Muscle knots in the tiny deep muscles that are located next to the spine, the Multifidi, Rotatores, and Semispinalis, they all share a similar, distinctive feeling because they are the tiny, deepest layers of back muscle. The pain referred from these muscle knots are localized but can refer pain to the sacrum, buttocks, or mimick sciatics. People usually describe it as a deep, aching pain that seems to be coming from the bone or joint itself, not the surface.