Bone plate

CA 02567321 2012-01-31

BONE PLATE

FIELD OF THE INVENTION

[002] The present invention relates generally to devices for bone fracture fixation and more specifically, to bone plates and systems for stabilization and/or compression of bone fractures.

BACKGROUND OF THE INVENTION

[003] The use of bone plate and screw systems for treatment of bone fractures is widespread. Conventional bone plate and screw systems promote healing of a fracture by compressing the fracture ends together and drawing the bone fragments into close apposition with each other. If the plate is not provided with the appropriate hole types adapted to receive the proper screw types, then the angular relationships between the plate and screws may change postoperatively. This can lead to malalignment and poor clinical results.

[004] Among the various different types of bone plate holes that are known in the art are the two different types of holes described below, each hole primarily intended for use with a different type of bone screw.

[005] The first type of hole is a non-threaded relatively smooth hole, through which a screw with a smooth (non-threaded) head is inserted. These screws do not lock with the bone plate and are thus referred to as “non-locking” screws. Because non-locking screws do not lock with the plate hole, non-locking screws are not limited to a fixed angle with respect to the plate, but rather can be inserted at numerous angles. Inserting non-locking screws through the non-threaded plate holes and threading them into the bone effectively provides the desired compression of fracture ends.

[006] The second type of hole is an internally threaded hole, which is adapted to mate with a screw having an externally threaded head. The threaded-head or “locking” screw is inserted at a fixed, predetermined angular relationship (determined by the central axis of

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WO 2005/112802 PCT/US2005/017987 the threaded hole) with respect to the bone plate. Locking screws, when mated with threaded bone-plate holes, possess high resistance to shear and torsional forces. Locking screws therefore resist loosening and thereby ensure stability between the screw and the bone plate. [007] Bone plates having both of the aforementioned types of holes are therefore desirable and are well known. Surgeons are limited, however, by the manufacturers’ placement of the varying holes on a given bone plate. A surgeon can achieve optimal compression when using a screw (e.g., a non-locking screw) without locking it to the plate. A surgeon can achieve desired stability between the screw, plate, and bone when using a locking screw with an internally-threaded hole.

[008] It would thus be advantageous for a hole in a bone plate to be adapted to receive, at the surgeon’s election, either non-locking screws for obtaining optimal compression or locking-screws for obtaining optimal stability, while minimizing any compromise in the strength of the bone plate.

SUMMARY OF THE INVENTION

[009] The bone plate of present invention is a bone plate used for bone fracture fixation. Various embodiments of a bone plate having coaxial combination holes are described.

[0010] Among the various different types of bone plate holes that are known in the art are threaded holes and non-threaded holes. “Locking” screws (screws with threaded heads) are typically used with threaded holes. Locking screws, when mated with threaded holes, possess high resistance to shear and torsional forces and therefore ensure stability between the screw and bone plate. “Non-locking” screws are typically used with unthreaded holes and, unlike locking screws that mate with threaded holes, may be inserted at any one of a number of angles. Non-locking screws provide optimal compression of fractured ends. [0011] A coaxial combination hole is, at once, adapted to receive (and utilize the benefits of) either a locking screw or non-locking screw. A coaxial combination hole is a hole which is threaded only partially through its length. In one preferred embodiment, the hole has a generally circular cross section with varying hole diameter. In a preferred embodiment, the hole has three regions: an upper region, a middle region, and a lower region. The upper region may be unthreaded and may have, in a direction from the plate’s upper surface to its lower surface, a curved inward taper. The middle region may be threaded and may have, in a direction from the plate’s upper surface to its lower surface, a conical inward

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WO 2005/112802 PCT/US2005/017987 taper. The lower region may be unthreaded and may have, in a direction from the plate’s upper surface to its lower surface, an outward taper.

[0012] It will be appreciated that either type of the aforementioned screws may be used (and produce its intended results) with a coaxial combination hole. The threaded head of a threaded-head screw may mate with threaded middle region of the hole. Alternatively, a screw with an unthreaded head (or even a screw with a threaded head) may be inserted through a coaxial combination hole, without any mating of any threads, at any one of a number of angles. The outward taper of the coaxial combination hole’s lower region provides room for the screw’s shaft to be inserted an angle (with respect to the center of the hole). Likewise the curved inward taper of the upper region of the hole provides a seat for the screw head to rest in, even when the screw is inserted ant an angle. It will be appreciated, then, that at any given coaxial combination hole, a surgeon may elect to use either a screw for screw-plate stability or a screw for compression of fracture ends.

[0013] Coaxial combination holes may be placed in any type of bone plate. Coaxial combination holes provide multiple options for the surgeon. And because the holes do not require a larger cavity in the bone plate than would otherwise be necessary for an ordinary hole, the strength, size, and integrity of the bone plate are not compromised. Coaxial combination holes are therefore particularly useful in relatively small bone plates (e.g., pubic symphysis plates).

[0014] A coaxial combination hole has a central axis and a vertical axis. The hole’s vertical axis is perpendicular to the plane formed by the plate’s upper surface (if the plate has a straight upper surface), or to the plane that is tangential to the pinnacle of the plate’s upper surface (if the plate is convex). A hole may have a central axis that is parallel to its vertical axis, or that is not parallel to its vertical axis (thereby biasing the shaft of the screw in one direction or another). A plate may have holes with any combination of foregoing hole orientations.

[0015] In preferred embodiments, bone plates have between 4 and 8 holes. In some embodiments, all plate holes are coaxial combination holes. In other embodiments, the bone plates may have some coaxial combination holes and at least one of another of a number of types of holes. One example of another type of hole is a dynamic compression (“DC”) hole. A dynamic compression hole may be an elongated hole having an oblique portion or ramp having an inclination such that when the ramp is engaged by the underside of the head of a screw, the bone plate is displaced in a direction to move the ramp away from the non-locking

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WO 2005/112802 PCT/US2005/017987 screw, causing the plate to apply a pressure to hold the fracture ends in contact or in tight engagement. Another example of another type of hole is a non-coaxial combination hole. A non-coaxial combination hole may be an elongated hole having a portion of its perimeter threaded and another portion of its perimeter unthreaded. In addition to, or in lieu of, the foregoing two examples, other types of holes may be formed in a bone plate having coaxial combination holes.

[0016] In one embodiment of the bone plate, the plate has a longitudinal axis, and has a straight center portion and curved ends. In one embodiment, the plate has two holes in the straight portion and two holes in each of the curved end portions. In one embodiment of this plate, all six holes may be coaxial combination holes. In another embodiment of this plate, the two holes on the straight portion may be either DC holes or non-coaxial combination holes, and the four holes on the curved end portions may be coaxial combination holes. In one embodiment of this plate, the width of the bone plate is narrower where there are no holes than where there are holes.

[0017] In another embodiment of the bone plate, the plate has a longitudinal axis and is straight. In one embodiment, the plate may have only coaxial combination holes, all of which may lie along the plate’s longitudinal axis.

[0018] In another embodiment of the bone plate, the entire plate may be curved. In one embodiment, the plate may have only coaxial combination holes, all of which may lie along the plate’s longitudinal axis (which runs along the center of the plate’s width).

[0019] In the various embodiments, the plate’s upper and lower surfaces may be straight or curved. In a preferred embodiment, the plate’s upper surface may be convex, while the plate’s lower surface may be concave.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] These figures represent preferred embodiments of the present invention.

Those skilled in the art will recognize that numerous variations and modifications may be made without departing from the scope of the present invention. Accordingly, it should be understood that these figures are not intended as limitations on the scope of the invention, which is defined only by the claims.

[0021] FIG. 1A is a side cross-sectional view of a first embodiment of a bone plate having coaxial combination holes.

[0022] FIG. IB is a plan view of the bone plate of FIG. 1 A.

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<td> [0023]</td><td> FIG. IC is a cross-sectional view of the bone plate of FIG. 1A taken along the</td>

cross section B-B.

<td> [0024]</td><td> FIG. 2A is a side cross-sectional view of a second embodiment of a bone plate</td>

having coaxial combination holes and having dynamic compression holes.

<td> [0025] [0026]</td><td> FIG. 2B is a plan view of the bone plate of FIG. 2A. FIG. 2C is a cross-sectional view of the bone plate of FIG. 2A taken along the</td>

cross section B-B.

<td> [0027] holes.</td><td> FIG. 3 A is a third embodiment of a bone plate having coaxial combination</td>

<td> [0028]</td><td> FIG. 3B is a plan view of the bone plate of FIG. 3A.</td>

<td> [0029] hole.</td><td> FIG. 4A is a cross-sectional view of one embodiment of a coaxial combination</td>

<td> [0030]</td><td> FIG. 4B is a magnified view of a portion of the thread of the coaxial</td>

combination hole of FIG. 4A.

<td> [0031]</td><td> FIG. 5 is a cross-sectional view of a screw, having a threaded head, inserted</td>

through a coaxial combination hole.

<td> [0032]</td><td> FIG. 6A is a cross-sectional view of a screw, having a non-threaded head,</td>

inserted through a coaxial combination hole at one angle.

<td> [0033]</td><td> FIG. 6B is a cross-sectional view of a unthreaded-head screw inserted through</td>

a coaxial combination hole at an angle different from that of the screw of FIG. 6A.

<td> [0034]</td><td> FIG. 7 is a plan view of a segment of a bone plate having non-coaxial</td>

combination holes.

<td> [0035] condition.</td><td> FIG. 8 is a plan view of the bone plate of FIGS. 3A and 3B, in a curved</td>

<td> [0036]</td><td> FIG. 9 is a side view of one embodiment of a screw that has a conically-</td>

tapered threaded head.

<td> [0037] head.</td><td> FIG. 10 is a side view of one embodiment of a screw having an unthreaded</td>

<td> [0038]</td><td> DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is described below with reference to the preferred</td>

embodiments. Those skilled in the art will recognize that numerous variations and modifications may be made without departing from the scope of the present invention.

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Accordingly, it should be understood that the embodiments of the invention described below are not intended as limitations on the scope of the invention, which is defined only by the claims.

[0039] Reference is now made to FIGS. ΙΑ, 2A, and 3A, which illustrate side, crosssectional views of various embodiments of a bone plate. The bone plates may have at least one coaxial combination hole 90, which has a length L that extends from the upper surface of the bone plate to the lower surface of the bone plate. The coaxial combination hole 90 is threaded only partially through the hole’s length L. As such, with a given coaxial combination hole, a surgeon may elect to: (1) thread a screw having a thread on at least a portion of its head into and through the hole; or (2) insert a screw having an unthreaded head through the hole and into the bone. In a preferred embodiment, the hole 90 has length L of approximately 3.4mm to 4.0mm, which preferably corresponds to the thickness T of the bone plate.

[0040] Reference is now made to FIGS. IB, 2B, and 3B, which illustrate plan views of various embodiments of the bone plate having at least one coaxial combination hole 90. Each bone plate may have at least a central region with a longitudinal axis L-L. Each bone plate hole 90 may have a vertical axis V-V, which is perpendicular to the plane on which the plate’s upper surface lies (if the plate has a straight upper surface), or to the plane that is tangential to the pinnacle of the plate’s upper surface (if the plate is convex). (See FIGS. IA, 2A, and 3A.)

[0041] Reference is now made to FIGS. IC and 2C, which illustrate cross-sectional views of the bone plates along the respective cross sections B-B. In a preferred embodiment, the upper surface of the plate may be convex and the lower surface of the plate may be concave, as shown in FIGS IC and 2C. In a preferred embodiment, the radius of curvature for both surfaces may be from about 15mm to about 35mm, and preferably about 25mm. In another embodiment, one or both of the plate surfaces may be flat.

[0042] As shown in FIG. 1 A, hole 90 may extend from the upper surface 20 to the lower surface 22 of the bone plate 10. In one embodiment, the diameters of the hole 90 at its uppermost surface and its lower most surface may be equal or close to equal. The hole 90 may be widest at the uppermost surface 20 and lowermost surface 22 of the plate 10. Each hole 90 may have a central axis C-C. (See FIGS. IA and 2A.) In some embodiments of the hole 90, the central axis C-C of hole 90 may be parallel to the vertical axis V-V, as shown in FIG. 3A (central axis C-C not shown). In other embodiments, the central axis C-C of hole 90

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WO 2005/112802 PCT/US2005/017987 will intersect with the vertical axis V-V at an angle Θ, as shown in FIGS. IA and 2A. In preferred embodiments, the angle Θ may vary from about 3° to about 17°, although other angles are contemplated.

[00431 As shown in FIG. 4A, the hole 90 may have three regions: an upper region 92, a middle region 94, and a lower region 96. The upper region 92 of the hole 90 may have an unthreaded inner surface 93 which, is preferably smooth, although texturing may be provided. In a preferred embodiment, the upper region 92 may have a curved inward taper, preferably concave, more preferably spherical, from the top surface of the plate to where the upper region 92 of the hole 90 meets the middle region 94. The upper region 92 of the hole 90 is preferably narrowest where it meets the middle region 94. Preferably, the upper region is approximately 1.0mm to approximately 1.2mm in length (along the axis C-C). In a preferred embodiment, the upper region may comprise about 25% to about 35% of the thickness T of the plate. In one embodiment, the diameter of the upper region 92, at the region’s broadest point, may be about 6mm and, at the region’s narrowest point, may be about 4mm. In another embodiment the diameter of the upper region 92, at the region’s broadest point, may be about 8mm and, at the region’s narrowest point, may be about 6mm. [0044] The middle region 94 of the hole 90 may have a threaded inner surface 95. In one embodiment, the threads have a pitch P (as shown in FIG. 4B, which is a magnified partial view of the threaded surface 95) of approximately 0.3mm to 0.5mm. In a preferred embodiment, the thread angle γ may be approximately 50° to 70°, and preferably about 60°. In a preferred embodiment, the threaded region has at least one thread revolution, and preferably about three thread revolutions. Referring again to FIG. 4A, the threaded inner surface 95 may, in a direction from the upper surface to the lower surface, have a conical inward taper. In a preferred embodiment, the threaded inner surface 95 may taper at an angle a of approximately 5° to 15°, and preferably approximately 10°. The middle region 94 may be the narrowest region (i.e., smallest-diameter region) of the hole 90. In a preferred embodiment, the middle region 94 may be approximately 1.5mm to approximately 1.9mm in length (along the axis C-C). In a preferred embodiment, the middle region 94 may comprise about 40% to 50% of the thickness T of the plate. In one embodiment, the diameter of the middle region 94 may vary only slightly (due to the relatively shallow conical taper) and may be about 4mm or, in another embodiment, about 6mm. The diameter or taper of the middle region 94 may of course vary depending upon the size and/or taper of the screw.

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[0045] The lower region 96 of the hole 90 may have an unthreaded inner surface 97 which is preferably smooth, although texturing may be provided. In a preferred embodiment, the lower region 96 may, from where it meets the middle region 94 to the lower surface of the plate, have a conical outward taper. In a preferred embodiment, the lower region 96 may taper outwardly at an angle β of approximately 35° to 55°, and preferably approximately 45°. In a preferred embodiment, the lower region 96 may be approximately 0.8mm to approximately 1.2mm in length (along the axis C-C). In a preferred embodiment, the lower region 96 may comprise about 20% to 35% of the thickness T of the plate. In one embodiment, the diameter of the lower region 96, at the region’s narrowest point, may be about 4mm and, at the region’s broadest point, may be about 6mm. In another embodiment, the diameter of the lower region 96, at the region’s narrowest point, may be about 6mm and, at the region’s broadest point, may be about 8mm.

[0046] Different types of screws may be used with the hole 90. One type of screw is a screw that has a conically-tapered threaded head (shown in FIG. 9). As shown in FIG. 5, the external threads of the screw’s head may mate with the internal threads 95 of the middle region 94 of the hole 90. This threaded-head screw 15 may be inserted at only one angle (with respect to the plate), which may be fixed by the threads 95 in the plate 10.

[0047] A second type of screw that may be used with the hole 90 is a screw with a threaded shaft, but with an unthreaded head (shown in FIG. 10). An unthreaded-head screw may be inserted into hole 90 at any one of a number of angles. FIG. 6A illustrates an unthreaded-head screw 17 inserted at an angle substantially perpendicular to the longitudinal axis of the plate 10. FIG. 6B illustrates an unthreaded-head screw 17 inserted at a nonperpendicular angle with respect to the plate 10. The conical outward taper (shown at surface 97) of the lower region 96 of the hole 90 provides room for screw shaft 18 to be inserted at an angle with respect to the center of the hole 90. Likewise, the curved inward taper of the upper region 92 of the hole 90 provides a seat (at surface 93) for the screw head to rest in when an unthreaded-head screw 17 is inserted at an angle. A threaded-head screw may be used with a coaxial combination hole 90 in the same manner as the aforementioned unthreaded-head screw 17.

[0048] Although virtually any type of bone plate may benefit from coaxial combination holes 90, coaxial combination holes are particularly useful for pubic symphysis plates and other relatively small bone plates. (The pubic symphysis is the connection between the two halves of the pubis and may be damaged as a result of an accident.) Because

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WO 2005/112802 PCT/US2005/017987 a surgeon may elect to use either a locking screw or a non-locking compression screw with a coaxial combination hole, a bone plate having a coaxial combination hole may be more versatile than plates having other types of holes. The benefits may include: (1) a reduced need to manufacture many different plates having varying hole arrangement patterns; and (2) enhancement of clinical results. Because a coaxial combination hole does not require a substantially larger cavity in the bone plate than would otherwise be necessary for a simple hole, a coaxial combination hole provides desired flexibility for the surgeon without unduly compromising the strength, size, or integrity of the bone plate. Plates having coaxial combination holes may thus find particular utilization in pubic symphysis plates and other relatively small bone plates.

[0049] In one embodiment, the bone plate of the present invention may be a pubic symphysis plate as shown in FIG. IB, and may have a plurality of holes, all of which may be coaxial combination holes 90. In one embodiment, the plate may have a length PL of approximately 70mm to 90mm. In one embodiment, the plate may have curved ends, as shown in FIG. IB, with a radius of curvature R. In a preferred embodiment, two coaxial combination holes 90 are located on the straight center portion of the plate. In a preferred embodiment, the plate ends may curve approximately at a 45mm-55mm radius R, spanning a 25°-35° angle δ. Preferably two coaxial combination holes 90 are placed along an arcs (on both sides of the plate’s straight center portion) having a radius of curvature of about 50mm. In a preferred embodiment, the hole 90 on the curved portion adjacent to the hole 90 on the straight portion is located approximately 12°-18° on the arc away from the hole 90 on the straight portion. Likewise, the two holes 90 on either curved portion may be placed along an arc approximately 12°-18° apart from each other. In a preferred embodiment, the plate may be symmetrical from one side to the other (i.e., a mirror hole arrangement on the other side of the plate is contemplated). In a preferred embodiment, the two holes near the center of the plate may lie along the longitudinal axis L-L of the center region of the plate 10. The remaining holes may be offset from the longitudinal axis L-L, as shown in FIG. IB.

[0050] In a preferred embodiment, the central axes C-C of the holes 90 are not parallel to the respective vertical axes V-V of the holes 90. In a preferred embodiment, as shown in FIG. 1 A, the two holes near the center of the plate have central axes C-C oriented to bias the tips of the screws in a direction away from the center of plate. In a preferred embodiment, the angle Θ between each of these two central axes C-C and the vertical axes VV is approximately 8° to 15°. In a preferred embodiment, as shown in FIG. 1A, each of the

-9CA 02567321 2012-01-31 holes 90, that are located near the ends of the plate, has a central axis C-C oriented to bias the tips of the screws in a direction towards the center of plate. In a preferred embodiment the angle Θ between each of these central axes C-C and the vertical axes V-V is approximately 4° to 10°.

[0051] In a preferred embodiment, the linear plate-surface distance dl between the edges of holes 90 may vary from hole to hole and may be approximately 10mm to 12mm. In a preferred embodiment, as shown in FIG. IB, there may be necking of the plate surface in between hole locations (i.e., the webs between the holes may be narrowed). This necking serves to achieve a desired balance between plate strength and plate size: plate strength is maximized, while plate size is minimized. In another embodiment the width of the plate between holes may be the same as the width of the plate where the holes are located.

[0052] In a preferred embodiment, the plate may have at least one hole 99, preferably near the center of the plate. Holes 99 may aid in the placement of the plate onto the bone (e.g., for use with a guide wire) or may be provided as a suture hole.

[0053] Generally, for all embodiments, a shorter bone plate having only a few (e.g.,

4) holes may be used when the fracture is relatively small or when the patient’s bone or joint (e.g., pubic symphysis) being operated on is relatively small.

[0054] A plan view of a second embodiment of a pubic symphysis plate is shown in

FIG. 2B. The primary difference between this embodiment and the foregoing embodiment (which is illustrated in FIGS. 1A and IB) is that the two holes near the center of tire plate 30 of this embodiment are dynamic compression (“DC”) holes 70 instead of coaxial combination holes 90. This embodiment of a bone plate is particularly useful when, to bring parts closer together, “extra” compression is desired. The DC holes are substantially similar to those disclosed in die specifications of United States publication No. 2002/0045901, in U.S. patent No. 6,669,701, and in reissued U.S. Patent No. RE. 31,628.

As shown in FIG. 2B, DC hole 70 is elongated in a direction substantially aligned with the longitudinal axis L-L of the plate 30. As shown in FIG. 2B, DC hole 70 has an oblique portion or ramp 35 having an inclination such that when ramp 35 is engaged by the underside 13 of the head of a screw, preferably a screw having a head that is not threaded, and is preferably smooth and curved on the underside 13 which contacts the bone plate, the bone plate 30 is displaced in a direction to move ramp 35 away from the non-locking screw, causing the plate 30 to apply a pressure to hold the fracture ends in contact, preferably in engagement, along at least a portion of the fracture length. In a

-10CA 02567321 2012-01-31 preferred embodiment, each of the holes 30 has a lèrigth X (illustrated in FIG. 2A) of approximately 6mm to 7mm.

[0055] Alternatively, the two holes near the center of the plate 30 may be non-coaxial combination holes 40 (instead of coaxial combination holes 90 or DC holes 70). The noncoaxial combination holes are substantially similar to those disclosed in the specifications of U.S. patent No. 6,669,701 and of United States publication No. 2002/0045901 .

Reference is now made to FIG. 7. FIG. 7 illustrates a bone plate having a plurality of combination holes 40, which extend from the plate’s upper surface to its lower surface. The holes 40 may be elongated (e.g., in a direction substantially aligned with a longitudinal axis of the plate) and may include a threaded portion 5 and a non-threaded portion 6. The threaded portion 5 may extend over a range of greater than about 180° with respect to a center point Cl. Tire threaded portion 5 of the hole 40 may be dimensioned and configured to engage a threaded head portion of a threaded-head bone screw, and fix the bone screw at a predetermined angle with respect to the bone plate. Preferably, the threaded portion 5 of the hole 40 extends through the full thickness of the bone plate (Le., from the plate’s upper surface to its lower surface) thus maximizing the stability of the bone screw to bone plate interface. A threaded-head screw or a non-threaded head screw may (e.g., for compression) pass through the non-threaded portion 6 of a combination hole 40.

[0056] Another embodiment of a plate having coaxial combination holes is illustrated in FIGS. 3 A and 3B. In one embodiment, the plate 50 may have a plurality of holes, all of which may be coaxial combination holes 90. Each of the holes 90 may lie along the longitudinal axis L-L of the plate 50. In one embodiment, the central axis C-C of each of the holes 90 may be parallel to the corresponding vertical axis V-V of each of the holes 90, as shown in FIG. 3A (central axis C-C not shown). In a preferred embodiment, the linear platesurface distance d2 between the edges of holes 90 may be approximately 6mm to 9mm. [0057] A variation on the aforementioned embodiment (illustrated in FIGS. 3A and

3B) is illustrated in FIG. 8. FIG. 8. is the bone plate of FIGS. 3A and 3B, in a “curved condition.” Though the bone plate of FIGS. 3A and 3B may be formed ôf such material to allow a surgeon to preoperatively bend the plate into a desired shape, a bone plate manufactured to a bend condition may be desirable. In tire human body, a ball-and-socket joint is formed by the two acetabula of the pelvis and the head of each femur. The bone plate of FIG. 9 may be especially useful for use on the posterior outer surface of a fractured

-11CA 02567321 2012-01-31 acetabulum. The plate may have a radius of curvature R, which in a preferred embodiment, is about 100-115mm.

[0058] While the present invention has been described with reference to the preferred embodiments, those skilled in the art will recognize that numerous variations and modifications may be made.