Patent Description:
Total knee arthroplasty (TKA) is a surgical procedure in which the articulating surfaces of the knee joint are replaced with prosthetic components, or implants. TKA requires the removal of worn or damaged articular cartilage and bone on the distal femur and proximal tibia. The removed cartilage and bone is then replaced with synthetic implants, typically formed of metal or plastic, to create new joint surfaces.

The position and orientation (POSE) of the removed bone, referred to as bone cuts or resected bone, determines the final placement of the implants within the joint. Generally, surgeons plan and create the bone cuts so the final placement of the implants restores the mechanical axis or kinematics of the patient's leg while preserving the balance of the surrounding knee ligaments. Even small implant alignment errors outside of clinically acceptable ranges correlate to significantly worse outcomes and increased rates of revision surgery. In TKA, creating the bone cuts to correctly align the implants is especially difficult because the femur requires at least five planar bone cuts to receive the femoral prosthesis. The planar cuts must be aligned in at least five degrees of freedom to ensure a proper orientation: anterior-posterior translation, proximal-distal translation, external-internal rotation, varus-valgus rotation, and flexion-extension rotation. Any misalignment in any one of the planar cuts or orientations may have drastic consequences on the final result of the procedure and the wear pattern of the implant.

Cutting guides, also referred to as cutting blocks or cutting jigs, are commonly used to aid in creating the bone cuts. The cutting guides include guide slots to restrict or align a bone removal device, such as an oscillating saw, in the correct bone resection plane. Cutting guides are advantageous for several reasons. For one, the guide slots stabilize the bone removal device during cutting to ensure the bone removal device does not deflect from the desired plane. Additionally, a single cutting guide may contain multiple guide slots to accurately align and resect two or more cutting places, such as a <NUM>-in-<NUM> cutting block. Finally, the guide slots and the working end of the oscillating saw are typically planar in shape, which make them ideal for creating planar bone cuts. The advantages of using a cutting guide are apparent, however, the cutting guide still needs to be accurately positioned on to the bone prior to executing the cut. In fact, it is the placement of the guide slots on the bone that remains one of the most difficult, tedious and critical tasks for surgeons during TKA.

<FIG> illustrate perspective views of a distal cutting guide <NUM> disclosed in <CIT> assigned to the assignee of the present application. <FIG> is a front elevation view of the distal cutting guide <NUM> and <FIG> is a perspective view thereof. In general, cutting guides <NUM> and alignment guides used herein are made of a rigid or semi-rigid material, such as stainless steel, aluminum, titanium, polyetheretherketone (PEEK), polyphenylsulfone, acrylonitrile butadiene styrene (ABS), and the like. The distal cutting guide <NUM> includes a guide portion <NUM> and an attachment portion <NUM>. The guide portion <NUM> includes a guide slot <NUM> and a bottom surface <NUM>. The guide slot <NUM> is for guiding a surgical saw in creating the planned distal cut CP (see <FIG>) on the femur F. The bottom surface <NUM> may abut against one or more bone pins P that are placed on the femur F as shown in <FIG>. The attachment portion <NUM> and the guide portion <NUM> clamp to the bone pins P using fasteners <NUM>. Here, the virtual pin plane PP for the distal cut guide <NUM> is defined in a surgical plan by planning software using the POSE of the planned distal cut plane CP (shown in <FIG>), and the distance between the guide slot <NUM> and the bottom surface <NUM> of the guide portion <NUM>. The planning software may also use the known width of the bone pins P. For example, the pin plane PP may be defined by proximally translating the planned distal cut plane CP by the distance between the guide slot <NUM> and the bottom surface <NUM> of the distal cutting guide <NUM>. The software may further proximally translate the planned distal cut plane CP by an additional half width of the pins P. Therefore, when the cutting guide <NUM> is clamped to the bone pins P as shown in <FIG>, the guide slot <NUM> is aligned with the planned distal cut plane CP.

<CIT> also describes a system and method for aligning a cutting guide on the bone. The system utilizes a dynamic two degree-of-freedom (DOF) hand-held articulating device and a patient specific surgical plan to accurately align one or more pins on to the bone. A cutting guide with one or more guide slots is assembled to the pins where the final POSE of the guide slot(s) correspond with the POSE of the desired bone cuts. Although the <NUM>-DOF hand-held system may accurately align the pins, one design challenge was determining how to removably secure the pin to the articulating device and maintain the rotational concentricity of the pin during operation. A simple approach was to use a standard <NUM> jaw chuck, or a collet system to hold and secure the pin to the driving tool. The problem with the <NUM>-jaw chuck or collet for securing a pin is that they require the use of both hands of the surgeon or involvement of a surgical assistant. One hand to insert the pin, and the second hand to close the chuck or the collet. This process that relies on use of both hands by the surgeon or involvement of an assistant may be a source of distraction and, is prone to the introduction of errors in the pin alignment, and surgeon fatigue.

Thus, there is a need for a system and method to accurately align and insert one or more pins in the bone using a pin driving device that does not require both of the surgeon or operator's hands to load a pin into the device and release the pin from the device once the pin is inserted in the bone. There is a further need for a mechanism and pin holder design that maintains the rotational concentricity of the pin while operating the device.

<CIT> discloses an insertion device for a surgical pin including a body defining a bore therein and a retainer disposed in the bore. In one embodiment the retainer includes a magnetic element for engaging a pin.

A surgical device for pin insertion in a bone of a subject to aid in performing a bone cutting procedure is provided that includes a drive portion configured to drive a pin for insertion into the bone. The drive portion has a pin drive assembly with a shaft having a shaft proximal end. At least one magnet is associated with the shaft proximal end adapted for attraction and retention of the pin in the shaft proximal end. A spindle assembly is adapted to drive the shaft so as to rotate the pin into the bone to a degree of bone retention that overcomes the attraction and the retention of the pin in the shaft proximal end.

An alignment system for surgical bone cutting procedures includes a surgical device and a plurality of bone pins inserted with the surgical device within a virtual plane relative to a cut plane to be created on a subject's bone. A tracking system tracks the position and orientation (POSE) of the working portion of the surgical device. A cutting guide is configured to be received on to the plurality of bone pins, with one or more guide slots within the cutting guide being present and configured to guide a surgical saw to make surgical cuts on the subject's bone. A computing system is part of the alignment system and programmed to:.

A method for aligning a cutting guide on a subject's bone is also provided in which one or more cut planes from a surgical plan obtained with planning software is determined. One or more virtual planes relative to each of the one or more cut planes to be created on the subject's bone is also then determined. The aforementioned surgical device is used for aligning and inserting a plurality of bone pins within a virtual plane from the one or more virtual planes. A cutting guide is attached that is configured to clamp on to the plurality of inserted bone pins and has one or more guides slots configured to guide a surgical saw to make surgical cuts on the subject bone that correspond to the one or more cut planes.

The present invention is further detailed with respect to the following drawings that are intended to show certain aspects of the present of invention, but should not be construed as limit on the practice of the invention, wherein:.

The present invention has utility as a system and method to aid a surgeon in quickly and precisely aligning a guide pin on a bone of a subject, with the aid of a pin placement holder in a pin driver assembly. In contrast to other prior art mechanisms, the present invention does not require an operator to use two hands to load and secure a pin. Certain embodiments of the inventive pin driver assembly use a pin guide that aligns an inserted pin to a shaft, where the shaft has a hex socket to rotationally lock the pin to the rotation of the shaft. The shaft also houses two small magnets to attract and secure the inserted pin, the magnets taking the place of a conventional <NUM>-jaw chuck, or a collet system to hold and secure the pin to the driving tool, and thereby eliminate the need for the operator to use both of their hands to secure the pin to the driving tool or rely on a second person to assist. The magnets pull the inserted pin into the hex socket and prevents the pin from falling out of the pin guide or the hex socket, the magnet or magnets have a limited Gauss strength balance to retain the pin prior to bone securement, yet release the pin upon securement. The operator or surgeon can freely articulate the tool in any angle without worry of the pin falling out of the device.

The system and method is especially advantageous for total knee arthroplasty and revision knee arthroplasty where the position and orientation (POSE) of the pins are used to assemble and align a cutting guide thereon to facilitate the creation of a desired cut plane. However, it should be appreciated that other medical applications may exploit the subject matter disclosed herein such as osteotomies and high tibial osteotomies, and the placement of screws for spinal fusions and spinal reconstruction, maxillofacial surgery, fractures, and other procedures requiring the precise placement of bone pins, screws, or nails. Similarly, embodiments of the invention described herein may be adapted for use in a non-medical setting wherever the precise placement of a screw, nail, or rivet is needed such as construction, aircraft assembly and carpentry with the proviso that at least a portion of the fasteners are ferromagnetic.

The following description of various embodiments of the invention is not intended to limit the invention to these specific embodiments, but rather to enable any person skilled in the art to make and use this invention through exemplary aspects thereof. As used herein, a patient, or synonymously a subject, is defined as a human, a non-human primate; or an animal of a horse, a cow, a sheep, a goat, a cat, a rodent and a bird; or a cadaver of any of the aforementioned.

It is to be understood that in instances where a range of values are provided that the range is intended to encompass not only the end point values of the range but also intermediate values of the range as explicitly being included within the range and varying by the last significant figure of the range. By way of example, a recited range from <NUM> to <NUM> is intended to include <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM>.

Referring now to the figures, <FIG> is a perspective view of an inventive drive portion <NUM> of a hand held surgical device <NUM>, also referred to herein as a pin-driver device (see <FIG>). <FIG> is a side view of the drive portion <NUM>, while <FIG> is a central plane, longitudinal cross-sectional view of <FIG>. <FIG> is an exploded view of <FIG>, and <FIG> is an exploded view of <FIG>. <FIG> are detailed individual perspective views of the major components that form the drive portion <NUM>. <FIG> is a detailed side view of the pin drive assembly <NUM>, and <FIG> is a detailed exploded and central longitudinal cross-sectional side view of the pin drive assembly <NUM>. It is noted that embodiments of the inventive pin driver assembly may also be used with end effectors for robots as well as hand held devices. The drive portion <NUM> has two major subassemblies a spindle assembly <NUM> and a pin drive assembly <NUM>. The modular design of the spindle <NUM> allows for the changing and integration of several different parts. The spindle <NUM> has the following major subcomponents: a bearing cap <NUM>, a bearing holder <NUM>, a set of disk springs <NUM>, a coupler <NUM>, a motor holder <NUM>, a motor <NUM>, and a spindle cartridge <NUM>. The bearing cap <NUM> squeezes the outer cage of the bearing to facilitate preloading on angular contact bearings. The bearing holder <NUM> holds an arrangement of bearings <NUM>, and provides a modular connection to the spindle cartridge <NUM>. The flange <NUM> is perpendicular to the bearing axis to guarantee perpendicularity to the spindle cartridge <NUM>. It is appreciated that the major subcomponents of the spindle <NUM> may be exchanged with minimal effects or changes to the other parts. For example, the motor holder <NUM> is readily changed to accommodate many different size motors and still be capable of attachment to the spindle cartridge <NUM>. The set of disk springs <NUM> reduce the impact and vibration forces between the bearings <NUM>. The coupler <NUM> attaches the pin driver assembly shaft <NUM> to the motor shaft <NUM>. The motor holder <NUM> holds the motor <NUM>, provides room for the coupler <NUM>, and has a flange <NUM> connection that attaches to the spindle cartridge <NUM>. The flat side of the flange <NUM> guarantees that the motor axis is perpendicular to the spindle cartridge wall <NUM>. In addition, the flange <NUM> has allowance to translationally move the motor axis shaft to decrease radial misalignment between the pin drive shaft <NUM> and the motor shaft <NUM>.

The spindle cartridge <NUM> serves as the centerpiece of the spindle assembly <NUM>. The spindle cartridge <NUM> has two parallel flange walls <NUM> to attach the bearing holder <NUM>, and the motor holder <NUM> to facilitate a corridor or parallel shafts between the motor <NUM> and the pin driver assembly <NUM>. The spindle cartridge <NUM> may also have a mechanism, such as a screw, clasp, or other fastener, to permit a fiducial marker array <NUM> to attach to the drive portion <NUM>. In other embodiments, the fiducial marker array <NUM> or individual fiducial markers are an integral part of the drive portion <NUM>. A hand-held attachment member <NUM> connects with the spindle cartridge <NUM> and is adapted to pivotally attach with the hand-held portion of the hand-held surgical device <NUM>. The fiducial markers may be active markers such as light emitting diodes (LEDs), passive markers such as retroreflective spheres, or other tracking reference markers such as magnetic sensors, ultrasonic beacons, inertial measuring units, and combinations thereof.

The pin driver assembly <NUM> is designed to increase surgical usability and accuracy. The pin driver assembly <NUM> has the following major subcomponents: a spindle shaft <NUM>, a pin guide <NUM>, and a magnet <NUM>. The pin driver assembly <NUM> assembles to the spindle assembly <NUM> by way of the spindle shaft <NUM>, where the spindle shaft <NUM> runs through the spindle cartridge <NUM> via the bearing holder <NUM>, and attaches to the motor <NUM> via the coupler <NUM>. In operation, a surgeon places a pin P into the pin guide <NUM>. At least one magnet <NUM>, which is fixed in the shaft <NUM>, snap a male hex end <NUM> of the pin P into a hex socket <NUM> of the shaft <NUM>. In a specific embodiment of the present invention, the magnets <NUM> are adhesively bonded to the shaft <NUM> in a magnet holder <NUM> that is proximal to the hex socket <NUM>. The magnet(s) <NUM> prevent the pin P from falling out of the pin guide <NUM> by keeping a magnetic attractive force on the magnetically attracted metallic pin P. The pin guide <NUM> has a distal end <NUM> and a proximal end <NUM>. The inner diameter of the distal end <NUM> is tightly dimensioned to the outer diameter of the pin P, and fits over the pin P with a small amount of clearance that constrains the pin's rotational axis to the shaft's rotational axis with a very little amount of play. The pin guide proximal end <NUM> has an inner diameter larger than that of the distal end <NUM> and is tightly dimensioned to the outer diameter of a distal portion <NUM> of the shaft <NUM>. The design of the pin guide <NUM> stabilizes the pin P and makes the pin P rotate concentrically about the longitudinal axis of the shaft as the motor <NUM> drives (i.e. rotates) the pin P. One may accomplish this stabilization and alignment by manufacturing the shaft <NUM> with a deeper hex socket; however, there are manufacturing constraints and added costs to do so. Therefore, the pin guide <NUM> is advantageous from a manufacturing point of view.

The hex socket <NUM> on the spindle shaft <NUM> rotates the pin P, which causes the pin P to drill deep inside a subject bone, and the grooves <NUM> on the pin P firmly hold the pin P in place. Once the pin P is firmly placed inside the subject bone, the magnetic pull force on the pin P is overcome and the pin P releases from the pin driver assembly <NUM> as the surgeon removes the pin driver assembly <NUM>. In a specific inventive embodiment, the pin P is made of magnetically attractive stainless steel and the pin guide <NUM> is made of aluminum.

<FIG> illustrates an example of a pin driving surgical system <NUM> in the context of an operating room (OR). The surgical system <NUM> generally includes an articulating surgical device <NUM> with embodiments of the drive portion <NUM>, a computing system <NUM>, and a tracking system <NUM>. The surgical system <NUM> is able to guide and assist a user in accurately placing pins coincident with a virtual plane that is defined relative to a subject's bone. The virtual plane is defined in a surgical plan such that a cutting guide when assembled to the inserted pins align one or more guide slots with the bone cuts required to receive a prosthetic implant in a planned position and orientation.

The pin-driver device <NUM> is controlled by commands from the computing system <NUM> to maintain the coincidence of the longitudinal axis of the pin P with a virtual plane defined in the surgical plan. The computing system <NUM> may include a planning computer <NUM> including a processor; a device computer <NUM> including a processor; a tracking computer <NUM> including a processor; and peripheral devices. Processors operate in the computing system <NUM> to perform computations associated with the inventive system and method. It is appreciated that processor functions are shared between computers, a remote server, a cloud computing facility, or combinations thereof.

The device computer <NUM> may include one or more processors, controllers, and any additional data storage medium such as RAM, ROM or other nonvolatile memory to perform functions related to the operation of the surgical device <NUM>. For example, the device computer <NUM> may include software, data, and utilities to control the surgical device <NUM>, receive and process tracking data, execute registration algorithms, execute calibration routines, provide workflow instructions to the user throughout a surgical procedure, as well as any other suitable software, data or utilities required to successfully perform the procedure.

The planning computer <NUM>, device computer <NUM>, and tracking computer <NUM> may be separate entities as shown, or it is contemplated that their operations may be executed on just one or two computers depending on the configuration of the surgical system <NUM>. For example, the tracking computer <NUM> may have the operational data to control the device <NUM> without the need for a device computer <NUM>. Or, the device computer <NUM> may include operational data to plan the surgical procedure without the need for the planning computer <NUM>. In any case, the peripheral devices allow a user to interface with the surgical system <NUM> and may include: one or more user-interfaces, such as a display or monitor <NUM>; and user-input mechanisms, such as a keyboard <NUM>, mouse <NUM>, pendent <NUM>, joystick <NUM>, foot pedal <NUM>, or the monitor <NUM> may have touchscreen capabilities.

The planning computer <NUM> contains hardware (e.g., processors, controllers, and memory), software, data and utilities that are dedicated to aid a user in planning a surgical procedure, either pre-operatively or intra-operatively. This may include reading medical imaging data, segmenting imaging data, constructing and manipulating three-dimensional (3D) virtual models, storing and providing computer-aided design (CAD) files, planning the POSE of implants relative to the bone, defining virtual pin planes, and generating the surgical plan data for use with the system <NUM>. The final surgical plan data may include an image data set of the bone, bone registration data points, subject identification information, the POSE of the implants relative to the bone, the POSE of one or more virtual planes defined relative to the bone, and any tissue modification instructions. The final surgical plan is readily transferred to the device computer <NUM> and/or tracking computer <NUM> through a wired or wireless connection in the operating room (OR); or transferred via a non-transient data storage medium (e.g., a compact disc (CD), a portable universal serial bus (USB) drive) if the planning computer <NUM> is located outside the OR.

The device computer <NUM> contains hardware, software, data and utilities that are primarily dedicated to the operation of the articulating device <NUM>. This may include controlling the position and/or orientation (POSE) of the pin P, controlling the speed of the motor <NUM>, the processing of kinematic and inverse kinematic data of the device <NUM>, the execution of registration algorithms, the execution of calibration routines, the execution of surgical plan data, coordinate transformation processing, providing workflow instructions to the user, and utilizing POSE data from the tracking system <NUM>.

The tracking system <NUM> includes two or more optical receivers <NUM> to detect the position of fiducial markers. A set of fiducial markers uniquely arranged on a rigid body is referred to herein as a fiducial marker array (<NUM>, 130a, 130b). Illustrative examples of the fiducial markers may include: an active transmitter, such as an LED or electromagnetic emitter; a passive reflector, such as a plastic sphere with a retro-reflective film; a distinct pattern or sequence of shapes, lines or other characters. An example of an optical tracking system is described in <CIT>. The tracking system <NUM> may be built into a surgical light <NUM>, located on a boom, a stand, or built into the walls or ceilings of the OR. The tracking system computer <NUM> may include tracking hardware, software, data and utilities to determine the POSE of objects (e.g., bones B, the articulating device <NUM>) in a local or global coordinate frame. The POSE of the objects is also referred to herein as POSE data, where this POSE data is readily communicated to the device computer <NUM> through a wired or wireless connection. Alternatively, the device computer <NUM> may determine the POSE data using the position of the fiducial markers detected directly from the optical receivers <NUM>.

The POSE data is determined using the position of the fiducial markers (130a, 130b, 130c) detected from the optical receivers <NUM> and operations/processes such as image processing, image filtering, triangulation algorithms, geometric relationship processing, registration algorithms, calibration algorithms, and coordinate transformation processing. POSE data from the tracking system <NUM> is used by the computing system <NUM> to perform various functions. For example, the POSE of a digitizer probe <NUM> with an attached probe fiducial marker array 130b may be calibrated such that the probe tip is continuously known as described in <CIT>. The POSE of the tip or axis of the pin P may be known with respect to a device fiducial marker array <NUM> using a calibration method as described in <CIT>. Registration algorithms are readily executed to determine the POSE and/or coordinate transforms between a bone B and the surgical plan, using the registration methods described in <CIT>, and <CIT>. For example, in a registration method, points on a patient bone may be collected from a tracked digitizer probe <NUM> to transform the coordinates of a surgical plan to the coordinates of the bone.

It should be appreciated that in certain examples, other tracking systems may be incorporated with the surgical system <NUM> such as an electromagnetic field tracking system, a mechanical tracking system or other tracking systems that utilize acoustic emitters or reflectors; magnetic emitters or reflectors; accelerometers; gyroscopes; and the like or any combinations thereof. Mechanical tracking systems may be used. The replacement of a non-mechanical tracking system with a mechanical tracking system should be apparent to one skilled in the art. In specific embodiments, the use of a mechanical tracking system may be advantageous depending on the type of surgical system used such as the one described in <CIT> assigned to the assignee of the present application.

The surgical plan is created, either pre-operatively or intra-operatively, by a user using planning software. The planning software may be used to a generate three-dimensional (<NUM>-D) models of the subject's bony anatomy from a computed tomography (CT), magnetic resonance imaging (MRI), x-ray, or ultrasound image data set. Alternatively, the surgical plan is created using data collected directly from the patient intraoperatively (e.g. digitized points, kinematic femoral head center, ankle center, statistical bone morphing) such as with typical imageless navigation systems rather than using a per-operative image data set. A set of <NUM>-D computer aided design (CAD) models of the manufacturer's prosthesis are pre-loaded in the software that allows the user to place the components of a desired prosthesis to the <NUM>-D model of the boney anatomy to designate the best fit, position and orientation of the implant to the bone.

The surgical plan contains the <NUM>-D model of the patient's operative bone combined with the location of one or more virtual pin planes. The location of the virtual pin plane(s) is defined by the planning software using the POSE of one or more planned cut planes and one or more dimensions of a cutting guide.

Intra-operatively, the surgical plan is registered to the bone. The surgical device <NUM> then articulates the pin in one-or-more degrees of freedom to align the pin P with a virtual pin plane. Once aligned, the user may command the device <NUM>, via a trigger, to drive (e.g., rotate) the pin P, while manually advancing the pin P into the bone coincident with the virtual pin plane. In some embodiments, the pin P is automatically advanced into the bone with components associated with the surgical device <NUM>. The pin P is inserted into the bone to a degree of bone retention that overcomes the attraction of the pin P to the magnet <NUM>. Therefore, the surgical device <NUM> may be easily removed from the pin P to assemble and install subsequent pins. Cutting guides are then assembled to the pins to facilitate the creation of the planar cuts that receive the knee prosthesis.

Claim 1:
A surgical device for pin insertion in a bone of a subject to aid in performing a bone cutting procedure, the surgical device comprising:
a pin (P) and a drive portion (<NUM>) configured to drive said pin (P) for insertion into the bone,
wherein the pin (P) comprises grooves (<NUM>) adapted to hold the pin (P) in place inside the bone,
a pin drive subassembly (<NUM>) of the drive portion (<NUM>) with a shaft (<NUM>) having a shaft distal end (<NUM>), at least one magnet (<NUM>) associated with the shaft distal end (<NUM>) is adapted for exerting an attractive force on the pin (P) placed in the shaft distal end (<NUM>); and
a spindle subassembly (<NUM>) of the drive portion (<NUM>) adapted to drive said shaft (<NUM>) so as to rotate the pin (P) into the bone to a degree of bone retention that is configured to overcomes the attractive force on the pin (P) exerted by the at least one magnet (<NUM>).