The apparatus of the invention comprises a mechanical joint that is adapted for use on a user's anatomical joint which has a proximal area, a distal area, a lateral side and a medial side. The preferred mechanical joint comprises a proximal body that is disposed adjacent to the proximal area of the user's anatomical joint and a distal race that is disposed adjacent to the distal area of the user's anatomical joint. The preferred mechanical joint also comprises a release plate, an iris, a roller bearing pin, a resilient tube and a drive pin that are substantially disposed in the proximal body. The preferred mechanical joint further comprises a pivot screw that is adapted to pivotally connect the proximal body and the distal race and a cable pull assembly that is adapted to permit the distal race and the proximal body to move relative to each other.