Method for producing a surgical navigation module

Abstract

The invention relates to a method for producing a surgical navigation module (1), the method comprising the following steps: - providing a navigation marker (2) comprising a retroreflective lens; - producing a shell (3) by moulding a rigid thermoplastic material, wherein the shell defines an interior cavity and has at least one coupling member for attachment to a rigid navigation support; - placing the navigation marker in the interior cavity of the shell while maintaining an interstitial space between the shell and the navigation marker; and - forming an intermediate cap (4) by moulding an elastomeric thermoplastic material at least in the interstitial space, such that the intermediate cap is moulded within the interior cavity and partially overmoulds the navigation marker, between the shell and the navigation marker.

Description

TITLE: Method for producing a surgical navigation module [Technical field] The invention relates to a method for producing a surgical navigation module, used in the field of surgical navigation and, in particular, in orthopedic surgery. More particularly, it relates to a method for producing a surgical navigation module including a reflective navigation marker and a coupling part configured to be mounted on a rigid navigation support. [Prior art] As is known, the surgical navigation implements a video capture system, particularly operating in the infrared range, which tracks the reflective navigation markers mounted on a rigid navigation support, itself fixed to a surgical instrument, an implant, or a part of a patient's body. Thus, the position of these reflective navigation markers is tracked by the video capture system in the operating room in order to monitor the position and orientation in space of the surgical instrument, implant, or relevant part of the patient's body. A first reflective navigation marker is in the form of a spherical marker having an opaque and reflective surface and intended for single use. An orifice is provided in the spherical marker, allowing mounting on a stud of the rigid navigation support, which itself is reusable, thereby limiting costs and waste to the spherical markers alone. Thus, the surgeon can remove the spherical markers from their sterile packages and then easily mount them on the studs of the rigid navigation support. During the surgery, these spherical markers may be subjected to splashes of fluid (particularly blood) and particles (such as bone debris), thereby reducing their visibility and tracking by the video capture system and consequently causing errors in the measurement of their positions. Moreover, the opaque and reflective surfaces of these spherical markers are fragile and prevent them from being wiped clean. To remedy this issue when performing procedures generating splashes, the surgeons either replace the spherical markers each time they become stained (thereby generating additional waste and costs) or place transparent protective covers over these spherical markers (thereby partially impairing their tracking by the video capture system). This attention that the surgeons must therefore pay to the cleanliness of the spherical markers makes their use difficult, particularly for guiding a surgical instrument (such as a cutting instrument) while the splashes are being generated. To overcome this problem, a second model of reflective navigation marker has been developed in the form of a retroreflective lens, generally spherical in shape and secured to an annular collar, wherein the retroreflective lens has a transparent and smooth surface, generally made of plastic, enabling it to be wiped clean and making it less sensitive to contamination by the fluid splashes and particles. An example of such a retroreflective lens is the Radix™ module from Northern Digital Inc. However, integrating such a retroreflective lens onto a rigid navigation support presents difficulties, particularly because the retroreflective lens is not designed to withstand a sterilization operation and is therefore intended for single use. It is customary to bond the annular collar inside a receiving orifice provided for this purpose on the rigid navigation support, thereby securing the retroreflective lens to the rigid navigation support. Such attachment therefore results in the rigid navigation support itself becoming single-use, which increases costs (since the rigid navigation support cannot be reused) and also generates a greater quantity of waste. Moreover, such bonding is a source of inaccuracy in mounting the retroreflective lens on the rigid navigation support, thereby adversely affecting the accuracy of tracking by the video capture system. [Summary of the invention] The object of the present invention concerns a method for producing a surgical navigation module comprising a retroreflective lens and a coupling part intended for coupling to a rigid navigation support, which is adapted to allow reuse of the rigid navigation support. Another object of the invention is to improve the accuracy of mounting the retroreflective lens on the rigid navigation support. To this end, the invention provides a method for producing a surgical navigation module, comprising the following steps: - providing a navigation marker including a retroreflective lens; - producing a shell by molding a rigid thermoplastic material, said shell defining an internal cavity and having at least one coupling member configured to enable coupling of the shell to a rigid navigation support; - placing the navigation marker in the internal cavity of the shell while maintaining an interstitial space between the shell and the navigation marker; and - producing an intermediate cap by molding an elastomeric thermoplastic material at least within the interstitial space, such that the intermediate cap is molded inside the internal cavity and partially overmolds the navigation marker between the shell and the navigation marker. Thus, the invention proposes producing the coupling part in the form of a two-material component composed of the shell and the intermediate cap, which are made from distinct thermoplastic materials. Once the shell has been produced, the navigation marker is placed within the internal cavity of the shell, and the elastomeric thermoplastic material is injected between the shell and the navigation marker, thereby promoting centering of the navigation marker independently of the molding tool accuracy. Thus, the surgical navigation module, as supplied to the surgeon, is in the form of this assembly comprising the two-material part overmolded around the navigation marker. A first advantage is that the surface of the retroreflective lens is protected by the rigid shell during the transportation. Moreover, the invention proposes two distinct thermoplastic materials because the intermediate cap and the shell do not perform the same function: - the function of the intermediate cap is to receive, center, and retain the navigation marker, which, it should be recalled, is a fragile component, such that the elastomeric nature of its material is particularly advantageous for avoiding any risk of damaging the surface of the retroreflective lens due to its flexibility; and moreover, an elastomeric thermoplastic material has a sufficiently low melting temperature, well suited to avoid damaging the surface of the retroreflective lens, which is sensitive to temperature; and - the function of the shell is to ensure coupling to and retention on the rigid navigation support, such that the rigid nature of its material is particularly advantageous because such coupling requires enhanced mechanical strength, as can be provided by a rigid thermoplastic material coupled to a rigid support. The fact that it works with two superimposed, two-material molds therefore improves the retention and centering of the navigation marker on the rigid navigation support. Advantageously, the rigid thermoplastic material is a semi-crystalline rigid thermoplastic material. According to one feature, the rigid thermoplastic material is selected from polypropylene-based or polyethylene-based rigid thermoplastic materials. According to one possibility, the elastomeric thermoplastic material is selected from thermoplastic polyurethane elastomers (TPU), styrenic thermoplastic elastomers (TPS), copolyester thermoplastic elastomers (TPC), copolyamide thermoplastic elastomers (TPA), non-vulcanized thermoplastic olefin elastomers (TPO), and vulcanized thermoplastic olefin elastomers (TPV). According to another possibility, the elastomeric thermoplastic material has a melting temperature less than or equal to 150°C. Indeed, this low melting temperature is advantageous for preserving the surface of the retroreflective lens, which is sensitive to temperature, so as to ensure that the contact temperature between the elastomeric thermoplastic material and the retroreflective lens remains below 150°C, thereby preventing damage to the coating of the retroreflective lens during molding with the elastomeric thermoplastic material. According to another feature, the elastomeric thermoplastic material has a Shore A hardness ranging from 40 to 70, and for example from 50 to 60, thereby promoting its shock-absorbing function during the molding and during use of the surgical navigation module. According to another feature, the at least one coupling member of the outer part is a snap-fastening member. In a particular embodiment, this coupling member comprises a snap-fastening hook projecting from and secured to a gripping tab. Variants are conceivable, such as a coupling member in the form of a threaded fastening element for a screw coupling. In a particular embodiment, the shell has a peripheral rim surrounding the internal cavity and provided with recesses, such that the elastomeric thermoplastic material at least partially fills said recesses during production of the intermediate cap. This configuration with recesses is advantageous for ensuring a strong assembly of the intermediate cap within the shell and, ultimately, for obtaining a compact and mechanically robust module that provides accurate centering and reliable retention. Advantageously, the shell has a peripheral wall in which at least one orifice is formed which emerges with the internal cavity so as to allow the elastomeric thermoplastic material to be introduced through said at least one orifice during production of the intermediate cap. Preferably, the rigid thermoplastic material and the elastomeric thermoplastic material are medical-grade materials. Advantageously, the rigid thermoplastic material and the elastomeric thermoplastic material are materials resistant to gamma sterilization. The invention also concerns a surgical navigation module obtained by the producing method as described above, this surgical navigation module comprising: - an intermediate cap made of an elastomeric thermoplastic material and partially overmolding a navigation marker including a retroreflective lens; and - a shell made of a rigid thermoplastic material and having at least one coupling member configured to enable coupling of the shell to a rigid navigation support, said shell defining an internal cavity within which the intermediate cap is assembled, the intermediate cap thus being arranged between the shell and the navigation marker. Of course, all the features relating to the producing method apply to the surgical navigation module, particularly with regard to the rigid thermoplastic material and the elastomeric thermoplastic material. The invention also relates to a surgical navigation assembly comprising: - a rigid navigation support comprising at least one housing; and - at least one surgical navigation module as described above; wherein the shell of the at least one surgical navigation module is mounted in the at least one housing and is retained by engagement of the at least one coupling member with at least one complementary coupling member provided on the at least one housing. According to a variant embodiment, the rigid navigation support comprises at least two arms, and the at least one housing comprises at least two housings provided on the respective at least two arms, such that the at least one surgical navigation module comprises at least two surgical navigation modules mounted in the respective at least two housings. [Brief description of the drawings] Other features and advantages of the present invention will become apparent upon reading the following detailed description of a non-limiting exemplary embodiment, given with reference to the accompanying drawings, in which: Figure 1 is a schematic perspective view of a shell obtained by molding a rigid thermoplastic material; Figure 2 is a schematic perspective view showing placement of a navigation marker within the internal cavity of the shell of Figure 1, prior to molding the intermediate cap; Figure 3 is a schematic perspective and axial sectional view of a surgical navigation module obtained after molding the intermediate cap between the shell and the navigation marker; Figure 4 is a schematic exploded perspective view of the surgical navigation module of Figure 3; Figure 5 is a schematic perspective view of a surgical navigation assembly comprising a rigid navigation support provided with four arms receiving four surgical navigation modules of Figure 4; Figure 6 is a schematic view of the surgical navigation assembly of Figure 5, wherein the rigid navigation support is fixed to a surgical instrument. [Detailed description of an embodiment of the invention] The following description concerns a method for producing a surgical navigation module 1, implementing the provision of a navigation marker 2 (shown in Figure 2) including a retroreflective lens 20 of generally hemispherical shape and surrounded by an annular collar 21. With reference to Figure 1, one step of this method consists in producing a shell 3 by molding, in a mold 30, a rigid thermoplastic material, and in particular a semi-crystalline rigid thermoplastic material, such as polypropylene or polyethylene, preferably a medical-grade material resistant to gamma sterilization. This shell 3 has a peripheral wall 31 defining or delimiting an internal cavity 32, and this peripheral wall 31 of the shell 3 has a peripheral rim 33 surrounding the internal cavity 32 and provided with recesses 34; in the illustrated example, there are three recesses 34. At least one orifice 35 is formed in the peripheral wall 31 so as to emerge with the internal cavity 32. The shell 3 further has a solid bottom wall 39 forming the bottom of the internal cavity 32, the internal cavity 32 thus extending from said bottom wall 39 to the peripheral rim 33. This shell 3 further has coupling members 36 configured to enable coupling of the shell 3 to a rigid navigation support 5 described hereinafter. In the illustrated embodiment, these coupling members 36 are two in number and are arranged diametrically opposite one another. Each coupling member 36 is in the form of a snap-fastening member comprising a projecting snap-fastening hook 37 secured to a gripping tab 38, thereby allowing snap-fit mounting onto the rigid navigation support 5. Next, the navigation marker 2 is placed within the internal cavity 32 of the shell 3 while maintaining an interstitial space between the shell 3 and the navigation marker 2. The annular collar 21 bears against a plurality of contact points provided for this purpose within the internal cavity 32. Finally, an elastomeric thermoplastic material is injected into the interstitial space through the orifice 35 in order to form an intermediate cap 4 by molding this elastomeric thermoplastic material, such that the intermediate cap 4 is molded within the internal cavity and partially overmolds the navigation marker 2 between the shell 3 and the navigation marker 2. The intermediate cap 4 at least partially overmolds the annular collar 21 around its periphery and thus provides assembly of the navigation marker 2 with the shell 3. Thus, the navigation marker 2 is secured to a coupling part, which is a two-material component formed by the shell 3 and the intermediate cap 4. The elastomeric thermoplastic material is selected from thermoplastic polyurethane elastomers (TPU), styrenic thermoplastic elastomers (TPS), copolyester thermoplastic elastomers (TPC), copolyamide thermoplastic elastomers (TPA), non-vulcanized thermoplastic olefin elastomers (TPO), and vulcanized thermoplastic olefin elastomers (TPV); and said elastomeric thermoplastic material has a melting temperature lower than or equal to 150°C, and for example lower than or equal to 120°C. This elastomeric thermoplastic material is preferably a medical-grade material resistant to gamma sterilization, having a Shore A hardness comprised between 40 and 70, and for example between 50 and 60. Upon completion of this producing method, the resulting surgical navigation module 1 comprises: - the navigation marker 2; - the intermediate cap 4 partially overmolding the navigation marker and made of the elastomeric thermoplastic material; and - the shell 3 made of the rigid thermoplastic material and defining the internal cavity 32 within which the intermediate cap 4 is assembled, the intermediate cap 4 thus being disposed between the shell 3 and the navigation marker 2. Accordingly, as explained above, the navigation marker 2 is overmolded by a two-material component formed by the shell 3 and the intermediate cap 4. With reference to Figures 5 and 6, a surgical navigation assembly 6 comprises the rigid navigation support 5, which may comprise a plurality of arms 50 (four in the illustrated example), each arm 50 having a free end provided with a housing 51 adapted to receive a surgical navigation module 1. The surgical navigation assembly 6 therefore also comprises as many surgical navigation modules 1 as there are housings 51 in the rigid navigation support 5. Within each housing 51, the shell 3 is mounted inside the housing 51 and retained in position by snap-fastening engagement, through coupling of these coupling members 36 with complementary coupling members provided on the housing 51. As shown in Figure 6, the rigid navigation support 5 may subsequently be fixed to a surgical instrument 7, and the position of the navigation markers 2 may then be tracked by the video capture system in the operating room in order to monitor the position and orientation in space of the surgical instrument 7. The rigid navigation support 5 may also be fixed to an implant or to a part of a patient's body in order to monitor the position and orientation in space of this implant or of this part of the concerned patient's body.

Claims

1. A method for producing a surgical navigation module (1), comprising the following steps:- providing a navigation marker (2) including a retroreflective lens (20);- producing a shell (3) by molding a rigid thermoplastic material, said shell (3) defining an internal cavity (32) and having at least one coupling member (36) configured to enable coupling of the shell (3) to a rigid navigation support (5);- placing the navigation marker (2) in the internal cavity (32) of the shell (3) while maintaining an interstitial space between the shell (3) and the navigation marker (2); and- producing an intermediate cap (4) by molding an elastomeric thermoplastic material at least within the interstitial space, such that the intermediate cap (4) is molded inside the internal cavity (32) and partially overmolds the navigation marker (2) between the shell (3) and the navigation marker (2).

2. The producing  method according to claim  1, wherein the rigidthermoplastic material is a semi-crystalline rigid thermoplastic material.

3. The producing method according to claim 2, wherein the rigidthermoplastic material is selected from rigid thermoplastic materials of the polypropylene or polyethylene type.

4. The producing method according to any one of claims 1 to 3, wherein the elastomeric thermoplastic material is selected from thermoplastic polyurethane elastomers (TPU), styrenic thermoplastic elastomers (TPS), copolyester thermoplastic elastomers (TPC), copolyamide thermoplastic elastomers (TPA), nonvulcanized thermoplastic olefin elastomers (TPO), and vulcanized thermoplastic olefin elastomers (TPV).

5. The producing method according to any one of claims 1 to 4, wherein the elastomeric thermoplastic material has a melting temperature less than or equal to 150°C.

6. The producing method according to any one of claims 1 to 5, wherein the elastomeric thermoplastic material has a Shore A hardness comprised between 40 and 70, and for example between 50 and 60.

7. The producing method according to any one of claims 1 to 6, wherein the at least one coupling member (36) of the shell (3) is a snap-fastening member.

8. The producing method according to claim 7, wherein the coupling member comprises a snap-fastening hook (37) projecting and secured to a gripping tab (38).

9. The producing method according to any one of claims 1 to 8, wherein the shell (3) has a peripheral rim (33) surrounding the internal cavity (32) andprovided with recesses (34), such that the elastomeric thermoplastic material at least partially fills said recesses (34) during production of the intermediate cap.

10. The producing method according to any one of claims 1 to 9, wherein the shell (3) has a peripheral wall (31) in which at least one orifice (35) is formed, which emerges with the internal cavity (32), so as to introduce the elastomeric thermoplastic material through this at least one orifice (35) during production of the intermediate cap (4).

11. The producing method according to any one of claims 1 to 10, wherein the rigid thermoplastic material and the elastomeric thermoplastic material are medical-grade materials.

12. The producing method according to any one of claims 1 to 11, wherein the rigid thermoplastic material and the elastomeric thermoplastic material are materials resistant to gamma sterilization.

13. A surgical navigation module (1) obtained by the producing method according to any one of the preceding claims, said surgical navigation module (1) comprising:- an intermediate cap (4) made of an elastomeric thermoplastic material and partially overmolding a navigation marker (2) including a retroreflective lens (20); and- a shell (3) made of a rigid thermoplastic material and having at least one coupling member (36) configured to enable coupling of the shell (3) to a rigid navigation support (5), said shell (3) defining an internal cavity (32) within which the intermediate cap (4) is assembled, said intermediate cap (4) thus being disposed between the shell (3) and the navigation marker (2).

14. A surgical navigation assembly (6) comprising:-     a rigid navigation support (5) comprising at least one housing (51); and-     at least one surgical navigation module (1) according to claim 13;wherein the shell (3) of the at least one surgical navigation module (1) is mounted in the at least one housing (51) and is retained by engagement of the at least one coupling member (36) with at least one complementary coupling member provided on the at least one housing (51).

15. The surgical navigation assembly (6) according to claim 14, wherein the rigid navigation support (5) comprises at least two arms (50), and the at least one housing (51) comprises at least two housings (51) provided on the respective at least two arms (50), such that the at least one surgical navigation module (1) comprises at least two surgical navigation modules (1) mounted in the respective at least two housings (51).

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