The effect of loading on position sense at the proximal interphalangeal joint of the human index finger.

1. Proprioceptive acuity was tested at the proximal interphalangeal joint of the index finger of normal subjects. 2. Examination of the ability of the subjects to match finger positions (position matching procedure) revealed that digital nerve block (DNB) of the finger resulted in characteristic alignment errors at the extremes in all subjects. 3. When one finger (target finger) is positioned close to full extension, all subjects hyperextended the anaesthetized matching finger, whilst target finger positioning towards full flexion resulted in hyperflexion of the matching finger. At intermediate positions the pattern of matching errors was more variable but tended to be consistent for a given subject. 4. When the matching finger was isotonically loaded into flexion, there was little change in matching performance for most subjects. However, when the matching finger was anaesthetized, such loading now produced clear alteration in performance in all subjects. This indicates that muscle receptors contribute to proprioceptive sensations at this joint, but require other afferent sources to optimally resolve position when the finger is loaded. 5. Two other test procedures (angle reproduction and assigned positions) were assessed and compared with the results obtained by the position matching technique. Although alterations in proprioceptive performance during DNB could be detected with these procedures, they tended to be less sensitive than the position matching procedure.