To the Editor:—
In their statistically elegant study of lower limb phantom posture during induction of spinal anesthesia, Dr. Isaacson et al. 1have rejected the concept that phantoms adopt an archetypal position of orthopedic rest. Instead, they have reverted to a plastic model determined by limb posture during the onset of anesthetic blockade.
Unfortunately, in their study, the authors chose an experimental protocol of proprioceptive acuity that was unlikely to guarantee reliable phantom development within the restricted 10-min period of their observations. In our earlier study of 169 clinically successful limb blocks, we reported that phantoms only began to occur approximately 10 min after injection. A much longer period usually was required before subjective phantoms became sufficiently intense and stable to be reportable in three-dimensional coordinates for all joint postures of the shoulder, elbow, wrist, and hand. The following incidences or “yield” of measurable subjective phantom postures were recorded after a significantly longer maturation period of 30–45 min from the time of completing the regional anesthetic procedure 2:
upper limb interscalene block (n = 110): 86% phantom yield
lower limb epidural (n = 50): 10% phantom yield
lower limb subarachnoid (n = 9): 55% phantom yield
Dr. Isaacson et al. 1did not comment on their yield of spontaneous lower limb phantoms, if any occurred, nor on the disappointingly low yield of measurable lower limb phantoms that we reported, even after a 30- to 45-min observation period. Nevertheless, comparison of our two studies may lead to a compatible resolution. In the meantime, Isaacson et al. 1have produced a scholarly mathematical presentation of changing proprioception within the limits of their short 10-min observation period. Unfortunately, those limits are poorly suited to the appreciably longer maturation period required by anesthetically deafferented phantoms before they are perceived consciously, with all phantom joints at mid point of joint range. Therefore, on the basis of our experience, we maintain that these investigators did not allow sufficient time for full maturation of a subjective phantom posture—a neuroanatomic–anesthetic process that remains incompletely understood, even after an interval of 25 yr after the publication of our investigation. This is an intriguing and largely speculative phenomenon worthy of further study, particularly from the point of view of sports medicine, but under more leisurely, prolonged, and stable experimental conditions than were afforded in the protocol of Isaacson et al. 1
