Gender-specific in vivo measurement of the structural and mechanical properties of the human patellar tendon.

Human patellar tendon stress (sigma), strain (epsilon), stiffness (K), and tensile or Young's modulus (E), are determined in vivo through voluntary isometric contractions monitored with B-mode ultrasonography. The limitations in previous studies are: (1) they have generally not accounted for the fact that the distal attachment of the patellar tendon (the tibial tuberosity) also displaces; thus, they have underestimated epsilon (and, hence, injury risk) while overestimating K; (2) no gender effect has been studied despite the fact that females are seen to have higher incidences of tendon-related injuries. The current investigation therefore aimed to determine the gender specific values of sigma, epsilon, K, and E of the patellar tendon while also accounting for distal displacement of the patellar tendon. Healthy young males (aged 23.1 +/- 1.3 years, n = 10) and females (aged 21.3 +/-0.9 years, n = 10) were tested. The maximal epsilon of the young males was approximately 5-10% higher than that reported in earlier literature. Average female versus male values for epsilon, sigma, K, and E, taken at the same force level as the males for comparison purposes, were respectively 10.6 +/- 1.0 versus 9.0 +/- 1.0%, 36.9 +/- 1.4 versus 28.9 +/- 0.9 MPa, 1053 +/- 108 versus 1652 +/- 216 N x mm(-1), and 0.61 +/- 0.08 versus 0.68 +/- 0.10 GPa (p < 0.05). There are gender differences in tendon structural and mechanical properties. The current methodology may be useful in a clinical context where early prediction of injury risk and/or monitoring of reconstructed tendon needs to be an accurate, objective, and reliable method if optimal functionality is to be achieved.