Objective
To establish the objective method of diagnosing the myofascial pain syndrome through diagnostic ultrasound and pathology.

Method
Hamstring muscles of 7 female house rabbits, weighing 2.5∼3.0 Kg, were studied. The existence of nodule was confirmed by palpation and through diagnostic ultrasound. A horizontal length, vertical length, thickness, and an area of hyperechoic region were measured. Hyperechoic regions were biopsied and stained with hematoxylin-eosin.

Results
All examined rabbits had muscular nodules in the medial hamstring. Characteristic increase of echogenecity was observed in the medial hamstring muscles. Some uneven hyperechoic areas were seen in the lateral hamstring muscles. Fatty degeneration and giant round cells were observed in the medial hamstring where the echogenecity was increased. The giant round cells were observed only in the lateral hamstring.

Conclusion
Increased echogenecity of the medial hamstring muscle is probably contributed by muscles cells with fatty degeneration and giant round cells, and some portions of hyperechogenecity of lateral hamstring requires further study.