Abstract:
An electrosurgical instrument for ablating cartilage while limiting collateral damage includes a non-conducting head with a small electrically conductive surface. The head of the instrument is coupled to a shaft by a flexible portion. The flexible portion biases the electrically conductive surface towards a tissue surface. The head is pivotably coupled to the shaft such that the electrically conductive surface is oriented substantially parallel to the tissue surface as the head slides across the tissue surface. A method of performing electrosurgery includes positioning the electrically conductive surface adjacent to the tissue surface, and sliding the shaft across the tissue surface with the head pivoting such that the electrically conductive surface is oriented substantially parallel to the tissue surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/117,800, filed May 27, 2011, titled “Cartilage Treatment Probe”, now U.S. Pat. No. 8,377,058, which is a divisional of U.S. patent application Ser. No. 10/766,894, filed Jan. 30, 2004, titled “Cartilage Treatment Probe”, now U.S. Pat. No. 7,951,142, which claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No. 60/443,840, filed on Jan. 31, 2003, titled “Cartilage Treatment Probe.” The contents of the prior applications are hereby incorporated by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     This disclosure relates generally to a probe for treating cartilage. 
     BACKGROUND 
     Articular cartilage is prone to diseases, such as chondromalacia and osteoarthritis, which result in fibrillation, or fraying, of the cartilage. Damaged cartilage is not as effective in maintaining stiffness and resilience, and in minimizing stress due to load. The diseases tend to degenerate over time if left untreated, and can result in the total loss of articular cartilage in the joint. It is desirable to treat these diseases to re-establish a smooth, stable articular surface. 
     SUMMARY 
     Radio-frequency energy delivered through a low-mass or low-surface area electrode can be used to rapidly debride cartilage fibrillations and smooth and/or seal the cartilage surface while producing minimal collateral damage, which typically occurs in the form of chondrocyte death and/or the excess removal of healthy tissue. Chondrocytes are the cells that maintain cartilage viability and growth. These cells are killed when exposed to temperatures of 45° C. or more. After death, chondrocytes tend not to regenerate. 
     The probe may include one or more of the following features. A non-conducting bumper that limits removal of excess amounts of cartilage; a flexible tip that facilitates optimum articular surface contact by the electrode over complex geometries, providing good accessibility to the tissue site of interest and safe operation; and software controls are designed such that the device operates in the ablative mode and effects of poor technique or misuse are minimized. The probe preferably operates in an ablative mode, with most of the RF energy involved in debriding and smoothing and little excess energy available to heat collateral tissue and cause excessive chondrocyte death. 
     The probe includes, e.g., a shaft and an electrically conductive surface. In embodiments, the electrically conductive surface is pivotably coupled, directly or indirectly, to the shaft, and is on a head or bumper at a distal portion of the shaft. The instrument can include a flexible portion, which is part of, or attached to, the shaft. 
     According to an aspect of the invention, an electrosurgical instrument includes a shaft, a flexible portion, and a head coupled to the shaft through the flexible portion. The head also is pivotably coupled to the flexible portion. The head includes an electrically conductive surface and the flexible portion is configured to bias the electrically conductive surface towards a tissue surface. 
     Embodiments of this aspect may include one or more of the following features. 
     The flexible portion includes a nitinol wire, a nitinol tube, a spring, or a distal portion of the shaft. The distal portion is corrugated, or has a radial cross section similar to a radial cross section of the remainder of the shaft. The flexible portion is configured to flex in at least one direction and the head is configured to pivot about an axis substantially perpendicular to that direction. The head also is configured to pivot in three dimensions about the flexible portion, wherein the head and the flexible portion are coupled by a ball-and-socket joint. 
     The head includes a slot about which the head is configured to pivot. The slot is a transverse slot pivotably receiving the flexible portion or pivotably receiving a wire, which may be rigid, coupled to the flexible portion. Alternatively, a living hinge is disposed between the head and the flexible portion. The living hinge is adjacent to and connects the head and the flexible portion, and the living hinge includes a section that is thinner than portions of the head and the flexible portion that are adjacent to the living hinge. 
     The head includes a non-conductive surface arranged relative to the electrically conductive surface to limit penetration of the electrically conductive surface into the tissue surface. The non-conductive surface is substantially planar. The electrically conductive surface projects from the non-conductive surface or is substantially flush with the non-conductive surface. The electrically conductive surface has a smaller surface area than the non-conductive surface. 
     The head includes an electrode that includes the electrically conductive surface. The electrode has a T-shape or an L-shape. The instrument further includes a return electrode, wherein the electrically conductive surface and the return electrode are configured to be coupled to opposite poles of an electrosurgical generator. 
     In illustrated embodiments, the head includes a first portion and a second portion. The first portion includes a projection and the second portion defines a hole that receives the projection. The projection is deformed to secure the projection in the hole. The first portion includes a groove and the second portion includes a ridge aligned with the groove. In a particular embodiment, the head has a substantially parallelepiped shape. 
     In another particular embodiment, the instrument further includes a sheath coupled to the shaft and moveable to at least partially cover the flexible portion and the head. 
     According to another aspect, a method of performing electrosurgery includes positioning an electrically conductive surface of a head of an instrument adjacent to a tissue surface. The head is pivotable relative to a shaft of the instrument. The method includes moving the shaft relative to the tissue surface with the head pivoting such that the electrically conductive surface is oriented substantially parallel to the tissue surface. The method may include biasing the electrically conductive surface towards the tissue surface using a flexible portion of the instrument. 
     According to another aspect, an electrosurgical instrument includes a shaft and a head that is coupled to the shaft. The head includes an electrically conductive surface. The head is pivotable relative to the shaft such that the electrically conductive surface is oriented substantially parallel to the tissue surface as the head moves across the tissue surface. 
     According to another aspect, an electrosurgical instrument includes a shaft and a head that is coupled to the shaft and pivotable relative to the shaft. The head includes an electrically conductive portion, for treating tissue, positioned at only one side of the head. 
     According to another aspect, an electrosurgical instrument includes a shaft and a head that is coupled to the shaft and that includes an electrically conductive surface. The head is configured to pivot relative to the shaft and to slide across a tissue surface as the electrically conductive surface is moved across the tissue surface. 
     According to another aspect, a method of performing electrosurgery includes positioning an electrically conductive surface of a head of an instrument adjacent to a tissue surface. The head is pivotably coupled to a shaft. The method includes sliding the head across the tissue surface. The head pivots relative to the shaft to facilitate the sliding. 
     According to another aspect, a method of treating chondromalacia includes positioning an electrically conductive surface of a head of an instrument adjacent to a cartilage surface. The head is pivotable relative to a shaft of the instrument. The method includes moving the shaft relative to the cartilage surface. The head pivots relative to the cartilage surface. The method includes applying electrical energy to the electrically conductive surface to treat chondromalacia. 
     According to another aspect, an electrosurgical instrument includes a shaft, a resiliently flexible portion, and a head. The head is pivotably coupled to the resiliently flexible portion and the head is coupled to the shaft through the resiliently flexible portion. The head includes a substantially planar tissue contact surface including an electrically conductive portion. 
     Embodiments of this aspect may include one or more of the following features. The shaft defines a longitudinal axis and the head is offset from the axis. The resiliently flexible portion includes a distal portion of the shaft. The substantially planar contact surface includes a non-conductive portion. The non-conductive portion has a larger surface area than the electrically conductive portion. An electrical lead is coupled to the electrically conductive portion. 
     According to another aspect, an electrosurgical instrument includes a conducting mean for applying energy to a region of tissue. The instrument includes a flexing means coupled to the conducting means for biasing the conducting means towards the region of tissue. The instrument includes a pivoting means for pivoting the conducting means relative to the flexing means. 
     According to another aspect, an electrosurgical instrument includes a shaft, a conducting means for applying energy to a tissue surface, and a pivoting means for pivoting the conducting means relative to the shaft. 
     Embodiments of this aspect may include one or more of the following features. 
     The electrosurgical instrument includes flexing means coupled to the conducting means for biasing the conducting means towards the tissue surface. The flexing means includes a flexible portion. The flexible portion is configured to bias the conductive surface towards the tissue surface. The conducting means includes an electrically conductive surface. The pivoting means includes a head pivotably coupled to the flexing means, and the head includes the electrically conductive surface. 
     The electrosurgical instrument includes a resiliently flexible portion. The conducting means includes an electrically conductive surface. The pivoting means includes a head coupled to the shaft through the resiliently flexible portion and pivotably coupled to the resiliently flexible portion. The head includes a substantially planar tissue contact surface including the electrically conductive portion. 
     The conducting means includes an electrically conductive surface. The pivoting means includes a head coupled to the shaft and including the electrically conductive surface. The head is pivotable relative to the shaft such that the electrically conductive surface is oriented substantially parallel to the tissue surface as the head moves across the tissue surface. 
     The pivoting means includes a head that is coupled to the shaft and that is pivotable relative to the shaft. The conducting means includes an electrically conductive surface included on, and positioned at only one side of, the head. 
     The conducting means includes an electrically conductive surface. The pivoting means includes a head coupled to the shaft and including the electrically conductive surface. The head is configured to pivot relative to the shaft and to slide across the tissue surface as the electrically conductive surface is moved across the tissue surface. 
     According to another aspect, a method of performing electrosurgery includes positioning an electrically conductive surface of a head of an instrument adjacent to a tissue surface. The head is pivotable relative to a shaft of the instrument. 
     Embodiments of this aspect may include one or more of the following features. The method includes moving the shaft relative to the tissue surface with the head pivoting such that the electrically conductive surface is oriented substantially parallel to the tissue surface. The method includes sliding the head across the tissue surface. The head pivots relative to the shaft to facilitate the sliding. The method includes moving the shaft relative to a cartilage surface of the tissue surface. The head pivots relative to the cartilage surface. The method further includes applying electrical energy to the electrically conductive surface to treat chondromalacia. 
     The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side view of an embodiment of a cartilage treatment probe; 
         FIG. 2  is a side view of an active tip of the probe shown in  FIG. 1 ; 
         FIG. 3  is a top view of the tip shown in  FIG. 1 ; 
         FIG. 4  is a bottom view of the tip shown in  FIG. 1 ; 
         FIG. 5  is an end view of the tip shown in  FIG. 1 ; 
         FIGS. 6 and 7  show the tip of the probe shown in  FIG. 1  positioned on an articular surface; 
         FIG. 8  shows the tip of the probe shown in  FIG. 1  with an outer sheath of the probe advanced over the tip; 
         FIG. 9  is a side view of a second embodiment of a cartilage treatment probe; 
         FIG. 10  is a side view of a third embodiment of a cartilage treatment probe; 
         FIG. 11  is a top view of an upper bumper portion of the cartilage treatment probe of  FIG. 10 ; 
         FIG. 12  is a side view of the upper bumper portion of the cartilage treatment probe of  FIG. 10 ; 
         FIG. 13  is a front end view of the upper bumper portion of the cartilage treatment probe of  FIG. 10 ; 
         FIG. 14  is a top view of a lower bumper portion of the cartilage treatment probe of  FIG. 10 ; 
         FIG. 15  is a side view of the lower bumper portion of the cartilage treatment probe of  FIG. 10 ; 
         FIG. 16  is a front end view of the lower bumper portion of the cartilage treatment probe of  FIG. 10 ; 
         FIG. 17  is a side view of a fourth embodiment of a cartilage treatment probe; 
         FIG. 18  is an exploded perspective view of the cartilage treatment probe of  FIG. 17 ; 
         FIG. 19  is a side view of a fifth embodiment of a cartilage treatment probe; 
         FIG. 20  is a top view of the cartilage treatment probe shown in  FIG. 19 ; 
         FIG. 21  is a side view of a sixth embodiment of a cartilage treatment probe. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a cartilage treatment probe  10  includes a proximal section  12  for attachment to a radiofrequency power supply, a shaft  14 , and a distal, active tip  16 . Shaft  14  is formed from a stainless steel tube  17  (see  FIG. 3 ) covered with insulation, e.g., heat shrink tubing, which is surrounded by a sheath  18 . 
     Referring to  FIGS. 2 and 3 , tip  16  extends from a distal end  20  of shaft  14 . Tip  16  includes a bumper, or head,  22  formed from one or more electrically insulating materials, e.g., an electrically insulating ceramic or tetrafluorethylene (TFE) material, that has a generally planar tissue contacting surface  22   a . Bumper  22  defines a transverse slot  24  for pivotably coupling bumper  22  to a flexible portion, i.e., a nitinol wire form  26 . 
     As shown in  FIG. 4 , nitinol wire form  26  loosely resides in transverse slot  24 . Wire form  26  is in a super-elastic state, as explained below. Wire form  26  is held in place by a retainer disk  28  that is glued to bumper  22  or snaps into bumper  22 , allowing bumper  22  to pivot freely about nitinol wire form  26 . The proximal ends  30 ,  32  of wire form  26  are attached to distal end  20  of shaft  14 , such as by being inserted into distal end  20  of shaft  14  and crimped to stainless steel tube  17 . Bumper  22  pivots about an axis defined by wire form  26  that is substantially perpendicular to the longitudinal axis of shaft  14 , although this orientation can be varied. Nitinol wire form  26  is arranged so that, in a relaxed state, bumper  22  is offset from a longitudinal axis of shaft  14  by a distance D and by an angle a, as shown in  FIG. 2 , to facilitate accessing tissue with bumper  22 . 
     Referring again to  FIG. 2 , bumper  22  has a height H in the range of about 0.05 to 0.15 inches, preferably about 0.09 inches, a width W in the range of about 0.10 to 0.19 inches, preferably about 0.14 inches, and a length L in the range of about 0.10 to 0.30 inches, preferably about 0.20 inches. Bumper  22  is offset from the longitudinal axis of shaft  14  distance D in the range of about 0.01 to 0.40 inches, preferably about 0.15 inches. The distance D is measured from the longitudinal axis of shaft  14  to a line parallel to the longitudinal axis that intersects transverse slot  24 , as shown in  FIG. 2 . The angle a is approximately 30 degrees. Angle a can range from about 0 to 45 at least about degrees on either side of the longitudinal axis. 
     Referring again to  FIGS. 3 and 4 , tip  16  includes a “T” shaped electrode  34  having a stem  38  and a top  44 . Electrode  34  is made from an electrically conductive material, e.g., stainless steel flat stock or a wire form. Bumper  22  defines a hole  36  and stem  38  of the “T” is located in hole  36 . Soldered, or otherwise attached, to the end of stem  38  is a power lead  40 . Power lead  40  is a thin flexible conductor strip chosen for its flexibility and low profile. Proximal of tip  16 , power lead  40  is positioned between tube  17  and the heat shrink tubing surrounding tube  17 , and extends to the proximal end of probe  10  for connection to a cable running to the power supply. Bumper  22  also defines a cut-out  42  in tissue contacting surface  22   a , in which top  44  of the “T” resides to form an electrically conductive, active portion  46  of the electrode, for applying energy to tissue. Top  44 , which forms an electrically conductive surface of portion  46 , is substantially planar but other surface geometries can be used. 
     Referring to  FIG. 5 , top  44  of the “T” is positioned in bumper  22  such that electrically conductive portion  46  is flush with tissue contacting surface  22   a  or extends out from tissue contacting surface  22   a  by about 0.0003 to 0.004 inches. Portion  46  also can be recessed in tissue contacting surface  22   a  by about 0.0003 to 0.004 inches. The active, electrically conductive portion  46  of the electrode preferably has a small surface area in the range of about 0.0002 to 0.0065 square inches, preferably about 0.0009 to 0.0036 square inches, more preferably in the range of about 0.0016 to 0.0021 square inches, and most preferably about 0.0018 square inches. The surface area of portion  46  is substantially smaller than the surface area of tissue contacting surface  22   a , which can be, for example, in the range of about 0.01 to 0.057 square inches, preferably about 0.028 square inches. Bumper  22  acts as a physical barrier to limit the depth of penetration of electrode  34  into the tissue. Bumper  22  also masks portions of electrode  34 , except for portion  46 , to limit the direction of current flow from electrode  34 . Power lead  40  and stem  38  of electrode  34  are surrounded by an insulating material (not shown) such that portion  46  is exposed only on tissue contacting surface  22   a  of bumper  22 . 
     Referring to  FIGS. 6 and 7 , in use, probe  10  can be positioned adjacent to a tissue surface  50  to be treated, so that the electrically conductive surface of portion  46  is substantially parallel to tissue surface  50 . Radio frequency power is delivered to portion  46  from a radio frequency generator (not shown), such as, for example, the Vulcan® generator sold by Smith &amp; Nephew, Inc, Andover, Mass. As probe  10  is moved across tissue surface  50 , bumper  22  pivots freely about nitinol wire form  26  to facilitate tissue contacting surface  22   a  sliding across tissue surface  50  and the surface of electrically conductive portion  46  remaining substantially parallel to tissue surface  50 . Nitinol wire form  26 , which is extremely flexible in multiple directions, provides tip  16  with a range of flexibility relative to shaft  14  such that bumper  22  and the active, electrically conductive portion  46  of electrode  34  remains substantially in contact with articular tissue surface  50  while traveling over complex geometries. The resistance to deformation of the nitinol in its superelastic state is constant, providing a spring action that helps bumper  22  and the electrically conductive surface of portion  46  follow the curvature of tissue surface  50  while maintaining a controlled, approximately uniform contact pressure of the bumper  22  and electrode  34  against articular cartilage surface  50  over complex geometries as nitinol wire  26  is deflected. The spring action of nitinol wire  26  also biases bumper  22  towards tissue surface  50  when probe  10  is pressed towards tissue surface  50 . Nitinol wire  26  can be referred to as a spring, and other springs or spring materials, such as, for example, stainless steel spring wire, can be used. 
     Referring to  FIG. 8 , sheath  18  can be slid forward relative to stainless steel tube  17  to cover tip  16  to provide temporary rigidity to flexible tip  16  for insertion into and removal from the joint capsule. Sheath  18  includes ribs  52  ( FIG. 1 ) that facilitate grasping of sheath  18  to extend and retract sheath  18 . When covering tip  16 , sheath  18  also protects tip  16  and limits catching of tip  16  on tissue. 
     Power is preferably delivered to probe  10  under the control of an impedance feedback loop to maintain the probe in an ablative mode. In addition, since the impedance rises when the probe is not being moved across tissue, impedance feedback can be used to recognize when the probe is not being moved and controls can be used to turn off the power and/or sound an alarm. Probe  10  also can include one or more temperature sensors, such as a thermistor mounted in tip  16 , to monitor the temperature at or near tip  16 . The temperature sensors and the power generator can be coupled by a feedback control system that regulates the amount of energy delivered to the probe based on the temperature at or near tip  16 , in order to control the temperature of tissue surface  50 . These control systems can be implemented, for example, in software. 
     The use of a small surface area electrode allows the probe to function in an ablative mode at low power and provides for low thermal penetration into the tissue such that the extent of cell death can be maintained at preferably less than about 200 microns. This results in surface smoothing of the cartilage of the articular surface with minimal tissue removal and cell death. The use of probe  10  is indicated, e.g., for chondromalacia lesions Outerbridge System Grades II and III, as well as for stabilizing the rim of Grade IV lesions. It is believed that an additional benefit of the use of probe  10  is the sealing of articular surfaces to stop or slow down the degradation process of the cartilage. 
     Probe  10  has been shown as a monopolar device. A monopolar device has certain advantages over a bipolar device, such as the smaller size of the monopolar device facilitating access to small joint spaces, and the presence of only one electrode in the joint space so the user does not have to be concerned with inadvertent contact of a return electrode with tissue. However, the probe can be bipolar by incorporating a return electrode on the shaft or elsewhere on the probe, as discussed with respect to  FIG. 9  below. 
     Stainless steel tube  17  need not define a lumen along its entire length, but need only be able to receive ends  30  and  32  of the nitinol wire  26  to attach ends  30  and  32  to the distal end  20  of tube  17 . For example, tube  17  can be solid along the majority of its length, providing additional rigidity to the probe, and include one or two openings at distal end  20  of tube  17  into which ends  30  and  32  of nitinol wire  26  are inserted. 
     Referring to  FIG. 9 , an alternate embodiment of a cartilage treatment probe  900  includes an active tip  916  that attaches to distal end  20  of shaft  14 , as discussed above. Active tip  916  includes a bumper, or head,  922 , having a tissue contacting surface  922   a.  Tissue contacting surface  922   a  includes an electrically conductive surface  935  of an active electrode  930  for applying energy to tissue. Electrically conductive surface  935  is rounded and extends out from tissue contacting surface  922   a  a small amount, such as approximately 0.0003 to 0.004 inches. Alternatively, electrically conductive surface  935  can be flush with or recessed in tissue contacting surface  922   a Electrically conductive surface  935  has a surface area substantially smaller than tissue contacting surface  922   a , as discussed above. 
     Bumper  922  defines a transverse slot  924  that receives a nitinol wire  940 , or more generally a flexible member, for pivotably coupling bumper  922  to shaft  14 , as discussed above. A portion  942  of nitinol wire  940  is located in slot  924  and is surrounded by a sleeve  944  to facilitate pivoting of bumper  922  about nitinol wire  940 . Slot  924  is closed off with a non-conductive filler material  928 , which can be the same as or different from the material of bumper  922 , in order to hold nitinol wire  940  in slot  924 , while allowing bumper  922  to pivot about nitinol wire  940 . 
     Active electrode  930  is L-shaped and bumper  922  defines a corresponding L-shaped aperture  925  for receiving active electrode  930 . Also within L-shaped aperture  925 , a distal portion  952  of an active power lead  950  is soldered, or otherwise attached, to a top surface  934  of active electrode  930 . Distal portion  952  of active power lead  950  and top surface  934  of active electrode  930  are closed off by an electrically insulating filler  954 , which is the same or a different material than bumper  922 . Accordingly, active electrode  930  is exposed only at electrically conductive surface  935 , and bumper  922  includes an electrically conductive portion for treating tissue positioned at only one side (tissue contacting surface  922   a ) of bumper  922 . It should be understood that electrode  930  and aperture  925  can have any other suitable geometry that allows electrode  930  to be mounted to bumper  922 . 
     Shaft  14  also includes an electrically conductive surface of a return electrode  960  coupled to a return power lead  962 . Return electrode  960  is shown flush with the outer surface of shaft  14 , but return electrode  960  can project from or be recessed in shaft  14 . For example, shaft  14  can be formed by a stainless steel tube covered with insulation, and return electrode  960  can be disposed over the insulation. Another layer of insulation can be disposed over a portion of return electrode  960  and/or return power lead  962 . Return electrode  960  and/or return power lead  962  also can be formed from the stainless steel tube. 
     Active power lead  950  and return power lead  962  are coupled to opposite poles of a bipolar electrosurgical generator (not shown), such as the aforementioned Vulcan® generator. Thus, probe  900  operates in a bipolar mode with current mainly flowing from electrically conductive surface  935 , through or around the tissue surface, to return electrode  960 . It should be understood that return electrode can be located on another part of probe  10 , such as, for example, on bumper  22  or on nitinol wire  940 . 
     Referring to  FIG. 10 , an alternative embodiment of a cartilage treatment probe  1000  includes an active tip  1016  that attaches to distal end  20  of shaft  14 , as discussed above. Active tip  1016  includes a bumper, or head,  1022  having a tissue contacting surface  1022   a.  Tissue contacting surface  1022   a  of bumper  1022  includes an electrically conductive surface  1035  of an electrode  1030  for applying energy to tissue. Electrically conductive surface  1035  is rounded and is recessed within tissue contacting surface  1022   a  a small amount, such as approximately 0.0003 to 0.004 inches. Alternatively, electrically conductive surface  1035  can be flush with or extend from tissue contacting surface  1022   a , as discussed above. Electrically conductive surface  1035  also has a surface area substantially smaller than a surface area of tissue contacting surface  1022   a , as discussed above. 
     Bumper  1022  defines a transverse slot  1024  that receives a flexible portion  1040 , which is a nitinol wire, for pivotably coupling bumper  1022  to shaft  14 , as discussed above. Bumper  1022  includes an upper bumper portion  1060  ( FIGS. 11-13 ) and a lower bumper portion  1070  ( FIGS. 14-16 ). Upper bumper portion  1060  and lower bumper portion  1070  are made of the same or different non-conductive materials, such as ceramic or TFE. 
     Referring to  FIGS. 10-13 , upper bumper portion  1060  includes transverse slot  1024 , an upper mating surface  1062 , and a cylindrical projection  1064  projecting down from upper mating surface  1062 . Upper bumper portion  1060  also includes an upper electrode receiving aperture  1066  configured to receive a top portion  1034  of L-shaped electrode  1030  and an end portion  1052  of a power lead  1050 . As shown in  FIGS. 10 and 12 , upper electrode receiving aperture  1066  includes a rectangular portion  1067  intersecting upper mating surface  1062  and a tapered portion  1068  intersecting an upper surface  1022   b  of bumper  1022 . 
     Referring to FIGS.  10  and  14 - 16 , lower bumper portion  1070  includes tissue contacting surface  1022   a  and a lower mating surface  1072 . Lower bumper portion  1070  also includes a substantially round projection receiving hole  1074  for receiving projection  1064  of upper bumper portion  1060 . Hole  1074  includes a tapered section  1075  that tapers from a larger diameter at a point near tissue contacting surface  1022   a  to a smaller diameter approximately halfway through hole  1074 . Hole  1074  also includes a constant diameter section  1076  that extends from the point halfway through the hole  1076  to lower mating surface  1072  as discussed below. Lower bumper portion  1070  also includes a lower electrode receiving aperture  1078  for receiving a lower portion  1032  of L-shaped electrode  1030 . 
     Bumper  1022  is assembled by passing nitinol wire  1040  through slot  1024 , seating electrode  1030  as explained below, and aligning upper mating surface  1062  of upper portion  1060  and lower mating surface  1072  of lower portion  1070  such that projection  1064  passes through projection receiving hole  1074 . L-shaped electrode  1030  is seated in electrode receiving apertures  1066  and  1078  such that bottom portion  1032  is seated in lower aperture  1078  and top portion  1034  is seated in rectangular portion  1067  of upper aperture  1066 . Bottom portion  1032  of electrode  1030  is exposed at tissue contacting surface  1022   a  to form electrically conductive surface  1035 . Projection  1064  is heated to deform projection  1064  so that projection  1064  fills tapered section  1075  of projection receiving hole  1074  and locks upper bumper portion  1060  to lower bumper portion  1070 . In doing so, projection  1064  is made to be flush with tissue contacting surface  1022   a.    
     End portion  1052  of power lead  1050  passes through tapered portion  1068  and into rectangular portion  1067  of upper aperture  1066  and is electrically connected to electrode  1030  to transmit electrical energy to electrode  1030 . The portion of power lead  1050  outside of bumper  1022  is covered with an electrically insulating material. When assembled, only electrically conductive surface  1035  of electrode  1030  is exposed, on tissue contacting surface  1022   a  of bumper  1022 . Power lead  1050  is coupled to an electrosurgical generator (not shown) for delivering monopolar energy to electrically conductive surface  1035 . 
     Referring to  FIG. 17 , an alternative embodiment of a cartilage treatment probe  1700  includes an active tip  1716 . Active tip  1716  includes a flexible portion  1740 , a bumper, or head,  1722  and a living hinge  1745 . Flexible portion  1740  is coupled to distal end  20  of shaft  14  (e.g., as shown in  FIG. 1 ), such as by ultrasonic welding. Flexible portion  1740  is resiliently flexible, has a rectangular cross section, and is made of an elastic or superelastic material, such as plastic. Flexible portion  1740  biases bumper  1722 , as discussed above. 
     Bumper  1722  has a tissue contacting surface  1722   a , which includes an electrically conductive surface  1735  of an L-shaped electrode  1730  for applying energy to tissue. Electrically conductive surface  1735  is rounded, extends out from tissue contacting surface  1722   a  a small amount and has a surface area substantially smaller than a surface area of tissue contacting surface  1722   a , as discussed above. Alternatively, electrically conductive surface  1735  can be flush with or recessed in tissue contacting surface  1722   a , as discussed above. Electrode  1730  is exposed only at electrically conductive surface  1735  on tissue contacting surface  1722   a.    
     Referring to  FIGS. 17 and 18 , bumper  1722  includes a lower bumper portion  1770  and an upper bumper portion  1760 . Lower bumper portion  1770  and upper bumper portion  1760  are made of the same or different non-conductive materials, such as ceramic or TFE. Lower bumper portion  1770  includes a portion of tissue contacting surface  1722   a . Lower bumper portion  1770  is substantially T-shaped, including a distal portion  1772  and a proximal portion  1773 . Projecting laterally from proximal portion  1773  are lateral ridges  1774  (only one of which is shown). Distal portion  1772  includes an electrode receiving aperture  1776  for receiving a bottom portion  1732  of L-shaped electrode  1730 . 
     Upper bumper portion  1760  includes a top wall  1762  and lateral depending walls  1764  arranged in a U-shaped configuration when viewed from a distal end of bumper  1722 . Each of lateral depending walls  1764  terminate has a terminal end  1765  that forms a portion of tissue contacting surface  1722   a . An interior surface  1761  of each lateral depending wall  1764  defines a groove  1766  for receiving lateral ridges  1774  of lower bumper portion  1770 . An interior surface  1763  of top wall  1762  and interior surfaces  1761  define a space  1767  for receiving a top portion  1734  of L-shaped electrode  1730 . 
     Bumper  1722  is assembled by inserting bottom portion  1732  of L-shaped electrode  1730  into aperture  1776  in lower bumper portion  1770 . Proximal portion  1773  of lower bumper portion  1770  is inserted into upper bumper portion  1760  so that lateral ridges  1774  are aligned with or fit into grooves  1766 , and top portion  1734  of electrode  1730  is received in space  1767  defined by interior surfaces  1761  and  1763 . Upper bumper portion  1760  and lower bumper portion  1770  are locked together by friction fit or by other means such as, for example, an adhesive. Assembled bumper  1722  defines a rear opening  1768  configured to receive a power lead (not shown) for attachment to electrode  1730 . The remaining space between electrode  1734  and interior surfaces  1731 ,  1733  is filled with a non-conductive material, such as, for example, a ceramic or plastic epoxy. 
     Bumper  1722  is pivotably coupled to flexible portion  1740  by a living hinge  1745  disposed between flexible portion  1740  and bumper  1722 . Living hinge  1745  includes a thin section  1747  of material integral with flexible portion  1740  and bumper  1722 . Thin section  1747  has a thickness of approximately 0.006 inches, although other dimensions can be used. Flexible portion  1740 , upper bumper portion  1760 , and living hinge  1745  are, for example, molded from a single piece of material. Living hinge  1745  is composed of a flexible material, such as, for example, polypropylene or polyethylene, that can flex a large number of times without failure. Living hinge  1745  allows bumper  1722  to pivot relative to flexible portion  1740 , about thin section  1747  as shown by arrow  1780 . 
     Referring to  FIGS. 19 and 20 , an alternate embodiment of a cartilage treatment probe  1900  includes a shaft  1914 , a wire  1980 , and a bumper, or head,  1922 . Bumper  1922  is indirectly pivotably coupled to a flexible distal portion  1940  of shaft  1914  by wire  1980 . Rather than wire  1980  being resiliently flexible, wire  1980  is made from a rigid material, such as stainless steel or plastic, and flexibility is provided by flexible distal portion  1940  of shaft  1914 . Flexible distal portion  1940  includes a plurality of cutouts  1942  to form a resiliently flexible, corrugated structure. At points between adjacent cutouts  1942 , flexible distal portion  1940 , has a radial (or transverse) cross-section that is circular and that is substantially similar to the radial cross-section of the remainder of shaft  1914  proximal of flexible portion  1940 . 
     Bumper  1922  can be, for example, any of bumpers  22 ,  922 ,  1022 , or  1722  and includes an electrode (not shown). Bumper  1922  is pivotably coupled to wire  1980 , as discussed above. Wire  1980  is bent so that bumper  1922  is offset from a longitudinal axis of shaft  1914  a distance, as discussed above, to facilitate accessing a tissue surface with a tissue contacting surface  1922   a  of bumper  1922 . Bumper  1922  is generally parallel to the longitudinal axis, but could be offset by an angle, as discussed above, such as by making flexible portion  1940  curved. 
     Referring to  FIG. 21 , an alternative embodiment of a cartilage treatment probe  2100  includes an active tip  2116  having a bumper, or head,  2122 , pivotably coupled to a resiliently flexible portion  2140 . Bumper  2122  includes an upper bumper portion  2160  and a lower bumper portion  2170 , each made of a non-conductive material, such as ceramic or plastic. Upper bumper portion  2160  and lower bumper portion  2170  are joined to one another, for example, by applying an adhesive, brazing, or ultrasonic welding, or by one of the other mechanisms discussed above. Flexible portion  2140  is coupled to shaft  14 , as discussed above. 
     Lower bumper portion  2170  includes a tissue contacting surface  2122   a  and an L-shaped recess  2172  for receiving an L-shaped electrode  2130 , as discussed above. L-shaped electrode  2130  includes an electrically conductive surface  2135  that is flush with tissue contacting surface  2122   a . Alternatively, an electrically conductive surface  2135   a  projects from tissue contacting surface  2122   a  or an electrically conductive surface  2135   b  is recessed in tissue contacting surface  2122   a . Electrically conductive surface  2135  has a surface area substantially smaller than tissue contacting surface  2122   a.    
     Upper bumper portion  2160  defines a recess  2162  and a cavity  2164  that receives, in mating relationship, a substantially dome-shaped member  2166 . Member  2166  is fixedly attached to a distal end of flexible member  2140 , which is, for example, a nitinol tube. Member  2166  and cavity  2164  function like a ball-and-socket joint, allowing bumper  2122  to pivot in three dimensions about dome shaped member  2166  and flexible member  2140 . The three-dimensional pivoting facilitates the sliding of tissue contacting surface  2122   a  across a tissue surface having a complex geometry while the surface of electrically conductive portion  2135  remains substantially parallel to the tissue surface. It should be understood that member  2166  and/or cavity  2164  can include stops or can be shaped differently so as to allow for more or less freedom of movement. Further, recess  2162  and cavity  2164  can be positioned in upper bumper portion  2160 , for example, more proximally or distally than shown. 
     Extending through flexible member  2140  and through an aperture  2155  in member  2166  is a power lead  2150 . A distal end portion  2152  of power lead  2150  is electrically coupled to L-shaped electrode  2130  to deliver energy to electrically conductive surface  2135 . Distal end portion  2152  has sufficient slack to avoid breaking or disconnecting from electrode  2130  while bumper  2122  pivots relative to flexible portion  2140 . A proximal end of power lead  2150  is coupled to an electrical energy source (not shown), as discussed above. It should be understood that power lead  2150  can be coupled to electrode  2130  without passing through flexible member  2140 . 
     A number of embodiments have been described. Nevertheless, it will be understood that various modifications can be made. For example, the bumper can be directly or indirectly pivotably coupled to the shaft. In addition, the bumpers can have any suitable number of sides arranged in any suitable shape, such as a parallelepiped, a triangular prism or a half dome with a planar tissue contacting surface. Also, in bumper  1022 , projection  1064  can be deformed by a method other than heating, such as, for example, by mechanical deformation. Moreover, upper bumper portion  1060  and lower bumper portion  1070  can be joined by another mechanism such as friction fit, press fit, or adhesive, or can be made as a single piece. Flexible portions  26 ,  940 , and  1040  can be a nitinol wire not in a superelastic state, or can be another elastic or superelastic component, such as a stainless steel or plastic spring. Both the shaft and the nitinol wire can be resiliently flexible to provide additional flexibility. In addition, the flexing action of the flexible portion can be in a direction other than that shown. Likewise, the bumper can pivot about an axis in a different direction than the direction shown. Also, the proximal ends of flexible portions  26 ,  940 ,  1040 , and  1740  can be attached to the shaft by any suitable means, such as, for example, by crimping, welding, or press-fitting. The electrodes can be made of any biocompatible electrically conductive material, such as, for example, stainless steel, tungsten, gold, silver, or platinum. The electrically conductive surface of an embodiment can, for example, be flush from the tissue contacting surface, project from the tissue contacting surface, or be recessed in the tissue contacting surface. In addition, the electrically conductive surfaces can be, for example, planar or curved. Moreover, the probe can include more than one electrically conductive surface and/or return electrode, such as, for example an array of electrically conductive surfaces on the bumper. The features described for the various embodiments are non-limiting. Further these features can be combined or interchanged with one another, as well as deleted and supplemented. Accordingly, these and other embodiments are within the scope of the following claims.