Origin: Posterior superior iliac spine, dorsal surface of sacrum, mammillary processes of lumbar vertebrae, transverse processes of thoracic vertebrae, articular processes of C4-C7 vertebrae. Insertion: Spinous processes of lumbar, thoracic, and cervical vertebrae. Action: Extends neck and trunk; stabilizes vertebral column. Innervation: Medial branches of posterior rami of cervical, thoracic, and lumbar nerves. The multifidus is a major pain generator of the spine and pelvis due to its insertio