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 80o , 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 0o and 80o 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 µST-K0  = 197·62 ± 31·93 kPa and µST-K80  = 77·76 ± 30·08. For TP, values were µTP-K0  = 23·45 ± 5·89 and µTP-K80  = 113·92 ± 57·23 kPa. Relative µ indexes were calculated for relaxed (IR = µST-K80 /µTP-K0 ) and tensioned conditions (IT = µST-K0 /µPT-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.