The ornamental design for a spinal supportcushion, as shown and described.
FIG. 1 is a frontal isometric view of my spinal support cushion showing my new design;
FIG. 2 is a lower isometric view thereof;
FIG. 3 is a top plan view thereof;
FIG. 4 is a bottom plan view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a left side elevational view thereof;
FIG. 7 is a front plan view thereof; and,
FIG. 8 is a rear plan view thereof.
The broken line showing of the seams on a spinal support cushion are included for the purpose of illustrating stitching and form a part of the claimed design.