I claim the ornamental design for an elbow support, as shown and described.
FIG. 1 is a perspective (back, bottom, left) view of my new design in an elbow support, as it would appear applied to the elbow and adjacent areas of the upper arm and forearm of a person;
FIG. 2 is a rear elevation view of my new design in the elbow support of FIG. 1;
FIG. 3 is a left elevation view of my new design in the elbow support of FIG. 1;
FIG. 4 is a front elevation view of my new design in the elbow support of FIG. 1; and,
FIG. 5 is a right elevation view of my new design in the elbow support of FIG. 1.
The parts shown by means of broken lines in the drawings are not part of the claimed design. The top elevation view and the bottom elevation view have been omitted because the surfaces of the top and bottom of the product bear no ornamentation.