Semitendinosus and patellar tendons shear modulus evaluation by supersonic shearwave imaging elastography.

Purpose: Shear modulus (μ) is directly correlated to the tissue stiffness and can predict the tendon ultimate force to failure. With the knee extended 0° (K0), semitendinosus tendon (ST) is tensioned while patellar tendon (PT) is relaxed. At 80 ^o , knee flexion (K80) tendons present an opposite stress pattern; however, the relation between ST and PT μ in both situations was not studied yet.
Method: We accessed the μ of the ST and PT at 0 ^o and 80 ^o knee flexion by supersonic shear wave imaging (SSI) elastography from 18 healthy males. Relative μ indexes were calculated for relaxed and tensioned conditions.
Result: The average μ for ST was μ _{ST -K0}  = 197·62 ± 31·93 kPa and μ _{ST -K80}  = 77·76 ± 30·08. For TP, values were μ _{TP -K0}  = 23·45 ± 5·89 and μ _{TP -K80}  = 113·92 ± 57·23 kPa. Relative μ indexes were calculated for relaxed (IR = μ _{ST -K80} /μ _{TP -K0} ) and tensioned conditions (IT = μ _{ST -K0} /μ _{PT -K80} ). The relative μ indexes were IR = 3·63 ± 1·50 and IT = 2·00 ± 0·96 (P<0·05).
Conclusion: Semitendinosus tendon μ was significantly higher than PT μ in both tensioned and relaxed positions. This can predict a higher ultimate force to failure and a less elastic behaviour in ST grafts when compared to PT grafts. This new parameter could aid physicians in graft choice previous to anterior cruciate ligament reconstruction.
(© 2018 Scandinavian Society of Clinical Physiology and Nuclear Medicine. Published by John Wiley & Sons Ltd.)