Clinical tests for it, from least to most sensitive, are Kernig sign (resistance to passive knee extension) Brudzinski sign (full or partial flexion of the hips and knees when the neck is flexed) Difficulty touching the chin to the chest with the mouth closed Difficulty touching the forehead or chin to the knee Nuchal rigidity can be distinguished from neck stiffness due to cervical spine osteoarthritis or influenza with severe myalgia; in these disorders, neck movement in all directions is usually affected.