Ultrashort echo imaging of cyclically loaded rabbit patellar tendon.

Tendinopathy affects individuals who perform repetitive joint motion. Magnetic resonance imaging (MRI) is frequently used to qualitatively assess tendon health, but quantitative evaluation of inherent MRI properties of loaded tendon has been limited. This study evaluated the effect of cyclic loading on T₂* values of fresh and frozen rabbit patellar tendons using ultra short echo (UTE) MRI. Eight fresh and 8 frozen rabbit lower extremities had MR scans acquired for tendon T₂* evaluation. The tendons were then manually cyclically loaded for 100 cycles to 45 N at approximately 1 Hz. The MR scanning was repeated to reassess the T₂* values. Analyses were performed to detect differences of tendon [Formula: see text] values between fresh and frozen samples prior to and after loading, and to detect changes of tendon T₂* values between the unloaded and loaded configurations. No difference of T₂* was found between the fresh and frozen samples prior to or after loading, p=0.8 and p=0.1, respectively. The tendons had significantly shorter T₂* values, p=0.023, and reduced T₂* variability, p=0.04, after cyclic loading. Histologic evaluation confirmed no induced tendon damage from loading. Shorter T₂* , from stronger spin-spin interactions, may be attributed to greater tissue organization from uncrimping of collagen fibrils and lateral contraction of the tendon during loading. Cyclic tensile loading of tissue reduces patellar tendon T₂* values and may provide a quantitative metric to assess tissue organization.