Orthopedic stabilization device and method

[0002] The instant invention is directed generally to devices used by orthopedic surgeons to stabilize and align skeletal structures. More specifically, the instant invention includes a fastener capable of rotation about an axis within a supporting cup, the cup contoured to receive a rod therein and a means to fix the rod and rotationally oriented fastener in a fixed position.

[0003] Orthopedic procedures involving stabilization of skeletal structure presently suffer from two common frailties: the first is the inability to orient the stabilizing structure for a multiplicity of common angulations and the second is the failure to provide a reliable thread portion which engages bone of the patient.

[0004] The instant invention provides the ability to address various skeletal components in a relational way by allowing articulation of the device in a multiplicity of angulations and to fasten to the skeletal structure to provide greater stabilization with an improved thread pattern which provides both axially compressive forces along the length of the fastener and radially inward drawing forces.

[0005] Accordingly, it is a primary object of the present invention to provide an orthopedic stabilization structure.

[0006] A further object of the present invention is to provide an improved threaded portion therefore.

[0007] A further object of the present invention is to accommodate a plurality of angulations when addressing a skeletal structure.

[0008] FIG. 1 is a top view of the fastener.

[0009] FIG. 2 is a side view of the fastener.

[0010] FIG. 3 is a sectional view of the fastener geometry.

[0011] FIG. 3A shows FIG. 3 with a taper.

[0012] FIG. 4 shows the fastener and stabilization structure.

[0013] FIG. 5 is another view of FIG. 4.

[0014] FIG. 6 displays angulation of the FIG. 4 structure.

[0015] FIG. 7 details a bolt used in the structure.

[0016] FIG. 8 details the bolt receiving area.

[0017] FIG. 9 shows one side of the cup.

[0018] FIG. 10 shows an adjacent side (90 degrees) relative to FIG. 9, showing a diametrical slot.

[0019] FIG. 11 is a top view of FIGS. 9 and 10.

[0020] FIG. 12 is a bottom view of FIGS. 9 through 11.

[0021] FIG. 13 is a sectional view of FIG. 9 along lines 13—13.

[0022] FIG. 14 is a sectional view similar to FIG. 4.

[0023] FIG. 15 adds a fastener and rod to FIG. 14.

[0024] FIG. 16 adds a fixing bolt to FIG. 15.

[0025] FIG. 17 shows the device deployed by way of example.

[0026] Considering the drawings, wherein like reference numerals denote like parts throughout the various drawing figures, reference numeral 100 is directed to the orthopedic stabilization device according to the present invention.

[0027] The device 100 allows a threaded fastener 10 to move about the arrow C as shown in FIG. 4 such that although the long axis of the threaded shaft is depicted as presently aligned, it can be rotated and skewed from a vertical long axis of a cup 130 as in FIG. 6. A rotational means 120 embodied as a disc has a cylindrical outer face 122 and planar top and bottom faces 124, 126. Thus, rotation about the arrow C occurs about a geometrical center 128. The disc 120 is integrally fixed to fastener 10. The rotational means 120 is constrained within a cup 130 having a central bore 132, an upper portion of which is provided with threads 111. In addition, a transverse slot 134 is cut along a diameter of the cup which allows slideable insertion therein of both the fastener 10 and integral disc 120 as well as a rod 136 transverse to a long axis of the cup 130. Please see FIGS. 9 through 16. The cup 130 is dimensioned such that the rotational means 120 is in tangential registry along one cylindrical face 122 with the rod 136. The threaded bore 132 receives a threaded fixing bolt 110 therewithin to press the rod 136 against the rotational means 120 to fix their relative relationship once appropriate orientation has occurred.

[0028] In its essence, the fastener 10 includes a threaded shaft 32 having a first thread pattern 12 at one end and a second thread pattern 14 at an opposite end. As shown in FIGS. 1 and 2, the first end thread pattern 12 terminates in a point 16 and the threads increase in diameter to form a thread pattern with its spiral increasing as it extends away from the point 16.

[0029] The second thread pattern 14 has a larger diameter but a similar thread contour which shall be discussed in detail infra. Preferably, the shaft 32 is of variable length and tapers and narrows from end 18 to point 16. Please see FIGS. 1 and 2.

[0030] A further nuance of the first and second thread patterns is that the first thread pattern 12 has a coarser thread than the second thread pattern 14 which is a finer thread. The point 16 is the point of initiation for insertion into a bone during an orthopedic procedure. To facilitate same, a pilot hole may be drilled in the bone but thereafter, because of the tapering nature of the first thread 12, this portion is thereafter self-threading. Notice that the crest 70 for both first and second thread patterns are sharp. This allows cutting into the bone which typically has a harder exterior than the interior. By providing a coarser thread pattern for the first thread 12, this thread will insert into the bone faster than the second thread pattern 14. As a consequence, when the bone begins to be engaged by the second thread pattern, an axial compression of the bone occurs along the direction of the two arrows A. In addition, because of the thread geometry, the threads will exert a radially inwardly directed force along the direction of the double-ended arrows B. Whereas in the prior art, conventional fasteners induced radially outwardly spreading (the opposite direction from arrow B), the instant invention provides radially inwardly or a drawing force B as well as the compressive force A.

[0031] The threads 60 of fastener 10 for threads 12 and 14 are actually one continuous helically wound thread which begins at the ends and spirals towards the medial portion of shaft 32 as it migrates from the ends. Please see FIG. 3.

[0032] The threads 60 include a sharpened crest 70 defining a major diameter 62 of the threads and a root 80 defining a minor diameter 64 of the threads 60. As shown in detail in FIG. 3, the threads 60 have an upper surface 66 which extends from a bottom edge 84 of the root 80 to the sharpened crest 70. The threads 60 also include a lower surface 68 which extends from a top edge 82 of the root 80 to the sharpened crest 70. Both the upper surface 66 and lower surface 68 angle toward the medial portion of the fastener as the surfaces 66, 68 extend from the root 80 to the crest 70.

[0033] In section, the surfaces 66, 68 extend linearly from the root 80 to the sharpened crest 70. However, as this contour is rotated helically about the threaded shaft 32 along with the threads 60, the upper surface 66 and lower surface 68 take on a curved surface appearance. This appearance is similar to that which would be formed by a linear section of the surface of a cone with a tip of the cone oriented downward and the cone rotated and translated upward along a central axis thereof. The upper surface 66 and lower surface 68 thus have a curved surface in three dimensions similar to that of a cone, but a linear character when viewed in section.

[0034] The upper surface 66 extends from the root 80 to the sharpened crest 70 at an upper surface angle α diverging from a reference plane orthogonal to the central long axis 2 of the fastener. The upper surface angle α is preferably 20° but could be any angle between 0° and 90°. The lower surface 68 extends from the root 80 to the sharpened crest 70 at a lower surface angle β with respect to the reference plane. The lower surface angle β0 is preferably 40° but could vary between 0° and 90°.

[0035] The upper surface angle α is preferably less than the lower surface angle β. In this way, the threads 60 are provided with greater thickness, and hence greater strength adjacent the minor diameter 64 than at the major diameter 62 and are thus more capable of bearing the loads experienced within the bone.

[0036] It is the angulation of the surfaces, especially upper surface 66 which encourages the radially inward force. When the upper and lower thread patterns are combined, axial compressive forces can be seen. Note the flat wall 54 of FIG. 3. This could replace point 16 and require a deeper pilot hole.

[0037] The second thread portion 14 has the same FIG. 3 geometry except that the threads 60aare inverted, and as mentioned earlier are a finer thread (greater threads per inch axially) than the first thread portion 12. In other words FIG. 3 would be viewed upside down for threads 14.

[0038] FIG. 3A shows a section of thread with a pronounced taper. For thread pattern 14, FIG. 3A would be viewed upside down and with a reverse taper to that shown.

[0039] A bottom 129 of cup 130 (FIG. 4) has clearance 22 which extends within an included arc preferably approaching 90 degrees to allow a wide range of fastener 10 rotation about arrow C. Rotation beyond this clearance 22 is prevented by cup wall structure 24 that survives both the clearance aperture 22 and the slot 134 that runs diametrically down two sides of the substantially cylindrical cup 100. Free ends 138 of the cup 100 need the support a bolt 110 (FIG. 16) to: (first) press the rod 136 in place by (second) applying pressure to the disk 120 and retaining it by (third) uniting the free ends 138.

[0040] The threads 60 of the threaded bolt 110 (FIGS. 7 and 16) are actually one continuous helically wound thread which begins at the bottom 54 and spirals up to the top 52. While this single thread design is preferred, other arrangements including compound series of threads which wind helically together from the bottom 54 to the top 52 could also be utilized.

[0041] The threads 60 include a crest 170 defining a major diameter 62 of the threads and root 80 defining a minor diameter 64 of the threads 60. As shown in detail in FIG. 7, the threads 60 have an upper surface 66 which extends from a bottom edge 84 of the root 80 to the upper edge 72 of crest 170. The threads 60 also include a lower surface 68 which extends from a top edge 82 of the root 80 to a lower edge 74 of the crest 170. Both the upper surface 66 and lower surface 68 angle upwards as the surfaces 66, 68 extend from the root 80 to the crest 170. Both the crest 170 and root 80 exhibit a constant distance from the central axis 2 between the top edge 82 and the bottom edge 84. Compared to FIG. 3, crest 170 is blunt, while crest 70 is sharpened. Also, bolt 110 and thread 111 could have sharp contours like crest 70 (replacing crest 170) and vice versa.

[0042] In section, the surfaces 66, 68 extend linearly from the root 80 to the crest 170. However, as this contour is rotated helically about the threaded bolt 110 along with the threads 60, the upper surface 66 and lower surface 68 take on a curved surface appearance. This appearance is similar to that which would be formed by a linear section of the surface of a cone with a tip of the cone oriented downward and the cone rotated and translated upward along a central axis thereof. The upper surface 66 and lower surface 68 thus have a curved surface in three dimensions similar to that of a cone, but a linear character when viewed in section.

[0043] The upper surface 66 extends from the root 80 to the crest 170 at an upper surface angle α diverging from a reference plane 4 orthogonal to the central axis 2. The upper surface angle α is preferably 20 degrees but could be any angle between 0 degrees and 90 degrees. The lower surface 68 extends from the root 80 to the crest 170 at a lower surface angle β with respect to the reference plane 4. The lower surface angle β is preferably 40 degrees but could vary between 0 degrees and 90 degrees.

[0044] The upper surface angle α is preferably less than the lower surface angle β such that a thickness of the threads 60 at the crest 170 is less than a thickness of the threads 60 between adjacent roots 80. In this way, the threads are provided with greater thickness, and hence greater strength adjacent the minor diameter 64 than at the major diameter 62 and are thus more capable of bearing the loads experienced within the threaded bore 132.

[0045] Referring now to FIG. 8, details of the threaded bore 132 on free ends 13 are shown. The bore is preferably substantially complemental in form to the threaded shaft of the bolt 110. The bore includes threads T. The thread geometry of the bolt 110 and threads T draw free ends 136 of cup 130 together along arrow D.

[0046] FIG. 17 shows a fractured bone and the device 100 being applied. The fasteners 10 with discs 120 and the cups 130 are located such that the fasteners 10 are located in the bone, but the disc can rotate within clearance 22 as described. Recall the threads 12, 14 axially compress and radially inwardly drawing in the bone. Next the rod 136 is placed within the slots 134 of the cups 130.

[0047] The rod is shown as having a bend 165 to demonstrate the system's versatility. Next the bolts 110 are threaded into threads 111 in the free ends 138 of the cups 130. As the bolts 110 bear on rod 136, the rod 136, disc 120 and fastener 10 become rigid. The free ends 138 also draw together tightly.

[0048] Moreover, having thus described the invention, it should be apparent that numerous structural modifications and adaptations may be resorted to without departing from the scope and fair meaning of the instant invention as set forth hereinabove and as described hereinbelow by the claims.