Factors affecting the accuracy of position matching at the proximal interphalangeal joint in human subjects.

1. The ability of normal subjects to match finger position at the proximal interphalangeal (PIP) joint was tested under a number of different conditions. One finger (target finger) was passively displaced in a pseudorandom manner whilst the other (matching) finger was actively positioned by the subject. 2. Digital nerve block of the target finger resulted in the matching finger only being displaced through a small range ('range compression') whilst anaesthesia of the matching finger produced the opposite effect ('range expansion'). 3. When the finger is unanaesthetized, the velocity of displacement of the target finger from one position to the next does not affect the accuracy of position matching. However, during digital nerve block of the target finger, matching errors increase with decreasing velocity. 4. The impairment of matching performance during digital nerve block is due specifically to loss of input from receptors in and around the PIP joint, as anaesthesia of the tip of the finger to produce any significant decrement in matching accuracy. 5. The results show that muscle receptors contribute to position sense at this joint but are not the exclusive source of proprioceptive sensations.