Ultrasound biomicroscopy for biomechanical characterization of healthy and injured triceps surae of rats

This work describes the use of ultrasound biomicroscopy (UBM) to follow up the degeneration-regeneration process after a laceration injury induced in the lateral gastrocnemius (LG) and soleus (SOL) muscles of rats. UBM (40 MHz) images were acquired and used for biomechanical characterization of muscular tissue, specifically using pennation angle (PA) and muscle thickness (MT). The animals were distributed in three groups: the variability group (VG; N=5), the gastrocnemius injured group (GG; N=6) and the soleus injured group (SG; N=5). VG rats were used to assess data variability and reliability (coefficients of variation of 9.37 and 3.97% for PA and MT, respectively). GG and SG rats were submitted to the injury protocol in the LG and SOL muscles of the right legs, respectively. UBM images of muscles of both legs were acquired at the following time points: before and after injury (immediately, 7, 14, 21 and 28 days). We observed an increase in PA for the non-injured leg 28 days after injury for both GG and SG rats (GG=10.68 to 16.53 deg and SG=9.65 to 14.06 deg; P<0.05). Additionally, MT presented a tendency to increase (GG=2.92 to 3.13 mm and SG=2.12 to 2.35 mm). Injured legs maintained pre-injury PA and MT values. It is suggested that a compensatory hypertrophic response due to the overload condition imposed to healthy leg. The results indicate that UBM allows qualitative and quantitative muscle differentiation among healthy and injured muscle at different stages after lesion.