WO2006102110A1

WO2006102110A1 - Screw head adapter for bone plate

Info

Publication number: WO2006102110A1
Application number: PCT/US2006/009774
Authority: WO
Inventors: James K. Rains; Joseph M. Ferrante; Paul Tornetta
Original assignee: Smith & Nephew, Inc.
Priority date: 2005-03-17
Filing date: 2006-03-17
Publication date: 2006-09-28

Abstract

A system (10, 200) for mounting a bone plate (12, 50, 112, 212) to a bone (100, 210) is disclosed. The bone plate (12, 50, 112, 212) has a hole (52, 90, 92, 152) with an angle less than about 30 degrees. The system (10, 200) includes a screw (40, 40', 70, 140) with a head (42, 72) and a screw head adapter (20, 120, 220). The screw head adapter (20, 120, 220) has an inner portion (22) adapted to mate with the head (42, 72) of the screw (40, 40', 70, 140) and an outer portion (24, 124) with a shape corresponding to the angle of the hole (52, 90, 92, 152). An assembly of the screw (40, 40', 70, 140) and the screw head adapter (20, 120, 220) connect the bone plate (12, 50, 112, 212) to the bone (100, 210).

Description

SCREW HEAD ADAPTER FOR BONE PLATE

Cross-Reference to Related Applications

[0001] This application claims the benefit of U.S. Provisional Application No. 60/662,879, filed March 17, 2005. Statement Regarding Federally Sponsored Research or Development.

[0002] Not Applicable. Appendix.

[0003] Not Applicable.

Background of the Invention I. Field of the Invention

[0004] This invention relates generally to bone plates and, more particularly, to a screw head adapter for mounting a screw to a bone plate. 2. RelatedArt

[0005] Bone fractures lead to complex tissue injuries involving both the bone and the surrounding soft tissue. Treated in a conservative way, fractures often result in malalignment or non-unions and may also lead to stiffness of adjacent joints. To reduce the occurrence of these problems, open reduction and internal fixation of the bone can be carried out. Anatomical reduction and stable internal fixation with plates and screws are very successful in treating bone fractures. [0006] Good bone healing can also result from relative stability, where the clinical outcome is often dependent on obtaining correct length, axis, and rotation of the fractured bone rather than on precise anatomical reduction and absolute stability. To achieve this, while at the same time minimizing the amount of additional soft tissue trauma, treatment of multi- fragmented metaphyseal and diaphyseal fractures with plates and screws was developed. [0007] An existing solution is plate and screw systems where the screws are locked in the plate. The plate and screws form one stable system and the stability of the fracture is dependent upon the stiffness of the construct. No compression of the plate onto the bone is required, which reduces the risk of primary loss of reduction and preserves bone blood supply. Locking the screw into the plate to ensure angular, as well as axial, stability eliminates the possibility for the screw to toggle, slide, or be dislodged and thereby strongly reduces the risk of postoperative loss of reduction. As the relationship between the locking screws and the plate is fixed, locking screws provide a high resistance to shear or torsional forces, but locking screws have a limited capability to compress bone fragments.

[0008] Often, however, the area available for placement of a screw is limited. There may be several reasons for this. As examples, the patient's anatomy, other fixation devices, or other implants may limit the area for screw placement. Further, in the case of periarticular fixation, there may be insufficient room to allow the screws to interdigitate because typical placement of standard sized screws may cause the screws to interfere with one another. While it may be possible to simply use smaller screws, this would necessitate the availability of bone plates with multiple sizes of threaded screw holes. Alternatively, it may be possible to create custom made screws that have a large head but a small shaft. However, either of these solutions would prohibitively increase manufacturing and distribution costs.

[0009] In addition to the limited area available for screw placement, it is almost always beneficial to take out the least amount of bone as necessary when mounting a bone plate. The use of smaller screws allows for the removal of less bone when installing a bone plate.

[0010] Thus, there remains a need in the art for a simple device that allows a standard small screw to be used with a standard bone plate. Summary of the Invention

[0011] It is in view of the above problems that the present invention was developed. The invention is a system for mounting a bone plate to a bone. The bone plate has a hole with an angle less than about 30 degrees. The system includes a screw with a head. The system also includes a screw head adapter having an inner portion adapted to mate with the head of the screw and an outer portion having a shape corresponding to the angle of the hole. An assembly of the locking screw and the screw head adapter can be used to connect the bone locking plate to the bone.

[0012] A locking member may be connected to the outer portion for securing the screw head adapter to the bone plate. As examples, the locking member may be a helical thread, a ridge, a knurl, a tab, or a snap ring. Thus, the outer portion may be threaded into the hole of the bone plate, pressed into the hole of the bone, or placed into the hole of the bone plate and secured with the snap ring.

[0013] hi some embodiments, the yield strength of the screw head adapter is less than that of the bone plate. As such, the screw head adapter is plastically deformable to allow for installation of the screw at an angle relative to the axis of the screw hole. For example, the locking member of the outer portion may plastically deform as the assembly of the screw and screw head adapter is installed into the bone plate.

[0014] The invention has several advantages over prior devices and techniques. First, the screw head adapter allows the use of smaller screws in a bone plate with larger screw holes. This allows a manufacturer to produce a bone locking plate with a standard hole size but also allows a surgeon some flexibility in the size selection of screws. Second, in the case of the plastically deformable screw head adapter, the screw is polyaxial. In other words, the screw may be installed at various angles relative to the axis of the screw hole. This provides the surgeon with flexibility in deciding how to install the bone plate.

[0015] Further features, aspects, and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.

Brief Description of the Drawings

[0016] The accompanying drawings, which are incorporated in and form a part of the specification, illustrate the embodiments of the present invention and together with the description, serve to explain the principles of the invention. In the drawings:

[0017] Figure 1 is a side view of an exemplary locking screw;

[0018] Figure 2 is a cross-sectional view of the locking screw of Figure 1 ;

[0019] Figure 3 is a top view of a portion of a bone plate, including a hole without the threads of the hole shown;

[0020] Figure 4 is a cross-sectional view of the portion of the bone plate shown in Figure 3 is as viewed along cross-section lines 4-4 of Figure 3;

[0021] Figure 5 is a top view of the portion of the bone plate shown in Figures 3 and 4, with the threads of the hole shown;

[0022] Figure 6 is a cross-sectional view of the portion of the bone plate shown in Figures 3-5 as viewed along cross-section lines 6-6 of Figure 5;

[0023] Figure 7 is a detailed view of the hole of the portion of the bone plate shown in Figures 3-6;

[0024] Figure 8 is a side view of the locking screw of Figures 1 and 2 threaded into the portion of the bone plate shown in Figures 3-7;

[0025] Figure 9 is a side view of an exemplary compression screw; [0026] Figure 10 is a side view of the compression screw of Figure 9 inserted into the portion of the bone plate shown in Figures 3-7;

[0027] Figure 11 is a top perspective view of a first embodiment of a bone plate system mounted on a bone;

[0028] Figure 12 is a detailed top perspective view of the bone plate system shown in Figure 1;

[0029] Figure 13 is an exploded side perspective view illustrating a screw head adapter;

[0030] Figure 14 is a side perspective view illustrating the screw head adapter as used in mounting a screw;

[0031] Figure 15 is a side view of the screw head adapter as mounted at an angle relative to the bone plate;

[0032] Figure 16 is a side perspective view of a plug;

[0033] Figure 17 is a top perspective view of a second embodiment of a bone plate system mounted on a bone;

[0034] Figure 18 illustrates an alternative embodiment of a locking screw;

[0035] Figure 19 is an exploded sectional side view of a second embodiment of a screw head adapter; and

[0036] Figure 20 is a sectional side view of the second embodiment of the screw head adapter shown in Figure 19.

Detailed Description of the Preferred Embodiments

[0037] Referring to the accompanying drawings in which like reference numbers indicate like elements, Figures 1 and 2 show an exemplary locking screw 40. The locking screw 40 includes a threaded head 42 and a shaft 44. Although the term "screw" typically means a threaded fixation device, as used herein the term "screw" includes both threaded fixation devices and non-threaded fixation devices, such as locking stems, locking pins, etc. Thus, in the embodiment depicted in Figures 1 and 2, the shaft 44 is threaded but equally could be non- threaded. For example, Figure 18 illustrates a locking screw 40' with a non-threaded shaft 44'. A diameter of the shaft 44, 44' may range from about lmm to about 12mm. As examples, the locking screw 40, 40' may be a 2.7mm, 3.5 mm, 4.5 mm, 6.5 mm, or other size locking screw, which is understood by those skilled in the art. hi the embodiment shown in Figures 1 and 2, the lead between the threads of head 42 and the threads of shaft 44 is broken or discontinuous. In the depicted embodiments, the threads in shaft 44 of the locking screw 40 are single lead and the threads in head 42 are triple lead, providing the locking screw 40 with same pitch throughout. However, the threads in shaft 44 and the threads of head 42 could have a single lead, a double lead, or a triple lead. It is preferable for certain embodiments of locking screws to have a constant pitch. In an exemplary 2.7 mm locking screw, the pitch is 1.00 mm and the angle of the thread form is about 45 to about 60 degrees. In an exemplary 3.5 mm locking screw, the pitch is 1.25 mm and the angle of the thread form is about 45 to about 60 degrees. In an exemplary 4.5 mm locking screw, the pitch is 1.75 mm and the angle of the thread form is about 60 degrees. The locking screw 40 also includes a driving head 46, an internal hex head as shown in Figure 2, that is used when tightening locking screw 40 into a bone plate and/or bone. Alternatively, the driving head 46 may be a slot, a Phillips slot, a Torx drive, or star drive.

[0038] Figures 3-7 illustrate different views of a portion of a bone plate. Such bone plates generally include one or more holes or other openings, such as in the exemplary bone plate shown in Figure 11, which is briefly described below. However, for ease of illustration, only a portion of bone plate 50 is shown in Figures 3-7.

[0039] The particular bone plate 50 shown in these drawings includes a hole 52 extending through an upper surface 54 and a bone contacting surface 56 of bone plate 50. Figures 3 and 4 show hole 52 without its threads to help illustrate certain aspects of this embodiment of the invention, while Figures 5-7 show hole 52 with its threads. It should be understood that the geometry of hole 52 is the same throughout these drawings, although the geometry of hole 52 is not as clearly visible in the drawings that show the threads of hole 52. As seen most clearly in Figure 4, hole 52 includes a top portion 58 extending downward from upper surface 54. Top portion 58 extends from upper surface 54 at a first angle θl relative to the plane of top surface 54, as shown in Figure 4. hi an exemplary embodiment, the first angle θl is about fifty-two degrees. In some embodiments, top portion 58 is omitted such that hole 52 is simply a locking hole. [0040] A bottom portion 60 of hole 52 extends from the end of top portion 58 through bone contacting surface 56 of bone plate 50. Bottom portion 60 includes threads 62, as shown in Figures 5-7. Some of threads 62 may extend into top portion 58 depending on the particular embodiment, but top portion 58 is not completely threaded.

[0041] hi the exemplary embodiment shown in Figures 3-7, bottom portion 60 is tapered. The included angle, which is a second angle Θ2 in Figure 4, of the taper of bottom portion 60 may be less than a maximum of about sixty degrees, hi the depicted embodiments, the second angle Θ2 is less than about thirty degrees, including zero degrees (i.e., no taper at all), hi an exemplary embodiment, the second angle Θ2 is about twenty degrees.

[0042] Figure 8 shows a side view of locking screw 40 threaded into hole 52 of bone plate 50. Head 42 of locking screw 40 is received by threads 62 of bone plate 50. Threads 62 surround the threads of head 42, and the top of head 42 is received within hole 52 such that head 42 of locking screw 40 sits substantially flush with upper surface 54 of bone plate 50. Shaft 44 of locking screw 40 is threaded into bone (not shown). Head 42 of locking screw 40 is tapered such that it properly mates with threads 62 of hole 52 of bone plate 50. Furthermore, a threaded portion of a head of a locking screw for use with certain embodiments of this invention has a taper generally corresponding to the taper, if any, of the threads of the hole of the bone plate.

[0043] Figure 9 shows a side view of an exemplary compression screw 70, which may also be referred to as a non-locking screw. The compression screw 70 includes a head 72 and a

> threaded shaft 74. Figure 10 shows compression screw 70 inserted within hole 52 of bone plate 50. As shown in Figure 10, head 72 of compression screw 70 rides along top portion 58 of bone plate 50. As shaft 74 is threaded into a bone (not shown), compression screw 70 may pull or push bone plate 50 in a particular direction as head 72 of compression screw 70 comes into contact with and rides along top portion 58 of hole 52 of bone plate 50. The first angle θl,

) shown in Figure 4, at top portion 58 of hole 52 is significant for compression of a fracture and is necessary to help shift the bone plate in the desired direction. If top portion 58 were to extend straight down from upper surface 54 of bone plate 50, compression would be less successful. Compression screw 70 may move bone plate 50 in more than one direction as compression screw 70 is fully inserted within hole 52. hi an exemplary embodiment, fine adjustment of fractures up j to about two millimeters in several directions is possible.

[0044] Figures 11 and 12 illustrate a system or assembly 10 for mounting a bone plate 12 to a bone 100. As an example, the bone plate 12 may be a periarticular plate for the distal end of the humerus. Further, the bone plate 12 may be a locking plate or a non-locking plate. The system 10 includes the bone plate 12, a screw head adapter 20, and one or more screws, such as

) locking screws 40 or compression screws 70. The bone plate 12 shown in Figure 11 has twelve holes but those skilled in the art would understand that a greater or lesser number of holes may be used. Moreover, the bone plate 12 may have any number of locking screw holes, compression screw holes, or combination locking and compression screw holes, such as hole 52 described above. In the embodiment depicted in Figure 11, the bone locking plate 12 has six combination holes and six compression holes.

[0045] Figure 13 is an exploded view illustrating the bone plate 12, the locking screw 40, and the screw head adapter 20. While the locking screw 40 is shown, those skilled in the art would understand that the compression screw 70 could equally be used. In the embodiment depicted in Figure 13, the bone plate 12 has a combination hole 52, a locking hole 90, and a nonlocking hole 92. The screw head adapter 20 has a shape that corresponds to the taper of the hole 52, 90, 92. The shape of the screw head adapter 20 may range from cylindrical to frusto-conical. In the embodiment depicted in Figure 13, the screw head adapter 20 is frusto-conical and has a twenty degree taper to substantially match the taper of the hole 52. The screw head adapter 20 can be made from metal, including metal alloys, wood, plastic, or a composite material. As examples, the screw head adapter 20 can be made from stainless steel, titanium, aluminum, cobalt chromium, polyetheretherketone, polyethylene, and resorbable materials.

[0046] The screw head adapter 20 has an inner portion 22 adapted to mate with the head 42, 72 of the screw 40, 70. The inner portion 22 is shaped to substantially match the head 42, 72. For example, the inner portion 22 may have a cylindrical or frusto-conical shape to match the shape of the head 42, 72. Further, the inner portion 22 may be threaded. In that case, the head 42 can be threaded into the inner portion 22.

[0047] The screw head adapter 20 also has an outer portion 24. The outer portion 24 has a shape corresponding to the angle or taper of the hole 52, 90, 92. The shape of the outer portion 24 may range from cylindrical to frusto-conical. In the embodiment depicted in Figure 13, the outer portion 24 is frusto-conical and has a twenty degree taper to match the taper of the hole 52.

[0048] In light of the above, the entire screw head adapter 20 may be defined to have a specific shape to match the hole 52, 90, 92 or only the outer portion 24 may be defined to have a specific shape to match the hole 52, 90, 92. Further, the inner portion 22 may be may be defined to have a specific shape concurrently or independently of the outer portion 24.

[0049] In some embodiments, a locking member 32 is operatively connected to the outer portion 24. The locking member 32 may be a helical thread, a ridge, a knurl, or a tab. Li the case of helical thread, the locking member 32 is dimensioned and arranged to have the same size and thread pitch as the hole 52, 90. As for the ridge, knurl, or tab, these features frictionally engage the hole 52, 90, 92 as the screw head adapter 20 and screw 40, 70 engage the bone plate and the bone.

[0050] Figure 14 is a perspective view illustrating the screw head adapter 20 as used in mounting the screw 40. An assembly of the locking screw 40 and the screw head adapter 20 may be used to operatively connect the bone plate 12 to the bone 100.

[0051] Figure 15 is a side view of the screw head adapter 20 as it is mounted at an angle relative to the bone plate 12. Typically, the screw head adapter 20 has a yield strength which closely approximates the yield strength of the bone plate 12. In the embodiment depicted in Figure 15, however, the screw head adapter 20 is made from a material having a yield strength less than that of the bone plate. Thus, when the screw head adapter 20 is inserted at an angle, the outer portion 24 permanently deforms. The permanent deformation creates a friction force between the two parts that is strong enough to hold the locking screw 40 at a fixed angle relative to the plate 12. The locking screw 40 has a first axis Al and the hole 52 has a second axis A2. La the embodiment depicted in Figure 15, the locking screw 40 and the screw head adapter 20 are installed at a third angle Θ3. The third angle Θ3 is less than about sixty degrees. In the embodiment depicted in Figure 15, the angle Θ3 is about three degrees.

[0052] As best seen in Figure 16, some embodiments may include a plug 80. The plug 80 may be a single component or made from multiple components. For example, the plug 80 may be used in conjunction with the screw head adapter 20. The plug 80 is adapted to mate with the hole 52. The plug 80 is used to increase the stiffness of the bone locking plate 12 by filling unused holes, which increases the mass moment of inertia of the bone locking plate 12. The plug 80 has a drive interface 82 that is used when tightening the plug 80 into a bone plate. For example, the plug 80 may have an internal hex head, similar to that of the hex head shown in Figure 2. Alternatively, the drive interface 82 may be a slot, a Phillips slot, a Torx drive, or star drive.

[0053] Figure 17 illustrates a second embodiment of the bone plate system 200 for mounting or fixating a first bone plate 212 and a second bone plate 214 to a bone 210. The bone i plate system 200 includes the first bone plate 212, the second bone plate 214, one or more screw head adapters 220, and a plurality of screws 240. The screws 240 may be locking or non-locking screws. As can be seen in Figure 17, the first bone plate 212 and the second bone plate 214 are mounted substantially on opposite sides of the bone 210. Depending on the nature of the fracture, the bone plates 212, 214 in fact may be diametrically opposed to one another. Thus, if a

> standard screw were to be used in the bone plates 212, 214, the shafts of the screws 240 would interfere with one another. With the use of the screw head adapter 220, however, a smaller screw with a smaller shaft can be used to replace the designated screw size of the bone plate 212, 214. As such, the screw head adapter 220 allows the screws 240 to interdigitate without interfering with one another due to the decreased shaft diameter.

) [0054] Figures 19 and 20 illustrate a second embodiment of the screw head adapter, generally indicated by reference numeral 120. The screw head adapter 120 is adapted for mounting on a screw 140, which may be a locking or a non-locking screw. The screw head adapter 120 is also adapted for mounting in a hole 152 of a bone plate 112. The screw head adapter 120 includes an outer portion 124. The outer portion 124 includes an annular groove 128, and the hole 152 includes an annular ring 114. A locking member 132 is operatively connected to the outer portion 124. As examples, the locking member 132 may be a spring, a snap ring, or an expandable clip. The locking member 132 is used to secure the screw head

adapter 120 to the hole 152.

[0055] For installation, the screw head adapter 120 is mounted on the screw 140. The locking member 132 is placed in the annular groove 128. The screw head adapter 120 and the screw 140 are placed in the hole 152 until the locking member 132 engages the annular ring 114.

[0056] In operation, a position for the bone plate is selected. The bone plate is then temporarily placed in this position, and a hole is selected for a locking screw. A pilot hole may

) be drilled for the screw. The screw head adapter is assembled to the screw. The screw is screwed into the bone and the screw head adapter is mated with the hole of the bone plate. Alternatively, the screw head adapter is assembled to the bone plate, and the screw is screwed into the bone and the screw head adapter. This process may be repeated for other screws.

[0057] As various modifications could be made in the constructions and methods herein

> described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. For example, while a periarticular plate is shown in Figures 11-16, those skilled in the art would understand that the present invention is applicable to any type of bone plate. Thus, the breadth and scope of the present invention should not be

) limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.

Claims

Wliat is Claimed Is:

1. A system (10, 200) for mounting a bone plate (12, 50, 112, 212) to a bone (100, 210), the bone plate (12, 50, 112, 212) having at least one hole (52, 90, 92, 152), said at least one hole (52, 90, 92, 152) having an angle (Θ2) less than about 30 degrees, the system (10, 200) including at least one screw (40, 40', 70, 140) having a head (42, 72), the system (10, 200) characterized by: a. at least one screw head adapter (20, 120, 220) having an inner portion (22) adapted to mate with the head (42, 72) of the at least one screw (40, 40', 70, 140) and an outer portion (24, 124) having a shape corresponding to the angle of the at least one hole (52, 90, 92, 152), wherein an assembly of the at least one screw (40, 40', 70, 140) and said at least one screw head adapter (20, 120, 220) operatively connect the bone plate (12, 50, 112, 212) to the bone (100, 210).

2. The system according to claim 1, wherein said outer portion (24, 124) is tapered.

3. The system according to claim 1 or 2, wherein said inner portion (22) is tapered.

4. The system according to claim 1 or 2, wherein said inner portion (22) is threaded.

5. The system according to claim 1, wherein said at least one screw head adapter (20, 120, 220) is made from a material having a yield strength less than that of the bone plate (12, 50, 112, 212).

6. The system according to claim 1, wherein said at least one screw head adapter (20, 120, 220) is made of a material selected from the group consisting of metal, wood, plastic, and composite material.

7. The system according to claim 1, wherein said at least one screw head adapter (20, 120, 220) is made of material selected from the group consisting of stainless steel, titanium, aluminum, cobalt chromium, polyetheretherketone, polyethylene, and a resorbable material.

8. The system according to claim 1, wherein the at least one hole (52, 90, 92, 152) has an axis (A2) and said at least one screw head adapter (20, 120, 220) is angularly fixated relative to said axis (A2).

9. The system according to claim 1, wherein the bone plate (12, 50, 112, 212) is a periarticular plate.

10. The system according to claim 1, further characterized by at least one other bone plate (214).

11. The system according to claim 1, wherein said at least one screw head adapter (20, 120, 220) is frusto-conical, said inner portion (22) is threaded and adapted to mate with the head (42) of the screw (40), and said outer portion (24) is threaded and adapted to mate with the at least one hole (52).

12. The system according to claim 1, further characterized by a locking member (32, 132) operatively connected to said outer portion (24, 124).

13. The system according to claim 12, wherein said locking member (32, 132) is selected from the group consisting of a helical thread, a ridge, a knurl, a tab, a snap ring, and an expandable clip.

14. The system according to claim 1, further characterized by a plug (80) adapted to mate with the at least one hole (52, 90, 92, 152).

15. The system according to claim 14, wherein said plug (80) has a drive interface.