Patent Description:
In computer-assisted surgery (CAS) systems which employ inertial-based or micro-electro-mechanical sensor (MEMS), trackable members continue to be developed. One of the principal steps in navigating a bone with inertial sensors is to determine a coordinate system of the bone relative to the sensors, so as to be able to determine the orientation of the bone. For the tibia, the orientation of the bone may be determined by its mechanical axis.

When traditional optical CAS navigation systems are used, the determination of the tibial mechanical axis can be achieved, for example, by using two optical bone sensors fixed to the bone at spaced apart locations, each optical sensor having six degrees of freedom (DOF) (i.e. <NUM> DOF in position and <NUM> DOF in orientation). When using trackable members having inertial sensors in an inertial-based CAS system, however, the inertial sensors do not necessarily provide six DOF. While the missing DOF can be calculated if necessary using integrated gyroscope and accelerometer readings, for example, a simpler and more efficient manner to digitize the mechanical axis of a tibia is nonetheless sought.

Therefore, there remains a need for an improved surgical tool which is used in conjunction with a CAS system in order to digitally acquire the mechanical axis of the tibia using readily identifiable anatomical reference points.

<CIT> relates to a device for determining an axis joining origins of at least two reference systems (Ref1, Ref2) of a rigid body (T). The device comprises at least a first and a second inertial sensor (<NUM>, <NUM>), provided with a triaxial accelerometer and a triaxial gyroscope, predisposed to be constrained to the rigid body (T) and for respectively defining the first and the second reference system. The device further comprises a processing unit (<NUM>), connected to the inertial sensors (<NUM>, <NUM>). The processing unit comprises an acquiring module (<NUM>) configured to acquire first data (d1) representing angular velocities and second data (d2) representing linear accelerations of the rigid body (T) detected by the first and second inertial sensor (<NUM>, <NUM>) during a movement of the rigid body (T) itself, comprises a first calculating module (<NUM>) configured to calculate third data (d3) representing angular accelerations of the rigid body (T) as a function of the first data (d1) acquired, comprises a second calculating module (<NUM>) configured to calculate a relative orientation between the first and the second reference system (Ref1, Ref2) as a function of the first data (d1), comprises a third calculating module (<NUM>) configured to calculate a vector (V1) which joins origins (O1, O2) of the first (Ref1) and of the second (Ref2) reference system as a function of the first, second and third data (d1, d2, d3) and as a function of the relative orientation calculated between the first and the second reference system (Ref1, Ref2), wherein the primary direction (DIR_1) of the primary vector (V1) is representative of the axis joining the origins of the two reference systems (Ref <NUM>, Ref2).

<CIT> relates to a computer-assisted surgery system comprising a first surgical device with a tracking unit tracked during a surgical procedure and adapted to perform a first function associated to the surgical procedure. A second surgical device is adapted to perform a second function associated to the surgical procedure. A triggered unit is triggered when the first surgical device and the second surgical device reach a predetermined proximity relation. A surgical procedure processing unit tracks the first surgical device. A trigger detector detects a triggering of the triggered unit. A CAS application operates steps of a surgical procedure. A controller commands the CAS application to activate a selected step associated with the second function in the surgical procedure when the trigger detector signals a detection. An interface displays information about the selected step in the surgical procedure.

According to the invention, there is provided an assembly for positioning a tibia cut guide on a tibia as set out in claim <NUM>. Optional features of the invention are set out in claims <NUM> to <NUM>.

<FIG> show a tibia cutting guide <NUM> used to guide a resection of a tibia <NUM> by a surgeon. The tibia cutting guide <NUM> has a cut slot <NUM> extending through the tibia cutting guide <NUM> (also referred to herein simply as "guide <NUM>"). The cut slot <NUM> receives a resection tool therein, such as a flat saw blade, and guides its displacement to effect the resection of the tibia. In the depicted example, the cut slot <NUM> is defined between two opposed planar surfaces to confine the resection tool to displace along a plane, whereby the resection of the tibia will create a tibial plane, also known as the tibial cut or proximal cut. The tibial plane may then support a tibial component, for example a metal plate anchored onto the tibial plane and a plastic spacer interfacing with a femoral component. The guide <NUM> is mounted to an orientation mechanism <NUM> of a guide holder <NUM>. The orientation mechanism <NUM> functions to adjust the orientation of the guide <NUM> with respect to the tibia <NUM> in varus/valgus and slope. For example, the orientation mechanism <NUM> is connected to a remainder of the guide holder <NUM> by a pair of rotational joints, the axes of which are generally aligned with the medio-lateral axis for slope adjustment, and with the anterior-posterior (AP) axis for varus-valgus adjustment. In the depicted example, the guide <NUM> is mounted to the guide holder <NUM> via a quick-release mechanism. The guide holder <NUM> is itself mounted to a guide rod <NUM> at a first end 16A of the guide rod <NUM>. The guide rod <NUM> is an elongated body extending between the first end 16A and an opposed second end 16B. The guide rod <NUM> is adjustable in length.

Referring to <FIG>, with the guide <NUM> mounted to the guide holder <NUM> and the guide holder <NUM> mounted to the guide rod <NUM>, the second end 16B of the guide rod <NUM> is mounted non-invasively about the skin S of the patient at the ankle A. In the depicted example, the guide rod <NUM> has an ankle clamp 16C at the second end 16B which is used to clamp the second end 16B of the guide rod <NUM> to the ankle. This locates the second end 16B of the guide rod <NUM> adjacent to a distal end of the tibia <NUM>. With the guide rod <NUM> mounted to the patient at its second end 16B, the length of the guide rod <NUM> can be adjusted to approximate the length of the tibia <NUM> of the patient. In the depicted embodiment, the guide rod <NUM> has a telescopic joint 16D. The telescopic joint 16D joins and locks two segments of the guide rod <NUM> together, and allows at least one of the segments to be displaced relative to the other to increase the overall length of the guide rod <NUM>.

Referring to <FIG>, the second end 16B of the guide rod <NUM> can be aligned with a patient landmark. In the depicted embodiment, a pointer 16E is attached to the guide rod <NUM> at the second end 16B. The pointer 16E is moved to align it with any suitable landmark. Displacement of the point 16E causes displacement of the guide rod <NUM>. For example, the pointer 16E may be aligned with the second toe T of the patient's foot F. By aligning the pointer 16E and thus the guide rod <NUM> with the second toe T of the foot F, the guide rod <NUM> is generally located at an approximate midpoint of the ankle A, which typically corresponds with a location of the mechanical axis of the tibia <NUM>. In an embodiment, the guide rod <NUM> is mounted to the ankle clamp 16C at a translational joint that is displaceable in a direction generally parallel to a line joining the malleoli of the ankle A.

At the other, first end 16A of the guide rod <NUM>, and referring to <FIG>, the guide <NUM> is aligned with a visual bone landmark of the tibia <NUM>. In the depicted example, the guide <NUM> is displaced by the orientation mechanism <NUM> to align a vertical slot <NUM> in the guide <NUM> with the <NUM>/<NUM> mark of the tibial tubercle 11A. The guide <NUM> is aligned with another bone landmark of the tibia <NUM> in other examples. Once the vertical slot <NUM> is properly aligned, the guide holder <NUM> can be secured to the tibia <NUM>. In the embodiment shown in <FIG>, a pin <NUM> is inserted through a pin hole 14A of the guide holder <NUM>. The pin <NUM> secures the guide holder <NUM> to the tibia <NUM>. The guide rod <NUM> is now mounted in place at both of its first and second ends 16A,16B, and is generally aligned with the mechanical axis of the tibia <NUM>.

With the guide rod <NUM> held parallel to the tibia <NUM>, the slope of the guide rod <NUM> with respect to the tibia <NUM> can be adjusted as desired. Inertial sensors can also be provided, as shown in <FIG>. In the depicted embodiment, a first inertial sensor 20A is mounted to a sensor bracket 14B of the guide holder <NUM>. The sensor bracket 14B moves with the orientation mechanism <NUM>, and thus with the cutting guide <NUM>. Since the guide holder <NUM> is attached with the pin <NUM> to the tibia <NUM>, the first inertial sensor 20A mounted to the guide holder <NUM> is indirectly mounted to the tibia <NUM> and in fixed relationship therewith. Referring to <FIG>, a second inertial sensor 20B is mounted at the second end 16B of the guide rod <NUM> to the ankle clamp 16C. Since the pointer 16E is aligned with the second toe T, and thus the guide rod <NUM> is aligned with the midpoint of the ankle A, the second inertial sensor 20B is similarly aligned with the ankle A. The second inertial sensor 20B therefore serves as a tibia reference, representative for example of the mechanical axis of the tibia <NUM>. The inertial sensors 20A,20B are sensors that are capable of detecting their own motion without the use of an external reference frames.

The orientation of the guide <NUM> with respect to the tibia <NUM> can now be adjusted based on data from the inertial sensors 20A,20B. This allows the surgeon to achieve the orientation of the guide <NUM> that is desired for the resection to be effected. Referring to <FIG>, the orientation mechanism <NUM> is used for adjusting the orientation of the guide <NUM> mounted to the guide holder <NUM>, with the second inertial sensor 20B moving concurrently with the guide <NUM>. In the depicted embodiment, the orientation mechanism <NUM> includes a first screw 22A for performing varus-valgus adjustments of the guide <NUM>, and a second screw 22B for performing slope adjustments of the guide <NUM>.

Referring to <FIG>, with an orientation of the guide <NUM> set, a stylus <NUM> is inserted into the cut slot <NUM> to adjust the resection level. The guide <NUM> is then secured into place on the tibia <NUM>, for example by pinning the guide <NUM> to the tibia <NUM>. The guide rod <NUM> and the guide holder <NUM> are then removed, leaving only the cutting guide <NUM> in place on the tibia <NUM>, as shown in <FIG>. The surgeon can now effect the resection operation.

Another example of the tibia cutting guide <NUM>, the guide holder <NUM>, and the guide rod <NUM> is shown in <FIG>, and is collectively referred to as a tibia cutting assembly <NUM>. Referring to <FIG>, the cut slot <NUM> of the cutting guide <NUM> has a substantially planar configuration to guide a planar resection of the tibia. The cutting guide <NUM> may be sized for the planar resection to be partial or complete. Partial resection entails removing only a portion of the tibial plateau, e.g., the portion of the plateau on the lateral condyle or on the medial condyle. The cutting guide <NUM> in <FIG> may have one or more mounting legs 112A which engage with the guide holder <NUM> to mount the cutting guide <NUM> to the guide holder <NUM>. The guide holder <NUM> in <FIG> is an assembly of different components. One of the components of the guide holder <NUM> includes a guide mount 114A having one or more slots or receptacles to receive therein the mounting legs 112A of the guide <NUM>, although other connection configurations are contemplated as alternatives to legs and slots/receptacles. The mounting legs 112A are secured in the slots to mount the guide <NUM> to the guide mount 114A. The guide mount 114A is an elongated body and has a sensor bracket 114B at a distal end for receiving the first inertial sensor 20A. The guide mount 114A and the sensor bracket 114B are integrally connected - for instance by being a monoblock component - and therefore move concurrently.

Another component of the guide holder <NUM> of <FIG> is an anterior/posterior (AP) slider 114C. The AP slider 114C is mounted to the guide mount 114A. In an alternate embodiment, the AP slider 114C is mounted directly to the guide rod <NUM>. The AP slider 114C allows a translational movement, to displace the cutting guide <NUM> closer or away from the tibia <NUM>. Another component of the guide holder <NUM> is a guide adjustment mechanism 114D which is mounted to the AP slider 114C. The guide adjustment mechanism 114D helps to adjust the orientation of the guide <NUM> before the resection operation, by having two rotational joints, respectively aligned with the medio-lateral axis for slope adjustment, and with the AP axis for varus-valgus adjustment. The guide holder <NUM> of <FIG> is shown in a fully assembled configuration, and components can be mounted onto the guide rod <NUM>.

Referring to <FIG>, the first component mounted onto the guide rod <NUM> may be the second inertial sensor 20B. The second inertial sensor 20B may be received in sensor bracket <NUM> (<FIG>) which may be slid along the outside surface of the guide rod <NUM> to position the second inertial sensor 20B in proximity to the ankle clamp 116C of the guide rod <NUM> at the second end 116B of the guide rod <NUM>. The ankle clamp 116C is of the type that may have malleolus pads for being mounted on the malleoli. The second inertial sensor 20B serves as a tibia reference, using for example the alignment with the malleolus line extending between the malleoli. Referring to <FIG>, components are then positioned at the first end 116A of the guide rod <NUM>. The guide holder <NUM> is mounted to the guide rod <NUM> by sliding the first end 116A of the guide rod <NUM> through a mounting slot in the guide adjustment mechanism 114D, concurrently forming a translational joint. After the guide holder <NUM> is mounted onto the guide rod <NUM>, an axis pointer <NUM> with a spike 118A is also mounted onto the guide rod <NUM> at its first end 116A. The guide <NUM>, guide holder <NUM>, and guide rod <NUM> are now ready to be mounted to the patient's anatomy.

Referring to <FIG>, the ankle clamp 116C of the guide rod <NUM> is mounted to the skin S about the malleoli of the patient. The guide rod <NUM> and components mounted thereon are then centered to approximately visually align with the longitudinal mechanical axis of the tibia <NUM>. The length of the guide rod <NUM> can be adjusted to approximate the length of the tibia <NUM>. In the depicted example, the length of the guide rod <NUM> can be adjusted telescopically, or by having the various components mounted to slide on the guide rod <NUM>. The location of the guide holder <NUM> on the guide rod <NUM> can also be modified by sliding the guide adjustment mechanism 114D along the guide rod <NUM>, for the cutting guide <NUM> to be approximately placed at a desired cut location.

To mount the first end 116A of the guide rod <NUM> to the tibia <NUM>, and as shown in <FIG>, the surgeon drives the spike 118A of the axis pointer <NUM> at the mechanical axis entry point of the tibia <NUM>. The guide rod <NUM> can then be rotated about the spike 118A to align the guide rod <NUM> with a visual bone landmark of the tibia <NUM>. In the depicted example, the guide holder <NUM> is rotated with the guide rod <NUM> to align the guide holder <NUM> with the <NUM>/<NUM> mark of the tibial tubercle 11A. The axis pointer <NUM> therefore serves as a connector between the tibial plateau and the guide rod <NUM>.

Once the guide holder <NUM> is properly aligned, the guide rod <NUM> can be set in a fixed position relative to the tibia <NUM>. In the depicted example, the ankle clamp 116C of the guide rod <NUM> is tightened about the malleoli of the ankle. A pin or other fastener can also be inserted to secure the axis pointer <NUM> to the tibia <NUM> and prevent rotation of the guide rod <NUM>. Navigation tracking may then be started by activating the inertial sensors 20A,20B. The orientation of the guide <NUM> with respect to the tibia <NUM> can then be adjusted based on data from the inertial sensors 20A,20B, as described above, with the rotational joints of the guide adjustment mechanism 114D. Once an appropriate varus/valgus and/or slope are obtained, the guide <NUM> can be displaced toward the tibia <NUM> by sliding the guide mount 114A and AP slider 114C relative to the guide adjustment mechanism 114D.

Referring to <FIG>, with the guide <NUM> in position and its resection level adjusted, the guide mount 114A is secured to the tibia <NUM> with one or more pins. The guide <NUM> itself may also be secured to the tibia <NUM> with one or more pins. With the guide <NUM> being securely mounted to the tibia <NUM>, some of the components of the guide holder <NUM> are removed from the guide <NUM>. In the depicted example, the AP slider 114C is removed from the guide mount 114A. The fasteners securing the axis pointer <NUM> to the tibia <NUM> may be removed in order to remove the axis pointer <NUM> from the tibia <NUM>. The guide rod <NUM> is removed from the malleoli, leaving only the cutting guide <NUM> attached to the tibia <NUM>, and the guide mount 114A with the first inertial sensor 20A attached to the guide <NUM>, as shown in <FIG>. The surgeon can now effect the resection operation.

<FIG> shows the tibia cutting assembly <NUM> in an assembled state. The axis pointer <NUM> includes an axis pointer bracket 118B with apertures therein. The axis pointer <NUM> is mounted to the guide rod <NUM> by inserting the first end 116A of the guide rod <NUM> through the apertures of the axis pointer bracket 118B, thereby forming a translation joint. The AP slider 114C is mounted to the guide mount 114A, and allows for it and the cutting guide <NUM> to displace along a direction parallel to the sagittal or AP axis <NUM>. The AP slider 114C may have a mounting arm 115A with a distal end mounted to the cutting guide <NUM> directly, or to the guide mount 114A. A proximal end of the mounting arm 115A is attached to a displacement tab 115B with a locking mechanism 115C. The locking mechanism 115C is operatively connected to two displacement bars 115D, which are each housed within sleeves 117A of the guide adjustment mechanism 114D, to displace the displacement bars 115D relative to the sleeves 117A along a translational direction aligned with the AP axis <NUM>. When a user wishes to displace the AP slider 114C along the AP axis <NUM>, to thereby effect displacement of the cutting guide <NUM> along the AP axis <NUM>, the user depresses the displacement tab 115B to unlock the locking mechanism 115C. However, the system may be without such locking mechanism as well. The user is thereby able to slide the displacement bars 115D relative to the sleeves 117A by pushing or pulling along the displacement tab 115B, thereby causing displacement of the cutting guide <NUM> along a direction parallel to the AP axis <NUM> toward or away from the tibia.

Still referring to <FIG>, the guide adjustment mechanism 114D in the depicted example includes a mounting bracket 117B with apertures therein. The guide adjustment mechanism 114D is mounted to the guide rod <NUM> by inserting the first end 116A of the guide rod <NUM> through the apertures of the mounting bracket 117B, thereby forming a translational joint. The mounting bracket 117B has a lever 117C (e.g., quick-release lever with cam surface) which is actionable by a user to tighten and loosen an engagement of the mounting bracket 117B with the outer surface of the guide rod <NUM>. By actuating the lever 117C to loosen the engagement of the mounting bracket 117B with the guide rod <NUM>, the user is able to displace the guide adjustment mechanism 114D, and thus the cutting guide <NUM>, along the guide rod <NUM>. The selected position of the guide adjustment mechanism 114D on the guide rod <NUM> is secured by actuating the lever 117C to tighten the engagement of the mounting bracket 117B with the guide rod <NUM>. The guide adjustment mechanism 114D in the depicted example may have a first rotational joint 117D which includes a bracket 117E including or attached to the sleeves 117A, and a first knob 117F connected to a rotatable shaft <NUM> which engages the bracket 117E, the bracket 117E being rotatably mounted to a remainder of the guide adjustment mechanism 114D at axis 111A. The first rotational joint 117D allows the AP slider 114C, and thus the guide mount 114A and the cutting guide <NUM>, to rotate about axis 111A, and thereby achieve a slope adjustment of the cutting guide <NUM>, i.e., the adjustment of the orientation of the cut plane in rotation about the medio-lateral axis. For example, the slope may be angled downwardly in posteriorly. To effect this rotation about the axis of the guide rod <NUM>, the first knob 117F is rotated in either direction to cause a rotation of the bracket 117E about axis 111A, which axis 111A is generally parallel to the medio-lateral axis of the patient during surgery. This allows the bracket 117E and the sleeves 117A to rotate, thereby causing the displacement bars 115D to also rotate, to in turn rotate the remainder of the AP slider 114C and the cutting guide <NUM>. The guide adjustment mechanism 114D is therefore able to adjust the cut guide <NUM> along a flexion-extension orientation relative to a tibia. The guide adjustment mechanism 114D in the depicted embodiment may have a second rotational joint <NUM> which includes a bracket 117I moving with the bracket 117E (or integral with it) and a second knob 117J. The second rotational joint <NUM> allows the AP slider 114C, and thus the guide mount 114A and the cutting guide <NUM>, to rotate about the anterior-posterior axis 111B to adjust the varus-valgus angle of the cutting guide <NUM> relative to the tibia. To effect this rotation about the anterior-posterior axis 111B, the second knob 117J is rotated in either direction, which allows the bracket 117E and the sleeves 117A to rotate about the anterior-posterior axis, as axis 111B is generally parallel with the anterior-posterior axis of the tibia, thereby causing the displacement bars 115D to rotate, to in turn rotate the remainder of the AP slider 114C and the cutting guide <NUM>. According to an example, the second knob 117J has an endless screw portion engaged with a fixed gear on a remainder of the guide adjustment mechanism 114D. Accordingly, a rotation of the knob 117J will result in a fine adjustment of the orientation of the bracket 117I about axis 111B.

Still referring to <FIG>, a second sensor bracket <NUM> for receiving the second inertial sensor 20B may be mounted about the outer surface of the guide rod <NUM>. The second sensor bracket <NUM> may be displaceable along the guide rod <NUM> between the first and second ends 116A, 116B by way of a translational joint therebetween, and it may be fixedly attached to the guide rod <NUM>. The second inertial sensor 20B is therefore displaceable along the guide rod <NUM> to position the second inertial sensor 20B in proximity to the second end 116B of the guide rod <NUM>, as shown in <FIG>, and to position it in proximity to the ankle clamp 116C.

As shown in <FIG>, the ankle clamp 116C is located at the second end 116B of the guide rod <NUM>. The ankle clamp 116C has two clamp arms 120A each having a clamp grip 120B at a distal end. The clamp arms 120A and the clamp grips 120B are manipulable to be displaced toward and away from the skin of the patient. Each clamp grip 120B is configured to engage the skin about one of the malleoli of an ankle of the patient. The grips 120B may be cups as shown, but may also have other configurations including pointy ends. When the clamp grips 120B are mounted to the skin about the malleoli of the patient, a line between the clamp grips 120B represents or approximates a malleolus line, which is a line extending between the malleoli. The clamp grips 120B therefore provide a tibia reference (i.e. the malleolus line), which can be used by the second inertial sensor 20B. The position and orientation of the ankle clamp 116C is adjustable. The ankle clamp 116C is mounted to the second end 116B of the guide rod <NUM> at an ankle clamp joint <NUM>. The ankle clamp joint <NUM> includes a mount arm 121A extending between a distal end attached to the second end 116B of the guide rod <NUM>, and a proximal end attached to a pivot bracket 121B. The pivot bracket 121B includes a protrusion 121C which is inserted into an elongated slot 121D to mount the ankle clamp 116C to the second end 116B of the guide rod <NUM>. The ankle clamp 116C is displaceable with respect to the second end 116B of the guide rod <NUM> with the ankle clamp joint <NUM>. More particularly, a position of the ankle clamp 116C with respect to the second end 116B of the guide rod <NUM> is adjustable by sliding the protrusion 121C within the slot 121D. The ankle clamp joint <NUM> also defines a rotational axis RA about which the clamp arms 120A are rotatable relative to the second end 116B of the guide rod <NUM>. The pivot bracket 121B defines the rotational axis RA in the depicted embodiment, and includes a knob 121E to selectively allow pivoting of the clamp arms 120A. The clamp arms 120A are displaceable toward and away from each other, in a direction substantially parallel to the elongated slot 121D, to vary the distance between the clamp arms 120A and accommodate ankles of different sizes.

Still referring to <FIG>, the length of the guide rod <NUM> can be adjusted to approximate the length of the tibia <NUM>. In the depicted example, the length of the guide rod <NUM> can be adjusted telescopically. For example, the guide rod <NUM> may include an inner rod segment nested within an outer rod segment, where the inner and outer rod segment are displaceable relative to each other to vary the length of the guide rid <NUM>. Navigation tracking is then started by activating the inertial sensors 20A,20B. The orientation of the guide <NUM> with respect to the tibia <NUM> can then be adjusted based on data or feedback from the inertial sensors 20A,20B, by adjusting the position of the cutting guide <NUM> using one or more of the AP slider 114C and the guide adjustment mechanism 114D, as described above.

Another example of the tibia cutting assembly <NUM> is shown in <FIG>, and includes the tibia cutting guide <NUM>, the guide holder <NUM>, and the guide rod <NUM>. Referring to <FIG>, the cut slot <NUM> of the cutting guide <NUM> has a substantially planar configuration to guide a planar resection of the tibia. The guide holder <NUM> in <FIG> is an assembly of different components. One of the components of the guide holder <NUM> of <FIG> is an anterior/posterior (AP) slider 214C, for translating the cutting guide <NUM> toward or away from the tibia. The AP slider 214C is mounted to the guide <NUM>. Another component of the guide holder <NUM> is a guide adjustment mechanism 214D which is mounted to the AP slider 214C, for adjusting the orientation of the cutting guide <NUM> relative to the tibia, in slope and varus-valgus. In the depicted example, the AP slider 214C is slid onto the guide adjustment mechanism 214D to mount the cutting guide <NUM> to the guide adjustment mechanism 214D. The guide adjustment mechanism 214D helps to adjust the orientation of the guide <NUM> before the resection operation. After the guide holder <NUM> is mounted onto the guide rod <NUM>, a tibia pointer <NUM> is mounted onto the guide holder <NUM> at the first end 216A of the guide rod <NUM>. The tibia pointer <NUM> has a screw attachment 218A that is rotated to mount the tibia pointer <NUM> to the guide adjustment mechanism 214D. The ankle clamp 216C is mounted to the other, second end 216B of the guide rod <NUM>. The guide <NUM>, guide holder <NUM>, and guide rod <NUM> as assembled in the manner shown in <FIG> are now ready to be mounted to the patient's anatomy.

Referring to <FIG>, the ankle clamp 216C of the guide rod <NUM> is mounted to the skin S about the malleoli of the ankle A. The guide rod <NUM> and components mounted thereon are then centered to approximately visually align with the longitudinal mechanical axis of the tibia <NUM>. The length of the guide rod <NUM> can be adjusted to approximate the length of the tibia <NUM>. In the depicted example, the length of the guide rod <NUM> is adjusted until the tibia pointer <NUM> abuts against an upper portion of the tibia <NUM>, as shown in <FIG>. The guide rod <NUM> can then be rotated about the point of contact between the tibia pointer <NUM> and the tibia <NUM> to align the guide rod <NUM> with a visual bone landmark of the tibia <NUM>. In the depicted example, the guide holder <NUM> is rotated with the guide rod <NUM> to align the guide holder <NUM> with the <NUM>/<NUM> mark of the tibial tubercle 11A. A pin or other fastener can also be inserted to secure the tibia pointer <NUM> to the tibia <NUM> and prevent rotation of the guide rod <NUM>. The tibia pointer <NUM> therefore serves as a connector between the tibial plateau and the guide rod <NUM>.

Referring to <FIG>, navigation tracking is started by activating one or both of the inertial sensors 20A,20B. The orientation of the guide <NUM> with respect to the tibia <NUM> can then be adjusted based on data from the inertial sensors 20A,20B, as described above using the rotational joints of the guide adjustment mechanism 114D. Once an appropriate varus/valgus is obtained, the guide <NUM> can be displaced toward the tibia <NUM> by sliding the AP slider 214C relative to the guide adjustment mechanism 214D. A stylus <NUM> is inserted into the cut slot <NUM> of the guide <NUM> to adjust the resection level. The guide <NUM> is now in the proper position for resection. The surgeon locks the height of the guide <NUM> with a locking device 214E on the guide adjustment mechanism 214D. In the depicted example, the locking device 214E includes a screw that can be tightened to fix the height of the guide adjustment mechanism 214D on the guide rod <NUM>, thereby fixing the height of the guide <NUM> mounted to the guide holder <NUM>.

The guide <NUM> is then secured into place on the tibia <NUM>, for example by pinning the guide <NUM> to the tibia <NUM>. In the depicted example, only a single component is removed prior to performing the resection operation, as shown in <FIG>. In the depicted example, the screw attachment 218A of the tibia pointer <NUM> is loosened to remove the tibia pointer <NUM> from the guide adjustment mechanism 214D, leaving the cutting guide <NUM>, the guide holder <NUM>, and the guide rod <NUM> in place on the tibia <NUM>. The surgeon can now effect the resection operation with a resection tool <NUM> having a resection blade 17A.

<FIG> shows the tibia cutting assembly <NUM> in an assembled state. The AP slider 214C is mounted directly to the cutting guide <NUM> to displace the cutting guide <NUM> along a direction parallel to the sagittal or AP axis <NUM>. The AP slider 214C has a displacement tab 215B with a locking mechanism 215C. The locking mechanism 215C is operatively connected to two displacement bars 215D, which are each housed within sleeves 217A of the guide adjustment mechanism 214D, to displace the displacement bars 215D relative to the sleeves 217A. When a user wishes to displace the AP slider 214C along the AP axis <NUM>, to thereby effect displacement of the cutting guide <NUM> along the AP axis <NUM>, the user depresses the displacement tab 215B to unlock the locking mechanism 215C. However, the system may be without such locking mechanism as well. The user is thereby able to slide the displacement bars 215D relative to the sleeves 217A by pushing or pulling along the displacement tab 215B, thereby causing displacement of the cutting guide <NUM> along a direction parallel to the AP axis <NUM> toward or away from the tibia.

Still referring to <FIG>, the guide adjustment mechanism 214D in the depicted example includes a mounting bracket 217B. The guide adjustment mechanism 214D in the depicted example has a first rotational joint 217D which includes a bracket 217E including or attached to the sleeves 217A, and a first knob 217F connected to a rotatable shaft which engages the bracket 217E, the bracket 217E being rotatably mounted to a remainder of the guide adjustment mechanism 214D at axis 211A. The first rotational joint 217D allows the AP slider 214C, and thus the cutting guide <NUM>, to rotate about axis 211A to achieve a slope adjustment of the cutting guide <NUM>, i.e., the adjustment of the orientation of the cut plane in rotation about the medio-lateral axis. To effect this rotation about the axis of the guide rod <NUM>, the first knob 217F is rotated in either direction to cause a rotation of the bracket 217E about axis 211A, which axis is generally parallel to the medio-lateral axis of the patient during surgery. This allows the bracket 217E and the sleeves 217A to rotate, thereby causing the displacement bars 215D to also rotate, to in turn rotate the remainder of the AP slider 214C and the cutting guide <NUM>. The guide adjustment mechanism 214D is therefore able to adjust the cut guide <NUM> along a flexion-extension orientation relative to a tibia. The guide adjustment mechanism 214D in the depicted example may have a second rotational joint <NUM> which includes a bracket 217I and a second knob 217J. The second rotational joint <NUM> allows the AP slider 214C, and thus the cutting guide <NUM>, to rotate about the anterior-posterior axis 211A to adjust the varus-valgus of the cutting guide <NUM> relative to the tibia. To effect this rotation about the anterior-posterior axis 211B, the second knob 217J is rotated in either direction, which allows the bracket 217E and the sleeves 217A to rotate about the anterior-posterior axis, as axis 211B is generally parallel with the anterior-posterior axis of the tibia, thereby causing the displacement bars 215D to also rotate, to in turn rotate the remainder of the AP slider 214C and the cutting guide <NUM>. According to an example, the second knob 217J has an endless screw portion engaged with a fixed gear on a remainder of the guide adjustment mechanism 214D. Accordingly, a rotation of the knob 217J will result in a fine adjustment of the orientation of the bracket 217I about axis 211B.

Still referring to <FIG>, a first sensor bracket 219A for receiving the first inertial sensor 20B may be mounted to the bracket 217E of the guide adjustment mechanism 214D. The first sensor bracket 219A may be displaceable with the guide adjustment mechanism 214D along the axis defined by the guide rod <NUM>, as explained in greater detail below. The second inertial sensor 20B is mounted to a second sensor bracket 219B which is fixedly attached at the second end 216B of the guide rod <NUM>, in proximity to the ankle clamp 216C.

As shown in <FIG>, the ankle clamp 216C is located at the second end 216B of the guide rod <NUM>. The ankle clamp 216C has two clamp arms 220A each having a clamp grip 220B at a distal end. The clamp arms 220A and the clamp grips 220B are manipulable to be displaced toward and away from the skin of the patient. Each clamp grip 220B is configured to engage the skin about one of the malleoli of an ankle of the patient. When the clamp grips 220B are mounted to the skin about the malleoli of the patient, a line between the clamp grips 220B represents or approximates a malleolus line, which is a line extending between the malleoli. The clamp grips 220B therefore provide a tibia reference (i.e. the malleolus line), which can be used by the second inertial sensor 20B. The position and orientation of the ankle clamp 216C is adjustable. The ankle clamp 216C is mounted to the second end 216B of the guide rod <NUM> at an ankle clamp joint <NUM>. The ankle clamp joint <NUM> includes a mount arm 221A extending between a distal end attached to the second end 216B of the guide rod <NUM>, and a proximal end attached to a pivot bracket 221B. The pivot bracket 221B includes a protrusion 221C which is inserted into an elongated slot 221D to mount the ankle clamp 216C to the second end 216B of the guide rod <NUM>. The ankle clamp 216C is displaceable with respect to the second end 216B of the guide rod <NUM> with the ankle clamp joint <NUM>. More particularly, a position of the ankle clamp 216C with respect to the second end 216B of the guide rod <NUM> is adjustable by sliding the protrusion 221C within the slot 221D. The ankle clamp joint <NUM> also defines a rotational axis RA about which the clamp arms 220A are rotatable relative to the second end 216B of the guide rod <NUM>. The pivot bracket 221B defines the rotational axis RA in the depicted embodiment, and includes a knob 221E to selectively allow pivoting of the clamp arms 220A. The clamp arms 220A are displaceable toward and away from each other, in a direction substantially parallel to the elongated slot 221D, to vary the distance between the clamp arms 220A and accommodate ankles of different sizes.

Still referring to <FIG>, the length of the guide rod <NUM> can be adjusted to approximate the length of the tibia <NUM>. In the depicted example, the length of the guide rod <NUM> can be adjusted telescopically. The guide rod <NUM> include an inner rod segment 213A nested within an outer rod segment 213B. The mounting bracket 217B of the guide adjustment mechanism 214D is positioned on the inner rod segment 213A, and the second sensor bracket 219B is positioned on the outer rod segment 213B. The inner rod segment 213A is displaceable relative to the outer rod segment 213B to vary the length of the guide rid <NUM>. The displacement of the inner rod segment 213A also displaces the guide adjustment mechanism 214D and the cut guide <NUM>. Navigation tracking is then started by activating the inertial sensors 20A,20B. The orientation of the guide <NUM> with respect to the tibia <NUM> can then be adjusted based on data or feedback from the inertial sensors 20A,20B, by adjusting the position of the cutting guide <NUM> using one or more of the AP slider 214C and the guide adjustment mechanism 214D, as described above.

<FIG> shows part of the tibia cutting assembly <NUM> shown in <FIG>, and like reference numbers therefore denote like features. The cutting guide <NUM> shown in <FIG> has a cut slot <NUM> which is half the size of the cut slot <NUM> shown in <FIG>. The cut slot <NUM> helps to effect a partial knee surgery, where instead of resecting both condyles and the full tibial plateau, only one condyle and/or one tibial plateau is removed.

An embodiment of the invention is shown in <FIG>. Referring to <FIG>, a spike <NUM> is driven into the entry point for the mechanical axis of the tibia <NUM>. An inertial sensor 20A serving as a tibia reference is mounted onto a sensor bracket 314B, which is then mounted onto the spike <NUM>. In the depicted embodiment, the sensor bracket 314B is slid along the spike <NUM> in the direction D until it abuts the tibia <NUM>. Once abutted against the tibia <NUM>, the sensor bracket 314B is secured to the tibia <NUM> with an appropriate fastener. Referring to <FIG>, the other inertial sensor 20B is mounted about the ankle A of the patient. The ankle clamp 316C in the depicted embodiment includes a clamp bracket 316F to mount the ankle clamp 316C about the malleoli of the ankle A. The ankle clamp 316C also includes a leg bracket <NUM> to mount the ankle clamp 316C about the lower leg portion L of the patient to ensure that the ankle clamp 316C is fixed in relation to the ankle A. The other inertial sensor 20B is mounted to a bracket <NUM> between the clamp and leg brackets 316F,<NUM>, and is thus instantly fixed in rotation with the tibia <NUM>. With the inertial sensors 20A,20B secured to the leg, the operator runs through a registration sequence to register the leg and tibia <NUM> in the reference coordinate system, as shown in <FIG>. The operator can verify whether the leg and tibia <NUM> are properly registered while moving through the sequence by consulting a visual display <NUM>. After the registration sequence has been completed, the ankle clamp 316C can be removed and its inertial sensor 20B used for other purposes, as the inertial sensor 20A on the sensor bracket 314B is calibrated to track the mechanical axis of the tibia <NUM>.

Referring to <FIG>, the inertial sensor 20B from the ankle clamp 316C may be removed and placed onto the guide holder <NUM>. The guide holder <NUM> in <FIG> is an assembly of different components. One of the components of the guide holder <NUM> includes a sensor mount 314C for receiving the inertial sensor 20B from the ankle clamp 316C, and another component includes the guide adjustment mechanism 314D which is mounted to the sensor mount 314C. In the embodiment of <FIG>, the sensor mount 314C is mounted to, or integral with, the cutting guide <NUM>, such that displacement of the guide adjustment mechanism 314D causes displacement of the sensor mount 314C and the guide <NUM>, in two rotational degrees of freedom, having an axis aligned with the medio-lateral axis for slope adjustment, and with the anterior-posterior axis for varus-valgus adjustment.

The guide adjustment mechanism 314D is then mounted to the sensor bracket 314B, which had been previously secured to the tibia <NUM>. The orientation of the guide <NUM> with respect to the tibia <NUM> can then be adjusted with the guide adjustment mechanism 314D based on concurrent data from the inertial sensors 20A,20B, as described above. Once an appropriate varus/valgus is obtained, the guide <NUM> can be displaced toward the tibia <NUM> by sliding the guide adjustment mechanism 314D along the sensor bracket 314B.

The guide <NUM> is then secured into place on the tibia <NUM>, for example by pinning the guide <NUM> to the tibia <NUM>. With the guide <NUM> secured in position, the guide adjustment mechanism 314D is removed from the sensor mount 314C and from the sensor bracket 314B, the sensor bracket 314B is removed from the tibia <NUM>, and the spike <NUM> is removed from the tibia <NUM>, leaving only the guide <NUM> and the attached sensor mount 314C and inertial sensor 20B in place, as shown in <FIG>. As shown in <FIG>, a cut slot body 310A is mounted to the guide <NUM>. The cut slot body 310A houses the cut slot <NUM> through which the resection operation is effected. In the depicted embodiment, the cut slot body 310A has a mounting leg 310B which is inserted into a mounting hole in the guide <NUM> to mount the cut slot body 310A to the guide <NUM>. The cut slot body 310A is then secured into place on the tibia <NUM>, for example by pinning the cut slot body 310A to the tibia <NUM>. The surgeon can now effect the resection operation through the cut slot <NUM>.

Claim 1:
An assembly for positioning a tibia cut guide (<NUM>,<NUM>,<NUM>,<NUM>) on a tibia (<NUM>), the assembly comprising:
a sensor bracket (314B) with a first inertial sensor (20A), the sensor bracket (314B) being configured to be mounted to the tibia (<NUM>) at a location thereon being representative of a mechanical axis of the tibia (<NUM>), the sensor bracket (314B) being configured to be mounted to the tibia cut guide (<NUM>,<NUM>,<NUM>,<NUM>); and
an ankle clamp (316C) configured to be mounted non-invasively about a skin (S) of an ankle (A) of a patient to be in fixed relation to the ankle (A) and having a second inertial sensor (20B), the ankle clamp (316C) being spaced apart from the sensor bracket (314B) along a length of a leg of the patient and free of interconnection therewith;
the first and second inertial sensors (20A,20B) being configured to be displaced with the tibia (<NUM>) to register the tibia (<NUM>) in a reference coordinate system defined by the first and second inertial sensors (20A,20B), and to calibrate the first inertial sensor (20A) with the mechanical axis of the tibia (<NUM>);
characterized in that the ankle clamp (316C) and the second inertial sensor (20B) are configured to be removed from the skin (S) of the ankle (A) after registering the tibia (<NUM>) in the reference coordinate system, wherein the first inertial sensor (20A) mounted to the sensor bracket (314B) is operable to track the mechanical axis of the tibia (<NUM>) after the ankle clamp (316C) and the second inertial sensor (20B) have been removed.