Bone Plate

The invention concerns a bone plate for stabilizing and/or compressing a bone.

A bone plate is known from French patent document 742,618 wherein circular boreholes in the plate slant relative to a normal to the plate and are fitted with inside threads. These boreholes accept bone screws fitted with a second threaded portion which is widened compared to the conventional threaded screw shank segment and corresponding to the inside thread of the plate boreholes. Because of the slant of the plate boreholes, the bone screws also can be anchored at a slant, determined by said boreholes, into the bone.

The known bone plate incurs the drawback that the slant of the bone screws cannot be selected at will but instead is predetermined by the slant of the boreholes and their inside thread.

The object of the invention is palliation and to create a bone plate of which the boreholes are designed selectively to make possible two different kinds of screw anchorings. In the first application, a bone screw with a spherical head may be screwed into an elongated slot of the plate within a wide and selectable range at an angle to the plate normal into the bone. By tilting the countersink of the plate boreholes, furthermore a compressive effect is made possible.

In the second application a bone screw with a head thread and in the form of a bracing screw can be vertically and rigidly screwed into the plate at the partial inside thread of the elongated slot.

The invention achieves its object by a bone including an elongated plate defining a longitudinal axis along its length. The bone plate has an upper surface and a lower surface for application to a bone. A plurality of elongated holes are arranged along the length of the plate for receiving bone screws. At least one of the elongated holes has a first diameter D.sub.L, which is measured along the length of the hole. A second diameter D.sub.Q is measured across the width of the hole. Advantageously, D.sub.L is greater than D.sub.Q and at least one of the elongated holes includes a partial threaded portion arranged in the area of diameter D.sub.Q. The threaded portion is configured for seating a bone screw which has a threaded head.

Essentially, the advantages offered by the invention are that the bone plate of this invention are ubiquitously applicable in the most diverse cases such as fixation, compression, and employment as fixateur interne (internal affixer) in the sense of a bracing screw, but especially in the maxillofacial field requiring three-dimensional matching.

The invention offers also the following advantages

compatibility with conventional cortical screws,

variable angular orientation of the bone screws in the plate boreholes

problem-free removal of bone screws even in the case of intra-oral access,

possibility of new operation using a new plate,

screw head affixation in the plate borehole using bone screws of conventional diameter, and

achieving compression using screws with spherical heads.

The invention and further embodiments of this invention are elucidated below in relation to partly diagrammatic drawings of an illustrative embodiment wherein.

FIG. 1 is a partial perspective of a bone plate of the invention,

FIG. 2 is a partial top view of the bone plate of the invention, FIG. 3 is a partial longitudinal section of the bone plate along line III--III of FIG. 2,

FIG. 4 is a cross-section orthogonal to the bone-plate longitudinal direction along line IV--IV of FIG. 2,

FIG. 5 is a partial longitudinal section of a bone plate of the invention with a double-threaded bone screw which is screwed-in perpendicularly,

FIG. 6 is a partial longitudinal section of a bone plate of the invention with a bone screw passing through the plate perpendicularly or at a slant, said bone screw comprising a spherical head and serving as a non-compressive affixation screw,

FIG. 7 is a cross-section perpendicular to the longitudinal section of FIG. 6 and located in the hole area of the bone plate, and

FIG. 8 is a partial longitudinal section of a bone plate of the invention through which passes a perpendicular bone screw with a spherical head and serving as a compressive affixation screw.

The bone plate shown in FIG. 1 comprises several holes 2 to receive diverse types of bone screws 6, 7 (shown in FIGS. 5, 6) with which to affix the bone plate to the bone.

As shown in detail in FIGS. 2-4, the holes 2 are designed to be so-called elongated slots, that is, when measured in the direction of the plate longitudinal axis 1 the major axis D.sub.L is larger than the minor axis D.sub.Q perpendicular to the plate longitudinal axis 1. D.sub.L /D.sub.Q is preferably within the range of 1.01 to 3 and most preferably within the range of 1.1 to 1.5.

As shown in FIG. 4, the lower part of the hole 2 facing the bone application surface 4 is approximately circular in the direction transverse to the plate and, as shown in FIG. 3, it flares approximately conically in the plate longitudinal direction toward the bone application surface 4. An inside thread is in the circular segment of the hole 2 and, because of design constraints, runs only in the lateral part of the plate over an angular range of about 60.degree. to 179.degree., preferably about 90.degree. to 150.degree..

As shown in FIG. 5, this partial inside thread is used to receive a bone screw 6 with a thread-head 9. By screwing the outside thread of the thread-head 9 into the corresponding and partial inside thread 3, rigid anchoring of bone screw 6 into the plate is achieved. Such screwed-in bone screw 6 serves as a bracing screw.

The upper part of hole 2 away from bone contact surface 4 is oval and comprises a conical flaring countersink area which, as shown in FIGS. 6, 7, slidingly receives a bone screw 7 with a spherical head 8. The expression "bone application surface" 4 denotes the plate surface which substantially directly contacts the bone.

Similarly to FIGS. 6 and 7, FIG. 8 shows a bone plate fitted with a bone screw 7 comprising a spherical head 8, the plate, as indicated by the arrow 10, being able to generate compression. For that purpose the conically flaring area 5 of the hole 2 (as shown in FIG. 3), is machined by a spherical or bevelling miller at an angle of 57.degree. relative to the plate longitudinal axis 1, whereby the elongated slot so produced acts like a ramp for the bone screw 7.

The special geometry of the hole 2 allows selective use of various types of bone screws 6, 7 on one and the same bone plate.