The ornamental design for an adjustableknee brace, as shown and described.
FIG. 1 is a perspective view of an adjustable knee brace according to the claimed design;
FIG. 2 is a first side view thereof;
FIG. 3 is a rear side view thereof; and,
FIG. 4 is a top view of the claimed design.
In the drawings, the broken lines show portions of an adjustable knee brace that form no part of the claim.
The adjustable knee brace is shown with a symbolic break in its length. The appearance of any portion of the article beyond the break lines forms no part of the claimed design.