Objective: To investigate the pathological characteristic of gastrocnemius (GM) and quantitatively assess GM tissue stiffness in spinal cord injury (SCI) rat models; to explore the novel method in evaluation of GM stiffness.
Methods: A total of 54 SD male rats (weight 260-280 g) were allocated into normal control group (0 w) and model groups (2, 4, 8 and 12 w) in this study. Complete SCI (T10 level) was applied in model groups. At the above different time points, Modified Ashworth Scale (MAS) was used to assess the GM spasticity; Basso, Beattie, and Bresnahan Locomotor Rating Scale (BBB) was used to assess the movement ability of lower limb. GM stiffness was assessed with shear wave sonoelastography technology in these groups. All GM at right side of rats was further checked by pathological examinations (muscle weight, ATP staining, myosin heavy chain (MyHC) electrophoretic analysis) after sonoelastography imaging examinations.
Results: After removing the overweight and underweight rat models which were alive, six rats were included in each group. There were some pathologic changes in GM in SCI rat models. Compared with normal control group, data from model groups showed ankle dorsiflexors MAS (1.5±0.8-0.8±0.7 score) was increased (P≤0.05), BBB scores of lower limb (3.2±1.0-7.2±1.3score) were decreased (P≤0.05). The GM elastic modulus was increased at dorsiflexion location in model group (25.1±2.4-37.4±5.5 kPa, P≤0.05); GM weights were decreased, ratio of type Ⅰ fibers was decreased and ratio of type Ⅱ fibers was increased in GM. Compared with normal control group, MyHC-Ⅰ was decreased, while MyHC-Ⅱ was increased according electrophoretic analysis.
Conclusions: Both pathological characteristic and muscle stiffness of GM change after SCI. Shear-wave sonoelastography technology can be used to assess the GM stiffness in SCI rat models.