Connection method for MEMS navigation unit for computer-assisted surgery

A computer-assisted surgery (CAS) navigation assembly comprises a micro-electromechanical sensor (MEMS) navigation unit having one or more MEMS to provide at least orientation data. A support receives the MEMS navigation unit therein, the support being adapted to be mounted on the instrument in a fixed orientation relative to established navigated features of the instrument. At least two mating ball-in-socket features are disposed between the MEMS navigation unit and the support at opposed ends thereof for releasably engaging the MEMS navigation unit in precise orientational alignment within the receptacle, the at least two mating ball-in-socket features comprising catches aligned along an axis extending between the opposed ends, at least one of the catches being a biased catch. A method of connecting a MEMS navigation unit with a mating support fixed to a CAS instrument navigated by the CAS system is also provided.

TECHNICAL FIELD

The present application relates generally to computer-assisted orthopedic surgery systems using micro-electromechanical sensors.

BACKGROUND

The use of micro-electromechanical sensors (MEMS), rather than more traditional optically-tracked sensors for example, for the purposes of communicating with a computer-assisted surgery (CAS) system such as to navigate tools, bones, reference markers, etc. within the surgical field is becoming more desirable because such MEMS sensors are not limited by line-of-sight requirements of previously used optical sensors. These MEMS, which may for example include accelerometers and/or gyroscopes, are able to wirelessly communicate with the CAS system with which they are employed, or are equipped with a processor and user interface providing guidance to a user, i.e., the MEMS unit is part of a portable CAS system that is directly on the CAS instrument. Accordingly, the CAS system is able to determine at least orientation information of the MEMS unit, and therefore able to locate and track (i.e. navigate) the tool or bone to which the MEMS unit is fastened.

One of the steps required to navigate any tracked bone reference or surgical tool using a CAS system, including one which employs MEMS, is to “calibrate” the CAS instrument (ex: either a bone reference or tool) by precisely locating the position and/or orientation of the sensor relative that of the CAS instrument to which it is fastened. In the event that the sensor is detached from the CAS instrument, it is typically necessary to re-calibrate the assembly once the sensor is again fixed in its normal position relative to the instrument.

It may be desirable to be able to switch MEMS from one CAS instrument to another, however this becomes problematic because each time the MEMS is removed and then re-fastened, either onto another instrument or even back onto the same original instrument from which it was detached, a new calibration step must be performed in order to ensure that the exact relative position of the MEMS and the CAS instrument to which it is fastened are determined by the CAS system.

Accordingly, there is a need for a MEMS-navigated CAS instrument which enables the MEMS to be readily removed and re-attached to the instrument with repeatable precision and accuracy such that the relative alignment and orientation of the instrument and the MEMS will remain constant, thereby avoiding the need to re-calibrate the entire instrument in the event that the MEMS sensor is removed and/or re-attached.

SUMMARY

There is accordingly provided, in accordance with a first aspect, a computer-assisted surgery (CAS) navigation assembly adapted for navigating an instrument, the navigation assembly comprising: a micro-electromechanical sensor (MEMS) navigation unit having one or more MEMS to provide at least orientation data; a support including a receptacle receiving the MEMS navigation unit therein, the support being adapted to be mounted on the instrument in a fixed orientation relative to established navigated features of the instrument; and one or more connection devices connecting and aligning the MEMS navigation unit and the support, the connection devices including a pair of spaced apart mating ball-in-socket features disposed between the MEMS navigation unit and the support at opposed ends thereof for releasably engaging the MEMS navigation unit in precise orientational alignment within the receptacle, the mating ball-in-socket features comprising catches aligned along an axis extending between the opposed ends, at least one of the catches being a biased catch, and the catches being received within respective sockets formed within the MEMS navigation unit or the support.

Further in accordance with the first aspect, the support comprises a receptacle for receiving a portion of the MEMS navigation unit therein, the ball-in-socket features being located in the receptacle.

Still further in accordance with the first aspect, the receptacle comprises at least one planar surface, with the MEMS navigation unit being in coplanar abutment with the at least one planar surface when releasably engaged in the fixed orientation.

Still further in accordance with the first aspect, the receptacle comprises at least two planar surfaces for coplanar with corresponding surfaces of the MEMS navigation unit, the two planar surfaces being transverse with respect to one another.

Still further in accordance with the first aspect, the receptacle comprises three planar surfaces arranged in a U, with normals of the planar abutment surfaces being transverse relative to said axis.

Still further in accordance with the first aspect, one of the catches is a fixed catch.

Still further in accordance with the first aspect, the fixed catch has a geometry defined by a sphere quarter merging with a half-cylinder.

Still further in accordance with the first aspect, the fixed catch protrudes from the MEMS navigation unit.

Still further in accordance with the first aspect, the biased catch is part of the support, and wherein a socket cooperating with the biased catch is on the MEMS navigation unit.

Still further in accordance with the first aspect, the socket is defined a raised plateau on the MEMS navigation unit.

Still further in accordance with the first aspect, the MEMS navigation unit comprises a ramp portion adjacent to the socket and transitioning to the raised plateau for guiding the biased catch into the socket during assembly.

Still further in accordance with the first aspect, an elastomer surrounds a periphery of the raised plateau in the releasable engagement.

Still further in accordance with the first aspect, a latch feature is on the support for latching engagement of the MEMS navigation unit to the support.

Still further in accordance with the first aspect, the latch feature comprises a lever for disengagement of the latch feature from the MEMS navigation unit.

In accordance with a second aspect of the present disclosure, there is also provided a method of connecting a micro-electromechanical sensor (MEMS) navigation unit of a computer-assisted surgery (CAS) system with a mating support fixed to a CAS instrument navigated by the CAS system, the method comprising: releasably engaging the MEMS navigation unit within the support in precise relative orientational alignment, comprising: aligning and matingly engaging a pair of ball-in-socket features disposed between the MEMS navigation unit and the support at opposed ends thereof, the pair of ball-in-socket features being aligned relative to each; and snap-fitting a biased catch of at least one of said ball-in-socket features within a corresponding socket to constrain and align the relative orientation of the MEMS navigation unit and the support together about a first axis.

Further in accordance with the second aspect, releasably engaging the MEMS navigation unit further comprises abutting at least one planar surface on the MEMS navigation unit against a planar surface on a receptacle of the support, the planar surfaces lying in a substantially common plane to constrain the MEMS navigation unit and the support about at least a second axis.

Still further in accordance with the second aspect, the MEMS navigation unit is latched to the support when releasably engaging the MEMS navigation unit to the support.

DETAILED DESCRIPTION

Referring toFIG. 1, computer-assisted surgery (CAS) navigation assembly of the present disclosure includes generally an electronic micro-electromechanical sensor (MEMS) navigation unit12and a corresponding connecting support14which is adapted to be fixed in place on a CAS instrument, such as a tool or bone reference for example, which is to be navigated using the CAS system. In an embodiment, the connecting receptacle14is part of the CAS instrument, whereby reference to the receptacle14may include the CAS instrument. The MEMS navigation unit12and the receptacle14are engaged together in the manner described hereinbelow in further detail. The MEMS navigation unit12includes one or more of an accelerometer and/or a gyroscope, and is operable to communicate (e.g., wirelessly or not) with the CAS system with which the navigation assembly10is employed. According to another embodiment, the MEMS navigation unit12has a processor and visual interface capable of producing navigation output, i.e., without necessarily communicating with a CAS system in that the MEMS navigation unit12is the CAS system. Accordingly, the CAS system is able to determine at least orientation information of the MEMS unit, and therefore able to locate and track (i.e. navigate) the CAS instrument to which the MEMS unit12is fastened via its connecting dock or receptacle14. In yet another embodiment, the MEMS navigation unit12is of the type having a preset calibration setting, in that its orientation about at least one axis may be known when activated and/or reset.

The support14is shown as being a connecting dock or receptacle14, and is accordingly adapted to be fixed in position and orientation to the CAS instrument to be navigated using the CAS system. For clarity, reference will be made to the support14as the receptacle14, in accordance with the illustrated embodiment. Accordingly, the receptacle14is disposed in a fixed orientation relative to the established navigated feature of the instrument to which it is fastened. As described below, the MEMS navigation unit12is readily engaged within this receptacle14in a manner which provides a quick-connect and quick-disconnect type interconnection, however even given this ease of connection between the two components they are removably engaged together in a fashion which enables their relative alignment and orientation to remain constant and exact each and every time. As such, the MEMS navigation unit12can be disconnected from the receptacle14and then re-attached thereto, without needing to re-calibrate the entire CAS instrument. This permits, for example, the same MEMS navigation unit12to be used during a surgery for navigating several different CAS instruments, each having the same receptacle14mounted thereon. A single MEMS navigation unit12could therefore be used, if necessary or desirable, to navigate several different instruments within the surgical field, provided of course they do not need to be tracked simultaneously.

To enable this, the MEMS navigation unit12is oriented in an exact position relative to the receptacle14using a predetermined and defined system of orthogonal planes, as seen inFIGS. 2a-2b, which are formed by the shape and configuration of the receptacle14. This permits a precise and repeatable relation between the MEMS navigation unit12and its receptacle14to be established each and every time the MEMS navigation unit12is engaged in place within the receptacle14, without requiring a new calibration procedure to be performed.

This precision alignment between the MEMS navigation unit12and the receptacle14of the CAS instrument is made possible by at least two connection devices16and30, each of which includes cooperating features on each of the receptacle14and MEMS navigation unit12, such as to interconnect the two components of the present navigation assembly10in repeatably precise orientation relative to each other about all three orthogonal axes (X, Y and Z).

As seen inFIGS. 2a-5, the first connection device16includes a pair of ball-in-socket features18and19which are vertically aligned relative to each other along the X-axis, as seen inFIG. 2b. The mating ball-in-socket features18,19between each end of the MEMS navigation unit12and the receptacle, forming the first connection device16, are thus used to constrain and align the relative orientation of the two components about the z-axis.

Referring to the mating ball-in-socket features18and19in more detail, as seen inFIGS. 3a-5, the first ball-in-socket feature18comprises a biased catch or catch ball element20and the second ball-in-socket feature19comprises a fixed catch or ball element26, each of which engage respective sockets24,28as will be seen.

In the depicted embodiment, best seen inFIG. 2bfor example, the biased ball-in-socket feature18having the biased catch element20is located at a top end of the MEMS unit12and the receptacle14; however it may alternately be disposed at the opposite, bottom, end of the components.

As best seen inFIG. 5, the first, or biased, the biased catch element20of the ball-in-socket feature18may include, in at least this embodiment, a displaceable ball20which is biased by a spring22or other suitable biasing element (such as an elastomer, etc.). The spring22accordingly permits the sprung ball20to be forced inwardly away from its normally outwardly biased position (as shown inFIG. 5), in order to be able to interconnect the two components12and14, but returns the ball20back into its outwardly biased engaged position. The spring or biasing element22is compliant within an established force range such as to permit compression thereof, and thus connection between the ball20and its mating socket24, without the use of high force while nevertheless maintaining the biased contact between the MEMS unit12and the receptacle14.

When the two components12and14are being interconnected, therefore, once the ball20disposed on the receptacle14is aligned with its mating socket24formed in the MEMS unit12, the ball20accordingly springs back outwardly such as to matingly engage with the socket24and thereby interconnect the two components12and14at this connection point16. Although in the present embodiment the sprung ball20of the biased ball-in-socket feature18is disposed on the receptacle and the correspondingly shaped mating socket24is disposed in the MEMS unit12, it is to be understood that the opposite configuration may also be used.

As best seen inFIG. 4a, the socket24which receives the sprung ball20of the biased ball-in-socket feature18may comprise be formed in a plateau raised from a remainder of the connection device16. An open-topped slot23is defined in the raised plateau and has an open end25and a closed end27, however circular or other shaped receptacles24may also be used. A ramp27amay be formed between the raised plateau and the remainder of the connection device16. The ramp27ais adjacent to closed end27. The biased ball, or catch element,20of the mating ball-in-socket feature18accordingly enables a “snap”-fit connection between the MEMS navigation unit12and the receptacle14at the respective end at which this feature18is disposed. It is pointed out that, despite a full sphere being illustrated being shown in the illustrated embodiment, other geometries may be used, such as a frusto-sphere, etc. The expression “ball” covers segments of a ball, of a sphere including at least a portion of the outer surface of the ball, sphere, etc. The expression “socket” covers a concavity shaped to have some mating contact with the ball.

As noted above, and seen inFIGS. 3band 4b, the opposed ball-in-socket feature19of the first connection device16, which is disposed at the opposite end of the two components12and14from the biased ball-in-socket feature18, includes a protruding fixed (i.e. rigid or non-biased) catch element26that is integrally formed with the base of the MEMS unit12. The rigid catch element26is received within its corresponding mating socket28formed in the receptacle14. However, the opposite configuration may also be used (i.e. the protruding fixed catch element26may be located on the receptacle14and the mating socket28may be formed in the body of the MEMS unit12). As observed inFIG. 3b, the rigid catch element26has a ball portion and more specifically a quarter of a sphere or ball, with a half-cylinder base, although a ball, a frusto-sphere or half-ball, etc could be used, all of which fall within the scope and definition of ball-and-socket feature. The combination of the ball and half-cylinder base may provide additional contact surface between components of the ball-in-socket feature19.

Regardless, as shown inFIGS. 7a-7b, the rigid ball-in-socket connection feature19is the first of the two alignment features18,19to be engaged when connected the MEMS unit12into the receptacle14(step “A”), following which the biased ball-in-socket feature18is engaged by pivoting the MEMS navigation unit12inward into the receptacle14(step “B”) until the point where the biased alignment feature18snaps into engagement, thereby securing the two components12,14together in mated engagement as shown inFIG. 7b.

In another possible embodiment, however, the first connection device16may comprise two biased ball-in-socket features18, rather than having one fixed feature19and one biased feature18as per the depicted embodiment described above. Regardless, the first connection device16includes a pair of mating ball-in-socket features which releasably interconnect the MEMS navigation unit12and the receptacle14and which are vertically aligned relative to each other along the X-axis, such as to constrain and align the relative orientation of the two components12,14about the z-axis (seeFIG. 2a).

As noted above, the MEMS navigation unit12and the receptacle14are interconnected in a repeatably precise orientation relative to each other by at least two connection devices16and30, each of which includes shared and cooperating features on each of the receptacle14and MEMS navigation unit12.

Referring now toFIGS. 6a-6d, the second of these connection devices30constrains the relative orientation of the MEMS navigation unit12and the receptacle14about the X-axis and the Y-axis. This second connection device30comprises the abutting contact between the rear planar surface32of the MEMS navigation unit12and the front planar surface34within the receptacle14. These two planar surfaces32,34accordingly abut and lay flat one on top of the other, albeit in a vertical orientation, when the MEMS navigation unit12and the receptacle14are engaged together as shown inFIG. 6b. By abutting the two planar surfaces32and34such that they lie in a substantially common plane XY as shown inFIG. 6b, in as much as two solid planar surfaces can, the relative orientation of the MEMS unit12and the receptacle14is thereby constrained about the X and Y axes. The U-shape of the receptacle14is well suited for retaining the MEMS unit12.

In order to make sure that the respective planar surfaces32and34of the MEMS unit12and the receptacle14remain in precise abutted contact, additional angular retention features36and38between the ball-in-socket connections18and19are additionally provided. As seen inFIGS. 6b-6d, the first angular retention feature36is formed on the MEMS unit12opposed from the biased connection18at the upper end thereof, and more particularly is defined at the closed end27of the slot23which forms the socket24receiving the biased ball20(seeFIG. 4a). Acting opposed to this first angular retention feature36(i.e. facing in a opposite direction), is a second angular retention feature38which is jointly formed at the connection point between the receptacle14and the MEMS unit12at the lower end thereof, where the fixed catch element26is matingly received within the corresponding socket28. This second angular retention feature38may be provided, for example, by the curved end wall39of the slot or socket28in the lower end of the receptacle14. The angular retention features36and38therefore act in concert such as to keep the respective planar surfaces32and34of the MEMS unit12and the receptacle14in forced abutted contact, which in turn ensures that the orientations of the two components12and14are constrained about the X and Y axes. It is observed that the connection of the MEMS unit12to the receptacle14is predictable, using the connection features described above. Hence, it is possible to program the MEMS unit12of the preset type with an orientation related to the predicted orientation of the MEMS unit12in the receptacle14. In doing so, the MEMS unit12could be pre-calibrated in such a way its orientation about at least one axis is known relative to a navigated feature of the instrument, when the preset MEMS unit12is activated or reset.

As described above, and referring again toFIGS. 7a-7b, the method of connected the MEMS navigation unit12and the receptacle14is performed by first aligning the rigid ball-in-socket connection feature19at the lower end of the two components12and14and matingly engaging this connection feature19by sliding the MEMS unit in direction A, and then pivoting or rotating the upper end of the MEMS unit12into the receptacle14in direction B such as to matingly engage the biased connection feature18at the upper end of the two components. The biased catch/ball20will be helped into reaching the socket24by moving along the ramp27a. Once the biased catch/ball20of the upper connection feature18is snapped into engagement with its mating socket24, the respective planar surfaces32and34of the MEMS unit12and the receptacle14are then in forced abutted contact, and the two components12and14are fastened together as shown inFIG. 7b. The MEMS navigation unit12and the receptacle14are thereby connected in precise engagement such that they are constrained in fixed position and orientation relative to each other.

While the interconnection system as described so far for fastening the MEMS navigation unit12within the receptacle14may be sufficient to maintain their alignment with precision and accuracy, in at least one embodiment of the present disclosure an additional, secondary, connection system is also provided to help maintain the MEMS navigation unit12within its receptacle14within established alignment precision and accuracy, which may be particularly useful during impaction and oscillatory vibration which sometimes occurs during surgery.

Accordingly, referring particularly toFIGS. 8 to 9b, and also seen inFIG. 6b, a secondary connection system40is provided between the MEMS navigation unit12and the receptacle14which includes a compliant member42which is disposed between the upper surface41of the MEMS unit12and the facing upper rim44of the receptacle14, such as to provide additional constraint in at least in a direction substantially parallel to the X-axis (seeFIGS. 2a-2b). The compliant member42may include, for example, a wire-form or O-ring for example, and may either be substantially rigid or may be at least somewhat elastically deflectable. In either case, however, the compliant member42provides additional constraint in at least the X-axis direction to limit relative movement between the MEMS unit12and the receptacle14, and may also provide damping therebetween such as to help absorb any vibrations.

In the event of impact or oscillatory vibration of the CAS tool to which the receptacle14is fixed, should the MEMS navigation unit12become slightly displaced within, or even momentarily disengaged from, the receptacle14(for example such that the biased catch/ball20become somewhat disengaged form its mating socket24), MEMS navigation unit12will contact the compliant member42which will limit such displacement within the receptacle14. The permitted displacement before the compliant member42comes into contact with the MEMS unit12may correspond to the limit at which the biased ball20can automatically return into its socket24. During insertion of the MEMS unit12into the receptacle14, the compliant member42will be moved upwards within its corresponding slot46in the upper rim44of the receptacle14, as the MEMS navigation unit12is slid into its engaged position within the receptacle14, whereupon the compliant member42will return to its original position as shown inFIG. 8.

In an alternate embodiment, an alternate secondary connection system50may be provided in lieu of, or possibly even in addition to, the connection system40described above. The alternate secondary connection system50also includes a compliant member in the form of a spring-return lever52which is mounted to the upper rim44of the receptacle14and includes a blade-spring54which is used to ensure that the lever52remains in continuous engaged contact with the top surface of the MEMS unit12. The spring-return lever52operates in much the same manner as the compliant member42described above, in that it ensures that the MEMS unit12remains engaged in position and orientation within the receptacle14even if the other connection mechanisms (such as the biased catch/ball20of the connection device18) become slightly disengaged. Accordingly, similar to the wire-form or other element of the compliant member42, the spring-return lever12is moved upwards as the MEMS unit12is pushed into place within the receptacle, and then returns into a latched position (seeFIG. 9a) wherein it is engaged with the top side edge of the MEMS navigation unit12once the MEMS unit12is completely connected in place within the receptacle14. As seen inFIG. 9b, the lever52includes a latch feature58at its outer edge which engages the correspondingly shaped ridge56on the top side edge of the MEMS unit12. The matching geometry of the ridge56on the MEMS unit12and the latch feature58on the lever52ensures that the MEMS unit12will not be disconnected from the receptacle during impaction and/or oscillatory vibration. To be able to disconnect the MEMS unit12from the receptacle14, the lever52must be manually and voluntarily lifted by the user. This accordingly provides an additional secure and fail-safe interconnection between the MEMS navigation unit12and the receptacle14.

The terms “top” and “bottom”, “upward” and “downward”, “vertical”, etc., are generally used herein with reference to the orientation of the assembly10as shown in the drawings for ease of description purposes only, however it is to be understood that depending on the orientation of the instrument to which the receptacle14is fixed, these directions may not actually correspond to a true or absolute vertical, upward and/or downward direction.