Bidirectional kinematic mount

A kinematic mounting key engageable with a kinematic mounting receiver is provided. The kinematic mounting key comprises a base kinematic element, a first protrusion, and a second protrusion. Each of the first protrusion and the second protrusion defines a clearance channel and comprises a kinematic element. The clearance channels and the kinematic elements are configured so that the kinematic mounting key is engageable with the kinematic mounting receiver in a first arrangement at six points of contact and in a second arrangement at six points of contact that are at least partially different from the six points of contact of the first arrangement.

BACKGROUND

Navigation systems assist users in locating objects. For instance, navigation systems are used in industrial, aerospace, and medical applications. In the medical field, surgical navigation systems assist surgeons in locating surgical instruments and anatomy for the purpose of accurately placing the surgical instruments relative to the anatomy.

Navigation systems may employ light signals, sound waves, magnetic fields, radio frequency signals, etc. in order to track the position and/or orientation of objects. Often the navigation system comprises tracking devices attached to the objects being tracked. A localizer cooperates with tracking elements on the tracking devices to determine positions of the tracking elements, and ultimately to determine a position and orientation of the objects. The navigation system monitors movement of the objects via the tracking devices. Often, there is a need for the tracking devices to be releasably attached to the objects. However, when the tracking device is removed from the object and then reattached, its positional relationship with respect to the object usually changes, requiring recalibration or re-registration of the tracking device to the object.

SUMMARY

A kinematic mounting key engageable with a kinematic mounting receiver is disclosed. The kinematic mounting key comprises a base kinematic element and a first protrusion. The first protrusion comprises a first pedestal having a proximal end and a distal end, the proximal end coupled to the base kinematic element. The first protrusion further comprises a first kinematic element coupled to the distal end of the first pedestal, and a first clearance channel defined within the first pedestal and within a portion of the first kinematic element. The kinematic mounting key further comprises a second protrusion. The second protrusion comprises a second pedestal having a proximal end and a distal end, the proximal end coupled to the base kinematic element. The second protrusion further comprises a second kinematic element coupled to the distal end of the second pedestal, and a second clearance channel defined within the second pedestal and within a portion of the second kinematic element.

A kinematic mounting assembly is also disclosed. The kinematic mounting assembly comprises a kinematic mounting receiver defining a cavity and having a first pair and a second pair of constraint surfaces accessible in the cavity. The kinematic mounting assembly further comprises a kinematic mounting key engageable with the kinematic mounting receiver and comprising a base kinematic element, a first protrusion comprising a first pedestal comprising a proximal end and a distal end, the proximal end coupled to said base kinematic element. The first protrusion further comprises a first kinematic element coupled to the distal end of the first pedestal and comprising a first clearance channel defined within the first pedestal and within a portion of the first kinematic element. The kinematic mounting key further comprises a second protrusion comprising a second pedestal comprising a proximal end and a distal end, the proximal end coupled to the base kinematic element, a second kinematic element coupled to the distal end of the second pedestal, and comprising a second clearance channel defined within the second pedestal and within a portion of the second kinematic element.

A surgical assembly is also disclosed. The surgical assembly comprises a first surgical component comprising a kinematic mounting receiver defining a cavity and having a first pair and a second pair of constraint surfaces accessible in the cavity. The surgical assembly further comprises a second surgical component comprising a kinematic mounting key engageable with the kinematic mounting receiver. The kinematic mounting key comprises a base kinematic element and a first protrusion. The first protrusion comprises a first pedestal comprising a proximal end and a distal end, the proximal end coupled to the base kinematic element, a first kinematic element coupled to the distal end of the first pedestal and comprising a first clearance channel defined within the first pedestal and within a portion of the first kinematic element. The kinematic mounting key further comprises a second protrusion, which comprises a second pedestal. The second pedestal comprises a proximal end and a distal end, the proximal end coupled to the base kinematic element, a second kinematic element coupled to the distal end of the second pedestal and comprising a second clearance channel defined within the second pedestal and within a portion of the second kinematic element.

DETAILED DESCRIPTION

With reference to the Figures, wherein like numerals indicate like parts throughout the several views, a navigation system20is illustrated. The navigation system20is shown in a surgical setting, such as an operating room of a medical facility. The navigation system20is configured to, among other things, track movement of various objects, such as surgical tools, a pointer, and parts of a patient's body B (e.g., bones or other anatomy). The navigation system20is able to monitor, track, and/or determine changes in relative position and/or orientation of one or more parts of the patient's body B, within a common coordinate system by utilizing various types of trackers22(e.g., multiple degree-of-freedom optical, inertial, and/or ultrasonic sensing devices), anatomical computer models (e.g., magnetic resonance imaging scans of the patient's anatomy), data from previous surgical procedures and/or previously-performed surgical techniques, and the like. To this end, the navigation system20employs a localizer24configured to sense the position and/or orientation of trackers22within a localizer coordinate system. A navigation controller (not shown) is disposed in communication with the localizer24and gathers position and/or orientation data for each tracker22sensed within a field of view of the localizer24in the localizer coordinate system.

In the representative example illustrated herein, the navigation controller and the localizer24are supported on a mobile cart26. The mobile cart26also supports a user interface, generally indicated at28, to facilitate operation of the navigation system20by displaying information to, and/or by receiving information from, the surgeon or another user. The user interface28is disposed in communication with the navigation system20and may comprise one or more output devices30(e.g., monitors, indicators, display screens, and the like) to present information to the surgeon or other users (e.g., images, video, data, graphics, navigable menus, and the like), and one or more input devices32(e.g., buttons, touch screens, keyboards, mice, gesture or voice-based input devices, and the like). One type of mobile cart26and user interface28that may be utilized with this type of navigation system20is described in U.S. Pat. No. 7,725,162 entitled “Surgery System”, the disclosure of which is hereby incorporated by reference in its entirety.

The navigation system20comprises at least one tracker22firmly affixed to the object that is to be tracked. The localizer24can sense the position and/or orientation of a multiple number of trackers22to track a corresponding multiple number of objects within the localizer coordinate system. By way of example, trackers22may comprise a first patient tracker assembly, a second patient tracker assembly, as well as additional patient trackers, trackers for additional medical and/or surgical tools such as a pointer tracker coupled to a pointer, and the like.

With continued reference toFIG.1, a first tracker22is firmly affixed to one bone of the patient's body B at or adjacent to a surgical site (e.g., to the femur near the knee), and a second tracker22is firmly affixed to a different bone (e.g., to a portion of the tibia). While not shown in detail, the trackers22can be coupled to a number of different bones in the patient's body in various ways, such as by threaded engagement, clamping, or by other techniques. Similarly, multiple trackers22may be coupled to the same bone B (such as the trackers22partially shown inFIG.2). Various trackers22may be firmly affixed to different types of tracked objects (e.g., discrete bones, tools, pointers, and the like) in a number of different ways.

The position of the trackers22relative to the objects or anatomy to which they are attached can be determined by known registration techniques. For example, the position of the trackers22relative to the portions of the patient's body to which they are attached can be accomplished with various forms of point-based registration, such as where a distal tip of a pointer is used to engage against specific anatomical landmarks (e.g., touching specific portions of bone) or is used to engage several parts of a bone for surface-based registration as the localizer24monitors the position and orientation of the pointer. Conventional registration techniques can then be employed to correlate the pose of the trackers22to the patient's anatomy (e.g., to each of the femur and the acetabulum). Other types of registration are also possible. Position and/or orientation data may be gathered, determined, or otherwise handled by the navigation controller using a number of different registration/navigation techniques to determine coordinates of each tracker22within the localizer coordinate system.

In the illustrated example, the localizer24is an optical localizer and includes a camera unit34with one or more optical sensors36. The navigation system20employs the optical sensors36of the camera unit34to sense the position and/or orientation of the trackers22within the localizer coordinate system. The trackers22may be further defined as tracker assemblies22. As illustrated herein, the tracker assemblies22each employ a tracker head38with markers that can be sensed by the optical sensors36of the camera unit34. One example of a navigation system20of this type is described in U.S. Pat. No. 9,008,757 entitled “Navigation System Including Optical and Non-Optical Sensors,” the disclosure of which is hereby incorporated by reference in its entirety.

In the representative example illustrated herein, the markers are active markers, which emit light that is sensed by the optical sensors36. More specifically, each tracker head38has at least three active markers for transmitting light signals to the optical sensors36of the localizer24. The active markers can be, for example, light emitting diodes (LEDs) transmitting light signals, such as infrared light. In some examples, the light signals from the LEDs are fired at different frequencies for each tracker assembly22. Each of the LEDs may be connected to a tracker controller (not shown) of the associated tracker assembly22.

In other examples, the trackers22may employ passive markers (e.g., reflectors), which reflect light emitted from the camera unit34or another light source. Although one example of the navigation system20is illustrated throughout the drawings, the navigation system20may have any other suitable configuration for monitoring trackers22, which may be of various types and configurations. For example, the navigation system20may comprise other types of localizers24and/or markers.

In some examples, the navigation system20and/or the localizer24may be radio frequency (RF) based. Here, the trackers22may comprise RF emitters or transponders, which may be passive or may be actively energized. Alternatively, in some examples, the navigation system20and/or localizer24may be electromagnetically (EM) based. For example, the navigation system20may comprise an EM transceiver coupled to the navigation controller and/or to another computing device, controller, and the like. Here, the trackers22may comprise EM components attached thereto (e.g., various types of magnetic trackers, electromagnetic trackers, inductive trackers, and the like), which may be passive or may be actively energized.

Referring toFIGS.2and3, the tracker assembly22further comprises an extension link40, and a bone plate42. The extension link40locates the tracker head38away from the object that is to be tracked. The bone plate42is used to firmly affix the tracker assembly22to one of the patient's bones B during a surgical procedure.

As illustrated throughout the drawings, the extension link40is shown as an elongated rod having a circular cross section extending between a first end and a second end. The extension link40may extend along a path that is curved or angled such that any obstructions between the first and second ends are avoided. The path may be suitable to place the tracker head38away from the surgical site of interest so that the tracker head38remains out of the way of the surgical site. The extension link40may be any suitable length or shape, such as U-shaped, C-shaped, S-shaped, or straight. Furthermore, the extension link40may have any suitable cross section shape, such as rectangular or hexagonal, or structural shapes, such as X-shaped or tubular.

In some examples, one or both of the ends of the extension link40may comprise an adjustable mount44that is usable by the surgeon to aim the tracker head38prior to registration of the tracker22during a surgical procedure. The adjustable mount44affords the surgeon increased adaptability of the tracker assembly22when placing the extension link40to avoid obstructions or other anatomy.

The bone plate42comprises three arms46each having a barb48to pierce the bone B and prevent the bone plate42from moving relative to the bone B. A bone screw50may be used in combination with the bone plate42, which defines an aperture52to receive the screw50in order to anchor the bone plate42to the bone B. The screw50is threaded into the bone B and draws the barbs48of the bone plate42into engagement with the bone B. The screw50may be placed in alternative apertures52of the bone plate42or multiple screws50may be employed in multiple apertures52to secure the bone plate42.

During a surgical procedure, a need may arise to remove a tracker22, or portion thereof, from the object to be tracked. For example, the tracker head38may limit the surgeon's access to a particular area of the surgical site, or hinder the procedure in other ways. In the scenario where the tracker head38has been disconnected from the tracked object, the position of the tracked object is unknown until the tracker head38is reconnected. When the tracker head38is reconnected, the surgical navigation system20can resume tracking the object. If the tracker head38is not reconnected to the tracked object in the same relative position, the tracked object's position may be inaccurate.

Coupling the tracker head38to the tracked object, bone B, in the same relative position involves kinematically constraining each of the six degrees-of-freedom in a repeatable manner. Each degree of freedom is constrained with a single point of contact, which avoids over or under-constraining the assembly. Repeatably de-coupling and coupling the tracker head38may be achieved using a tracker22with a kinematic connector assembly. One example of a tracker22of this type is described in U.S. Pat. No. 10,537,395 entitled “Navigation tracker with kinematic connector assembly”, the disclosure of which is hereby incorporated by reference in its entirety.

With continued reference toFIGS.2and3, a kinematic mounting assembly100is used to repeatably couple the tracker head38to the extension link40in either a first arrangement or a second arrangement throughout the surgical procedure. Each time the tracker head38is coupled to the extension link40in the first arrangement, the tracker head38and the extension link40are in the same relative position. Similarly, each time the tracker head38is coupled to the extension link40in the second arrangement, the tracker head38and the extension link40are in the same relative position. The kinematic mounting assembly100allows the tracker head38to be disconnected from and repeatably connected to either the extension link40or the bone plate42without requiring the navigation system20to be recalibrated and/or the tracker assembly22to be re-registered to the object. Likewise, the tracker head38and the extension link40could be disconnected from, and connected to, the bone plate42as a unit without requiring the navigation system20to be recalibrated or the tracker assembly22to be re-registered to the object. At least one kinematic mounting assembly100is used to couple the tracker head38and the bone plate42to either end of the extension link40.

In order to facilitate connection and removal of components of the tracker assembly22, each of the kinematic mounting assemblies100shown inFIGS.2and3comprises a kinematic mounting key102and a kinematic mounting receiver104. The kinematic mounting key102is configured to be secured in engagement with the kinematic mounting receiver104in a first arrangement and in a second arrangement. The kinematic mounting key102comprises a triplicity of kinematic elements106,108,110to position the kinematic mounting key102in the kinematic mounting receiver104.

In the example shown, the tracker head38is coupled to a first end of the extension link40using a first kinematic mounting assembly100. The bone plate42is coupled to a second end of the extension link40using a second kinematic mounting assembly100. In some instances, the second kinematic mounting assembly100is the same as the first kinematic mounting assembly100, such that components from the first kinematic mounting assembly100are interchangeable with components from the second kinematic mounting assembly100, and vice versa. In this way, the tracker head38may be coupled directly to the bone plate42such that the tracker assembly22only comprises one kinematic mounting assembly100.

Here, the extension link40comprises a key102coupled to the adjustable mount44at the first end, and a receiver104affixed to the second end. The tracker head38comprises another receiver104and the bone plate42comprises another key102. The key102at the first end of the extension link40is engageable with the receiver104on the tracker head38to couple the tracker head38to the extension link40. The key102on the bone plate42is engageable with the receiver104at the second end of the extension link40to couple the bone plate42to the extension link40.

In some examples, the kinematic mounting assembly100is constructed from a metal, such as a surgical grade stainless steel. However, other materials may be used in the construction of the kinematic mounting assembly100, such as metals, polymers, ceramics, and composites thereof. These materials may be plated, coated, or otherwise treated in order to modify physical characteristics of the material, such as biocompatibility, hardness, friction, etc.

As previously discussed, the first and second kinematic mounting assemblies100are interchangeable. Any key102is compatible with any receiver104such that tracker heads38, extension links40, bone plates42, and other accessories may be used interchangeably as needed. For example, as mentioned above, the key102on the bone plate42is engageable with the receiver104on the tracker head38to couple the bone plate42directly to the tracker head38.

Furthermore, while the tracker head38comprises the receiver104, the bone plate42comprises the key102, and the extension link40comprises both the key102and the receiver104, each of the tracker head38, the extension link40, and the bone plate42can comprise either of the key102or the receiver104in any combination, such that various configurations of the tracker assembly22are possible. For example, the tracker head38may comprise the key102and the extension link40may comprise the receiver104. Alternatively, the extension link40may comprise two receivers104in order to prevent the tracker head38from being coupled to the bone plate42and vice versa.

In general, an object that is a rigid body has six degrees of freedom in 3-dimensional space: three translational degrees of freedom along axes X, Y, Z, and three rotational degrees of freedom through rotation about the axes X, Y, Z, known as pitch, roll, and yaw. In order to control the position and orientation of a rigid body, all six degrees of freedom must be constrained. The rigid body can be constrained in one degree of freedom at one point of contact with a second rigid body. Therefore, two rigid bodies with exactly six points of contact will be constrained in all six degrees of freedom. Here, the kinematic mounting assembly100is able to repeatably couple the key102to the receiver104in the same relative position by constraining all six degrees of freedom. The kinematic mounting assembly100allows the key102to be disconnected from and repeatably connected to the receiver104without requiring the navigation system20to be recalibrated and/or the tracker assembly22to be re-registered to the object.

As previously discussed, it is desirable for the position of the object, in this case the patient's bones B, to be tracked throughout the duration of a surgical procedure. While it may be unavoidable to occasionally remove a tracker22or tracker head38in order to facilitate access to the surgical site, it is advantageous to position or reposition the tracker22so as to reduce the likelihood that its removal is necessary. Further, adaptability of the tracker assembly22is advantageous by allowing the tracker assembly22to be affixed to the object in an orientation that reduces obstruction to the surgeon and other users. In some situations, the orientation in which the bone plate42is secured to the patient may prevent the surgeon from placing the tracker head38in a non-obstructing position. By providing multiple arrangements for the kinematic mounting assembly100to couple each component of the tracker assembly22, the surgeon is afforded greater flexibility when positioning each component at the beginning of the surgical procedure.

Adaptability of the tracker assembly22is advantageously promoted by the kinematic mounting assembly100, which allows the kinematic mounting key102to be kinematically constrained with the kinematic mounting receiver104in more than one discrete position. Here, the kinematic mounting key102is engageable with the kinematic mounting receiver104in a first arrangement and in a second arrangement.FIG.2shows two tracker assemblies22, one tracker assembly22is configured with the extension link40coupled to the bone plate42in the first arrangement, and another tracker assembly22is configured with the extension link40coupled to the bone plate42in the second arrangement. In the exemplary surgical procedure illustrated here, it is advantageous for both of the extension links40to be oriented in generally the same direction (i.e. up, or toward the top of the page). Due to the particular features of the patient's bone B, each of the bone plates42is affixed in a different orientation. By coupling one extension link40to one of the bone plates42in the first arrangement and another extension link40to the other bone plate42in the second arrangement, both extension links40can be oriented as desired.

More specifically, when a surgeon is affixing a bone plate42to a patient, the number of viable positions and/or orientations may be limited by factors such as the type of surgery being performed, the patient's individual anatomy, the surgeon's preferences, etc. If the extension link40can only be coupled to the bone plate42in a single orientation, the position of the bone plate42may result in sub-optimal placement of the tracker head38(i.e. out of view of the localizer24). A kinematic mounting assembly100that permits the extension link40to be coupled to the bone plate42in multiple orientations may increase the number of positions that the bone plate42can be affixed to the bone B that will result in an acceptable tracker head38placement, or may aid optimization of tracker head38placement. Further, the navigation system20may be programmed to recognize both arrangements of the tracker assembly22, thereby allowing the surgeon to alternate between each arrangement during the procedure as necessary.

FIG.3shows an exploded view of the two arrangements of the tracker assembly22; two extension links40and two tracker heads38are shown spaced from the same bone plate42. One of the extension links40and one of the tracker heads38are shown spaced from the bone plate42in the first arrangement and the other extension link40and tracker head38are shown spaced from the bone plate42in the second arrangement. Because the tracker head38and the extension link40can be coupled to the bone plate42in the first arrangement and the second arrangement, each tracker assembly22can be utilized in orientations that may have been previously unavailable. In this way the number of unique parts that may normally be kept for use during a surgical procedure can be reduced. For example, a kit of parts provided for a surgical procedure may contain three “vertical” extension links and three “horizontal” extension links some of which may not be used during that procedure. Alternatively, a kit of parts containing four extension links40usable in both the “vertical” and “horizontal” configuration may be provided without limiting usability.

Referring now toFIGS.8-11, the receiver104of the kinematic mounting assembly100is shown. The receiver104defines a cavity112for receiving the key102. The cavity112is defined, at least partially, by a plurality of constraint surfaces114accessible in the cavity112. The constraint surfaces114define three channels116,118,120to receive the key102in the cavity112. A first channel116and a second channel118extend through the cavity112and are substantially parallel to one another. A third channel120intersects the first channel116at an angle θ (seeFIG.9). The angle θ is approximately 120°, but other angles such as 45°, 60°, and 240° are also possible. As illustrated, the second and third channels118,120terminate at a mouth portion122of the cavity112. The mouth portion122is tapered such that the cavity112reduces in size further into the receiver104. A preload bore124is further defined in the receiver104and extends therethrough. The preload bore124intersects with the second channel118in the cavity112.

The constraint surfaces114of the receiver104define each channel116,118,120such that at least one constraint surface114in each channel116,118,120contacts one of the kinematic elements106,108,110at only two points. The channels116,118,120may each be defined by two planar constraint surfaces114. The two planar surfaces may be joined by a third surface that does not contact the kinematic elements106,108,110. In the present example, the channels116,118,120are substantially trapezoidal with two constraint surfaces114interconnected by a third non-contacting surface. The constraint surfaces114may also intersect such that the channels116,118,120form a V-shape. Each channel116,118,120may further define a single constraint surface, such as a curved U-shape, arch shape, or other arcuate shape of which two contact points are made.

Best shown inFIGS.10and11, the kinematic mounting assembly100further comprises a preloading mechanism126having a load member128arranged to secure the key102in engagement with the receiver104. The preloading mechanism126urges the key102into engagement with the receiver104such that the key102is kinematically constrained to the receiver104by six points of contact130with the kinematic mounting receiver104. The preloading mechanism126further comprises a shaft132, a biasing device134, and a push-button136. The load member128and the push-button136are coupled to opposing ends of the shaft132with the biasing device134arranged therebetween.

The load member128is disposed in the preload bore124of the receiver104and movable between a clamped position and an unclamped position. In the unclamped position, the load member128permits the key102to be inserted into the cavity112of the receiver104; and in the clamped position, the load member128contacts the key102urging the key102into engagement with the receiver104. The load member128is coupled to one end of a shaft132disposed in the preload bore124and extending therethrough.

The load member128is substantially cylindrical with a first end and a second end. A spherical segment138is formed on the first end of the load member128. The load member128may be fixed to the shaft132through any suitable mechanism such as a press fit or screw threads. Alternatively, in some examples, the load member128may be an integral extension of the shaft132or other form of rigid force-applying body attached to the shaft132.

The biasing device134is disposed about the shaft132and biases the load member128toward the clamped position. In one example, the biasing device134is a spring. The spring may have a spring rate of approximately 10 to approximately 25 pounds per inch (lbs/in). Alternatively, the spring may have a spring rate of approximately 20 to approximately 25 lbs/in. Additional spring rates are further contemplated.

The push-button136is engageable by the surgeon or user to move the load member128toward the unclamped position from the clamped position. The load member128and the push-button136are fixed to opposite ends of the shaft132. The push-button136is substantially cylindrical and defines a pocket configured to accept the biasing device134. The push-button136may be coupled to the shaft132through any suitable mechanism, such as a press fit or screw threads.

FIGS.4-7show the key102of the kinematic mounting assembly100. The key102comprises two protrusions, a first protrusion140and a second protrusion142. Each protrusion140,142comprises one of the kinematic elements. Each of the protrusions140,142further comprises a pedestal152,154and a clearance channel144,146defined within the respective pedestal152,154. Each pedestal152,154comprises a proximal end172,174coupled to the base kinematic element106and a distal end176,178coupled to the respective kinematic element108,110. Said differently, each pedestal152,154is arranged between the respective kinematic element108,110and the base kinematic element106. The first protrusion140comprises a first pedestal152and the second protrusion142comprises a second pedestal154. Each pedestal152,154has a cylindrical cross section that is smaller than the kinematic elements106,108,110.

Each of the first protrusion140and the second protrusion142further comprises a clearance channel144,146defined within the respective pedestal152,154and within a portion of the respective kinematic element108,110. The first protrusion140comprises a first clearance channel144defined within the first pedestal152and within a portion of the first kinematic element108. The second protrusion142comprises a second clearance channel146defined within the second pedestal154and within a portion of the second kinematic element110.

As mentioned above, the key102comprises three kinematic elements, which are further defined as a base kinematic element106, a first kinematic element108, and a second kinematic element110. Each protrusion140,142is coupled to the base kinematic element106, and each of the protrusions140,142has a respective kinematic element, the first protrusion140having the first kinematic element108, and the second protrusion142having the second kinematic element110. Said differently, the first protrusion140defines the first clearance channel144and has the first kinematic element108, and the second protrusion142defines the second clearance channel146and has the second kinematic element110. As used throughout the detailed description, the terms “first” and “second” are used merely to differentiate between each of the protrusions. As will be discussed in further detail below, the first kinematic element108and the second kinematic element110are configured so that the kinematic mounting key102is engageable with the kinematic mounting receiver104in both the first arrangement and the second arrangement, the second arrangement being different from the first arrangement.

Each protrusion140,142is coupled to the base kinematic element106and extends distally therefrom along a respective axis. Best shown inFIG.7, the first protrusion140defines a first axis148extending through the base kinematic element106and the first kinematic element108, and the second protrusion142defines a second axis150extending through the base kinematic element106and the second kinematic element110. In the example illustrated throughout the drawings, the first axis148and the second axis150are approximately perpendicular to each other. However, in other examples, the axes may be arranged at an angle other than 90 degrees to each other.

Both the first kinematic element108and the second kinematic element110are spaced from the base kinematic element106along the first axis148and the second axis150, respectively. The first kinematic element108is spaced from the base kinematic element106by the first pedestal152. The second kinematic element110is spaced from the base kinematic element106by the second pedestal154.

In order to accommodate coupling the key102to the receiver104in both the first and second arrangement, the key102must engage the receiver104and the preloading mechanism126in the same way. To this end, the protrusions140,142are similar to each other; specifically, the first kinematic element108has a first distal end160, and the second kinematic element110has a second distal end162. Shown inFIGS.4and7, each distal end160,162is equally spaced from the base kinematic element106along the respective axis148,150such that a distance D can be measured between each distal end160,162and the opposite axis. More specifically, the distance D between the first distal end160and the second axis150is equal to the distance D between the second distal end162and the first axis148.

Best shown inFIGS.4-7, the clearance channels144,146are defined within the distal end176,178of each pedestal152,154and within a portion of the respective kinematic element108,110. The clearance channels144,146are configured to provide space for operation of the preloading mechanism126. Each of the first clearance channel144and the second clearance channel146comprises a loading surface156,158that is engageable with the load member128to kinematically constrain the kinematic mounting key102. The first clearance channel144comprises a first loading surface156, and the second clearance channel146comprises a second loading surface158. The loading surfaces156,158may be partially defined in the respective kinematic element108,110. Each clearance channel144,146provides space for the preloading mechanism126to engage the loading surfaces156,158from the second channel118. To this end, each of the clearance channels144,146open toward the preload bore124when engaged with the receiver104in the respective first and second arrangements.

As mentioned above, the key102must engage the receiver104and the preloading mechanism126the same way in both the first and second arrangements. As such, the loading surfaces156,158are further defined as a first loading surface156and a second loading surface158. Each of the first loading surface156and the second loading surface158is a flat planar surface that is engageable with the load member128at a single point of contact. The loading surfaces156,158are angled at an angle1of greater than 90 degrees and less than 180 degrees, and at an angle α of greater than 90 degrees and less than 180 degrees from their respective axis148,150. The first loading surface156is non-parallel to the second loading surface158. Because the loading surfaces156,158are angled as such, the first loading surface156and the second loading surface158are oblique to the first axis148and the second axis150.

The kinematic elements106,108,110each contact the receiver104at the plurality of constraint surfaces114such that the key102is kinematically constrained to the receiver104by being constrained by six points of contact130with the receiver104(seeFIGS.10and11). When the kinematic mounting key102is secured in the kinematic mounting receiver104in the first arrangement, the kinematic mounting key102engages the kinematic mounting receiver104at exactly six points of contact130; and when the kinematic mounting key102is secured in the kinematic mounting receiver104in the second arrangement, the kinematic mounting key102engages the kinematic mounting receiver104at exactly six points of contact130that are at least partially different from the six points of contact130of the first arrangement. Each time the kinematic mounting key102is engaged with the kinematic mounting receiver104in the first arrangement, each of the kinematic elements106,108,110contacts the plurality of constraint surfaces114at the same six points of contact130. Likewise, each time the kinematic mounting key102is engaged with the kinematic mounting receiver104in the second arrangement, each of the kinematic elements106,108,110contacts the plurality of constraint surfaces114at the same six points of contact130. One or more of the six points of contact130resulting from engagement in the first arrangement may be different from the six points of contact130resulting from engagement in the second arrangement.

Referring toFIG.9, a cross section of one example of the key102engaged with the receiver104is shown. Here, the construction of the key102can be seen. The first protrusion140and the first kinematic element108are integrally formed with the base kinematic element106. The base kinematic element106further defines a cross bore164extending along the second axis150to receive the second protrusion142. The second protrusion142comprises a stem166coupled to the proximal end174of the pedestal154opposite the second kinematic element110. The stem166is engageable with the cross bore164for coupling the second protrusion142to the base kinematic element106. In one example, the stem166is pressed into the base kinematic element106and coupled to the cross bore164with an interference fit. In some examples, the second protrusion142may be further secured to the base kinematic element106by welding.

In other examples, it is possible to construct the key102with different manufacturing processes. For example, the second protrusion142may be integrally formed with the base kinematic element106, while the first protrusion140is coupled with an interference fit. Alternatively, both of the protrusions140,142may be integrally formed with the base kinematic element106. It is further contemplated that the cross bore164and the stem166may comprise screw threads to couple one of the protrusions140,142to the base kinematic element106.

In order to couple the key102to the object to be tracked, a fixation post168is coupled to the base kinematic element106, shown inFIG.4. The fixation post168is engaged with the bone plate42to enable the tracker22to be affixed to the patient. The fixation post168has a circular cross-section that extends away from both the first kinematic element108and the second kinematic element110. Here, the fixation post168protrudes from the base kinematic element106and along the first axis148. In the example shown, the fixation post168defines a cross hole170(FIG.7) to secure the key102to the object to be tracked. A pin (not shown) may be inserted through the assembled fixation post168and bone plate42, preventing the key102from being readily removed from the bone plate42.

Shown inFIGS.10and11, the six points of contact130kinematically constrain the key102in the receiver104by constraining all six degrees of freedom. Each kinematic element/channel engagement constrains two degrees of freedom because of the two points of contact. More specifically, each of the base kinematic element106, the first kinematic element108, and the second kinematic element110comprises a spherical segment. Engagement between any one of the spherical segments and one of the constraint surfaces114of the kinematic mounting receiver104is only at a single point of contact. For instance, in the example shown, the base and second kinematic elements106,110are seated in the second and third channels118,120, respectively, to constrain four degrees of freedom of the key102. The first kinematic element108is seated in the first channel116to constrain the remaining two degrees of freedom of the key102in the receiver104.

In the example illustrated throughout the drawings, the kinematic mounting key102has only the base kinematic element106, the first kinematic element108, and the second kinematic element110. However, in other examples, the receiver104and key102can be configured with additional kinematic elements, such that two kinematic elements each constrain two degrees of freedom, and to other kinematic elements each constrain one degree of freedom, for a total of four kinematic elements that collectively constrain six degrees of freedom. Other configurations are contemplated, so long as exactly six degrees of freedom are constrained.

Because the key102is constrained at exactly six points of contact130in the receiver104, the key102will always be coupled to the receiver104in the same position and orientation relative to the receiver104. This allows the key102to be de-coupled from and coupled to the receiver104in a known position such that the connection is repeatable and deterministic.

The preloading mechanism126secures the key102in the receiver104so as to be fully constrained by directing each kinematic element106,108,110to contact the receiver104at exactly two points. As shown inFIGS.9-11the first kinematic element108is inserted into the cavity112of the receiver104and seated in the first channel116. The base and second kinematic elements106,110are inserted in the mouth portion122of the cavity112, with the base kinematic element106seated in the second channel118and the second kinematic element110seated in the third channel120.

Referring toFIGS.2,3,10, and11, the first and second arrangements of the kinematic mounting assembly100are shown. In this example, the extension link40is shown coupled to the receiver104opposite to the mouth portion122of the cavity112. The extension link40is approximately parallel with the first and second channels116,118of the receiver104. InFIG.10, the first arrangement of the kinematic mounting assembly100is shown, where the key102is engaged with the receiver104such that the extension link40is approximately parallel with the first axis148of the key102. InFIG.11, the second arrangement of the kinematic mounting assembly100is shown, where the key102is engaged with the receiver104such that the extension link40is approximately parallel with the second axis150of the key102. Transitioning the key102between engagement in the first arrangement and engagement in the second arrangement rotates the key102relative to the receiver104. The key102is rotated 180 degrees about one of the first axis and the second axis between the first arrangement and the second arrangement.

When the key102is engaged with the receiver104, the spherical segment138of the load member128contacts one of the loading surfaces156,158of the key102. Owing to the spring force of the biasing device134, a force is generated that urges the key102into the receiver104. The angle Φ of the loading surface156,158allows the load member128to exert a force that urges the key102into the receiver104, as well as into a fully constrained position with exactly six points of contact130with the receiver104. The spherical segment138can only apply force perpendicular to the loading surface156,158. Because the spherical segment138of the load member128acts against the planar loading surface156,158, the key102does not become over-constrained in the receiver104. The angle1is also such that the kinematic mounting assembly100is not back-drivable. For example, a pull-out force on the key102increases frictional force on the loading surface156,158, preventing the load member128from moving to the unclamped position.

The kinematic mounting assembly100described herein may be used for connecting together other surgical components. For example, the kinematic mounting assembly100may be used to couple a tracker to a powered instrument such as a high-speed drill. The kinematic mounting key102may be coupled to, or integrally formed on, the powered instrument to mount a tracker head38. Likewise, surgical hand tools may also include a kinematic mounting key102that is engageable with the kinematic mounting receiver104of the tracker head38. As with above, the ability to couple the key102and the receiver104in more than one arrangement may be used to advantageously configure both the powered instruments and hand tools. For example, the surgeon could position the tracker head38to protrude perpendicular to the tool to optimize visibility to the localizer, or parallel to the tool to enhance the surgeon's visibility of the surgical site. The kinematic mounting assembly100may also be used in combination with a robotic surgical system to attach a tracker head38to a robotic arm and/or an end effector.