HK1100895B - Surgical device for treating flat foot and corresponding surgical kit - Google Patents

Description

The present invention relates to the general technical field of surgical devices used for the treatment of flat foot disease, particularly in children and adults.

The present invention relates in particular to a surgical device for the treatment of flat foot pathology comprising at least two components: an expandable outer shell,an expansion organ,capable of moving within that outer shell in a compression direction, that outer shell and that expansion organ being so shaped that the movement of the expansion organ in the compression direction results in the radial expansion of that outer shell.

Such a surgical device is described in US-6136032.

The flat foot phenomenon is very often due to misalignment of the astragalus and the calcaneum, which causes deformation of the arch of the foot:

To remedy this type of pathology, it is known to introduce an implant, also known as endortesis into the tarsal sinus. This implant then acts as a groove whose function is to restore alignment between the calcaneum and astragalus. When the realignment of the calcaneum and astragalus is satisfactory, that is usually about nine months after placement, the implant is removed by extraction with tweezers.

The implant has a polyethylene outer shell, a cylinder with a hole in the center of the shell, and a screw is inserted into the inner shell, which expands to open the sinus canal and reposition the astragalus to the calcaneus.

The major disadvantage of this type of implant is that it does not have an additional shape to the tarsial sinus cavity in its expanded configuration.

To overcome this disadvantage, another surgical device has been developed, consisting of three components: a central body with an external thread, with a translational locking head,an expansion cone, with an internal thread, capable of cooperating with the external thread of the central body,and an external crown which can be expanded by the movement of the expansion cone into the external crown when the central body is screwed.

These devices generally work well, in particular because their special shape makes them easily trapped in the sinus cavity of the tarsus, but they also have several significant drawbacks.

In particular, the screw-on assembly system, which has the advantage of being reversible and thus of facilitating early removal of the implant by reducing its diameter by un-screwing the expansion cone, suffers from the fact that the expansion cone can un-screw itself while the device is implanted.

The objects of the invention are therefore intended to remedy the various disadvantages listed above and to propose a new surgical device for the treatment of flat foot disease with improved reliability compared with previous devices.

Another object of the invention is to propose a new surgical device which can be easily inserted and then locked into position in the tarsial sinus cavity.

Another object of the invention is to propose a new surgical device whose expanded configuration is particularly well suited to the geometry of the tarsian sinus cavity.

The objects of the invention also aim to propose a new surgical kit for the treatment of flat foot pathology which allows the precise and reliable implantation of a surgical device into the tarsial sinus cavity.

Another object of the invention is to propose a new surgical kit for the treatment of flat foot pathology which is particularly easy to handle by a surgeon.

The objects of the invention are also intended to propose a new surgical method of treatment of flat foot pathology which would enable the realignment of the calcaneum and astragalus to be achieved with the aid of an implantable surgical device with improved reliability compared with previous methods of the art.

The objects of the invention are achieved by means of a new surgical device for the treatment of flat foot pathology comprising at least two components: an expandable outer shell,an expansion organ,capable of moving within the outer shell in a compression direction, the outer shell and the expansion organ being so shaped that the expansion organ moves in the compression direction to radial expansion of the outer shell, characterised by having anti-return locking devices, designed to allow the expansion organ to move in the direction of compression to a functional position within the outer shell and to prevent the expansion organ from moving in the opposite direction once the functional position has been reached, so as to prevent the expansion organ from being ejected.

The objects of the invention are also achieved by means of a new surgical kit for the treatment of flat foot pathology comprising: a surgical device as described above, comprising a means of grasping,a placement device, capable of being mechanically attached by means of a grip and of applying a tensile force on the grip, while pushing the expansion organ back in the direction of compression so that the expansion organ gradually penetrates into the outer shell, causing it to expand.

The objects of the invention are also achieved by a new surgical method of treatment of flat foot pathology, including: an implantation stage, during which a surgical device, including an expandable outer shell, is inserted into the sinus of the tarsus of the foot,an expansion stage, during which an expansion organ is inserted and moved into the outer shell in such a way as to cause it to expand, The expansion organ is characterised by a locking stage, during which the expulsion of the expansion organ from the outer envelope is prevented by means of anti-return locking once its functional position within the outer envelope has been reached.

Other purposes and advantages of the invention will be described in more detail by reading the following description and by means of the accompanying drawings, which are given for illustrative and non-limiting purposes only, in which: Figure 1 shows, from a profile view, a surgical device for the treatment of flat foot disease according to the invention, in a pre-assembly position prior to radial expansion.Figure 2 shows, from a cutting view following the line A-A shown in Figure 1, the surgical device shown in Figure 1.Figure 3 shows, from a cutting view, the surgical device shown in Figures 1 and 2,in its functional position, with a means of grip.Figure 4 shows, from a cut-out view, the surgical device shown in Figures 1, 2 and 3 in its functional position, after the removal of the means of grip.Figure 4a shows, from a cut-out view, a detail of the means of anti-return locking of the surgical device shown in Figure 3.Figure 5 shows, from a perspective view, the components forming the surgical device shown in Figures 1 to 4.Figure 6 shows, from a partial cut-out side view, the surgical kit for the treatment of flat foot in accordance with the invention.Figure 7 shows, in a cut-out view, a variant of the manufacture of a surgical device conforming to the invention, in a configuration prior to the diameter expansion of the device.Figure 8 shows, in a cut-out view, the surgical device shown in Figure 7 in its expanded functional configuration.Figure 8a shows, in a cut-out view, a detail of the means of anti-return locking of the surgical device shown in Figure 8.

Figure 1 shows a surgical device 1 for the treatment of flat foot pathology, before being fitted into the tarsial sinus cavity.

As shown in Figure 1, surgical device 1 consists of at least two components: an expandable outer shell 2 and an expansion organ 3.

The expansion organ 3 shall be capable of moving within the outer shell 2 in a compression direction F preferably parallel to the longitudinal axis X-X', the outer shell 2 and the expansion organ 3 being so shaped that the movement of the expansion organ 3 in the compression direction F causes the radial expansion of the outer shell 2.

The outer shell 2 is preferably a conical crown with the main axis confused with the longitudinal axis X-X. The outer shell 2 is preferably made of a biocompatible deformable material, e.g. metal or polyethylene.

The outer envelope 2 has an outer surface 5 which is useful for supporting the surgical device 1 against the wall of the sinus cavity during expansion. The outer envelope 2 also has an inner surface 6 which is useful for supporting the inner envelope 4.

In order to allow the diameter expansion of the outer shell 2, the outer shell has 7 grooves on the outer surface 5 and 8 grooves on the inner surface 6. Preferably, outer shell 2 has four grooves 7 spread over its outer surface 5 and four grooves 8 spread over its inner surface 6, the said grooves 7, 8 being preferentially angularly offset from each other in order to allow the diameter expansion of the outer shell 2. In particular, the grooves 7 arranged on the outer surface 5 are preferably excavated 45° perpendicularly to the grooves 8 arranged on the inner surface 6.

Preferably, as shown in Figures 1, 2 and 5, the outer envelope 2 has 9 flippers on its outer surface 5 to prevent the ejection of the surgical device 1 after it has been placed and expanded within the sinus cavity, thus the flippers 9 are placed in positive support against the cavity wall when the surgical device 1 is expanded, thus preventing the ejection of the surgical device 1.

The expansion organ 3 has an expansion cone 10 with an external face 11 so shaped that it is superficially supported against the outer shell 2 and preferably against the inner surface 6 of the outer shell 2 so as to cause the latter to gradually expand by the movement of the expansion cone 10 in the direction of compression F.

Preferably, the expansion organ 3 and in particular the expansion cone 10 is formed by a biocompatible metallic material, e.g. titanium or stainless steel.

The surgical device 1 extends between a proximal end 1A, which in the functional position shown in Figure 4 is at the bottom of the sinus of the tarsus, and a distal end 1B facing outwards from the cavity, opposite the proximal end 1A. The advantage is that the smallest diameter of the expansion icon 10 is on the side of the proximal end 1A of the surgical device 1, and the largest diameter is on the opposite side of the distal end 1B of the surgical device 1.

The advantage is that the conical outer face 11 of the expansion cone 10 is supported against the internal surface 6 of the internal housing 4 which is also conical.

In order to allow radial expansion of the outer shell 2, the outer diameter of the expansion cone 10 is significantly larger than the corresponding inner diameter of the inner housing 4 when the outer shell 2 is at rest, i.e. in its un-expanded configuration.

According to a key feature of the invention, the surgical device 1 has anti-return locking devices 12 designed to allow the expansion organ 3 to move in the direction of compression F to a functional position within the outer shell 2 and to prevent the expansion organ 3 from moving in the opposite direction once the functional position has been reached, so as to prevent the expansion organ 3 from being ejected from the outer shell 2.

In particular, the function of the anti-return locking devices 12 is, once the expansion organ 3 and the outer shell 2 are assembled in the functional position, to prevent the gradual and uncontrolled separation of the components (or parts) forming the surgical device 1, by locking the expansion organ 3 in its functional position, thus giving the latter an indemnable character.

The advantage of the anti-return locking means 12 is that they have a first and second mutual engagement means 13, 14, preferably directly or indirectly associated with the expansion organ 3 and the outer shell 2 respectively, and capable of cooperating together to allow unidirectional movement, following the compression direction F, of the expansion organ 3 to its functional position within the outer shell 2.

The term associated refers to the fact that the first mutual-engagement medium 13 and the expansion organ 3 form, during the expansion stage of the surgical device 1, a unitary assembly in the kinematic plane, capable of moving in a monobloc manner to ensure expansion of the outer envelope 2. Similarly, the second mutual-engagement medium 14 is associated directly or indirectly with the outer envelope 2, i.e. it is either directly attached to the outer envelope 2, or indirectly connected, by an intermediate piece, to the outer envelope 2 so as to be immobile relative to the outer envelope 2 during expansion of the outer organ 3, and will form, with the outer envelope 2, an assembly in accordance with the above-defined definition, moved in the outer envelope. In the following, the term associated with the outer envelope 2 will be interpreted as moving in the outer envelope 2 in accordance with the description of the outer organ 3, and will form a moving ensemble in the outer envelope 2.

The advantage is that at least one of the mutual means of attachment 13 is conformed and arranged so as to fade to cross the other mutual means of attachment 14 when the expansion organ 3 moves in the compression direction F, thus forming an escapeable means of attachment.

Preferably, the removable means of attachment 13 has an elastic character which allows it to fade away from the complementary mutual means of attachment 14 This elasticity may be obtained from an elastic means of attachment, such as a spring, mechanically connected to the removable means of attachment 13 so that when the mutual means of attachment 14 is supported against the corresponding removable means of attachment 13, the latter is pushed back against the pulling force exerted by the removable means of attachment.

Preferably, the retractable means of attachment 13 has its own elastic character, derived from its inherent flexibility and suppleness.

As shown in Figure 4a, the first and second mutual-engagement means 13, 14 have a first and second engagement face 15, 16 which are oriented obliquely to the compression direction F and are capable of sliding against each other when the expansion organ 3 is moved to its functional position.

Preferably, the first and second mutual-engagement means 13, 14 also include a first and second stop faces 17, 18 capable of coming into contact with each other in such a way as to prevent the reversal, according to an expulsion direction F' opposite to the compression direction F, of the expansion organ 3 once the functional position has been reached.

The advantage of the surgical device 1 is that it has pre-assembly means 19 conformed to connect the expansion organ 3 with the outer envelope 2, directly or indirectly, by clipping. This pre-assembly configuration facilitates the placement of the surgical device 1 by the surgeon, who then only has to insert the surgical device 1 in its pre-assembled configuration into the sinus cavity, and then expand the outer envelope 2 by relative displacement of the expansion organ 3 and the said outer envelope 2.

Several embodiments of the invention are now described by reference to Figures 1 to 5 and 7 to 8.

In a first embodiment of the invention, shown in Figures 7 and 8, the surgical device 1 is made up of the outer shell 2 and the expansion organ 3, thus forming a surgical device 1 with two components (or parts).

According to this variant, the outer shell 2 extends between a proximal end 2A, towards the corresponding proximal end 1A of the surgical device 1, and a distal end 2B, on the opposite side. The surgical device 1 has a translational locking head 20 arranged at the proximal end 2A of the outer shell 2 in such a way as to close the inner housing 4. The locking head 20 may be formed by a plug, joined or joined with the outer shell 2.

According to this variant, the expansion organ 3 is formed by the expansion cone 2 which is in the form of a full truncated cone. As shown in Figures 7, 8 and 8a, the second mutual attachment 14 is located on the inner surface 6 of the inner housing 4 in such a way as to cooperate with the first mutual attachment 13 on the outer face 11 of the expansion organ 3.

Preferably, as shown in Figure 8a, the first mutual-engagement medium 13 is preferably formed by a circular lip 21 extending around the expansion organ 3 in a plane appreciably perpendicular to the compression direction F. The circular lip 21 is advantageously protruding from the outer face 11 of the compression organ 3. The second mutual-engagement medium 14 is preferably formed by a first circular groove 22 on the inner surface 6 of the outer shell 2 and of a shape preferably complementary to that of the circular lip 21. Preferably, the circular lip 21 and the first circular groove 22 have a triangular cross-section.

According to this variant, the pre-assembly means 19 are preferably formed by the circular lip 21 and at least a second circular groove 23 located on the inner surface 6 of the outer shell 2 and upstream of the first circular groove 22 in consideration of the compression direction F, the circular lip 21 being intended to cooperate with the second circular groove 23 as shown in Figure 7.

The operation of the surgical device 1 shown in Figures 7, 8 and 8a is as follows.

Moving in the compression direction F, the expansion organ 3 is supported positively and compressively on the inner surface 6 of the outer shell 2 by its outer face 11 and the circular lip 21, causing the latter to expand diametrically. When the pre-assembly configuration, shown in Figure 7, is reached, the circular lip 21 is lodged in the second circular groove 23 which prevents the expansion organ 3 from moving backwards in the direction of expulsion F. In this pre-assembly configuration, however, the expansion organ 3 can be moved in the compression direction F until it reaches its functional position shown in Figure 8.where it is locked in position by means of the anti-return locking devices 12 preventing its movement in the direction of ejection F', and by the translation locking head 20 limiting its movement in the direction of compression F. In its functional position, the circular lip 21 is placed in the first circular groove 22 provided for this purpose, so that the first and second stopping faces 17, 18 support each other.

In a second preferred embodiment of the invention, as shown in Figures 1 to 5, the surgical device 1 has a guide organ 25 designed to cooperate with the expansion organ 3 in such a way as to guide the latter in translation within the outer envelope 2. More specifically, the guide organ 25 has a central rod 26 extending considerably to the centre of the outer envelope 2 along the longitudinal axis X-X', and the expansion organ 3 has a central passage 30 allowing it to slide along the said central rod 26. The surgical device 1 is then made up of three components, namely the expansion organ 3, the outer envelope 2 and the guide organ 25.

According to a particularly advantageous feature of the invention, the guide organ 25 also includes a translational locking head 27 capable of limiting the movement of the expansion organ 3 in the compression direction F by forming a stub against it.

Preferably, the guidance organ 25 is made of a biocompatible metallic material, such as titanium or stainless steel.

According to this second embodiment of the invention, the second mutual attachment 14 is preferably located on the perimeter of the central rod 26 in such a way as to cooperate with the first mutual attachment 13 located on the surface of the central passage 30. The second mutual attachment 14 is then associated with the outer envelope 2 indirectly, via the middle part formed by the guiding organ 25.

Even more preferably, as shown in Figure 4a, the anti-return locking means 12 and in particular the first and second mutual binding means 13, 14 are formed by at least one first lip 31 associated with the outer shell 2 and more preferably located on the perimeter of the central rod 26 so as to form a circular lip, and at least one back lip 32 associated with the expansion organ 3, and more preferably arranged so as to protrude in the central passage 30.

It is advantageous, as shown in Figures 3 and 5, that the expansion organ 3 extends to the proximal end 1A of the surgical device 1 by an edged neck 33 surrounding the central passage 30 and the cleft lip 32 is arranged around the neck 33 so as to protrude inwards into the central passage 30.

In a particularly advantageous way, as shown in Figure 5, slots 34 are arranged along column 33 in such a way as to delimit several flexible tongues 35 capable of fading out like clicks from the first lip 31 when the expansion organ 3 is moved in the compression direction F. The counter-lip 32 is thus broken down into a plurality of 32' counter-lips arranged on the flexible tongues 35 and, in conjunction with the first lip 31, forms advantageously an enclave.

The perimeter of the central bar 26 and the surface of the central passage 30 are preferably mostly smooth, except for the presence of the means of mutual engagement 13, 14 which form reliefs.

According to this embodiment, the means of pre-assembly 19 are preferably formed by the back lip 32 and at least a second lip 36 associated with the outer shell 2, and more precisely spaced around the central rod 26 and located upstream of the first lip 31 in consideration of the compression direction F, the said back lip 32 being intended to cooperate with the said second lip 36 in the pre-assembly configuration shown in Figure 2.

According to a particularly advantageous feature of the invention, shown in Figures 1 to 3 and 5, the surgical device 1 has a means of grip 40 to be mechanically connected to a laying instrument 50 (Figure 6) designed to provide clipping (or linkage) of the components forming the surgical device 1 by applying a tensile force on the means of grip 40, preferably in a direction opposite to the compression direction F. Preferably, the means of grip 40 has a tip 41 with an external thread 42 to enable its connection by screwing to the instrument 50 (Figure 5).

The means of attachment 40 is preferably formed by an extension of the central rod 26 opposite the locking head 27. The means of attachment 40 is also advantageously removable and preferably secable. To this end, the central rod 26 and the means of attachment 40 are preferably formed by a single piece of local shrinkage 43 defining a breaking zone at which the separation of the means of attachment 40 and the central rod 26 takes place when a tensile force exceeding a threshold value is exerted on the means of attachment 40.

The break zone, and in particular the local narrowing 43, is located during the entire expansion stage of the surgical device 1 in the central passage 30 of the expansion organ 3, which prevents premature rupture of the grip 40 particularly by preventing the bending and angular deflection of the grip 40 in relation to the longitudinal axis X-X' and the central rod 26.

The effective rupture may only occur when the expansion organ 3 has reached its functional position within the outer envelope 2, the rupture zone then adjoining the distal end 3B of the expansion organ 3 in such a way as to allow the interlocking of the means of grip 40 in particular by pulling on the latter and tilting it with respect to the longitudinal axis X-X' at the level of the local narrowing 43.

The surgical device 1 according to the invention is advantageously sized so that when the expansion organ 3 is in its functional position, the rupture zone (or local narrowing 43) is located significantly at the distal end 3B of the expansion organ 3, opposite the block head 27.

The advantage of the grip 40 is that it has a flat plate 44 designed to facilitate the surgeon's grip to ensure that the tip 41 is unscrewed from the fixing instrument 50.

The present invention also relates to a surgical kit 100 for the treatment of flat foot pathology comprising: a surgical device 1 as described above, comprising a means of grip 40, a placement device 50, capable of being mechanically attached by means of grip 40 and of applying a tensile force to the device while pushing the expansion organ 3 in the direction of compression F, so that the device gradually penetrates into the outer shell 2 causing its expansion, including its diametric expansion.

As shown in Figure 6, the instrument 50 has a main body 51, cylindrical in shape, with a cavity 52 into which a rod is mounted, 53 and a free end 53A, on which the surgical device 1 is mounted. The latter is for example screwed on the free end 53A of the rod 53 The movement of the rod 53 following the compression direction F is controlled by handles 54, including a fixed handle 55, solidary with or coming from material from the main instrument 51 and a mobile handle 56, mounted with a possibility of rotation relative to the main body 51. The lever 56 is extended between the first end 56A and a second end 56B, and the movement of the rod 53 is mechanically connected to the rotation of the main rod 53 and a rotation of the rod 56 which results in a rotation of the rod 56 corresponding to the free end of the main body.

Finally, the present invention concerns a surgical method of treatment of flat foot pathology which first involves an implantation stage, during which a surgical device 1 comprising an expandable outer shell 2 is inserted into the sinus of the tarsus of the foot. The surgical method according to the invention then includes an expansion stage, during which an expansion organ 3 is inserted and moved into the outer shell 2 in order to cause its expansion.

The surgical method according to the invention also includes, according to one essential feature, a blockade step in which the expulsion of the expansion organ 3 from the outer shell 2 is prevented by means of anti-return blocking 12 once its functional position within the outer shell 2 has been reached.

The method according to the invention has a particularly advantageous first pre-assembly step before the expansion step, in which the expansion organ 3 is directly or indirectly assembled with the outer shell 2 to form an indemnable unit assembly, e.g. by means of an intermediate part, using a pre-assembly device. The pre-assembly step is preferably performed by clipping, using pre-assembly means. This step is preferably performed at the production site of the surgical device 1, preferably sold in its assembly configuration.

The surgical method according to the invention also includes, before the expansion stage, a connection step, during which the surgical device 1 is mechanically connected to a placement instrument 50 by means of a gripper 40 integrated into the surgical device 1.

The expansion step is then carried out by traction on the grip 40 using the placement instrument 50 so that the traction force on the grip 40 causes the expansion organ 3 to move into the outer shell 2 and the expansion of the latter diametrically. The expansion step continues until the expansion organ is locked in position, using the anti-return locking means 12. According to a particularly advantageous feature of the invention, the blocking step is carried out by clipping or gluing the expansion organ 3 with the outer shell 2 directly or indirectly, i.e. by means of a combination of the head of the anti-return locking organ 1 and the head of the expansion organ 12 through a guide, which in the latter case is a combination of the head of the anti-return locking organ 12 and the head of the expansion organ 12 and the head of the organ 12 by means of a guide, which in turn is a means of guiding the body of the organ 12 through the head of the expansion organ 12 and the head of the organ 12 by means of a guide.

The surgical method according to the invention also includes, in a particularly advantageous way, a separation step, during which the means of grip 40 of the surgical device 1 is separated, for example by cutting, after the expansion and blocking steps have been completed.

The modes of operation and use of the surgical device 1 and the surgical kit 100 according to the invention are now described by reference to Figures 1 to 6.

The insertion of the surgical device 1 is carried out as follows: a single incision is made in the tarsal canal and all the components of the surgical device of the invention are inserted in a pre-assembled configuration as shown in Figure 2.

The surgical device 1 is connected to the fitting instrument 50 by means of the gripper 40, which protrudes from the outside of the surgical device 1. Specifically, the tip 41 of the gripper 40 is preferably screwed to the free end 53A of the rod 53 of the fitting instrument 50.

Once the surgical device 1 has been implanted, its expansion and blockage in the sinus cavity of the tarsus is carried out by pressing the handles 55, 56 against each other in such a way as to exert a tensile force on the means of grip 40 (and therefore on the outer shell 2) by means of the rod 53, while pushing the expansion organ 3 in the direction of compression F through the end 51A of the main body 51, which is supported against the expansion organ 3.

The expansion organ 3, and in particular the expansion cone 10, then gradually penetrates into the inner housing 4 of the outer envelope 2 and exerts centrifugal compression on the latter due to the difference in diameter between the expansion cone 10 and the inner housing 4. More specifically, as the outer envelope 2 expands, the incisions 7, 8 gradually open and the aplet 9 come into contact with the sinus cavity of the tarsus, blocking the surgical device 1 within the said cavity.

The functional position of the expansion organ 3 is reached when the expansion organ comes into contact with the locking head 27, particularly via the neck 33 (Figure 3) and/or when the first and second mutual engagement means 13, 14 come into contact with each other.

The surgeon may then continue the tensile effort on the grip 40 by pressing the handles 55, 56 against each other, while tilting the placement instrument 50 so as to separate, by bending and tensile rupture at the local narrowing 43, the grip 40 from the central rod 26 and more generally from the surgical device 1 which is then locked in position in the tarsian sinus cavity.

The present invention allows for the easy installation and locking of the surgical device 1 in the sinus of the tarsus, with a limited number of operations, while providing good reliability and in particular a limited risk of expulsion of the surgical device 1 or any of its components.

Claims (25)

1. A surgical device (1) for treating the pathology of flat feet, said surgical device comprising at least two components:

   an expansible outer casing (2); and

   an expansion member (3) suitable for moving inside said outer casing (2) in a compression direction, said outer casing (2) and said expansion member (3) being shaped so that moving the expansion member (3) in the compression direction (F) causes said outer casing (2) to expand radially, characterized in that it comprises non-return check means (12) shaped to allow the expansion member (3) to move in the compression direction (F) towards an operating position inside the outer casing (2), and to oppose movement of the expansion member (3) in the reverse direction once said operating position is reached, so as to prevent the expansion member (3) from being expelled.
2. A device according to claim 1, wherein the check means (12) comprise first and second mutual engagement means (13, 14) associated respectively with the expansion member (3) and with the outer casing (2), and suitable for co-operating together to enable the expansion member (3) to move one-way only, towards its operating position.
3. A device according to claim 2, wherein at least one of said mutual engagement means (13, 14) is shaped and arranged so as to retract in order to go past the other mutual engagement means while the expansion member (3) is moving in the compression direction (F), thereby forming retractable engagement means.
4. A device according to claim 3, wherein the retractable engagement means (13) are resilient.
5. A device according to anyone of claims 2 to 4, wherein the first and second mutual engagement means (13, 14) have first and second engagement faces (15, 16) extending slantingly relative to the compression direction (F) and suitable for sliding against each other while the expansion member (3) is moving towards its operating position.
6. A device according to anyone of claims 2 to 5, wherein the first and second mutual engagement means (13, 14) have first and second stop faces (17, 18) suitable for coming into abutment against each other so as to prevent the expansion member (3) from moving back the other way once the operating position is reached.
7. A device according to anyone of preceding claims, wherein the check means (12) are formed by at least a first lip (31) associated with the outer casing (2) and by at least one backing lip (32) associated with the expansion member (3).
8. A device according to anyone of preceding claims, the device being provided with preassembly means (19) shaped to assemble the expansion member (3) to the outer casing (2) by clipping.
9. A device according to claims 7 and 8, wherein preassembly means (19)are formed by the backing lip (32) and by at least a second lip (36) associated with the outer casing (2) and situated upstream from the first lip (31) relative to the compression direction (F), said backing lip (32) serving to co-operate with said second lip (36).
10. A device according to anyone of claims 2 to 9, wherein the expansion member (3) comprises an expansion cone (10), the outside face (11) of the expansion cone (10) coming into surface abutment against the outer casing (2) so as to cause said outer casing to expand progressively under the effect of the expansion cone (10) moving in the compression direction (F).
11. A device according to anyone of claims 2 to 10, the device being constituted by the outer casing (2) and by the expansion member (3), thereby forming a device made up of two components.
12. A device according to claims 2 and 11, wherein the outer casing (2) defines an internal recess (4) with an inside surface (6), and wherein the second engagement means (14) are situated on said inside surface (6) so as to co-operate with the first engagement means (13), situated on the outside face (11) of the expansion member (3).
13. A device according to anyone of claims 2 to 10, further comprising a guide member (25) shaped to co-operate with the expansion member (3) so as to guide said expansion member in translation inside the outer casing (2).
14. A device according to claim 13, wherein the guide member (25) comprises a central rod (26) extending substantially at the center of the outer casing (2), and wherein the expansion member (3) is provided with a central passageway (30) enabling it to slide along the central rod (26).
15. A device according to claim 13 or 14, wherein the guide member (25) further comprises a blocking head (27) suitable for limiting movement in translation of the expansion member (3) in the compression direction (F), the blocking head (27) and the check means (12) locking the expansion member (3) in the operating position.
16. A device according to claim 14, wherein the second engagement means (14) are situated on the periphery of the central rod (26), so as to co-operate with the first engagement means (13) that project into the central passageway (30).
17. A device according to claims 7 and 16, wherein the expansion member (3) is extended by a thin neck (33) surrounding the central passageway (30), the backing lip (31) being disposed at said neck (33) so as to project towards the inside of the central passageway (30).
18. A device according to claim 17, wherein slots (34) are provided along the neck (33) so as to define a plurality of flexible tongues (35) suitable for retracting relative to the first lip (31) while the expansion member (3) is moving in the compression direction (F).
19. A device according to anyone of preceding claims, further comprising a graspable member (40) serving to be connected mechanically to a fitting instrument (50) designed to clip together the components making up the surgical device by exerting a traction force on the graspable means (40).
20. A device according to claims 14, 15 and 19, wherein the graspable means (40) are formed by an extension to the central rod (26), that is situated opposite from the blocking head (27).
21. A device according to anyone of claims 19 or 20, wherein the graspable means (40) are removable, preferably by being suitable for being broken off.
22. A device according to claim 21, wherein the central rod (26) and the graspable means (40) are formed in one piece provided with a local narrow portion (43) defining a break zone at which the graspable means (40) are separated from the central rod (26) when traction exceeding a threshold value is exerted on the graspable means (40).
23. A device according to anyone of preceding claims, wherein the outer casing (2) is provided with notches (7, 8) in its outside surface (5) and in its inside surface (6), which notches are offset angularly so as to enable said outer casing (2) to expand diametrically.
24. A device according to anyone of preceding claims, wherein the outer casing (2) is made of a biocompatible deformable material, e.g. metal or polyethylene.
25. A surgical kit for treating the pathology of flat feet, said surgical kit comprising:

    a surgical device (1) according to anyone of claims 1 to 24, including graspable means (40); and

    a fitting instrument (50) suitable for being connected mechanically to the graspable means (40) and for exerting a traction force on said graspable means, while also pushing the expansion member (3) away in the compression direction (F) so that said expansion member penetrates progressively into the outer casing (2) while causing said outer casing to expand.