Quantification of skeletal muscle fibrosis at different healing stages using sonography: a morphologic and histologic study in an animal model.
OBJECTIVE
This study attempted to quantify the degree of muscle fibrosis on sonograms of injured gastrocnemius muscles at different healing stages in a rat model. Correlations between the quantifications and histologic assessments of the injured muscles were also determined.


METHODS
Sonograms and histologic findings of gastrocnemius muscle fibrosis were obtained during the second, third, and fourth weeks after surgically induced lesions in the right gastrocnemius muscles of 15 Wistar rats. The echo intensity, reflecting the degree of brightness on a sonogram, was divided into 256 gray levels instead of decibels. The mean echo intensity of each pixel in the region of interest was calculated as a summation of the echo intensities in all pixels divided by the pixel numbers in the region. To control individual variations among the rats, we calculated a K value, defined as the difference in the mean echo intensity between normal and affected muscles.


RESULTS
Significant correlations (r > 0.7; P < .05) between mean echo intensity and K values and the fibrous tissue percentage were identified. The mean echo intensity in the injured gastrocnemius muscles was significantly (P = .029) greater than that in the normal muscles 3 weeks after injury. In histologic assessments, muscle fibrosis was most prominent 3 weeks after injury. However, the differences in fibrosis at different healing stages were not significant.


CONCLUSIONS
Mean echo intensity and K values can reflect the extent of fibrosis in affected muscles and may be valuable for quantifying muscle fibrosis in clinical practice.
Department of Physical Medicine and Rehabilitation, Chang Gung Memorial Hospital, Keelung, Taiwan.
Ching-Fang
CF
Hu
Carl Pai-Chu
CP
Chen
Wen-Chung
WC
Tsai
Li-Lin
LL
Hu
Chih-Chin
CC
Hsu
Shih-Ting
ST
Tseng
Yio-Wha
YW
Shau
D000818:Animals; D004195:Disease Models, Animal; D005355:Fibrosis / Q000000981:diagnostic imaging; D008297:Male; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging* / Q000473:pathology* / Q000648:ultrastructure; D051381:Rats; D017208:Rats, Wistar; D014463:Ultrasonography; D014945:Wound Healing