Surgery – Instruments – Orthopedic instrumentation
Patent
1999-09-30
2000-08-15
Buiz, Michael
Surgery
Instruments
Orthopedic instrumentation
606 73, 606 76, 600426, A61B 1784
Patent
active
061029149
DESCRIPTION:
BRIEF SUMMARY
The present invention lies in the field of orthopaedic surgery and relates more in particular to caps for screws which are used in this field. These screws are referred to in this description and the attached claims as "bone screws".
Bone screws are widely used as temporary medical implants for the fixation of skeletal fractures and/or for the fixation of orthopaedic implants. Important areas of application are (i) fixation of the spinal cord after a geometric correction, (ii) healing of fractures in the knee, heel, elbow or hip, and (iii) fixation of hip prostheses. Bone screws are generally made of a metallic material, e.g. of titanium, cobalt-chrome alloys and stainless steel. The metallic materials used should have an excellent biocompatibility in contact with bone and surrounding tissues.
As said, bone screws generally are temporary implants. They play an important role in keeping the integrity of the bone tissue after, e.g. a fracture.
The length of the bone screw used by the orthopaedic surgeon is normally as short as possible. The shorter a bone screw is the less discomfort is caused to the body, while the bone screw can be screwed down or fixated more tightly.
In the course of the several months or years that the bone screw stays in the body, bone growth leads to reinforced bone structures. This makes the presence of the bone screw superfluous, so that the bone screw is removed in a surgical operation. In addition, removal of the bone screw eliminates possible long-term complications, such as allergic reactions and irritations.
The removal of the fixation bone screws is, contrary to what one might expect, not a straight forward operation; it is usually associated with several complications. The first problem is associated with the fact that the bone screws used normally comprise holes or grooves, such as sockets, for screwing down, and/or comprise other irregularities. These holes and so on, generally hexagonal in shape, which are normally found on top of the screw, are filled and/or surrounded with scar tissue and/or newly formed (bone) tissue. Obviously, this tissue has to be removed prior to the introduction of the screw driver in the bone screw. This removal of tissue is highly time-consuming as it has to be performed with great care. Moreover, the risk of infections increases with the operation time.
Further, the screws cannot easily be located. Although the screws are clearly visible under e.g. X-ray fluoroscopy, the images obtained only provide a two-dimensional picture, so that it is often difficult to find the exact position of the screw.
In the Russian patent application 2,026,648 it has been proposed to design an osteosynthesis screw having a head with a very specific slot. The slot has a trapezoid-section, whereby the smaller base of the trapezoid faces outward. This slot may be covered with a cap made from material which has a so-called shape memory effect, and a very specific form comprising feet to engage with the trapezoid-shaped slot, a vertical rib on its outer surface which has at least one hole in it, and a flexible insert between the screw head and the cap. In order to attach and remove the cap, heating and cooling steps are needed. It is indicated that the cap with the rib with hole(s) is advantageous for an easier location. The problem of tissue in growth in cavities or other irregularities of the screw or cap is not addressed in this document.
U.S. Pat. No. 3,918,440 discloses a device for promoting formation of bone material. The device comprises a plastic-cap locking element which fits into the socket of the head of a bone screw. The cap is attached to a coil through a connecting wire, which coil is located outside of the treated patient, for applying an A.C. signal to the bone in order to promote bone growth. The cap comprises protruding elements, such as the connecting wire, which elements in fact create similar problems in respect of the surrounding and newly formed tissue, as uncapped bone screws.
The problem underlying the present invention is to safely facilitate an
REFERENCES:
patent: 3918440 (1975-11-01), Kraus
patent: 5372503 (1994-12-01), Elia
patent: 5730130 (1998-03-01), Fitzpatrick et al.
Bulstra Sjoerd
Bulstra Teake
Koole Leo H.
Biomat B.V.
Buiz Michael
Reip David O.
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