Shear wave elastographic study of the myotendinous junction of the medial gastrocnemius : normal patterns and dynamic evaluation

Objectives The myotendinous junction (MTJ) represents a specialized anatomic region through which the contractile strength is transmitted from the muscle to the tendon. The integrity of this region is essential to permit force transmission and to optimize energy expenditure during walking, running, and globally for human movement. We evaluated the MTJ with shear wave elastography to assess its elasticity variation during a functional test.Methods Forty professional soccer players were enrolled in the study. Shear wave elastography was performed at the level of the medial gastrocnemius MTJ both in a resting position and during a standing calf rise position to assess functional contraction.Results All 40 participants were male, aged between 18 and 38 years (mean age, 25 years). The results of the elastographic study showed mean stiffness values +/- SD of 4.19 +/- 0.86 m/s for the right medial gastrocnemius and 4.20 +/- 0.87 m/s for the left medial gastrocnemius with the muscle relaxed. During contraction, the stiffness values were 8.33 +/- 0.5 m/s for the right medial gastrocnemius and 8.30 +/- 0.48 m/s for the left medial gastrocnemius.Conclusions Our study showed an increase of stiffness at the level of the MTJ during muscle contraction. This result is in line with the physiologic stiffening of the MTJ to resist the high level of force applied during muscle contraction. Shear wave elastography could be a useful method to assess the characteristics of the MTJ under both physiologic and pathologic conditions.