A middle age female of rheumatoid ahritis on treatment develops upper motor neuron signs in her limbs. The investigation required to evaluate her fuher is:

Rheumatoid ahritis (RA) may lead to atlanto-axial instability. Atlantoaxial instability (AAI)- excessive movement at the junction between the atlas (C1) and axis (C2) as a result of either a bony or ligamentous abnormality. Neurologic symptoms occur when the spinal cord is involved and is upper motor neuron signs in limbs. The assessment involves flexion extension lateral view of cervical spine that can assess this instability. Open mouth view is for atlantoaxial area specially dens but will not demonstrate instability. Swimmers view is for cervicothoracic junction assessment. Broden's view is for subtalar joint.