Testing the posterior columns

Fibres for vibration and proprioception travel in the posterior columns and travel to the nucleus gracilis and nucleus cuneatus before decussating in the medulla.

Various modalities may be tested:

• vibration testing - a 128 Hz tuning fork is used rather than the 256 Hz fork that is used for hearing tests. The patient is asked to close his eyes and then the vibrating tuning fork is placed on a bony surface, e.g. the ulna at the wrist, and the examiner then stops the vibrations from the tuning fork - by touching it. The patient should be able to identify when the tuning fork has stopped vibrating.
• proprioception - a distal interphalangeal joint is tested. The examiner grasps the distal phalanx and then moves it slightly upwards and then slightly downwards whilst telling the patient what movements are being undertaken. The patient is then told to close his eyes. Similar movements of the distal phalanx are then undertaken and each time the patient is asked to say whether the phalanx is going 'up' or 'down'. If there is an abnormality then proceed to test the next joint proximal to the phalanx, e.g. the wrist in the arm.
• light touch - some fibres for light touch travel in the posterior columns - ipsilateral - and some in the anterior spinothalamic tract - contralateral. Thus testing this carries the least discriminatory information. Light touch is tested using cotton wool which the examiner gently touches - do not stroke - the skin in each dermatome. The patient closes his eyes and asked to say 'yes' when he feels the cotton wool touching.