Multi-thread bone screw

[0001] The subject of the invention is a bone screw, in particular a bone screw with a thread divided into segments of different pitch, adapted to different types of bone tissue.

Background Art [0002] Various types of fixation components for bone tissue are used in medicine. In the case of the spine, plates, rods and other implants and dentures attached to one or more vertebrae are attached with bone screws. Fig. 1 shows a bone screw 10 known from the prior art equipped with a threaded rod 12 for screwing into bone tissue and a head 14 connecting by means of a coupling mechanism to an elongated member (not shown), for example a rod. Exemplary connecting mechanisms for joining the vertebral rod inserted into the bone screw head 14 are exemplified in US Patent No. 5,643,263 (Simonson), in US Patent No. 5,947,967 (Braker) and in US Patent No. 6,471,703 (Ashman).

[0003] The threaded pin 12 of the bone screw is provided with a mono thread 16 with a constant pitch. The pitch of the thread 16 is quite large and is adapted to be embedded in the spongy bone tissue, for example in the spongy internal tissue of the spine. It is also possible to use a thread 16 with a smaller pitch to achieve greater stability in hard cortical tissue, however, such a thread gives a less stable fixation in the spongy bone. In addition, threads with a smaller pitch require more turns to screw the screw into the bone.

[0004] WO 02/09601 (Orthopedic Bio Systems Limited, Inc.) describes a medical threaded screw consisting of a first diameter thread intertwined with another second diameter thread. This alternating thread arrangement is more favorable than other bone screw configurations due to the mechanical strength of the fastening.

[0005] Despite the existing solutions presented, however, there is still a need for a bone screw with an improved design. The bone screw according to the invention fulfills this demand by obtaining advantageous solutions in a new and not obvious way.

SUMMARY OF THE INVENTION [0006] The subject of the invention is a bone screw according to claim 1, equipped with various threaded segments intended for embedding in various types of bone tissue. The invention also relates to the use of such a screw. Although the actual idea of ​​the invention is contained in the appended claims, the following details the detailed solutions of the invention characteristic of the preferred examples disclosed herein.

[0007] In a preferred embodiment of the invention, the bone screw is provided with a threaded rod provided with a free end and an inner end. The threaded mandrel consists of a first threaded segment adapted to be embedded in the spongy bone, starting at the free end and extending toward the inner end, and adapted to be embedded in the cortex of the second threaded segment sandwiched between the first threaded segment and the inner end of the threaded mandrel. The thread pitch of the second segment is smaller than the thread pitch of the first segment.

[0008] In another embodiment of the invention, there is provided a spine implant system equipped with a bone screw consisting of a threaded rod provided with a free end, an internal end and a screw head located at the internal end of the threaded mandrel. The threaded mandrel includes a first threaded segment for embedding in a spongy bone positioned from the free end side toward the inner end and a second cortical segment for insertion between the first threaded segment and the inner end. The second threaded mandrel segment is provided with a finer thread than the thread of the first segment. Such a spine treatment device is further equipped with a spinal implant connected to the head of the bone screw.

[0009] In another embodiment of the invention, the bone screw is provided with a threaded rod provided with a free end and an inner end. The mandrel consists of the first segment equipped with a single-turn thread, intended to be embedded in a spongy bone, placed between the outer end of the mandrel and the segment equipped with a double thread, and the second segment, in which the thread extension of the first segment is applied to the second thread forming a dual-thread system located between first segment and the inner end of the stem. This second segment with double thread is deposited in cortical bone tissue.

[0010] The object of the invention is to provide a bone screw with an improved design. Other features of the solution as well as the advantages and other aspects of the invention are explained on the basis of the attached drawings and description.

Brief description of the drawing [0011]

Fig. 1 is a side view of a bone screw known in the art.

Fig. 2 - bone screw according to the invention, side view.

Fig. 3 - the bone screw according to Fig. 2 embedded in bone tissue and connected to the spinal rod, in a side view.

Fig. 4 - a bone screw in another embodiment of the invention, embedded in bone tissue and connected to the spinal rod, in a side view.

Fig. 5 - a bone screw in yet another embodiment of the invention, embedded in bone tissue and connected to the spinal plate, in a side view.

Fig. 6 - a bone screw embedded in bone tissue yet another embodiment of the invention connected to the spinal plate in a side view.

Description of preferred solutions according to the invention [0012] Hereinafter, examples of solutions according to the invention are described based on the drawings. These exemplary solutions do not limit the scope of protection of the invention, and changes and further modifications of the presented devices or the extended application of the invention are regarded as understood by the person skilled in the art to which the invention relates.

[0013] Fig. 2 shows one embodiment of a bone screw 50 according to the invention. A bone screw 50 with a longitudinal axis L and is equipped with a free end 50a and an inner end 50b. The bone screw 50 is provided with a threaded stem section 52 intended for embedding in bone and a head 54 for attachment to the implant, further details of which will be provided below. The bone screw 50 may be made of any suitable and biologically compatible material, such as, for example, titanium, titanium alloy, stainless steel, metal alloys or other materials known to those skilled in the art whose mechanical and biological properties enable the screw to be inserted into the patient's body and anchored in the bone.

[0014] In an exemplary embodiment of the invention, the threaded spindle 52 is provided with a leading end 56 with a shape adapted for bone insertion. In the embodiment shown, this leading end 56 is cone-shaped or pointed to facilitate insertion into bone tissue. In other embodiments, however, the leading end 56 may be blunted or rounded. In further exemplary embodiments, the leading end 56 or other portion of the segment located at the end 50a may be provided with one or more cutting edges or grooves (not shown in the drawing) that make the bone screw 50 a self-tapping screw. In yet other exemplary solutions, the bone screw 50 may be equipped with an axial channel (not shown) extending through its entire length or part of the length from the inner end 50b, forming a cannula insertion hole, and may also be equipped with an axial channel connected through transverse channels. The cannula mounting holes and transverse channels can be used to feed material such as, for example, bone cement from the free end section 50b of the bone screw 50a or other part of the threaded rod 52.

[0015] In the exemplary embodiment of the invention, the screw head 54 consists of a relatively smooth mandrel 58 on which the implant component or implant connector is slidably mounted. Of course, other configurations and types of heads of 54 bone screws are also possible. Some examples of such solutions will be discussed below. In addition, bone screw designs that are not equipped with a screw head are also contemplated. The bone screw 50, and in particular the head 54 of this screw, is preferably made so as to allow detachable connection with a tool or instrument for screwing the screw (not shown), for example with a screwdriver. In one example of the invention, the screw head 54 may be provided with a recess or recess (not shown in the drawing) for seating the tip of the screwing tool. Such a recess or recess is preferably made in a shape other than a circle, for example, hexagonal or rectangular, whereby a connection of the head 54 with a screwing tool is obtained, which facilitates the screwing of the bone screw 50 into the bone. Alternatively, the outer surface of the screw head 54 may be made so as to allow connection to the tip of the screwing tool.

[0016] The threaded spindle 52 with an overall length l consists of a first threaded segment 60 with a first length l1 starting from the free end 50a towards the inner end 50b and a second threaded segment 62 with a length l2 sandwiched between the first threaded segment 60 and the inner end 50b. As will be discussed in more detail below, the first threaded segment 60 is provided with a first thread 64 that is adapted to embed in spongy bone tissue, and the second threaded segment 62 is equipped with a smaller pitch thread 66 for embedding in cortical tissue.

In addition, the second threaded segment 62 may form a thread runout 68 located at the inner end 50b of the threaded rod.

[0017] In the exemplary embodiment of the invention, the length l1 of the first threaded segment 60 is equal to at least half of the total length 1 of the threaded spindle 52, wherein the length l2 of the second threaded segment 62 is equal to the remaining length l of the mandrel. In another exemplary embodiment, the length I1 of the first threaded segment 60 approximately corresponds to at least two-thirds of the total length I of the threaded spindle 52, wherein the length I2 of the second threaded segment 62 is equal to the remainder of the entire length I of the mandrel. In yet another example, the length I1 of the first threaded segment 60 is equal to at least three-quarters of the entire length I of the threaded spindle 52, and the length I2 of the second threaded segment 62 is equal to the remainder of the entire length I of the spindle. However, it should be understood that other values ​​of the length I1 of the first threaded segment 60 relative to the total length I of the threaded rod 52 are also considered to fall within the scope of the invention.

[0018] It should be noted that the ratio between the lengths I1, I2 of the first and second thread segments 60, 62 should preferably be selected based on the properties of the bone with which the screw 50 will be connected. As discussed above, the first threaded segment 60 is provided with a thread that is particularly preferably selected for embedding in spongy tissue, and the second thread segment 62 is particularly adapted for embedding in cortical bone tissue. In order to maximize the bone anchoring efficiency of the screw 50, the lengths l1, l2 of the first and second threaded segments should preferably correspond to the desired length of embedding in bone spongy tissue and cortical tissue.

[0019] In the exemplary embodiment of the invention, the first thread 64 is provided with a single helical winding forming the first threaded segment 60. The second thread 66 is superimposed on the first thread 64, resulting in a double winding in the form of a double helical thread forming a second threaded segment 62. In the exemplary embodiment illustrated, the first and second threads or windings 64, 66 are made in the form of a spiral, which extends continuously around the longitudinal axis L and along the length of the shaft 52. Since the second thread 66 is preferably uniformly and centrally offset from the first thread 64, the threads 64, 66 looking like continuous, spirally arranged along the length l2 of the second threaded segment 62, are in fact separate windings. As will be discussed below, the creation of separate threads along the second threaded segment 62 allows, if necessary, to achieve an equal thread pitch for both segments 60 and 62 of the stem 52.

[0020] In the exemplary solution of the invention, the pitch of the first thread 64 is p1 of the thread, and the pitch of the second thread 66 overlapping the first thread 64 is p2. The pitch size p2 is essentially equal to the pitch size p1 of the first thread. It should be noted that because the first and second threads 64, 66 work together to form a dual-threaded thread of the second threaded segment 62 and because the pitch of the threads 64, 66 are equal, inserting the second threaded segment 62 into the bone will not require any additional rotation relative to the first threaded segment 60. In addition, in the example shown, the second thread 66 is approximately 180 degrees from the first thread 64, such that the threads of the second thread 66 are generally located in the middle between the adjacent turns of the first thread 64. In the example, the shape and arrangement of the thread with reference to bone screw 50, however, it should be understood that according to the invention other thread configurations and arrangements are also applicable.

[0021] It should be noted that the use of the first thread 64 with a single winding with a relatively large pitch improves the stability of the fixation in the bone spongy tissue, while allowing the strength and structural integrity of this bone to be maintained. In addition, the implementation of the second thread with a double winding provides increased fastening strength and stability in relatively harder and higher cortical bone density. In addition, as indicated above, the implementation of the second threaded segment 62 with a double winding, in which the pitch p of both turns are equal, will not require any additional rotation of the bone screw 50 for embedding in the cortex compared to the embedding of the first threaded segment 60 in the spongy bone .

[0022] In the solution of the invention, the first and second threaded segments 60, 62 define the diameter di of the inner thread core, which varies over the distance between the free end 50a and the inner end 50b. In the exemplary embodiment, the diameter di of the inner thread core increases from the first diameter d1 of the core at the free end 50a to the larger second diameter d2 at the middle section of the threaded spindle 52 up to the even larger third diameter d3 of the core at the inner end 50b. In another embodiment, the inner diameter d of the thread core increases uniformly between the diameter d1 of the core at the free end 50a and the diameter d3 of the core at the inner end 50b. In yet another exemplary embodiment, the inner diameter di of the thread core increases significantly along the entire length I of the threaded rod 52 between the free end 50a and the inner end 50b. In a characteristic embodiment, the inner diameter di of the thread core increases approximately by at least 15% from the diameter of the core di at the free end 50a to the diameter d3 of the core at the inner end 50b. In another example, the inner diameter di of the thread core increases approximately by at least 25% from the diameter d1 of the core to the diameter d3 of the core. In yet another embodiment, the inner diameter di of the thread core increases approximately by at least 50% between the diameter d1 of the core and the diameter d3.

[0023] It should also be noted that increasing the inner diameter di of the thread over the free end 50a towards the inner end 50b reduces the depth of the first and second threads 64, 66 (measured from the thread core diameter to the outer thread diameter) along the mandrel. threaded on a line from the free end 50a towards the inner end 50b. It should further be noted that the relatively large depth of the first thread 64 (or relatively small diameter di core) facilitates the attachment of the screw in the spongy bone and improves the desired pull-out resistance compared to the smaller depth of the second thread 66. In contrast, the reduced depth of the second thread 66 (or larger inner diameter di thread of the thread) compared to the first thread 64 provides increased strength and stability of attachment in a relatively harder and denser cortical bone, and further reduces resistance when screwing the thread into the bone. In one embodiment of the invention, the depth of the first and second threads 64, 66 decreases approximately by at least 50% from the free end 50a to the inner end 50b. It should be noted that the depth of threads 64, 66 is maximized along the first threaded segment 60, and especially at the free end 50a, to provide increased fastening capabilities in the spongy bone and desirable pulling properties.

[0024] According to the invention, the outer diameter d0 of the threads of the first and second threaded segments 60, 62 is equal between the free end 50a and the inner end 50b. In one exemplary embodiment, the outer diameter d0 of the thread at the free end 50a is at least 15% larger than the inner diameter d of the thread core. In another example, the outer diameter d0 of the thread at the free end 50a is approximately at least 25% larger than the inner diameter d of the thread at the inner end 50b. In yet another exemplary embodiment, the outer diameter d0 of the thread is approximately at least 50% larger than the inner diameter of the thread core di at the free end 50a. It should be noted that the greater difference between the outer diameter d0 of the thread and the inner diameter di of the thread improves bone embedding, which is particularly important for the first threaded segment 60 which is embedded in spongy tissue.

[0025] According to another aspect of the invention, the thread pitch p at the free end 50a is equal to or greater than the inside diameter d of the thread core at this section. In the exemplary embodiment, the pitch p of the thread is equal to or greater than the inside diameter d of the thread along the entire length I1 of the first threaded segment 60 threaded rod 52. In another example, the thread pitch p is equal to or greater than the inside diameter d of the thread core along the entire length l of the threaded spindle 52.

[0026] As indicated above, the head 54 of the bone screw 50 is preferably adapted to be connected to the implant. As shown in Fig. 3, in an exemplary embodiment of the invention, the screw head 54 is equipped with a non-threaded spindle section 58, and the implant is equipped with an elongated spinal rod R, which is connected to the screw head 54 by means of a connecting mechanism 70. This connecting mechanism 70 is provided with a body 72 forming a first hole 74b for seating the spinal rod R. Coupling member 76 can be positioned between the spine rod R and the unthreaded spindle 58, and the fastener or set screw 78 is screwed into the hole in the body 72 and presses the spinal rod R, which in turn connects via the engaging member 76 to the spindle 58 head 64 screws, setting the angular alignment of the spine rod R and bone screw 50. Further details about the joining mechanism 70 and other types of joining mechanisms are presented and described, for example, in US Patent 5,643,263 (Simonson), in US Patent No. 5,947,967 (Barker) and in US Patent No. 6,471,703 (Ashman).

[0027] In the solution of the invention, another bone screw 80 connecting to the spinal rod R is shown in Fig. 4. In particular, the bone screw 80 is equipped with a threaded rod 52 and the head 84 adapted to engage with the spinal rod R. The threaded rod 52 is same as described above and shown in Figures 2 and 3. In contrast, the bone screw head 84 forms a U-shaped channel 86 in which the vertebral rod R is embedded, the vertebral rod R itself being fastened inside the channel 86 by means of a fastening element or screw 88 coupled to the head of the bone screw 84.

[0028] Fig. 5 shows a bone screw 90 in another embodiment of the invention that attaches to the implant, for example to the spinal plate

P. In this solution, the vertebral plate P is provided with one or more holes 92 in which one or more bone screws 90 with an enlarged head 94 are mounted. In the example shown, the bottom part of the hole 92 is dimensionally adapted to the threaded through it and the upper part of this hole is adapted to the dimensions of the enlarged head 94 of the bone screw. It should be noted that screwing the bone screw 90 into the bone causes the spinal plate P to be pressed against the outer surface of the bone, as a result of which the spinal plate P is gripped between the enlarged head 94 and the outer surface of the bone.

[0029] Fig. 6 shows a bone screw 90 'according to another embodiment of the invention used to connect to the spinal plate P'. Bone screw

90 'is equipped with a threaded spindle 52, enlarged head 94' and a threaded spindle section 96 protruding from the enlarged head 94 'on which the spine plate P' is mounted, provided with one or more holes 92. Threaded stem sections 96 are inserted in these holes one or more 90 'bone screws. In addition, the bone screw 90 'is equipped with a set nut 98 mounted on the protruding threaded stud 96 so that the spine plate P' is clamped between the enlarged head 94 'and the set nut 98. It should be noted that the bone screw 90' shown in Fig. 6 moving the spinal plate P 'away from the outer surface of the bone.

[0030] After describing the components and properties of the solution according to the invention, the method of joining the bone screw with the bone will be presented below. As shown in Figs. 3-6, in an exemplary embodiment of the present invention, the bone is a vertebral body V consisting of the inner region of the spongy bone 100 and the outer region of the cortical bone 102. As described above, the outer cortical bone 102 of the V vertebral body is harder and more dense compared to the internal spongy bone 100. The threaded stem 52 of the bone screw is screwed into the V vertebral body, with a second threaded segment 60 equipped with a single-thread 64 being embedded in the internal area spongy bone 100, and a second threaded segment 62 with a relatively finer two-threaded thread 66 is screwed into the outer cortical region 102.

[0031] It should be noted that the relatively wide mono-thread 64 provides better bone anchoring capabilities and desirable pull properties compared to the finer dual-thread 66, which is particularly advantageous when depositing in soft spongy bone. In addition, it should be noted that the relatively fine double-threaded thread 66 provides better fastening strength and stability compared to the single-threaded thread 64, which is more advantageous when inserting the screw into harder and denser cortical bone. In addition, because the pitch p1, p2 of the single-threaded thread 64 and the double-threaded thread 66 are essentially the same, screwing the second threaded segment 62 into the cortical bone 102 will not require any additional rotation compared to screwing the first threaded segment 60 into the spongy bone 100 to achieve complete seat of the bone screw in the vertebral body V. It should be noted that a spinal implant, for example a rod or plate, can be connected to one or more bone screws, which in turn are anchored in the respective V vertebral bodies.

[0032] The bone screws of the invention may be embedded in any number of V vertebral bodies, i.e., either in a single vertebral body or in two or more vertebral bodies. In an exemplary embodiment of the present invention, the bone screws are anchored in the region of the arches of the vertebral body. Bone screws may also be embedded in other parts or areas of the vertebral body. It should also be understood that the bone screws of the invention may be attached to any part of the spine, i.e., the cervical, thoracic or lumbar region, as well as to bone structures other than the vertebral bodies, for example, to the bones of the upper or lower extremities.

[0033] Although the invention has been described in detail in the exemplary embodiment shown in the drawing, this solution should be regarded as merely explanatory, which does not limit the scope of the invention. Notwithstanding the examples shown and described, all changes and modifications within the scope of the invention are protected.