Yes, as a matter of fact, muscular adaptations to SIJ injury are the main cause of sciatic pain for two reasons, which are both related to compression of the sciatic nerve. In combination, the pelvic muscles alter the structural balance, causing narrowing of the nerve root opening, which puts pressure on the sciatic nerve roots as they exit the spine. The piriformis is one particular muscle that plays a more direct role in protecting an injured SIJ. The sciatic nerve runs either through, or just below this muscle so that, when tight to protect the SIJ, the piriformis can compress the sciatic nerve.