Artificial Leg With Stable Link-type Knee Joint

Abstract

The invention provides an artificial knee joint comprised by two parts of links joining a stump socket portion to a shin portion in such a manner as to impart stability to the joint over initial flexure from the upright, such stability being derived from an initial rise in the effective center of rotation.

Parent Case Text

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of application Ser. No. 229,318, filed Feb. 25, 1972 and now abandoned.

Description

BACKGROUND OF THE INVENTION

This invention concerns improvements in artificial legs, and its object is to provide an improved joint for fitment between a socket for an amputee's upper leg stump and a shin portion of such legs.

In certain cases of amputation the stump includes knee structure and the proper locus of the knee pivot lies within the lower part of the patient's stump, so that, for attainment of a simulated natural gait, the shin portion of an artificial leg must pivot about a point or points above the base of the stump socket.

SUMMARY OF THE INVENTION

According to the invention, an artificial leg having an upper leg stump socket portion and a skin portion in which a rearwardly and downwardly sloped plate within the shin portion is connected to a substantially horizontal plate at the base of the socket portion by two pairs of pivoted links, of which the links of a forward pair are shorter than those of a rearward pair, and which together form an articulation between the said portions whose instantaneous center of rotation (the intersection point of a line drawn through the pivot points of a forward link and a line drawn through the pivot points of a rearward link) lies upon an ascending curve for a predetermined angle of relative rotation between the two portions of the leg from the fully extended position. The resultant articulated joint provides a stable weight support until it has been flexed through the predetermined angle from the extended position, which may be about 15.degree..

Preferably the joint should be capable of flexure through more than a right angle, say 120.degree., to permit a natural sitting posture. To this end both the forward and rearward links are preferably cranked rearwardly from about their mid points to avoid mutual interference. Springs and/or friction or hydraulic gait-control mechanism may be incorporated in the joint in a manner familiar to those skilled in the art. Likewise, alteration of the lengths of the links and of their pivot points can be made to adapt the characteristics of the joint to suit the individual stump condition of a patient. However, it has been found that the angulation between lines intersecting the pivot axes of the links is critical.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation of the knee section of an artificial leg in the extended position;

FIG. 2 is a similar view of the leg in fully flexed position;

FIG. 3 is a rear elevation of the leg in extended position;

FIG. 4 shows the locus of the instantaneous center of rotation when a socket portion moves relative to a stationary shin portion and vice versa, and

FIG. 5 shows the derivation of points D and E shown in FIG. 4.

DETAILED DESCRIPTION OF THE DRAWINGS

The shin portion 1 of the artifical leg embodies a tubular load-bearing member 2 attached to a casting 3. A plate 4 incorporating upwardly extending lug portions 5 and 6 is screwed to the upper face of the casting 3. The stump socket portion of the leg is carried by a substantially horizontal plate 7, screwed to which are lugs 8 and 9. A dished fairing plate 10 is slotted for the passage of two pairs of pivoted links 11 and 12 secured to lugs 5, 8 and 6, 9 by bolts 13.

Both links 11 and links 12 are cranked so as to permit flexure to a sitting posture without interference as shown in FIG. 2. In this particular form of construction the lower pivot points of the forward air of links 11 are spaced about 35/8 inch from those of the rearward pair 12, while the upper pivots are spaced by about 11/4 inch. The significant length of the links 11 is 21/4 inch and that of the rearward links 12 is 37/8 inch.

The rearward slope of the line joining the lower pivot points in the lugs 5 and 6 is about 30.degree., and the line joining the upper pivot points in the lugs 8 and 9 gives a forward slope of about 15.degree.. The locus of the instantaneous center of rotation upon commencement of flexure of the upper leg socket portion relative to the shin portion in this example rises from a point about 43/4 inch above the level of the rear lower pivot bolt 13 by about 1 inch before beginning to descend.

Lines drawn through the pivot points of the forward links subtend an angle of 41.degree. with the vertical when the leg is fully extended, subtend angles of 79.degree. with the lines joining the two pivot points on the shin, subtend angles of 146.degree. with the lines joining the pivot points on the socket portion and in that the lines joining the pivot points of the rear links subtend angles of 53.degree. with the said lines joining the pivots on the shin portion.

The stated angles are found in practice to be absolutely vital. In an experiment, moving the pivot points one at a time by a mere 1/16 inch (equivalent to an average change of included angle of about 0.5.degree.) was found to produce quite unacceptable loss of function. Gapping at the knee between fairing plate 10 and the front upper edge of the shin casing occurred, the maximum degree of flexion was reduced and there was a tendency for angular movement to become locked.

In FIGS. 4 and 5 the socket portion of the artificial leg is shown in broken lines, upright and flexed through 40.degree. and 65.degree. (FIG. 4) and through 85.degree. and 115.degree. (FIG. 5). The abscissa of the bold lines drawn through the pivot points of the links 11 and 12 are marked A, B, C, D and E and show the precise locus of the instantaneous center of rotation corresponding to the upright and given angles of flexure. The locus of the instantaneous center of rotation, assuming a stationary socket portion and flexing shin portion, follows a similar but tighter curve shown by the bold dash line in FIG. 4.

It will be appreciated that the geometry of the joint linkage provides a stable weight-bearing characteristic throughout a considerable angle of flexure.

Claims

I claim:

1. An artificial leg comprising an upper leg stump socket portion and a shin portion in which a rearwardly and downwardly sloped plate within the shin portion is connected to a substantially horizontal plate at the base of the socket portion by a forward pair and a rearward pair of pivoted links, the links of said forward pair being shorter than the links of said rearward pair, said forward and rearward pairs of links connected to said horizontal plate and to said sloped plate by pivots, the pivots on said sloped plate being spaced apart by more than twice the distance separating the pivots on said horizontal plate, with the pivots on said horizontal plate disposed at intermediate positions relative to the horizontal positions of the pivots on said sloped plate when the leg is in a fully extended position, said pairs of links jointly forming an articulation between said socket and shin portions and having an instantaneous center of rotation constituted by the intersection point of a line drawn through the pivot points of a forward link and a line drawn through the pivot points of a rearward link, said center of rotation being located in substantially the region of that of a natural knee and lying upon a curve which is ascending through approximately 15.degree. of relative rotation between said socket and shin portions of the leg from the fully extended position, said articulation exhibiting flexure exceeding 90.degree. to enable natural sitting posture.

2. An artificial leg according to claim 1, in which said links are curved such that end portions are disposed rearwardly of central portions thereof.

3. An artifical leg according to claim 1, wherein said pivots are disposed so that lines drawn through the pivot points of the forward links subtend an angle of 41.degree. with the vertical when the leg is fully extended, subtend angles of 79.degree. with the lines joining the two pivot points on the shin, subtend angles of 146.degree. with the lines joining the pivot points on the socket portion and in that the lines joining the pivot points of the rear links subtend angles of 53.degree. with the said lines joining the pivots on the shin portion.