Orthopaedic screw for the sacroiliac joint

Abstract

The invention relates to an orthopaedic screw (1) for the sacroiliac joint (71), the screw comprising a core (2) extending between a distal end (1a) and a proximal end (1b), and a first thread (3), wherein the core (1) comprises a central conical portion (21) having a first slope (α1), a distal portion (20) having a second slope (α2) smaller than the first slope (α1), and a proximal portion (22) having a third slope (α3) smaller than the first slope (α1), and wherein the first thread (3) has a height (D) that increases from the proximal end (21b) towards the distal end (21a) of the central conical portion (21), over a retaining portion (210) of the central conical portion (21), so as to enhance screw retention, in particular in osteoporotic bone.

Description

[0001] "Orthopedic screw for the sacroiliac joint"

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] The present invention relates to the field of orthopedic screws. Its application is particularly advantageous in the field of screws for pelvic fractures, and especially for implantation at the sacroiliac joint.

[0004] STATE OF THE ART

[0005] Today, following a pelvic fracture, such as a fragility fracture, surgeons typically use CT scans and then digitally reconstruct the skeleton to select a suitable physical implant. By manipulating the implant digitally in this virtual environment, the surgeon must choose the most appropriate implant based on the type of fracture, the patient's anatomy, and bone quality.

[0006] However, particularly based on pelvic surgery experience with elderly patients with sacral fractures, currently available implants rarely provide complete satisfaction. Post-operatively, secondary implant displacement can occur, for example, due to inadequate fixation in osteoporotic bone.

[0007] Osteoporotic bone is typically less dense internally, while retaining hard outer walls in the cortical areas. Therefore, an orthopedic screw will not grip the internal bone material as well in osteoporotic bones.

[0008] One problem surgeons face is the lack of screws on the European market specifically designed for the bone characteristics of elderly patients. Thus, despite cutting-edge medical equipment (medical imaging, surgical planning tools, augmented reality, etc.) enabling increasingly complex minimally invasive procedures, medical implants tailored to the specific needs of these elderly patients, who are highly susceptible to developing this type of fracture, are unavailable.

[0009] The US2014 / 277193 A1 document describes a screw for the spine having a core with a diameter reduction.

[0010] One object of the present invention is therefore to improve the bony retention of an orthopedic screw, and more particularly at the sacroiliac joint. A more specific objective of the invention is to improve the retention of an orthopedic screw in osteoporotic bones.

[0011] The other objects, features, and advantages of the present invention will become apparent from an examination of the following description and accompanying drawings. It is understood that other advantages may be incorporated.

[0012] SUMMARY OF THE INVENTION

[0013] To achieve this objective, according to a first aspect, an orthopedic screw is planned, preferably for the sacroiliac joint, comprising a core extending along a main extension direction between a distal end and a proximal end.

[0014] Advantageously, the soul understands:

[0015] - a central conical portion having a first slope, the central conical portion having a distal end and a proximal end,

[0016] - a distal portion with a second slope less steep than the first slope,

[0017] - a proximal portion with a third slope lower than the first slope,

[0018] The screw includes a first thread carried by said portions, the first thread having a height increasing from the proximal end of the central conical portion towards the distal end of the central conical portion, along the main extension direction of the screw, on at least a part of the central conical portion, called the "holding part".

[0019] This series of different slopes in the screw's core allows for variation in its diameter. The screw thus exhibits an increase in diameter at the central conical portion, from its distal end to its proximal end, thereby inducing radial compression on the outer wall of the bone at its cortical zone, in order to improve the screw's retention at this wall.

[0020] This is particularly advantageous in the case of osteoporotic bones, whose interior has generally lost density but which retain hard outer walls. Here, the holding force is concentrated in the hard cortical zone at the junction between two bones, as is the case for the sacroiliac joint, at the junction between the central conical portion and the proximal portion of the screw.

[0021] Furthermore, a greater thread height is achieved in the central portion at its junction with the proximal portion. This improves grip in hard materials to solidify a joint between two bones, accompanying the increase in the core diameter.

[0022] This allows for easier screw traction when radial compression is greatest and improves its stability. The screw's bone retention is therefore enhanced. Thanks to this improved stability, the patient's rehabilitation can proceed more quickly with a reduced risk of dislodgement of the implanted osteosynthesis hardware.

[0023] A second aspect concerns a method of fixing an orthopedic screw including implantation of the screw according to the first aspect at the level of a bone fracture, and more particularly a fracture of the pelvis.

[0024] For example, the screw is implanted at a joint between two separate bones such that the central conical portion, and more specifically the proximal end of the central conical portion, is located at the junction between these two bones. For example, the screw is implanted at the sacroiliac joint.

[0025] BRIEF DESCRIPTION OF THE FIGURES

[0026] The aims, objects, features and advantages of the invention will become clearer from the detailed description of an embodiment thereof, which is illustrated by the following accompanying drawings in which:

[0027] Figures 1A and 1B represent a view of the implantation of the screw in the pelvis, at the level of the sacroiliac joint, according to an example of embodiment and according respectively to a front view (or equivalently, in the frontal plane) and a cross-sectional view in the plane of the screw seen from above.

[0028] Figures 2 to 6A and 8 show a cross-sectional view of the screw in an example of an embodiment. Figure 3 shows the screw in relation to the tissues and bones of the body into which it is implanted, in an example of an embodiment.

[0029] Figure 6B schematically represents the distribution of the screw threads, at the level of the proximal part, in relation to the sacroiliac joint, according to an example of embodiment.

[0030] Figures 7A to 7C represent a general view and two detail views illustrating the variation of widths at the top of the net, according to an example of an embodiment.

[0031] Figure 9 shows a cross-sectional view of the distal end of the screw, according to an example embodiment.

[0032] The drawings are given as examples and are not limiting to the invention. They constitute schematic representations of principle intended to facilitate understanding of the invention and are not necessarily to scale with practical applications.

[0033] DETAILED DESCRIPTION OF THE INVENTION

[0034] Before beginning a detailed review of embodiments of the invention, optional features that may be used in combination or alternatively are stated below.

[0035] According to one example, at the level of the central conical portion, the first thread delimits a plurality of outer envelopes so as to form:

[0036] - a central, conical outer shell with a fourth slope,

[0037] - a distal outer envelope having a fifth slope lower than the fourth slope, for example cylindrical or conical in shape,

[0038] - a proximal outer envelope having a sixth slope lower than the fourth slope, for example cylindrical or conical in shape, at least at the level of the retaining part.

[0039] The surgical method for screw implantation is percutaneous screwing, which is generally performed "blindly" because these operations are not "open." X-ray imaging systems are used to guide the surgeon during the procedure. However, the implantation accuracy with this type of system is on the order of millimeters, or even less. This series of outer sheaths allows the screw to create a path without damaging the cortical areas, by rebounding against them. This guides the screw while minimizing the risk of damaging the cortical areas where the force required to hold the screw in place is concentrated.

[0040] According to an example, the first net has, at the level of the distal outer envelope, a height greater than the height of the net at the level of the proximal and central envelopes.

[0041] According to one example, at the central conical portion, the first fillet has a height increasing at the distal outer envelope, towards the distal end of the central conical portion.

[0042] For example, at the central conical portion of the screw's core, the distal outer sheath is cylindrical. This distal outer sheath facilitates screw insertion into the bone and subsequent guidance, minimizing the risk of damaging the cortical areas where the screw's retention force is concentrated, working synergistically with the previously mentioned characteristics. Furthermore, the thread height is greater at the distal end of the central conical portion to occupy a larger volume within the bone, particularly in cancellous bone in the case of osteoporotic bone. This further improves screw retention.

[0043] For example, the distal outer sheath has a smaller dimension, such as a diameter, than the corresponding dimension of the proximal portion of the core. Inserting the screw into the bone and then guiding it are facilitated by minimizing the risk of damaging the cortical areas, in synergy with the aforementioned characteristics.

[0044] For example, the first thread, at the distal end of the thread, defines a distal outer sheath with a diameter less than or equal to the maximum diameter of the thread at the central conical portion. Thus, the thread of the screw at the central conical portion bears against material that has not been weakened by the passage of the distal thread. The screw's retention is therefore further improved.

[0045] In one example, the screw also includes a second thread, which is initiated on a section of the central conical portion, known as the "starting thread," extending over a distance greater than or equal to the pitch of the second thread in the main direction of screw extension. This thread initiation allows for a gradual increase in screw tightening torque. Thus, the initiation of a new thread does not generate a sudden tightening torque during implantation. The surgeon is therefore not overwhelmed during the advancement of the screw into the bone.

[0046] According to one example, the first thread is continuous at least from the proximal end to the distal end of the central conical portion.

[0047] For example, the starting zone of the second thread ends at the central outer sheath, where the central outer sheath reaches its maximum diameter. Thus, there are a greater number of threads and greater thread heights engaging in parts of the cortical areas, to accommodate the increase in the core diameter at the central conical portion. This further facilitates screw traction when its radial compression is at its greatest.

[0048] In one example, the second net forms the proximal outer envelope with the first net. At the level of the proximal outer envelope, the second net can have a height equal to the height of the first net.

[0049] In one example, the second thread is self-tapping in the starting area of ​​the second thread. This further reduces the tightening torque required during its initial engagement.

[0050] As an example, the distal portion of the core supports a total of one to two threads, while the proximal portion of the core and the central tapered portion support a total of three to four threads. Since the primary retention point of the screw is at the junction between the central tapered portion and the proximal portion of the screw, a minimum of three threads eliminates rotational degrees of freedom of the screw within the bone, further improving its retention.

[0051] According to one example, the distal portion of the core supports between one and two first threads and the proximal part of the core and the retaining part support between one and two first threads and between one and three second threads.

[0052] For example, the first thread is continuous from the distal to the proximal portion of the core. This facilitates screw insertion by the surgeon by continuously guiding their movements.

[0053] For example, the first thread has a wider profile at its apex in the distal portion of the web, and a wider profile at its apex in the proximal portion of the web, with the first profile being strictly greater than the second. In the distal portion, this provides a larger bearing surface on the fragile cortical bone (on the inner side of the bone), thus reducing pressure during screw insertion.

[0054] Furthermore, a large thread apex width is unnecessary in the proximal portion, as the screw's guidance effect during insertion is not desired at this point. A thinner thread width facilitates screw penetration into denser bone (outer cortical areas) and a more rigid anatomical structure (the sacroiliac joint), minimizing the risk of damage.

[0055] According to one example, the proximal portion of the core is cylindrical or conical and the distal portion of the core is cylindrical.

[0056] As an example, the proximal portion of the core is conical. The conicity of this part provides additional radial compression in areas of the skeleton where such compression would be required.

[0057] In one example, the first thread has a variable pitch on at least one of the proximal and central portions of the web. An increase in web diameter results in increased radial compression within the bone. Here, with a variable thread pitch in the proximal portion, axial compression or traction is achieved, creating a self-locking effect of the screw at the iliac bone and sacroiliac joint. This further improves screw retention.

[0058] The first thread and the second thread may exhibit a variable pitch on at least one of the proximal and central portions of the core.

[0059] According to an alternative example, the first thread presents a constant pitch on at least one of the proximal and central portions of the core.

[0060] According to one example, the first thread has a constant pitch on the distal portion of the core.

[0061] In one example, the first thread defines an outer sheath at the distal end of the screw, and the distal end of the screw includes a rounded surface whose projection is tangent to the outer sheath at the distal end of the screw. This further facilitates guiding the screw during its insertion into the bone, synergistically with the previous features.

[0062] For example, at the central conical portion of the screw's web, the web has a maximum diameter reached at a distance, measured from the screw head, greater than or equal to the sum of the thickness of the iliac bone, the thickness of the sacroiliac joint, and the thickness of the outer cortex on the sacral joint side—for example, 25 mm, preferably greater than or equal to 30 mm. Thus, the maximum diameter of the web at the central conical portion extends beyond the sacroiliac joint. In the case of osteoporotic bone, this ensures that the screw's retention force is exerted by contact with hard material (cortical areas) unaffected by osteoporosis, resulting in strong radial compression and improved screw retention in the fragile bone. This distance can be chosen according to the patient's physiological dimensions.

[0063] In one example, the core has a smooth surface. Because of the improved screw fixation, it is not necessary for the screw to have openings designed for the diffusion of biocompatible cement. The medical procedure is therefore simplified. The risk of extra-osseous cement leakage, exacerbated by osteoporotic bones, is avoided.

[0064] According to an alternative example, the core has openings on at least one of the proximal, central, and distal portions, preferably forming an interconnected network. These openings allow the diffusion of a biocompatible cement to aid embedding in low-density cancellous bone.

[0065] In the following description, the term "on" does not necessarily mean "directly on." Thus, when it is stated that a part or component A rests "on" a part or component B, this does not mean that parts or components A and B are necessarily in direct contact with each other. These parts or components A and B may be either in direct contact or supported by one or more other parts. The same applies to other expressions such as, for example, "A acts on B," which can mean "A acts directly on B" or "A acts on B through one or more other parts."

[0066] In this patent application, the term mobile corresponds to a rotational movement or a translational movement or a combination of movements, for example the combination of a rotation and a translation, or several of them.

[0067] In this patent application, when two parts are described as distinct, it means that these parts are separate. They may be:

[0068] - positioned at a distance from each other, and / or

[0069] - mobile relative to each other and / or

[0070] - joined together by being fixed by added elements, this fixing being removable or not.

[0071] A single, monobloc part cannot therefore be made up of two separate parts.

[0072] In this patent application, the term "fixed" used to describe the connection between two parts means that the two parts are linked / fixed to each other with respect to all degrees of freedom, unless explicitly stated otherwise. For example, if it is stated that two parts are fixed in translation along a direction X, this means that the parts can move relative to each other, possibly with several degrees of freedom, excluding freedom in translation along the X direction. In other words, if one part is moved along the X direction, the other part moves in the same direction.

[0073] In the detailed description that follows, terms such as "horizontal," "vertical," "longitudinal," "transverse," "superior," "inferior," "high," "low," "front," "back," "proximal," "distal," "internal," and "external" may be used. These terms should be interpreted relatively, considering the longitudinal axis of principal extension of the screw in a horizontal plane, and its insertion into the bone from the distal end to the proximal end, i.e., from front to back or from distal to proximal.

[0074] The figures also include a coordinate system whose longitudinal or front / back direction corresponds to the X-axis, whose transverse direction corresponds to the Y-axis, and whose vertical or up / down direction corresponds to the Z-axis. A parameter "approximately equal to / greater than / less than" a given value is understood to mean that this parameter is equal to / greater than / less than the given value, to within ±10% of that value. A parameter "approximately between" two given values ​​is understood to mean that this parameter is at least equal to the smaller of the two given values, to within ±10% of that value, and at most equal to the larger of the two given values, to within ±10% of that value.

[0075] In the context of the present invention, the diameter of an element, portion, or envelope is measured along a plane perpendicular to the longitudinal direction A of the screw. The thread height is measured along a plane perpendicular to the longitudinal direction A of the screw, and more particularly along the Z direction. The thread height is measured more specifically between the outer surface of the web and the crest of a thread, that is, its outer edge or a face of the thread facing the outside of the screw. A slope is defined as the angle formed between the surface, envelope, or projection in question and a direction X parallel to the longitudinal direction A.

[0076] The expression "A and / or B" means (A), (B), or (A and B). The expression "A, B and / or C" means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B and C).

[0077] The orthopedic screw 1 and its implantation are now described according to particular examples of implementation and with reference to the figures.

[0078] Screw 1 can be implanted to repair a bone fracture. Screw 1 can be implanted at a junction between two bones in the human or animal body, particularly in the pelvis, as illustrated for example in Figures 1A and 1B. For example, screw 1 is more specifically intended to be implanted at the sacroiliac joint 71, which can also be referred to as the sacroiliac junction 71.

[0079] The sacroiliac joint 71 corresponds to the articular junction between the vertebral column and the pelvis 7. It is a junction between the sacrum 70 and each of the two hip bones (also called iliac bones) 72. A hip bone is the result of a fusion between the ilium, ischium, and pubic bone during skeletal maturation. These bony areas are connected by cartilage in children. The bony pelvis is formed by the ring created by the right hip bone, the left hip bone, and the sacrum. The sacrum is also part of the vertebral column. Posteriorly, the sacrum articulates with each hip bone on the right and left by the right and left sacroiliac joints.

[0080] In the case of a pelvic fracture 7, for example a fragility fracture of the pelvis (FFP), screw 1 can be used to maintain the fractured pelvic bone(s) 7. As an example, screw 1 may be particularly suitable for a fracture located at the level of the sacrum, a Denis type I, II or III fracture. Screw 1 can more specifically be implanted so as to pass through the sacroiliac joint 71, as illustrated in Figures 1A and 1B for example.

[0081] In osteoporotic bones, bone density decreases, making the skeletal structure more fragile, especially in older adults. Osteoporosis typically begins around age 50 in women and somewhat later in men. An osteoporotic bone typically retains hard outer walls in the cortical areas, although their thickness tends to decrease significantly.

[0082] The orthopedic screw 1 includes a core 2 extending along the longitudinal direction A between its distal end 1a and its proximal end 1b. The screw 1 may further include, at its proximal end 1b, a head 5 from which the core 2 extends, and a point 6 located at its distal end.

[0083] To improve the retention of the screw 1 in the fracture zone, particularly in osteoporotic bones, the web 2 comprises a distal portion 20, a central conical portion 21, and a proximal portion 22. As illustrated, for example, in Figure 2, the central conical portion 21 has a slope forming an angle a1 with respect to a direction X parallel to the longitudinal direction A. The distal portion 20 and the proximal portion 22 frame the central conical portion 21, being located on either side of this portion 21 along the longitudinal direction A. The distal portion 20 and the proximal portion 22 have, respectively, a second slope a2 and a third slope a3, which are strictly less than the first slope a1. It is therefore understood that the distal portion 20 and / or the proximal portion 22 can be conical, with non-zero slopes less than that of the central conical portion 21, or cylindrical (and therefore with zero slope).The diameter of the web 2 therefore increases between the distal portion 20 and the proximal portion 22, and more specifically at least along the central conical portion 21. The web 2 thus bears against the bone on a surface undamaged by the passage of the preceding web portion during screwing. The distal portion 20 and the proximal portion 22 each have, respectively, a distal end, 20a, 22a, and a proximal end, 20b, 22b.

[0084] In one example, the distal portion 20 is cylindrical. This allows for force transmission without stress peaks, compared to a conical shape. In another example, the proximal portion 22 is cylindrical. In a second, alternative example, not shown here, the proximal portion 22 can be conical. This strengthens the screw's retention in the iliac bone by increasing radial compression, as seen below.

[0085] The core 2 also supports at least one first thread 3, and for example several first threads 3. In the following, unless explicitly stated otherwise, the screw 1 is considered, for non-limiting purposes, to include a first thread 3. As illustrated, for example, by Figure 2, the first thread 3 has a height D. The height D increases from the proximal end 21b of the central conical portion 21, towards the distal end 21a of this portion 21, along the X direction, so as to improve the grip of the screw 1 at this retaining part 210. The height D increases over at least a portion 210 of the central conical portion 21, called the retaining part 210. The retaining part extends from the distal side of the end 21b over a non-zero distance.

[0086] As illustrated in Figure 3, screw 1 is configured to maximize the radial compression exerted by screw 1 in the bone at the proximal portion 22 and the retaining portion 210, corresponding to the hard cortical areas located on either side of the sacroiliac joint 71. To achieve this, screw 1 can be further configured so that the retaining portion 210 is located at the hard cortical area on the outer surface of the sacrum 70. Screw 1 can also be configured so that the proximal portion 22 of the web 2 passes through the sacroiliac joint 71 and is anchored in the iliac bone 72. The head 5 of screw 1 can rest on the iliac bone 72, for example, on soft tissue 73.

[0087] The dimensions of screw 1, and more specifically the lengths of each portion of web 2 along the X direction, can be adapted accordingly, for example, based on the body's size and bone structure. Assuming that the primary anchoring point of screw 1 in osteoporotic bone is the sacroiliac joint 71, it is advisable to have already reached the maximum diameter D2 of web 2 at this joint 71. This ensures that screw 1 is in contact with intact bone tissue, i.e., bone not impacted by the previous screwing of screw 1, resulting in strong radial compression and therefore improved stability of screw 1 in the fragile bone.

[0088] For example, the maximum diameter D2 of the web 2 at the central conical portion 21 can be reached at a distance D1 measured from below the screw head 5 along the X direction, D1 being greater than or equal to 25 mm, preferably 30 mm, this distance being adjustable according to the patient's physiological dimensions. The distance D1 can be greater than or equal to the sum of the thickness of the iliac bone traversed by the screw, the thickness of the tissues of the SI joint, and the thickness of the external cortex of the sacrum on the joint side, which may vary according to each patient's physiological dimensions. D1 can be approximately equal to the length of portion 22. It should also be noted that this value is valid for a given orientation of the sacroiliac screw; an orientation which is not necessarily in the transverse (top) plane of Figure 1B (for example).

[0089] The retaining part 210 preferably represents only a part of the central conical portion 21. For example, the retaining part 210 has a length substantially between 5 mm and 15 mm, preferably between 5 mm and 10 mm.

[0090] At least the first thread 3, and where applicable, all the threads supported by the web 2, can define a plurality of outer sheaths. By outer sheath, we mean the external surface extending by projection between the vertices of the thread(s), as illustrated, for example, by the dotted line in Figures 2 and 3. The term sheath is understood as a geometric construction, without physical existence, forming a closed contour passing through the vertices of the thread(s). The screw 1 can thus have a proximal outer sheath 32, a central outer sheath 31, and a distal outer sheath 30. The proximal outer sheaths 32 and distal outer sheaths 30 frame the central outer sheath 31, being located on either side of this sheath 31 along the longitudinal direction A.The envelopes 30, 32 are formed at least at the level of the central conical portion 21, and preferably extend along the core 2 as illustrated on at least part of the other portions 20, 22.

[0091] The central outer shell 31 can be conical in shape and have a fourth slope a4. The central outer shell 31 is preferably located at a part of the central conical portion 20 of the web 2. This allows the increase in diameter of the web 2 to be accommodated on the corresponding part of the central conical portion 21.

[0092] The distal outer sheath 30 can extend over the distal portion 20 of the core 2, as well as a portion of the central conical portion 21, in a manner complementary to the central outer sheath 31. The distal outer sheath 30 may have a fifth slope a5 lower, preferably strictly lower than the fourth slope a4. Preferably, the distal outer sheath 30 is cylindrical and therefore has a constant diameter. Equivalently, the slope a5 is substantially zero.

[0093] The proximal outer shell 32 extends at least over the retaining part 210, and preferably also over the proximal portion 32 of the core 2. Note that the proximal portion 22 of the core may have an unthreaded proximal part 35 below the head 5. This allows the threading tool to retract during manufacturing without increasing the diameter of the core below the screw head.

[0094] The proximal outer sheath 32 may have a sixth slope a6 that is lower, preferably strictly lower, than the fourth slope a4. As illustrated, the proximal outer sheath 32 may be cylindrical and thus have a constant diameter. Equivalently, the slope a6 is essentially zero. As an example, the proximal outer sheath 32 may be cylindrical at least in the retaining portion 210. Alternatively, but not illustrated, the proximal outer sheath 32 may be conical. The thread height in the proximal portion 32 can thus be increased to improve the retention of the screw 1 in the iliac bone 72.

[0095] To promote contact of the screw with the intact bone material, and as illustrated in Figure 4, the distal outer sheath 30 may have a diameter D3 less than or equal to, and preferably strictly less than, the maximum diameter D2 of the web 2 at the central conical portion 21. Thus, the web 2 at the proximal portion 22 comes into contact with the undamaged bone through the passage of the distal 20 and central 21 portions of the web 2. The diameter of the web 2 at the proximal portion 22 may be greater than or equal to the maximum diameter 22.

[0096] In one example, the outer sheaths 30, 31, 32 are offset from the corresponding web portions 20, 21, 22 by one or more non-zero distances, possibly distinct between the different sheaths, along directions parallel to the principal extension direction of the screw. The thread is thus more incisive distally and then decreases with a relative increase in the web, which "presses" the cancellous bone against the screw web. This improves the screw's retention force in the bone.

[0097] The outer sheaths 30, 31, 32 may be at least partially parallel and at a given distance from the external surface of the corresponding core. Note that the distances between these parallels and the external surface of the core 2 are not necessarily equal. This allows the thread to accommodate the increase in the diameter of the core 2 along the screw 1, particularly in synergy with the core 2 bearing against the intact bone material.

[0098] In addition to the first thread 3, the screw 1 may include at least one second thread 4. Hereafter, unless explicitly stated otherwise, the screw 1 is considered, for the sake of completeness, to include two second threads 4a, 4b. These second threads 4a, 4b are referred to equivalently as "the second thread 4". The second threads 4a, 4b may be present on only a portion of the web 2. The second threads 4a, 4b may be created in a thread starting zone 40. "Thread starting" refers to the initiation of thread formation from the web surface to a predetermined height, distinct from any variation in the height of an existing thread. In the thread starting zone 40, the second thread 4 therefore has increasing height. The second net 4 can then present a second part, outside the priming zone 40, whose height can advantageously be constant.

[0099] As an example, Figures 5 and 6A distinguish the first thread 3 from the second thread 4 along the screw 1. The second thread 4 can be initiated at the central conical portion 21. Thus, the tightening torque is increased in synergy with the increase in the diameter of the web 2 at the central conical portion 21. The second thread 4 is preferably initiated over a distance D4 greater than or equal to the pitch D5 of the second thread 4; for example, D4 ​​is approximately equal to 2D5. The increase in tightening torque is therefore gradual.

[0100] The priming zone 40 of the second thread 4 can be positioned on the distal side of the retaining portion 210, these two parts being directly juxtaposed. This corresponds to the area of ​​the screw 1 in contact with the hard cortical areas and the sacroiliac joint 71. Priming of the second thread 4 can be completed when the central outer sheath 31 has reached its maximum diameter D13, as illustrated, for example, in Figures 5 and 6A.

[0101] A rapid increase in tightening torque is also preferable when the underside of the screw head 5 makes contact with the outer surface of the iliac bone 72, indicating to the surgeon that the screw 1 is fully inserted. The surgeon can then stop tightening, minimizing the risk of overtightening and fracturing the iliac bone. To achieve this, the first 3 and / or second 4 threads can be started under the screw head 5 over a distance shorter than the thread pitch.

[0102] In one example, the pitch of the first 3 and second 4 threads is equal for a given point on screw 1. For example, the pitch of the first 3 and second 4 threads can be constant along the web 2. In an alternative example, the pitch of the first 3 and second 4 threads can vary along the web 2, with the pitches remaining equal. Varying the pitch of threads 3 and 4 allows for manipulation of the tensile or compressive force when tightening screw 1. The pitch variation can be very small to achieve the tensile / compressive effect. A variability on the order of 0.1 to 0.2 mm of the main pitch (for a main pitch approximately equal to 3 mm) is sufficient to obtain the desired effect.

[0103] The screw 1 may have one or two first threads 3. The screw 1 may have one or two second threads 4. Preferably, and as illustrated in Figures 6A and 6B, the proximal portion 22 of the web 2 and the retaining portion 210 may support between one and two first threads 3 and between one and three second threads 4. Preferably, the proximal portion 22 of the web 2 and the retaining portion 210 support at least three threads in total, that is, considering both the first and second threads together. Thus, the screw 1 is fixed to the bone such that the rotational degrees of freedom of the screw 1 relative to the bone are eliminated, except for rotation about the longitudinal direction A. The threads preferably function in multiples.For example, if there is a first thread 3 at the distal portion 20, it is possible to have three or four threads in total at the proximal portion 22 and the retaining part 210, i.e., two or three second threads 4. Conversely, if there are two first threads 3 at the distal portion 20, it is preferable to have four threads in total at the proximal portion 22 of the web 2 and the retaining part 210 if the first two threads 3 are to be symmetrical, and therefore two second threads 4a and 4b. By "symmetrical" we mean that the apparent pitch is constant when viewed from both sides of the thread apex (distal and proximal sides). In the case of a triple net, if one net is removed, two remain joined together, then there is a "jump" to find these two nets joined together on the next turn; this configuration is therefore asymmetrical.

[0104] Preferably, the first 3 and second 4 threads are continuous to avoid any discontinuity in feel for the surgeon during tightening. This also ensures that the same impression left by the first 3 thread is maintained at the distal portion 20, when the pitch of the first 3 thread is constant. Preferably, the first 3 thread is continuous for at least 80% of the length of the screw 1, and preferably for at least 95% of its length.

[0105] The screw 1 can also be configured so that the width at the apex 3b, 4c of the threads 3, 4 varies between different portions of the screw 1. As illustrated, for example, in Figures 7A to 7C, the first thread 3 can have, at the distal portion 20 of the web 2, a width D9 at the apex 3b strictly greater than the width D6 at the apex 3b, 4c of the first 3 and / or second 4 threads. For example, D9 = n.D6, where n is a non-zero positive number between 1 and 3. In one particular example, D9 is approximately 0.5 mm and D6 is approximately 0.3 mm. This change in apex width depends, in particular, on the thread height, determined by the machining tool used to create the threads. For example, if D11 decreases, D9 increases. Alternatively, we can assume that the width at the top of the first 3 and / or second 3 fillet is constant.

[0106] In the illustrated example, and with reference to Figures 7B and 7C, D11 is strictly greater than D8. This can have the geometric consequence that the length of the distal cylindrical outer shell 30 is greater than the length of the distal conical portion 20. In a case where D11 were strictly less than D8, the opposite would result. Manipulating the ratio between D11 and D8 allows for a so-called "honey spoon" effect when D11 is significantly greater than D8, that is, preserving a maximum amount of bone in the dentition.

[0107] According to an alternative example, D11 can be expected to be approximately equal to or slightly smaller than D8, in order to have a larger distal portion of the web, thus maximizing the space within the sacrum and providing support where there is bone (close to the cortical bone). This will depend on the advanced stage of osteoporosis in the patient's sacrum. When D11 is approximately equal to or slightly smaller than D8, D9 can be approximately equal to D6.

[0108] As an example, the second thread 4 may have threading structures (progressive threads, grooves, axially notched thread) at least on the starting area 40 of the second thread 4. As an example, the first thread 3 may be self-tapping on the central conical part, when the diameter of the outer envelope 31 changes. The torque force can then be reduced when starting a new thread and / or changing the outside diameter of the screw 1. By being self-tapping, the screw, when screwed in, cuts by itself the bone material that the thread will replace, without the prior intervention of another tool (tap).

[0109] Dimensions and diameters are now given as non-limiting examples.

[0110] At the proximal portion 22 of the web 2, and more specifically at the proximal outer sheath 32, the first 3 and / or second 4 threads may have a height D8 of approximately between 0.5 and 1 mm, for example, approximately 0.75 mm. Two directly consecutive threads 3, 4 may be separated by a distance D7 (apparent pitch) of approximately between 0.5 and 2 mm. This distance depends on the number of threads. A thread pitch 1 of approximately between 2 mm and 6 mm is advantageous, and therefore:

[0111] - with 3 threads and a 3 mm pitch, the apparent pitch can be approximately 1 mm,

[0112] - with 4 threads and a pitch of 3 mm, the apparent pitch can be approximately 0.75 mm.

[0113] The first 3rd and second 4th threads can have an angle α7 relative to the normal to the external surface of the web 2, equal or different between the first 3rd and second 4th threads, approximately between 30° and 40°, and preferably approximately 35°. The larger the angle α7, the smaller D7. If D7 decreases too much, there is no longer enough material to drive the screw, and the grip is reduced. The smaller α7, the more the "tooth" is weakened because it loses material at its base. The range above therefore represents a good compromise between these two extremes.

[0114] At the distal portion 20 of the core, and more specifically at the distal outer sheath 30, the first thread 3 may have a height D11 of approximately between 0.5 mm and 3 mm, preferably between 1.5 and 2 mm, for example approximately 1.70 mm. D11 may be approximately equal to or greater than D8, depending on the apex widths D6 and D9, as discussed previously. Two turns of a first thread 3 or two directly consecutive first threads 3 may be separated by a distance D10 (apparent pitch, depending on the pitch and the number of threads) of approximately between 1 mm (for example, for two distal threads, with a pitch of 2 mm) and 6 mm (for example, with one distal thread, and a pitch of 6 mm), for example approximately between 3 and 5 mm. The first thread 3 may have an angle a8 with respect to the normal to the external surface of the web 2 approximately between 30° and 40 and preferably approximately equal to 35°.Due to manufacturing constraints, angle a8 is preferably approximately equal to angle a7. It can be expected that two distinct threads will have different tooth angles.

[0115] For osteoporotic bone, it is preferable to maximize the contact area between screw 1 and the bone. In other words, the overall diameter of screw 1, for example the diameter of its outer sheaths and / or the diameter of the core 2, can be chosen so that screw 1 fills as much space as possible in the bone, allowing bone regeneration over a larger area. This, in the long term, embeds the screw in the bone and reduces the chance of a new fracture occurring in that area.

[0116] For example, at the distal portion 20, the core 2 can have a diameter D12 approximately between 1.2 mm and 7.9 mm, preferably between 5 mm and 6 mm, and for example, approximately 5.6 mm. D12 can be more specifically constrained by the height of teeth D11 and D3. D3 can be constrained according to the dimension of the "sacral corridor," referring to the bony channel between the outer part of the sacrum and the central part, between the sacral foramina. The S1 corridors can range from 8 mm to 11 mm in diameter. D3 is preferably smaller than the diameter of the corridor (for example, D3 is between 6 and 10 mm). D12 is preferably between D11 + 1 mm = 4 mm and D3 maximum - 0.5 mm = 9.5 mm.

[0117] The maximum diameter of the central outer sheath 31, and where applicable the diameter of the proximal outer sheath 32, can be substantially between 2 mm and 12.7 mm. The diameters of the outer sheaths in the proximal 32 and central 31 areas are, for example, 10.5 mm and 9 mm, respectively. The maximum diameter D2 of the core at the central conical portion, and where applicable the diameter D14 of the proximal portion, can be substantially between 1.2 mm and 7.9 mm. The diameter D14 can be greater than or equal to the diameter D2.

[0118] The screw 1 may also have a recess 23, also called a cannula, inside the core 2, configured to retain the implantation instrument (e.g., a screwdriver) inserted into the recess 23. The cannula 23 may have several portions, including a proximal portion with a diameter D16 in which the screwdriver is retained. The cannula 23 may have a distal portion with a diameter D15, allowing the passage of a guide pin. This proximal portion is preferably threaded to securely attach the implantation instrument to the screw (to prevent the screw from being lost in the patient during implantation). This retention also allows for the application of traction force for material removal if necessary.

[0119] Typically, a guide pin is inserted into the bone, then the bone is pre-drilled if necessary with a cannulated drill bit that fits onto the guide pin, and finally, screw 1 is screwed onto the guide pin. Additionally, the threaded proximal portion allows for the insertion of an ancillary (a hollow threaded rod). Once screwed into cavity 23, the ancillary allows for the extraction of screw 1 from the patient.

[0120] The angle a9 shown in Figure 8 is a clearance configured to finish the thread without increasing the web diameter. This angle typically results from manufacturing constraints.

[0121] The screw surface can also be adapted to the desired application. Thanks to improved screw retention, the web surface can be smooth. This eliminates the need for a bone-fixing cement, which can be particularly detrimental in osteoporotic bone with potential extra-osseous cement leakage. Alternatively, and as an example not shown, the web surface can feature openings, more commonly known as fenestrations, on all or part of it. These fenestrations can form an interconnected network. The fenestrations can be configured to allow the diffusion of a biocompatible cement.

[0122] The distal end 1a of the screw 1 may be at least partially rounded to allow the screw to create a path without damaging the hard cortical areas. For this purpose, the tip 6 of the screw 1 may include a curved chamfer 60. The curvature of the chamfer 60 may be configured to exhibit rotational symmetry about the longitudinal direction A. The tip 6 may further include a flat 61 on the distal side of the chamfer 60, and preferably the flat is substantially perpendicular to the longitudinal direction A.

[0123] The curvature of the chamfer can be configured more specifically so that, if the surface of the chamfer 60 is geometrically extended—that is, from a geometric construction point of view and without physical existence—the geometric extension 33 of the chamfer 60 is tangent to the vertex 3a of the first thread 3, and preferably on a starting zone 34 of the first thread 3 originating from the chamfer 60. The vertex 3a of the first thread in its starting zone 34 can be configured in a complementary way to coincide with this projection 33. For example, the vertex 3a is oblique with respect to the longitudinal direction A.

[0124] The invention is not limited to the embodiments described above and extends to all embodiments covered by the invention. The present invention is not limited to the examples described above. Many other embodiments are possible, for example, by combining features described above, without departing from the scope of the invention. The illustrated example describes a first thread and two second threads. The features described above can be applied to different thread configurations. Furthermore, the features described with respect to one aspect of the invention can be combined with another aspect of the invention.

Claims

DEMANDS 1. Orthopedic screw (1) for the sacroiliac joint (71), comprising: • a core (2) extending along a principal extension direction (A) between a distal end (1a) and a proximal end (1b), the core (2) comprising: o a central conical portion (21) having a first slope (a1), the central conical portion (21) having a distal end (21a) and a proximal end (21b), o a distal portion (20) having a second slope (a2) lower than the first slope (a1), o a proximal portion (22) having a third slope (a3) ​​lower than the first slope (a1), • a first thread (3) carried by said portions, and characterized in that the first thread (3) has a height (D) increasing from the proximal end (21b) of the central conical portion (21) towards the distal end (21a) of the central conical portion (21), along the main extension direction of the screw (A), on at least a part (210) of the central conical portion (21), called the "retaining part" (210).

2. Orthopedic screw (1) according to the preceding claim, wherein, at the level of the central conical portion (21), the first thread (3) delimits a plurality of outer sheaths (30, 31, 32) so as to form: • a central outer envelope (31) of conical shape having a fourth slope (a4), • a distal outer shell (30) having a fifth slope (a5) lower than the fourth slope (a4), for example cylindrical or conical in shape, • a proximal outer envelope (32) having a sixth slope (a6) lower than the fourth slope (a4), for example cylindrical or conical in shape, at least at the level of the retaining part (210).

3. Orthopedic screw (1) according to the preceding claim, wherein, at the level of the central conical portion (21) of the core (2), the distal outer casing (30) is cylindrical in shape.

4. Orthopedic screw (1) according to any one of the preceding claims, wherein the first thread (3) delimits, at the level of the distal portion (20) of the web (2), a distal outer envelope (30) of diameter (D3) less than or equal to a maximum diameter (D2) of the web (2) at the level of the central conical portion (21).

5. Orthopedic screw (1) according to any one of the preceding claims, further comprising a second thread (4), the second thread (4) being started on an area of ​​the central conical portion, referred to as the "starting" area (40), extending over a distance (D4) greater than or equal to the pitch (D5) of the second thread (4) along the main extension direction (A) of the screw (1).

6. Orthopedic screw (1) according to the preceding claim, wherein the priming zone (40) of the second thread (4) terminates at the level of the central outer envelope (31), when the central outer envelope (31) reaches a maximum diameter (D13).

7. Orthopedic screw (1) according to any one of the two preceding claims, wherein the second thread (4) is self-tapping on the priming area (40) of the second thread (4).

8. Orthopedic screw (1) according to any one of the preceding claims and claim 5, wherein the distal portion (20) of the web (2) supports a total number of thread(s) (3) between one and two, and the proximal portion (22) of the web (2) and the retaining part (210) of the central conical portion (21) support a total number of threads (3, 4) between three and four.

9. Orthopedic screw (1) according to any one of the preceding claims, wherein the first thread (3) is continuous from the distal portion (20) to the proximal portion (22) of the core (2).

10. Orthopedic screw (1) according to any one of the preceding claims, wherein the first thread (3) has at its apex (3b) a first width (D9) at the level of the distal portion (20) of the web (2), and the first thread (3) has at its apex (3b) a second width (D6) at the level of the proximal portion (22) of the web (2), the first width (D9) being strictly greater than the second width (D6).

11. Orthopedic screw (1) according to any one of the preceding claims, wherein the proximal portion (22) of the web (2) is cylindrical or conical and the distal portion (20) of the web (2) is cylindrical.

12. Orthopedic screw (1) according to any one of the preceding claims, wherein the first thread (3) has a variable pitch on at least one of the proximal portion (22) and the central portion (21) of the core (2).

13. Orthopedic screw (1) according to any one of the preceding claims, wherein the first thread (3) delimits an outer casing (33) at the distal end (1a) of the screw (1) and the distal end (1a) of the screw (1) includes a rounded surface (60) whose projection is tangent to the outer shell (33) at the distal end (1a) of the screw (1).

14. Orthopedic screw (1) according to any one of the preceding claims, wherein, at the level of the central conical portion (21) of the web (2), the web (2) has a maximum diameter (D2) attained at a distance (D1), taken from the head (5) of the screw (1), greater than or equal to 25 mm.

15. Orthopedic screw (1) according to any one of the preceding claims, wherein the core (2) has a smooth surface.

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