Bone plate for the fixation of fractures of the proximal humerus

CA 02448522 2010-04-13

Bone Plate For The Fixation Of Fractures Of The Proximal Humerus

The invention relates to a bone plate for fixation of proximal humerus fractures.

These bone plates are used for fixation of all types of fractures on the proximal humerus, but especially for all three-part and four-part fractures and for dislocated fractures on the proximal humerus.

A frequent cause of fractures of the proximal humerus in recent years has been high energy trauma. This type of fracture increases with age since in the area of the proximal humerus the bone structure is very degraded so that only in the edge zone of the bone is there intact bone structure. In a fall on an outstretched arm at advanced age the bone then breaks preferably at this point.

A generic bone plate is already known from US-A 6,096,040 ESSER.

The disadvantages of this arrangement consist in that the plate in a spoon-like part has a hole position with which it is not possible to grip good bone structure in the edge zone of the proximal humerus, as is well known.

Moreover, the implant which is described in ESSER is a plate without angularly stable options in the plate holes. When using the plate it is pressed by bone screws against the bone. This process is called compression osteosynthesis. In doing so the forces which occur are transferred via friction between the implant and the bone, while the bone must bear most of the load. The great axial pressure to which the bone screws are exposed for relative stable retention of the plate on the bone under dynamic conditions causes the bone screws to tear out of the bone, and associated with this, a loss of the stability of the plate-bone construct.

The discussion of the prior art above serves only to explain the environment of the invention and does not mean that the cited art at the time of this application or its priority had in fact been published or was publicly known.

CA 02448522 2008-03-20

The invention is intended as a remedy here. The object of the invention is to devise a bone plate for fixation of proximal humerus fractures with which angularly stable osteosynthesis can be achieved. Important advantages of the invention are the angular stability of the screw holes in combination with screws with head threads, simple handling, optimum anatomic matching to the bone and no impediment to the relevant anatomic structures of the proximal humerus. By using screws with a threaded head an angularly stable bone construct is formed which can maintain the hold even under dynamic conditions.

This object is achieved with a bone plate having a handle-shaped part (1), whose length is greater than its width x, and a spoon-shaped part (2), whose width y is greater than width x of the handle-shaped part (1), with the handle-shaped part (1) and the spoon-shaped part (2) having a common longitudinal axis (3) and being connected with one another via a transition area (26), and at least 2 screw holes (9,10,16,17,24) each being disposed in the handle-shaped part (1) and in the spoon-shaped part (2), characterized in that: A) at least one of the screw holes (24) in the handleshaped part (1) has an at least partial inside thread (28) or partially circumferential grooves; B) at least one of the screw holes (9,10,16,17) in the spoon-shaped part (2) has an inside thread (27) or partially circumferential grooves; C) the pitch of the inside threads (27,28) or the partially circumferential grooves lies in the range between 0.5 mm and 1.1 mm; and D) the thickness (7) of the bone plate is in the range between 1.7 and 2.3 mm.

The small thread pitch allows secure anchoring of the screw in the plate on a very short section, conventionally in the range from 1 to 2 mm. In this way the thickness of the plate can be made very thin without adversely affecting the stability of the plate-screw construct.

One preferred development consists in that the pitch of the inside thread or the partially peripheral wedge-shaped grooves is in the range from 0.7 to 0.9 mm; this further optimizes the described effect.

In another preferred embodiment the transition area widens from the width x of the handle2

CA 02448522 2003-11-25 shaped part to the width y of the spoon-shaped part, preferably exponentially.

Thus, optimum matching to the unbroken human proximal humerus can be achieved. The plate thus rests cleanly on the bone and none of the relevant anatomic structures are impeded.

The thickness of the plate is preferably in the range from 1.7 to 2.3 mm, preferably between 1.9 to 2.1 mm. The advantage of the thickness which is comparatively low compared to conventional bone plates is mainly that thin plates do not impede the relevant structures and when the arm is lifted do not hit the acromion of the shoulder.

Preferably the handle-shaped part of the plate, viewed in the direction of the central axis, is made curved in at least one component area.

In another preferred embodiment the handle-shaped part of the plate, viewed in the direction of the central axis (3), is curved at least in one component area in the form of an elliptical arc (21). The length of the major axis (22) of the ellipse which belongs to the elliptical arc (21) is preferably in the range between 150 and 170 mm, typically in the range from 157 to 163 mm. The length of the minor axis of the ellipse which belongs to the elliptical arc is preferably in the range between 60 and 80 mm, typically in the range between 67 and 73 mm.

The free end of the handle-shaped part and of the spoon-shaped part (2) are preferably essentially in planes which are parallel to one another.

All these preferred measures have the advantage that improved matching to the unbroken human proximal humerus is possible, the plate resting cleanly on the bone, and none of the relevant anatomic structures being impeded.

In another preferred embodiment the bone plate at least in one component area has a

CA 02448522 2003-11-25 curvature which runs transversely to the central axis, preferably with a radius of curvature in the range from 18 to 22 mm.

In another embodiment the bone plate has a curvature which runs transversely to the central axis over its entire length. The advantage which can be attained with it is that no irritation of the soft parts which are present occurs. When the arm is raised the bone plate is prevented from hitting the acromion of the shoulder.

In another preferred embodiment the free end portion of the spoon-shaped part has two holes which are located symmetrically to the central axis, with parallel hole axes, the hole axes forming an angle from 92° to 98°, preferably from 94° to 96°, with the surface which has been formed by the spoon-shaped part. In order to achieve angularly-stable repositioning, in implants from the prior art blades are necessary which are replaced by the screws which are to be inserted into the angularlystable holes. The surgical technique of blades however requires greater time expenditure and is more complex to use than that with angularly-stable screws as in the invention. The contact angle of roughly 95° increases the contact surface with the solid bone since solid bone material is present only in the edge zones of the relatively hollow humerus head.

In another preferred embodiment the portion of the spoon-shaped part bordering the transition area has two holes which are arranged asymmetrically to the central axis and the axes of the two holes lie in planes which are parallel to one another and which are preferably orthogonal to the central axis. The projection of the one hole axis into the parallel plane which contains the other hole axis includes with the axis of the hole an angle of 40° - 60°, preferably 46° - 54° among one another.

CA 02448522 2003-11-25

The advantage of this means lies in that the screws which are to be inserted into these crossing holes allows the small tuberculum which often breaks in fractures of the proximal humerus to be used.

Another preferred embodiment is that at least one of the holes which are arranged symmetrically and/or asymmetrically to the central axis has an inside thread or partially peripheral wedge-shaped grooves. Here advantageously none of the axes of the holes which are arranged symmetrically and/or asymmetrically to the central axis intersect. In this way the advantage is achieved that the screws which are to be inserted into the holes do not mutually impede one another.

In another embodiment the axes of the holes which are made in the handle-shaped part are perpendicular thereto.

The inside threads are preferably multithreaded, typically double-threaded.

The bone plate as claimed in the invention can be used both for the left and also for the right humerus and is optimally matched to the shape of the healthy proximal humerus.

The invention and development of the invention are detailed below using a partial schematic of one embodiment.

Figure 1 shows an overhead view of the bone plate as claimed in the invention;

Figure 2 shows a section along the line II-II in Figure 1;

Figure 3 shows a perspective representation of the bone plate as claimed in the invention;

and

Figure 4 shows a side view of the bone plate as claimed in the invention.

The bone plate which is shown in Figures 1 to 4 and which is used for fixation of proximal

CA 02448522 2003-11-25 humerus fractures consists of a handle-shaped part 1 with a length which is greater than its width x, and a spoon-shaped part 2 with a width y which is greater than the width x of the handle-shaped part

1. The handle-shaped part 1 and the spoon-shaped part 2 have a common longitudinal central axis 3 and are interconnected by a transition area 26 which widens exponentially from the width x of the handle-shaped part 1 to the width y of the spoon-shaped part 2.

In the handle-shaped part 1 and also in the spoon-shaped part 2 a larger number of screw holes (9,10,16,17; 24) is made. All the screw holes 24 made in the handle-shaped part 1 of the bone plate have an inside thread 28 (it could be replaced by partially peripheral wedge-shaped grooves).

Four of the screw holes (9,10,16,17) which are made in the spoon-shaped part 2 of the bone plate likewise have an inside thread 27 (here the inside thread could also be replaced by partially peripheral wedge-shaped grooves).

The pitch of this inside thread 27; 28 (or the partially peripheral wedge-shaped grooves) is 0.8 mm. The thickness of the bone plate is 2 mm.

As is apparent from Figure 4, the handle-shaped part 1, viewed in the direction of the central axis 3, is made curved in a partial area, in the form of a elliptical arc 21. The length of the major axis 22 of the ellipse which belongs to the elliptical arc 21 is 160 and the length of the minor axis 23 of the ellipse which belongs to the elliptical arc 21 is 70 mm. Due to the curvature of the handle-shaped part 1 the free end 5 of the handle-shaped part 1 and of the spoon-shaped part 2 is essentially in planes which are parallel to one another.

As is apparent from Figure 2, the bone plate over its entire length has a curvature 6 which

CA 02448522 2003-11-25 runs transversely to the central axis 3 with a radius of curvature of 20 mm.

As is apparent from Figures 1 and 2, the free end portion 8 of the spoon-shaped part 2 has two holes 9,10 which are arranged symmetrically to the central axis 3 with parallel hole axes, the axes 11,12 of the holes forming an angle 13 of 95° with the surface 14 which is formed by the spoon-shaped part 2.

The portion 15 of the spoon-shaped part 2 bordering the transition area 26 moreover has two holes 16,17 which are arranged asymmetrically to the central axis 3. The axes 18,19 of the two holes 16,17 lie in planes which are parallel to one another and which are orthogonal to the central axis 3. The projection of one axis 18 of a hole into the parallel plane which contains the other axis 19 of the hole includes an angle 20 of 50° with the axis 19 of the hole.

The pairs 9,10,16,17 of holes which are arranged symmetrically and asymmetrically to the central axis 3 have an inside thread 27 which could also be replaced by partially peripheral wedgeshaped grooves. None of the axes 11; 12; 18; 19 of the pairs 9,10,16,17 ofholes which are arranged symmetrically and asymmetrically to the central axis 3 intersect. The inside threads 27,28 are double threaded.

The axes of the holes 24 which have been made in the handle-shaped part 1 are perpendicular to the handle-shaped part 1.