Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
1999-09-13
2001-07-10
Reip, David O. (Department: 3731)
Surgery
Instruments
Orthopedic instrumentation
C606S075000, C606S071000
Reexamination Certificate
active
06258092
ABSTRACT:
This invention relates to cortical bone screws, and to methods of using such screws in securing plates and the like to bones in the conduct of surgical operations.
Traditionally, bone screws are provided in a variety of different lengths, and are broadly similar in appearance to conventional wood screws. Their use is a cumbersome procedure which requires the careful selection of a screw in each case. The present invention is directed at a bone screw which avoids this selection procedure by being adaptable to a wide range of lengths of hole. By this means, there is no longer any need to keep a range of bone screws for a surgeon's use. In each case the same screw is selected.
According to the invention a bone screw assembly for use in surgical operations comprises a threaded shaft and a nut therefor which nut includes a radially resilient body with a normal internal diameter less than the pitch diameter of the shaft thread, and accommodates radial expansion of the body to allow translational movement of the nut along the shaft over the threads thereof but precluding such translational movement when radial expansion of the body is prevented. Thus, such translational movement of the nut is possible over an exposed length of shaft. However, when the nut is in a restricted volume which prevents expansion of the resilient body, the nut is bound to the shaft by the body. The assembly of the invention is adapted for use in circumstances where final axial movement of the nut is by rotation within a socket to secure the socket or the body in which it is formed, in place.
In assemblies of the invention, portions of the resilient body will upon radial expansion, project beyond the lateral boundary defined by the nut. Thus, this lateral boundary defines the cross-section required to prevent the resilient body from expanding to pass over the shaft thread in translational axial movement therealong. The resilient body is typically received in an annular groove formed in the nut, and is typically a split ring of resilient material. The housing itself may be formed in two parts to facilitate installation of the resilient body.
Because the nut in the assembly of the invention is adapted to be received in a restricted volume, conventional turning mechanisms that engage the peripheral surface thereof are inappropriate. In assemblies according to the invention therefore, the nut is adapted for coupling to a turning device engaged with its exposed axial end. Typically this is accomplished by the provision of castellations on the nut end, and a turning device may be provided which fits over the exposed length of screw shaft to engage the castellations. This has the advantage of providing for alignment of the turning device with the nut, and in certain variants of the invention the turning device may include a mechanism for severing the exposed length of shaft at the end face of the nut when the nut has been sufficiently tightened.
The restricted volume into which nuts and assemblies of the invention are adapted to be received is typically defined by a socket having an opening with an internal cross-section corresponding to a lateral boundary defined by the nut. The socket can be a sleeve which is axially movable relative to the nut to be engaged therewith when translational movement of the nut along the shaft is to be prevented. Such a socket can be adapted to be received in a plate for example to be secured to a bone surface, enabling the screw to be used to hold the plate against the surface. However, in preferred embodiments of the invention the socket is itself formed as part of the plate whereby the nut is received directly in an opening in the plate having a stepped cross-section. As the nut is received in the larger cross-section of the opening, which prevents radial expansion of the resilient body, the nut can then be turned to engage the step in the opening, and thereby clamp the plate to the bone surface.
While the use of bone screw assemblies according to the invention will normally be in conjunction with a pre-drilled and tapped hole in the bone, the shaft of the screws can be made with a self-tapping section at the end which is driven into the bone. In preferred embodiments, the self-tapping section has a conical cutting end with a plurality of flutes extending axially therefrom across the shaft thread. This enables the screw to be used not only to tap the thread in the hole formed in the bone, but also in the formation of the hole itself. For this purpose, the cutting end may be formed with a plurality of edges with different radii. This enables the hole to be cut progressively at different radii to reduce the generation of heat as the hole is drilled.
Flutes in the surface of the screw shaft provide a convenient means by which rotation of the nut on the shaft can be prevented. Thus, the nut may be formed with inwardly projecting pillars for receipt in the flutes, and around which the resilient body extends. In this variant, translational movement of the nut on the shaft is to some extent controlled, and when this is prevented by the nut entering the hole in the plate the rotational “lock” is particularly secure.
Bone screws according to the invention are typically metallic, usually being formed in corrosion resistant alloys. However, in some circumstances the shaft and/or the nut can be formed in plastics materials, and this can be of particular value where a degree of flexibility is desired.
REFERENCES:
patent: 3550668 (1970-12-01), Coyle
patent: 5167664 (1992-12-01), Hodorek
Reip David O.
Wallenstein & Wagner Ltd.
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