WO2012038756A1

WO2012038756A1 - Trocar tip

Info

Publication number: WO2012038756A1
Application number: PCT/GB2011/051797
Authority: WO
Inventors: Michael White
Original assignee: Surgical Innovations Limited
Priority date: 2010-09-24
Filing date: 2011-09-23
Publication date: 2012-03-29
Also published as: GB201016056D0

Abstract

A trocar tip has a longitudinal axis and comprises: an end portion coincident with the longitudinal axis; and a tapered portion extending to the end portion and narrowing in the direction towards the end portion. The tapered portion comprises a conical surface about the longitudinal axis and two concave surfaces which are defined by cut outs from the conical surface and which extend along the entire length of the of the tapered portion. The concave surfaces are preferably on opposite sides of the tapered portion and symmetrical about a plane passing through the longitudinal axis. The trocar tip with this construction is simple to manufacture and effective at enlarging an incision.

Description

TROCAR TIP

The present application relates to trocar tips for use in surgery and in particular to a trocar tip which can enlarge a small incision.

During minimally invasive surgery, openings are required which - although smaller than is required for conventional surgery - are still large enough to allow access through the incision for a surgical instrument. It has been found that rather than creating a single large incision, spreading a smaller incision with an enlargement device results in less trauma to the tissue. The resultant wound is easier to close at the end of the procedure and enhances patient recovery.

A number of trocar tips which can be used to enlarge a small incision have been proposed. The "Pencil Point trocar" commercially available from Surgical Innovations Limited provides a conical dilating surface. The tapering nature of the conical dilating surface enables the Pencil Point trocar to enlarge an incision as it is inserted.

Alternative trocar tip profiles have also been proposed. For example, WO-A-02/01998 (Taut, Inc.) discusses a penetrating tip for a trocar assembly. The form of the tip of '998 is more complicated than a conical surface, having an elliptical cross-section perpendicular to a longitudinal axis creating a complex curved surface. The complex curved surface can be difficult to manufacture, increasing cost.

US-5601559 relates to an intraosseous needle, the needle includes a fluted pencil point tip which is substantially conical. A pair of diametrically opposed flutes are milled into the end of the tip. Immediately adjacent the fluted pencil point tip is shaft having buttress threads. The leading thread is interrupted by the milling process, so that the leading thread terminates in one of the flutes and one flute is longer than the other. WO-2008/103400 discusses an obturator tip. In one construction, the obturator tip comprises a first pair of opposed planar surfaces. The first pair of surfaces intersect with a second pair of opposed surfaces, which may be planar or slightly concave. The second pair of surfaces intersect with a third pair of opposed surfaces which are substantially planar. This creates a complex profile with a shallow taper angle of 15° about the longitudinal axis for the second pair of opposed surfaces. It would be desirable to provide an improved trocar tip which can enlarge a small incision.

Accordingly, the present invention provides a trocar tip which combines a conical surface with two concave surfaces. This configuration has been shown to reduce the force required to enlarge an incision compared to a purely conical surface and can be manufactured relatively easily.

According to a first aspect of the invention, there is provided a trocar tip having a longitudinal axis, wherein the trocar tip comprises an end portion coincident with the longitudinal axis; and a tapered portion extending to the end portion and narrowing in the direction towards the end portion; wherein the tapered portion comprises a conical surface about the longitudinal axis and two concave surfaces which are defined by cut outs from the conical surface and which extend along the entire length of the conical surface.

The reference to the length of conical surface is the length in the direction of the longitudinal axis. The trocar tip of this construction can enlarge an incision requiring less force than a purely conical tip and is simpler to manufacture than more complex profiles. The concave surfaces enable the tip to be rotated to enlarge the incision. The concave surfaces act in a similar way to a screwdriver blade, but with less trauma to tissue, to open the incision further. The trocar tip can therefore enlarge an incision by a combination of longitudinal force and rotation.

Such a trocar tip is simple to construct and effective in use. Neither US-5601559 nor WO- 2008/103400 include a concave surface which extends the entire length of a tapered portion. In WO-2008/103400, the second pair of surfaces do not extend the entire length of a tapered potion. In US-5601559 the difference in length of the flutes means that the flutes cannot both extend the entire length of a conical section. Preferably, the two concave surfaces are on opposite sides of the tapered portion and are symmetrical about a plane through the longitudinal axis. This helps ensure that the concave surfaces work together at opposite portions of the incision during rotation of the trocar tip.

Preferably, the two concave surfaces are concave in a single direction. Concave in a single direction is used to mean that the curve of the concave surface is defined in a single plane, rather than two or more planes. This avoids the presence of a central dip or recess within the concave surface which could inhibit movement. It is also directly against the teaching in US-55601559 to use flutes which have a curved cross-section by definition and therefore will include a central dip or recess.

The trocar tip may have a cross-section taken perpendicular to the longitudinal axis through the tapered portion and the two concave surfaces which has the shape of a circle intersected by two parallel chords. The two parallel chords correspond to the position of the concave surfaces at that point along the length of the tip. The circle corresponds to the conical profile of the remainder of the tip.

The conical portion may define an angle between 19° and 25° with the longitudinal axis. This allows for gradual enlargement of the incision without requiring excessive force. The precise choice of angle will depend on the maximum diameter of the conical portion and its longitudinal extent. As an example, tip with a conical portion having a maximum diameter of 5mm may have an angle of about 20°, and a conical portion with a maximum diameter of 10mm or 12 mm may have an angle of about 23°. The two concave surfaces may have a substantially constant curvature in some

embodiments. This enables the concave surface to be manufactured more easily. The radius of curvature will vary depending on the dimensions of the tapered portion, for example it may be dependent on the length of the tapered portion along the longitudinal axis and the offset of the concave surface from the longitudinal axis at a distal end of the tapered portion. A tangent to the two concave surfaces may be parallel to the longitudinal axis at a distal end of the tapered portion. This, when combined with a substantially constant curvature, means that the distance between the two concave surfaces increases in the direction away from the end portion.

The end portion may be either rounded, which can minimise trauma to tissue, or pointed, which can enable use with a smaller incision than a rounded tip. This is unlike the configuration in WO-2008/103400 suggests a more complex tip profile where the second pair of surfaces is adjacent planar surfaces, not an end portion which is rounded or pointed.

Preferably the tapered portion includes exactly two concave surfaces.

The trocar tip may form part of a medical instrument. For example it may removably or permanently attached to a shaft of a medical instrument.

Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic representation of a perspective view of a trocar tip according to the present invention;

Figure 2 is a diagrammatic representation of a plan view of the trocar tip of Figure 1 showing the symmetry between concave surfaces;

Figure 3 is a diagrammatic representation of a side view of the trocar tip of Figure 1, perpendicular to the plan view of Figure 2; and

Figure 4 is a diagrammatic representation of a cross-section of the trocar tip of Figure 1, taken perpendicular to a longitudinal axis and in the region of a concave surface;

Figure 5 is a diagrammatic representation of an example of how the dimensions of the concave surface of the trocar tip of Figure 1 may be determined.

Figure 1 depicts a perspective view of a trocar tip according to the present invention. The trocar tip is attached to a shaft 2 of a medical instrument and extends in a distal direction along a longitudinal axis 4. The trocar tip comprises a tapered portion 6 which narrows in the direction along the longitudinal axis to a rounded end point 8. The tapered portion 6 of this embodiment has a maximum diameter of around 5mm and has a generally conical profile with a taper angle of around 20°. Alternative embodiments may have different dimensions, for example in embodiments with a maximum diameter of 10mm to 12mm the taper angle may be around 23.2°.

At two opposite sides of the tapered portion 6, symmetrical about a plane through the longitudinal axis 4, two concave surfaces 10 are defined by removing material from the tapered portion 6. The nature of the concave surface 10 can be seen in more detail in the plan view in Figure 2. The remainder of the tip, away from the cut out surfaces 10 retains the conical profile, so that when looking perpendicular to the direction of Figure 2, Figure 3 illustrates how the tip appears to have a standard conical profile.

In this embodiment the cut outs 10 extend the entire length of the tapered portion. In other embodiments (not shown) the cut outs may not extend the entire length of the tapered portion, so that the tapered portion includes a part which is conical around its entire circumference.

Figure 4 illustrates the cross-section of the trocar tip taken along line A-A illustrated in Figure 1. This shows how the cut out concave surfaces define a straight line which is parallel to a plane of symmetry 14. The cut out surfaces 10 form parallel chords cut from the circle of the otherwise conical shape of the tip. The remainder of the cross-section is therefore the edge of the circle between the two parallel chords. The cross-section depicted in Figure 4 has the form of a circle intersected by two parallel chords because in this embodiment the tapered surface is tapered in a single direction, in alternative embodiments where the concave surface is tapered in two directions, this cross- section would show the tapered surface to be curved, rather than a straight line. The trocar tip of the present invention may be manufactured from any suitable medical grade material. Its simple form enables it to be created by moulding or machining, for example from stainless steel for a reusable device or Gamma Radiation stable

Polycarbonate for a single use product.

In this embodiment, the trocar tip is typically around 20.3mm long (in the direction of the longitudinal axis). In alternative embodiments, the length may be different, for example in a 10mm maximum diameter trocar tip the length may be around 23 mm, in a 12mm maximum diameter trocar tip the length may be around 26mm.

Figure 5 is a diagrammatic representation of one way in which the dimensions of the concave surfaces 10 can be determined. In this example the concave surface 10 has a constant radius of curvature 16. The concave surface 10 extends for the length 18 of the tapered portion and the tapered portion has a maximum diameter 17. It is desired to ensure that the tangent to the curved surface 10 is parallel to the longitudinal axis adjacent the end portion (the end portion is not shown in Figure 5 for clarity). In this example the rounded end portion has a diameter 20 of about 1.4mm centred on the longitudinal axis. Therefore, the tangent of the curved surface is parallel to the longitudinal axis with an offset of about 0.7mm at point 22. The radius of curvature 16 is then determined based on the length 18 of the tapered portion and possibly also the maximum diameter 17. In this embodiment the length 18 is about 12.35mm, the maximum diameter is about 5.7mm and the radius of curvature is determined as about 36.5mm.

This technique can be adapted to the particular dimensions of each tip. It can also be adapted if the curved surface is not required to extend the entire length of the tapered surface by adjusting the offset from the longitudinal axis and possibly also the radius of curvature as required.

In use, a surgeon initially makes a small incision, for example for around 2mm in length. The end 8 of the trocar tip is then inserted into the incision and the trocar tip pushed through the incision. The action of the tapered portion enlarges the incision by spreading the tissue as it enters the incision. The force required to insert the trocar tip can be reduced by a combination of longitudinal pushing movements and rotation. The presence of the concave surfaces means that the rotation enlarges the incision by a greater amount than the cross-section of the tip, so that less force is required to insert it further and enlarge the incision after a rotational movement. The surgeon will therefore typically enlarge the incision by a combination of rotation and longitudinal movement. The present invention therefore provides a trocar tip which requires less force to insert into a patient than prior art designs and which is simple to manufacture.

Claims

1. A trocar tip having a longitudinal axis, wherein the trocar tip comprises:

an end portion coincident with the longitudinal axis; and

a tapered portion extending to the end portion and narrowing in the direction towards the end portion;

wherein the tapered portion comprises a conical surface about the longitudinal axis and two concave surfaces which are defined by cut outs from the conical surface and which extend along the entire length of the of the tapered portion.

2. A trocar tip according to claim 1, wherein the two concave surfaces are on opposite sides of the tapered portion and are symmetrical about a plane through the longitudinal axis.

3. A trocar tip according to claim 2, wherein the two concave surfaces are concave in a single direction.

4. A trocar tip according to claim 2 or 3, wherein a cross section perpendicular to the longitudinal axis through the tapered portion and the two concave surfaces has the shape of a circle intersected by two parallel chords.

5. A trocar tip according to any one of the preceding claims, wherein the conical portion defines an angle between 19° and 25° relative to the longitudinal axis.

6. A trocar tip according to any one of the preceding claims, wherein the two concave surfaces have a substantially constant curvature.

7. A trocar tip according to claim 6, wherein the radius of curvature of the two concave surfaces is dependent on the length of the tapered portion along the longitudinal axis and the offset of the concave surface from the longitudinal axis at a distal end of the tapered portion.

8. A trocar tip according to claim 6 or 7, wherein a tangent to the two concave surfaces is parallel to the longitudinal axis at a distal end of the tapered portion.

9. A trocar tip according to any one of the preceding claims, wherein the end portion is rounded.

10. A trocar tip according to any one of the preceding claims, wherein the end portion is pointed.

11. A trocar tip according to any one of the preceding claims, wherein the tapered portion comprises exactly two concave surfaces.

A medical instrument including a trocar tip according to any one of the preceding