Abstract:
An apparatus for maintaining a positional relationship between a trocar cannula and body tissue into which the cannula is inserted includes a tissue engaging member having a conical outer surface with a thread helically disposed thereon. A guide tube is insertable into a bore in the tissue engaging member, the guide tube having a camming surface. A collet with flexible projections is engageable with the guide tube. When the collet is tightened onto the guide tube the flexible projections bend inward to frictionally engage and hold a trocar cannula inserted through the axial bore of the apparatus.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a device for retaining a medical instrument in engagement with body tissue and, more particularly, to an improved device for maintaining the desired positional relationship between a trocar tube and body tissue. 
     2. Background of the Related Art 
     Devices for holding medical instruments in penetrating relationship with body tissue are known. See, for example, U.S. Pat. No. 2,256,942 which discloses an instrument having a fluted or undulated surface for retaining the device in the walls of the bladder or viscus; U.S. Pat. No. 3,750,667 which discloses a device having a thread which serves to measure the depth of introduction of the device into osseous tissue; and U.S. Pat. No. 4,670,008 which discloses a high flux threaded needle for injecting or removing fluids from the body, the needle having a threaded portion to permit easy insertion of the needle and secure the device in the patient. 
     Threaded structures have also been applied to larger diameter trocars which are used for introducing viewing and surgical instruments into the body. Such trocars are shown and described in U.S. Pat. Nos. 4,601,710; 4,654,030, and 4,902,280. One commercially available trocar includes a cannula having an integrally molded threaded portion for holding the cannula in the patient&#39;s skin. Another device marketed under the trademark SURGIGRIP by U.S. Surgical Corporation, Norwalk, Conn., provides a depth penetration indicator adjustable to a desired position along a cannula and including a threaded portion for holding the cannula in the patient&#39;s skin. 
     Such devices are especially useful in open laparoscopy procedures wherein a surgeon inserts a cannula into an opening in body tissue made with a scalpel. The scalpel-made opening may have a greater tendency to leak gas and/or fluid from around the cannula than does a trocar created opening. 
     SUMMARY OF THE INVENTION 
     An apparatus is provided herein for maintaining a positional relationship between an elongated surgical instrument and body tissue into which the surgical instrument is inserted. The apparatus includes first means at least partially insertable into an opening in the body tissue, and, associated with the first means, second means possessing a conical surface having disposed thereon at least one thread for engaging the edges of the opening in the body tissue. More particularly, the apparatus includes a first member for insertion into an opening in a wall of body tissue, the first member having distal and proximal ends, a camming surface, a cylindrical tube portion, and an axial bore configured and dimensioned to receive the elongated surgical instrument. Also included are tissue engaging means in conjunction with the first member, the tissue engaging means having a conical outer surface and at least one tissue engaging thread helically disposed around the conical surface. A second member is provided which includes collet means adapted to cooperate with the first member and having an axial bore configured and dimensioned to receive the elongated surgical instrument. The collet means is movable with respect to the first member to a position wherein projections associated with the collet means engage the camming surface of the first member and are moved radially inward to frictionally engage and hold the elongated surgical instrument when positioned within the axial bore. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevational view of the tissue gripping device of the present invention in conjunction with a trocar assembly. 
     FIG. 2 is a sectional view of the tissue gripping device inserted into body tissue. 
     FIG. 3 is an exploded perspective view of the tissue gripping device. 
     FIG. 3a illustrates a sectional view of the threads of the conical tissue engager. 
     FIG. 3b illustrates a sectional view of an alternative thread configuration for the conical tissue engager. 
     FIGS. 4 and 5 are perspective and sectional views, respectively, of an alternative embodiment of the threaded conical portion of the tissue gripping device. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The tissue gripping device of the present invention is intended to be used in conjunction with a trocar assembly during laparoscopic, and particularly open laparoscopic, procedures. The trocar assembly can be of known design and may have either a sharp pointed obturator or a blunt obturator. 
     Referring to FIG. 1, a trocar assembly 300 having obturator 310 mounted to obturator housing 330, and cannula 350 mounted to cannula housing 320 is employed in conjunction with tissue gripping device 100. The cannula 350 is disposed through an axially extending bore in the tissue gripping device 100 and the obturator 310 is disposed through the axial bore of the cannula 350. A tube 340 provides means for communicating a gas to or from the interior of the body cavity penetrated by the cannula. 
     FIG. 2 illustrates a sectional view of the tissue gripping device implanted into a body through a wall of tissue 400. Referring to FIGS. 2 and 3, the tissue gripping device 100 includes a threaded conical tissue engager 110, a taubular guide member 120, and a locking collet 130. 
     More particularly, the tissue engager 110 includes a thread 114 extending helically around a conically shaped outer surface 111 from the proximal end 112 to the distal end 113 of the tissue engager 110. A cylindrical bore 116 extends axially through the tissue engager 110 and is adapted to receive cylindrical tube 121 of tubular guide 120. Notches 115 extend radially along the proximal end 112 of the tissue engager 110 and are adapted to receive corresponding detents 125 in the tubular guide 120. 
     Referring to FIG. 3a, the thread height H, thread width W, thread spacing S, and angle A of the conical surface 111 are chosen so as to provide optimum entry and removal force and fluid sealing with minimum tissue trauma, and sufficient holding power to retain the laparoscopic instrumentation in the desired position. Typically, the thread height H can be from about 0.005 to 0.1 inches; thread width W can be from about 0.02 to 0.15 inches; thread spacing S can be from about 0.1 to 0.3 inches; and angle A between the surface of bore 116 and the conical surface 111 can be from about 5 degrees to about 45 degrees. 
     Referring to FIG. 3b, an alternative thread shape is illustrated in sectional view. The thread 114a has a distal sloping surface 114c extending from a curved distal foot region 114b to a curved thread apex 114d disposed radially outward of surface 111. Distal sloping surface 114c preferably is curved and has a radius R 1  in the range of about 0.07 to 0.09 inches, and most preferably has a radius of about 0.08 inches. Curved distal foot region 114b is connected to and extends from base surface 111 to join sloping surface 114c to the base surface 111. Curved distal foot region 114b should have a radius R 2  in the range of about 0.01 to 0.03 inches, and preferably has a radius of about 0.02 inches. Thread 114a also has a proximal end wall 114e substantially perpendicular to base surface 111 extending from a proximal foot region 114f to thread apex 114d. Thread apex 114d preferably defines a curved surface connecting distal sloping surface 114c to proximal end wall 114e. The curve of thread apex 114d preferably defines a radius R 3  of about 0.01 inches. Proximal foot region 114f joins proximal end wall 114e to base surface 111, and preferably is a curved surface defined by a radius R 4  of about 0.01 inches. The total longitudinal thread width W is measured from the point where distal curved foot region 114f joins base surface 111 to the point where proximal curved foot region 114 joins base surface 111. For tissue such as skin, the thread width W should be about 0.10 to 0.11 inches and the thread height H should be about 0.08 to 0.09 inches. It has also been found that for skin tissue the optimum longitudinal thread spacing &#34;S&#34; along base surface 111 should be about 0.275 to 0.300 inches, and most preferably is about 0.285 inches. 
     Referring again to FIG. 3 the tubular guide 120 includes a tubular shaft portion 121 having an exterior diameter adapted to fit into bore 116 in the conical tissue engager 110. The inner diameter of axial bore 126 in the guide 120 is of such dimension to accommodate a cannula of a trocar assembly (See, e.g. FIG. 1). The distal end 127 of tubular shaft 121 preferably is beveled to facilitate its insertion into bore 116. The distal portion of guide 120 includes a knob 122 with a knurled circumferential surface. At the distal surface of the knob detents 125 are positioned in radial orientation, the detents being dimensioned and configured so as to fit into the corresponding notches 115 of the tissue engager 110. The inner surface 123 of the knob 122 is threaded. Proximally extending camming ridge 124 extends circumferentially around the proximal opening of bore 125 and possesses an inwardly sloped camming surface 124a defining an angle of about 20° to about 25° relative to the longitudinal axis L of guide 120. 
     The collet 130 is a generally cylindrical member which comprises distal tube portion 131 with a threaded outer surface, 131a. A plurality of flexible locking projections 135 extend distally and generally longitudinally in a circumferential pattern around the distal opening of axial bore 136. The threaded tube portion 131 is adapted to screw into the proximal end, i.e. the knurled knob, of the tubular guide 120, whereupon the locking projections 135 engage sloped surface 124a of the ridge 124 and are cammed radially inwardly to frictionally engage a trocar cannula or other such implement positioned within the bore. 
     The proximal end of the collet 130 includes a circumferential ridge 132 with depressions 133 for accommodating the fingers of a user. The proximal end 134 of bore 36 is sloped so as to facilitate insertion therethrough of a trocar cannula, obturator, or other laparoscopic instrument. 
     Referring to FIG. 2, the tubular guide 120 is inserted into the tissue engager 110 such that detents 125 engage notches 115. Thus, rotation of the knurled knob 122 causes rotation of the tissue engager 110. The collet 130 is screwed part way into the proximal opening of the guide 120. 
     After a surgeon has created an incision, for example, in the skin 400, the assembly 100 is inserted into the incision and the knurled knob 122 is rotated counterclockwise so as to screw tissue engager 110 into the incision. A trocar cannula 350 and obturator 310 are inserted through the axial bore of the collet 130 and the guide 120. When the surgeon is satisfied with the positioning of the cannula 350, the collet 130 is turned so as to hold cannula 350 in place by means of cammed projections 135. The guide 120 is disengageable from gripper 110 by lifting it out from slots 115. Thus, fitting 120 can be rotated independently of tissue engager 110. 
     Referring to FIGS. 4 and 5, an alternative embodiment of the invention is shown wherein the tissue engager and the tubular guide are integrated in a single piece 200. Thus, integrated piece 200 has a tubular portion 121 with distal bevelled edge 127, conical surface 111 with threads 114, knurled knob 122 with threaded inner surface 123, proximally extending camming ridge 124 with sloped camming surface 124a and axial bore 126. The detents 125 and notches 115 are not employed with integrated piece 200. 
     The individual pieces of the gripping assembly 100 may be molded from a synthetic polymer such as glass filled acetal or polycarbonate. In a preferred embodiment, the tubular guide 120 and tissue engager 110 are constructed of glass-filled acetal and locking member 130 is constructed of polycarbonate. The preferred acetal material is available from LNP Division of ICI America Inc. under the trade specification KFL 4023, and the preferred polycarbonate material is available from General Electric Company under the trade name LEXAN. The preferred acetal-polycarbonate arrangement reduces binding at the threaded engagement of the tubular guide 120 and collet 130 threaded sections. Of course, the same result may be obtained by constructing the tubular guide 120 of polycarbonate and the collet 130 of acetal, but an acetal collet may slide on a metal cannula or guide tube. 
     While the above description contains many specifics, these specifics should not be construed as limitations on the scope of the invention, but merely as exemplifications of preferred embodiments thereof. Those skilled in the art will envision many other possible variations that are within the scope and spirit of the invention as defined by the claims appended hereto.