One can estimate the perception of this modality simply by pressing deeply on the tendons, muscles, or bony prominences. Pain can be elicited by heavy pressure even when superficial sensation is diminished; conversely, in some diseases, such as tabetic neurosyphilis, loss of deep-pressure pain may be more striking than loss of superficial pain. This uncomfortable examination should be omitted in routine neurological cases. Deep pain, strictly speaking, is a proprioceptive sense because it is below the skin surface, but the sensory pathways are spinothalamic and therefore more allied with pain.
Testing of Proprioceptive Sense
Awareness of the position and movements of our limbs, fingers, and toes is derived from receptors in the muscles, tendons (Golgi tendon organs, according to Roland and Ladegaard-Pederson), and joints and is probably facilitated by the activation of skin receptors (Moberg). The two modalities comprising proprioception, that is, sense of movement and of position, are usually impaired in parallel, although clinical situations do arise in which perception of the position of a limb or digits is lost while that of passive and active movement (kinesthesia) of these parts is retained. The opposite occurs but is infrequent. Moreover, it is our impression that within the limits of what is done in bedside examination, patients more easily perceive joint movement (arthresthesia) than static joint position or posture (statognosis).
Perception of passive movement is first tested in the fingers and toes as the defect, when present, is reflected maximally in these parts. It is important to grasp the digit at the sides, perpendicular to the plane of movement; otherwise the pressure applied by the examiner may allow the patient to identify the direction of movement. This applies as well to testing of the more proximal segments of the limb. The patient may be instructed to first report the perception of joint movement and then to indicate each movement as being “up” or “down.” It is useful to demonstrate the test with a large and easily identified movement, but once the idea is clear to the patient, the smallest detectable changes should be determined. The part being tested should be moved rapidly. Normally, a very slight degree of movement is appreciated in the digits (as little as 1 or 2 degrees of an arc). The test should be repeated enough times to account for the possibility of chance guessing.
Defective perception of passive movement is judged by comparison with a normal limb or, if perception is bilaterally defective, on the basis of what the examiner has learned through experience to be normal. Slight impairment may be disclosed by a slowness of response or, if the digit is displaced very slowly, by an unawareness or uncertainty that movement has occurred; or, after the digit has been displaced in the same direction several times, the patient may misjudge the first movement in the opposite direction; or, after the examiner has moved the digit, the patient may make a number of small voluntary movements of the toe in an apparent attempt to determine its position or the direction of the movement. Inattentiveness will also cause some of these errors. If joint position sense is impaired at a distal site, the next proximal joint may be tested. The lack of position sense in the legs can also be demonstrated by displacing the limb from its original position and having the patient, with eyes closed, place the other leg in the same position or point to the great toe. The same is true for the arm and hand.