Which muscle stabilizes vertebrae and assists in extension and contralateral rotation?

• A. Multifidus
• B. Interspinales
• C. Rotatores
• D. Semispinalis capitis

Answer: (A)

Segmental stabilization of the spine is being tested. The multifidus are deep intrinsic back muscles that run from the sacrum and transverse processes of each vertebra up to the spinous processes of the vertebrae above. They stabilize the vertebrae by controlling fine movements between adjacent bones, which is essential during any motion. When they contract on both sides, they help extend the spine; when they contract on one side, they contribute to rotation of the vertebral segments to the opposite side (contralateral rotation) while still supporting stability. This combination—strong vertebral stabilization with the ability to assist in extension and contralateral rotation—defines the multifidus. Interspinales mainly connect adjacent spinous processes and contribute to extension and stabilization but are smaller in role for rotation. Rotatores are short rotators that help with local rotation and proprioception rather than broad segmental stabilization. Semispinalis capitis acts on the head and neck, extending and rotating the head rather than stabilizing the trunk’s vertebrae.