Patent Description:
Robotic systems are often used in applications that require a high degree of accuracy and/or precision, such as surgical procedures or other complex tasks. Such systems may include various types of robots, such as autonomous, teleoperated, and interactive. This disclosure is directed towards interactive robotic systems with haptic control.

Interactive robotic systems are preferred for some types of surgery, such as joint replacement surgery, because they enable a surgeon to maintain direct, hands-on control of the surgical procedure while still achieving a high degree of accuracy and/or precision. For example, referring to <FIG>, in hip replacement surgery, a surgeon can use an interactive, haptically guided robotic arm equipped with a semi-spherical cutting tool or cutting tool <NUM> in a passive manner to sculpt a semi-spherical indentation in the acetabulum <NUM>, which is a cup-shaped socket in the pelvis <NUM>. The acetabulum <NUM> receives a cup commonly referred to as an acetabular cup (not shown) that, in turn receives a resurfaced femoral head in a partial hip arthroplasty or, in the case of a total hip arthroplasty (THA), the ball portion of the hip implant. To sculpt bone or, in this example, the portion of the acetabulum <NUM> where the cup is to be located, the surgeon manually grasps and manipulates the robotic arm <NUM> to move a cutting tool or cutting tool <NUM> that is coupled to the robotic arm. As long as the surgeon maintains the cutting tool within a predefined virtual cutting boundary defined by a straight line haptic path, the surgeon can move the robotic arm freely with low friction and low inertia. However, if the surgeon attempts to move the cutting tool to cut bone off of the haptic path, the robotic arm provides haptic (or force) feedback that prevents or inhibits the surgeon from moving the cutting tool beyond the virtual cutting boundary.

In other types of surgeries, haptic volumes are used instead of straight-line haptic paths. For example, as disclosed in commonly assigned <CIT>, haptic volumes having various geometric volumes may be modeled using planes, spheres, cones, cylinders, etc..

Returning to hip replacement surgeries, such as THAs, surgical robotic tools are typically limited haptically to a straight line path, normal to where the rim of the planned cup will be after installation or possibly offset a known distance from the planned central axis of the acetabular cup. The semi-spherical cutting tool <NUM> that is extended along a straight line results in a reamed volume that is cylindrical in shape, except at the semi-spherical end. The intention of a straight line haptic path is to constrain the center of the semi-spherical cutting tool <NUM> along a path that is normal to the rim of the planned acetabular cup and to provide a semi-spherical reamed end for receiving the cup. To avoid unintended reaming and inaccurate bone preparation, if the center of the cutting tool <NUM> is not maintained along the straight line haptic path, the controller may not allow the cutting tool <NUM> to operate.

The above-described interactive robotic system, though useful for THA, is not optimally suited for THA and other types of replacement surgeries that require the use of multiple surgical tools having different functions (e.g., reaming, impacting), different configurations (e.g., straight, offset), different sizes (e.g. multiple cutting tools of different sizes) and different weights. A system designed to accommodate a variety of tools may be prohibitively complex for haptic control because it would require removing and attaching different types of tools to the robotic arm during a surgical procedure which may affect the accuracy of the haptic path and could increase the time needed to perform the procedure.

Further, in THA, in addition to maintaining an appropriate cutting boundary, an angular orientation of surgical tools and implants is important. For example, in conventional THA, the surgeon uses the semi-spherical cutting tool <NUM> (<FIG>) to resurface the acetabulum <NUM> (<FIG>). Then, an acetabular cup is attached to a distal end of an impactor tool (not shown). The surgeon implants the acetabular cup into the reamed socket by repeatedly striking a proximal end of the impactor tool with a mallet. Angular orientation of both the reamed socket and the implanted acetabular cup is important because incorrect orientation can result in misalignment of the acetabular cup away from the appropriate version and inclination angles of the acetabular anatomy. Misalignment can lead to post-operative problems, including joint dislocation, impingement of the femur on the acetabular cup at extreme ranges of motion, and accelerated wear of the acetabular cup due to improper loading of the femoral head-to-acetabular cup interface. Alignment is also important to maintain correct leg length and medial/lateral offset. Even more problematic, recent advances in THA reveal that the ideal acetabular cup position is in a narrower range than previously appreciated and that acetabular cup position is dependent on femoral component anteversion.

Use of a straight line haptic path or straight line reaming does not allow for a single-stage reaming process in most cases. Specifically, the surgeon typically uses cutting tools of different sizes in order to achieve the correct size and orientation for the acetabular cup. Single stage reaming is desirable because it is fast, reduces the possibility of infection and reduces operating room time. However, a straight line haptic path is not possible, for example, if the tool center is pushed away from the haptic path by the surface of the acetabular rim. Because the center of the cutting tool is pushed off the haptic path in these cases, before the bowl-shaped indentation for the cup is reamed, the surgeon is required to employ multi-stage reaming with different cutting tools or ream free-handed without the benefits of haptic constraint.

For at least these reasons, more accurate acetabular cup positioning techniques will be important because it is well known that misalignment of the acetabular component in THA may result in dislocation, reduced range of motion or accelerated wear. Further, improved haptic control systems for hip replacement and other surgeries are needed that afford the surgeon some additional flexibility while still employing haptic control.

According to the invention, a haptic robotic surgical system for reaming an indentation in a bone of a patient is disclosed. The system includes a cutting tool and a controller that is programmed to compare an intended indentation in the bone and a position of the cutting tool when placed proximate to the bone. The controller is also programmed to generate a haptic volume that includes a tapered section that narrows parabolically as the haptic volume extends towards the bone. The controller is also programmed to generate control signals that will allow movement of the cutting tool within the haptic volume and provide haptic feedback to constrain movement of the cutting tool outside of the haptic volume.

Improved parabolic haptic volumes for both single-stage reaming and multi-stage reaming are disclosed by way of Equations (<NUM>) and (<NUM>) below.

The haptic robotic surgical system can be used in a method for reaming an indentation in an acetabulum of a patient. The method includes determining a location for a intended indentation in the acetabulum including a bottom point where a central axis of a final indentation intersects the intended indentation, selecting a cutting tool having a radius, placing the cutting tool at an initial position on the acetabulum, comparing the intended indentation on the acetabulum and the initial position of the cutting tool on the acetabulum, and generating a haptic volume that includes a tapered section that narrows as the haptic volume extends towards the acetabulum. The method also includes allowing movement of the cutting tool within the haptic volume and providing haptic feedback to constrain movement of the cutting tool to within the haptic volume.

According to the invention, a haptic robotic surgical system for total hip arthroplasty (THA) surgeries is disclosed. The system includes a cutting tool which is a reamer, and a controller. The controller is programmed to compare an intended indentation in the acetabulum and a position of the cutting tool when initially placed on the acetabulum. The controller is also programmed to generate a haptic volume that includes a tapered section that narrows parabolically as the haptic volume extends towards the acetabulum. The controller is also programmed to generate control signals that will allow movement of the cutting tool within the haptic volume and provide haptic feedback to constrain movement of at least a portion of the cutting tool to within the haptic volume.

The haptic robotic surgical system can be used in a method for reaming an indentation in an acetabulum of a patient. The method includes determining a location for an intended indentation in the acetabulum including a bottom point where a central axis of a final indentation intersects the intended indentation; selecting a cutting tool having a radius larger or smaller than the final indentation; placing the cutting tool at an initial position proximate to the acetabulum; comparing the intended indentation on the acetabulum and the initial position of the cutting tool on the acetabulum; generating a haptic volume including a tapered section that narrows as the haptic volume extends towards the acetabulum; allowing movement of the cutting tool within the haptic volume; wherein, if the final indentation has a diameter that is about equal to a diameter of the selected tool, generating the haptic volume from Equation (<NUM>): <MAT>.

Other advantages and features will be apparent from the following detailed description when read in conjunction with the attached drawings.

The invention is defined in claim <NUM> and in claim <NUM>, with further embodiments defined in the dependent claims.

Turning to <FIG>, in order to accommodate single-stage reaming, the cutting tool <NUM> may be within the haptic constraint of the system (not shown in <FIG>) even when the central axis <NUM> of the cutting tool <NUM> is not co-linear with the intended cup normal or central axis <NUM> of the intended indentation <NUM>, yet not compromise the final location and shape of the indentation <NUM>. Specifically, in <FIG>, the cutting tool <NUM> has been placed against the acetabulum <NUM> but the surgeon is unable to position the cutting tool <NUM> so that its central axis <NUM> is co-linear with the intended tool path or the straight-line haptic path <NUM> because of interference between the cutting tool <NUM> and the acetabular rim <NUM>. In other words, the architecture of the acetabulum <NUM> prevents the surgeon from placing the cutting tool <NUM> in an initial position that would allow a single-stage reaming process defined by the haptic path <NUM>. Thus, prior to this disclosure, a multiple-stage reaming process would need to be carried out which requires the surgeon to use multiple cutting tools <NUM> of different sizes. Multi-stage reaming increases the amount of time needed for the surgery, the amount of operating room time consumed and, because multiple cutting tools <NUM> of different sizes would be used, may also increase the possibility of infection.

One solution to the problem illustrated in <FIG> is provided by one aspect of this disclosure illustrated in <FIG> and another aspect of this disclosure illustrated in <FIG>.

Part of the solution to the problem illustrated in <FIG> is shown in <FIG>. Specifically, the final reamed surface or intended indentation <NUM> is illustrated with a central axis <NUM>. The initial position of the cutting tool <NUM> on the acetabulum <NUM> and the acetabular rim <NUM> (see <FIG>) is shown at 23a. Clearly, the central axis 24a of the cutting tool <NUM>, while in the position shown at 23a, is offset from the central axis <NUM> of the intended indentation <NUM>. If a surgeon were to follow the central axis 24a, the location of the final indentation (not shown) would be offset from the location of the intended indentation <NUM>. However, because the position of the cutting tool shown at 23a does not interfere with the intended rim <NUM> of the indentation <NUM>, reaming may begin from the position shown at 23a. However, a straight path cannot be taken and, instead, a curved or parabolic path <NUM> may be used instead. The parabolic path <NUM> represents the maximum displacement of the central axis shown at 24a or the tool center shown at 32a (see also the bottom center <NUM> in <FIG>) and the central axis <NUM> of the intended indentation <NUM>. By following the parabolic path <NUM>, one can see the position of the cutting tool <NUM> moving from the position shown at 23a to the position shown at 23b, 23c, 23d, etc. until the cutting tool <NUM> reaches its final position shown at <NUM> which coincides with the intended indentation <NUM>. Thus, a curved or parabolic path <NUM> provides for more opportunities for a single stage reaming process and, as shown in <FIG> below, provides greater flexibility for the surgeon.

Turning to <FIG>, the parabolic path <NUM> allows for the greatest radial translation of the bottom center <NUM> (see <FIG>) of the cutting tool <NUM> without over-reaming the intended indentation <NUM>, particularly at its rim <NUM>. The specific shape of the tool path <NUM> is dependent on the diameter or radius of the final indentation <NUM> but is asymptotic as the path <NUM> approaches the tool end point <NUM> or the maximum depth reached by the upper rim <NUM> of the cutting tool <NUM> as shown in <FIG>. In order to avoid disrupting the shape of the intended indentation <NUM>, or in order to avoid over-reaming, the radial translation r of the bottom center <NUM>, at a height h above the tool end point <NUM>, must be less than or equal to final indentation radius R (see also <FIG>) minus the square root of (R<NUM> - h<NUM>) as shown by Equation <NUM>: <MAT>.

The three dimensional volume of the parabolic path <NUM> is shown in <FIG>. A haptic volume <NUM> may include an initial cylindrical section <NUM> that leads to a parabolic section <NUM> that is defined by Equation <NUM> and that may optionally lead to a short straight-line section <NUM> where the tangents of the narrow portion of the parabolic curve are vertical lines. The bottom of the parabolic section <NUM> as shown at <NUM> intersects with the tool end point <NUM>. Despite the offset <NUM> between the central axis 24a of the cutting tool <NUM> when it initially engages the acetabular rim <NUM> and acetabulum <NUM>, the intended indentation <NUM> may still be reamed using a single cutting tool <NUM> or a single-stage process.

For procedures where single stage reaming is not desired or practical, Equation <NUM> may be modified so that to allow smaller reamers of a diameter d to ream a larger cavity having an intended radius R where 2R>d for conducting multi-stage reaming (i.e., not single-stage reaming). The revised equation is presented below as Equation <NUM>:
<MAT>.

<FIG> illustrates the placement of the cutting tool <NUM> on the acetabular rim <NUM> which causes the initial misalignment between the cutting tool <NUM> and the intended placement of the acetabular cup <NUM>. <FIG> illustrates the measurement of the offset between the central axis <NUM> of the cutting tool <NUM> and the central axis <NUM> of the planned cup placement or the intended indentation <NUM>.

Not forming part of the invention, <FIG> illustrate the use of conically-shaped haptic volumes <NUM> which may include an initial cylindrical section <NUM> which leads into the conical section <NUM>, which is tapered as it extends to the straight line section <NUM>. Because of the conical section <NUM> of the haptic volume <NUM>, the largest possible volume created using this technique or tool path is also conical in shape as shown in <FIG>, which is in contrast to the cylindrical tool volumes of prior art straight-line haptic reaming paths. In the embodiment illustrated in <FIG>, the vertex angle of the conical section <NUM> is <NUM>° and the half vertex angle between the central axis <NUM> and the outer boundary of the conical section <NUM> is <NUM>°. The half vertex angle can vary greatly and can range from about <NUM>° to about <NUM>°, more preferably from about <NUM>° to about <NUM>°, still more preferably from about <NUM>° to about <NUM>° and still more preferably from about <NUM>° to about <NUM>°. While the half vertex angle <NUM>° may be increased to increase the possibility of reaming the intended indentation <NUM> in a single-stage process, the same goal may be achieved by switching to a parabolic-shaped haptic volume as indicated by the parabolic line <NUM> as shown in <FIG>.

<FIG> illustrates, schematically, a cutting tool <NUM> that is initially offset from an intended end point <NUM> and the central axis <NUM> of the indentation <NUM>. An initial straight-line reaming may be carried out in the cylindrical section shown at <NUM>, but haptic control may be initiated at the base <NUM> of the conical section <NUM>. The boundary of the conical section <NUM> and the boundaries of the other haptic volumes discussed herein, represent the widest path that the bottom center <NUM> of the cutting tool <NUM> can take before it reaches the straight line section <NUM> which insures that the axes <NUM>, <NUM> of the cutting tool <NUM> and indentation <NUM> respectively are co-linear as the cutting tool <NUM> reaches the tool end point <NUM>.

<FIG> illustrates the employment of this method. The planned cup position is shown at <NUM> and interference by the acetabular rim <NUM> causes the initial placement of the cutting tool <NUM> to be offset from the central axis <NUM> of the planned indentation <NUM>, which causes the bottom center <NUM> of the cutting tool <NUM> to be offset from the central axis <NUM>, which may also be referred to as the original haptic path, the conventional haptic path or the straight line haptic path. However, the bottom center <NUM> of the cutting tool <NUM> is disposed along the boundary of the conical section <NUM> of the haptic volume <NUM>.

Simulated data for three different conically-shaped haptic volumes are graphically illustrated in <FIG>. Specifically, the horizontal marks shown at <NUM> illustrate the required allowance or the distance between the bottom center <NUM> of the cutting tool <NUM> when it is initially placed on the acetabulum <NUM> and a straight-line haptic path with a <NUM> variance as indicated by the small circles with the horizontal lines and shown at <NUM>. <FIG> represent simulated data based on <NUM> different histories. As can be seen from <FIG>, the distance between the horizontal marks <NUM> and the straight line haptic marks <NUM> vary from case to case. If this distance is too great, such as for case number <NUM> in <FIG>, each of the haptic volumes <NUM>, <NUM> and <NUM> fail to provide a sufficient amount of haptic allowance in order for the cutting tool <NUM> to reach its final destination and form the intended indentation <NUM> at the correct place in a single-stage reaming process. However, for case number <NUM>, the haptic volume <NUM> with the half vertex angle of <NUM>° and a <NUM> millimeter straight line section (see <NUM> in <FIG>) provides for a sufficient haptic allowance as indicated by the circle representing the haptic volume <NUM> being disposed above the horizontal mark <NUM>, thereby indicating that the haptic volume <NUM> with a <NUM>° half vertex angle and a <NUM> millimeter straight line section <NUM> (<FIG>) can be used for case number <NUM> and a single-stage reaming process may be carried out. In other words, for purposes of understanding <FIG>, a haptic volume provides sufficient haptic allowance in order to enable a single-stage reaming process when a mark indicative of a haptic volume <NUM>, <NUM>, <NUM> is disposed above its corresponding horizontal mark <NUM>. This means that the haptic volume <NUM>, <NUM>, <NUM> provides enough haptic allowance to compensate for the presence of the acetabular rim or other structure that otherwise would prevent the use of a single-stage reaming process. Thus, <FIG> shows that for some, but not all cases, a single-stage reaming process is available.

Specifically, the haptic volume <NUM> with the <NUM>° half vertex angle and the two millimeter straight-line section <NUM> enables <NUM> of the <NUM> cases to be reamed with a single-stage reaming process (<NUM>%). In contrast, the haptic volume <NUM> with the <NUM>° half vertex angle and the two millimeter straight-line section <NUM> enables <NUM> of the <NUM> cases to be reamed in a single-stage reaming process (<NUM>%) while the haptic volume <NUM> with the <NUM>° half vertex angle and <NUM> millimeter final straight-line section <NUM> provides the least amount of haptic allowance and enables <NUM> of the <NUM> cases to be reamed in a single-stage reaming process (<NUM>%). It will be noted that straight-line sections such as straight line section <NUM> of <FIG> are not necessary for parabolic haptic volumes like the haptic volume <NUM>. In contrast, for conical haptic volumes like the haptic volume <NUM> of <FIG>, the straight line section <NUM> is needed. A straight-line section that is too long can be detrimental to the possibility of a single-stage reaming when using conical haptic volumes as shown by comparing the results for the haptic volumes <NUM> and <NUM>.

The haptic volume is designed to preserve the integrity of the bone surface required for primary stability of the implant, while providing flexibility to ream the acetabulum. This is achieved by defining the shape and dimensions of the haptic volume that accommodate the surgical technique used for reaming during traditional THA surgery with minimal constraints on the surgeon. The haptic or tactile feedback does not constrain the orientation of the reamer shaft but only the position of its center of rotation. This allows the surgeon to pivot the reamer shaft during reaming to maximize the cutting surface while preserving the bone that will support the implant. In addition, the tactile boundaries were designed to be curvilinear to ensure fluid transitions between the different sections of the haptic volume and replicate the standard reaming technique. Finally, the system will automatically detect the position of the reamer center relative to the haptic volume and will provide a signal to the user indicating that the cutting tool is within the tactile boundaries.

As noted above in connection with <FIG>, a straight-line haptic is not possible in many cases as the cutting tool center is pushed away from the intended path by the surface of the acetabular rim. In such a case, since the cutting tool or reamer center cannot be translated to its intended path, the surgeon would be required to multi-stage ream or ream freely with no haptic constraint. Typically, surgeons must employ a multi-stage reaming procedure where they use several reamer sizes before using the final planned reamer to prepare the final indentation or surface.

Claim 1:
A haptic robotic surgical system for reaming an indentation in a bone (<NUM>) of a patient, the system comprising:
a cutting tool (<NUM>); and
a controller programmed to:
compare a position of an intended indentation (<NUM>) in the bone (<NUM>) and a position of the cutting tool (<NUM>) when placed proximate to the bone (<NUM>); and
generate control signals causing the robotic surgical system to constrain movement of the cutting tool (<NUM>) to within a haptic volume (<NUM>) comprising a tapered section that narrows parabolically as the haptic volume extends towards the bone.