System for handling a patella

Abstract

The invention relates to a system (1) for handling a patella (9), comprising: - first and second jaws (31, 32); - a structure (6) comprising first and second supports (61, 62) which are integral with the first and second jaws (31, 32) respectively, the first and second supports being able to move relative to one another so as to modify the spacing between the first and second jaws, the structure comprising a temporary connection interface (611, 621) for connecting a clamp (8) to the structure so as to bring the first and second jaws closer together by means of such a clamp (8); - a locking device (63, 64, 65, 66) for locking the spacing between the first and second jaws; - optical reflectors (5) integral with said structure.

Description

Description Title of the invention: System for manipulating a ball joint

[0001] [The invention relates to orthopedic surgical operations, and in particular robotic or navigated surgical operations for prosthetic knee surgery with patellar resurfacing.

[0002] The patella articulates with the femoral trochlea, forming the patellofemoral compartment. The patellofemoral compartment is the third joint of the knee, located at the front of the knee. Patellar stability is ensured by two tendons, one superior and one inferior, and the two patellar retinacula. This complex combination of bone structure, muscles, cartilage, and tendons can lead to the development of pathologies, particularly wear and tear such as osteoarthritis.

[0003] The kneecap is subjected to extremely high mechanical stresses; its role is essential in extension and flexion, as well as in movements such as squatting and jumping. The kneecap also acts as a shock absorber. Wear and tear of the patellar cartilage is irreversible, and a misalignment or dislocation will not heal spontaneously. Movements become painful, some even impossible, and walking becomes increasingly difficult.

[0004] Many conditions can lead to premature wear of the knee cartilage, resulting in pain, limping, joint stiffness, and limited activity for the patient. In some cases, the patient may require a total knee replacement. This operation requires very precise cuts and bone preparation. It is a complex procedure that, in some cases, does not provide complete patient satisfaction.

[0005] Implanting a prosthesis requires highly precise prior machining of the bone intended to receive the prosthesis. Certain surgical procedures allow for even greater precision in making the bone cuts. These surgical procedures utilize robots or infrared navigation systems. These methods employ infrared sensors fixed in the femur and tibia for the duration of the surgical procedure, particularly during total knee replacement. These sensors enable the robot / system to R012565 PCT Depot Text.docx navigation to position cutting tools in real time and precisely to best adapt to the geometry of prosthetic parts.

[0006] In addition to ensuring a perfect fit between the bone and the implant, the surgeon must consider ligament tension as well as patellar mobility. Every error, however minor, can lead to an imperfect result. Therefore, there is a need to minimize the risk of performing a procedure that does not fully satisfy the patient.

[0007] US patent 20070162142 describes a bony patellar clamp comprising first and second jaws, and a structure including first and second supports attached to the first and second jaws respectively and movable relative to each other to modify the distance between the first and second jaws. The clamp allows for locking the distance between the first and second jaws. The clamp includes optical reflectors attached to said structure.

[0008] The invention aims to resolve one or more of these drawbacks. The invention thus relates to a system for manipulating a ball joint, as defined in attached claim 1.

[0009] The invention also relates to variants of the dependent claims. Those skilled in the art will understand that each of the features of the dependent claims or of the description can be combined independently with the above features, without thereby constituting an intermediate generalization.

[0010] The invention also relates to a method for controlling a tool-carrying robot, as defined in the attached claims.

[0011] Other features and advantages of the invention will become clear from the description given below, by way of example and not limitation, with reference to the accompanying drawings, in which:

[0012] [Fig.1] a perspective view of a first example of an embodiment of a manipulation system according to the invention, at the end of positioning;

[0013] [Fig.2], [Fig.3], [Fig.4] and [Fig.5] are different perspective views of the manipulation system of figure 1 at different intermediate stages; R012565 PCT Deposit Text.docx

[0014] [Fig.6] and [Fig.7] are perspective views of a second example of an embodiment of a manipulation system according to the invention;

[0015] [Fig.8] is a front view of an example of a reported reflector antenna;

[0016] [Fig.9] is a schematic side view of a reflecting antenna attached to a manipulation system;

[0017] [Fig.10] is a side view of a kneecap and various tendons;

[0018] [Fig.11] is a side view of the ball joint of figure 10 associated with the clamp in a first manipulation configuration;

[0019] [Fig.12] is a side view of the ball joint of figure 10 associated with the clamp in a second handling configuration;

[0020] [Fig.13] is a plan view of salient elements of an example of a clamp of the invention;

[0021] [Fig.14] is a side view of the ball joint of figure 10 associated with the clamp in a third handling configuration;

[0022] [Fig.15] is a side view of advantageous dimensions of the end of a jaw.

[0023] Figure 1 is a perspective view of a first embodiment of a manipulation system 1 for a ball joint 9 according to the invention, at the end of its positioning. The system 1 comprises first and second jaws 31 and 32, a structure 6 including first and second supports 61 and 62, a spacing locking device, and optical reflectors (not shown in this view). The system 1 is designed to engage with a ball joint 9, enabling its manipulation by a practitioner, as well as its use for controlling a tool-holding robot.

[0024] The first and second supports 61 and 62 are fixed respectively to the first and second jaws 31 and 32. The first and second supports 61 and 62 are movable relative to each other so as to modify the spacing between the first and second jaws 31 and 32, here along the Y direction. The spacing allows a ball joint 9 to initially pass between the jaws 31 and 32, and then to clamp it in order to fix the structure 6 to this ball joint 9. The jaws 31 and 32 can advantageously be spaced within a range of 30 to 50 mm to allow a ball joint 9 to selectively pass or clamp between these jaws 31 and 32. This spacing can advantageously be reduced to 20 mm, or even to 15 mm. This spacing can also be increased to 70 mm.

[0025] Structure 1 includes a temporary interface for connecting a gripper 8 to structure 6, for example in the form of openings for receiving the ends of the gripper (an example of which is detailed in another embodiment). The interface allows the gripper 8 to bring the first and second jaws 31 and 32 together, as detailed later.

[0026] Structure 1 further includes a locking device for the gap between the first and second jaws 31 and 32, an example of which is detailed below. The gap locking device allows the jaws 31 and 32 to grip a ball joint 9 once they are in position.

[0027] Structure 1 also includes optical reflectors 5 attached to structure 6. These optical reflectors 5 will be described in detail later with reference to Figures 8 and 9. The optical reflectors 5 can, in particular, be used for reflecting infrared radiation. The optical reflectors 5 are used, as is known, to be identified by optical sensors in order to determine their position in space.

[0028] The combination of system 1 with the removable clamp 8 allows the jaws 31 and 32 to be positioned correctly in relation to the ball joint 9, the ball joint 9 of the jaws 31 and 32 to be tightened, the jaws 31 and 32 to be locked in the tightened position, and then the clamp 8 to be removed to free the operating field.

[0029] The jaws 31 and 32 each include two protruding elements forming an acute angle at their end, in order to grip the ball joint 9 well. Thus, the jaws 31 and 32 each have only two protruding elements of this type, to provide optimal stability for gripping the ball joint 9. Advantageously, the protruding elements form an angle of less than 20 degrees over a length of at least 5mm. R012565 PCT Deposit Text.docx

[0030] Advantageously, a removable gripping handle 2 is attached to the structure 6, allowing the practitioner to more easily manipulate the patella 9 and change its position. The gripping handle 2 is screwed into a threaded hole in the structure 6. Alternatively, the gripping handle can be snapped into a hole in the structure 6.

[0031] The use of system 1 according to the invention allows for its precise localization in space relative to a patella 9, on which a three-dimensional scan or bone shape scan is performed. The position of system 1 and the patella 9 are then perfectly identified for the control of a tool-holding robot (not shown). The tool-holding robot can then constrain the movements of the tools in real time relative to the patella 9 and system 1, in order to prevent surgical incidents. The tools are typically saws or milling cutters used to shape a face of a patella to which a prosthesis is to be attached.

[0032] In the example, structure 6 comprises two shafts 63 and 64 projecting along the Y direction relative to support 62. Support 61 is mounted to slide relative to these shafts 63 and 64 along this Y direction. One free end of shafts 63 and 64 is threaded. Knobs 65 and 66 are screwed onto the threaded shafts 63 and 64, respectively. The combination of knobs 65 and 66 and the threaded shafts 63 and 64 forms a locking mechanism for the gap between jaws 31 and 32.

[0033] The clamp 8 comprises two arms 861 and 862 with a joint 85 at an intermediate point. One end of the arms 861 and 862 engages with supports 61 and 62 respectively, allowing their spacing to be adjusted. The clamp 8 advantageously includes a ratchet mechanism 83, preventing the clamp 8 from reopening unintentionally after it has been tightened.

[0034] Advantageously, the system 1 further includes a positioning device for the ball joint 9. The positioning device is integrated into a clamp 7. The positioning device includes third and fourth jaws 741, 744 movable relative to each other so as to modify their spacing along the direction z, perpendicular to the direction Y. The positioning device is removably attached to the structure 6. R012565 PCT Depot Text.docx Thus, the positioning device can be used beforehand to hold the ball joint 9, fix the structure 6 to the ball joint 9, then remove the positioning device so as not to interfere with subsequent operations.

[0035] Advantageously, the structure 6 is mounted to slide along the Z direction relative to the positioning device. For this purpose, the positioning device includes a shaft 742 extending along the Z direction. The structure 6 is mounted to slide along this shaft 742 along the Z direction. The shaft 742 is, for example, guided in an opening in the support 62.

[0036] The clamp 7 comprises two arms 71 and 72 having a joint 75 at an intermediate point. One end of the arms 71 and 72 is fixed to the jaws 741 and 744, respectively, to allow their opening to be adjusted. The clamp 7 advantageously includes a ratchet mechanism 73, preventing the clamp 7 from reopening unintentionally after it has been tightened. The clamp 7 is advantageously removably fixed to the jaws 741 and 744.

[0037] Figure 8 is a front view of an example of an optical reflector system 5. Figure 9 is a side cross-sectional view of the structure 6 carrying this optical reflector system.

[0038] In this example, the reflectors 5 are arranged on the same support 61. It can also be envisaged that the reflectors 5 are fixed independently in different locations on the structure 6.

[0039] The reflectors 5 typically comprise a frame 50 and at least one reflector element 52 attached to the frame 50. In the illustrated example, 4 reflector elements 52 are attached to a frame 55 of the frame 50.

[0040] Advantageously, the frame 50 is selectively removable from the structure 6. Thus, different reflectors 5 can be fixed to the structure 6 and the system 1 can also be more compact for storage.

[0041] For this purpose, the frame 50 has a threaded end 53 intended to be screwed into the structure 6. In the illustrated example, the frame 50 is fixed in the structure 6 by several threaded ends 53. The threaded ends 53 are typically provided on rods 51, driven in rotation relative to the frame 50 by means of wheels 54. R012565 PCT Deposit Text.docx

[0042] The procedure for using system 1 can be as follows.

[0043] As illustrated in figure 2, the ball joint 9 is positioned on the jaw 741. By acting on the clamp 7, the ball joint 9 is then clamped between the jaws 741 and 744, as illustrated in figure 3.

[0044] As illustrated in Figure 4, structure 6 is mounted on shaft 742, with jaws 31 and 32 spread apart. Structure 6 can be positioned against a shoulder of shaft 742. Clamp 8 is then fixed to structure 6. Jaws 31 and 32 are then positioned at the correct level along the Z-axis relative to the ball joint 9.

[0045] As illustrated in Figure 5, clamp 8 is tightened to bring supports 61 and 62 closer together along the Y axis and clamp ball joint 9 between jaws 31 and 32. Then the knobs 65 and 66 are tightened to immobilize jaws 31 and 32 in their clamping position, as illustrated in Figure 1.

[0046] The clamp 7 and clamp 8 are then removed. The handle 2 can be attached to the structure 6. The handle 2 can be attached to the structure 6 before or after the removal of clamps 7 and 8. The optical reflectors 5 are also installed on the structure 6.

[0047] The invention also relates to a method for subsequently controlling a tool-carrying robot, this method comprising, for example, the steps of: -filming a space in which structure 6 is positioned; -by digital processing, identify the position of the optical reflectors 5 in the filmed space, and determine the position of the structure 6 from the position of the identified optical reflectors 5; -generate a digital model in the space of the ball joint 9; -to restrict the movement of a robot tool relative to the manipulation gripper according to the position determined for structure 6. A bone cut of the patella 9 can be performed according to a pre-operative plan and an intra-operative modification can be performed according to patellar follow-up.

[0048] The optical reflectors 5 can be removed for the placement of the ball joint implant 9. R012565 PCT Deposit Text.docx

[0049] The process is thus used to restrict the movement of the robot's tools by the practitioner, in order to avoid any handling errors.

[0050] Figures 6 and 7 are perspective views of a second embodiment of a manipulation system 1 according to the invention. System 1 is shown here without grippers 7 and 8 for the sake of clarity.

[0051] The structure 6 and the jaws 3 have substantially the same configuration as in the previous embodiment. A positioning device 4 for the ball joint 9 is provided here, independent of the clamp 7. The positioning device 4 here comprises jaws 41 and 44. The gap between the jaws 41 and 44 along the Z-axis is adjustable, so that a ball joint can initially be positioned between these jaws 41 and 44, and then clamped between these jaws 41 and 44. For this purpose, the jaw 44 is mounted to slide along the Z-axis relative to the jaw 41. The device 4 here includes a shaft 42 on which the jaw 44 is mounted to slide. The jaw 41 can also be mounted to slide along the shaft 42. The positions of the jaws 41 and 42 along the shaft 42 can be fixed, for example, by means of compression screws.The positions of the jaws 41 and 44 along an X-axis (perpendicular to the Y and Z axes) are advantageously adjustable and can be locked. The jaws 41 and 44 may include an interface for securing the gripper 7, for example, openings to receive the ends of the arms 71 and 72, respectively. The jaws 41 and 44 can thus be tightened using the removable gripper 7.

[0052] The shaft 42 is mounted to slide along the Z-axis relative to a connecting piece 43. The connecting piece 43 is itself fixed to the structure 6. Thus, the position of the jaws 41 and 44 relative to the structure 6 along the Z-axis can be adjusted. This relative position can be locked, for example, by means of a set screw as illustrated. The shaft 42 can be separated from the connecting piece 43, so that the device 4 is removable. In the example, the connecting piece 43 is mounted to slide along the Y-axis relative to the structure 6. In particular, the connecting piece 43 is mounted to slide along the Y-axis on the shaft 63 of the structure 6. Thus, the relative position between the device 4 and the structure 6 along the Y-axis can be adjusted. R012565 PCT Deposit Text.docx

[0053] Openings 611 and 621 are provided in supports 61 and 62, respectively. These openings allow the respective ends of the gripper arms 861 and 862 to be inserted along the Z direction. Supports 61 and 62 also have threaded bores 612 and 622, respectively, for attaching gripping handles 2 or optical reflectors. The threaded bores extend along the Z direction. Threaded bores extending along the X or Y directions can also be provided.

[0054] It is also possible to consider that structure 6 can be manipulated directly without the handles 2, by grasping supports 61 and 62. Supports 61 and 62 then advantageously extend over a length greater than 40 mm, preferably 50 mm, in the same direction. This length can also reach 60 mm, or even 70 mm. Such an extension of supports 61 and 62 in one direction facilitates their grasping by a practitioner.

[0055] An example of the use of a clamp 1 according to the invention will be detailed. Figure 10 illustrates, in a side view, a patella 90 with its patellar tendons 95 and the quadriceps tendons 96. Figure 11 illustrates a configuration of the clamp 1 fixed to the patella 9. The jaws 31 and 32 clamp the patella on either side of the patella 9, along an axis perpendicular to the direction of the tendons 95 and 96. The clamp 1 is positioned here on the medial side of the patella 9.

[0056] In practice, the manipulation clamp 1 also allows for another mode of operation: positioning the clamp 1 on the external side of the patella 9, as illustrated in Figure 12. Such a configuration proves particularly advantageous for a surgical procedure: by leaving the clamp 1 fixed on the patella 9, it is possible to perform its machining, make adaptation tests with the prosthesis, make a machining correction, all this while keeping the clamp 1 fixed and therefore without losing the positioning reference of this clamp 1 relative to the patella 9. The jaws 31 and 32 here clamp the patella on either side of the patella 9, along an axis perpendicular to the direction of the tendons 95 and 96.

[0057] In both configurations, it can be observed that the surfaces of the ball joint 9 accessible for machining are very large, allowing machining at various angles and with tools such as saw blades or milling cutters. It is thus possible to machine in the plane including the protruding elements of the R012565 PCT Depot Text.docx jaws 31 and 32. The shape of the machining carried out on the ball joint 9 is thus independent of the shape of the clamp 1.

[0058] As illustrated in the gripper examples in the various figures, projecting elements of the jaws 31 and 32 extend perpendicularly from arms. These projecting elements extend perpendicularly from one end of their respective arms. The arms are driven by their other end. This allows the gripping area of ​​the jaws 31 and 32 to be offset from the drive area of ​​the arms, thus freeing up as much space as possible in the gripping area. Furthermore, it can be seen that in the plane including the projecting elements of the jaws 31 and 32, the spaces between two successive projecting elements are free, allowing access for tools. These spaces are shown as dashed lines in Figure 13, which is a view in the plane including the ends of the projecting elements of the jaws 31 and 32.

[0059] Figure 14 illustrates another advantage of this clamp 1: the jaw 41 (which here has a flat-shaped end) allows the patella 9 to be moved to the desired position before the jaws 31 and 32 are attached to it. This allows the jaws 31 and 32 to be positioned relative to the tendons 95 and 96 to expose the maximum volume of the patella 91 for machining, typically flush with the soft tissues or tendons. The clamp 1 is positioned here on the inner side of the patella 9.

[0060] Figure 15 illustrates an example of the end of a jaw 31. The jaw 31 has a projecting element, the end 311 of which, along the Y direction, forms a sharp point of contact with the ball joint 9. Advantageously, this end is located at or nearly at the end of the jaw 31 along the Z direction. If the jaw 31 has an end point (such as point 312 in Figure 15) positioned beyond the end 311 along the Z direction, the gap between the ends 311 and 312 along the Z direction is advantageously a maximum of 3 mm, preferably a maximum of 2 mm, and advantageously a maximum of 1 mm. Such a configuration allows the clamp 1 to be fixed in the configuration of Figure 14 as close as possible to the tendons 95 and 96, so as to free up a maximum of surface area available for machining. R012565 PCT Deposit Text.docx

[0061] Advantageously, the jaw 31 has a fixing end 313 with the support 61 offset along the Y axis relative to the end 311. Advantageously, the offset between the mounting end 313 and the end 311 along the Y direction is at least 10 mm, preferably at least 15 mm, and potentially at least 20 mm. Such a configuration allows for maximum working space for machining the ball joint 9, particularly in the configuration shown in Figure 14.

[0062] Figure 16 illustrates another advantage of clamp 1: the jaw 41 (which here has a flat-shaped end) allows the patella 9 to be moved to the desired position before the jaws 31 and 32 are attached to it. The jaws 31 and 32 can then be positioned to pass through the tendons 95 and 96, exposing as much of the patella 91 as possible for machining, typically flush with the soft tissue or tendons. Clamp 1 is positioned here on the outer side of the patella 9. Figure 17 illustrates the use of clamp 1 in such a configuration. The practitioner simply pivots the structure 6 to fully expose the inner surface of the patella 9 for machining. R012565 PCT Deposit Text.docx

Claims

Demands

1. [Manipulation system (1) of a knee patella (9), characterized in that it comprises: -of the first and second jaws (31, 32); -a structure (6) comprising first and second supports (61, 62) attached respectively to the first and second jaws (31, 32) along a first direction (y), the first and second supports being movable relative to each other so as to modify the spacing between the first and second jaws, the structure comprising a temporary linking interface (611, 621) of a clamp (8) with the structure so as to cause the first and second jaws to come together by means of such a clamp (8); -a locking device (63, 64, 65, 66) for the gap between the first and second jaws; -optical reflectors (5) attached to said structure; a positioning device (4) comprising third and fourth jaws (741, 744) movable relative to each other so as to modify their spacing along a second direction (z) perpendicular to the first, the positioning device (4) being attached to said structure (6) in a removable manner.

2. A handling system (1) for a ball joint (9) according to claim 1, further comprising a clamp (8) capable of being selectively linked to said structure (1) via said linking interface (611, 621).

3. A handling system (1) for a ball joint (9) according to claim 1 or 2, wherein said structure (6) is mounted to slide along the second direction relative to said positioning device (4).

4. A handling system (1) for a ball joint (9) according to any one of the preceding claims, comprising a clamp (7) configured to exert pressure on the third and fourth jaws (741, 744) so ​​as to modify their spacing in the second direction. R012565 PCT Depot Text.docx

5. A handling system (1) for a ball joint (9) according to claim 4, wherein the clamp is removably attached to the third and fourth jaws.

6. A handling system (1) for a ball joint (9) according to any one of the preceding claims, further comprising a removable gripping handle (2) attached to said structure (6).

7. A handling system (1) for a ball joint (9) according to any one of the preceding claims, wherein said reflectors (5) comprise an armature (50) and at least one reflector element (52) fixed to the armature.

8. A handling system (1) for a ball joint (9) according to claim 7, wherein the armature (5) is selectively removable from said structure (6).

9. A handling system (1) for a ball joint (9) according to any one of the preceding claims, wherein the first and second movable jaws (31, 32) can be at least spread apart over a range of 30 to 50 mm.

10. A handling system (1) for a ball joint (9) according to any one of the preceding claims, wherein the first and second jaws (31, 32) each comprise two protruding elements forming an acute angle at their end.

11. A system for manipulating (1) a bony patella (9), characterized in that it comprises: -of the first and second jaws (31, 32); -a structure (6) comprising first and second supports (61, 62) attached respectively to the first and second jaws (31, 32), the first and second supports being movable relative to each other so as to modify the spacing between the first and second jaws, the structure comprising a temporary linking interface (611, 621) of a clamp (8) with the structure so as to cause the first and second jaws to come together by means of such a clamp (8); -a locking device (63, 64, 65, 66) for the spacing between the R012565 PCT Depot Text.docx first and second jaws; -optical reflectors (5) attached to said structure.

12. A manipulation system (1) for a bony patella (9) according to claim 11, further comprising a clamp (8) capable of being selectively linked to said structure (1) via said linking interface (611, 621).

13. A manipulation system (1) for a bony patella (9) according to claim 11 or 12, wherein the first and second supports (61, 62) are movable relative to each other so as to modify the spacing between the first and second jaws (31, 32) in a first direction (y), the system further comprising a positioning device (4) comprising third and fourth jaws (741, 744) movable relative to each other so as to modify their spacing in a second direction (z) perpendicular to the first, the positioning device (4) being removably attached to said structure (6).

14. A manipulation system (1) for a bony patella (9) according to claim 13, wherein said structure (6) is mounted to slide in the second direction relative to said positioning device (4).

15. A manipulation system (1) for a bony patella (9) according to claim 13 or 14, comprising a clamp (7) configured to exert pressure on the third and fourth jaws (741, 744) so ​​as to modify their spacing along the second direction.

16. A manipulation system (1) of a bony patella (9) according to claim 15, wherein the clamp is attached to the third and fourth jaws in a removable manner.

17. A manipulation system (1) for a bony patella (9) according to any one of the preceding claims, further comprising a removable gripping handle (2) attached to said structure (6).

18. A manipulation system (1) of a bony patella (9) according to any one of the preceding claims, wherein said reflectors (5) comprise a frame (50) and at least one reflector element (52) fixed to the frame. R012565 PCT Depot Text.docx

19. A manipulation system (1) of a bony patella (9) according to claim 18, wherein the frame (5) is selectively removable from said structure (6).

20. A manipulation system (1) of a bony patella (9) according to any one of the preceding claims, wherein the first and second movable jaws (31, 32) can be at least spread apart over a range of 30 to 50 mm.

21. A manipulation system (1) for a bony patella (9) according to any one of the preceding claims, wherein the first and second jaws (31, 32) each comprise two protruding elements forming an acute angle at their end.

22. A method for controlling a tool-carrying robot, comprising the steps of: - to film a space in which is positioned a structure (6) comprising first and second supports (61, 62) attached respectively to first and second jaws (31, 32) enclosing a bony patella (9), the first and second supports being movable relative to each other so as to selectively modify the spacing between the first and second jaws, the structure (6) further comprising a locking device (63, 64, 65, 66) for the spacing between the first and second jaws (31, 32), optical reflectors (5) being attached to said structure (6); - by digital processing, to identify the position of the infrared reflectors (5) in the filmed space, to determine the position of the structure (6) from the position of the optical reflectors (5) identified; -to restrict the movement of a robot tool relative to the structure (6) according to its determined position.

23. A method for controlling a tool-carrying robot, comprising the steps of: - to film a space in which is positioned a structure (6) comprising first and second supports (61, 62) attached respectively to first and second jaws (31, 32) enclosing a bony patella (9), the first and second supports being mobile relative to each other so as to selectively modify the spacing between the first and second R012565 PCT Depot Text.docx jaws, the structure (6) further comprising a locking device (63, 64, 65, 66) for the gap between the first and second jaws (31, 32), optical reflectors (5) being integral with said structure (6); -by digital processing, identify the position of the infrared reflectors (5) in the filmed space, determine the position of the structure (6) from the position of the optical reflectors (5) identified, determine the shape and position of the filmed ball joint (9); -to restrict the movement of a robot tool relative to the ball joint (9) according to the determined shape and position, j R012565 PCT Deposit Text.docx

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