Correlation between patellar tendon mechanical properties and oxygenation detection by near infrared spectroscopy in males

Background. The purpose of this study was to determine the correlation between the patellar tendon mechanical properties and oxygenation in healthy men. Methods. In two subsequent sessions, eight (mean age ± SD: 27 ± 4) recreationally active, healthy males performed 4-sec isometric knee extensions of the dominant leg at 20-80% of maximal voluntary contraction (MVC), maintaining a knee joint angle of 90° of flexion. In the first session, B-mode ultrasonography was used to record tendon length, cross-sectional area (CSA), and elongation, parameters needed to calculate stiffness. In the second session, tendon/peritendon hemodynamic parameters, namely total hemoglobin ΔtHb, ΔHHb and tissue oxygenation index (TOI% = O2 Hb/tHb x 100), as indicators of blood flow and oxygen extraction respectively were measured by near infrared spectroscopy (NIRS). Correlations between blood volume (tHB), tissue oxygenation and tendon mechanical properties were tested using Pearson’s correlation coefficient (R). Results. At all % of MVCs, a reduction of tHb and TOI%, and an increase of HHb were observed. At 80% MVC, ΔTOI% was negatively correlated with strain (R =-0.64) and elongation (R =-0.48), whereas a significant positive correlation was found with Young modulus (R = 0.69) and stress (R = 0.62); as regards blood volume, a significant negative correlation was found between elongation and ΔtHb (R =-0.44) and a positive correlation was found between stress and ΔtHb (R = 0.4). Conclusions. Patellar tendon mechanical properties and tendon/peritendon oxygen extraction and blood volume appears to be moderately correlated when studied by ultrasound and NIRS.