Orthopaedic and prosthetic joint

Claim 1

An orthopaedic or prosthetic joint comprising: (a) a first fixed-length link member provided with two spaced-apart pivotal connections at one end thereof and a third pivotal connection remote from that end; (b) a second fixed-length link member pivotally connected at one end thereof to one of said first two pivotal connections on said first link member; (c) a third fixed-length link member pivotally connected at one end thereof to the other one of said first two pivotal connections on said first link member, said third link member being provided with a further pivotal connection at an intermediate portion thereof; (d) a fourth fixed-length link member arranged end-to-end with respect to said first link member but spaced therefrom by said second link member, said fourth link member being provided with two spaced-apart pivotal connections at that end nearer the first link member with one of said pivotal connections, on the fourth link member being pivotally connected to said second link member at that end of the second link member remote from the first link member; (e) a fifth fixed-length link member pivotally connected at one end thereof to the other one of said two pivotal connections on said fourth link member and pivotally connected at the other end thereof to that end of said third link member remote from the first link member whereby the second link member on the one hand and the third and fifth link members on the other hand extend between, and connect together, the opposing ends of the first and fourth link members; (f) a pivotal connection on the third link member between the ends thereof; (g) a spring link extending between said third pivotal connection on the first link member and said further pivotal connection on the intermediate portion of the third link member, said spring link being arranged to hold the joint in any selected one of a plurality of angular positions of the fourth link member with respect to the first link member; and (h) joint-release means connected to said third link member whereby the joint-holding function of the spring link may be overcome by operation of the joint-release means in order to permit the fourth link member to move to another angular position with respect to the first link member.