GB1579575A - Implants - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO IMPLANTS (71) We, T. A. ENGLISH BIOMECHANICS LIMITED, a British Company, of Box 2, Welton Garth, Welton, Humberside, formerly of Midland Bank Chambers Goole, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to implants for use in bone surgery and more particularly to a so-called "bone plate" for use in connecting together, and maintaining in connected relationship, severed or fractured sections of a bone.

Bone plates are well known in the art and are used by surgeons in many different applications but it is an essential feature that all bone plates must present a surface for direct contact with the surface of the bone and thus, in all applications, the surface area of the bone engaged by the bone plate is permanently isolated from the surrounding tissue. It is well recognised that all the points on the surface area of the bone engaged by the bone plate must be within a predetermined distance of tissue-engaged bone if the covered bone is to remain healthy and to overcome this difficulty prior art bone plates present a long, but narrow, bone engaging surface.

Throughout this specification the term "acceptable width" is intended to mean the width of bone surface which can be isolated from surrounding tissue without damage to the bone and, as will be appreciated from above, prior art bone plates present a boneengaging surface having a width less than the "acceptable width", When a bone plate is to be used to unite the two sections of a severed or fractured elongate bone the plate must be substantially rigid to maintain the bone sections in their correct relationship and, in view of the necessity to present an "acceptable width" for the bone-engaging surface, the only way known in the art to obtain the desired rigidity is to make the plate of substantial thickness. In practice plates having a thickness in excess of 5mm are not unusual with the penalty of substantial weight and the disadvantage of occupying substantial volume within the limb, with adverse consequences affecting wound closure. Further in certain sites, the bone plate will, because of its substantial thickness, lie immediately under the skin with the obvious and well recognised disadvantage thereof.

A further disadvantage of prior art bone plates is that to achieve the required rigidity of apposition of the bone sections in two planes of bending it is often necessary to employ two or more such plates, applied to different aspects of surfaces of the bone, consequently accentuating the disadvantages recited above, as well as prolonging the operation.

A further disadvantage of prior art bone plates is that said plates must be fastened to the bone by securing means conventionally screws, which pass through clearance holes in the bone plate and are screwed into the bone therebeneath. To draw and retain the bone against the bone-engaging surface of the plate, the clearance holes pass through the long, narrow bone-engaging surface of the plate; the axes of the screws thereby lie in a substantially common plane in the longitudinal direction of the plate, and as such do not afford the best method for retaining the bone sections to resist rotary or bending forces acting upon those sections.

A further disadvantage of prior art bone plates is that, due to the relatively great thickness, the long narrow bone engaging surface is inflexible, different bones have different surface configuration, and the same bone in different adults often differs widely in shape and configuration.

Thus, the selection of a particular bone plate for use with a particular bone can only be made after the bone has been exposed and measured; this means that a plurality of different bone plates must be available to the surgeon during the operation. Further, as this bone plate, of relatively thick rigid section, must be bent to fit the bone, such working of the plate can upset the metal crystalline structure, with consequent in creased risk of crevice corrosion, crack propagation, and of fatigue fracture of the plate.

A further disadvantage of known plate designs is that their shape limits the number of screws which can be used at optimum intervals on the bone section, unless a plate of excessive length is used. Such length is an unnecessary and disadvantageous feature which does not contribute to tne strength of the plate at or near the level of the bone fracture, where it is most necessary.

The present invention seeks to provide a bone plate capable of affording substantial longitudinal and transverse support for bone sections against forces in all axes.

According to the present invention there is provided a bone plate comprising two longitudinal side members connected together by transverse members to define a single row of openings spaced apart in the length direction of the plate, with two rows of fixing screw apertures spaced apart in the transverse direction of the plate and extending in the length direction thereof.

Preferably said longitudinal side members each define a bone-engaging surface extending in the length direction of the plate.

Preferably said tranverse members present bone-engaging surfaces.

Preferably the transverse members are inclined to the length and width directions of the plate.

Preferably the width dimension of the plate varies in the longitudinal direction of the plate.

In a preferred embodiment in accordance with the invention the plate is bent in its width direction to present the bone-engaging surface of one longitudinal side member inclined to the bone-engaging surface of the other longitudinal side member and conveniently the bone-engaging surface of one longitudinal side member is inclined to lie at an angle in the region of 90 to the boneengaging surface of the other longitudinal side edge member.

The bend in the width direction of the plate may be limited to a mid region thereof, whereupon the plate has an angle cross section, but preferably the bend in the width direction of the plate extends across the width of the plate.

In a preferred embodiment the bone plate has an arcuate configuration in the width direction and conveniently the curvature varies in the longitudinal direction of the plate.

Preferably the bone plate has a curvature in the longitudinal direction thereof.

The bone plate proposed by the invention may be fabricated or made from a single sheet of material of substantially uniform thickness and, conveniently, the plate may have a thickness less than three millimeters.

The invention will now be described further by way of example with reference to the drawings accompanying the Provisional Specification in which: Fig. 1 shows a plan view of a bone plate in accordance with the invention, Fig. 2 shows a cross-section which may be applied to the bone plate on the line II-II in Fig. 1, to allow the plate to be secured to a bone as illustrated, Fig. 3 shows a plan view of a second embodiment of a bone plate in accordance with the invention, Fig. 4 shows an end view of the bone plate of Fig. 3 in the direction of the arrow "X" illustrating one transverse configuration which can be applied to the plate, and Figs. SA and 5B show respectively two other cross sectional shapes which may be imparted to the bone plate on the line III-III in Fig. 3.

The bone plate illustrated in Fig. 1 of the drawings is stamped from a flat sheet of rigid material, conveniently a metal of substantially uniform thickness and has the general form of a parallelogram defined by generally parallel longitudinal side members 11 and 12 with generally parallel transverse members 13 and 14 inclined at an angle of some 45" to the longitudinal directions of members 11 and 12. An internal transverse member 15, lying substantially at right angles to end member 13, extends between the junction member 13 with member 11 and member 12, an internal transverse member 16, substantially at right angles to end member 14, connects the junction of member 14 and member 12 with member 11, and an internal transverse member 17 connects the junction of member 15 with member 12 to the junction of member 16 with member 11.

Countersunk screw clearance holes 18 and 19 are provided at the junction of end member 13 with elongate side members 11 and 12 respectively, countersunk screw clearance holes 20 and 21 are provided at the junctions of end member 14 with members 11 and 12 respectively, and countersunk screw clearance holes 22 and 23 are provided at the junctions of member 15 with members 11 and 12 respectively.

In the illustrated bone plate the width of each member 11 to 17 inclusive, measured at right angles to the length direction of that member, is less than the "acceptable width". Screws are intended to pass through the clearance holes 18 to 23 inclusive into the bone and thus whilst at each or certain junctions of the members an area of bone having a minimum dimension greater than the "acceptable width" is covered by the bone plate the distance from the edge of each screw hole in the bone to the closest edge of a bone plate member will be less than half the "acceptable width". When the bone plate illustrated in Fig. 1 is applied to a bone and measured thereto by screws passing through the holes 18 to 23 respectively, surrounding tissue can contact the bone exposed through openings A, B, C and D and whereupon no part of the surface area of the bone contacted by the bone plate is spaced by an amount greater than one half the "acceptable width" from tissue engaged bone.

It will be observed that the members 15 and 16 include indentations 11 5a and 1 6a for location of a tool for applying compression to the bone whilst the plate is being attached thereto and the member 17 has a greater length than the members 15 and 16 Thus, with the illustrated arrangement, clearance holes 18, 19 and 23 and the clearance holes 20, 21 and 22 lie on opposite sides, and are longitudinally spaced from, the mid point of the plate so that, when the bone plate is applied to an elongate bone having a break therein and the centre point of the bone plate is located on the break, screw holes 18, 19 and 23 can support screws into the bone to one side of the break and holes 20, 21 and 22 can support screws on the other side of the break. The hole 18 is transversely spaced from the plane passing through the axes of holes 19 and 23 and the hole 21 is spaced from the plane passing through holes 20 and 22 so that the screws through the plate at each side of the break do not lie in a common plane.

For the application shown in Fig. 2 the bone plate illustrated in Fig. 1 has a transverse curvature imparted thereto conforming substantially to the curvature of the crosssection of the bone Z, to which the plate is applied and whereby the bone Z can seat snugly against the bone engaging surface of the plate. The curvature of the plate allows the screws 24 passing through holes 19, 21 and 23 to lie in one common plane and the screws 25 passing through holes 18, 20 and 22 to lie in a common plane substantially at right angles to the plane of the screws 24 and whereby an effective securement of the bone to the bone plate is obtained and the bone sections are supported against longitudinal, transverse, and rotational displacement relative to the plate. Washers or inserts 26, conveniently of a plastics material, are interposed between screws 24 and 25 and the plate.

The bone plate illustrated in Fig. 3 is peripherally defined by longitudinal side members 30 and 31, inclined to the longitudinal axis AA of the plate, an inclined transverse member 32 connecting the widely spaced apart ends of members 30 and 31, and an inclined transverse member 33 connecting the narrowly spaced apart ends of members 30 and 31. Internal transverse members 34, 35, 36, 37 3and 38 interconnect the side members 30 and 31 to define generally triangular openings E, F, G, H, J and K through the plate. Countersunk bores 39, 40, 41, and 42 pass through the juncture of side member 30 with trnasverse member 32, internal transverse members 34 and 35, internal transverse members 36 and 37, and internal transverse member 38 and transverse member 33 respectively. Countersunk bores 43, 44, 45, and 46 pass through the junctures of side member 31 with transverse member 32 and internal transverse member 34, internal transverse members 35 and 36, internal transverse members 37 and 38, and transverse member 33 respectively.

The bone plate may have a transverse curvature imparted thereto and, as will be seen from Fig. 4, the curvature may increase from the narrow end of the plate towards the broader end thereof. By this means the bone plate can be applied to a tapered bone length (most elongate bones taper outwardly from the mid region thereof) and by providing a curvature increasing towards the broad end of the plate some degree of longitudinal adjustment of the plate relative to a specific bone is afforded to the surgeon to obtain the best possible fit and support for the bone.

Further, all the securing screws passing through the holes 39, 40, 41 and 42 can lie in the same plane passing through the central axis of the bone and the securing screws passing through the bores 43, 44, 45 and 46 can also lie in a common plane passing through the axis of the bone and inclined, substantially at 90 , to the plane passing through the screws in holes 39, 40, 41 and 42 and whereby an ideal support and securement of the bone to the bone plate is obtained.

Because the bone plate proposed by the present invention has substantial width and is primarily intended to have a transverse curvature, such substantial width and curvature greatly strengthens the plate against deformation. The plate can therefore be made much thinner than plates known in the art and, in fact, the plate may have a thickness less than 3mm and conveniently in the region of 2mm. This greatly reduced thickness allows a degree of flexibility in the longitudinal and transverse directions whereby a degree of flexibility is afforded to the boneengaging surface. Further, when the transverse curvature varies in the length direction of the plate, and with the added advantage of flexibility, a single bone plate may be used for any one of a plurality of different bones, or different locations along a specific bone and the surgeon's task in selecting a bone plate for a particular bone is thereby substantially eased, if not eliminated.

In the Fig. 4 embodiment the transverse curvature, although varying along the length of the plate, is substantially constant across each transverse section and Figs. 5A and 5B show two examples of different forms which may be imparted to the bone plate.

In the Fig. 5A embodiment the bone plate has a varying transverse curvature and thus, at the illustrated section, the curvature may vary from a radius of 18mm adjacent the outer edge of member 30 to a radius of 20mm adjacent the outer edge of member 31. As few bones have, in cross section, a periphery of uniform radius the variable transverse curvature allows the surgeon to angularly displace the bone plate about the axis of the bone as well as longitudinally of the bone to obtain the best location for seating the plate on the bone.

In the Fig. 5B embodiment the plate is bent along the longitudinal axis with a relatively small curvature whereby the boneengaging surfaces of members 30 and 31 lie in planes substantially at right angles. With this arrangement the area of contact between the bone and the plate may be relatively less than for the Figs. 4 and 5A cross sections but the angle form can give the plate greater rigidity and strength, the securing screws can pull the bone into the angle to afford a very different retention of the bone sections and, as the plate may have a degree of flexibility along members 30 and 31 at right angles to the planes of the bone-contacting surfaces of said members, the Fig. 5B embodiment can readily deflect to accommodate variations in the surface configuration of the bone sections.

Although the present invention has been described by way of example with reference to specific embodiments it will be appreciated that many modifications and variations will be apparent to persons skilled in the art and, by way of example, instead of the plate being stamped from a sheet, the plate may be fabricated, conveniently by a welding process, and may have different peripheral shapes with openings of different shapes.

Further the plate may include more than two longitudinal members and/or the transverse members may by wholly or partially displaced from the plane of the bone contacting surfaces of the longitudinal members.

Thus, the transverse members may lie out of contact with the bone. Further, the members defining the plate may have recesses or deflections formed therein to increase the rigidity thereof and for example, the members 11 and 12 may have the peripheral edges deflected from the general plane of said members to increase the longitudinal rigidity thereof.

WHAT WE CLAIM IS: 1. A bone plate comprising two longitudinal side members connected together by transverse members to define a single row of openings spaced apart in the length direction of the plate, with two rows of fixing screw apertures spaced apart in the transverse direction of the plate and extending in the length direction thereof.

2. A bone plate as claimed in claim 1 in which said longitudinal side members each define a bone-engaging surface extending in the length direction of the plate.

3. A bone plate as claimed in claim 2 in which the plate is bent in its width direction to present the bone-engaging surface of one longitudinal side member inclined to the bone-engaging surface of the other longitudinal side member.

4. A bone plate as claimed in claim 3 in which said bone-engaging surfaces lie at an angle in the region of 90" to one another.

5. A bone plate as claimed in claim 3 or 4 in which the bend in the width direction of the plate is limited to a mid region thereof.

6. A bone plate as claimed in claim 3 or 4 in which the bend in the width direction of the plate extends across the width of the plate.

7. A bone plate as claimed in claim 6 in which said plate has an arcuate configuration in the width direction.

8. A bone plate as claimed in claim 6 or 7 in which the curvature varies in the longitudinal direction of the plate.

9. A bone plate as claimed in any pre-' ceding claim in which the bone plate has a curvature in the longitudinal direction thereof.

10. A bone plate as claimed in any preceding claim in which said transverse members present bone-engaging surfaces.

11. A bone plate as claimed in any preceding claim in which the transverse members are inclined to the length and width directions of the plate.

12. A bone plate as claimed in any preceding claim in which the width dimension of the plate varies in the longitudinal direction of the plate.

13. A bone plate as claimed in any preceding claim made from a single sheet of material of substantially uniform thickness.

14. A bone plate as claimed in any preceding claim having a thickness less than three millimeters.

15. A bone plate substantially as hereinbefore described with reference to and as illustrated in Figs. 1 or 3 of the drawings accompanying the provisional specification or Figs. 1 or 3 having a curvature in the width direction described with reference to and as illustrated in Figs. 2, 4, 5A or 5B of the drawings accompanying the provisional specification.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (15)

**WARNING** start of CLMS field may overlap end of DESC **. each transverse section and Figs. 5A and 5B show two examples of different forms which may be imparted to the bone plate. In the Fig. 5A embodiment the bone plate has a varying transverse curvature and thus, at the illustrated section, the curvature may vary from a radius of 18mm adjacent the outer edge of member 30 to a radius of 20mm adjacent the outer edge of member 31. As few bones have, in cross section, a periphery of uniform radius the variable transverse curvature allows the surgeon to angularly displace the bone plate about the axis of the bone as well as longitudinally of the bone to obtain the best location for seating the plate on the bone. In the Fig. 5B embodiment the plate is bent along the longitudinal axis with a relatively small curvature whereby the boneengaging surfaces of members 30 and 31 lie in planes substantially at right angles. With this arrangement the area of contact between the bone and the plate may be relatively less than for the Figs. 4 and 5A cross sections but the angle form can give the plate greater rigidity and strength, the securing screws can pull the bone into the angle to afford a very different retention of the bone sections and, as the plate may have a degree of flexibility along members 30 and 31 at right angles to the planes of the bone-contacting surfaces of said members, the Fig. 5B embodiment can readily deflect to accommodate variations in the surface configuration of the bone sections. Although the present invention has been described by way of example with reference to specific embodiments it will be appreciated that many modifications and variations will be apparent to persons skilled in the art and, by way of example, instead of the plate being stamped from a sheet, the plate may be fabricated, conveniently by a welding process, and may have different peripheral shapes with openings of different shapes. Further the plate may include more than two longitudinal members and/or the transverse members may by wholly or partially displaced from the plane of the bone contacting surfaces of the longitudinal members. Thus, the transverse members may lie out of contact with the bone. Further, the members defining the plate may have recesses or deflections formed therein to increase the rigidity thereof and for example, the members 11 and 12 may have the peripheral edges deflected from the general plane of said members to increase the longitudinal rigidity thereof. WHAT WE CLAIM IS:

1. A bone plate comprising two longitudinal side members connected together by transverse members to define a single row of openings spaced apart in the length direction of the plate, with two rows of fixing screw apertures spaced apart in the transverse direction of the plate and extending in the length direction thereof.

2. A bone plate as claimed in claim 1 in which said longitudinal side members each define a bone-engaging surface extending in the length direction of the plate.

3. A bone plate as claimed in claim 2 in which the plate is bent in its width direction to present the bone-engaging surface of one longitudinal side member inclined to the bone-engaging surface of the other longitudinal side member.

4. A bone plate as claimed in claim 3 in which said bone-engaging surfaces lie at an angle in the region of 90" to one another.

5. A bone plate as claimed in claim 3 or 4 in which the bend in the width direction of the plate is limited to a mid region thereof.

6. A bone plate as claimed in claim 3 or 4 in which the bend in the width direction of the plate extends across the width of the plate.

7. A bone plate as claimed in claim 6 in which said plate has an arcuate configuration in the width direction.

8. A bone plate as claimed in claim 6 or 7 in which the curvature varies in the longitudinal direction of the plate.

9. A bone plate as claimed in any pre-' ceding claim in which the bone plate has a curvature in the longitudinal direction thereof.

10. A bone plate as claimed in any preceding claim in which said transverse members present bone-engaging surfaces.

11. A bone plate as claimed in any preceding claim in which the transverse members are inclined to the length and width directions of the plate.

12. A bone plate as claimed in any preceding claim in which the width dimension of the plate varies in the longitudinal direction of the plate.

13. A bone plate as claimed in any preceding claim made from a single sheet of material of substantially uniform thickness.

14. A bone plate as claimed in any preceding claim having a thickness less than three millimeters.

15. A bone plate substantially as hereinbefore described with reference to and as illustrated in Figs. 1 or 3 of the drawings accompanying the provisional specification or Figs. 1 or 3 having a curvature in the width direction described with reference to and as illustrated in Figs. 2, 4, 5A or 5B of the drawings accompanying the provisional specification.