Adjustable Link For Prosthetic Limb

Abstract

A link between members of a prosthetic limb, such as a connector between a knee joint and an artificial shank, has a frustopyramidal four-sided boss divergingly projecting from a spherically convex base which slidably engages a correspondingly concave annular socket surrounding the boss. Two pairs of setscrews, lodged 90.degree. apart in the annular socket, bear upon the sides of the frustopyramidal boss to enable its adjustment, within a limited swing angle, in two mutually orthogonal planes.

Description

My present invention relates to an adjustable link designed to interconnect adjoining members of a prosthetic appliance, such as a stump support and a thigh member, a knee joint and a shank member, or the lower end of a shank member and an artificial foot.

In a prosthetic leg, for example, the body structure of the user and his attitude when standing or walking may require certain adjustments in the relative position of the aforementioned parts, frequently in two mutually orthogonal planes. The use of a universal joint of the ball-and-socket type for this purpose is inconvenient since it affords no stability against rotation about the major axis of the limb and since, once dislodged, the assembly cannot be accurately returned to its original position without the help of external references.

On the other hand, prior attempts at solving this problem by a cross-hinge articulation resulted in cumbersome and relatively expensive structures.

The object of my present invention, therefore, is to provide a simple mechanism for enabling the relative adjustment of two members of a prosthetic limb, i.e. an arm or a leg, in two mutually perpendicular planes with avoidance of the aforestated drawbacks.

I realize this object by providing a male and a female part, respectively, on the two artificial limb members to be relatively adjusted, one of these parts having two pairs of contact surfaces which are bisected by mutually orthogonal planes, the other part having adjustable abutment means such as setscrews engaging these surfaces for retaining the two parts in a selected angular position within predetermined swing ranges in these two planes.

More particularly, in a preferred embodiment, the male part has a spherically convex base from which a substantially frustopyramidal boss rises divergingly within an annular socket constituting the female part, the contact surfaces being represented by the respective sides of the preferably four-sided frustopyramid. The setscrews bearing upon these sides, and extending at right angles thereto, are lodged in the socket.

The divergence of the frustopyramidal boss in the direction away from the base helps prevent a separation of the two members; for this purpose it may be advantageous to impart a slight concavity to these pyramid sides, at least in their planes of swing, whereby the pressure exerted upon them by the tips of the setscrews has a transverse component tending to draw the parts toward each other.

The invention will be described hereinafter in greater detail with reference to the accompanying drawing in which;

FIG. 1 is a side-elevational view of a prosthetic leg embodying several adjustable links according to the invention;

FIG. 2 is a front-elevational view of the appliance of FIG. 1;

FIG. 3 is a side-elevational view, partly in section and drawn to a larger scale, of one of the links shown in FIGS. 1 and 2; and

FIG. 4 is a sectional elevation view, on the scale of FIG. 3, of another link illustrated in FIGS. 1 and 2.

The prosthetic appliance shown in FIGS. 1 and 2 comprises, as its principal constituent, a thigh member 6, a shank member 7, a foot 8 and a stump support 9. Thigh member 6 terminates at its lower end in a knee joint which includes a lug 1 having a pivot 11 (FIG. 3) received in holes 12 of a bracket 10 rigid with thigh 6. The lug 1 is adjustably connected with shank 7 by a joint generally designated 20 and described in greater detail hereinafter; similarly, joints 20' and 20" connect the lower end of shank 7 with foot 8 and the hip socket 9 with the top of thigh 6, respectively.

The three joints are substantially identical and two of them, i.e. joints 20 and 20', will be described in detail hereinafter with reference to FIGS. 3 and 4, respectively. FIG 3 shows the joint 20 as comprising a spherically convex base 2 rigid with lug 1. A central boss 3 of frustopyramidal configuration has a disk-shaped pedestal 21 firmly secured to base 2 with the aid of a screw 22 whose head is received with clearance in the top of the tubular shank 7. The frustopyramid formed by the main portion of boss 3 has four sides, slightly concave as shown at right in FIG. 3, which are engaged by the tips of respective setscrews 5 threaded into an annular socket 4 whose concave upper ring surface has the same radius of curvature as the base 2 and slidably hugs the latter. Lines 3a tangent to the curved generatrices of the pyramid sides, converge in a point 3b on the axis of base 2; upon a loosening of the pair of screws 5 visible in FIG. 3 and the other pair perpendicular thereto, the shank 7 can be swung out of line with axis 3c within a limited range as illustrated in dot-dash lines for the knee-action plane.

The ankle joint 20' of FIG. 4 includes a convex base 2' secured by a bolt 16 to the foot 8 (FIGS. 1 and 2), its frustopyramidal boss 3' being surrounded by an annular socket 4' holding the screws 5'. The operation of this joint is analogous to that of the joint 20 of FIG. 3. Corresponding elements 2", 3", 4" and 5" have been illustrated in FIGS. 1 and 2 for the upper joint 20".

When the user places his weight on the appliance, as illustrated at W in FIG. 1, the relative position of the members 6-9 should be such that the center of gravity of his body is substantially in line with the center of foot 8. Screws 5, 5' and 5" allow for an easy and convenient adjustment of the joints 20, 20' and 20" to accomplish this aim.

Claims

I claim:

1. An adjustable link interconnecting two members of a prosthetic limb, comprising a male part rigid with one of said members and a complementary female part rigid with the other of said members; said male part including a spherically convex base and a boss of substantially frustopyramidal configuration divergingly rising from said base, two pairs of opposite sides of said boss forming respective pairs of contact surfaces bisected by mutually orthogonal planes; said female part comprising an annular socket surrounding said boss, said socket having a spherically concave ring surface complementary to and of the same radius of curvature as said base and in slidable engagement therewith; and adjustable abutment means on said socket engaging said surfaces for retaining said parts in a selected angular position within predetermined swing ranges in said planes.

2. A link as defined in claim 1 wherein said frustopyramidal boss is four-sided.

3. A link as defined in claim 1 wherein said abutment means comprises two pairs of setscrews extending perpendicularly to said sides of the frustopyramid.

4. A link as defined in claim 3 wherein said sides have a slight concave curvature in the planes bisecting same.