Bone plate internal fixation device

Abstract

A bone plate internal fixation device (101; 501; 701) for epiphyseal fixation is provided. [Solution] The device includes a pair of retaining elements (102, 103; 502, 503; 702, 703), each having a through-hole (104, 105; 504, 505; 704, 705) configured to receive a respective fixation screw (301) in the bone. The device further includes a central portion (106; 506; 706) that structurally connects and constrains the retaining elements to one another. The central portion is flexible to allow bending of the bone plate (101; 501; 701). Each through-hole has a threaded surface (108, 109; 508, 509; 708, 709) adapted to mate with a corresponding surface (304) of a respective fixation screw (301). The retaining elements and central portion are provided as a composite structure.

Description

[Technical field]

[0001] The present invention relates to an internal fixator device intended to be used as a corrective measure, particularly for pediatric patients, of the type having a bone plate provided with at least a pair of through holes for receiving bone fixation screws.

[0002] The present invention relates to a bone plate internal fixation device, particularly intended for epiphysiodesis surgery, used to block natural growth or correct limb axis deviations by restricting the natural growth of the growth plate.

[0003] The invention can be usefully applied in the pediatric orthopedic sector for epiphyseal fixation at the ends of deformed long bones in pediatric patients, and the following description is therefore given with non-limiting reference to use within that sector. [Background technology]

[0004] Known techniques of epiphysiodesis limit the development of the growth plate through the insertion of devices such as longitudinally placed screws, staples, or bone plates into the bone.

[0005] Among the techniques used for epiphyseal fixation, blocking the growth plate with a bone plate is widely used.

[0006] Such bone plates are applied to the bone by fixation screws which are secured to the epiphysis and metaphysis at the convexity of the bone deformity, respectively, and both the epiphysis and epiphysis portions of the bone plate have at least one through hole configured to receive one of said fixation screws.

[0007] In the particular field of the present invention, there are known problems relating to patient tolerability of the above-mentioned bone plates.

[0008] Indeed, when the fixation screws of the bone plate are placed above and below the growth plate, they must accommodate the constraints of the bone plate and the curve resulting from variations that occur during growth.

[0009] Therefore, in order to avoid excessive compression of the growth plate and to carefully guide the natural growth process of the physis and bone, specific bone plates are known which are constrained to the bone by fixation screws which tend to diverge from one another.

[0010] One solution disclosed in US Pat. No. 5,399,633 relates to a plate fixation device for angular correction of bone deformities, which has a rotatable hinge located laterally within the plate to allow relative rotation of the plate under the influence of the load of the fixation screws to support the curvature variations that occur during growth.

[0011] However, the solution known from US Pat. No. 5,399,633 constitutes a major encumbrance due to the presence of hinges which may reduce the tolerability of the bone plate especially in areas that are poorly covered by soft tissue. Moreover, the solution known from US Pat. No. 5,399,633 further does not allow to have a proper centering reference on the growth plate due to the use of Kirschner wires for temporary fixation of the bone plate by known surgical techniques.

[0012] One further solution disclosed in US Pat. No. 5,399,633 refers to a plate fixation device for controlling bone growth, in particular for correcting bone deformities, which device comprises two fixation screws which are inserted into appropriate holes provided in a bone plate.

[0013] In one example disclosed in the patent application WO 2005 / 023363, the head of each fixation screw has a spherical profile that allows it to rotate properly in the elongated seat obtained in the plate, thereby allowing the fixation screw to angulate. To allow rotation of the screw stem, the screw requires a spherical profile of the head of the screw, which also includes the engagement portion through which the screw is operated during the screwing operation. Thus, in this known example, the screw head and the bone plate in general are a major obstacle in terms of height that can reduce the tolerance of the bone plate, especially in areas that are little covered by soft tissue.

[0014] In a further example described in US 6,893,513, a flexible central connection between the bone plate holes is provided so that the fixation screws can follow the movements of the bone sections. Examples of flexible connections known from US 6,893,513 include a middle part of the plate made of a flexible material, one plate made of fabric with a rigid material surrounding the opening, or using a flexible band instead of a plate that surrounds the fixation screws and finally provides a compression in the middle.

[0015] Although implants known in the art partially improve patient tolerance of the bone plate and allow for relative rotation of the plate ends so that the fixation screws can support variations that occur during growth, they have some limitations.

[0016] First, excessive flexibility of the bone plate can cause problems in fixing it in the desired position.

[0017] Moreover, even if they follow the movements of the bone sections, flexible bone plates can in any case be such an obstacle, especially with regard to height, to promote a burst of an inflammatory process in the soft tissues.

[0018] In addition, flexible bone plates are too fragile and run the risk of breaking when subjected to stresses caused by bone growth.

[0019] Also, the flexible bone plate geometries employed by known techniques can lead to crushing of the growth plate, thus further reducing the tolerability of the implant. [Prior art documents] [Patent documents]

[0020] [Patent Document 1] U.S. Patent No. 8029,507 [Patent Document 2] US Patent Application Publication No. 2004 / 0111089 Summary of the Invention

[0021] The object of the present invention is to solve the problems of the prior art.

[0022] One particular object of the present invention is to provide a bone plate implant that allows optimal fixation to the bone.

[0023] One further specific object of the present invention is to provide a bone plate implant that is well tolerated by patients, even when applied in anatomical regions that are poorly covered by soft tissue.

[0024] One further specific object of the present invention is to provide a bone plate implant that is robust and suitable for epiphysiodesis applications.

[0025] One further specific object of the present invention is to provide a bone plate implant that does not interfere with the growth plate.

[0026] One idea of ​​the solution underlying the present invention is to provide a bone plate internal fixation device for epiphyseal fixation, which comprises a pair of retaining elements, each of which has a through hole for receiving a respective fixation screw into the bone, and further comprises a central part structurally connecting and restraining the retaining elements to each other, the central part being flexible to allow bending of the bone plate.

[0027] The invention is a bone plate internal fixation device as defined by the features of independent claim 1.

[0028] Each of the through holes has a threaded surface adapted to mate with a corresponding surface of a respective fixation screw.The retaining element and the central portion are provided as a composite structure.

[0029] Advantageously, the threaded surface of the through hole provides improved engagement with the fixation screw, which can provide a more precise embedment in the bone while at the same time providing a more structurally stable assembly.

[0030] Furthermore, the presence of a threaded surface on the through hole allows the connection between the head of the fixation screw and the bone plate to be achieved with less obstruction in terms of height and without protrusions, thus resulting in better tolerance, especially when the implant is applied in anatomical areas that are poorly covered by soft tissue.

[0031] Additionally, the flexible central portion allows for a wide range of angular opening of the bone plate, but during progression of the epiphysiodesis, the fixation screws always remain flush with the plane encompassing the flexion angle, and the axis of each fixation screw remains substantially perpendicular to each retention element.

[0032] Also, the construction of internal fixation devices with threaded surface holes is generally more robust and therefore more suitable for epiphyseal fixation applications, even with the stresses associated with the plate.

[0033] Furthermore, to improve tolerability, the internal fixation device is preferably characterized by a raised central portion relative to the bottom surface of the retention element, thereby limiting pressure on the bone physis and avoiding lateral crushing of the growth plate.

[0034] Further features and advantages of the bone plate internal fixation device of the present invention will become more apparent from the following description of exemplary and non-limiting embodiments. [Brief description of the drawings]

[0035] The present description refers to the accompanying drawings.

[0036] [Figure 1] 1 shows a perspective schematic view of one embodiment of a bone plate internal fixation device according to the present invention; [Diagram 2] 2A-2C show schematic perspective views of the fixation device of FIG. 1 in an exploded configuration from different perspectives. [Diagram 3] FIG. 2 shows a perspective schematic view of one fixation screw for a bone plate internal fixation device according to the present invention. [Figure 4] 4 shows a side view of an implant having a pair of locking screws from FIG. 3 and the bone plate internal fixation device from FIG. 1. [Diagram 5] FIG. 2 shows a schematic perspective view of a second embodiment of a bone plate internal fixation device according to the invention. [Figure 6] 6 shows a schematic perspective view of the fixation device of FIG. 5 seen from below. [Figure 7] FIG. 2 shows a perspective schematic view of a third embodiment of a bone plate internal fixation device according to the invention. [Figure 8] 8 illustrates the fixation device of FIG. 7 in a partially disassembled configuration. [Figure 9] 8 shows a schematic perspective view of the fixation device of FIG. 7 seen from below.

[0037] In the different figures, similar elements are designated by similar reference numbers. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] With reference to the example of FIG. 1, a first embodiment of a bone plate internal fixation device 101 is shown diagrammatically.

[0039] The fixation device according to the invention is particularly suitable for orthopedic epiphyseal fixation, i.e. the treatment of long bone deformities by application of a fixation device across the epiphysis of such bones, especially in pediatric and / or adolescent patients.

[0040] The internal fixation device 101 has a first retaining element 102 and a second retaining element 103, which have through holes 104 and 105, respectively, which are configured to receive one respective fixation screw when the fixation device is embedded in bone.

[0041] Retention elements 102 and 103 are preferably constructed of a rigid, biocompatible material (eg, titanium) and have a substantially circular shape with a uniform thickness.

[0042] The retaining elements 102 and 103 are structurally interconnected by a central portion 106 that constrains the retaining elements 102 and 103 to one another to provide a bone plate structure.

[0043] The retaining elements 102 and 103 and the central portion 106 are provided as a composite structure.

[0044] A "composite structure" is a structure that is made of at least two different materials or that includes at least two different material configurations (ie, solid metal and braided metal) and that exhibit different mechanical properties.

[0045] In other words, the retaining element and the central portion of the internal fixation device according to the invention are at least partially made of two different or differently configured materials.

[0046] Typically, the retention element and at least a portion of the central portion are originally provided as separate components of the internal fixation device, which are connected to form a composite structure during manufacture of the internal fixation device.

[0047] The central portion 106 is flexible to allow relative bending between the retaining elements 102 and 103, i.e. bending of the bone plate, while at the same time having a tensile strength that ensures the structural integrity of the bone plate during the tension-flexion phase.

[0048] The flexion of the bone plate accommodates relative rotation of the individual planes of the retention elements 102 and 103, thereby allowing the fixation screws to be angled to support the angular variations that occur during bone growth, providing improved tolerance of the implant in epiphysiodesis.

[0049] In particular, the flexible central portion 106 allows a wide range of angular opening of the retaining elements 102 and 103 of the internal fixation device 101. In this way, the angular variation allowed by the internal fixation device 101 during bone growth in the epiphysiodesis can be further improved.

[0050] The central portion 106 preferably has one through hole 107 configured to allow insertion of a wire guide (not shown) for use with a Kirschner wire for centering the bone plate during implantation in such a way that the central portion precisely traverses the growth plate.

[0051] If one considers the retaining elements 102 and 103, each of them has one respective threaded surface 108 and 109 realized on the inside of the through holes 104 and 105, respectively.

[0052] In particular, preferably, through holes 104 and 105 are substantially cylindrical and threaded surfaces 108 and 109 are the inner sides of the cylindrical holes, in other words, through holes 104 and 105 comprise threaded cylindrical holes extending coaxially with inlet and outlet diameters that are approximately equal to one another.

[0053] As will be further explained, such threaded surfaces 108 and 109 are configured to mate with corresponding threaded surfaces of respective fixation screws to achieve an implant structure.

[0054] In particular, the through holes 104 and 105 and the threaded surfaces 108 and 109 are configured so that the fixation screws always remain flush with respect to a plane encompassing the bend angle and the axis of each fixation screw remains substantially perpendicular to the respective retaining element 102 or 103.

[0055] In FIG. 2, the fixation device 101 is seen in an exploded configuration to appreciate the particular embodiment of the flexible central portion 106 .

[0056] In this embodiment, the flexible central portion has four elastic elements 201a, 201b, 202a, 202b arranged in pairs between each other to restrain the retaining elements 102 and 103. In other possible embodiments, a different number of elastic elements can be provided, for example one single pair.

[0057] The elastic elements 201a, 201b, 202a, 202b comprise metal wires or cables that are restrained at each end to one of the retaining elements 102 and 103 respectively.

[0058] The number of metal wires or cables, their size and construction can be calibrated according to the bending elasticity and tensile strength desired for the bone plate.

[0059] The restraint or blocking of the wires in the retaining elements can be obtained by welding, plastic deformation (crimping) or other mechanical restraint. In particular, the restraint in the retaining elements occurs by threading the metal wires or cables inside suitable holes 203 realized tangentially in the retaining elements 102 and 103.

[0060] In general, the term "wire" refers to an elongated, wire-like element of any cross-section, but preferably circular; such a "wire" can be made of a uniform and solid material or of material arranged in strands or other composite configurations.

[0061] In general, the term "cable" refers to an elongated wire-like element, preferably having a circular cross-section, made of a uniform material or of material arranged as strands, in particular of a metallic or non-metallic material.

[0062] Preferably, the elastic elements 201 a , 201 b , 202 a , 202 b are arranged symmetrically with respect to the longitudinal axis of the fixation device 101 , ie a longitudinal axis ideally connecting the centres of the holes 104 and 105 .

[0063] Thus, the elastic elements 201a, 201b, 202a, 202b represent one particular embodiment of the flexible central portion 106 already described.

[0064] FIG. 3 illustrates one embodiment of a fixation screw 301 that is particularly configured for use with a bone plate internal fixation system according to the present invention.

[0065] The fixation screw 301 is preferably constructed from a rigid, biocompatible material (eg, titanium).

[0066] The fixation screw 301 has a threaded stem 302, preferably including a triangular profile thread. The fixation screw 301 further has a tip 303, preferably of the self-tapping type. The fixation screw 301 further has a head 304, which is provided with a thread on its external cylindrical surface. The head 304 is provided with suitable grasping means 305, for example a hexagonal hole, for screwing the fixation screw 301 into a bone.

[0067] The head threads 304 are configured to mate with the threaded surfaces 108 and 109 of a correspondingly threaded internal fixation device to provide an implant structure.

[0068] Preferably, the threaded surfaces 108 and 109, and therefore the corresponding head threads 304, also provide a two-start thread, simplifying screw tightening during implant application and allowing advancement equal to the pitch of the threads on the stem 302.

[0069] Preferably, the threads of the stem 302 of the fixation screw 301 have a different thread pitch than the thread pitch of the surfaces 108 and 109, which further contributes to simplifying the application of the implant. In particular, the threads of the stem 302 have a double pitch compared to the thread pitch 304 in order to allow proper advancement and more accurate application in the final screwing section when the head threads 304 engage with the threads 108 or 109 of the bone plate.

[0070] 4 shows an implant for epiphyseal fixation according to the invention, i.e. an assembled kit with a pair of fixation screws 301 and a bone plate internal fixation device 101. The fixation screws are applied via the threads of the head 304 to the threads 108 and 109 in the through holes 104 and 105 of the retaining elements 102 and 103, respectively.

[0071] Thus, by means of the fixation screw 301, the retaining elements 102 and 103 are configured to be fixed, respectively, via assembly screws to the epiphysis and metaphysis of a long bone of a pediatric patient, e.g., a bone having an angular deformity that is to be corrected by application of the fixation device 101.

[0072] The central portion 106 being flexible allows the stem of the screw 301 to be angulated and is well tolerated by the patient even during different phases of bone growth.

[0073] As described above, the bone plate internal fixation device 101 is configured such that each of the fixation screws 301 always remains flush with respect to the plane of its respective retaining element 102 or 103, thereby avoiding undesirable stress on the internal fixation device 101 and improving the tolerability of the implant.

[0074] Thus, the threaded surfaces 108 and 109 of the retaining elements 102 and 103 are configured to rigidly constrain each of the retaining elements 102 and 103 with the respective fixation screws 301 , thereby achieving a bone plate assembly that is flexible only at the central portion 106 .

[0075] The threaded connection between the head of the fixation screw 301 and the retaining elements 102, 103 makes it possible to obtain improved constraint, so that the internal fixation device 101 can be implanted with greater precision and is structurally more stable.

[0076] As can be seen in Fig. 4, the presence of threaded surfaces of the through holes of the retaining elements 102 and 103 allows a connection between the head of the fixation screw 301 and the bone plate 101 without protruding parts and with a small obstruction in terms of height. Indeed, according to the invention, it is not necessary for the fixation screw 301 to "butt" the bottom head surface of the retaining element, but it is sufficient that the respective threads of the screw head and the through hole engage each other to achieve a stable assembly.

[0077] Thus, the internal fixation device according to the invention is more tolerable, especially when the implant is applied in an anatomical area that is poorly covered by soft tissue.

[0078] Additionally, the structure of the internal fixation device 101 with threaded surface holes is generally more robust and adapted to withstand the stresses in epiphysiodesis applications.

[0079] As can be seen in Fig. 4, in order to improve tolerability, the internal fixation device has a raised central portion 106 that is raised with respect to the bottom surface 401 of the retaining elements 102 and 103 and is arranged to be placed in contact with the bone surface, thus limiting the pressure on the bone physis and thus avoiding lateral crushing of the bone plate.

[0080] In other words, the internal fixation device 101 is substantially flat, but the central portion 106 is elevated relative to the bottom surface 401 of the retaining elements 102 and 103 that is configured to face towards the stem of the fixation screw 301. This makes it possible to limit pressure on the bone ends.

[0081] With reference to the example of FIG. 5, a second embodiment of a bone plate internal fixation device 501 is shown diagrammatically.

[0082] The internal fixation device 501 has one first retention element 502 and one second retention element 503, each having a respective through hole 504 and 505, similar to the elements already described with reference to the internal fixation device 101.

[0083] Central portion 506 structurally connects and constrains retaining elements 502 and 503 between one another and is flexible to allow bending of the bone plate.

[0084] Central portion 506 preferably has one central through hole 507 configured to allow insertion of a wire guide (not shown) for use with Kirschner wires.

[0085] The through holes 504 and 505 of the retaining elements 502 and 503 each have one threaded surface 508 and 509, respectively.

[0086] Such threaded surfaces 508 and 509 are configured to mate with corresponding surfaces on the head of the fixation screw 301 in a similar manner as described with reference to the internal fixation device 101 .

[0087] Central portion 506 has a pair of bridge elements 501a and 501b made from a flexible plastic material separated from each other by a through hole 507. In an alternative embodiment, central hole 507 may be omitted resulting in a single bridge element.

[0088] Generally, the pair of bridge elements 501 a and 501 b are constructed of a flexible plastic material and are symmetrically positioned about the longitudinal axis of the internal fixation device 501 .

[0089] A typical plastic material with suitable resistance and biocompatibility properties is polyether-ether-ketone (PEEK).

[0090] Preferably, the retaining elements 502 and 503 are also made from a plastic material, more preferably made in one single mould in one piece with the bridge elements 501a and 501b.

[0091] Advantageously, plastic material elements can be more easily obtained by moulding processes, making these embodiments cheaper than those including metallic material elements.

[0092] Furthermore, the plastic material parts, in addition to being radiolucent and biocompatible, also ensure adequate mechanical strength and elasticity.

[0093] In an alternative embodiment, the retaining elements 502 and 503 may be made of a metallic material connected to the bridge element by suitable joints.

[0094] Thus, embodiments of the fixation device 501 may envisage different elements for providing a flexible central portion 506 while at the same time keeping the functionality of the bone plate unchanged with respect to that already described for the fixation device 101.

[0095] 6 shows the fixation device 501 from below. In this view, the central portion 506 has a recess 601 on its bottom surface, which allows the central portion 506 to be further elevated and create one preferred bending axis of the plate 501. The elevated central portion 506 is thus further adapted to limit pressure on the bone ends when the fixation device 501 is implanted.

[0096] With reference to the example of FIG. 7, a third embodiment of a bone plate internal fixation device 701 is shown diagrammatically.

[0097] The internal fixation device 701 has one first retaining element 702 and one second retaining element 703 with respective through holes 704 and 705. A central portion 706 structurally connects and constrains the retaining elements 702 and 703 between each other and is flexible to allow bending of the bone plate. The central portion 706 preferably has one central through hole 707 configured to allow direct passage of a Kirschner wire, preferably without the aid of a guide wire.

[0098] The through holes 704 and 705 of the retaining elements 702 and 703 each have one respective threaded surface 708 and 709. Such threaded surfaces 708 and 709 are configured to mate with corresponding surfaces of the head of the fixation screw 301, similar to that described with reference to the internal fixation device 101.

[0099] The central portion 706 has a pair of bridge elements 710a and 710b that implement, among other things, the geometry of the through-hole 707. Generally, the bridge elements 710a and 710b are symmetrically disposed about the longitudinal axis of the internal fixation device 701.

[0100] Thus, embodiment of fixation device 701 is distinct from fixation devices 101 or 501 due to the different support structure.

[0101] 8, the partially disassembled fixation device 701 has one support frame 801 made of one piece of plastic material, which allows for perimetric portions 802 and 803 that are part of the structure of each of the retention elements, whereby the retention elements' perimetric portions 802 and 803 together with the bridge elements 710a and 710b are made in one piece.

[0102] The support frame 801 is associated with a pair of annular elements 804 and 805 which can be embedded in the peripheral portions 802 and 803, respectively.

[0103] Annular elements 804 and 805 are preferably made from a stronger material, such as a metallic material, and include threaded surfaces 708 and 709 as previously described.

[0104] This results in a threaded connection between the screw 301 and the threaded surfaces 708 , 709 of the annular elements 804 , 805 , which is structurally more robust and leaves the frame 801 with the task of contributing to the flexibility of the central portion 706 .

[0105] The fixing device 701 thus obtained makes it possible to improve size tolerances and mounting quality, while leaving unchanged the optimal functionality described above.

[0106] The engraftment of the annular elements 804 and 805 in their respective seats obtained in the peripheral portions 802 and 803 preferably occurs through suitably knurled surfaces to avoid undesired rotation of the annular elements subjected to the tightening torque of the fixing screw 301.

[0107] Figure 9 shows the fixation device 701 seen from below. In this view it can be seen that the central part 706 has one recess 901 on its bottom surface, which allows the central part 706 to be further elevated. Thus, as already explained, the elevated central part 706 limits the pressure on the bone ends.

[0108] Generally, it is possible to see how in all embodiments the internal fixation device advantageously has a rounded lower periphery and a higher periphery for better tolerance.

[0109] In particular, generally, the embodiments provide a bone plate internal fixation device that is substantially flat and has an oblong shape without narrowing, and in this sense, the embodiments described herein differ from the typical "eight plates" known in the art.

[0110] The flexible central part of the internal fixation device according to the invention provides a member such as an elastic or bridging element that is arranged tangentially to the circumference of the retaining element, thereby ensuring adequate flexibility of the bone plate but providing improved mechanical stability. Furthermore, the non-constricting oblong shape of the part allows improved manipulation by the surgeon during application of the implant.

[0111] In conclusion, with reference to FIG. 4, the use of the bone plate internal fixation device of the present invention is comprehensively described.

[0112] Once a relatively atraumatic incision has been made in the skin and flesh of the patient for implantation, the fixation device 101 is positioned across the physis such that the two retention elements 102 and 103 are in contact with the epiphysis and metaphysis, respectively, of the bone to be treated.

[0113] A fixation wire, inserted through a central through-hole in the flexible central portion 106 into the physis cartilage, allows the fixation device 101 to be held in place, albeit temporarily.

[0114] The fixation screw 301 is first inserted into the through hole so that it penetrates corresponding portions of the epiphysis and metaphysis of the bone until the head 304 reaches and engages the threaded surfaces of the through hole.

[0115] During epiphyseal tissue growth, the fixation screw 301 undergoes a dragging action which determines the angular opening, i.e. the tension and bending of the bone plate of the internal fixation device 101 throughout the treatment.

[0116] Allowing the bone plate 101 to flex also allows for angulation of the fixation screws 301, following bone growth throughout the healing period.

[0117] Advantageously, the bone plate internal fixation device according to the invention has a flat conformation and a uniform thickness without protrusions in order to avoid areas of friction with the soft tissue surrounding the implant.

[0118] At the same time, advantageously, the bone plate internal fixation device of the present invention provides increased structural stability due to the constraint between the threaded surface of the through hole and the screw head, thereby improving the implant's performance and ability to follow curvature variations due to bone growth.

[0119] Advantageously, the configuration of the fixing device is adapted to have a rational structure and to be manufactured with qualitatively good tolerances.

[0120] The bone plate according to the invention solves the technical problem and achieves several advantages, among them ensuring complete bone deformity correction by one epiphysiodesis.

[0121] The following additional note is added: (Appendix 1) A bone plate internal fixation device for epiphysial fixation, comprising a pair of retaining elements, each of said retaining elements having a through hole for receiving a respective fixation screw in a bone, said bone plate internal fixation device further comprising a central portion structurally connecting and constraining said retaining elements to each other, said central portion being flexible to allow bending of said bone plate, each of said through holes having a threaded surface adapted to mate with a corresponding surface of said respective fixation screw, said retaining elements and said central portion being provided as a composite structure. Bone plate internal fixation device. (Note 2) The threaded surface is configured to rigidly constrain each of the retaining elements with a respective fixation screw, providing a bone plate that is flexible only at the central portion. 2. The bone plate internal fixation device of claim 1. (Appendix 3) The through hole is substantially cylindrical, and the threaded surface is an inner side surface of the substantially cylindrical through hole; 3. The bone plate internal fixation device of claim 1 or 2. (Appendix 4) The central portion of the composite structure has at least one bridge element made of a flexible plastic material. 4. The bone plate internal fixation device of any one of claims 1 to 3. (Appendix 5) The central portion of the composite structure has at least one pair of bridge elements made of a flexible plastic material and arranged symmetrically with respect to a longitudinal axis of the bone plate internal fixation device. 5. The bone plate internal fixation device of claim 4. (Addendum 6) Each peripheral portion of the central portion of the composite structure is made of a flexible plastic material made in one piece with the at least one pair of bridge elements, and further has a pair of annular elements of a metal material, each of the annular elements being coupled to a respective one of the peripheral portions, each of the annular elements having the threaded surface. 6. The bone plate internal fixation device of claim 4 or 5. (Appendix 7) The central portion of the composite structure has a plurality of elastic elements, the elastic elements having at least one pair, preferably two pairs of metal wires or cables, each of which is constrained at its own end with each of the retaining elements of the composite structure. 4. The bone plate internal fixation device of any one of claims 1 to 3. (Appendix 8) The elastic elements are arranged symmetrically with respect to the longitudinal axis of the bone plate internal fixation device. 8. The bone plate internal fixation device of claim 7. (Appendix 9) The bone plate internal fixation device is substantially flat with an oblong shape without narrowing, and the central portion of the composite structure has members arranged tangentially to the periphery of the retaining element. 9. The bone plate internal fixation device of any one of claims 1 to 8. (Appendix 10) The bone plate internal fixation device is substantially flat, and the central portion of the composite structure is elevated relative to a bottom surface of the retaining element, the bottom surface being configured to face toward the stem of the fixation screw, and the elevated central portion is configured to limit pressure on the bone end. 10. The bone plate internal fixation device of any one of claims 1 to 9. (Supplementary Note 110) The central portion of the composite structure further includes a central through hole configured to allow passage of a guide wire for temporary fixation of the bone plate internal fixation device. 11. The bone plate internal fixation device of any one of claims 1 to 10. (Appendix 12) The threaded surface has a double thread. 12. The bone plate internal fixation device of any one of claims 1 to 11. (Supplementary Note 13) At least a portion of the retaining element and the central portion are initially provided as separate components of the internal fixation device, which are connected to form the composite structure. 13. The bone plate internal fixation device of any one of claims 1 to 12. (Appendix 14) A bone-epiphyseal fixation kit comprising the bone plate internal fixation device according to any one of claims 1 to 13, further comprising at least two fixation screws for a bone, each of the two fixation screws having a head threaded on its outer surface, the head being configured to engage with the threaded surface of the respective through hole. Epiphysial fixation kit. (Appendix 15) The fixing screws each have a respective threaded stem having a pitch different from, and preferably larger than, the pitch of the threaded surface of each of the through holes; 15. The epiphysis fixation kit of claim 14.

Claims

1. 1. A bone plate internal fixation device for epiphyseal fixation comprising a pair of retaining elements, each of said retaining elements having a through hole configured to receive a respective fixation screw into a bone, said bone plate internal fixation device further comprising a central portion structurally connecting and constraining said retaining elements to each other such that ends of said central portion are constrained by said retaining elements; the central portion is flexible to allow bending of the bone plate internal fixation device and angular opening of the retaining elements during bone growth in the epiphysiodesis to allow relative bending between the retaining elements; the set screws in the through holes always remain in a first plane, the first plane being coplanar with a second plane that encompasses the bending angle between the set screws, and the first axis of each set screw remains parallel to the second axis of the through hole of each of the retaining elements; Bone plate internal fixation device.

2. The central portion has at least one bridge element made of a flexible plastic material.

2. The bone plate internal fixation device of claim 1.

3. The flexible plastic material is polyether-ether-ketone (PEEK); 3. The bone plate internal fixation device of claim 2.

4. The holding element is made of a plastic material.

3. The bone plate internal fixation device of claim 2.

5. the retaining element is made in one piece with the at least one bridge element, and the retaining element and the at least one bridge element are made in one single mold.

5. The bone plate internal fixation device of claim 4.

6. The bending of the bone plate internal fixation device corresponds to a relative rotation in the respective plane of the retaining elements, the retaining elements being adapted to allow the fixation screws to form an angle.

6. A bone plate internal fixation device according to any one of the preceding claims.

7. The bending of the bone plate internal fixation device further allows for angular expansion of the fixation screws as the patient grows.

6. A bone plate internal fixation device according to any one of the preceding claims.

8. the bone plate internal fixation device is flat, the central portion is elevated relative to a bottom surface of the retaining element, the bottom surface being configured to face towards the stem of the fixation screw, and the elevated central portion is configured to limit pressure on the bone epiphysis; 6. A bone plate internal fixation device according to any one of the preceding claims.

9. the central portion further comprises a recess in the bottom surface, the recess allowing the central portion to be elevated further and to generate one bending axis of the bone plate internal fixation device.

9. The bone plate internal fixation device of claim 8.

10. the retaining element and the central portion are provided as a composite structure made of at least two different materials between the retaining element and the central portion, the central portion of the composite structure having at least one bridge element made of a flexible plastic material; 6. A bone plate internal fixation device according to any one of the preceding claims.

11. the central portion of the composite structure has at least one pair of bridge elements made of a flexible plastic material and arranged symmetrically with respect to a longitudinal axis of the bone plate internal fixation device; 11. The bone plate internal fixation device of claim 10.

12. a peripheral portion of each of the retaining elements of the composite structure is made of a flexible plastic material made in one piece with the at least one bridge element, and further comprises a pair of annular elements of a metal material, each of the annular elements being coupled to a respective one of the peripheral portions, each of the annular elements having a threaded surface; 11. The bone plate internal fixation device of claim 10.

13. the bone plate internal fixation device is flat with an elongated shape without narrowing, and the central portion of the composite structure has members arranged tangentially to the periphery of the retaining element; 11. The bone plate internal fixation device of claim 10.

14. each said through hole having a threaded surface adapted to mate with a corresponding surface of a respective said fixation screw, said threaded surface being configured to capture each of said retention elements with a respective said fixation screw and provide flexibility to the bone plate of said bone plate internal fixation device only at said central portion; 6. A bone plate internal fixation device according to any one of the preceding claims.

15. the through hole is cylindrical and the threaded surface is an inner side of the through hole; 15. The bone plate internal fixation device of claim 14.

16. the central portion further comprising a central through hole configured to allow passage of a guide wire for temporary fixation of the bone plate internal fixation device.

6. A bone plate internal fixation device according to any one of the preceding claims.

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