38 CFR § 4.63 - Loss of use of hand or foot.
Loss of use of a hand or a foot, for the purpose of special monthly compensation, will be held to exist when no effective function remains other than that which would be equally well served by an amputation stump at the site of election below elbow or knee with use of a suitable prosthetic appliance. The determination will be made on the basis of the actual remaining function of the hand or foot, whether the acts of grasping, manipulation, etc., in the case of the hand, or of balance and propulsion, etc., in the case of the foot, could be accomplished equally well by an amputation stump with prosthesis.
(a) Extremely unfavorable complete ankylosis of the knee, or complete ankylosis of 2 major joints of an extremity, or shortening of the lower extremity of 3 1/2 inches (8.9 cms.) or more, will be taken as loss of use of the hand or foot involved.
(b) Complete paralysis of the external popliteal nerve (common peroneal) and consequent, footdrop, accompanied by characteristic organic changes including trophic and circulatory disturbances and other concomitants confirmatory of complete paralysis of this nerve, will be taken as loss of use of the foot.