ABSTRACT
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.
ABSTRACT
PURPOSE: Quadriceps strength and patellar tendon (PT) are directly linked and intimately related to daily activities and lower limb function. However, the correlation between knee extension torque (KT) and PT Young's modulus (E) measured directly is still unknown. METHOD: We used supersonic shearwave imaging (SSI) to evaluate the elastic property of PT in healthy young men and analysed its correlation with KT. Twenty-two healthy young males were included and both knees were examined. The E of the PT in the dominant and non-dominant legs was assessed by SSI elastography. KT in maximal voluntary isometric contraction was measured with an isokinetic dynamometer. RESULT: No correlations between KT and PT E were observed in dominant or non-dominant side (P = 0·458 and 0·126, respectively). No significant differences in KT or PT E were observed between both legs (P = 0·096 and 0·722, respectively). Intra-day ICC was rated good (D1 - 0·886, P<0·001 and 0·88, P<0·001) and excellent (D2 - 0·928, P<0·001 and 0·900, P<0·001) for both legs. Inter-day ICC was rated moderate for both legs (0·651, P = 0·016 and 0·630, P = 0·018, respectively). CONCLUSION: No significant correlations were found between KT and PT E, suggesting that quadriceps strength is not an accurate predictor for PT mechanical properties in subjects with no specific training engagement. Habitual loading pattern can play a determinant role in PT mechanical properties, regardless of quadriceps strength. Further investigation on SSI acquisition protocols should be conducted to guarantee higher inter-day ICC values.
