Patent Publication Number: US-2021177441-A1

Title: Computer-assisted shoulder surgery and method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The application claims the priorities of U.S. Patent Application No. 62/947,295, filed on Dec. 12, 2019, and U.S. Patent Application No. 63/027,653, filed on May 20, 2020, both of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The application relates generally to computer-assisted surgery of the type used in shoulder surgery involving the humerus and/or the scapula. 
     BACKGROUND OF THE ART 
     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 humerus, the orientation of the bone may be expressed in terms of retroversion and inclination, relative to anatomical axis of the humerus. In contrast, navigation of the scapula may rely on preoperative planning or on physical landmarks, due to the thinness of the bone. 
     There remains a need for improved surgical tools which may be used in conjunction with a CAS system in order to digitally navigate a surgical cut of a humerus and/or position an implant on a glenoid. 
     SUMMARY 
     In one aspect, there is provided a humerus cutting assembly comprising: a guide frame having an attachment member adapted to be secured to a humerus adjacent to a humeral head, and a cutting guide releasably connected to the guide frame, the cutting guide configured to guide a tool in altering the humeral head; at least one inertial sensor unit on the cutting guide, the inertial sensor unit tracking an orientation of the cutting guide relative to the humerus based on the releasable connection between the cutting guide and the guide frame. 
     In another aspect, there is provided a system for guiding an alteration to a head of a humerus comprising: a processor unit, and a non-transitory computer-readable memory communicatively coupled to the processor and comprising computer-readable program instructions executable by the processor unit for: setting a reference orientation of a humerus when an assembly featuring a cutting guide is attached to the humerus in a given orientation, obtaining an output from at least one inertial sensor on the cutting guide as an orientation of the cutting guide relative to the humerus is varied, tracking a current orientation of the humerus relative to the reference orientation using the output, and calculating and outputting at least one angle being indicative of an alteration to the head of the humerus associated to the current orientation of the cutting guide. 
     In a further aspect, there is provided a glenoid navigation assembly comprising: a pin guide having a cannulated shaft, the cannulated shaft adapted to receive a guide pin therein; a registration interface at the end of the cannulated shaft and configured for abutting a glenoid, the registration interface having at least one visual alignment member for visually assisting in a positioning of the guide pin on the glenoid; and at least one inertial sensor unit on the glenoid navigation assembly, the inertial sensor unit tracking an orientation of the cannulated shaft relative to the glenoid based on a contact between the registration interface and the glenoid surface. 
     In a still further aspect, there is provided a system for guiding an alteration to a glenoid comprising: a processor unit, and a non-transitory computer-readable memory communicatively coupled to the processor and comprising computer-readable program instructions executable by the processor unit for: setting a reference orientation of a glenoid when an assembly featuring a guide is applied against the glenoid at a given position, obtaining an output from an inertial sensor on the guide as an orientation of the guide relative to the glenoid is varied, tracking a current orientation of the guide relative to the reference orientation using the output, and calculating and outputting an angle, the angle being indicative of an alteration to the glenoid associated to the current orientation of the guide. 
     In a still further aspect, there is provided a system for guiding an alteration to a head of a humerus comprising: a processor unit, and a non-transitory computer-readable memory communicatively coupled to the processor and comprising computer-readable program instructions executable by the processor unit for: setting a reference orientation of a humerus when an assembly featuring a cutting guide is attached to the humerus in a predetermined manner, robotically manipulating the guide relative to the humerus with a robotic arm, obtaining an output representative of a current orientation of the guide as the guide is robotically manipulated, tracking a current orientation of the humerus relative to the reference orientation using the output, calculating and outputting at least one angle being indicative of an alteration to the head of the humerus associated to the current orientation of the cutting guide, and auto-blocking the robotic arm when a desired value for the angle is reached. 
     In a still further aspect, there is provided a system for guiding an alteration to a glenoid comprising: a processor unit, and a non-transitory computer-readable memory communicatively coupled to the processor and comprising computer-readable program instructions executable by the processor unit for: setting a reference orientation of a glenoid when an assembly featuring a guide is applied against the glenoid in a given position, robotically manipulating the guide relative to the glenoid with a robotic arm, obtaining an output representative of a current orientation of the guide as the guide is robotically manipulated, tracking a current orientation of the guide relative to the reference orientation using the output, calculating and outputting at least one angle being indicative of an alteration to the glenoid associated to the current orientation of the guide, and auto-blocking the robotic arm when a desired value for the angle is reached. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Reference is now made to the accompanying figures in which: 
         FIG. 1  is a perspective view of a humerus cutting assembly in accordance with the present disclosure; 
         FIG. 2  is a perspective view of a guide frame of the humerus cutting assembly of  FIG. 1 ; 
         FIG. 3  is an assembly view of the humerus cutting assembly of  FIG. 1 ; 
         FIG. 4  is a perspective view showing a relation between a cutting guide and the guide frame of the humerus cutting assembly of  FIG. 1 , during positioning of the cutting guide on the humerus; 
         FIG. 5  is a perspective view of the humerus cutting assembly as positioned for performing a resection of the humeral head; 
         FIG. 6  is a graphic user interface showing virtual navigation of a glenoid implant model in inclination and version in preoperative planning; 
         FIG. 7  is a perspective view of a glenoid navigation assembly in accordance with the present disclosure; 
         FIG. 8  is a lateral view of the glenoid navigation assembly; 
         FIG. 9  is a perspective view of the glenoid navigation assembly of  FIG. 7  with a registration interface being removed; 
         FIG. 10  is a perspective view of the glenoid navigation assembly as removed after the positioning of a guide pin in the glenoid; and 
         FIG. 11  is a perspective view of a robotic arm that may be used with humerus cutting assembly of  FIG. 1  and/or the glenoid navigation assembly of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings and more particularly to  FIGS. 1-5 , a humerus cutting assembly in accordance with the present disclosure is generally shown at  10  as positioned on an arm of a user. The arm of the user is shown schematically with the humerus fully exposed, but in an operative setting, only a limited portion of the humerus may be exposed, i.e., at the shoulder joint, with a limited part of the glenoid exposed. The humerus cutting assembly  10  is of the type that may be used to assist in altering the humeral head. In an embodiment, the humerus cutting assembly  10  is used to cut a plane on the humeral head, for instance in the context of glenoid surgery or reverse glenoid surgery. The humerus cutting assembly  10  may be used for different operations as well. The plane of resection on the humeral head is typically oriented to a desired retroversion and/or inclination. These angle values may be relative to an anatomical axis of the humerus that extends along the length of the humerus. Retroversion, a.k.a., retroversion angle, may be defined as being a projection of a normal of the resection plane onto a transverse plane of the humerus, relative to a medio-lateral axis. Inclination, a.k.a., inclination angle, may be defined as a projection of a normal of the resection plane onto the frontal plane of the humerus, relative to the anatomical axis of the humerus. Other or different angles may also come into consideration when planning and performing a cut on the humeral head. 
     The humerus cutting assembly  10  may have a guide frame  20  and a cutting guide  30 . The frame  20  and guide  30  are described as two components (or groups of components) for clarity, but they may be viewed as a single group of components, or more than two components as well. The guide frame  20  is used to form a structural reference for the cutting guide  30  and/or assist in defining a reference coordinate system, a.k.a., frame of reference. The guide frame  20  may for instance be attached to the arm of a patient in a given orientation, such as being generally parallel to the anatomical axis of the humerus. The cutting guide  30  is used to guide alteration tools, such as a flat saw blade, in the manner configured in the illustrated embodiment. Other cutting implements or guides could be used, such as a drill guide for a drill among possible tools. Other tools may include a reamer, etc. 
     Referring to  FIGS. 1 to 3 , the guide frame  20  is shown as having a main arm  21 . AS a possibility, the main arm  21  extends generally parallel to the humerus when installed onto the arm of the patient. The main arm  21  may have a translational joint so as to expand or contract to adapt the guide frame  20  to the user&#39;s arm length. In an embodiment, the translational expansion may be possible by a telescopic joint  21   a . As another option, the main arm  21  ha a cylindrical joint enabling a translation and a rotation. In an embodiment, the telescopic joint  21   a  defines a plurality of indexed positions with appropriate snap-fit indexing features (e.g., spring loaded ball and groove). Other joint configurations may be used, such as endless screw engagement, set screw locking, and/or biasing force to block the movement of the segments of the main arm  21 . As shown, a push button or detent  21   b  may be present to release the lock of the arm portions and allow expansion or contraction of the main arm  21 . The main arm  21  may maintain a desired length by such self-blocking features at the telescopic joint  21   a.    
     A clamp  22  may be located at a bottom end of the main arm  21 . The clamp  22  may be provided to non-invasively attach and fix the guide frame  20  to a user&#39;s forearm, for example. In another embodiment, the clamp  22  could be used to attach the guide frame  20  to a lower part of the humerus. Other configurations are contemplated. In an embodiment, the clamp  22  has an inverted V frame  22   a  at the end of which are positioned jaws  22   b . The jaws  22   b  may be pivotally connected to the V frame  22   a . As shown, the jaws  22   b  may be curved inwardly so as to emulate the generally circular shape of the forearm or of the upper arm near the elbow joint. In an embodiment, the jaws  22   b  are biased toward one another so as to naturally exert pressure and clamp onto the forearm. Other configurations are considered as well. If the jaws  22   b  are biased, the biasing force should be sufficient to allow a suitable clamping force while not preventing the jaws  22   b  from being manually separated from one another. In an embodiment, the clamp  22  is relatively symmetric to allow the self-centering of the clamp  22  on the portion of the arm it will grasp. 
     Other bottom end configurations may be present on the guide frame  20 . For example, as an alternative to the jaws, it is considered to provide a strap, an elastic, and/or an U-shaped structure or the like, located at the bottom end of the main arm  21  or at the end of the V frame  22   a . Therefore, when positioning the guide frame  20  on the arm, the position of the lower part of the guide frame  20  can readily be adjusted by manipulations of the jaws  22   b  or equivalent. Such configurations are non-invasive as they attach to the surface of the skin, but invasive attachments are considered as well. 
     A support  23  may be provided on the main arm  21  or on any other portion of the guide frame  20 , the support  23  being configured to receive an inertial sensor unit  24  thereon, as one of the possible types of tracking technologies that may be used with the guide frame  20 . In an embodiment, the inertial sensor unit  24  is in the form of a pod that is releasably connectable to the support  23 . The inertial sensor unit  24  may include a processor and a non-transitory computer-readable memory communicatively coupled to the processor and comprising computer-readable program instructions executable by the processor. Moreover, as seen in the figures, the inertial sensor unit  24  may be self-contained, in that it is precalibrated for operation, has its own powering or may be connected to a power source, and has an interface, such as in the form of a display thereon (e.g., LED indicators). Hence, the humerus cutting assembly  10  may be qualified as being a computer-assisted solution by the presence of the inertial sensor unit(s)  24  alone. It is also considered to have a computerized ecosystem including the inertial sensor unit(s)  24 , a monitor, another processing unit, a tablet or like portable hand-held device, etc. 
     The inertial sensor unit  24  may also be directly integrated onto the guide frame  20 , though the releasable configuration may be well suited for preprogramming, sterilization, etc. As the main arm  21  may preferably be oriented in a generally parallel manner to the anatomical axis of the humerus, the positioning of the support  23  on the main arm  21  may facilitate the calibrating of the inertial sensor unit  24 . In an embodiment, the interconnection between the support  23  and the inertial sensor unit  24  is such that it is calibrated into the inertial sensor unit  24 . Stated differently, once the inertial sensor unit  24  is in the support  23 , the inertial sensor unit  24  may have been pre-calibrated in such a way that a coordinate system maintained and tracked by the inertial sensor unit  24  thereof is aligned with a length of the main arm  21 . Accordingly, if the main arm  21  is generally parallel to the humerus anatomical axis, the inertial sensor unit  24  may automatically track the anatomical axis of the humerus in its XYZ coordinate system. Therefore, in an embodiment, once the inertial sensor unit  24  is turned on, with the guide frame  20  attached to the arm, the inertial sensor unit  24  may continuously track an orientation of the upper arm, in phi, theta, rho (i.e., three rotational degrees of freedom—DOF). 
     Referring to  FIG. 2 , a side arm  25  may project from the main arm  21 . In an embodiment, the side arm  25  is perpendicular or transverse to the main arm  21 . The side arm  25  may also have a telescopic joint, shown as  25   a , with a push button  25   b . The configuration of the telescopic joint  25   a  may be as described above for the telescopic joint  21   a , with the possibility of forming a self-blocking joint. It is also contemplated to have the side arm  25  be of fixed length as well. An attachment plate  26 , or like attachment member, is located at an end of the side arm  25 . The attachment plate  26  is of the type that will abut against the bone. In an embodiment, the attachment plate  26  may be provided with a patient-specific contour being the result of pre-operative modelling of the humerus, for the attachment plate  26  to be seated in an unique complementary manner against a predefined portion of the humerus. The patient-specific surfacing of the attachment plate  26  may be known as being a negative contour of the bone portion. The predictability of the patient-specific contour may contribute to the pre-calibration of the inertial sensor unit  24 . The patient-specific contour is optional as the attachment plate  26  may be a stock plate not specifically designed with the user&#39;s anatomical model. The attachment plate  26  has attachment holes  26   a  by which fasteners  27  may be used to secure the attachment plate  26  and therefore the guide frame  20  to the humerus. Fasteners  27  may be screws, for example. Straps may be an alternative to screws. The holes  26   a  may be oriented for the fasteners  27  to converge into the bone. 
     Therefore, as shown in  FIGS. 3 and 4 , the guide frame  20  may be rigidly connected to the humerus, with a position of the lower portion of the guide frame  20  being readily adjustable, for instance to achieve a visual parallel relation between the main arm  21  and the upper arm, though this is only an option. A connector  28  may be integral with the main arm  21  or other portions of the guide frame  20 . In an embodiment, the connector  28  is in a fixed relation with respect to the inertial sensor unit  24 . The connector  28  may have any appropriate shape or configuration. In an embodiment, the connector  28  is a tube having a receptacle. As observed, the receptacle has a non-circular rotation. Stated differently, once a complementary connector is received in the connector  28 , rotation is precluded by the non-circular shape of the connector  28 . Any appropriate anti-rotation feature may be used, and ensure a fixed orientation of a component connected to the guide frame  20  via the connector  28 . 
     Referring to  FIGS. 3 and 5 , the cutting guide  30  is shown as having a cutting block  31 . The cutting block  31  is of the type that defines a cutting slot  31   a  sized so as to receive a saw blade therein, in accordance with an embodiment. Holes  31   b  may also be defined in the cutting block  31  so as to secure the cutting guide  30  via the cutting block  31  to the humeral head or in proximity thereof, as shown in  FIGS. 4 and 5 . The humerus cutting assembly  10  is shown as being of the type used to define a cutting plane on the humeral head but other cutting implements may be used instead of the cutting guide  30 . 
     An arm  32  may project from the cutting block  31  and has a support  33  at its end. The support  33  is similar to the support  23  and may therefore be shaped to receive a tracker device such as another inertial sensor  34 . Again, the complementary coupling of the inertial sensor unit  34  and the support  33  allows the initialization of the inertial sensor unit  34  to be in a calibrated arrangement with the cutting guide  30  and more particularly with the cutting slot  31   a . Stated differently, once the inertial sensor unit  34  is in the support  33  and is turned on, the inertial sensor unit  34  may track the location in space of the plane of the cutting slot  31   a  through its readings. Fasteners  37  (e.g., screws, pins) may be used in conjunction with the cutting guide  30  and into the cutting holes  31   b  so as to secure the cutting guide  30  to the humerus in the manner shown in  FIG. 5 . A connector  38  is part of the cutting guide  30 . In an embodiment, the connector  38  is a pin, nipple, coupler or the like that has a shape complementary to that of the connector  28  for complementary male-female coupling, that may provide a unique coupling orientation. The unique coupling orientation may be defined as a single possible orientation of the cutting guide  30  when coupled to the guide frame  20  when the pair is interconnected via the releasable connection. The reverse arrangement is possible as well (female at  38 , male at  28 ), as are other complementary couplers. 
     The inertial sensor units  24  and  34  are preprogrammed, taking into consideration the geometrical relation between the guide frame  20  and the cutting guide  30 , such that when the cutting guide  30  is coupled to the guide frame  20  in the manner shown in  FIG. 1 , the inertial sensor units  24  and  34  may perform a handshake such that a subsequent movement of the cutting guide  30  as detached from the guide frame  20  is tracked at least in orientation, relative to the frame of reference of the humerus, i.e., the anatomical axis of the humerus tracked by the inertial sensor unit  24  as described above. For this reason, the coupling between the connector  38  and the connector  28  is complementary and unique. Therefore, once this handshake is done, the cutting guide  30  is navigated via its inertial sensor unit  34 , e.g., using a dead reckoning tracking technique, such that it may be positioned in the manner shown in  FIGS. 4 and 5 , relative to the virtual reference system of the humerus. In doing so, desired retroversion and inclination values may be attained. If the humerus moves, the inertial sensor unit  24  secured thereon may track its movements for such movement to be compensated for. In an embodiment, the retroversion and inclination values have been preplanned and/or may be output by the inertial sensor unit  24  and/or  34 . In another embodiment, a single inertial sensor unit  24  is used, and this may require that the humerus be constrained from moving. The single inertial sensor unit  24  may set the virtual reference system for the humerus, including the anatomical axis. The virtual reference system may include other axes, a transverse and a frontal plane of the humerus. If a single inertial sensor unit is used, the inertial sensor unit  24  may be detached from the support  23  and attached to the support  33  in the cutting guide  30 , while the arm is fixed and the guide frame  20  and cutting guide  30  being in a known geometrical relation, e.g., via the complementary coupling of the connectors  28  and  38 . A dead reckoning tracking technique is used during the transfer of the inertial sensor unit  24  from the support  23  to the support  33 , such that the orientation of the virtual reference system of the humerus is preserved. The cutting guide  30  may be detached from the guide frame  20 , and is tracked relative to the fixed humerus, using dead reckoning tracking technique, for the retroversion and inclination values to be calculated and output in real-time by the inertial sensor unit  24 , or  34 . 
     The movements of the cutting guide  30  may be effected using a robotic arm such as the one shown at  100  in  FIG. 11 . The cutting guide  30  may therefore have a coupler  39  thereon for being connected to the robotic arm  100 . The coupler  39  may have any appropriate configuration. The robotic arm  100  of  FIG. 11  may be suited to maintain a desired orientation of the cutting guide  30  while it is drilled to the humerus, as a possibility. If the humerus is fixed, the robotic arm  100  may maintain a desired orientation of the cutting guide  30  without the use of the fasteners  37 , as a possibility. 
     Although the guide frame  20  and the cutting guide  30  are shown as being separable components, it is contemplated to have these components interconnected by a mechanism as well, for instance through the bone altering. 
     Referring now to  FIG. 6 , there is illustrated a graphic user interface (GUI) showing a scapula with a virtual model of an implant thereon. The scapula may for example be a virtual model of the patient&#39;s scapula obtained from imaging such as CT or MRI, or the combination of imaging and other techniques, such as 2D to 3D X-Ray images, with a merge to a generic scapula from a bone atlas. As observed from the right-hand side, the positioning of the fastener in the glenoid is strategic considering that the scapula is relatively thin. A functionality of the present disclosure is to locate the implant in such a way that the fastener does not pierce through the hidden side of the scapula. For example, the position of the fastener may be determined as a function of depth, whereas the orientation of the trajectory of the fastener is defined in terms of inclination and version. The inclination, a.k.a., inclination angle, may be the projection of the axis of the fastener onto the frontal plane, relative to the mediolateral axis. The version, a.k.a., the version angle, may be defined as the projection of the fastener axis on the transverse plane, relative to the mediolateral axis. Other angles may be monitored. 
     The GUI of  FIG. 6  may help a surgeon or other operator in planning a desired trajectory for the fastener. Therefore, the data input into the GUI in  FIG. 6 , for instance in the form of a virtual movement of the model of the implant on the scapula, may serve in a planning stage occurring pre-operatively. Thereafter, a glenoid navigation assembly, as shown as  50  in  FIGS. 7 to 10 , may be used to replicate the planned position and orientation (i.e., trajectory) of the fastener or implant (e.g., implant peg). However, the glenoid navigation assembly may also be used without any pre-planning. 
     Referring to  FIG. 7 , the glenoid navigation assembly  50  is shown having a pin guide  60 , a registration interface  70  and a pin  80 . In an embodiment, the pin guide  60  and the registration interface  70  are available as a kit and separately from the pin  80  which may not be part of the glenoid navigation assembly  50 . In an embodiment, the pin  80  is stock in that it may not be specifically designed to be used with the glenoid navigation assembly  50 . 
     The pin guide  60  has an elongated cannulated shaft  61 . The cannulated shaft  61  therefore has an internal channel through which the pin  80  may slide in at least one translational DOF—together the elongated cannulated shaft  61  and the pin  80  form a cylindrical joint. As observed from  FIG. 9 , the cannulated shaft  61  may have a tapered end  61   a  to facilitate its movement against the glenoid, for instance by limiting a contact surface between the shaft  61  and the glenoid. A handle  62 , or any other coupler, may project generally laterally from the cannulated shaft  61 . The handle  62  may be used to maneuver the pin guide  60 . A support  63  with inertial sensor unit  64  may be positioned on any part of the pin guide  60  though it may conveniently be positioned on the handle  62 . The set of support  63  and inertial sensor unit  64  is generally as described above for the humerus cutting assembly  10  in the form of the supports  23  and  33  in the inertial sensor units  24  and  34 . As described for the humerus cutting assembly  10 , the inertial sensor unit  64  may be self-contained and/or may also be connected directly to the handle  62 , etc. The inertial sensor unit  64  may therefore be in a precise location on the pin guide  60  such that, when turned on, the inertial sensor unit  64  may continuously track the orientation of the cannulated shaft  61 . Therefore, once initialized, it is possible to track an orientation of the cannulated shaft  61  and pin  80  therein in a coordinate system of the inertial sensor unit  64 . The tracking may be in three rotational DOFs. A connector  68  may be at an end of the handle  62  for connection to the robotic arm  100  of  FIG. 11 , according to an embodiment, through the glenoid navigation assembly  50  may be operated in a free hand mode as well. It is also observed that the cannulated shaft  61  may have a non-circular cross-section on its outer surface, or like anti rotation feature. 
     As observed from  FIG. 7 , the glenoid navigation assembly  50  may be moved relative to the scapula so as to position the pin  80  in a desired position and orientation in the glenoid. Referring to  FIGS. 7 and 8 , the registration interface  70  is at the end of the cannulated shaft  61  of the pin guide  60 . Therefore, when the glenoid navigation assembly  50  is positioned against the glenoid as in  FIG. 7 , the registration interface  70  may be in contact with the glenoid. The registration interface  70  may be patient-specific in that it may be shaped as a function of the patient-specific bone geometry. This may be done for instance using negative contouring, with a virtual model of the bone. In another embodiment, the registration interface  70  is not patient-specific. The registration interface  70  may come in different sizes depending on the patient&#39;s bone size, and the selection of the registration interface  70  may be guided by preoperative imaging or in situ sighting. The registration interface  70  is a visual indicator to assist an operator, such as a surgeon, in positioning the pin  80  in the glenoid. 
     As illustrated, the registration interface  70  has a joint portion  71  that may be generally centralized within the registration interface  70 . The joint portion  71  may be defined by a bore  71   a  that has a shape complementary to that of the cannulated shaft  61  of the pin guide  60 . Therefore, once the registration interface  70  is mounted to the cannulated shaft  61 , the registration interface  70  may slide along an outer surface of the cannulated shaft  61 . As mentioned above, the cannulated shaft  61  has a non-circular cross-section, or like anti-rotation feature, such that the only degree of freedom between the registration interface  70  and the pin guide  60  is a translation, though other embodiments are considered. It is also possible to lock the registration interface  70  at the end of the cannulated shaft  61  of the pin guide  60 . Any appropriate locking feature may be provided therefor, including for example a set screw. 
     Referring to  FIGS. 7 and 8 , the registration interface  70  may have different alignment member(s)  72 , for providing visual alignment. As an example, the alignment members  72  may include arcs  72   a  at the bottom and at the top of the registration interface  70 . The arcs  72   a  may be spaced apart by a distance corresponding to the size of the glenoid, or of an implant (e.g., glenosphere). It is also contemplated to use abutments such that the arcs  72   a  may abut against, for example, a rim of the glenoid. Wings  72   b  may also be present and may be used to assist in spacing the registration interface  70  from sides of the glenoid. For example, the registration interface  70  may be positioned so as to have one of the wings  72   b  aligned with the periphery of the glenoid. As another possible alignment member  72 , a pointer  72   c  may project from a remainder of the registration interface  70 . The pointer  72   c  may be aligned with a vertical axis or towards any anatomical feature of the scapula that may be seen, such as the coracoid process. One or more of  72   a ,  72   b    72   c  may be present in the alignment member  72 . Therefore, in the manner shown in  FIG. 8 , the registration interface  70  may be used to place the pin guide  60  in an appropriate location such as a pre-operatively planned position. 
     Once the appropriate location of the alignment member  72  is attained, an orientation of the pin  80 , i.e., its trajectory, may be navigated. So as not to have the registration interface  70  interfere with the movement of the pin guide  60 , the registration interface  70  may be slid away by moving same along the cannulated shaft  61 , as shown in  FIG. 9 . In another embodiment, the registration interface  70  could simply be clipped off of the pin guide  60 , in an embodiment without the translational DOF. From that point on, the inertial sensor unit  64  is used to achieve the proper orientation of the pin  80 . As the inertial sensor unit  64  has been turned on and has been programmed with the inclination and version of the pin  80 , for instance as pre-programmed using the GUI of  FIG. 6 , the inertial sensor unit  64  may provide guidance, for instance through LEDs thereon, to indicate when the pin  80  is properly oriented relative to the glenoid. To do so, a plane of the glenoid may have been determined based on the interaction between the registration interface  70  and the glenoid, during the positioning step. As the registration interface  70  is in a fixed orientation on the pin guide  60 , an orientation of the glenoid may be set in the virtual coordinate system tracked by the inertial sensor unit  64  when the registration interface  70  is against the glenoid. A modelling of the scapula/glenoid, for instance pre-operative with any appropriate imaging modality, may be used to determine an orientation of the surface of the glenoid. Therefore, when the registration interface  70  is against the glenoid, as planned, and considering the fixed orientation of the registration interface  70  on the pin guide  60 , the inertial sensor unit  64  may be calibrated or set with the orientation from the modelling. It is assumed that the scapula is fixed in space during these operations. It is however contemplated to provide an inertial sensor unit on the glenoid so as to monitor any movement. The shape of the end  61   a  may assist in preserving a position (x,y,z) of the shaft  61 , for instance by having a rounded surface (e.g., hemispherical), contacting the glenoid, with an orientation (phi, theta and/or row) of the shaft  61  varies. 
     The maneuvering of the pin guide  60  may be achieved by the robotic arm  100  of  FIG. 11 , in a collaborative mode with maneuvers of a user. The robotic arm  100  may preserve the position of the tip  61   a  of the cannulated shaft  61  against the glenoid and rotate a remainder of the pin guide  60 . Once the desired orientation or trajectory for the pin  80  is achieved, the pin  80  may be screwed into the glenoid. As shown in  FIG. 10 , the pin guide  60  may then be slid off of the pin  80 . The pin  80  will serve as a trajectory guide for a cannulated drill, for a reamer, for example. A location of the pin  80  may correspond to a location of a peg of an implant, such as a glenosphere, that will be implanted onto the glenoid. 
     The robotic arm  100  of  FIG. 11  is an example of an arm that may be used with the with humerus cutting assembly  10  of  FIG. 1  and/or the glenoid navigation assembly  50  of  FIG. 7 . In an embodiment, the assemblies  10 / 50  connected to an effector end of the robotic arm  100 . The robotic arm  100  may provide  6  DOFs of movement to the effector end, though fewer or more may be possible. In an embodiment, the robotic arm  100  is used in a collaborative mode, as manipulated by a user, with the possibility to provide some movement constraints, such as preserving the position of pin  80  on the glenoid as described above. Alternatively, the arm may be a rapidly repositionable surgical support arm, such as the WalterLorenz® Surgical Assist Arm (Zimmer Biomet, Jacksonville, Fla.), which allows for the user to navigate the position and orientation of the assemblies by hand but then lock the joints of the support arm once the desired position and orientation is attained according to the GUI of the respective inertial support units of the assemblies. 
     The robotic or rapidly repositionable support arm  100  of  FIG. 11  may for example be as described in United States Patent Application Publication No. 2018/0116758, incorporated herein by reference. The robotic arm  100  may be referred to as a lockable support assembly that may have a base arm portion  101  having a lower end  101 A and an upper end  101 B, and a distal arm portion  102  having a proximal end  102 A and a distal end  102 B. A central joint  103  may be linking the upper end  101 B of the base arm portion  101  to the proximal end  102 A of the distal arm portion  102 . For example, the central joint  103  is a rotational joint (e.g., one DOF revolute joint). A lower joint  104  may be at the lower end  101 B of the base arm portion  101 , and may serve to connect the robotic arm  100  to a structure, to a station, etc. The lower joint  104  may also be for instance a rotational joint, such as a spherical joint or universal joint (e.g., two or more rotational DOFs). In  FIG. 11 , the lower joint  104  is shown having a ball, with the proximal end  102 A. An upper joint  105  may be at the distal end  102 B of the distal arm portion  102 . The upper joint  105  may also be for instance a rotational joint, such as a spherical joint or universal joint (e.g., two or more rotational DOFs). The effector end  106  of the robotic arm  100  may be at the upper joint  105 , with the assemblies  10 / 50  connected to the effector end  106  of the robotic arm  100 . A locking mechanism may be integrated inside the robotic arm  100  in the manner described in United States Patent Application Publication No. 2018/0116758, so as to selectively block movement of one or more of DOFs of the robotic arm  100 . For instance, all of the DOFs of the robotic arm  100  may be locked by the locking mechanism, so as to block movement between the structure, the base arm portion  101 , the distal arm portion  102 , and the effector end  106 . The locking mechanism may be coupled to the base arm portion  101  at a location above the lower joint  104  and configured to simultaneously deliver locking forces to the central joint  103 , the lower joint  104 , and to the upper joint  105 . Moreover, the locking mechanism may increase or decrease a resistance at the various joints  103 ,  104 ,  105 , for the user of the robotic arm  100  to experience variation of resistance in displacing the effector end  106 , or arm portions. The joints  103 ,  104  and/or  105  may employ frictional forces to block movements, and a reduction in forces applied at a joint may reduce friction, and hence permit some movement, though with a resistance that may be proportional to the frictional forces. This may be used to guide the user in the manipulations. 
     In an embodiment, a controller  110  is provided to operate the robotic arm  100 , for instance in conjunction with the assemblies  10 / 50 . The controller  110  may be operatively connected to the robotic arm  100  and inertial sensor units  24 ,  34 , and/or  64  via a wireless connection, or alternatively may be connected via wire or may be integral to the assemblies  10  and  50 . For example, the controller  110  may be part of a computer-assisted surgery system, and may include a processor unit, and a non-transitory computer-readable memory communicatively coupled to the processor and computer-readable program instructions executable by the processor unit for operating the robotic arm  100 . The controller  110  may operate a surgical flow based on the procedure being performed. Accordingly, various interfaces may be provided if necessary. This may include button  110 A on the robotic arm  100 , which button  110 A may activate and/or deactivate the locking mechanism in the robotic arm  100 . In an embodiment, the controller  110  receives signals from the inertial sensor unit  24 ,  34 , and/or  64  to receive orientation information related to the assemblies  10  and  50 . An inertial sensor unit  114  may optionally be provided on the robotic arm  100 , such as at the effector end  106 , or other location, to provide navigation data to the controller  110 . The inertial sensor unit  114  may be integrated into the robotic arm  100 , or may be an add-on pod, in the manner shown for the assemblies  10  and  50 . 
     Consequently, the robotic arm  100  and controller  110  could be used in the surgical workflows related to the assemblies  10  and/or  50 , or in other procedures. According to an embodiment, the robotic arm  100  may automatically lock by actuating its locking mechanism, once the robotic arm  100  has sensed that it has reached its desired orientation, for instance by the signals from the inertial sensor unit  114 . The signals of the inertial sensor unit  114  may be used jointly with the data of other inertial sensor units (e.g.,  24 ,  34 , and/or  64 ) and may be with respect to the reference coordinate system in which the anatomical features are registered. The user could then unlock the robotic arm  100 , for instance via the button  110 A. Alternatively, the function of the button  110 A may be reversed—the user may depress the button  110 A during the surgical navigation, during which the robotic arm  100  is unlocked, and maintain the depressed state when the automatically locking occurs. In such an embodiment, releasing the button  110 A would reset the automatically locking functionality and the arm  100  would remained locked until unlocked by the user, by, for example, double tapping the button  110 A. After being unlocked the controller  110  would revert to a state where it monitors whether the robotic arm  100  has sensed that it has reached its desired orientation, i.e., sensing for an automatic lock or “auto lock”. 
     Another contemplated feature of the robotic arm  100  and controller  110  would be an automatic locking when the inertial sensor unit  114  senses that the robotic arm  100  has not been moved around for a given period of time. The joint resistance may block the robotic arm  100 , but the automatic lock would preclude any movement, such as movements due to gravity or accidental contact, for example. 
     It is contemplated to achieve some of these functions without any inertial sensor unit on the robotic arm  100 . For example, the robotic arm  100  could be calibrated using the inertial sensor units on the assemblies  10  and/or  50 , and additional data such as a pre-operative plan. For example, a single inertial sensor unit could be used in humeral resection to align the robotic arm  100  with the humeral axis, with such an orientation being recorded as a “ 0 ” reference, and then match version and inclination based on the “0” reference. Encoders or like joint sensors in the robotic arm  100  may be coupled to the controller  110  to navigate the robotic arm  100  after such a calibration. 
     In accordance with an embodiment, a reference location is established on the bone or like anatomical landmark. The robotic arm  100  with inertial sensor unit  114  is calibrated while locked at the reference location. Navigation may be initiated, for instance by triggering the inertial sensor unit  114 . Thus, live navigation begins on the inertial sensor unit  114  and/or interface of the controller  110 . The “auto lock” or “auto block” feature may be deployed through live navigation, as the sensing on the inertial sensor unit  114  monitors the orientation of the robotic arm  100 . To move the robotic arm  100 , it may be required that the user press the button  110 A to unlock the locking mechanism in the robotic arm  100  and enable a repositioning of the instrument at the effector end  106 , for instance to a target orientation/location. It may be required that the button  110 A be depressed and held to maintain the arm  100  in the unlocked state, though a single discrete press of the button  110 A could put the robotic arm  100  in a collaborative mode. Various features may be programmed during navigation. When the controller  110  determines that the target orientation has been achieved and held for a predefined period of time, the robotic arm  100  may be forced to “auto lock.” When the button  110 A is still depressed, the “auto lock” may still occur, and a release of the button  110 A may reset the “auto lock” functionality. As additional programmable feature, a standard double tap press on the button  110 A or other parts of the robotic arm  100  would unlock the robotic arm and/or initiate the “auto lock” sensing again, for instance for a further step of the surgical workflow. This would enable for instance a user to move the robotic arm  110  out of the way, with the possibility of navigating back to the target orientation for “auto lock” again. The “auto lock” sensing feature may be programmed to end when the inertial sensor unit  114  is unclipped/turned off or the navigation application is no longer running on the controller  110 . 
     In accordance with another embodiment, the robotic arm  100  could be used to support retractors. The controller  110  may operate an auto release function, in which the robotic arm  100  releases the lock temporarily. This may occur for example in the event that the inertial sensor unit  114  detects an unexpected motion/forces on the robotic arm  100 . As yet another embodiment, the robotic arm  100  may vary the friction in the joints, so as to cause a reduced/force or ‘drag’, or an increase thereof. For example, this may occur when the robotic arm  100  is used to manipulate the cutting guide  30 , as the inertial sensor unit  34  indicates to the controller  110  that the target orientation is nearing. 
     The embodiments of the humerus cutting assembly  10  of  FIG. 1  and/or of the glenoid navigation assembly  50  of  FIG. 7  provided above are described with reference to inertial sensor tracking (e.g., accelerometers), but other tracking technologies are contemplated. 
     The humerus cutting assembly  10  of  FIG. 1  may be programmed in such a way that it defines a system for guiding an alteration to a head of a humerus, with the processing unit associated with the inertial sensor unit(s)  24  and/or  34 . The system may thus perform any of setting a reference orientation of a humerus when an assembly featuring a guide is attached to the humerus in a predetermined manner, obtaining an output as an orientation of the guide relative to the humerus is varied, tracking a current orientation of the humerus relative to the reference orientation using the output, and/or calculating and outputting an inclination angle and/or a retroversion angle as a function of the current orientation of the guide, the inclination angle and/or a version angle being indicative of an alteration to the head of the humerus associated to the current orientation of the guide. 
     The glenoid navigation assembly  50  of  FIG. 7  may be programmed in such a way that it defines a system for guiding an alteration to a glenoid, with the processor unit associated with the inertial sensor unit  64 . The system may thus perform any of setting a reference orientation of a glenoid when an assembly featuring a guide is applied against the glenoid in a predetermined manner, obtaining an output as an orientation of the guide relative to the glenoid is varied, tracking a current orientation of the guide relative to the reference orientation using the output, and calculating and outputting an inclination angle and/or a version angle as a function of the current orientation of the guide, the inclination angle and/or a version angle being indicative of an alteration to the glenoid associated to the current orientation of the guide. 
     EXAMPLES 
     The following examples can each stand on their own, or can be combined in different permutations, combinations, with one or more of other examples. 
     Example 1 is a humerus cutting assembly comprising: a guide frame having an attachment member adapted to be secured to a humerus adjacent to a humeral head, and a cutting guide releasably connected to the guide frame, the cutting guide configured to guide a tool in altering the humeral head; at least one inertial sensor unit on the cutting guide, the inertial sensor unit tracking an orientation of the cutting guide relative to the humerus based on the releasable connection between the cutting guide and the guide frame. 
     In Example 2, the subject matter of Example 1 includes, wherein the attachment member includes a plate configured to be applied against the humerus. 
     In Example 3, the subject matter of Example 2 includes, wherein the attachment member includes at least one fastener to secure the plate to the humerus. 
     In Example 4, the subject matter of Examples 2-3 includes, wherein the plate includes at least one patient-specific surface being a negative of a corresponding surface of the humerus. 
     In Example 5, the subject matter of Examples 1-4 includes, wherein the guide frame has an elongated arm configured to be connected to a portion of an arm of the humerus, away from the humerus. 
     In Example 6, the subject matter of Example 5, including a clamp at an end of the elongated arm configured to be connected to the portion of the arm of the humerus. 
     In Example 7, the subject matter of Example 6 includes, wherein the clamp has biased jaws. 
     In Example 8, the subject matter of Examples 5-7 includes, wherein the elongated arm defines a joint with at least one translational degree of freedom. 
     In Example 9, the subject matter of Example 8 includes, wherein the joint with at least one translational degree of freedom is a lockable telescopic joint. 
     In Example 10, the subject matter of Examples 5-9, including a support for the at least one inertial sensor unit on the elongated arm. 
     In Example 11, the subject matter of Examples 5-10, including a side arm projecting from the elongated arm, the plate being at an end of the side arm. 
     In Example 12, the subject matter of Examples 1-11 includes, wherein the side arm defines a side-arm joint with at least one translational degree of freedom. 
     In Example 13, the subject matter of Example 12 includes, wherein the side-arm joint with at least one translational degree of freedom is a lockable telescopic joint. 
     In Example 14, the subject matter of Examples 1-13, including a support for releasably receiving the at least one inertial sensor unit on the cutting guide. 
     In Example 15, the subject matter of Example 14 includes, wherein the support is on an arm projecting from a remainder of the cutting guide, a coupler being at an end of the arm. 
     In Example 16, the subject matter of Examples 1-15 includes, wherein the cutting guide has at least one cut slot, and holes for receiving fasteners to secure the cutting guide to the humerus. 
     In Example 17, the subject matter of Examples 1-16 includes, wherein the releasable connection is a male-female coupling between the guide frame and the cutting guide, the male-female coupling defining a unique coupling orientation. 
     Example 18 is a system for guiding an alteration to a head of a humerus comprising: a processor unit, and a non-transitory computer-readable memory communicatively coupled to the processor and comprising computer-readable program instructions executable by the processor unit for: setting a reference orientation of a humerus when an assembly featuring a cutting guide is attached to the humerus in a given orientation, obtaining an output from at least one inertial sensor on the cutting guide as an orientation of the cutting guide relative to the humerus is varied, tracking a current orientation of the humerus relative to the reference orientation using the output, and calculating and outputting at least one angle being indicative of an alteration to the head of the humerus associated to the current orientation of the cutting guide. 
     In Example 19, the subject matter of Example 18 includes, wherein setting the reference orientation includes setting the reference orientation when the cutting guide is coupled to a guide frame mounted to the humerus. 
     In Example 20, the subject matter of Example 19 includes, wherein setting the reference orientation includes setting the reference orientation with the at least one inertial sensor on the guide frame. 
     In Example 21, the subject matter of Example 20 including tracking the at least one inertial sensor on the guide frame being detached from the guide frame and connected to the cutting guide, after the setting. 
     In Example 22, the subject matter of Examples 19-21 further including obtaining the output from the at least one inertial sensor on the cutting guide includes obtaining an output from another inertial sensor on the guide frame. 
     In Example 23, the subject matter of Example 22 includes, wherein tracking the current orientation of the humerus relative to the reference orientation includes using the output of the inertial sensor on the cutting guide and the output of the inertial sensor on the guide frame. 
     In Example 24, the subject matter of Examples 18-23 includes, wherein calculating and outputting at least one angle includes calculating and outputting the inclination angle and/or the retroversion angle as a function of the current orientation of the cutting guide. 
     Example 25 is a glenoid navigation assembly comprising: a pin guide having a cannulated shaft, the cannulated shaft adapted to receive a guide pin therein; a registration interface at the end of the cannulated shaft and configured for abutting a glenoid, the registration interface having at least one visual alignment member for visually assisting in a positioning of the guide pin on the glenoid; and at least one inertial sensor unit on the glenoid navigation assembly, the inertial sensor unit tracking an orientation of the cannulated shaft relative to the glenoid based on a contact between the registration interface and the glenoid surface. 
     In Example 26, the subject matter of Example 25 includes, wherein the at least one alignment member includes a pair of spaced apart members indicative of a size of the glenoid. 
     In Example 27, the subject matter of Examples 25-26 includes, wherein the at least one alignment member includes a member configured to abut against a rim of the glenoid. 
     In Example 28, the subject matter of Examples 25-27 includes, wherein the at least one alignment member includes a pointer configured to point to a landmark of the glenoid. 
     In Example 29, the subject matter of Examples 25-28 includes, wherein the registration interface is patient specific, wherein the at least one alignment member is based on patient imaging. 
     In Example 30, the subject matter of Examples 25-29 includes, wherein a translational joint is formed between the registration interface and the cannulated shaft, for the registration interface to be movable along the cannulated shaft. 
     In Example 31, the subject matter of Examples 25-30 includes, wherein the cannulated shaft has a tapered end configured to be in contact with the glenoid. 
     In Example 32, the subject matter of Examples 25-31 includes, wherein an end of the cannulated shaft is rounded, the end configured to be in contact with the glenoid. 
     In Example 33, the subject matter of Examples 25-32 includes, wherein the at least one inertial sensor unit is secured to a handle projecting from the cannulated shaft. 
     In Example 34, the subject matter of Example 33, including a support for releasably receiving the at least one inertial sensor unit on the handle. 
     In Example 35, the subject matter of Example 34, including a robot arm coupler on the handle. 
     Example 36 is a system for guiding an alteration to a glenoid comprising: a processor unit, and a non-transitory computer-readable memory communicatively coupled to the processor and comprising computer-readable program instructions executable by the processor unit for: setting a reference orientation of a glenoid when an assembly featuring a guide is applied against the glenoid at a given position, obtaining an output from an inertial sensor on the guide as an orientation of the guide relative to the glenoid is varied, tracking a current orientation of the guide relative to the reference orientation using the output, and calculating and outputting an angle, the angle being indicative of an alteration to the glenoid associated to the current orientation of the guide. 
     In Example 37, the subject matter of Example 36 includes, wherein setting the reference orientation includes setting the reference orientation when a registration interface positions the guide against the glenoid in the given position. 
     In Example 38, the subject matter of Examples 36-37 includes, wherein the guide is a cannulated shaft, and wherein obtaining the output from the inertial sensor on the guide includes obtaining the output as the cannulated shaft is rotated relative to the given position. 
     In Example 39, the subject matter of Examples 36-38 includes, wherein calculating and outputting an angle includes calculating and outputting an inclination angle and/or a version angle as a function of the current orientation of the guide. 
     Example 40 is a system for guiding an alteration to a head of a humerus comprising: a processor unit, and a non-transitory computer-readable memory communicatively coupled to the processor and comprising computer-readable program instructions executable by the processor unit for: setting a reference orientation of a humerus when an assembly featuring a cutting guide is attached to the humerus in a predetermined manner, robotically manipulating the guide relative to the humerus with a robotic arm, obtaining an output representative of a current orientation of the guide as the guide is robotically manipulated, tracking a current orientation of the humerus relative to the reference orientation using the output, calculating and outputting at least one angle being indicative of an alteration to the head of the humerus associated to the current orientation of the cutting guide, and auto-blocking the robotic arm when a desired value for the angle is reached. 
     In Example 41, the subject matter of Example 40 includes, wherein setting the reference orientation includes setting the reference orientation when the guide is coupled to a guide frame mounted to the humerus. 
     In Example 42, the subject matter of Example 41 includes, wherein setting the reference orientation includes setting the reference orientation with the at least one inertial sensor on the guide frame. 
     In Example 43, the subject matter of Examples 42 including tracking the at least one inertial sensor on the guide frame being detached from the guide frame and connected to the guide, after the setting. 
     In Example 44, the subject matter of Examples 41-43 further including obtaining the output from the at least one inertial sensor on the guide includes obtaining an output from another inertial sensor on the guide frame. 
     In Example 45, the subject matter of Example 44 includes, wherein tracking the current orientation of the humerus relative to the reference orientation includes using the output of the inertial sensor on the guide and the output of the inertial sensor on the guide frame. 
     In Example 46, the subject matter of Examples 40-45 includes, wherein calculating and outputting at least one angle includes calculating and outputting the inclination angle and/or the retroversion angle as a function of the current orientation of the cutting guide. 
     In Example 47, the subject matter of Example 46 includes, wherein auto-blocking the robotic arm when a desired value of the angle is reached includes auto-blocking the robotic arm when the inclination angle and/or the retroversion angle is/are reached. 
     In Example 48, the subject matter of Examples 40-47 includes, wherein auto-blocking the robotic arm when a desired value for the angle is reached includes increasing a frictional force in the robotic arm as the robotic arm approaches the desired value. 
     In Example 49, the subject matter of Examples 40-48 includes, wherein auto-blocking the robotic arm when a desired value for the angle is reached includes auto-blocking when a detent on the robotic arm is being depressed. 
     In Example 50, the subject matter of Example 49, including releasing the robotic arm from the auto-blocking as a response to an action on the detent. 
     Example 51 is a system for guiding an alteration to a glenoid comprising: a processor unit, and a non-transitory computer-readable memory communicatively coupled to the processor and comprising computer-readable program instructions executable by the processor unit for: setting a reference orientation of a glenoid when an assembly featuring a guide is applied against the glenoid in a given position, robotically manipulating the guide relative to the glenoid with a robotic arm, obtaining an output representative of a current orientation of the guide as the guide is robotically manipulated, tracking a current orientation of the guide relative to the reference orientation using the output, calculating and outputting at least one angle being indicative of an alteration to the glenoid associated to the current orientation of the guide, and auto-blocking the robotic arm when a desired value for the angle is reached. 
     In Example 52, the subject matter of Example 51 includes system according to claim  51 , wherein setting the reference orientation includes setting the reference orientation when a registration interface positions the guide against the glenoid in the given position. 
     In Example 53, the subject matter of Examples 51-52 includes, wherein the guide is a cannulated shaft, and wherein obtaining the output from the inertial sensor on the guide includes obtaining the output as the cannulated shaft is rotated relative to the given position by the robotic arm. 
     In Example 54, the subject matter of Examples 51-53 includes, wherein calculating and outputting an angle includes calculating and outputting an inclination angle and/or a version angle as a function of the current orientation of the guide. 
     In Example 55, the subject matter of Example 54 includes, wherein auto-blocking the robotic arm includes auto-blocking the robotic arm when the desired inclination angle and/or the version angle is/are reached. 
     In Example 56, the subject matter of Examples 51-55 includes, wherein auto-blocking the robotic arm when a desired value for the angle is reached includes increasing a frictional force in the robotic arm as the robotic arm approaches the desired value. 
     In Example 57, the subject matter of Examples 51-56 includes, wherein auto-blocking the robotic arm when a desired value for the angle is reached includes auto-blocking when a detent on the robotic arm is being depressed. 
     In Example 58, the subject matter of Example 57 including releasing the robotic arm from the auto-blocking as a response to an action on the detent.