WO1997032530A1

WO1997032530A1 - Cannula for a trocar system

Info

Publication number: WO1997032530A1
Application number: PCT/GB1996/000521
Authority: WO
Inventors: Nicholas Richard Kemp
Original assignee: Microsurgical Equipment Ltd.
Priority date: 1996-03-07
Filing date: 1996-03-07
Publication date: 1997-09-12

Abstract

A cannula (2) is provided with a retractable guard (8) so that it can be used with an unguarded trocar (10). The guard (8) comprises a collar having an external diameter equal to the external diameter of the cannula and a tubular sleeve (20) which is telescopically supported within the cannula (2). A pin (32) on the sleeve (20) engages an L-shaped slot (34) in the cannula. A coil spring (30) biases the pin to one end of the slot to lock the guard in its extended position where it can guard the head of the trocar (10). To release the guard (8) the cannula must be rotated against the bias of the spring to a position in which the pin (32) can be urged to the opposite end of the slot.

Description

CANNULA FOR A TROCAR SYSTEM

The present invention relates to the cannula of a trocar system.

A trocar is a medical cutting tool used in laparoscopy. In laparoscopy a hollow tube or cannula is inserted through the wall of the abdominal cavity of a patient to allow surgical tools to be used within the abdominal cavity. The tools are inserted and withdrawn through the cannula. Any surplus tissue or organ can be withdrawn from the cavity through the cannula. One or more cannulae can be inserted through the abdominal wall according to requirements.

In order to penetrate the abdominal wall, the wall must first be cut and this is accomplished with a trocar. A known trocar is in the form of an elongate shaft supporting at its free end, a head of circular cross-section, which is profiled at its free end portion to form a solid three or four sided pyramid defining three or four cutting edges leading away from the tip. The shaft and head are encased in a retractable guard of plastics material. The guard can be displaced longitudinally of the shaft to expose the head but is spring biased so as to envelop the head once any displacement forced is removed. In operation the trocar is inserted into the cannula until its free and projects from the forward end. The cannula and trocar are then urged against the abdominal wall. The resistance of the wall acts to displace the guard and so exposes the cutting edges. The head pierces and cuts the abdominal wall until it emerges from the other side of the wall whereupon, with the resistance of the wall removed, the guard is resiliently displaced once again to cover the head so that the head is prevented from damaging any organs within the abdominal cavity. Continued penetration will allow the cannula to enter the abdominal cavity. The guard system on the trocar and the surrounding cannula mean that the size of opening which can be cut in the abdominal wall is very much smaller than the size of the opening needed to accommodate the cannula. Thus, when the cannula is forced through the opening but by the trocar, the opening is stretched and there is a very real danger of the tissue of the abdominal wall tearing or being otherwise damaged.

It is an object of the invention to provide an improved cannula for a trocar system.

According to the present invention there is provided a cannula for a trocar system comprising a tubular elongate tail section extending from an enlarged head section, the enlarged head section defining a cavity to receive the handle of a trocar when the cutting head of the trocar is inserted via the cavity into the tail section, the tail section including a guard which is telescopically supported by the tail section for movement between a first position in which it covers the head of the trocar and a second position in which it exposes the head of the trocar, and locking mechanism which automatically tends to lock the guard in the first position whenever the guard reaches the first position. A cannula and trocar system will now be described by way of example, with reference to the accompanying diagrammatic drawings, in which:

Figure 1 is a plan view of the system with the trocar inserted in the cannula, with the cannula guard extended; Figure 2 is a view similar to that of Figure 1 but with the cannula guard retracted;

Figure 3 is a fragmentary sectional view, to an enlarged scale, through the system showing the operating mechanism for the cannula guard; Figure 4 is a fragmentary sectional view of the distal end portion of the cannula with the guard extended; and

Figures 5a to 5c are plan views of the system with parts cut away showing the cannula guard in three different positions.

The cannula and trocar system to be described comprises a cannula 2 having an enlarged body section 4 with an elongate tubular tail section 6 extending therefrom. The distal end portion of the tail section 6 houses a retractable guard 8.

Partially housed within the cannula is an unguarded trocar 10. The trocar 10 has a handle portion 12 which projects from the body section 4 of the cannula 2 and an elongate shaft 5 extending from the handle portion 12. A cutting head 14 is supported at the distal end of the shaft 5. The enlarged body section 4 has a cylindrical cavity 28 arranged partially to accommodate the handle portion 12 of the trocar. A channel of circular cross-section leading from the cavity 28 accommodates an end portion of the tail section 6 and the tail section 6 is rigidly secured to the body section 4 at this point.

During insertion of the trocar 10 into the cannula 2, the movement of the trocar 10 is arrested when the handle portion 12 abuts an abutment surface of the body section 4 of the cannula. In this position with the retractable guard 8 retracted, the cutting head 14 projects from the tail section 6 as shown in Figure 2. When the retractable guard 8 is then extended, it contains the cutting head 14 within it, see Figure 1.

As shown in Figures 3 and 4, the retractable guard 8 consists of a sleeve 20 telescopically supported within the tail section 6 and terminating at its distal end with an enlarged collar 22 having an outside diameter substantially equal to the outside diameter of the tail section. At its other end the sleeve 20 is slidably supported on a hollow stub shaft 26.

The stub shaft 26 has an enlarged end portion 26A which has an outside diameter equal to the inside diameter of the tail section and is rigidly secured to the tail section 6 at a location adjacent the cavity 28. The outside diameter of the remainder of the stub shaft 26 has a diameter just less than the inside diameter of the sleeve 20. Thus, the sleeve 20 is slidable in the annular channel between the stub shaft 26 and the tail portion 6.

A coil spring 30 is located in the annular channel and extends around the stub shaft 26. One end of the coil spring is secured to the enlarged end portion 26A of the stub shaft while the other end is secured to the adjacent end portion 20A of the sleeve 20 (see Figure 3). The spring 30 acts to urge the adjacent end 20A of the sleeve 20 away from the enlarged end portion 26A of the stub shaft 26.

A pin 32 projects radially outwardly from the end portion 20A of the sleeve 20 and engages an L-shaped slot 34 in the tail portion 6. The engagement of the pin 32 in the slot 34 thus limits the degree of relative movement between the sleeve 20 and the tail section 6. One slot portion 34A of the L-shaped slot 34 extends axially of the tail section 6 while the other slot portion 34B extends circumferentially of the tail section 6.

When the coil spring 30 is fitted, it is fitted in a manner to urge the sleeve 20 to rotate in an anti¬ clockwise sense (when viewed from its distal end) so that when the pin 32 engages the slot portion 34B of the slot, it is displaced away from the other slot portion 34A (see Figure 5a) .

The length of the slot portion 34A is equal to the distance that the guard can travel between its extended and retraced positions. In the retracted position of the guard 8, the pin 32 lies in the slot portion 34A at a location remote from the slot portion 34B (see Figure 5c) . When the guard is extended, the pin 32 is moved to a location at the junction of the two slot portions 34A, 34B (see Figure 5b) .

In operation with the guard initially extended, the pin 32 lies in the slot portion 34B and is urged in an anti-clockwise sense away from the slot portion 34A. The guard is thus locked against longitudinal displacement relative to the cannula. When the cannula and trocar are applied to the abdominal wall of a patient and rotated in a clockwise sense, the pressure of the guard against the wall will stop it rotating with the cannula and so the pin 32 will move into the slot 34A (see Figure 5B) . Continued an increasing pressure against the abdominal wall will start to retract the guard 8 and allow the trocar to incise the wall itself. The pin 32 will thus move along the slot portion 34A to a position remote from the slot portion 34B (see Figure 5C) . As soon as the trocar has pierced the wall, the pressure on the guard will be released and the coil spring will urge the guard back along the slot portion 34A and then into the slot portion 34B. In this position the guard 8 once again guards the trocar and is locked against displacement relative to the trocar so that should the cannula and trocar be inadvertently pushed in through the abdominal wall to reach the underlying organs, little or no damage will be sustained by the organs. The trocar can now be removed to provide access to the abdominal cavity via the cannula for various surgical devices and instruments.

It will be appreciated that once the collar 8 has passed through the opening of the abdominal wall, the opening will close around the narrower portion of the guard, thus making it more difficult to be inadvertently dislodged from the opening. The provision of a guard on the cannula rather than on the trocar has a number of advantages. Firstly, on the cannula there is more space in which to accommodate the spring mechanism. Secondly, the trocar without a guard and spring mechanism can more readily be disinfected and thirdly because the guard on the cannula can be more cheaply installed than on the trocar, the cannula can be made to be a disposable item.

An indicator (not shown) is provided to give indication that the guard is in the retracted or extended position or both.

The distal end of the guard is provided with a roughened exterior surface to provide a grip between the guard and the skin of the patient.

It will be appreciated that in one modification the spring may be mounted on the outside of the tail section and coupled to the pin.

In another modification the pin may be provided on the tail section 6 and the slot in the guard.

In yet a further modification the pin may be provided on the guard to extend radially inwardly and the slot provided in the stub shaft or vice versa.

Claims

1. A cannula for a trocar system comprising a tubular elongate tail section extending from an enlarged head section, the enlarged head section defining a cavity to receive the handle of a trocar when the cutting head of the trocar is inserted via the cavity into the tail section, the tail section including a guard which is telescopically supported by the tail section for movement between a first position in which it covers the head of the trocar and a second position in which it exposes the head of the trocar, and locking mechanism which automatically tends to lock the guard in the first position whenever the guard reaches the first position.

2. A cannula according to Claim 2, wherein the guard is telescopically slidable within the tail section and has a collar at its distal end, having an external diameter substantially equal to that of the tail section.

3. A cannula according to Claim 1 or to Claim 2, wherein the locking mechanism includes spring means normally urging said guard into said first position and normally urging said guard to rotate in one sense relative to said cannula.

4. A cannula according to Claim 3 , including a stub shaft extending from said cavity into said tail section, said stub shaft having a first portion adjacent said cavity with an external diameter substantially equal to the internal diameter of said tail section and a second portion having an external diameter smaller than the external diameter of the guard whereby to define with the tail section an annular channel along which the guard can slide.

5. A cannula according to Claim 4, wherein the resilient means comprises a coil spring housed in said annular channel between said first portion of said stub shaft and the adjacent end of said guard, the spring being fixed at one end to said first portion and at its other end to said guard.

6. A cannula according to Claim 5, including an L- shaped slot in one of said cannula and said guard, and a pin engaging said slot rigid with the other of said cannula and said guard, the slot having one portion extending longitudinally of said cannula and being of a length at least equal to the distance between said first and second positions of said guard and a second portion extending circumferentially substantially at right angles to said one portion of the slot, said coil spring being longitudinally tensioned to urge said pin along said one portion of the slot towards said other portion and angularly tensioned to urge said pin along said second portion in a direction away from said first portion of the slot.

7. A cannula according to Claim 6, wherein said slot lies in said tail section and said pin extends radially outwardly from said guard.

8. A cannula according to Claim 5, including an L- shaped slot in one of said guard and the second portion of the stub shaft and a pin engaging said slot, rigid with the other of said guard and the second portion of the stub shaft, the slot having one portion extending longitudinally of the cannula and being of a length at least equal to the distance between the first and second positions of said guard, and second portion extending circumferentially substantially at right angles to said one portion of said slot, said coil spring being longitudinally tensioned to urge said pin along said one portion of the slot towards said other portion of the slot and angularly tensioned to urge said pin along said other portion of the slot away from said one portion.