CANNULA WITH SENSORS TO MEASURE PATIENT BODYWALL FORCES

Abstract

A cannula is provided that includes a head portion that defines a proximal opening sized to receive one or more surgical instruments; an elongated inner tube rigidly fastened to the head portion defines an elongated conduit; a surgical instrument can be inserted within the conduit; an elongated overtube rigidly fastened to the head portion is coaxially aligned with the inner tube and extends about a portion of the inner tube; an inner wall of the overtube is spaced apart from an outer wall of the inner tube; sensors are disposed on the overtube to provide an indication of forces applied to the outer wall of the overtube in a direction generally transverse to the longitudinal dimension of the overtube.

Claims

1. (canceled)

2. A surgical system cannula comprising: a head portion; an elongated portion coupled to the head portion; and one or more tissue load strain sensors; wherein a surgical instrument conduit extends distally from the head portion through the elongated portion; and wherein the one or more tissue load strain sensors are positioned on the elongated portion at a first location that is proximal to a second location at which the elongated portion contacts a patient body wall.

3. The surgical system cannula of claim 2, wherein: the elongated portion is a lever having a fulcrum positioned at the second location; and the one or more tissue load strain sensors are positioned proximal to the fulcrum.

4. The surgical system cannula of claim 3, wherein: the lever has an elongated longitudinal dimension that includes a proximal portion and a distal portion; the proximal portion depends from and is rigidly fastened to the head portion; and the distal portion is positioned to extend within a body cavity of a patient.

5. The surgical system cannula of claim 2, wherein: the head portion and the elongated portion are monolithically formed.

6. The surgical system cannula of claim 2, wherein: the elongated portion is an overtube; the surgical system cannula includes an inner tube; the inner tube is positioned axially with reference to the overtube; the inner tube includes the surgical instrument conduit; the inner tube includes a first portion that extends within the overtube; and the inner tube includes a second portion that extends outside the overtube.

7. The surgical system cannula of claim 6, wherein: a gap extends between the overtube and the first portion of the inner tube that extends within the overtube.

8. The surgical system cannula of claim 2, wherein: the surgical system cannula includes an insufflation port; and the insufflation port is positioned at a location that is proximal to the first location.

9. A surgical system, comprising: a surgical instrument including a proximal portion; an overtube surrounding the proximal portion of the surgical instrument; and at least one strain sensor on the overtube, the at least one strain sensor is positioned to provide an indication of a force imparted to the overtube by the surgical instrument.

10. The surgical system of claim 9, wherein: the surgical instrument includes a distal portion; the surgical system includes an inner tube; the inner tube surrounds the distal portion of the surgical instrument and includes a proximal portion and a surgical instrument conduit; the proximal portion of the inner tube is surrounded by the overtube; the surgical instrument conduit is sized to receive the surgical instrument; and during a condition in which the surgical instrument is under a load, the surgical instrument has at least one point of contact with the surgical instrument conduit of the inner tube.

11. The surgical system of claim 10, wherein: the overtube includes an inner wall; and the at least one strain sensor is positioned about the inner wall of the overtube.

12. The surgical system of claim 9, wherein: the overtube includes a fulcrum location; the at least one strain sensor is positioned distally of the fulcrum location; and the force is imparted by the surgical instrument at a location distal of the at least one strain sensor.

13. The surgical system of claim 9, wherein: the overtube includes an inner wall; the at least one strain sensor has an annular shape; the annular shape surrounds the surgical instrument; and the annular shape is positioned about the inner wall of the overtube.

14. The surgical system of claim 9, wherein: the surgical system includes a head portion; and the overtube depends from and is rigidly fastened to the head portion.

15. A surgical system cannula comprising: a head portion; an elongated portion having a proximal portion and a distal portion; and a sensor device; wherein the elongated portion includes a surgical instrument conduit that extends distally from the head portion; wherein the proximal portion of the elongated portion is coupled to the head portion; wherein the sensor device is positioned between the proximal portion and the distal portion of the elongated portion; and wherein the distal portion is coupled to the proximal portion via the sensor device.

16. The surgical system cannula of claim 15, wherein: the sensor device is positioned at a first location proximal to a second location at which the distal portion contacts a patient body wall.

17. The surgical system cannula of claim 15, wherein: the elongated portion is a lever having a fulcrum located at a second location; and the sensor device is positioned proximal to the fulcrum.

18. The surgical system cannula of claim 15, wherein: the sensor device is an annular sensor; and the sensor device surrounds the surgical instrument conduit.

19. The surgical system cannula of claim 18, wherein: the proximal portion of the elongated portion depends from and is rigidly coupled to the head portion; the proximal portion of the elongated portion includes a first annular flange; the first annular flange is sized to operatively contact a proximal surface region of the sensor device; the distal portion of the elongated portion includes a second annular flange; the second annular flange is sized to operatively contact a distal surface region of the sensor device; and the distal portion of the elongated portion is suspended from the sensor device.

20. The surgical system cannula of claim 18, wherein: the sensor device is a six degree-of-freedom sensor device.

21. The surgical system cannula of claim 15, wherein: the elongated portion is an overtube; the surgical system cannula includes an inner tube; the inner tube includes the surgical instrument conduit; the inner tube is positioned axially with reference to the overtube; a portion of the inner tube extends within the overtube; and a portion of the inner tube extends outside the overtube.

22. The surgical system cannula of claim 21, wherein: a gap extends between the overtube and the portion of the inner tube that extends within the overtube.

23. The surgical system cannula of claim 16, wherein: the surgical system cannula includes an insufflation port; and the insufflation port is positioned proximal to the first location.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

[0013] FIG. 1 is an illustrative side elevation cross-sectional view drawing showing a known cannula that acts as a conduit for one or more instruments extending through a patient's bodywall.

[0014] FIG. 2 is an illustrative drawing representing certain forces exerted upon an instrument inserted within a cannula and resultant force upon a patient's bodywall.

[0015] FIG. 3A is an illustrative side elevation drawing of a first cannula in accordance with some embodiments.

[0016] FIG. 3B is a cross-sectional view of the first cannula of FIG. 3A in accordance with some embodiments.

[0017] FIG. 4 is an illustrative side elevation drawing of a second cannula in accordance with some embodiments.

[0018] FIG. 5 is a perspective view of a six degree-of-freedom sensor in accordance with some embodiments.

[0019] FIG. 6A is an illustrative cross-sectional drawing of the first cannula showing an instrument disposed to collide with an inner tube in accordance with some embodiments.

[0020] FIG. 6B is an illustrative cross-sectional drawing of the first cannula showing an instrument disposed to impart a lever force to an inner tube in accordance with some embodiments.

[0021] FIGS. 6C1-6C4 are illustrative drawings showing longitudinal cross-sectional views of a portion of the overtube with four alternative sensor placement configurations in accordance with some embodiments.

[0022] FIG. 7 is an illustrative drawing representing an object that is subjected to axial force that changes its length dimension.

[0023] FIG. 8 is an illustrative drawings showing example of strain gauges mounted on opposite sides of a longitudinal structure subjected to a force transverse to a longitudinal axis of the structure.

[0024] FIG. 9 is an illustrative drawing of showing strain gauges arranged in a rosette-like configuration in accordance with some embodiments.

[0025] FIG. 10 is an illustrative cross-sectional drawing of the second cannula in accordance with some embodiments.

DESCRIPTION OF EMBODIMENTS

[0026] The following description is presented to enable any person skilled in the art to create and use a cannula with sensors isolated from forces resulting from instrument-cannula collisions. Various modifications to the embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the inventive subject matter. Moreover, in the following description, numerous details are set forth for the purpose of explanation. However, one of ordinary skill in the art will realize that the inventive subject matter might be practiced without the use of these specific details. Identical reference numerals may be used to represent different views of the same item in different drawings. Thus, the inventive subject matter is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.

[0027] FIG. 2 is an illustrative drawing representing certain forces exerted upon an instrument inserted within a cannula and resultant force upon a patient's bodywall. Both during laparoscopic surgery and telesurgery, insertion and movement of the cannula and instruments inserted within the cannula results in forces exerted upon a patient's abdominal bodywall. The cannula and an instrument inserted within the cannula have longitudinal axes, e.g., that extend generally parallel to a y-axis as shown. A surgeon, during laparoscopic surgery or telesurgery, may impart to a proximal end of the instrument that is disposed outside the patient's body, a lateral force having a force component generally perpendicular to the longitudinal axes of the cannula and the instrument. The surgeon force upon the instrument is imparted to the cannula. In reaction, internal body tissue that is contacted by a distal end of the instrument, inside the body cavity, may exert to a distal end of the instrument that is disposed inside the patient's body, a lateral force having a force component directed generally perpendicular to the longitudinal axes of the cannula and the instrument. The internal body tissue force upon the instrument is imparted to the cannula. The bodywall, which is disposed between a site of the surgeon imparted force and a site of the tissue imparted force, exerts a lateral direction reactive force, in response to a combination of the surgeon's force and the tissue's force having a force component directed generally perpendicular to the vertical axis of the cannula. More specifically, forces created in response to manipulation of instruments inserted within a cannula create a lever action in which a patient's bodywall is disposed at or near the fulcrum. These forces associated with the lever action exert stresses upon the bodywall tissue that can result in tissue trauma.

[0028] FIG. 3A is an illustrative side elevation drawing of a first cannula 302 in accordance with some embodiments. FIG. 3B is a cross-sectional view of the first cannula 302 of FIG. 3A in accordance with some embodiments. The first cannula 302 includes a head portion 304 and an elongated portion 306 that includes a coaxial elongated inner tube 308 and elongated overtube 310. The elongated portion 306, which includes the elongated inner tube 308 and elongated overtube 310 are generally cylindrical in contour. The elongated portion 306 depends from the head portion 304. More particularly, the inner tube 308 and the overtube 310 are rigidly fastened (i.e. welded or otherwise mechanically connected) to the head portion 304. In some embodiments, the inner tube 308 and the overtube 310 are formed integrally with the head portion.

[0029] The inner tube 308 includes inner walls that define an elongated inner conduit sized to receive one or more surgical instruments 312 (only one shown). The overtube 310 surrounds at least a portion of the inner tube 308, and extends distally enough to come into contact with the bodywall such that all the loads from the bodywall are imparted on the overtube and not the inner tube. The inner tube 308 is longer than the overtube 310, and therefore, extends distally past the distal end of the overtube 310. The inner tube 308 extending beyond the distal end of the overtube ensures that the instrument does not come into direct contact with the overtube during normal operation. The first cannula is shown with the elongated portion 306 extending through a patient's bodywall 314. The inner tube 308 has a lateral dimension that is sized to receive one or more surgical instruments and defines a distal opening at a distal end so as to provide surgical access within the patient's body. As more fully clearly represented in FIGS. 6A-6B, which are explained below, the overtube 310 is coaxially aligned with the inner tube 308 and is laterally spaced apart therefrom so as to not contact the inner tube 310 during normal operation. More particularly, as shown more clearly in FIGS. 6A-6B, the inner tube outer diameter is sufficiently smaller than the overtube inner diameter so that the inner tube and the overtube do not come into contact during normal operation. Sensor devices 311 disposed in contact with the overtube 310 wall are configured to provide an indication of forces imparted to the overtube 310 by the bodywall 314.

[0030] During a typical surgical procedure, the head portion 304 of the first cannula 302 is disposed outside of the patient's body cavity, and at least a portion of the elongated portion 306, which includes a portion of the inner tube 308 and a portion of the overtube 310, extends through the bodywall 314 to an interior of the patient's body cavity. The elongated portion 306 has a longitudinal axis, e.g., generally parallel to a y-axis as shown. One or more surgical instruments can be inserted through the head portion 304 and extend generally parallel to the center axis through an instrument-receiving conduit defined by the inner tube 308 so as to project out from the open distal end of the inner tube to the interior of a patient's body.

[0031] In some embodiments, the head portion 304 and the inner tube 308 comprise an integral structure that defines the instrument-receiving conduit in which the one or more instruments may be inserted. The head portion 304 defines a proximal opening 316 to the conduit. The proximal opening is enlarged so as to provide ease in insertion and removal of instruments, and conduit walls within the head portion are inclined so as to provide guide surfaces to guide instruments to the narrower diameter elongated portion of the conduit defined by the inner tube. In some embodiments, the head portion 304 also includes a gas conduit (not shown) to introduce one or more gases through the inner tube for insufflating the body cavity during a surgical procedure. In some embodiments, the head portion 304 also includes a seal (not shown) for preventing gas from escaping the body cavity during insufflation in a surgical procedure. In some embodiments adapted for use during laparoscopic surgery, the head portion 304 is sized and shaped to be held by a surgeon, for example, during insertion of a trocar (not shown) or withdrawal of an obturator (not shown), which form no part of the present invention.

[0032] The overtube 310 has stiffness such that it can deflect at one or more locations along its longitudinal axis in response to forces imparted generally transverse to its longitudinal axis by a patient's bodywall 314, e.g., including forces imparted generally in an x-axis or a z-axis direction, during a typical surgical procedure. Moreover, the overtube 310 stiffness and its lateral spacing from the inner tube 308 are such that an inner wall of the overtube and an outer wall of the inner tube do not physically contact each other when the overtube deflects relative to its longitudinal center axis in response to forces imparted to a patient's bodywall 314 during a typical surgical procedure. In some embodiments, spacing between the overtube and the inner tube comprises a gap 307, which is represented more clearly in FIGS. 6A-6B as gap 607, which is narrow enough to not add significantly to overall diameter of the elongated portion 306 of the cannula 302 so as to not significantly increase the size of a surgical incision required to insert the elongated portion 306 into a patient's body.

[0033] During normal operation, the gap region 307 (described more fully below and illustrated with reference to FIGS. 6A-6B) defined between the inner tube and the overtube isolates the overtube 310 from deflections that may be imparted to the inner tube 308 due to instrument contact with the inner tube in the course of a surgical procedure, for example. Such instrument contact may involve an instrument banging against an inner wall of the inner tube due to a surgeon's or a teleoperated robot's manipulation of instruments during a surgical procedure. The sensor devices (described more fully below) in contact with the overtube 310, therefore, are isolated from the effects of deflection forces imparted due to collisions between the instrument and the inner tube 308. Thus, a cannula in accordance with some embodiments can disambiguate forces imparted by instrument collisions with an inner wall of the inner tube from bodywall loads imparted to the overtube.

[0034] FIG. 4 is an illustrative side elevation drawing of a second cannula 402 in accordance with some embodiments. Features of the second cannula that are substantially identical to those of the first cannula 302 are identified by the same reference numerals used to identify the corresponding features in FIGS. 3A-3B and are not further described. The second cannula 402 includes a six degree-of-freedom (6-dof) sensor device 403. In some embodiments, the 6-dof sensor 403 includes a Stewart platform based force/torque sensor. The second cannula 402 includes a head portion 404 and coaxially aligned elongated inner tube 408 and elongated overtube 410. The inner tube 408 is sized to receive one or more surgical instruments 412 (only one shown). The overtube 410 of the second cannula 402 includes a first overtube portion 410-1 and a second overtube portion 410-2, and the 6-dof sensor 403 is disposed between the first and second overtube portions.

[0035] FIG. 5 is a perspective view of a six degree-of-freedom sensor 403 in accordance with some embodiments. The 6-dof force/sensor has an annular shape that defines a central opening 424 through which instruments (not shown) and the inner tube 408 can extend. In some embodiments, the 6-dof sensor includes silicon strain gages to sense forces. Referring again to FIG. 4, first overtube portion 410-1 rigidly depends from a head portion 404 of the second cannula 402. The first overtube portion 410-1 includes a distal end that defines a first annular flange 428-1 sized to operatively contact a proximal surface region 430 of the 6-dof sensor 403. The second overtube portion 410-2 incudes a proximal end that defines a second annular flange 428-2 sized to operatively contact a distal surface region 426 of the 6-dof sensor 403. Attachment fasteners (e.g., screws) 429 are visible also.

[0036] FIG. 6A is an illustrative cross-sectional drawing of the first cannula 600 representing an example collision between an instrument 622 and the inner tube 604 in accordance with some embodiments. The first cannula 600 includes the head portion 602 and the elongated portion 603. The head portion 602 defines an insufflation conduit 640 through which an insufflating gas can be introduced inside the inner tube 604 and inside the patient's body cavity via the inner tube during a surgical procedure. The elongated portion 603 includes the coaxial inner tube 604 and overtube 606, which depends from the head portion 602. The inner tube includes an inner wall 605 that defines the instrument-receiving conduit and an outer wall 619. The gap 607 is defined by an outer wall 619 of the inner tube and an inner wall 616 of the overtube. Together, the head portion 602 and the inner wall 605 of the inner tube 604 define the instrument-receiving conduit 608. The head portion 602 defines the proximal opening 610 to the conduit 608. A distal end of the inner tube 604 defines a distal opening 612 to the conduit 608 adjacent to a patient's body cavity. Strain sensors 614 are disposed to contact an inner wall 616 of the overtube 604 and/or an outer wall 618 of the overtube 604 and are configured to measure strain imparted to the overtube.

[0037] Referring to the illustrative drawings of FIGS. 6C1-6C4, there are shown longitudinal cross-sectional views of a portion of the overtube 606 with four alternative sensor placement configurations in accordance with some embodiments. FIG. 6C1 shows an illustrative first sensor placement on outer wall 618 of the overtube 606. On one side of the outer wall 618, there is a sensor 614 and 180 degrees apart on the opposite outer wall 618 from that sensor 614 there is the complementary sensor 614. FIG. 6C2 shows an illustrative second sensor placement on inner wall 616 of the overtube 606. On one side of the inner wall 616, there is a sensor 614 and on an opposed facing portion of the inner wall 616 there is the complementary sensor 614. FIG. 6C3 shows an illustrative third sensor placement on both inner wall 616 and outer wall of the overtube 606. On the inner wall 616, there is a sensor 614 and on a portion of the outer wall 618 directly opposite that sensor 614 there is a complementary sensor 614. FIG. 6C4 shows an illustrative fourth sensor placement with redundant sensor placements like that of FIG. 6C3.

[0038] Referring again to FIG. 6A, during performance of a surgical procedure, the first cannula 600 extends through a patient's bodywall 620, and an instrument 622 extends within the conduit 608 to reach inside the patient's body cavity. The instrument 622 may include an end-effector 624 for use in performing a surgical procedure. An operator 626, such as a surgeon or a teleoperation surgical system manipulates the instrument 622 while it extends within the conduit 608 and into a patient's body.

[0039] During the procedure, a force F.sub.Operator imposed by the operator 626 upon the instrument 622 and/or a force F.sub.Tissue imposed by patient tissue upon the instrument 622 may cause the instrument to collide with the inner wall 605 of the inner tube 604, which imparts a force F.sub.Instrument upon the inner wall 605 of the inner tube 604. However, the instrument collision force is not imparted to the overtube 606 since it is isolated from the inner tube 604 by the gap 607. Thus the sensors 614 configured to sense strain in the overtube 606 do not detect deflections from force F.sub.Instrument imparted due to collisions between the instrument 622 and the inner tube 604.

[0040] It will be appreciated that the force F.sub.Instrument upon the inner wall 605 of the inner tube 604 imparts a load through the overtube 606 to the patient's bodywall. However, the gap 607 between the inner tube 604 and the overtube 606 isolates the overtube 606 from incurring deflections due to collisions between the inner tube 604 and the instrument 622. Thus, deflections imparted to the overtube 606 result from patient bodywall forces, which may be responsive to a force F.sub.Instrument upon the inner wall 605 of the inner tube 604, but such deflections are not imparted due to the collisions between the instrument 622 and the overtube 606, since there are no such collisions.

[0041] The overtube 606 has a stiffness such that it can deflect relative to its longitudinal axis in response to lateral forces imparted by the patient's bodywall 620, in a direction generally perpendicular to its longitudinal axis, e.g. in an x-axis or z-axis direction, but having an component force in the y-axis when the angle between the cannula and bodywall, e.g., θ, is not 90 degrees. Additionally the overtube 606 has a compressive strength such that it can compress or stretch along it's longitudinal axis in response to non-lateral bodywall forces, e.g. in the y-axis direction.

[0042] More specifically, in some embodiments the overtube stiffness has a predictable and linear strain response to stress, i.e. a known young's modulus. More specifically, in some embodiments, the stiffness of the overtube is great enough for the tube to deflect and not permanently deform under typical body wall loads of approximately 0-30 Newtons. Even more specifically, in some embodiments, the stiffness of the overtube is great enough for the tube to deflect and not permanently deform under loads of approximately 0-50 Newtons. In some embodiments, a stainless steel overtube with a wall thickness of approximately 0.005-0.050, with a preferred of approximately wall thickness range of approximately 0.012-0.030, and an outside diameter of approximately 0.25-1 inches, with a preferred range of approximately 0.4-0.6 inches, has an acceptable stiffness to deflect but not permanently deform under normal loads from the bodywall. Preferably, in some embodiments, Spacing between the overtube and the inner tube should be great enough such that the inner diameter (ID) of the overtube does not touch the outer diameter (OD) of the inner tube when the overtube deflects, but small enough such that the outer diameter of the overtube represents typical cannula diameters in minimally invasive surgery. In some embodiments, the spacing, 607 of FIG. 6A, between the overtube ID and inner tube OD is approximately 0.007-0.1 inches, with a preferred range of approximately 0.015-0.035 inches.

[0043] FIG. 6B is an illustrative cross-sectional drawing of the first cannula 600 showing an instrument 622 disposed to impart a lever force to the inner tube 604 in accordance with some embodiments. It will be appreciated that FIG. 6A and FIG. 6B are identical except for the disposition of the instrument within the inner tube and the forces imparted. Assume that an operator imparts a force F.sub.Operator and the tissue imparts a force F.sub.Tissue that cause the instrument 622 to push to the left in FIG. 6B against an inner wall 605 of the inner tube 604 adjacent a proximal end of the inner tube 604 and that cause the instrument 622 to push to the right in FIG. 6B against the inner wall 605 of the inner tube 604 adjacent a distal end of the inner tube 604. Under these conditions, for example, the first cannula 600 acts as a lever having a fulcrum at a location generally indicated by dashed lines 630, at about the location of the bodywall 620.

[0044] Under these conditions, a bodywall force F.sub.Bodywall is imparted to the patient's bodywall 620. The bodywall force can be a torque or a force, for example, in which a distal end of the overtube 606 imparts a force in a direction generally to the right in the drawing and a proximal end of the overtube 606 imparts a force in a direction generally to the left in the drawing, for example. The torque force to the overtube 606 about an x-axis and/or the z-axis, for example, centered at about the location of the bodywall 620. In accordance with some embodiments, the bodywall force F.sub.Bodywall is imparted to the overtube 606, which may deflect in response to the bodywall force. The sensors 614 can detect strain in the overtube that results from the force or torque and can provide a measure of the strain.

[0045] The sensor devices 614 are disposed in physical contact with the overtube 606 to measure deflection of the overtube 606. Sensor devices can be disposed in contact with an external wall 618 of the overtube, in contact with an interior wall 616 of the overtube or in contact with both. In some embodiments, the sensor devices 614 are configured to act as strain gauges. Strain is a measure of the amount of deformation of a body due to an applied force. More specifically, strain can be defined as the fractional change of length.

[0046] FIG. 7 is an illustrative drawing representing an object 702 that is subjected to axial force that changes its length dimension. The length of the object in the absence of the forces is L. The change in the object's length in response to the forces is ΔL.

Strain can be defined as: ε=ΔL/L.

[0047] FIG. 8 is an illustrative drawings showing example of first and second strain gauges 802-1, 802-2 mounted on opposite sides of a longitudinal structure 804 that depends horizontally from a fixture 806 and that is subjected to a force transverse to a longitudinal axis (L) of the structure 804. An example generally downward uniaxial force imparted transverse to a longitudinal axis of the structure places the first strain gauge 802-1 having an at rest length L.sub.1 mounted on a side of the structure to which the force is imposed in tension, resulting in an increase in the length dimension of the first strain gauge 802-1 to L.sub.1+ΔL.sub.1. Conversely, the downward uniaxial force imparted transverse to the longitudinal axis of the structure 804 places the second strain gauge 802-2 having an at rest length L.sub.1 mounted on a side of the structure 804 opposite to that to which the force is imposed in compression, resulting in a decrease in the length dimension of the second strain gauge 802-2 to L1−ΔL.sub.2. In accordance with some embodiments, strain gauges are mounted to the inner wall 616 and the outer wall 618 of the overtube 606 and may be spaced around the overtube in a variety of configurations in order to measure the applied forces in multiple directions.

[0048] As explained above with reference to FIG. 6B, moments from the bodywall can create complex tube deflection that includes tension and compression simultaneously along various points in length of the loaded member. In some embodiments, such moments can be calculated when a staggered configuration of strain gauges is used because the strain gauges are experiencing both tension and compression at known points along inner and outer walls of the surface of the overtube.

[0049] FIG. 9 is an illustrative drawing of showing strain gauges 902 arranged in a rosette-like configuration in accordance with some embodiments. Strain gauges are well known to persons of ordinary skill in the art. In some embodiments, a strain gauge may comprise a grid pattern 904 that includes a very fine metallic wire, foil, fiber, etc. arranged in a grid pattern. The grid 904 is bonded to a thin backing (not shown), commonly referred to as a carrier which is directly attached to an item for which strain is to be measured. Strain that is experienced by such item is transferred directly to the strain gauge, which responds with a known, e.g., linear, change in electrical resistance. In a rosette-like configuration, multiple strain gauges are positioned at known angles (e.g., α, β, γ) to one another in a rosette-like layout to convert longitudinal strain into three independent components of plane strain. In accordance with some embodiments, groupings of sensors arranged in a rosette structure can be staggered along the inner wall 616 and outer wall 618 of the overtube 606 to measure moments about the x-axis and z-axis.

[0050] FIG. 10 is an illustrative cross-sectional drawing of the second cannula 1000 in accordance with some embodiments. The second cannula 1000 includes an annular 6-dof sensor 632. The overtube 606 includes the first overtube portion 636 that includes the first annular flange 638 sized to operatively contact a proximal surface region 640 of the 6-dof sensor 632. The overtube 606 includes the second overtube portion 642 that has a proximal end that defines the second annular flange 644 sized to operatively contact a distal surface region 646 of the 6-dof sensor 632. Thus, the second overtube portion 642 is suspended from the 6-dof sensor 632. It will be appreciated that in other respects the first and second cannulas of FIG. 6A-6B and FIG. 10 are substantially the same.

[0051] The foregoing description and drawings of embodiments in accordance with the present invention are merely illustrative of the principles of the invention. Therefore, it will be understood that various modifications can be made to the embodiments by those skilled in the art without departing from the spirit and scope of the invention, which is defined in the appended claims.