Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Leg – Knee
Reexamination Certificate
1998-06-26
2001-03-27
Snow, Bruce (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Leg
Knee
Reexamination Certificate
active
06206933
ABSTRACT:
This invention relates to a knee prosthesis.
It is usual for a leg amputee to wear a prosthesis in order to provide the wearer with improved mobility. Such a prothesis should be comfortable to wear, and should simulate the natural movement of the replaced limb.
A known knee prosthesis includes a pair of split collars pivotally attached, in use, to a thigh member and a shin member respectively. One of the collars carries a brake drum, around which a brake band passes. In use, as the knee is loaded, an actuating lever engages the brake band to tighten it against the brake drum, thereby locking the knee in any desired position. The disadvantage of this known artificial knee is that it requires the use of machined elements, and so is relatively expensive.
The aim of the invention is to provide an improved form of artificial knee.
The present invention provides an artificial knee comprising first and second pivotally interconnected knee components, and first and second interengaging brake components for locking the knee components together, the first and second brake components being associated respectively with the first and second knee components, wherein one of the brake components is made of a resiliently deformable material, and the arrangement is such that, when the artificial knee is subjected to a first load condition, the brake components are substantially free to slide against one another, and, when the artificial knee is under a second, higher load condition, said one brake component is resiliently deformed against the other brake component to lock the two brake components together, thereby locking the two knee components together, wherein the first and second brake components are provided with interengaging surfaces which are inclined to the axis about which the two knee components are pivoted, and the first and second brake components constitute the pivotal interconnection between the two knee components.
As the brake components constitute the pivotal interconnection between the two knee components, they also constitute a load/weight bearing for the artificial knee, thereby reducing the number of components needed to make the knee, leading to a cost reduction.
Generally speaking, the first load condition is when the artificial knee is subjected to substantially no axial load; and the second load condition is when the knee is subjected to a weight-bearing axial load.
Preferably, the first brake component is separate from, and supported by, the first knee component; and the second brake component is separate from, and supported by, the second knee component.
Advantageously, the artificial knee further comprises means for preventing rotation of the first brake component relative to the first knee component.
Conveniently, the first and second brake components are inner and outer brake members, the outer brake member being rotatable about the inner brake member about the axis of rotation of the knee. Thus, when the knee is subjected to an actuating load, the outer brake member grips the inner brake member.
Thus, for example, the brake components may be a shaft defining the knee axis and secured to one of the knee components, and a clamp substantially encircling the shaft and secured to the other of the knee components, with the shaft and clamp having an interengaging rib and groove of complementary wedge-shaped cross-section. The rib and groove are in sliding engagement with each other in the first load condition when the knee components are rotated with respect to each other, and grip each other to resist such rotation when the clamp is tightened around the shaft in response to the second load condition.
Advantageously, the brake components have, respectively, a projection outwardly tapered in cross-section, and a recess which receives the projection and is of complementary shape. Thus, on application of an actuating load, the projection is urged into the recess to engage the recess surfaces in a wedging action.
Preferably, the first brake component is an externally screw-threaded member, the flanks of the threads being inclined to the pivot axis. Conveniently, the first brake component is provided with an acme screw thread, and is made of a generally rigid (non-resiliently deformable) material such as stainless steel or aluminium alloy.
In a preferred embodiment, the second brake component has a base portion and a pair of arms, the internal surface of the base portion being rounded and being provided with an internal screw thread which complements the external screw thread of the first brake component. The second brake component may be said one brake component, and said resiliently deformable material may be a plastics material such as nylon 6,6.
Advantageously, the free ends of the arms of the second brake component are connected to the second knee component by first and second pins. Preferably, the second knee component defines a pair of supports between which the second brake component is mounted, the first pin passes through aligned circular apertures in the supports and through a circular aperture in one of the arms of the second brake component, and the second pin passes through aligned apertures in the supports and through an aperture in the other arm of the second brake component.
In a preferred embodiment, the second pin passes through aligned elongate apertures in the supports and through a circular apertures in said other arm. In this case, the apertures in the supports may be so positioned that, when the artificial knee is subjected to the second load condition, the second pin is forced along the elongate apertures in the supports so that the internal screw threads of the rounded base portion of the second brake component are forced against the external screw threads of the first brake component, thereby locking the two brake components together. Moreover, as the second pin is forced along the elongate apertures in the supports, the distance between the two pins decreases, and this leads to “hoop stress” in the second brake component, thereby increasing the force locking the two brake components together. This “hoop stress” is increased by the flexion moment and the friction between the two brake components.
Advantageously, the circular aperture in said other arm of the second brake component is more remote from the second knee component than the circular aperture in said one arm of the second brake component. Preferably, the free ends of the arms of the second brake component are directed towards the anterior of the knee.
In a preferred embodiment, said other arm of the second brake component is tangential to the hyper-extension moment when the knee is in hyper-extension. This leads to the hyper-extension moment being resisted by the second pin, so that the second brake component is subjected only to tension fores. Conveniently, the fulcrum of the hyper-extension moment is constituted by an abutment between portions of the two knee components, the abutment being anterior to the knee axis of rotation, and being on the side of said axis remote from the free end of said other arm of the second brake component.
In another preferred embodiment, the second pin passes through aligned circular apertures in the supports and through a circular aperture in said other arm. In this case, the apertures in the supports and the apertures in the arms of the second brake component may be positioned such that the first and second pins are substantially aligned with the axis about which the two knee components are pivoted.
The artificial knee may further comprise means, such as a threaded pin, for pre-tensioning the arms of the second brake component towards one another. This enables the artificial knee to be adjusted to suit amputees of different body weights.
Where the second pin passes through circular apertures in the supports, the pre-tensioning means may be constituted by a pin member associated with said one arm, an abutment member associated with said other arm, and a spring acting to bias the two arms apart, the pin member being fixed to the abutment member in such a m
Aulie Alan
Shorter John Jeffrey
Barnes & Thornburg
Chas. A. Blatchford & Sons Limited
Snow Bruce
LandOfFree
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