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

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.

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.

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).

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.