Shoulder prosthesis baseplate with compression screw

Abstract

A shoulder prosthesis baseplate (100) comprises a through hole (102) for a compression screw (101), the through hole (102) having a circular profile portion and including a protruding edge (106) disposed within the through hole (102) perpendicular to an axis (102') of the through hole (102), the protruding edge (106) configured to axially retain the head (103) of the compression screw (101) inserted into the through hole (102). The protruding edge (106) has an arcuate shape and defines a corresponding free portion (108) of the circular profile portion within the through hole (102), the free portion (108) configured to allow the threaded stem (104) of the compression screw (101) to pass over the protruding edge (106).

Description

[Technical Field]

[0001] The present invention relates to a shoulder prosthesis base plate with a through hole for a compression screw. The present invention also relates to a bone anchor assembly with a shoulder prosthesis base plate and a compression screw. [Background technology]

[0002] The use of compression screws is a very common practice in shoulder prosthesis baseplates. The presence of a central compression screw can significantly increase the primary stability of the implant and reduce the relative micromotion between the shoulder prosthesis baseplate and the bone interface, thereby reducing the likelihood of premature implant mobilization or fracture.

[0003] In this context, there is a need to have compression screws at disposal of different lengths, depending on the bone anatomy of the individual patient and possibly different diameters, required for adequate stability.

[0004] While the choice of providing screws of different lengths does not affect the dimensions and geometry of the prosthetic shoulder baseplate, difficulties arise when screws of various thread diameters are required: the diameter of the screw thread is actually constrained by the diameter of the through-hole in the prosthetic shoulder baseplate through which the screw must pass.

[0005] Screws with different thread diameters, typically increasing in diameter, may be required depending on the bone quality of the individual patient, depending on the surgeon's tactile feedback, or if it is decided to use a thread type for cancellous bone with an increased screw diameter rather than a thread for cortical bone.

[0006] In the specific case of glenoid prosthesis shoulder baseplates, the choice is made to use central compression screws with increased diameter (e.g., φ6.0 mm or φ6.5 mm) compared to the usual crush, which is often necessary from the perspective of bone preservation and to accommodate the morphological limitations associated with the joint anatomy of having a baseplate pin with a small diameter size.

[0007] In this context, the prior art proposes several solutions for using a central compression screw with an increased diameter associated with an appropriately configured glenoid baseplate.

[0008] Document US2020289180A1 refers to a bone anchor base with a protrusion belonging to an artificial joint. The protrusion has an opening at its distal free end, and a screw is engaged via the protrusion and configured to be screwed into a spongy part of the bone through the opening. The opening is threaded with the same pitch as the screw thread, and the diameter of the distal wall allows the screw to be placed therein more than half a turn, so that during positioning of the screw, the screw thread engages with the distal wall.

[0009] Document EP3598957A1 shows a prosthetic shoulder implant with a base plate or metagrein configured to be connected to the pelvis. A through-hole is provided for the insertion of a central bone screw, accommodating the maximum screw diameter. A pin extends distally and provides a threaded portion configured to support and retain the head of the screw.

[0010] Prior art solutions that provide a threaded portion of the base plate with a true helical fit between the screw and the base plate require that the threads of the exit hole correspond to the geometry of the threads of the central screw, which in effect are made into the pin.

[0011] This threading of the exit hole can be difficult to manufacture in the context of the production of certain shoulder prosthesis baseplates.

[0012] This threading of the outlet hole allows the use of only one type of enlarged central screw, and the threading of the threaded stem corresponds to the geometry of the threaded form. For example, if the diameters are equal, different thread pitches could not be used.

[0013] Prior art solutions are not entirely effective and therefore can be improved. Summary of the Invention

[0014] An object of the present invention is to allow for the insertion of increased diameter compression screws into a shoulder prosthesis baseplate without significantly affecting the dimensions of the hole or central pin.

[0015] A further object of the present invention is to allow compatibility between a shoulder prosthesis baseplate and further modular products already developed for the same connection area.

[0016] A further object of the present invention is to allow for more efficient manufacturing in the context of manufacturing shoulder prosthesis baseplates.

[0017] It is a further object of the present invention to provide a shoulder prosthesis baseplate that is adapted to more flexibly accommodate a variety of screws having different and even increased thread sizes.

[0018] It is a further object of the present invention to provide a prosthetic shoulder baseplate having structural and functional features that enable it to overcome the shortcomings of the prior art.

[0019] The solution underlying the present invention is to provide for the passage of a compression screw through an outlet hole having a shaped slot that is only locally larger in diameter than the thread through which it passes, while in other parts it has a diameter smaller than the outer diameter of the thread and is shaped to hold the head of the compression screw. In particular, the larger diameter of the slot is preferably an arc of less than 180°.

[0020] Based on the above solution, the present invention provides a shoulder prosthesis base plate including a through-hole for a compression screw. The through-hole has a circular profile portion and a protruding edge disposed within the through-hole perpendicular to the axis of the through-hole. The protruding edge is configured to axially hold the head of a compression screw inserted into the through-hole. The protruding edge has an arc shape and defines a corresponding free portion of the circular profile portion within the through-hole. The free portion is configured to allow the threaded stem of the compression screw to pass over the protruding edge.

[0021] Based on the above solution, the present invention also provides a bone anchor assembly including a shoulder prosthesis base plate and a compression screw inserted into the through-hole, the compression screw having a head configured to abut against the protruding rim and thus be axially held in the through-hole, and a threaded stem having a thread diameter and a thread pitch, the threaded stem allowing a screwing trajectory in the free portion to clear the protruding rim of the through-hole.

[0022] Advantageously, the present invention does not require any threaded portion of the outlet hole, but the trajectory of the compression screw is based on the presence of a free portion, opening along an arc sufficient for the trajectory of the screw.

[0023] Preferably, the protruding edge has a substantially flat, non-helical shape.

[0024] Advantageously, the present invention does not require any helical shaping of the through-hole, but simply a slot, which is easier and less complicated to make.

[0025] In a preferred embodiment, the prosthetic shoulder baseplate has a central pin. The application of the present invention to a prosthetic shoulder baseplate with a central pin has the advantage that different types of central compression screws can be used, even if they are of increased diameter (closer to the through-hole), without changing the dimensions of the pin and without affecting the overall geometry of the prosthetic shoulder baseplate.

[0026] Advantageously, the present invention allows for greater flexibility in using compression screws of various thread diameters in components of a modular system of shoulder prostheses having a shoulder prosthesis baseplate.

[0027] Further features and advantages of the invention will become apparent from the following detailed description of embodiments given by way of non-limiting illustration and from the claims, which form an integral part of this description. [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 1 illustrates an exemplary embodiment of a shoulder prosthesis baseplate. [Figure 2] FIG. 2 shows a shoulder prosthesis baseplate with a central compression screw inserted into a through hole according to a known solution. [Figure 3] FIG. 3 illustrates application of the shoulder prosthesis baseplate of FIG. 1 to a patient's scapula. [Figure 4] FIG. 4 shows a cross-sectional view of a shoulder prosthesis baseplate according to the present invention with a first compression screw inserted into the through hole. [Figure 5] FIG. 5 illustrates a cross-sectional view of the shoulder prosthesis baseplate of FIG. 4 with a different second compression screw inserted through the through hole. [Figure 6] FIG. 6 shows a top view of a shoulder prosthesis baseplate according to the present invention. [Figure 7] FIG. 7 illustrates a top view of the through-hole geometry of a shoulder prosthesis baseplate in accordance with the present invention. [Figure 8] FIG. 8 illustrates a cross-sectional view of the through-hole geometry of a shoulder prosthesis baseplate in accordance with the present invention. [Figure 9] FIG. 9 illustrates the passage of a compression screw over a protruding edge in a shoulder prosthesis baseplate according to the present invention. [Figure 10] FIG. 10 illustrates a compression screw abutting a protruding edge on a shoulder prosthesis baseplate according to the present invention. [Figure 11] FIG. 11 illustrates an exemplary embodiment of a shoulder prosthesis baseplate with associated arthrodesis pins. DETAILED DESCRIPTION OF THE INVENTION

[0029] In different figures, similar elements are designated by similar reference numerals. Often, when one figure contains more similar elements, for the purpose of improving readability, only one or some of them will be designated by the respective reference numeral, and the others will also be restricted to be included in the discussion.

[0030] 1 illustrates an exemplary embodiment of a shoulder prosthesis baseplate 100. The baseplate 100 is an example of a reverse shoulder prosthesis, but may alternatively be for an anatomical shoulder prosthesis.

[0031] In general, the present invention is applicable to other types of shoulder prosthesis baseplates, such as different elements of a prosthesis, in particular different elements of a modular prosthesis, or plates for osteosynthesis. The embodiment of baseplate 100 referenced below is therefore intended as a preferred but non-limiting embodiment.

[0032] Generally, the shoulder prosthesis base plate or baseplate 100 includes through holes for compression screws 101, which function to penetrate the bone surface and provide anchors, as will be further described.

[0033] Instead, FIG. 2 shows a shoulder prosthesis baseplate 10 having a central compression screw 11 inserted into a through-hole 12 made in accordance with an overall prior art solution and is provided here to better illustrate the technical constraints involved with possible variations in the thread diameter of the compression screw associated with the baseplate 10.

[0034] The base plate 10 and compression screw 11 are optimized to maintain a small size due to the central pin 13 protruding from the base plate 10. In general, the shoulder prosthesis illustrated herein provides a connector 14, an assembly screw 15, and a ball 16.

[0035] Returning to the compression screw 11, it should be noted that the maximum diameter of the stem thread and the diameter of the screw head are strictly constrained by the dimensions of the circular hole 17 of the pin in the base plate 10. In fact, to ensure proper tracking of the threaded stem of the screw 11, which may have a diameter of, for example, 5.0 mm, a larger diameter circular hole 17 is provided, e.g., 5.3 mm. The head of the screw must have a diameter large enough to be retained by the recess defined in the circular hole 17, e.g., 6.3 mm. This diameter of the head of the screw 11, in turn, dictates the minimum dimension of the channel defined by the through hole 12, which may have a diameter of, for example, 6.5 mm.

[0036] From obvious geometrical considerations, it can be seen that the geometry of the base plate 10 in the example of the prior art solution makes it impossible to use screws of increased size, with a maximum diameter of the stem thread larger than the diameter of the circular hole 17; for example, when the diameter of the circular hole is φ5.3 mm, it is clearly impossible to implement a threaded stem with a diameter of φ6.0 mm or φ6.5 mm.

[0037] To accommodate screws with threaded stems of diameter 6.0 mm, it may be necessary to enlarge all diameters, for example by creating circular holes 17 with a diameter of 6.4 mm, in order to assume a different structure of the base plate 10, but this would also result in an increase in the outer diameter of the pins of the base plate 10, for example to 10.4 mm, while maintaining the minimum thickness necessary for the structural strength of the prosthetic element.

[0038] It is understood that a possible enlargement of the hole dimensions not only entails dimensional deformation (for example, the pins would have to be enlarged, which can only be carried out for base plates of larger dimensions, but which may interfere with the transverse holes, especially in the case of base plates of smaller diameter), but also affects all subsequently embedded modular components, for example by connecting the assembly screws 15 with threads M7, which must be modified in the case of enlarging the pins of the base plate 10, thereby making the modular elements incompatible between the various versions of the base plate 10.

[0039] FIG. 3 illustrates the application of a base plate 100 to a patient's scapula with fixation provided by a compression screw 101 .

[0040] As already mentioned, the presence of the central compression screw 101 allows for primary stability of the implant and reduces relative micromotion between the baseplate 100 and the bone interface.

[0041] To obtain better fixation, the surgeon may also select compression screws 101 of different lengths and different diameters depending on the bone surface available in the individual patient.

[0042] The compression screw 101 with different threads, typically of larger diameter, is actually required depending on the bone quality of the individual patient, depending on the surgeon's tactile feedback, or if it is decided to use a type of screw for cancellous bone with a larger thread diameter rather than a thread for cortical bone.

[0043] 4 and 5 show cross-sectional views of the same shoulder prosthesis base plate 100 or base plate 100 associated with a first compression screw 101a or a second compression screw 101b inserted into a through hole 102.

[0044] It should be noted that the axis of the through hole 102 generally corresponds to the insertion axis of the compression screw 101a or 101b.

[0045] Although not drawn to scale, Figures 4 and 5 reveal that the first compression screw 101a has the same diameter of head 103 as the head 103 of the second compression screw 101b, but the diameter of threaded stem 104a is smaller than the diameter of threaded stem 104b of the second compression screw 101b.

[0046] For example, threaded stem 104a has a maximum diameter of φ5.0 mm, while threaded stem 104b has a maximum diameter of φ6.3 mm.

[0047] As mentioned above, the base plate 100 has a protruding central pin 105, and the through-hole 102 is also provided inside the central pin 105.

[0048] The through-hole 102 has a circular profile, ie, is shaped as a substantially circle.

[0049] As will be explained further, the base plate 100 includes a protruding lip 106 on the inside of the through-hole 102. In a preferred embodiment, such protruding lip 106 is located at an intermediate position inside the through-hole 102, i.e., axially recessed relative to the end 105' of the central pin 105. In this way, the central pin 105 is housed more proximal to the screw head 103, making it not only more accessible from the top of the base plate 100 but also better protected during implantation.

[0050] Preferably, the base plate 100 further comprises a plurality of peripheral through-holes 107 configured to accommodate additional fixation screws (not shown), in particular angular stabilization screws.

[0051] FIG. 6 shows a top view of the base plate 100, making the through holes 102 for the compression screws clearly visible.

[0052] The through hole 102 comprises a protruding lip 106 disposed inside the through hole 102 perpendicular to the axis 102' of the through hole 102.

[0053] The protruding lip 106 is configured to axially retain the head 103 of the compression screw 101 inserted into the through hole, as previously described in connection with FIGS.

[0054] As can be seen in FIG. 6, the protruding edge 106 has an arc shape, i.e., is curved as an arc of a circumference.

[0055] The protruding edge 106 also defines a corresponding free portion 108 inside the through hole 102. The corresponding free portion 108 is also located in the circular profile portion of the through hole 102.

[0056] As will be further explained, the free portion 108 is configured to allow the threading trajectory of the threaded stem 104 of the compression screw 101 to pass over such protruding edge 106 .

[0057] FIG. 7 shows a top view of the geometric shape of the through-hole 102, in which the arcuate shape of the protruding edge 106 is visible, as mentioned above, which defines a corresponding free portion 108 inside said through-hole 102.

[0058] The free portion 108 extends in a second circular arc having a central angle α governing it, the central angle α being less than 180°, preferably greater than 90°, and more preferably equal to 155°. These values of the central angle α are intended to allow stable accommodation of different screws with different maximum thread diameters.

[0059] FIG. 8 illustrates a cross-sectional view of the geometry of the through-hole 102, in which it can be seen that the protruding edge 106 has a generally flat and non-helical shape that remains perpendicular to the axis 102' of the through-hole 102.

[0060] Figure 9 illustrates the passage of the compression screw 101 over the protruding edge 106 of the through hole 102. Figure 10 instead illustrates the compression screw 101 abutting the protruding edge 106. In such a view, there is an enlarged box highlighted with a dashed line.

[0061] The bone anchor assembly 100, 101 includes a shoulder prosthesis base plate 100, or base plate 100, as previously described, and a compression screw 101, as previously described.

[0062] As previously described, the compression screw 101 is inserted into the through hole 102. The head 103 of the screw is configured to abut against the protruding lip 106 to be axially retained in the through hole 102 when fully inserted.

[0063] The compression screw comprises a threaded stem 104 having a thread diameter and thread pitch to allow a threading trajectory in a free portion 108 defined by the protruding edge 106 to extend beyond the protruding edge 106 .

[0064] Thus, a compression screw 101 having an increased maximum thread diameter can be secured into the bone beyond the protruding edge 106 while still being axially retained in the through hole 102 to provide fixation to the base plate 100.

[0065] Very advantageous geometric proportions of the elements of the base plate 100 can be defined as follows:

[0066] The first inner diameter defined by the protruding lip 106 is smaller than the second inner diameter defined by the through hole 102 .

[0067] The maximum diameter defined by the threaded stem 104 is greater than the first inner diameter defined by the protruding lip 106 and at the same time is less than the second inner diameter defined by the through-hole 102 .

[0068] The third diameter defined by the head 103 of the compression screw 101 is larger than the first inner diameter defined by the protruding rim 106, such that the head 103 is configured to abut against the protruding rim 106, as shown in FIG. 10.

[0069] The fourth diameter defined by the free portion 108 is larger than the first inner diameter defined by the protruding edge 106. Preferably, the fourth diameter defined by the free portion 108 corresponds to the second inner diameter defined by the through hole 102, i.e., the lateral walls of the through hole 102 are neither elevated nor hollow in the free portion 108. The fourth diameter defined by the free portion 108 is related to a circular arc that locally fits the outer contour of the free portion 108, outside which the protruding edge 106 is located, as can be clearly seen in FIG. 7. The axial thickness S of the protruding edge 106 is smaller than the minimum or nominal thread pitch P of the threaded stem 104, so that the threading path of the threaded stem 104 in the free portion 108 exceeds the protruding edge 106.

[0070] Preferably, the protruding edge 106 is tapered towards the through hole 102 at least in the area configured to abut the head 103 of the compression screw 101 .

[0071] Generally, for a given compression screw 101 defined by the thread geometry (thread pitch, thread diameter, core diameter), there are several combinations of protruding edges 106 of increased diameter and thickness that fit with the screw head 103 and allow the compression screw 101, when threaded, to pass over the protruding edges 106 while avoiding any interference.

[0072] Similarly, for a given protruding edge 106 defined by its geometry (increased diameter of the free portion 108, edge thickness, extension), there are several geometries of the compression screw threads that fit in terms of the threading trajectory that passes through the protruding edge 106 while avoiding any interference.

[0073] In a specific example of the central pin 105, a compression screw 101 with a threaded stem 104 was developed that has a maximum diameter of φ6.3 mm and can pass through the inside of the through hole 102 in the free portion 108 having an angle α of 155° and a thickness S of 1.0 mm.

[0074] The stable axial retention of the abutment and the head 103 of the screw 101 is generally ensured by the fact that the protruding edge is defined along an arc following a central angle greater than 180° equal to 205° (i.e., 360° minus 155°).

[0075] 11 shows an exemplary embodiment of a shoulder prosthesis base plate 100' or base plate 100' with which, next to the compression screw (not shown), an arthrodesis pin 99 may be associated, which is a further element of the modular glenoid prosthesis. Note that in this variant of the base plate 100', the protruding lip 106 is located at a distal position inside the through hole 102, i.e., directly at the end of the central pin 105.

[0076] It will be apparent to those skilled in the art that further implementations and modifications of the present invention are possible to meet particular needs.

[0077] For example, because the compression screw is not constrained to engage a standardized screw hole but is intended to thread into bone, different specific geometries of the compression screw may be provided that will be broadly adapted to allow the threaded stem's threading track to overcome protruding edges and function with multiple threads.

[0078] Therefore, the above-described embodiments should be understood as being provided as non-limiting illustrations.

Claims

1. It has a through hole (102) for a compression screw (101), the through hole (102) has a circular profile and is provided with a protruding edge (106) disposed inside the through hole (102) perpendicular to the axis (102') of the through hole (102); The protruding edge (106) is configured to axially hold the head (103) of the compression screw (101) inserted into the through hole (102); The protruding edge (106) has an arcuate shape and defines a corresponding free portion (108) of the circular profile portion internally relative to the through hole (102); The free portion (108) is configured to allow the threaded stem (104) of the compression screw (101) to thread past the protruding edge (106).

2. The shoulder prosthesis baseplate of claim 1, wherein the protruding edge (106) is substantially flat and has a non-helical shape.

3. 3. The shoulder prosthesis base plate according to claim 1, wherein the free portion (108) extends in a second arc defined by a central angle (α) smaller than 180°, preferably larger than 90°, more preferably equal to 155°.

4. The shoulder prosthesis baseplate according to any one of claims 1 to 3, wherein the first inner diameter of the protruding edge (106) is smaller than the second inner diameter of the through hole (102).

5. 5. The artificial shoulder joint base plate of claim 4, wherein a maximum diameter of the threaded stem is greater than the first inner diameter of the protruding edge and less than the second inner diameter of the through hole.

6. 6. The artificial shoulder joint base plate according to claim 4, wherein the third diameter of the head portion (103) is larger than the first inner diameter of the protruding edge (106), and the head portion (103) is configured to abut against the protruding edge (106).

7. 7. The artificial shoulder joint base plate according to claim 4, wherein a fourth diameter of the free portion (108) is larger than the first inner diameter of the protruding edge (106) and preferably corresponds to the second inner diameter of the through hole (102).

8. 8. The base plate for a shoulder prosthesis according to claim 4, wherein the axial thickness (S) of the protruding edge (106) is smaller than the thread pitch (P) of the threaded stem (104) of the compression screw (101).

9. 9. The shoulder prosthesis base plate according to claim 1, wherein the protruding edge (106) is tapered relative to the through hole (102) at least in a region configured to abut against the head (103) of the compression screw (101).

10. 10. The artificial shoulder joint base plate according to claim 1, further comprising a central pin (105) protruding from the artificial shoulder joint base plate, the through hole (102) being provided inside the central pin (105).

11. 11. The shoulder prosthesis base plate of claim 10, wherein the protruding edge (106) is located at an intermediate position of the through hole (102) and is axially retracted relative to the end (105') of the central pin (105).

12. 12. The shoulder prosthesis base plate of any one of claims 1 to 11, further comprising a plurality of peripheral through-holes (107), preferably configured to accommodate angular stabilization screws.

13. A shoulder prosthesis base plate (100) according to any one of claims 1 to 12, The bone anchor assembly further comprises a compression screw (101) inserted into the through hole (102), the compression screw (101) having a head (103) configured to abut against the protruding edge (106), the head (103) being axially held in the through hole (102), and the compression screw (101) further comprising a threaded stem (104) having a thread diameter and a thread pitch (P) such that a screwing trajectory in the free portion (108) can exceed the protruding edge (106).

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