Abstract:
Apparatus and methods are described, including a method for treating a paranasal sinus of a subject. The method includes forming an artificial hole in a wall of the paranasal sinus, and, via the artificial hole, opening a natural ostium of the paranasal sinus. Other applications are also described.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a divisional of U.S. application Ser. No. 13/189,896 to Gross et al., entitled “Sinus Stent,” filed Jul. 25, 2011, which published as US 2013/0030545 (now U.S Pat. No. 8,998,985) and is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     Applications of the present invention relate generally to treatment of sinus disorders, and specifically to implantable medical devices for treating sinus disorders. 
     BACKGROUND 
     Sinusitis is a common condition, characterized by symptoms such as nasal discharge, facial and ear pressure and pain, headache, loss of smell, fever, cough and fatigue. Physiological clearing of paranasal sinuses is via mucociliary transport through the ostia (natural sinus openings into a nasal cavity). Disruption of this function, often associated with partial blockage of an ostium, allows stagnation of mucous secretions and alteration of pH and other physiologic parameters, making the sinus conditions more favorable to microbiological growth and, therefore, susceptible to sinusitis. Treatment of chronic sinusitis typically includes antibiotics, steroids, decongestants and, in some cases, surgical procedures such as lavage. 
     SUMMARY OF THE INVENTION 
     In some applications of the invention, a hole-forming member is coupled to an implant. The hole-forming member forms a hole in a bone wall of a sinus, and facilitates implantation of the implant in the formed hole. The apparatus disclosed according to these applications of the invention allows hole-forming and implantation to be performed conveniently. Several versions of the implant are described, each being shaped to define a lumen which, following implantation, provides communication between the sinus and the nasal cavity of the subject. This allows drainage from the sinus, access to the sinus by medical instruments, and the possibility of administering therapeutic substances to the sinus. Typically, the implant is left in place for at least several days, allowing repeated access to the sinus without the need for repeated hole-forming. 
     In some applications of the invention, the paranasal sinus implant is self-tapping. In these applications, no separate hole-forming member is used. 
     In some applications of the invention, a stent is implanted in a natural sinus ostium in order to treat sinusitis. The stent is typically implanted using a balloon catheter, which is inserted into the sinus ostium, typically via an artificial hole in the bone wall of the sinus. For example, the insertion of the stent into the sinus ostium is performed following implantation of an implant with a lumen, as described above. The stent is positioned in the ostium while in a compressed configuration on the balloon of the balloon catheter. Inflation of the balloon expands the stent, which remains expanded after the balloon is deflated and removed, thereby holding the ostium in an open configuration. Alternatively, the stent may be delivered to the ostium in a contracted form, such as within a sheath, expanding upon removal of the sheath. 
     In some applications of the invention, a rivet implant is implanted in an anatomical wall or other tissue of a subject. The rivet implant typically acts as a blind rivet. Deformation of a distal portion of the implant secures the implant in the tissue. 
     In some applications of the invention, a cauterizing hole-forming member is used to form the hole in the wall of the sinus. The wall of the sinus includes a bone layer and membranous layers. In these applications of the invention, the hole-forming member comprises a drill bit slidably coupled to at least one radio frequency (RF) electrode, the drill bit being configured to penetrate the bone layer and the RF electrodes being configured to penetrate and cauterize the membranous layers. Axially sliding the drill bit and RF electrodes with respect to each other allows penetration of the appropriate layer with the respective appropriate component of the hole-forming member. 
     There is therefore provided, in accordance with an application of the present invention, paranasal sinus apparatus including:
         a hole-forming member configured to form a hole through a wall of a paranasal sinus of a subject; and   an implant having a proximal end, a distal end, and shaped to define a lumen, the implant:
           being couplable to the hole-forming member,   being securable to the wall and extendable through the hole, such that the proximal end is disposed external to the paranasal sinus and the distal end is disposed within the paranasal sinus, and   including a biodegradable material.   
               

     In an application, at least part of the hole-forming member is disposable within the lumen of the implant, and the implant is slidably movable over at least part of the hole-forming member. 
     In an application, the apparatus includes a tube, disposable within the lumen of the implant, and the implant is slidably movable over the tube. 
     In an application, at least part of the implant is disposable within a void defined by the hole-forming member, and the implant is slidably movable through at least part of the hole-forming member. 
     In an application, the apparatus includes a tube, disposable within the lumen of the implant, and the hole-forming member is disposable within the tube, and the hole-forming member is slidably movable within the tube. 
     In an application, the hole-forming member is configured to form the hole in a wall that is a part of a maxilla of the subject that divides a nasal cavity of the subject and a maxillary sinus of the subject, and the implant has a length appropriate to extend through the hole in the bone wall. 
     In an application, the hole-forming member includes a drill bit. 
     In an application, the hole-forming member includes a piercing device. 
     In an application, the hole-forming member includes an ultrasonic drill. 
     In an application, the hole-forming member includes a water jet cutter. 
     In an application, the hole-forming member includes a laser cutter. 
     In an application, the implant is securable to the wall in an irreversible manner. 
     In an application, the implant is securable to the wall in a reversible manner. 
     In an application, the hole-forming member is coupled to the implant. 
     In an application, the hole-forming member is decouplable from the implant. 
     In an application, the implant is shaped to define the lumen, the lumen having a diameter sufficient to allow flow of liquid secretions from the distal end to the proximal end of the implant. 
     In an application, the implant is shaped to define the lumen, the lumen having a diameter of between 0.5 mm and 15 mm (e.g., at least 0.5 mm and/or less than 2 mm; at least 2 mm and/or less than 6 mm; or at least 6 mm and/or less than 15 mm). 
     In an application, the implant has a length of between 1 mm and 30 mm (e.g., at least 1 mm and/or less than 4 mm; at least 4 mm and/or less than 12 mm; or at least 12 mm and/or less than 30 mm). 
     In an application, the apparatus includes a medical instrument, passable through the lumen of the implant. 
     In an application, the apparatus includes a control unit and a radio frequency electrode, wherein: 
     the hole-forming member is couplable to the radio frequency electrode, 
     the radio frequency electrode is couplable to the control unit, and 
     the control unit is configurable to drive a radio frequency current through the electrode. 
     In an application, the control unit is configured to configure the current to reduce bleeding from tissue in a vicinity of the hole formed by the hole-forming member. 
     In an application: 
     the apparatus further includes a control unit, 
     the hole-forming member includes a radio frequency electrode, couplable to the control unit, and 
     the control unit is configured to drive a radio frequency current through the electrode. 
     In an application, the control unit is configured to configure the current to form the hole through at least a part of the wall of the paranasal sinus of the subject. 
     In an application, the hole-forming member further includes a drill bit, slidably coupled to the radio frequency electrode. 
     In an application, the apparatus further includes a cooling element, configured to apply cooling in conjunction with forming the hole by the hole-forming member. 
     In an application, the cooling element is configured to apply the cooling at least prior to the forming of the hole by the hole-forming member. 
     In an application, the cooling element is configured to apply the cooling to a site of forming of the hole by the hole-forming member. 
     In an application, the cooling element includes a compressed gas. 
     In an application, the cooling element includes a cooled liquid. 
     In an application, the cooling element is configured to apply the cooling to the hole-forming member. 
     In an application, the cooling element is coupled to the hole-forming member. 
     There is further provided, in accordance with an application of the present invention, paranasal sinus apparatus including:
         an implant, the implant:
           having a length of between 1 mm and 30 mm (e.g., at least 1 mm and/or less than 4 mm; at least 4 mm and/or less than 12 mm; or at least 12 mm and/or less than 30 mm),   being shaped to define a lumen, and the lumen has a diameter of between 0.5 mm and 15 mm (e.g., at least 0.5 mm and/or less than 2 mm; at least 2 mm and/or less than 6 mm; or at least 6 mm and/or less than 15 mm),   having a proximal portion, a middle portion and a distal portion, each portion has an external diameter, and the external diameter of the middle portion is between 1 mm and 20 mm (e.g., at least 1 mm and/or less than 4 mm; at least 4 mm and/or less than 10 mm; and/or at least 10 mm and/or less than 20 mm); and   
           a hole-forming member, couplable to the implant and configured to form a hole in a wall of a paranasal sinus of a subject.       

     In an application, at least part of the hole-forming member is disposable within the lumen of the implant, and the implant is slidably movable over at least part of the hole-forming member. 
     In an application, the apparatus includes a tube, disposable within the lumen of the implant, and the implant is slidably movable over the tube. 
     In an application, the hole-forming member is coupled to the implant. 
     In an application, the hole-forming member is decouplable from the implant. 
     In an application, the implant is securable to the wall of the paranasal sinus of a subject. 
     In an application, the implant is securable to a wall that is a part of a maxilla of the subject that divides a nasal cavity of the subject and a maxillary sinus of the subject. 
     In an application, the implant is securable to the wall in an irreversible manner. 
     In an application, the implant is securable to the wall in a reversible manner. 
     In an application, the implant includes a biodegradable material. 
     In an application, the implant is entirely biodegradable. 
     In an application, the apparatus includes a tube, disposable within the lumen of the implant, the hole-forming member is disposable within the tube, and the hole-forming member is slidably movable within the tube. 
     In an application, the hole-forming member includes a drill bit. 
     In an application, the hole-forming member includes a piercing device. 
     In an application, the hole-forming member includes an ultrasonic drill. 
     In an application, the hole-forming member includes a water jet cutter. 
     In an application, the hole-forming member includes a laser cutter. 
     In an application, the apparatus includes a control unit and a radio frequency electrode, wherein: 
     the hole-forming member is couplable to the radio frequency electrode, 
     the radio frequency electrode is couplable to the control unit, and 
     the control unit is configurable to drive a radio frequency current through the electrode. 
     In an application, the control unit is configured to configure the current to reduce bleeding from tissue in a vicinity of the hole formed by the hole-forming member. 
     In an application: 
     the apparatus further includes a control unit, 
     the hole-forming member includes a radio frequency electrode, couplable to the control unit, and 
     the control unit is configured to drive a radio frequency current through the electrode. 
     In an application, the control unit is configured to configure the current to form the hole through at least part of the wall of the paranasal sinus of the subject. 
     In an application, the hole-forming member further includes a drill bit and 
     In an application, the apparatus further includes a cooling element, the cooling element being configured to apply cooling in conjunction with formation of the hole by the hole-forming member. 
     In an application, the cooling element is configured to apply the cooling at least prior to formation of the hole by the hole-forming member. 
     In an application, the cooling element is configured to apply the cooling to a site of formation of the hole by the hole-forming member. 
     In an application, the cooling element includes a compressed gas. 
     In an application, the cooling element includes a cooled liquid. 
     In an application, the cooling element is configured to apply the cooling to the hole-forming member. 
     In an application, the cooling element is coupled to the hole-forming member. 
     There is further provided, in accordance with an application of the present invention, paranasal sinus apparatus including: 
     a blind rivet implant, shaped to define a lumen and having a proximal end and a distal end, the implant:
         having a length appropriate to extend through a hole in a wall of a paranasal sinus of a subject so that the proximal end is disposed external to the paranasal sinus and the distal end is disposed within the paranasal sinus,   being securable to the wall, and   including at a distal region of the implant a buck-tail, being deformable from a first shape to a second shape, the geometry of the first shape permitting passage of the distal region through the hole in the wall of the paranasal sinus, and the geometry of the second shape preventing such passage; and       

     an applicator, shaped so that a distal region of the applicator is disposable within the lumen of the implant, the applicator being removable from the implant. 
     In an application, the apparatus includes a restraint disposable within the lumen of the implant, wherein: 
     the applicator is couplable to the restraint, 
     the first shape of the buck-tail is a constrained shape and the second shape of the buck-tail is an unconstrained shape, 
     the restraint is configured to retain the buck-tail in the first shape when the restraint is disposed within the lumen of the implant, and 
     the buck-tail is configured such that it moves from the first shape to the second shape upon removal of the restraint from the implant. 
     In an application: 
     the first and second shapes of the buck-tail are unconstrained shapes, and 
     the buck-tail and the distal region of the applicator are configured such that a force applied to the buck-tail by the distal region of the applicator deforms the buck-tail from the first shape to the second shape. 
     In an application, the length appropriate to extend through the hole in the wall of the paranasal sinus of the subject is a length appropriate to extend through an artificial hole in a wall that is a part of a maxilla of the subject that divides a nasal cavity of the subject and a maxillary sinus of the subject. 
     In an application, the implant is securable to the wall of the subject in an irreversible manner. 
     In an application, the implant is securable to the wall of the subject in a reversible manner. 
     In an application, the lumen of the implant has a diameter sufficient to allow flow of liquid secretions from the distal end to the proximal end of the implant. 
     In an application, the lumen of the implant has a diameter of between 0.5 mm and 15 mm. 
     In an application, the implant has a length of between 1 mm and 30 mm. 
     In an application, the implant includes a biodegradable material. 
     In an application, the implant is entirely biodegradable. 
     In an application, the apparatus includes a medical instrument, passable through the lumen of the implant. 
     In an application, the medical instrument includes at least one instrument selected from the group consisting of: an endoscope, an aspirator, and a syringe. 
     There is further provided, in accordance with an application of the present invention, paranasal sinus apparatus including: 
     An implant, implantable in a wall of a paranasal sinus of a subject, and shaped to define a lumen; 
     a catheter slidable through the lumen of the implant; 
     a balloon, couplable to a distal portion of the catheter; and 
     an expandable stent, slidable through the lumen of the implant, shaped to define a lumen, and configured such that it may be expanded from a first shape to an expanded shape by an applied force, 
     the balloon being inflatable via the catheter, and disposable within the lumen of the expandable stent such that inflation of the balloon expands the expandable stent, and 
     the expandable stent being maintainable in the expanded shape when the balloon is deflated. 
     In an application, the balloon is coupled to the distal portion of the catheter. 
     In an application, the stent includes a biodegradable material. 
     In an application, the apparatus further includes a guidewire, and the catheter is advanceable over the guidewire. 
     There is further provided, in accordance with an application of the present invention, a method for implanting an implant in a wall of a paranasal sinus of a subject, the implant being shaped to define a lumen, the method including: 
     coupling a hole-forming member to a portion of a body of the subject; 
     forming a hole at a site on the wall of the paranasal sinus using the hole-forming member, while the hole-forming member is coupled to the implant; and 
     while the hole-forming member is coupled to the portion of the body of the subject, inserting at least part of the implant into the hole. 
     In an application, at least part of the hole-forming member is disposable within the lumen of the implant and the implant is slidably couplable to the hole-forming member, and inserting at least part of the implant into the hole includes sliding the implant along at least part of the hole-forming member. 
     In an application, at least part of the implant is disposable within a void defined by the hole-forming member, and inserting at least part of the implant into the hole includes sliding the implant through at least part of the hole-forming member. 
     In an application, forming the hole at the site on the wall of the paranasal sinus includes forming a hole at a site on a wall that is between a nasal cavity and a maxillary sinus of the subject. 
     In an application, forming the hole at the site on the wall of the paranasal sinus includes forming the hole at a site that is inferior to an inferior turbinate of a lateral nasal wall. 
     In an application, the implant has a proximal end and a distal end, and inserting at least part of the implant into the hole includes inserting the implant such that the proximal end is disposed external to the paranasal sinus and the distal end is disposed within the paranasal sinus. 
     In an application, the method includes facilitating drainage of material from the sinus via the lumen of the implant. 
     In an application, the method includes administering a substance to the sinus via the lumen of the implant. 
     In an application, inserting at least part of the implant into the hole includes inserting at least part of an implant that includes a biodegradable material into the hole. 
     In an application, inserting at least part of the implant into the hole includes advancing the hole-forming member distally. 
     In an application, inserting at least part of the implant into the hole includes pushing the implant using the hole-forming member. 
     In an application, the method further includes applying cooling in conjunction with forming the hole using the hole-forming member. 
     In an application, applying cooling includes applying cooling to the hole-forming member. 
     In an application, applying cooling includes applying cooling at least prior to the forming of the hole using the hole-forming member. 
     In an application, applying cooling includes applying cooling to the site on the wall. 
     In an application, applying cooling includes applying cooling at least prior to the forming of the hole using the hole-forming member. 
     In an application, applying cooling includes expanding a compressed gas. 
     In an application, applying cooling includes applying a liquid. 
     There is further provided, in accordance with an application of the present invention, a method for implanting an implant in a subject, the method including: 
     inserting the implant through a hole in a tissue of the subject, the implant being configured to act as a blind rivet and including a buck-tail at a distal region of the blind rivet; and 
     deforming the buck-tail from a first shape that allows passage of the buck-tail through the hole into a second shape that does not allow passage of the buck-tail through the hole. 
     In an application, deforming the buck-tail includes applying a deforming force. 
     In an application, deforming the buck-tail includes removing a restraint. 
     In an application, the implant is shaped to define a lumen, and the method further includes facilitating drainage of the sinus via the lumen of the implant. 
     In an application, the implant is shaped to define a lumen, and the method further includes administering a substance to the sinus via the lumen of the implant. 
     In an application, inserting the implant through the hole includes inserting the implant through a hole in an anatomical wall of the subject. 
     In an application, inserting the implant through the hole in the anatomical wall of the subject includes inserting the implant through a hole in a wall of a hollow organ of the subject. 
     In an application, inserting the implant through the hole in the anatomical wall includes inserting the implant through a hole in a wall of a maxillary sinus of the subject. 
     In an application, the method further includes forming the hole. 
     In an application, forming the hole includes forming the hole with the implant. 
     There is further provided, in accordance with an application of the present invention, a method for implanting a stent in a natural ostium of a paranasal sinus of a subject, the method including: 
     inserting the stent into the paranasal sinus via an artificial hole in a wall of the sinus, 
     placing the stent in the ostium from inside of the sinus; and 
     securing the stent in the ostium by expanding the stent. 
     In an application, inserting the stent into the paranasal sinus includes inserting the stent into a maxillary sinus of the subject. 
     In an application, inserting the stent into the sinus via the artificial hole includes inserting the stent into the sinus via a lumen of an implant implanted in the hole. 
     There is further provided, in accordance with an application of the present invention, a method for forming a hole in a multilayered tissue of a subject, the method including: 
     forming a hole in one layer of the tissue of the subject with a drill bit, the drill bit being slidably coupled to a radio frequency electrode; 
     forming a hole in another layer of the tissue of the subject with the radio frequency electrode; and 
     axially sliding the radio frequency electrode with respect to the drill bit. 
     In an application, the multilayered tissue of the subject includes a bone layer and at least one membrane layer, and forming the hole in the one layer includes forming a hole in the bone layer, and wherein forming the hole in the other layer includes forming a hole in the membrane layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-B  are schematic illustrations of apparatus for forming a hole in a wall of a paranasal sinus and implanting a paranasal sinus implant in the hole, in accordance with respective applications of the invention; 
         FIG. 2  is a schematic illustration of a paranasal sinus implant, secured in the hole in the wall of the paranasal sinus, in accordance with an application of the invention; 
         FIG. 3  is a schematic illustration of access of a medical instrument to the paranasal sinus via the paranasal sinus implant, in accordance with an application of the invention; 
         FIGS. 4A-E  are schematic illustrations of the hole-forming member used to form a hole in the bone wall of a paranasal sinus, in accordance with respective applications of the present invention; 
         FIGS. 5A-E  are schematic illustrations of a paranasal sinus implant, in accordance with respective applications of the present invention; 
         FIGS. 6A-B  are schematic illustrations of two sequential steps in the implantation of a rivet implant, in accordance with an application of the invention; 
         FIG. 7  is a schematic illustration of the implantation of an expandable stent in a sinus ostium, in accordance with an application of the invention; and 
         FIGS. 8A-C  are schematic illustrations of sequential steps in the formation of a hole in the wall of the paranasal sinus with a cauterizing hole-forming member, in accordance with an application of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Reference is made to  FIG. 1A , which illustrates a therapeutic approach, in accordance with one application of the invention. The figure includes an anatomical representation showing paranasal sinuses located within the head of a subject. Between the eyes are ethmoid sinuses  22 . Located behind the cheek are maxillary sinuses  24 . Within nasal cavity  38  are middle turbinate  28  and inferior turbinate  30 . Separating nasal cavity  38  from maxillary sinus  24  is bone wall  32 , which is part of the maxilla bone of the skull. The sinus cavities have a mucosal lining  36  over the bone. The figure illustrates pus  34  present in sinuses due to sinusitis. The maxillary sinus ostia  26  are located high on the wall of the sinus cavity. Therefore drainage of the sinuses is not aided by gravity, making the maxillary sinuses particularly susceptible to sinusitis. 
     A hole-forming member  50  is inserted through nasal cavity  38  at an angle such that it contacts bone wall  32 , and is operated to form a hole  40  in bone wall  32 , below the inferior turbinate. Hole  40  thereby becomes an opening into maxillary sinus  24 . For some applications, hole-forming member  50  itself enters bone wall  32 . As hole-forming member  50  is advanced into hole  40 , an implant  52  is pushed into the hole, optionally accompanied by sliding of the implant along the hole-forming member, typically until a shoulder  102  of the implant meets the surface of the bone wall. For other applications, hole-forming member  50  does not itself penetrate the bone wall. In such a case, implant  52  is typically inserted into hole  40  by sliding it along hole-forming member  50 . 
     Reference is made to  FIG. 1B , which illustrates an alternative application of the invention. Hole-forming member  50  is disposed within a sleeve  54  which, itself, fits within the lumen of implant  52 . Sleeve  54  is placed in contact with bone wall  32 ; this contact is maintained throughout some or all of the procedure. For example, sleeve  54  may be pressed against the bone, and may have anchors (e.g., sharp protrusions) which enter the bone. Hole-forming member  50  is extended through sleeve  54  and forms hole  40 . Alternatively, hole-forming member  50  is disposed at a fixed position within sleeve  54 . (Examples of versions of hole-forming member  50  are included in  FIGS. 5A-E .) 
       FIG. 2  illustrates implant  52  secured in bone wall  32  of maxillary sinus  24 , following the removal of hole-forming member  50 , in accordance with an application of the present invention. Implant  52  is shaped to define a lumen. A distal end of the implant is disposed in maxillary sinus  24 , and a proximal end is disposed in nasal cavity  38 , thus providing communication between the sinus and the nasal cavity. An application of the invention is the implantation of implant  52  in order to facilitate passage of secretions and gaseous exchange between the sinus and nasal passage. Such passage may be passive, such as by circulation of a gas, or by gravity-driven drainage, or the passage may be actively induced by a medical practitioner, using a medical device, for example as described with reference to  FIG. 3 . 
     In some applications of the invention, implantation of implant  52  is performed in combination with other procedures such as functional endoscopic sinus surgery (FESS), orthognathic surgery, and treatment of facial fractures and nasal polyps. Implant  52  may be used to facilitate the procedure (e.g., by improving access), or to facilitate pre- or post-procedure treatments, such as the application of therapeutic substances. 
     In some applications of the invention, hole-forming member  50  (e.g., drill  150 ) is hollow, or shaped to define a void. Implant  52  is typically disposed within the hollow or void while hole  40  is formed by the hole-forming member. Implant  52  is then moved out of the void, distally, typically by sliding the implant through hole-forming member  50 . Implant  52 , or a part thereof (e.g., wings  104 , described with reference to  FIG. 5A ) expands within hole  40 , securing the implant in place. 
     In some applications of the invention, implant  52  is self-tapping, comprising a self-tapping screw-thread. In these applications of the invention, no independent hole-forming member is required. Rather, implant  52  is pushed against bone wall  32  and rotated such that it cuts into, and becomes implanted in, the bone wall. 
     Reference is now made to  FIG. 3 , which is a schematic illustration of a medical instrument  70  being inserted through the lumen of implant  52 , in accordance with an application of the present invention. The implantation of implant  52  may allow repeated access by medical instruments  70  to maxillary sinus  24 . In the application illustrated in  FIG. 3 , an endoscope  72  is used to examine the sinus cavity. Similarly, medical instruments  70  may be used to aspirate the sinus or to introduce a drug or other substance to the sinus. In some applications of the invention, medical instrument  70  may be used to prepare the maxillary sinus for a sinus lift operation (e.g., by delivery of a drug to the sinus), in order to reduce inflammation (such as inflammation of mucosal lining  36 , e.g., the Schneiderian membrane). Alternatively or additionally, medical instrument  70  may be used to treat pain and/or swelling following a sinus lift operation. 
     Reference is made to  FIGS. 4A-E , which illustrate hole-forming member  50 , in accordance with five respective applications of the present invention. 
       FIG. 4A  illustrates hole-forming member  50 , comprising a drill  150 . The hole-forming function of drill  150  is imparted, as per a classical drill, by rotation of a drill bit  160 .  FIG. 4A  further illustrates a cooling element  151  for use in conjunction with hole-forming member  50 . Cooling element  151  may be used to administer cooling to hole-forming member  50  prior to formation of hole  40 . Alternatively or additionally, cooling element  151  may be used to administer cooling to bone wall  32  at the site of hole formation, prior to formation of hole  40 . Alternatively or additionally, cooling element  151  is used to administer cooling to hole-forming member  50  and/or bone wall  32  during and/or after formation of hole  40 . Cooling element  151  typically utilizes the expansion of a compressed gas to apply its cooling effect. For example, a compressed gas may be applied to drill bit  160  via nozzle  153 , whereby expansion of the gas cools the drill bit. Alternatively, cooling element  151  utilizes a cooled liquid (e.g., saline) to apply its cooling effect. Cooling of hole-forming member  50  and/or bone wall  32  is hypothesized to reduce pain and/or the damage caused to tissue in the area of hole formation. 
       FIG. 4B  illustrates hole-forming member  50 , comprising a piercing device  152 . The hole-forming function of piercing device  152  is imparted by distal movement of a piercing element  162 . 
       FIG. 4C  illustrates hole-forming member  50 , comprising an energy applicator  154 , typically comprising a control unit  155 , a handle  166  and a tip  164 . For some applications, energy applicator  154  comprises an ultrasonic drill, for example, an ultrasonic/sonic driller/corer (USDC). The hole-forming function of the ultrasonic drill is imparted by ultrasonic vibration of the tip  164  in contact with bone wall  32 . The ultrasonic vibration is typically provided by a piezoelectric actuator in handle  166 . 
     For some applications, energy applicator  154  comprises a radio frequency (RF) electrode. In this example, tip  164  comprises the RF electrode, typically driven by the control unit  155  to apply a current having a frequency and amplitude suitable for forming a hole in bone wall  32 . The control unit may also drive the electrode to apply a current having a frequency and amplitude suitable for cauterizing the area of hole-formation. A cauterizing RF electrode may also be employed in combination with other embodiments of hole-forming member  50  (e.g., those described with reference to  FIGS. 4A, 4B, 4D and 4E ), in order to reduce bleeding during and after formation of hole  40  (see  FIGS. 8A-C  for an example of such a combination). 
       FIG. 4D  illustrates hole-forming member  50 , comprising a laser cutter  156 . A laser  170  generates a laser beam  168  which imparts energy sufficient to form hole  40  in bone wall  32 . The laser is controlled by control unit  157 . 
       FIG. 4E  illustrates hole-forming member  50 , comprising a water jet cutter  158 . A pump  174  forces water at high pressure through the water jet cutter where it is optionally mixed with an abrasive  176 . Abrasive  176  typically comprises particles of a solid substance such as a mineral, a polymer or a frozen aqueous solution (e.g., frozen saline). A water jet  172  is ejected, forming hole  40  in bone wall  32 . 
     Both laser cutter  156  and water jet cutter  158  function by formation of an energetic stream (laser beam  168  and water jet  172 , respectively). These applications of the invention may comprise multiple converging streams which focus their energy at a specific distance, reducing the risk of damage to the inside of the sinus due to inadvertent entry of the stream immediately following successful formation of the hole  40 . Alternatively, laser cutter  156  generates a straight beam  168 , and/or water jet cutter  158  generates a straight water jet  172  (as shown). 
     Cooling element  151  is illustrated in  FIG. 4A  in conjunction with drill  150 , but may be used in conjunction with numerous embodiments of hole-forming member  50  including, but not limited to, piercing device  152 , energy applicator  154 , laser cutter  156  and water jet cutter  158 , as well as other hole-forming members. 
     Reference is now made to  FIGS. 5A-D , which illustrate four versions of implant  52 , in accordance with respective applications of the present invention. Each version of implant  52  is shaped to define a lumen  100 . Each version features a shoulder  102  which, being wider than more distal regions of implant  52 , inhibits implant  52  from entering the sinus cavity entirely. Alternatively, versions of implant  52  may not include shoulder  102 . Each version of implant  52  illustrated in this figure has a fastener which, together with, or independently from, shoulder  102 , fastens implant  52  in hole  40  formed in bone wall  32 . Optionally, implant  52  may comprise a biodegradable material such as (but not limited to) polyglycolide (PGA), polylactide (PLA) or another biodegradable material known in the art. Implant  52  may be entirely biodegradable. 
       FIG. 5A  is a schematic illustration of implant  52 , embodied as a push-in implant  90 . The fastener of this implant is one or more extendable members, such as wings  104 . Due to their flexibility and angle, wings  104  are able to flex inwardly and pass through the formed hole  40  in bone wall  32  when implant  52  is inserted through the bone wall. Wings  104  return to their original position once on the sinus side of bone wall  32 , fastening implant  52  in place. 
       FIG. 5B  is a schematic illustration of implant  52 , embodied as a push-in implant  92 . Implant  92  comprises a fastener comprising one or more extendable members, such as wings  106 . Wings  106  are similar to wings  104  of implant  90 , but are coupled to the body of the implant by a support  107  at an additional longitudinal site along the implant, and provide greater contact with the sinus-side of bone wall  32 , compared to contact provided by wings  104  of implant  90 . 
       FIG. 5C  is a schematic illustration of implant  52 , embodied as a screw-in implant  94 . The fastener of this implant is a screw thread  108 . Following positioning of implant  94  at hole  40 , the implant is fastened into the hole by rotation, as per a classical screw. For some applications, this rotation may be imparted by the hole-forming member  50 . In applications in which hole-forming member  50  forms hole  40  by rotation, implant  94  may be fastened using the same rotational force that is used to form the opening in bone wall  32 . In these applications of the invention, implant  94  may be reversibly coupled to hole-forming member  50  in a manner that prevents independent rotation (e.g., using a hex socket). For example, screw-in implant  94  may be reversibly coupled to drill  150 , such that, after formation of hole  40 , continued rotation of drill  150  fastens implant  94  into the hole. Alternatively or additionally, rotational force may be applied separately, after hole  40  has been formed. 
     As described hereinabove, in some applications of the invention, implant  52  (or screw-in implant  94 ) is self-tapping, comprising a self-tapping screw-thread. In these applications of the invention, no independent hole-forming member is required. Rather, implant  52  is pushed against bone wall  32  and rotated such that it cuts into, and becomes implanted in, the bone wall. 
     Reference is made to  FIG. 5D , which illustrates implant  52 , embodied as a rivet implant  96 . Rivet implant  96  has a configuration similar to a blind rivet. The fastener of this version is buck-tail  112 . The implant is supplied in a restrained first configuration (left drawing) and is maintained in this configuration by a restraint, such as splint  114 . Upon removal of splint  114 , buck-tail  112  moves to a relaxed second configuration (right drawing). The relaxed configuration of buck-tail  112  is wider than the hole  40  formed in bone wall  32  and therefore fastens the implant in place. 
     Reference is now made to  FIG. 5E , which illustrates a rivet implant  98 , according to an application of the invention. Rivet implant  98  is similar to rivet implant  96  but does not comprise a restraint; rather the buck-tail is distorted from a first configuration to a second configuration by a force applied by an applicator.  FIG. 6  illustrates such an applicator, according to an application of the invention. 
       FIGS. 6A-B  are schematic illustrations, showing two sequential steps in the implantation of rivet implant  98 , in accordance with an application of the invention. Reference is made to  FIG. 6A . Rivet assembly  74 , comprising an applicator  76  and rivet implant  98 , is inserted into hole  40  in the direction of arrow  77 , until a shoulder  102  of the rivet implant abuts the proximal surface of bone wall  32 . As described with reference to  FIG. 5E , rivet implant  98  is configured so as to act as a blind rivet. Correspondingly, applicator  76  is configured so as to act as an appropriate mandrel. 
     Reference is now made to  FIG. 6B . Applicator  76  is withdrawn in the direction of arrow  79 , driving a mandrel head  78  into and then out of buck-tail  112 . Mandrel head  78  deforms buck-tail  112  of rivet implant  98  into a configuration that fastens the implant in place. 
     Although  FIGS. 6A-B  illustrate rivet implant  98  being implanted in a hole in bone wall  32  of a paranasal sinus, rivet implant  98  may be implanted in a hole in other tissues (e.g., an anatomical wall, such as a wall of a hollow organ, for example, a bone wall) of a subject. Alternatively or additionally, rivet implant  98  is solid, i.e., not shaped to define a lumen. 
     Reference is made to  FIG. 7 , which is a schematic illustration of an application of the invention. After implantation of implant  52 , a medical instrument  70 , which in this application comprises a balloon catheter  134 , is used to implant an expandable stent  130  in a natural sinus ostium  26 . In its initial form, balloon  132  is disposed within the lumen of stent  130  in a deflated form. Catheter  134  is used to insert stent  130  and balloon  132  through hole  40 , through sinus  24  and finally into ostium  26 . The balloon  132  is then inflated, expanding stent  130  and opening the ostium. Balloon  132  is then deflated and removed using balloon catheter  134 . Due to its configuration, stent  130  remains expanded, supporting ostium  26  in an open configuration. Alternatively, expandable stent  130  may be delivered to ostium  26  in a contracted form and configured to expand passively when a force contracting the stent is removed. For example, stent  130  may be delivered within a sheath. Upon removal of the sheath, the stent expands, supporting ostium  26  in an open configuration. 
     Such implantation of stent  130  in a sinus ostium may also be performed without passage through a formed hole in a sinus wall. For example, stent  130  could be advanced through the nasal cavity, between inferior turbinate  30  and middle turbinate  28  and into ostium  26 . Implantation of stent  130  may be assisted by the use of a guidewire and/or an endoscope. Stent  130  may comprise a biodegradable material such as (but not limited to) polyglycolide (PGA), polylactide (PLA) or another biodegradable material known in the art. Implant  130  may be entirely biodegradable. 
     Reference is made to  FIGS. 8A-C , which are schematic illustrations of a hole being formed in bone wall  32 , in accordance with an application of the invention. In this application of the invention, hole-forming member  50  comprises one or more RF electrodes  180  and drill bit  160 . As described hereinabove, hole-forming member  50  is used to create hole  40  in bone wall  32  that divides nasal cavity  38  from maxillary sinus  24 . In this application of the invention, electrodes  180  are configured to penetrate soft tissue  37  of the nasal cavity and mucosal lining  36  of the sinus, and to cauterize these tissues. 
     Reference is now made to  FIG. 8A . Hole-forming member  50  is advanced toward bone wall  32 . The distal tips of electrodes  180  are disposed distal to the distal tip of drill bit  160 . Electrodes  180  penetrate and cauterize soft tissue  37 . 
     Reference is now made to  FIG. 8B . Drill bit  160  is extended distally through the hole formed in soft tissue  37 , and is rotated in order to drill through bone wall  32 . 
     Reference is now made to  FIG. 8C . Electrodes  180  are extended distally through the hole formed in bone wall  32 , and penetrate and cauterize mucosal lining  36 .  FIG. 8C  shows drill bit  160  as retracted prior to this extension of electrodes  180 . Alternatively, electrodes  180  may slide over drill bit  160 , drill bit  160  remaining in the hole in bone wall  32  until after mucosal lining  36  has been penetrated. 
     It is noted that the cauterization described with reference to  FIG. 8A  may be performed without the step of cauterization described with reference to  FIG. 8C , and that the cauterization described with reference to  FIG. 8C  may be performed without the step of cauterization described with reference to  FIG. 8A . 
     In an alternative application of the invention, hole-forming member  50  does not comprise RF electrodes  180 ; rather, RF electrodes  180  are coupled to hole-forming member  50 , and are configured to cauterize. Typically, RF electrodes  180  are controlled by a control unit (such as control unit  155 , described with reference to  FIG. 4C ). In this application of the invention, hole-forming member  50  (e.g., drill bit  160 ) penetrates soft tissue  37  and mucosal lining  36 , in addition to bone wall  32 . Electrodes  180  cauterize soft tissue  37  and mucosal lining  36  following the penetration of these tissues by the hole-forming member. Typically, RF electrodes  180  are fixed in position with respect to drill bit  160 , such that the tips of electrodes  180  are slightly proximal to the tip of drill bit  160  (e.g., less than 3 mm from the tip). Alternatively, RF electrodes  180  may be slidable with respect to hole-forming member  50 . 
     It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof that are not in the prior art, which would occur to persons skilled in the art upon reading the foregoing description.