Proprioception with the proximal interphalangeal joint of the index finger. Evidence for a movement sense without a static-position sense.

Proprioceptive ability with the proximal interphalangeal (PIP) and metacarpophalangeal (MCP) joints of the index finger in human subjects was examined using a method that could assess static-position sense independently of movement sense (Clark et al., 1985). The similarity in location and function of these joints would suggest similar proprioceptive mechanisms, but proprioceptive ability was found to be quite different for the two joints. The method of distinguishing a static-position sense from a movement sense was based on whether a subject's ability to detect a small change in joint position was impaired when the rate of rotation was progressively reduced. An awareness of static-position should not depend on the rate at which a joint is placed into position. However, if subjects use movement signals to detect changes in joint position, slowing the rate of displacement should reduce the intensity of these signals and make the displacements more difficult to detect. This method indicated a static-position sense with the MCP joint but only a movement sense with the PIP joint. It was confirmed that sensory input from regions of skin not stretched or deformed by rotation of the joint can influence proprioceptive sensibility with the fingers. Anaesthesia of the tip of the index finger or of the thumb blunted subject's perceptions of movement of the PIP joint of the index finger. However, anaesthesia of the PIP joint itself had no observable effect on the ability to sense movement of the joint.