There are three possible methods of assessing passive flexor tone in the neonate. The first is extensor stretch or passive flexion, which may better be described as flexibility, and is used to evaluate the degree to which a limb can be flexed passively at the joint by the examiner. This maneuver requires no tone or extensor resistance on the part of the infant. We may be looking at mobility, flexibility or resistance to extensor stretch rather than at passive flexor tone.
The second method of assessing passive flexor tone is resistance to passive extension. These maneuvers require;
a) that the untested portion of the extremity be resting quietly on a supporting surface;
b) that the examiner be very sensitive to the infant's slight tendency to resist extension; and
c) that the examiner avoid placing pressure on flexors being tested, thereby interfering with their function.
The third method of testing passive flexor tone is measurement of angles of recoil to a previously flexed position. This maneuver requires that the examiner;
a) pre-set the extremity to a flexed position; and
b) avoid fatiguing the flexors by maintaining the extremity in the extended position for too long a period of time prior to releasing.