The present invention generally relates to nested cannula design and configurations that are customized for a patient to facilitate minimally invasive surgical procedures. The present invention specifically relates to a cannula interlocking mechanism that facilitates a fixed relative orientation of the telescoping tubes to each other.

International Application WO 2008/032230 entitled "Active Cannula Configuration for Minimally Invasive Surgery" to Karen I. Trovato teaches systems and methods related to nested cannula design and configurations that are customized for a patient to facilitate minimally invasive surgical procedures. Generally, the nested cannulas design is created for a specific patient based on a pre-acquired 3D image of a particular anatomical region of the patient, and an identification of a target location within the anatomical region. Specifically, nested cannulas (or a nested cannula configuration) are designed by utilizing the 3D image to generate a series of arc and straight shapes from a particular position and orientation in the 3D image of the anatomical region. The generated arc and straight shapes are utilized to calculate a pathway between an entry location and the target location. The generated pathway is utilized to generate a plurality of nested telescoping tubes that are configured and dimensioned with pre-set curved shapes. The tubes are typically extended largest to smallest, and the planner specification defines the lengths and the relative orientations between successive tubes to reach the target location.

The tubes are fabricated from a material exhibiting desirable levels of flexibility/elasticity. For example, the material may be Nitinol, which has superelastic properties that allow the Nitinol to bend when a force is applied and to return to its original shape once the force is removed. The tubes should maintain a relative orientation to each other when fully extended to comply with the generated pathway. Tubes with circular cross sections have proven to be potentially unstable for certain configurations of the tubes. For example, long thin tubes with circular cross section may exhibit instability when curvatures of two (2) adjacent tubes are oriented at 180 degrees. In this case, movement of the tubes (e.g., for example due to vibration or extension through other curved shapes) may cause a sudden 'snap', where the tubes suddenly lose their 180 degree relative orientation. This uncontrolled movement may significantly deviate the tubes from the desired pathway and can damage tissue. Additionally, even in orientations other than 180 degrees, the tubes may twist relative to one another and cause inconsistent orientation.

The present invention is premised on an interlocking of telescoping tubes to facilitate a consistent relative orientation throughout the nested tubes that is preserved as the tubes are being extended. This ensures that the orientation set by the pathway planner can be achieved by the tubes.

One form of the present invention is an interlocking nested cannula set having a plurality of interlocking telescoping tubes cooperatively configured and dimensioned to reach a target location relative to an anatomical region. In this set, each tube has a preset interlocking shape. Additionally, a nesting of an inner tube within an outer tube includes a gap between the tubes, which interlock within the gap to limit rotation of the tubes relative to the gap.

Another form of the present invention is a nested cannula system employing a pathway planner for designing a plurality of interlocking telescoping tubes configured and dimensioned to reach a target location relative to an anatomical region. In this system, each tube has a pre-set interlocking shape. Additionally, a nesting of an inner tube within an outer tube includes a gap between the tubes, which interlock within the gap to limit rotation of the tubes relative to the gap.

The foregoing forms and other forms of the present invention as well as various features and advantages of the present invention will become further apparent from the following detailed description of various embodiments of the present invention read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the present invention rather than limiting, the scope of the present invention being defined by the appended claims and equivalents thereof.

FIG. 1. illustrates an exemplary pair of interlocking tubes in accordance with the present invention prior to the inner tube being nested within the outer tube.

FIGS. 2-4 illustrates the interlocking principle of the present invention. FIG. 5 illustrates a first exemplary interlocking of the tubes shown in FIG. 1 in accordance with the present invention.

FIG. 6 illustrates a second exemplary pair of interlocking of the tubes shown in FIG. 1 in accordance with the present invention. FIGS. 7-20 illustrate various interlocking shapes in accordance with the present invention.

FIG. 21 illustrates an exemplary embodiment of a nested cannula system in accordance with the present invention.

FIG. 22 illustrates an exemplary 3-D neighborhood of arcs representing a nested cannula set of interlocking telescoping tubes in accordance with the present invention having pre-set shapes and curvatures.

The present invention is premised on a nested pair of tubes having interlocking shapes to limit rotation of the tubes relative to a gap between the tubes. One benefit of this interlocking of the tubes is a fixed or consistent orientation of the inner tube relative to the outer tube as the inner tube is extended into or retracted from the outer tube. This benefit is particularly important in the context of the inner tube having a non-zero curvature (e.g., an arc).

For example, FIG. 1 illustrates an inner tube 30 and an outer tube 40 for purposes of demonstrating the premise of the present invention. Tubes 30 and 40 are configured and dimensioned to facilitate a nesting of inner tube 30 within outer tube 40 with a gap 50 between tubes 30 and 40 as shown in FIGS. 2-4. Gap 50 is required to facilitate a nesting of inner tube 30 within outer tube 40 with minimal friction. Tubes 30 and 40 have a square interlocking shape that limits rotation of tubes 30 and 40 relative to gap 50 as shown in FIGS. 2-4. More particularly, FIG. 2 illustrates a symmetrical nesting of inner tube 30 within outer tube 40, FIG. 3 illustrates a rotation of inner tube 30 within outer tube 40 that is limited by outer tube 40, and FIG. 4 illustrate a rotation of outer tube 40 about inner tube 30 that is limited by inner tube 30.

In practice, the gap between nested tubes will typically be small relative to the size of the tubes. However, tubes 30 and 40 are not drawn to scale for purposes of demonstrating the premise of the present invention. Nonetheless, FIGS. 2-4 exemplify a benefit of interlocking tubes 30 and 40 in achieving a consistent orientation of inner tube 30 relative to outer tube 40 as inner tube 30 is extended into or retracted from the outer tube 40. For example, FIG. 5 illustrates a consistent orientation of inner tube 30 relative to outer tube 40 with gap 50 therebetween in view of both tubes 30 and 40 having a zero curvature (i.e., straight) and FIG. 6 illustrates a consistent orientation of inner tube 30 relative to outer tube 40 with gap 50 therebetween in view of inner tube 30 having a non-zero curvature and outer tube 40 having a zero curvature.

In practice, a nested cannula set of the present invention employs two or more telescoping tubes with each tube having a pre-set interlocking shape and a pre-set curvature . For the outermost tube of the set, the pre-set interlocking shape is relevant for the inner surface of such tube. For the innermost tube of the set, the pre-set interlocking shape is relevant for the outer surface of such tube. For any intermediate tube of the set, the pre-set interlocking shape is relevant for both the external and outer surfaces of such tube.

Also in practice, the interlocking shape of each tube is any shape that interlocks an inner tube to an outer tube whenever the inner tube is nested within the outer tube whereby any individual rotation about the gap therebetween by the inner tube is limited by the outer tube and any individual rotation about the gap therebetween by the outer tube is limited by the inner tube. Such interlocking shapes for the tubes include, but are not limited to, a polygonal interlocking shape, a non-circular closed curve interlocking shape, a polygonal-closed curve interlocking shape, and a keyway interlocking shape. Yet another variety of interlocking shapes relies on non-scaled versions of a single shape, for example a rectangle or triangle interlocked within a hexagon.

For example, FIG. 7 illustrates a triangular interlocking shape of an inner tube 90 and an outer tube 91 with a gap 92 therebetween.

FIG. 8 illustrates a rectangular interlocking shape of an inner tube 100 and an outer tube 101 with a gap 102 therebetween.

FIG. 9 illustrates a hexagonal interlocking shape of an inner tube 110 and an outer tube 111 with a gap 112 therebetween.

FIG. 10 illustrates an octagonal interlocking shape of an inner tube 120 and an outer tube 121 with a gap 122 therebetween. FIG. 11 illustrates an alternative square interlocking shape of an inner tube 130 and an outer tube with square inner shape and octagonal outer shape 131 with a gap 132 therebetween. FIG. 12 illustrates an alternative triangular interlocking shape of an inner tube 140 and an outer tube with triangular inner shape and hexagonal outer shape 141 with a gap 142 therebetween.

FIG. 13 illustrates an elliptical interlocking shape of an inner tube 150 and an outer tube 151 with a gap 152 therebetween.

FIG. 14 illustrates a semicircular interlocking shape of an inner tube 160 and an outer tube 161 with a gap 162 therebetween.

FIG. 15 illustrates a flute interlocking shape of a flute inner tube 170 and a flute outer tube 171 with a gap 172 therebetween. FIG. 16 illustrates an alternative flute interlocking shape of an inner tube having a fluted outer shape and circular inner shape 180 and an outer tube having a fluted inner shape and circular outer shape 181 with a gap 182 therebetween.

FIG. 17 illustrates a cardioid interlocking shape of an inner tube 190 and an outer tube 191 with a gap 192 therebetween. FIG. 18 illustrates a keyway interlocking shape of an inner tube 200 and an outer tube 201 with a gap 202 therebetween.

FIG 19 illustrates a rectangular interlocking shape of an inner tube 210 and an outer hexagonal tube 211 with a gap 212 therebetween.

FIG 20 illustrates a triangular interlocking shape of an inner tube 220 and an outer hexagonal tube 221 with a gap 222 therebetween.

Referring to FIGS. 5, 7, 9-12 and 20, each of the illustrated polygon interlocking shapes have an N number of equal sides of the larger locking polygon, wherein N > 2. In practice, compliance with the following equations [1] and [2] as associated with corresponding sides of such tubes facilitates an interlocking of the tubes in accordance with the present invention:

K = cos(π/N) [2]

where OSu is the length of each outer side of the inner tube, IS _OT is the length of each inner side of outer tube, and N is the number of sides of the inside of the larger polygonal tube. For example, referring to FIG. 1, a ratio of a length Ll of each outer side 31 of inner tube 30 to a length L2 of each inner side 41 of outer tube 40 must be equal to or great than factor K based on N = 4. In FIG. 9 for example, N=6, therefore K= cos(π /6) = sqrt(3) / 2 or about 86.6%. This means that the outer side of the inner tube must be at least 86.6% of the length of the inner side of the outer tube in order to interlock. Clearly, as the number approaches 100%, there is a smaller gap, and lower error in possible rotation.

FIG. 21 illustrates a pathway planner 230 as known in the art for designing a plurality of telescoping tubes with configured and dimensioned with pre-set shapes and curvatures. Pathway lanner 230 specifies the specific lengths that the tubes are extended to reach a target location relative to an anatomical region. Specifically, pathway planner 230 uses a neighborhood of arc and straight threads to encapsulate a set of fundamental motions of a nested set of interlocking tubes 231 of the present invention that can be performed in free space based on available controls and mechanical properties of the tubes 231, and more particularly, based on the available fixed orientations between nested tubes 231. Based on the neighborhood, pathway planner 230 defines the extension of each tube to achieve a specific length, and the orientation of each tube relative to the previous tube.

An example set of tubes might be specified as follows, wherein the term thread is used to describe the selected arc having a specific tube orientation relative to the prior tube, and the length is the extension of the current tube relative to the prior tube:

Number of tubes needed for this path is: 8

Tube number 1 length= 17.4994mm, thread = 6 Tube number 2 length= 63mm, thread = 0 Tube number 3 length= 7.49973mm, thread = 1

Tube number 4 length= 28.5mm, thread = 0 Tube number 5 length= 7.99971mm, thread = 5 Tube number 6 length= 7.5mm, thread = 0 Tube number 7 length= 1.99993mm, thread = 4 Tube number 8 length= 3.5mm, thread = 0 Generally, a neighborhood may have discrete rotational arcs in view of the fact that discrete rotational symmetries minimize the number of pre-manufactured tubes by providing multiple ways to use each tube. For example, FIG. 22 illustrates an exemplary neighborhood 240 having a straight thread 241 and six (6) 14mm turning radius arcs 242-247. Each of the arcs 242-247 can be extended to any length, following the same curvature. Each arc is preferably short enough so that the arc does not return to the same point (position and orientation). The optimal interlocking shape for the tubes 231 (FIG. 21) resulting from this neighborhood 240 is a hexagonal interlocking shape corresponding to the discrete rotational symmetry of arcs 242-247, which would yield six (6) settable angles for each nested tube 231.

Hexagonal tubing can be formed by extrusion, casting, creasing, drawing, forming and shrinking. The extrusion process is accomplished by pushing molten material through a die with the desired tubes shape. Casting is accomplished by cooling molten material held within a mold. Creasing is accomplished by pressing deformable tube to create the desired corners; a roughly hexagonal shape can thus be created by pressing the originally circular tube flat three times (each time the tube is by rotated sixty degrees). Another form of manufacturing hexagonal tubes using creasing is to introduce five 120 degree creases in a sheet of material and to weld the two ends of the sheet together. Forming is accomplished by heating a deformable material and constraining it to take the desired hexagonal shape. Shrinking is accomplished by heating heat shrink tubing around a hexagonal form. Though extrusion followed by drawing is an exemplary process for large-scale production, prototypes can be made by using the shrinking method. Often it is desirable to curve each of the tubes. This is performed by shaping the die to create curved tubing by: generating a curved mold, or creasing an already curved circular tube, or forming onto or with a curved mold, or shrinking onto a curved form. Curving the tube can also be done after the hexagonal shape has been made by heating the material and constraining its path to the desired curve. An exemplary method for curving drawn tubes is to deform the tubes at ambient temperature. An exemplary method of curving shrink tubes is to create the tubes around an already curved mandrel. The cannula may consist of any single material, or of a composite of multiple materials. The desired materials will depend on the application and the manufacturing processes that are available. Often flexible materials that can support their own weight and the weight of the payload without considerable deflection under the gravitational force are desired. If the cannula must apply forces at its tip or along its surface, the cannula constructed should be rigid enough to apply these forces without considerable deflection. It is also desirable for the tube to be firm enough to hold its shape; if the tube deforms too readily the cannulas may not hold their angles. When the tubes are to be translated with respect to one another it is desirable to select tube materials that minimize friction along the interface. Some materials and applications may require an intercannular lubricant to reduce the frictional resistance. For surgical application is also important that the material be fit for internal human contact. Additionally, some surgical applications require a non- ferromagnetic material to allow MRI imaging during the procedure. For flexible surgical applications that also require very small cannula diameters, or when significant forces are present, autoclavable superelastic nickel titanium alloys may be used. For other applications a wide variety of polymers may be used. These include, but are not limited to Polycarbonate, Nylon, Polypropylene, Polyolefins, and Teflon PTFE.

While various embodiments of the present invention have been illustrated and described, it will be understood by those skilled in the art that the methods and the system as described herein are illustrative, and various changes and modifications may be made and equivalents may be substituted for elements thereof without departing from the true scope of the present invention. In addition, many modifications may be made to adapt the teachings of the present invention to entity path planning without departing from its central scope. Therefore, it is intended that the present invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out the present invention, but that the present invention include all embodiments falling within the scope of the appended claims.