Patent Description:
A conventional tissue shaver cutter head assembly <NUM> is shown in <FIG>. The cutter head assembly <NUM> has an outer cutter head <NUM> and an inner cutter head <NUM>. The inner cutter head <NUM> is sized to be inserted into the outer cutter head <NUM>, with both extending along a longitudinal axis <NUM>. When assembled, the inner cutter head <NUM> can rotate, relative to the outer cutter head <NUM>, about the longitudinal axis <NUM>. Each cutter head <NUM>, <NUM> has a respective cutter opening <NUM>, <NUM> that leads into an internal cannula <NUM>, <NUM> extending through the head <NUM>, <NUM>. Each opening <NUM>, <NUM> is defined between edges <NUM>, <NUM> extending along the longitudinal direction <NUM>, and each edge <NUM>, <NUM> has teeth <NUM>, <NUM>. As the inner cutter head <NUM> and outer cutter head <NUM> rotate relative to each other, the teeth <NUM>, <NUM> of the two cutter heads slide past each other to sever adjacent tissue. The severed tissue is pulled through the inner cannula <NUM> for collection or disposal.

Referring for example to the illustrations of the outer cutter head <NUM>, each tooth <NUM> as a proximal surface 28a and a distal surface 28b, which join at a tooth point 28c. The proximal surface 28a and distal surface 28b also form a tooth edge 28d, that extends from the tooth point 28c in a direction away from the respective opening edge <NUM>.

The cutter opening <NUM>, edges <NUM> and teeth <NUM> typically are formed by using a cutting tool to remove a portion of the tubular wall of the cutter head <NUM>. The cutting tool may be a cutting wheel, a grinder, a laser cutter, or the like. The cutting tool operates along a cutting path <NUM> that extends perpendicular to the longitudinal axis <NUM>, and so the proximal surface 28a, distal surface 28b, and tooth edge 28d all extend parallel to the cutting path <NUM>, and perpendicular to the longitudinal axis <NUM>. When the cutter head <NUM> has a cylindrical shape (i.e., a circular profile extending along the longitudinal axis <NUM>), as typically is the case, the cutting path <NUM> defines a chord of the circular profile of the cutter head <NUM>. Thus, in this case, the proximal surface 28a and distal surface 20b are defined by a continuous series of chord lines, and the tooth edge 28d forms a single chord line.

The teeth <NUM>, edges <NUM> and opening <NUM> of the inner cutter head <NUM> typically are made like those of the outer cutter head <NUM> - i.e., using a cutting tool that moves along a cutting path <NUM> that is perpendicular to the longitudinal axis <NUM>. Thus, the proximal and distal surfaces and tooth edge of each tooth <NUM> also extend parallel to the cutting path <NUM> and perpendicular to the longitudinal direction <NUM>.

The foregoing construction is known to be beneficial because it allows simple and cost-effective fabrication using machine tools, such as a cutting wheel or grinder. This is particularly important in the context of shaver cutting heads, which can be very small (e.g., <NUM> or smaller in diameter, and having a wall thickness of well below <NUM>) and difficult to using complex machining motions. For example, a cutter head as described above can be fully formed from a tube by moving a grinding wheel back and forth along the cutting path, while indexing the tube along the longitudinal axis after each cutting tool pass (or indexing the cutting tool while holding the tube still). Each pass of the cutting tool forms a root of a tooth on each side of the opening, as well as the portion of the opening between those teeth. The shape of the grinding wheel defines the shapes of the teeth, and a full opening with all of the teeth can be formed in, for example, just four passes.

The foregoing construction is also known to be beneficial because it allows simple and cost-effective fabrication using laser cutting tools. For example, a laser cutter can be oriented to project along a cutting path that is perpendicular to the longitudinal axis, and, while maintaining a perpendicular relationship with the longitudinal axis, the laser cutter is moved along the cutter head along as shown by arrows <NUM> in <FIG>. As the laser cutter moves, it simultaneously cuts through the tube at two locations - i.e., one on each side of what will become the opening. At the end of the motion, the waste falls free from the remainder of the tube, leaving the opening with its edges and teeth.

With this conventional understanding in place, the concept of modifying the particular shape of the cutter head teeth has not been developed, and its benefits have remained undiscovered.

<CIT> discloses an arthroscopic shaver with an inner cutting window having a plurality of teeth positioned along the lateral cutting edges, the teeth being configured for easy penetration into tissue to prevent ejection of tissue from the cutting window during closure. The inner cutting edges are formed complete by a predetermined sequence of positioning moves and grinding passes on a multi-axis grinding machine. The teeth may be symmetrically or asymmetrically placed about the tube axis when viewed in a plan view.

<CIT> discloses a surgical shaver blade provided with a stationary elongated outer tube, having a cutting window at its distal tip and a rotatable elongated inner tube having a cutting window at its distal tip. Each cutting window is not symmetrical about any line in a sectional view through the window normal to the tube axis. In a preferred embodiment the cutting edges of each window have a plurality of teeth, the teeth of one lateral cutting edge being offset axially from the teeth of the other lateral edge so that the teeth of one edge align axially with the valleys between teeth on the opposite edge.

<CIT> discloses surgical tool systems and methods of use thereof for performing endoscopic surgical procedures, which systems include a handpiece and a surgical accessory which detachably connects to the handpiece. The surgical accessory has a distal end which defines a cutting head incorporating two different types of tissue-treating areas.

The invention is defined in claims <NUM> and <NUM>. In a first exemplary embodiment, there is provided a surgical tissue shaver comprising: a shaft extending from a proximal shaft end to a distal shaft end, the shaft comprising a tubular body defining a cannula extending from the proximal shaft end to the distal shaft end; and a cutter head at the distal shaft end and extending along a longitudinal axis, the cutter head having a cutter opening in fluid communication with the cannula, wherein at least a portion of the cutter opening extending along the longitudinal axis is defined between a first row of teeth and a second row of teeth opposite the first row of teeth with respect to the longitudinal axis. At least one tooth of the first row of teeth is defined by a respective proximal tooth surface and a respective distal tooth surface that intersect at a respective tooth edge, and wherein the respective tooth edge is oriented at a respective angle of less than <NUM>° relative to the longitudinal axis.

In another exemplary embodiment, there is provided a method for manufacturing a tissue shaver cutter head, the method comprising: providing a cutter head blank comprising a hollow tube extending along a longitudinal axis; orienting a cutting tool along a first cutting path, wherein the first cutting path extends at a first angle less than <NUM>° relative to the longitudinal axis and intersects the cutter head blank; and activating the cutting tool to cut along the first cutting path to cut a first tooth defined by a respective proximal tooth surface and a respective distal tooth surface that intersect at a respective tooth edge, wherein the respective tooth edge is oriented parallel to the first cutting path.

The following is a description of exemplary and non-limiting embodiments of a surgical tissue shaver, and parts thereof. Surgical tissue shavers are devices that might be used during arthroscopic surgical procedures to collect body tissue (bone, ligament, muscle, lesions, etc.), but the embodiments are not necessarily limited to such uses.

Referring now to <FIG>, an example of a surgical tissue shaver assembly <NUM> is schematically illustrated. The shaver assembly <NUM> includes an outer shaft <NUM>, and an inner shaft <NUM> arranged concentrically within the outer shaft <NUM>. The outer shaft extends from a proximal outer shaft end <NUM> to a distal outer shaft end <NUM>, and comprises a hollow tubular body having a cannula <NUM> extending from the proximal outer shaft end <NUM> to the distal outer shaft end <NUM>. Likewise, the inner shaft <NUM> extends from a proximal inner shaft end <NUM> to a distal inner shaft end <NUM>, and comprises a hollow tubular body having a cannula <NUM> extending form the proximal inner shaft end <NUM> to the distal inner shaft end <NUM>. In this case, the inner and outer distal shaft ends <NUM>, <NUM> terminate at approximately the same point when the parts are assembled together. As used herein, the terms "distal" refers to a direction facing towards the patient, and "proximal" refers to a direction facing towards the person operating the instrument. The distal direction D and proximal direction P are shown by a double-headed arrow in <FIG>.

The outer shaft <NUM> and inner shaft <NUM> may include or be securable to features, such as a handle <NUM>, a syringe <NUM>, a drive motor <NUM>, or the like, as known in the art.

One or both of the outer shaft <NUM> and the inner shaft <NUM> may comprise respective rigid tubular structures made of surgical steel or other materials suitable for the application. The outer shaft <NUM> and/or inner shaft <NUM> also may be constructed with a flexible region <NUM>, <NUM>. For example, the outer shaft <NUM> and inner shaft <NUM> may have coterminous flexible regions <NUM>, <NUM>, such as schematically illustrated in <FIG> and <FIG> show exemplary constructions for flexible regions <NUM>, <NUM>. <FIG> shows the inner shaft <NUM> having a flexible region <NUM> formed by separate but interlocking links <NUM>', which together form a segmented flexible tube. Such segmented flexible tube structures are described in <CIT> and are also known in various other forms. <FIG> shows the outer shaft <NUM> having a flexible region <NUM> being formed by a continuous helical ribbon <NUM>' of material that forms a spring-like structure, and the inner shaft <NUM> being formed by concentric helical, spring-like ribbons <NUM>'. Such structures and variation thereof, as well as alternative structures, are known in the art, and need not be described further herein.

As shown in <FIG>, the outer shaft <NUM> terminates at an outer cutter head <NUM> having an outer cutter head opening <NUM>, and the inner shaft <NUM> terminates at an inner cutter head <NUM> having an inner cutter head opening <NUM>. When assembled together, the outer cutter head <NUM> and inner cutter head <NUM> extend along a common longitudinal axis <NUM>, with the outer cutter head <NUM> concentrically surrounding the inner cutter head <NUM>. The outer cutter head <NUM> and inner cutter head <NUM> are rotatable relative to each other about the axis <NUM>. In typical use, the outer cutter head <NUM> is held still, while the inner cutter head <NUM> is rotated, but this is not always the case.

When assembled together for use, the outer cutter head opening <NUM> and inner cutter head opening <NUM> are aligned along the longitudinal axis <NUM>, such that relative rotation of the shafts <NUM>, <NUM> causes the cutter head openings <NUM>, <NUM> to attain different states of alignment. In the position shown in <FIG>, and <FIG> (when assembled), the cutter head opening <NUM>, <NUM> are fully aligned to form a collective opening that into the inner cannula <NUM>. Rotation to either side causes the collective opening to become smaller, until eventually it is closed completely. At the openings <NUM>, <NUM> reach the closed state, the opposite edges of the opening <NUM>, <NUM> pinch and shear tissue, and deposit the tissue into the inner cannula <NUM>. In typical use, the openings <NUM>, <NUM> are reciprocated back and forth relative to each other at a very high oscillation rate, such as <NUM>,<NUM> to <NUM>,<NUM> cycles per minute, but other oscillation rates can be used. In some cases the shafts <NUM>, <NUM> may be continuously rotated in one both directions (i.e., continuously rotated to open and close the collective opening more than one time, rather than reversing rotation after the collective opening closes as in normal oscillatory operation).

<FIG> illustrates an example of a cutter head <NUM>. The cutter head <NUM> may be an outer cutter head <NUM> or an inner cutter head <NUM>. The cutter head <NUM> is located at the distal end of a tubular shaft <NUM> having a cannula <NUM> extending from the proximal shaft end to the distal shaft end. The cutter head <NUM> extends along a longitudinal axis <NUM>, and includes a cutter head opening <NUM> that defines a fluid communication path from outside the cutter head <NUM> to the cannula <NUM>.

The cutter opening <NUM> is defined, in a direction transverse to the longitudinal axis <NUM>, between a first row of teeth <NUM> and a second row of teeth <NUM>. The remainder of the cutter opening <NUM> may be defined, along the longitudinal axis direction, between a proximal edge <NUM> and a distal edge <NUM>, but a distal edge <NUM> is not strictly required (i.e., the cutter head <NUM> may be open at the distal end).

The two rows of teeth <NUM>, <NUM> are located opposite each other with respect to the longitudinal axis <NUM>. One or more teeth <NUM>, <NUM> of each row may be aligned along a line parallel to the longitudinal axis <NUM>, but this is not required. For example, in the shown embodiment, the proximal two teeth <NUM>, <NUM> of each row are arranged in parallel along the longitudinal axis <NUM>, while the distal tooth <NUM>, <NUM> of each row is not aligned with the others. The first and second rows of teeth <NUM>, <NUM> may extend the full length of the cutter opening <NUM> (length being measured in the longitudinal axis <NUM>), but this is not required in all cases. In the shown examples, each row has three teeth, but more or fewer teeth may be present. The number of teeth in one row also may be different from the other row.

Referring specifically to the left row of teeth <NUM>, each tooth <NUM> is defined by a proximal tooth surface 614a and a distal tooth surface 614b. The proximal and distal surfaces 614a, 614b intersect each other at a tooth edge 614c. The tooth edge 614c terminates, at the inner surface of the cannula <NUM>, at a tooth point 614d.

As will be appreciated from <FIG>, the orientation of each tooth edge 614c relative to the longitudinal axis <NUM> is defined by the shapes of the proximal and distal surfaces 614a, 614b. In the case of the proximal-most tooth <NUM>', the tooth edge 614c is oriented at an angle A of less than <NUM>° relative to the longitudinal axis <NUM>. As understood herein, <NUM>° to the longitudinal axis <NUM> refers to extending in a single imaginary plane that is orthogonal to the longitudinal axis <NUM>, so a tooth edge 614c that is oriented at an angle A of less than <NUM>° relative to the longitudinal axis <NUM> has only a single point in an single imaginary plane that is orthogonal to the longitudinal axis <NUM>. For simplicity, the term "angled" tooth is used herein to describe at tooth having a tooth edge oriented an angle A of less than <NUM>° relative to the longitudinal axis <NUM>. Teeth not angled as such are referred to as "conventional" teeth.

The angle A in the embodiment of <FIG> is an acute angle opening in the distal direction D. For purposes herein, the magnitude of the angle A is measured as viewed from a direction that is perpendicular to the longitudinal axis <NUM> and facing the centerline of the cutter opening <NUM>, such as shown in <FIG>. In this case, the magnitude of the angle A may be, for example, between <NUM> and <NUM> degrees, between <NUM> and <NUM> degrees, or <NUM> degrees (it will be understood that, in practice, some manufacturing variables will be present that might somewhat expand the foregoing ranges and values, even if an effort is made to achieve a precise dimension of the angle A, and such variations are within the scope of the identified ranges and values).

The angled tooth <NUM>' is expected to generate various benefits. First, the angled tooth, and especially the proximal surface 614a and/or distal surface 614b, can generate a longitudinal force along the longitudinal axis <NUM>, which can help move tissue longitudinally. Without being bound to any theory of operation, it is believed that the proximal surface 614a tends to push tissue away from the longitudinal axis <NUM> because the proximal surface 614a is oriented to face generally away from the longitudinal axis <NUM>, and the distal surface 614b tends to push tissue towards the longitudinal axis <NUM> because the distal surface 614b is oriented to face generally towards the longitudinal axis <NUM>. In this case, the net result is that the severed tissue is generally driven in the distal direction D, which can help mix the severed tissue and move severed tissue back into the path of the cutting edges to be cut into smaller pieces. This can help provide a more homogenous mixture of severed tissue, and reduce large pieces that might otherwise lead to clogging problems or the like.

Another expected benefit of the angled tooth <NUM>' is that the side edges of the tooth engage the corresponding tooth edges of the other cutter head to generate a greater shearing component to the cutting force, which can potentially decrease the force necessary to cut the tissue, and provide a cleaner cut.

Other benefits may become apparent with practice of embodiments.

Still referring to <FIG>, and particularly angled tooth <NUM>' of the right-hand row of teeth, the angled tooth <NUM>' optionally may be modified to remove all or some of the tooth edge. Here, tooth <NUM>' has a proximal surface 616a and a distal surface 616b that form a virtual tooth edge 616c that extends at an angle A of less than <NUM>° relative to the longitudinal axis <NUM>. The virtual tooth edge 616c is an edge that would be present if the proximal and distal surfaces 616a, 616b were continued to intersect each other. The condition of having a virtual tooth edge 616c may be achieved, for example, by forming a tooth edge, then cutting away the material in the shaded region 616a. The tooth edge 616c alternatively may be partially removed, leaving a shorter tooth edge 616c, or material may be removed to also eliminate the tooth point 616d and leave a linear edge.

<FIG> shows another embodiment, in which the middle tooth of each row of teeth <NUM>, <NUM> is an angled tooth <NUM>', <NUM>'. Here, each angled teeth <NUM>', <NUM>' is defined by a respective proximal surface 714a, 716a and a respective distal surface 714b, 716b that form a respective tooth edge 714c, 716c oriented at an acute angle A opening in the proximal direction P. In this case, the angled teeth <NUM>', <NUM>' can generate a net force to drive the cut tissue in the proximal direction P, and into the cannula <NUM>, and thus help evacuation and collection of the tissue.

<FIG> shows an example in which each row of teeth <NUM>, <NUM> has multiple angled teeth <NUM>', <NUM>', and one or more conventional teeth. In this case, all of the angled teeth <NUM>', <NUM>' are oriented at respective acute angles A opening in the proximal direction P. Such an embodiment may be useful to adjust the magnitude of force generated along the longitudinal axis <NUM>.

<FIG> shows an example in which each row of teeth <NUM>, <NUM> has multiple angled teeth <NUM>', <NUM>', and one or more conventional teeth. In this case, one opposite pair of angled teeth <NUM>' and <NUM>' are oriented at respective acute angles A opening in the proximal direction P, and another opposite pair of angled teeth <NUM>' and <NUM>' are oriented at respective acute angles A opening in the distal direction D. Such an embodiment may be useful to adjust the direction of force generated along the longitudinal axis <NUM> at particular locations to achieve different localized effects.

<FIG> shows an example, in which each row of teeth <NUM>, <NUM> entirely comprises angled teeth <NUM>', <NUM>'. In this case, all of the angled teeth <NUM>', <NUM>' are oriented at respective acute angles A opening in the proximal direction P. In other cases, all of the teeth may be oriented at acute angles A opening in the distal direction D.

<FIG> shows another example in which each row of teeth <NUM>, <NUM> entirely comprises angled teeth <NUM>', <NUM>'. In this case, some opposite pairs of angled teeth <NUM>', <NUM>' are oriented at respective acute angles A opening in the proximal direction P, which other opposite pairs of angled teeth <NUM>', <NUM>' are oriented at respective angles A opening in the distal direction D.

<FIG> shows an example in which the rows of teeth <NUM>, <NUM> include opposite pairs of angled teeth <NUM>', <NUM>' that are angled in opposite directions. Here, the distal-most angled tooth <NUM>' on one side is oriented at an angle A opening in the distal direction D, while the distal-most angled tooth <NUM>' on the other side is oriented at an angle A opening in the proximal direction P. The proximal-most angled teeth <NUM>', <NUM>' are also oriented like this. The remaining teeth may be conventional, or also may be oriented in the same way. This embodiment may provide a mixing or swirling effect within the cutter head <NUM>, or other potentially-beneficial movements of the severed tissue.

<FIG> shows an example in which the rows of teeth <NUM>, <NUM> include opposite pairs of angled teeth <NUM>', <NUM>' that are angled in both the same, and in opposite directions. Here, the distal-most angled tooth <NUM>' on one side is oriented at an angle A opening in the distal direction D, while the distal-most angled tooth <NUM>' on the other side is oriented at an angle A opening in the proximal direction P. In contrast, the proximal-most angled teeth <NUM>', <NUM>' are both oriented with angles A opening in the distal direction D. The remaining teeth may be conventional, or also angled.

<FIG> shows a side view of a cutting head <NUM> in which there are five angled teeth <NUM> in each row. As will be apparent from the positions of the distal tooth surfaces 1416b, each tooth <NUM> is oriented at an angle A opening in the proximal direction P. As indicated above, this arrangement helps drive the severed tissue into the cannula in the proximal direction.

As will appreciated from the foregoing, it is anticipated that various combinations of using all angled teeth, and combinations of angled and non-angled teeth can provide various benefits. Such variations include having rows of teeth that are mirror images of each other (i.e., symmetrical about a plane parallel to the longitudinal axis <NUM> and intersecting the center of the cutter opening), or not. Similarly, it will be understood that angled teeth in some locations may have angles A of different magnitudes. For example, the distal angled tooth <NUM>' may be oriented at an angle A of <NUM> degrees, while the proximal angled tooth <NUM>' may be oriented at an angle A of <NUM> degrees. The number of teeth can also be changed to potentially gain further benefits. Other alternatives and embodiments will be apparent to persons of ordinary skill in the art in view of the present disclosure.

It will also be appreciated that the foregoing embodiments of angled teeth may be used with an inner cutter head <NUM>, an outer cutter head <NUM>, or both. When use only in one cutter head <NUM>, <NUM>, the remaining cutter head can have a conventional construction. In addition, one cutter head may have different types of angled teeth than the other. For example, an outer cutter head <NUM> may be provided with teeth having angles A opening distally, as shown in <FIG>, and the corresponding inner cutter head <NUM> may be provided with teeth having angles that open proximally. Other alternatives and embodiments will be apparent to persons of ordinary skill in the art in view of the present disclosure.

Embodiments of tissue shaver cutter heads with angled teeth may be manufactured using various methods. <FIG> illustrates one embodiment of a method of manufacture. Here, the cutter head blank is provided as a tubular shaft <NUM> having a closed hemispherical distal end <NUM>. A cannula (not shown) extends along the shaft <NUM>, as in the foregoing examples. The shaft <NUM> extends along a longitudinal axis <NUM>. The cutter head opening <NUM> is shown in broken lines where the blank will be cut.

In this example, a laser cutter <NUM> is provided to cut the cutter head opening <NUM>. The laser cutter <NUM> is oriented along a cutting path <NUM> that extends at an angle of less than <NUM>° relative to the longitudinal axis and intersects the blank at the edge of the intended cutter head opening location. As shown in <FIG>, the cutting path <NUM> extends at an angle Ac, which is less than <NUM>° (compare with the illustrated <NUM>° angle). The cutting path <NUM> may lie in a plane <NUM> that is offset from the centerline of the shaft <NUM> (which is collinear with the longitudinal axis <NUM>) by a radial distance R.

Once oriented, the laser cutter <NUM> is activated to direct the cutting beam <NUM> along the cutting path <NUM>. The laser cutter <NUM>, shaft <NUM>, or both, may be moved to guide the cutting beam <NUM> to form the cutter head opening <NUM>. The cutting angle <NUM>, as well as the angular orientation and radial distance R of the plane <NUM>, may vary as the laser cutter <NUM> and/or shaft <NUM> moves to create the cutter head opening <NUM>.

As the cutting beam <NUM> contacts the shaft <NUM>, it cuts away material to form the proximal tooth surface and the distal tooth surface of each tooth <NUM>. When complete, the proximal tooth surface and distal tooth surface intersect to form a tooth edge lying along the cutting direction <NUM>. The laser cutter <NUM> can thus be used to cut the entire cutter head opening <NUM>, at which time the remaining waste of the tubular blank will be removed.

In the embodiment of <FIG>, the cutting angle Ac, and thus the tooth edge angle, is an acute angle opening in the proximal direction. In other cases, the cutting angle Ac and tooth edge angle may be an acute angle opening the distal direction. Other embodiments use other cutting angle orientations, such as those necessary to make the angled tooth embodiments described previously herein.

In other embodiments, the cutter head opening <NUM> may be created using an abrasive grinder or other mechanical cutting device, or a combination of devices (e.g., an abrasive grinding wheel to cut the proximal and distal edges of the opening, and a laser cutter to cut the rows of teeth). Other alternatives and embodiments will be apparent to persons of ordinary skill in the art in view of the present disclosure.

It is noted that the angled cutting path Ac can add a difficulty not present in conventional cutting operations. Specifically, advancing the cutting tool along an angled cutting path Ac across the entire blank will result in asymmetrical cuts on each side of the cutter head opening <NUM>. This is in contrast to conventional cutting methods, in which the cutting tool is traversed across the full width of the blank along a cutting path that is perpendicular to the longitudinal axis <NUM>, in which the cuts on both sides of the cutter head opening <NUM> are identical and symmetrical.

It has been found that such undesirable asymmetrical cutting can be avoided when using a laser cutter <NUM>, by reducing the output and/or increasing the cutting movement speed to limit the cutting laser to penetrate the hollow blank at only a single location at any given time. This method result in some internal scarring of the cannula where the cutting laser impinges upon penetrating the opposite side of the blank, but it has been found that such scarring is not detrimental to the function of the device. In methods using mechanical cutters, undesirable asymmetrical cutting can be avoided by operating the cutter head at different angular orientations, or by rotating the blank between cuts or during cutting. Other alternatives and embodiments will be apparent to persons of ordinary skill in the art in view of the present disclosure.

Claim 1:
A surgical tissue shaver comprising:
a shaft (<NUM>, <NUM>, <NUM>) extending from a proximal shaft end (<NUM>, <NUM>) to a distal shaft end (<NUM>, <NUM>), the shaft (<NUM>, <NUM>, <NUM>) comprising a tubular body defining a cannula (<NUM>, <NUM>, <NUM>) extending from the proximal shaft end (<NUM>, <NUM>) to the distal shaft end (<NUM>, <NUM>); and
a cutter head (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) at the distal shaft end (<NUM>, <NUM>) and extending along a longitudinal axis (<NUM>), the cutter head (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) having a cutter opening (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) in fluid communication with the cannula (<NUM>, <NUM>, <NUM>), wherein at least a portion of the cutter opening (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) extending along the longitudinal axis (<NUM>) is defined between a first row of teeth (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) and a second row of teeth (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) opposite the first row of teeth (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) with respect to the longitudinal axis (<NUM>);
wherein a first tooth selected from the first row of teeth (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) is defined by a respective proximal tooth surface (614a, 616a, 714a, 716a) and a respective distal tooth surface (614b, 616b, 714b, 716b) that intersect at a respective tooth edge (614c, 616c, 714c, 716c), and wherein the respective tooth edge (614c, 616c, 714c, 716c) of the first tooth is oriented at a first angle of less than <NUM>° relative to the longitudinal axis (<NUM>);
characterized in that
a second tooth selected from the first row of teeth (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) and the second row of teeth (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) is defined by a respective proximal tooth surface (614a, 616a, 714a, 716a) and a respective distal tooth surface (614b, 616b, 714b, 716b) that intersect at a respective tooth edge (614c, 616c, 714c, 716c), and wherein the respective tooth edge (614c, 616c, 714c, 716c) of the second tooth is oriented at a second angle relative to the longitudinal axis (<NUM>), the second angle being different from the first angle.