Janse relates that any cervical subluxation (particularly atlantal, axial, or occipital) producing muscle spasm, may produce constriction unilaterally or bilaterally of the
[chiro.org]
[…] shifting of the occiput may cause pressure upon the tubercle of Rolando, producing pain in the trigeminal distribution, headache, sinus discomforts, occular neuralgias, and jaw
[chiro.org]