Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
1999-03-05
2001-05-01
Philogene, Pedro (Department: 3732)
Surgery
Instruments
Orthopedic instrumentation
C606S068000
Reexamination Certificate
active
06224600
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention refers to a device for fracture fixation. Devices for fracture fixation are known from EP 0 698 800, which discloses affixing an elongated rod on the bone. Further, documents GB 2 268 068 and DE 923 085 disclose devices for fracture fixation comprising at least a deformable element and compression means to apply a compression force to the deformable element, so the deformable element deforms laterally.
Each of the well established fixation methods (rigid compression planting, reamed intramedullary nailing, with or without interlocking of the fracture fragments, external fixation and dynamic hip screw) has advantages and disadvantages as well as special biomechanical characteristics. Vast clinical experience combined with the data produced from theoretical and experimental studies have described many of the problems related to the biomechanics of these fracture fixation devices.
Today's understanding of bone biology has led us to a new approach to bone fixation. This approach considers the importance of the preservation of the soft tissue and of careful protection of the viability of bone. This invention aims to add to the theory and practice of bone fixation the concept that the fracture fixation device introduces into the broken bone equilibrium tensions to restore the intraosseous forces and make the bone capable of receiving the load stresses and muscle-spasm stresses right at the beginning of the healing period, as opposed to the prior concept that it is the device that receives these stresses.
A first attempt towards these goals is disclosed by Protogirou in PCT International Publication Number WO 91/19461 (title: Device for Osteosynthesis with Axially Guided Prestressing Elements). This device was also trying to solve some of the problems related to the biomechanics of bone fixation using axial prestressing to achieve stable and elastic osteosynthesis thus restoring the intraosseous forces. The resetting of the fragments remains stable by the medullary guide and the axial prestressing is applied through the tendons.
SUMMARY OF THE INVENTION
According to the invention the device for fracture fixation comprises, a tendon and at least a deformable element at the focus of the fracture, whereby the deformable elements may be 2, 3, 4, 5, or more, with the tendon and the deformable element being disposed almost along the same direction, whereby the device further comprises compression means to apply a compression force to the deformable elements, so that the deformable elements deforms laterally. The device described can be used for fractures of long bones as well as for proximal femoral fractures. When used for long bone fractures, the device is an intramedullar flexible bar, by which is applied adjustable and readable axial prestressing in order to compress the bone fragments and preload the bone, and not a supportive intramedullar nail as the devices used sofar for fracture fixation. When used for proximal femoral fractures, the device is the same intramedullar flexible bar, by which is applied adjustable and readable lateral prestressing when anchoring it on the external femoral shaft. By doing so the bone fragments are compressed in order to neutralize the tension forces on the fracture and to avoid the interfragments motions. The terms “axial prestressing” and “lateral prestressing” refer to the axis of the long bone.
With the prosthetic device of the invention it is possible to apply simultaneously axial and transversal pre-stressing to pre-load the bone and obtain stable and elastic osteosynthesis of fractures. The device focuses on the concept of biological internal fixation with minimal damage and with consideration for the natural frequency of the bone.
The device according to the invention presents a different approach to the problem of fracture fixation in that it allows achievement of predetermined and readable intramedullar transversal prestressing, which is a prerequisite for the application either of axial prestressing or of lateral prestressing. The transversal prestressing holds in place the repositioned bone fragments and contributes to the neutralization of the bending moments and the shearing forces between the fracture angle and the mechanical axis of the bone caused by the axial prestressing in the case of long bone fractures. In the case of proximal femoral fractures the transversal prestressing diminishes the interfragmentary motions. The term “transversal prestressing” refers to the “axial prestressing” and the “lateral prestressing” and is vertical to them.
Moreover, because the transversal prestressing can diminish the bending moments and the shearing forces caused by muscular spasm, the same device can be used as bone distractor for unstable long bone fractures.
The ability to compress the bone ends uniformly, In the case of long bone fractures, can be achieved through intramnedullary axial prestressing. But the fractured bone cannot receive compression forces if it is not repositioned in a stable way, because of bending and shearing forces occurring as a result of compression. The resetting of the fragments remains stable and allows for the application of axial prestressing because of the prior application of intramedullary transversal prestressing. In order to achieve this bi-axial prestressing a tendon is inserted intremedullarly and anchored in the one end of the bone. The tendon is passing through cylindrical bodies, which fit into one another and form a flexible bar. At least one pair of cylindrical bodies bear attachment means for deformable elements. By applying compression to the cylinders by the compression nut the cylinders we brought together and compress the deformable elements, which deform laterally and exercise pressure on the inner wall of the bone (transversal prestressing). As the tendon is already anchored in the one end of the bone, tension is exercised on the tendon by a screw bolt with support on an anchor means, which is anchored into the other end of the bone (axial prestressing). In spite of the application of tension, the flexible bar does not become a straight bar, but on the contrary it follows all the curvatures of the bone.
The neutralization of tension forces on the fractured proximal femoral bone can be achieved through lateral prestressing (tension band). The application of lateral prerstressing becomes more efficient if the interfragmentary motions are diminished. This is achieved by the prior application of transversal prestressing. In order to achieve this double prestressing an anchor screw is anchored in the head of the femur. The other end of this anchor screw is formed as a cylinder with attachment means at both its ends for the deformable elements. By applying compression to a compression means at the end of the cylinder other than the end bearing the screw, the deformable elements are compressed, which deform laterally and exercise pressure on the inner wall of the bone (transversal prestressing). The one end of the tendon is anchored at the end of the cylinder other than the end bearing the screw. The tendon is anchored by a ball means in order to form an articulation at this point and thus diminish the motion between implant and bone. The tendon bends on the lateral femoral shaft with support on a fulcrum attached on a plate, which plate is screwed in the lateral femoral shaft. The other end of the tendon passes through a cylinder fixed to the plate. Tension is exercised on this end of the tendon with support on the cylinder fixed to the plate and the tendon is then anchored on the plate (lateral prestressing). In some cases of unstable fractures a second tension band (wire) is added to the above described device ends of the wire are introduced in the form of a slip knot into the bone from the opening made for the anchor means
2
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, towards the base of the femoral neck. The slip knot is then anchored on the anchor screw, tightened over the greater trochanter, and both its ends then anchored on the plate.
The following advantages can be observed compared wi
Blank Rome Comisky & McCauley LLP
Philogene Pedro
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