Quantification of Motion Palpation

The palpation of motions is at the heart of the practice of foreign-trained osteopaths. When practicing osteopathic manual therapy (care provided by foreign-trained osteopaths) in the cranial field or osteopathic cranial manipulative medicine, the palpation of small motions (several tens of micrometers) is a key process. However, to the authors' knowledge, the smallest detectable motion has not been identified.

To quantify motion detection capacity by passive palpation.

Participants were instructed to hold a mechanical device containing a micrometric actuator between their hands and report when they felt motion while 6 series of 27 random motions were generated by the actuator. After each series, if a participant succeeded or failed to detect motion with a confidence level of greater than 98%, the motions in the next series were set to a smaller or larger magnitude, respectively. After 6 series, the individual motion detection capacity was recorded. Statistical significance was set at P=.02.

A total of 21 participants were selected, comprising 14 osteopaths and 7 nonosteopaths. The average performance of the sample was 148 μm. Thirteen participants (62%) perceived motions of 200 μm or less, and 7 participants (33%) detected motions of 50 μm or less with bare hands. Osteopathic training did not notably affect the performance. Osteopaths were twice as likely to claim detection of nonexisting motions than to miss existing ones, whereas nonosteopaths were equally subject to both types of errors.

The data show human passive palpatory sensitivity to be in the range of several tens of micrometers. This range is comparable to that reported for calvarial motion (10-50 μm).