In osteosynthesis there are a multitude of requirements for reciprocal fixation of the involved bone fragments. For this reason, a great number of fixation devices are already known, such as plate/screw systems, external fixators, internal fixators, spinal column fixation systems, etc.
Many of these known devices permit working only in two dimensions, which severely limits their applicability. A further disadvantage is the lack of ability, or only limited ability, to adapt the fixation device during the operation, i.e. to loosen the connection between the individual fixation parts easily and quickly and then lock them to each other in another relative position.
From DE-A-30 27 148, a bone plate, for example, with a hemispherical-shaped screw hole opening upwards, into which a spherical, slotted clamping piece with a conical borehole can be inserted, is known. Through the conical borehole of the clamping piece seated in the plate, a bone screw with a matching conical head can be screwed into the bone, until the conical screw head comes into contact in the conical inner borehole with the clamping piece. It expands the clamping piece and locks it within the screw hole of the plate.
The disadvantage of this known device is that the bone screw is not rigidly attached to the bone plate. As soon as the screw loses its attachment in the bone material, it can easily become loosened from the clamping piece or from the plate. This known anchoring concept can therefore be used only on bone plates. This concept cannot be applied to an external fixator or to a spinal column fixation system, because a rigid attachment between the individual parts is lacking; the fixation is maintained temporarily, only as long as the bone screw is securely seated in the bone material, and the bone plate presses against the bone.
From EP-A2 355 035 another bone plate is known, in which, similar to DE-A 30 27 148, the screw hole is equipped with an inner wall formed of spherical segments, which here, however, extends on both sides of a great circle, i.e., it narrows down against both sides of the plate from a line of maximum girth or circumference. The document goes on to disclose an automatic locking of the component parts. However, the following are disadvantages of this known device:
The locking of the screw in the clamping piece is done by rotation at the same time it is screwed into the bone using a hex wrench. While this is going on, there is a rapid onset of friction forces between the conical adjoining surfaces of both parts, which hinders screwing in of the bone screw. PA1 The screw can be set into the bone only after the complete positioning of the bone plate. Attachment of an already implanted screw to the plate or to another part acting as an attachment piece is not possible. PA1 The concept only works as long as the plate securely lies upon the bone and the bone exhibits good anchoring properties. As soon as the plate ceases to contact the bone, the attachment no longer functions.
In this regard the invention will constitute a remedy. The purpose of the invention is to create an osteosynthetic fixation device that is adjustable in three dimensions, and permits the individual parts easily and quickly to be locked in rigid fashion to each other, and also unlocked.