Water Movement in Tendon in Response to a Static Tensile Load Using One-Dimensional Magnetic Resonance Imaging

Hydration is an important factor in determining the static and viscoelastic properties of soft tissues. Though the role water plays in determining the material properties of a soft tissue under compression is well known, there is little direct evidence of how water is mobilized in tensile-loaded soft tissues. Here, the redistribution of water in response to static tensile loading was investigated in rabbit Achilles tendons in vitro (N=7). The distribution of water was measured along a radially-oriented line, using a one-dimensional proton-density (M₀) map created from fits to T₂-weighted magnetic resonance imaging data. Experiments were performed on a 9.4 T/89 mm micro-imager. Proton density was measured before and during application of two cycles of a 7.5N tensile load. Cycle durations were 3 min preload, 42.67 min load on, 21.33 min off, 21.33 min on, and 21.33 min off. The load protocol resulted in a steady increase in proton density in the outside edge (rim) of the tendon during the load periods followed by a decrease during the unloaded periods. Proton-density values did not return to baseline following removal of load, signaling that the rehydration time constant is longer than that for extrusion. Proton-density values in the core or the tendon decreased during loading and were relatively constant during unloading.