Despite the recent progress in physiological studies of acupuncture, few morphological studies from the viewpoint that acupuncture stimulation produces with a small tissue injury have been reported. In this study, we evaluated the mechanism of acupuncture stimulation by a histopathological approach. First, we confirmed the tissue structure from the skin to the muscle layer in a corpse. In the human body, free terminals (endings) of unmyelinated nerve fibers (1.5μmin diameter, Group III or Group IV) were present subcutaneously or in the endomysium of muscle tissues. Next, the extent of tissue injury caused by insertion of needles 0.20-0.95mm in diameter evaluated in human and animal tissues. The extent of the injury was in proportional to the diameter of the needle. These confirmed that acupuncture stimulation is clearly a small tissue injury. Also, the free terminals (endings) of unmyelinated nerves similar to those observe in the human tissue were obsurved in the endmysium near the injury site. These morphological findings suggest that acupuncture stimulation is related to Group III or Group IV fibers.

Recently, magnetic resonance imaging (MRI) has brought significant advancements in the diagnosis of spinal disorders. But there is much debate about the abnormalities detected by MRI clinically. In this study, we try to clarify the correlation between spinal abnormalities detected by MRI and physical signs in 45 patients with neck, shoulder, and low back pain. Physical signs were segmental sensory disturbance, amyotrophy, and radicular pain, and the abnormalities of MRI were bulging, protrution, extrution, and osteophytes. MRI showed a symptomatic change, that is a false positive (abnormality of MRI^* (+), physical sign^** (-)), in 26 of the 45 patients (57.7%), a true positive (+, ^**+) in 15 of 45 patients (31.1%), a true negative (^*+, ^**-) in the remaining 5 patients (11.1%).
These results suggested that the physical signs are more important than the abnormalities of MRI in patients with neck, shoulder and low back pain. We think that the acupuncture therapist should carry out a more detailed physical examination of the patients clinically.