, there is provided a method for performing percutaneous cryotherapy that comprises the step of automatically shutting down by a controller an imposed thermal variation of a conductive portion of a cryoprobe inserted in a patient's body once a signal from a single temperature sensor placed on a thermally insulating portion of the cryoprobe for sensing a size of an ice ball in surrounding tissues has reached a threshold value.

In still another aspect of the invention, there is provided a kit comprising at least two cryosurgical probes as defined here above. Each one of the probes has its temperature sensor located at a different longitudinally distance from the conductive portion.

In yet another aspect of the invention, there is provided a kit comprising at least two sleeves as defined here above. Each one of the sleeves has its temperature sensor located at a different longitudinally position.

DETAILED DESCRIPTION OF THE INVENTION

The present invention may be used for thermotherapy, either by submitting a patient to heat or to cold. Because transmission of cold in a human body is more predictable than transmission of heat, cryotherapy is more often used. Hence, the present invention will now be described with respect to a cryoprobe used for cryosurgery.

FIG. 1generally represents a cryoprobe10. The cryoprobe10is fitted with a conductive portion12, a body14that comprises a grabbing portion16for holding by a surgeon, and an insulating portion18. The cryoprobe10is typically equipped with a Joule-Thomson cooler20for providing a high-pressure gas to a cooling chamber22inside the conductive portion12. When a high-pressure cooling gas such as argon expands in cooling chamber22, so as to form a cryogenic pool, it effectively cools the surface of conductive portion12. The conductive portion12is made of a thermally conductive material such as stainless steel. The function of the conductive portion12is to induce a zone of thermo-surgical temperature in surrounding tissues of a patient. In the case of cryotherapy, this zone of thermo-surgical temperature corresponds to a treated tissue zone having the shape of an ice ball of treated tissues24, created around the conductive portion12. Thermo surgical temperatures are temperatures that induce irreversible damages to treated tissues.

Alternatively, a high-pressure heating gas such as helium may be used for operating conductive portion12in a heating mode via a reverse Joule-Thomson process, so as to enable treatment by cycles of cooling-heating, and further for shortening the treatment time by thawing the ice ball of treated tissues24and preventing it to stick to the cryoprobe10when extracting the cryoprobe10from the patient's body.

The insulating portion18of the body14is made of an insulating material such as Teflon. Alternatively, the whole body14could be made of the insulating material. This allows for preventing surrounding tissues that need not be desensitized by cryotherapy from being affected by the cold. The insulating portion18is fitted with a temperature sensor26. The temperature sensor26senses the temperature of surrounding tissues and in use, the temperature of the ice ball of treated tissues24.

Turning now toFIG. 2, a gas distribution module28controls the flow of pressurized gas, such as argon, into the cryoprobe10thorough delivery tube30. The gas, upon expanding into the cooling chamber22, cools the conductive portion12. The gas then returns to the gas distribution module28through return tube32. As the conductive portion12gets cooled, the tissues surrounding the conductive portion become frozen and the ice ball of treated tissues24starts forming around the conductive portion12. As the process continues, the ice ball grows in size. The temperature sensor26records a decrease in body temperature and sends a signal34to a controller36. The controller36compares the temperature signal34sent by the temperature sensor26with a threshold temperature. Although it may be otherwise, the water freezing temperature (0° C.) is often used as the threshold temperature. Hence, the temperature sensor26is used to monitor the progression of a forming front of the ice ball of treated tissues24. In order to correlate the temperature at the temperature sensor26with a size of the ice ball of treated tissues24, the temperature sensor26is placed at a predetermined position with respect to the conductive portion12. It is possible to correlate different temperatures than 0° C. with the size of ice ball of treated tissues24by modeling the response of the tissues to temperature changes as a function of time. However, it has been found that monitoring the forming front of the ice ball of treated tissues24is more convenient and gives a direct indication of the ice ball size. As the ice ball of treated tissues24continues to grow in size, the temperature further decreases at temperature sensor26until the signal34sent to the controller36reaches the threshold temperature. At that point, the controller36automatically shuts down the gas distribution module28, thereby stopping the growth of the ice ball of treated tissues24. Alternatively, the controller36may be set-up such that it shuts down the gas distribution module28only after a predetermined amount of time has elapsed after the temperature sensor26has read the threshold temperature or only when the temperature sensor26has read a predetermined shut down temperature that is different from the threshold temperature. It will be understood that when the controller36shuts down the gas distribution module28when the temperature sensor26reads the threshold temperature, it is because the shut don temperature is set up to be the same as the threshold temperature. Typically, the temperature sensor26is located on the insulating portion18approximately 10 mm from the conductive portion. A user may adjust the controller such as to vary the size of the ice ball of treated tissues24. Another way of adjusting the size of the ice ball of treated tissues24is to locate the temperature sensor26at different longitudinal positions from the conductive portion12. This may be either accomplished by having different models of cryoprobe10where the temperature sensor26is located at different distances from the conductive portion12, or by providing the cryoprobe with many temperature sensors26that are located at different longitudinal positions along the insulated portion24of the cryoprobe10. Then, the controller decides which temperature sensor26to monitor. This information may also be provided manually to the controller36by a user.

For better reliability, it is possible to equip the insulating portion18with more than one temperature sensor26at the same distance from the conductive portion12. The controller36then processes the information gathered by the temperature sensors26and takes a decision to shut down or to continue cooling accordingly.

The details of the structure of the cooling system used in the probe are well known in the art and as such will not be described in further details in the present description.

FIG. 3schematically shows the detail of the controller36, which may be a computer. The controller36comprises a thermal model storage medium38, a size determinator40, a comparator42and a thermal application module46. The thermal model storage medium38stores all thermal models. The thermal models are mathematical models of heat transfer in a body based on parameters such as the type of surgery, type of tissue, type of gas used for cooling, probe model, etc. For instance, tissue types vary whether they are intradiscal or interdiscal tissues, flesh surrounding prostate gland, etc. The thermal model includes the size of the ice ball of treated tissues24. The thermal model storage medium38feeds a desired size signal48to the comparator42. From a user interface50, the surgeon may select a thermal model desired52. Optionally, the surgeon may bypass the thermal model storage medium38and impose the size of the ice ball of treated tissues24with the desired size signal48of his own. Optionally, the surgeon may bypass all parameters. The surgeon sends a start command54, through the user interface50, to the comparator42. The size determinator40determines the actual size of the ice ball of treated tissues24based on the signal34received from the temperature sensor or sensors26. The comparator42compares an actual size signal56received from the size determinator40with desired size signal48received from the thermal model52. Whenever the actual size signal56indicates a smaller size than the desired size signal48, the comparator42sends an “ON” signal58to the thermal application module46. In turns, the thermal application module46sends a thermal application command signal60to the gas distribution module28to send cooling gas to the probe10. Preferably, the size determinator40is hooked to a display62to show the surgeon the actual size of the ice ball of treated tissues24.

FIG. 4shows another embodiment of the invention. In this case, a sleeve64having an insulating portion18is fitted over a standard cryoprobe66which has its body14ended by the conductive portion12. In the present description, the term “sleeve” is used to describe a device that covers a probe and that may be either open at both its extremities, or closed at one extremity. In the present embodiment, the sleeve64is open at both extremities. The sleeve64is specially designed to fit over a given model of standard cryoprobe66. The sleeve64is equipped with the temperature sensor26. The sleeve64is positioned over the body14such that the conductive portion12extends from the sleeve64. Similarly to the previous embodiment, in use, the ice ball of treated tissues24forms at the conductive portion12and grows until it reaches the temperature sensor26, which continuously sends a signal to the controller36(not shown in the Figure). The position of the temperature sensor26on the sleeve64is adjusted so that the longitudinal position of the temperature sensor26with respect to the conductive portion12corresponds to the desired size of ice ball of treated tissues24. The position of the temperature sensor26with respect to the conductive portion12may be set by way of locating means68. Here, the locating means68are depicted as a stopper against which the standard cryoprobe66abuts. However, the locating means could be a mark on the standard cryoprobe66or simply an edge of the sleeve64used to locate the sleeve64, and therefore the temperature sensor26, with respect to the conductive portion12. Optionally, the sleeve64may comprise an air chamber70, which also thermally insulates the temperature sensor26from the standard cryoprobe66. For example, the standard cryoprobe66may be 4 mm in diameter, the air chamber70may be 1 mm thick and the sleeve64may be 2 mm thick, including the air chamber70. Preferably, Teflon is used as the insulating material of the sleeve64. As shown inFIG. 5, now concurrently referred to, this type of cryoprobe is particularly well adapted for cryosurgery of discs of a spine.

FIG. 6shows yet another embodiment of the present invention. This design of cryoprobe10is adapted for the cryotherapy of facets, as shown inFIG. 7and now concurrently referred to. In this embodiment, the conductive portion12is not located at a tip72of the cryoprobe10, but rather at a mid-portion of the cryoprobe10. The tip72is made of the insulating material so as to become the insulating portion18. As can be seen, in the case of facet cryotherapy, the insulating portion18is placed at the tip72to prevent nerve roots in this spine area from being damaged by the cold. The temperature sensor26may be placed on either the insulated tip72or the body14as long as it is on a thermally insulated portion of the cryoprobe10and as long as it is at the predetermined distance from the conductive portion12such as to detect a condition of the surrounding tissues. However, it might be advantageous to place the temperature sensor26on the insulated tip72such as to monitor the ice ball growth closer to the freeze sensitive region where major nerve roots are located. The insulating portion18may also be used to position the cryoprobe10. When the insulating portion18abuts a bone or a disc, for example, the conductive portion12is in contact with surrounding tissues, such as sensitive nerve cells, where cellular destruction is desired. Positioning the temperature sensor26at the insulated tip72of the insulating portion18enables constant thermal monitoring of the surrounding tissues. Once the temperature sensor26detects the front of the ice ball of treated tissues24, that is when the temperature sensor26reads temperatures close to the freezing point, cryotherapy may be automatically stopped if the threshold temperature corresponds with the shut down temperature.

FIG. 7depicts a variant of the present embodiment where a sleeve64, closed at its distal extremity, is fitted to a standard cryoprobe66. The sleeve64comprises the insulated tip72, the conductive portion12and the grabbing portion16. Optionally, the grabbing portion16may be made of metal. However, in this case, gap is required between the standard cryoprobe66and the sleeve64in the grabbing portion16. As shown inFIG. 8, now concurrently referred to, this type of cryoprobe is particularly well adapted for cryosurgery of facets joints.

In a particular example, the insulated tip72may be 6 mm in diameter and made of an insulating material such as Teflon. An interior air chamber70may be provided for added insulation. The temperature sensor26is positioned on the insulated tip72, approximately 6 mm or more from the distal end of the insulated tip72. The conductive portion12is made of a conductive metal and is in contact with the standard cryoprobe66inside the sleeve64. The conductive portion12is also 6 mm in outside diameter. The length of the conductive portion12depends on the size of the desired treated tissue zone. The standard cryoprobe66may be 2 mm in diameter, and the insulated tip72may be 1 mm thick, which leaves 1 mm thickness for the air chamber70.

FIG. 9shows yet another embodiment of the present invention. A thermally conductive tip cover76is screwed to the insulating portion18. The tip cover76closely matches the external surface of a probe tip78such that heat transfer occurs between the probe tip78and the tip cover76. The temperature sensor26is precisely positioned with respect to the probe tip78due to the fact that the probe tip78bottoms out in the tip cover76.

Now turning toFIGS. 10aand10b, there is depicted yet another embodiment of the present invention where kits80are provided that comprise a plurality of sleeves64for fitting to a standard cryoprobe. InFIG. 10a, the kit comprises sleeves64having the insulating portions24. The sleeves64are provided with two opposed openings so that the standard cryoprobe protrudes through each sleeve64, such as described previously and shown inFIG. 4. The only difference between each sleeve64of the kit is that the temperature sensor26is placed at different longitudinal locations on the insulating portion18. Hence, a surgeon may select, prior to cryotherapy, the required sleeve64depending on the particular needs of the surgery, or depending on the patient. Similarly, inFIG. 10b, the kit80also comprises sleeves64. This time, the sleeves64are of a close-ended model where the insulating portion18corresponds to the insulating tip72. The sleeves64are adapted to fit a standard cryoprobe66(not shown in this Figure), such as described previously and shown inFIG. 7. The insulated tips74are differentiated from each other by the fact that the temperature sensors26are placed at different longitudinal locations from the conductive portion12, for the particular needs of a given cryosurgery. For convenience, the kit80, or the sleeves64themselves may carry an identification of an ice ball size for each sleeve64. The ice ball size may be a function of a predetermined body part tissue as the ice ball may grow differently depending on the body part tissue.

Surgery

When operating, the surgeon has to precisely monitor both the placement of the cryoprobe10into the patient's body and the growth of the ice ball of treated tissues24such as to avoid damaging fragile tissues. With the cryoprobes of prior art, MRI was often used as an imaging system. Advantageously, with the present invention, such costly techniques are not absolutely required since the controller36automatically shuts down the gas distribution module28, thereby not requiring continuous visual monitoring of the growth of the ice ball of treated tissues24by the surgeon. With the thermotherapy system of the present invention, less costly and more readily available imaging techniques such as fluoroscopy, diagnostic ultrasound, etc, can be used. Moreover, when using techniques other than MRI, the composition of the cryoprobe10is not restricted to non-ferromagnetic materials, which lowers its cost.

Reference is now made toFIG. 8. For facet cryosurgery, the cryoprobe10is inserted under local anaesthesia using a preliminary trocar through a 6 mm incision. For facet cryotherapy, the cryoprobe10is positioned on a posterior-inferior portion of foramina close to the nerve root for protection and the conductive portion12is placed alongside a lateral facet joint for joint denervation. Position is verified on both antero-posterior and lateral fluoroscopy.

The freezing process is then started: A first step of freezing takes place at −180° C. (temperatures colder than −140° C. are preferred) while monitoring the growth of the ice ball of treated tissues24with the temperature sensors26. The controller36shuts down the gas distribution module28when the first temperature threshold is reached, which normally takes approximately 7 minutes. The controller36maintains the gas distribution module28shut down for 2 minutes for passive thawing to occur. The controller36then turns on the gas distribution module28once again for a second step of freezing at −180° C. until a second temperature threshold is reached, which takes approximately another 7 minutes. The first and second threshold temperatures may be the same or different, depending on the desired results. To remove the cryoprobes10, heating the cryoprobes10for a few seconds is sometimes required. Stitches are then applied to the patient. The patient is encouraged to resume his normal activities rapidly and weak to moderate analgesia is necessary for the first week. Cryoprobe tract pain normally disappears after one to two weeks.

Discs Cryosurgery

Reference is now made toFIG. 5. For discs cryosurgery, 6 mm pointed trocars are inserted through a 6 mm skin puncture. The trocar is inserted bilaterally to postero-lateral corners of the targeted disc82at a 45 degrees angle from the skin at 10 cm from a midline under local anaesthesia with AP and lateral fluoroscopy. Through this trocar is inserted a 2 mm drill to perforate the annulus. The drill is then replaced by the cryoprobe10which conductive portion12penetrates 1-1.5 cm deep into the disc82. The insertion into the disc82is bottomed by a conic end of the insulating portion18. Typically, two cryoprobes10are used for disc cryosurgery, one on each side of the disc82. Both cryoprobes10should nearly meet in the middle of the disc82. The freezing process, similar to the one used for facets cryosurgery, is then started while monitoring treated tissues temperatures with the temperature sensors26is performed. To remove the cryoprobes10and the trocar, heating the cryoprobes10for a few seconds is sometimes required. A stitch is then applied to the skin once the cryoprobes10are removed and normal activities may be resumed shortly. Mild to moderate analgesia is prescribed for the first week.

While the invention has been described with particular reference to the illustrated embodiment, it will be understood that numerous modifications thereto will appear to those skilled in the art. For example, the assembly of some parts of the probe were depicted as a threaded assembly. However, the person skilled in the art would readily understand that this assembly could also be a snap-fit or other adequate assembly method, for example. Accordingly, the above description and accompanying drawings should be taken as illustrative of the invention and not in a limiting sense.