Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
2000-10-26
2003-06-10
Lewis, Ralph A. (Department: 3732)
Surgery
Instruments
Orthopedic instrumentation
C606S068000
Reexamination Certificate
active
06575973
ABSTRACT:
FIELD OF INVENTION
The invention relates to surgical devices for fixing broken bones and in particular to an improved intramedullary fixation device for securing broken bone fragments during the process of fracture healing.
BACKGROUND
Bone fractures are treated by realigning the broken bone fragments and immobilizing them in their formerly healthy positions relative to one another until the body causes the bone to heal and restore its structural integrity. Immobilization or fixation of the segments is accomplished by the use of rigid devices that span the fracture site and are located either external to the body or internally on the bone surface or inside the medullary canal.
Intramedullary fixation devices, which are indicated primarily in the fracture of long tubular bones, offer substantial advantages over external devices or those that are attached to the external surface of the bone. Such advantages include restoring functional rehabilitation of the limb within a relatively short time, freedom from the need for multiple surgical incisions to insert and remove holding pins and screws, reduced fluoroscopy, reduced incidence of infection and, unlike external holding devices, they are not easily susceptible to inadvertent movement.
Although intramedullary nailing has been used for many years, the devices presently in use are not completely satisfactory. Prior art reflects a multiplicity of devices, each with different characteristics:
The Kuntschner nail, developed in Germany in the 1930s, relies upon a cloverleaf cross-section, coupled with the lateral resilience afforded by a longitudinal slot, to maintain a stationary position within the medullary canal. It offers no other holding means to anchor it to the osseous wall of the canal. While this may be somewhat effective in holding the proximal bone fragment due to the relatively large area of surface contact, it is not reliable in holding the distal fragment, particularly when the fracture is located well into the distal portion of the bone where the medullary canal widens in cross-section. Attempts have been made to solve this problem by designing intramedullary nails which abandon the clover leaf cross-section design and instead rely upon expanding mechanisms within the nail to gain purchase on the osseous wall of the medullary canal within the distal bone fragment. None does so effectively.
U.S. Pat. No. 4,453,539, granted to Raftopoulos, et al, discloses a nail having a uniform circular cross-section and elements which extend radially out the sides of the distal portion, effectively increasing the diameter of the shaft near its distal end. While this device is capable of making contact with the inside of the medullary canal, because of the shape and orientation of the extending elements, it is not capable of attaining a good grip on it. Moreover, the extending elements engage only the distal bone fragment and do not engage the proximal fragment. Therefore, this nail provides only limited lateral support and allows potential rotational and migratory movement of the bone fragments relative to one another.
The problem with this nail and the other examples of the prior art is their inability to get a good purchase on the osseous wall of the medullary canal. Typically, the longitudinally extending medullary canal within a tubular bone has an irregular contour that generally converges in the central portion of the bone and diverges in a longitudinal direction near the ends of the bone. Consequently, an intramedullary nail that merely extends elements radially to make contact with the osseous wall will not secure a good grip, particularly when the bone is subjected to the substantial forces of functional rehabilitation, such as walking, prior to its healing. Moreover, an intramedullary nail having a uniform circular cross-section with no gripping means at its proximal end will only contact the inner wall of the medullary canal over a small region. Without a gripping method within both the proximal and the distal fragment, such a nail fails to provide sufficient lateral support to the fractured bone.
The intramedullary device disclosed by Wills, et al, in U.S. Pat. No. 4,519,100, similarly has a circular cross section and employs an expanding mechanism to grip the distal fragment of the bone. The device employs pivotal blades which rotate outwardly to engage the distal end of the fractured bone, resting in a flared configuration at the distal end of the medullary canal. Accordingly, these blades do not provide a positive force opposing movement of the distal fragment in the distal direction, particularly as their proximal edges are sharp and may allow movement as they easily penetrate the osseous wall. Moreover, this device does not securely engage the proximal fragment. Therefore, it too suffers the same deficiencies in providing lateral support. Indeed, the Wills patent acknowledges the deficiency by suggesting the insertion of a screw through the proximal bone fragment wall into the device in order to afford fixation.
Kurth U.S. Pat. No. 4,590,930 deploys an expanding device at the distal end of a cloverleaf cross-section nail. This device has three drawbacks. The first is that the mechanism employed for extending and retracting the blades is unduly complicated and relies on close tolerances in order to function within the clover leaf cross-section. The second is that the extending blades are necessarily of a very short length and may not reach or securely attach to the canal wall. The third is that it continues to rely upon the cloverleaf shape to grip the proximal fragment. While superior to a circular cross-section, this method is far less effective than an expansion device that securely engages the osseous wall within the medullary canal.
Prior art discloses other fixation devices that attempt to address the dual objectives of attaining secure anchoring into the bone fragment and securely gripping both the proximal and distal bone fragments in a manner that does not cause compression of the fragments. However, none of them satisfactorily achieves either of these goals. There exists no intramedullary device that employs a holding means that grips the bone fragment in both longitudinal directions so that it can withstand the forces caused by functional rehabilitation prior the complete healing of the bone. Moreover, all of those devices that have a holding means in both the proximal and distal fragments exert compressive force on the fragments in order to achieve anchoring. This is not always indicated nor desirable after reduction of the fracture, particularly in the case of comminuted fractures.
U.S. Pat. No. 4,091,806 to Aginsky shows a device that secures the distal fragment by means of a distally located expanding mechanism that consists of a conical member, which rides on a longitudinally disposed threaded rod, which spreads the split distal end of the nail apart when the rod is rotated. This method grips poorly because the split portion of the nail making contact with the inside of the medullary canal in the distal fragment is of circular shape which is not able to penetrate for holding securely to the osseous wall. Substantial pressure against the wall of the fragment is needed which holds the potential for additional damage to the bone. Moreover, this device exerts considerable compression on the fragments because the force opposing the movement of the conical member longitudinally along the shaft is a nut embedded in the proximal end of the proximal fragment. This design has additional drawbacks. One or more of the split ends can break off when extended by the conical member. When it is necessary to remove the nail after the bone is healed, this design relies solely on the restorative resiliency of the split nail ends to contract the expanded portion of the nail; a small piece of bone fragment or marrow growth lodging between the threaded rod and one or more of the split nail ends could frustrate the nail removal process.
U.S. Pat. No. 4,275,717 to Bolesky is another example of a device which engages both the pr
G.E. Ehrlich Ltd.
Lewis Ralph A.
Safedrip Ltd.
LandOfFree
Self locking intramedullary nail does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Self locking intramedullary nail, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Self locking intramedullary nail will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3100971