Polyaxial bushing for locking plate

[0001] This application claims the benefit of U.S. Provisional Application No. 61/259,500, filed Nov. 9, 2009, the entire disclosure of which is incorporated by reference herein.

[0002] The present invention relates to bone plates having locking bushings.

[0003] Bone plates known in the art are typically provided with self-tapping bone plate screws that allow the bone plate to be secured to a surface of the bone. The screws are inserted through holes, which are formed into the bone plate and which contain washers or bushings that are rotatable in the holes. When the screw is inserted, the head of the screw typically spreads the bushing (for example, a split-sleeve bushing) as the screw advances and ultimately locks the bushing to the bone plate. The bushings may provide for variable angles of insertion for the screws. During insertion of the screws into the bone plate, the bushings may inadvertently rotate within the screw hole or even dislodge from the through-hole of the bone plate, causing a delay in the surgical procedure.

[0004] Accordingly, there is a need for a bone plate provided with a new design that prevents the bushing from rotating and/or dislodging from the screw hole during screw insertion. Also needed is a bushing design that allows the screw to be locked at variable angles.

[0005] The present invention provides a bone plate, preferably a humeral plate, with a new design that prevents the bushing from rotating and/or dislodging from the screw hole during screw insertion. The bushing design of the present invention also allows the screw to be locked at variable angles.

[0006] The plate of the present invention is provided with through-holes having internal walls with at least one flat that is configured to align with a corresponding flat provided on the outer wall of the bushing. The bushing is inserted by orienting the bushing in a direction perpendicular to the through-hole of the plate (screw hole) so that the center of the bushing is aligned with the center of the through-hole and the flat on the bushing is aligned with the flat on the through-hole of the bone plate. The bushing is introduced into the through-hole until the centers are aligned, and then the bushing is rotated about 90 degrees so that the bushing is captured within the through-hole of the plate. Once captured, the bushing cannot rotate, dislodge from, or come out of the plate unless the bushing is turned 90 degrees. The flat on the bushing mates with the flat on the internal wall of the hole (screw hole) to prevent it from rotating within the screw hole. This important aspect avoids the need for a bushing guide during screw insertion.

[0007] In an alternate embodiment, the bushing may be provided with an optional post in addition to the flat to prevent the bushing from rotating.

[0008] These and other features and advantages of the invention will be more apparent from the following detailed description that is provided in connection with the accompanying drawings and illustrated exemplary embodiments of the invention.

[0027] The present invention provides a bone plate with a locking design that prevents the bushing from rotating and/or dislodging from the screw hole during screw insertion. The design of the plate and bushing of the present invention also allows the screw to lock at variable angles.

[0028] Referring now to the drawings, where like elements are designated by like reference numerals, FIGS. 1-6 illustrate a bone plate 100, 200 of the present invention provided with bushings 50, 150 that are designed to engage and lock within through-holes 20 of the plate, to form plate/bushing assembly 101, 201. As detailed below, the bushing 50, 150 is first inserted into the plate 100, 200 in a direction about perpendicular to the plate 100, 200, i.e., with the axis of the bushing oriented about perpendicularly to the axis of through-hole 20 of the plate, so that the center of the bushing is aligned with the center of the through-hole, and a flat on a lateral side of the bushing is aligned with a corresponding flat on an inner wall of the through-hole. At this step, the bushing is in an unlocked position. The bushing is then rotated within the through-hole 20 of the plate so that the top surface of the bushing is about parallel to the top surface of the plate, preferably in the same plane, to lock and constrain the bushing within the through-hole of the plate. At this step, the bushing is in a locked position. Unlocking of the bushing from the plate requires a manual step of physically rotating the bushing within the through-hole, so that the axis of the bushing is again oriented about perpendicularly to the axis of through-hole 20 of the plate, to allow the bushing to be pulled from the through-hole.

[0029] As shown in FIG. 1A, bone plate 100 has a body 10 provided with at least one through-hole (screw hole) 20. Body 10 may be formed of a metal, preferably titanium. As shown in FIGS. 1A-B, bone plate 100 has through-hole (screw hole) 20 with a generally spherical cross-section provided with a flat 22 on the inner wall of the through-hole. Flat 22 may have a square or rectangular configuration (surface area) and is configured to be aligned with a corresponding flat 55 on the bushing, as described below.

[0030] FIGS. 2A-C illustrate various views of bushing 50 of the present invention that is configured to engage the through-hole (screw hole) 20 of the plate 100 of FIG. 1, and to further allow a screw to lock at variable angles relative to body 10 of the plate. Bushing 50 may have a general donut-shape configuration, with upper and lower surfaces preferably planar, and sized so that it is inserted into the through-hole 20 and locked therein, as detailed below. Bushing 50 is provided with a generally spherical outer shape having at least one flat 55 (preferably, with two flats 55 as shown in FIG. 2) and a small cut (split) 59. Flat 55 may have a square or rectangular configuration (surface area) and is configured to be aligned with flat 22 on the plate. Preferably, flat 22 has a geometry similar to that of flat 55, and surface area about equal to the surface area of the flat 55.

[0031] During assembly with the plate to form assembly 101, as illustrated in FIG. 3A, the bushing 50 is first inserted by introducing the bushing in a direction about perpendicular to the through-hole of the plate, so that a longitudinal axis of the bushing is about perpendicular to the longitudinal axis of the through hole; aligning the center of the bushing with the center of the through-hole; and aligning the flat 55 of the bushing with the flat 22 of the plate, to place the bushing in the proper orientation for assembly.

[0032] As shown in FIG. 3B, rotating the bushing about 90 degrees allows the bushing to be constrained within the through-hole of the plate. The alignment of the flat 55 of the bushing 50 and the flat 22 of the bone plate 10 prevents rotation of the bushing within the through-hole 20. The bushing 50 is constrained within bone plate 10 due to the diameter of the bushing being larger than the diameter of the through-hole as shown in FIG. 3D. In this orientation, a top surface 51 of the bushing 50 is about parallel to a top surface 11 of the plate 100, preferably in the same plane, to lock and constrain the bushing 50 within the through-hole 20 of the plate 100 (as shown in FIGS. 3B-3D).

[0033] Once positioned within the through hole 20, the bushing 50 cannot rotate, or dislodge from, or otherwise come out of, the plate 100 unless the bushing 50 is turned again about 90 degrees relative to the plate. The flat 55 on the bushing 50 mates with the flat 22 on the internal wall of the hole (screw hole) 20 to prevent it from rotating within the screw hole 20. This aspect is important to avoid the need for a bushing guide during insertion of the screw. As the screw is inserted through the bushing, the head of the screw expands the bushing against the plate, locking the bushing to the plate. As the screw is advanced, the outward taper of the screw head spreads the split (small cut) 59 of the bushing, causing the bushing to become locked due to the frictional interference between the outer surface of the bushing and an inner surface (the walls) of the through-hole 20 of the plate 100. The process is repeated for a plurality of bushings and screws, and for each bushing individually, until the plate is secured to the bone.

[0034] During the screw insertion, as a result of the alignment/locking design of the bushing and through-hole, the bushing is prevented from rotating and/or dislodging from the screw hole. The bushing design also allows the screw to be locked at variable angles. If desired, the bushing is provided with internal threads corresponding to external threads on the body of the screw, to facilitate advancement of the screw through the passageway of the bushing.

[0035] Referring now to FIGS. 5A-C, bushing 150 according to a second exemplary embodiment of the present invention may be provided with an optional post 180 to prevent the bushing 150 from rotating. In an exemplary embodiment, post 180 extends about perpendicular to flat 155. Referring now to FIGS. 4A-B, bone plate 210 of the present invention may have a modified through-hole 220 to accommodate the bushing 150 with post 180. As shown, bone plate 210 has a through-hole 220 having a generally spherical shape with a slot 280 sized to fit the post 180 of bushing 150. The slot 280 captures the post 180 of the bushing 150 and prevents rotation of the bushing during screw insertion.

[0036] FIGS. 6A-D illustrate exemplary steps of assembling the bushing 150 to the bone plate 210 to form assembly 201. During assembly with the plate, and as illustrated in FIG. 6A, the bushing 150 is first inserted by introducing the bushing in a direction about perpendicular to the through-hole 220 of the plate, so that a longitudinal axis of the bushing is about perpendicular to the longitudinal axis of the through hole; aligning the center of the bushing with the center of the through-hole; and aligning the post 180 of the bushing with the slot 280 of the plate, placing the bushing in the proper orientation for assembly. As shown in FIG. 6B, rotating the bushing about 90 degrees allows the bushing to be constrained within the through-hole of the plate. The alignment of the post 180 of the bushing 150 and the slot 280 of the bone plate 10 prevents rotation of the bushing within the through-hole 220. The bushing 150 is constrained within bone plate 210 due to the diameter of the bushing being larger than the diameter of the through-hole as shown in FIG. 6D.

[0037] The present invention also provides a method of providing a bushing/plate assembly by inter alia: (i) providing a bushing with an alignment/locking mechanism configured to mate with a corresponding alignment/locking mechanism of an inner wall of a through-hole of a bone plate, when the bushing is inserted into the plate; (ii) introducing the bushing in a direction about perpendicular to the through-hole of the plate, so that the bushing is about perpendicular to the through hole, and the center of the bushing is aligned with the center of the through-hole; and (iii) rotating the bushing about 90 degrees so that the bushing is captured within the through-hole of the plate, and the alignment/locking mechanism of the bushing is aligned with the alignment/locking mechanism of the plate. The alignment/locking mechanism of the bushing may be a flat, a pin, or a combination of a flat and a pin. The alignment/locking mechanism of the wall of the through-hole of the plate may be a flat, a pin slot, or a combination of a flat and a pin slot.

[0038] The present invention also provides a method of assembling a bushing to a bone plate by inter alia: (i) providing a bushing with a first flat on the outer wall of the bushing, and providing a second flat on an inner wall of a through-hole of a bone plate, the second flat being configured to align with the first flat when the bushing is inserted into the plate; (ii) introducing the bushing in a direction about perpendicular to the through-hole of the plate, so that a longitudinal axis of the bushing is about perpendicular to a longitudinal axis of the through hole, and the center of the bushing is aligned with the center of the through-hole; and (iii) rotating the bushing about 90 degrees so that the bushing is captured within the through-hole of the plate (with the first flat aligned with the second flat).

[0039] Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. Therefore, the present invention is to be limited not by the specific disclosure herein, but only by the appended claims.