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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 hadMR 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 T2* 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 cyclicloading. 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. [ABSTRACT FROM AUTHOR]

Bone marrow lesions (BMLs) are radiologic abnormalities in magnetic resonance images of subchondral bone that are correlated with osteoarthritis. Little is known about the physiologic processes within a BML, although BMLs are associated with mechanical stress, bone tissue microdamage and increased bone remodeling. Here we establish a rabbit model to study the pathophysiology of BMLs. We hypothesized that in vivo loads that generate microdamage in cancellous bone would also create BMLs and increase bone remodeling. In vivo cyclic loading (0.2–2.0 MPa in compression for 10,000 cycles at 2 Hz) was applied to epiphyseal cancellous bone in the distal femurs of New Zealand white rabbits (n = 3, right limb loaded, left limb controls experienced surgery but no loading). Magnetic resonance images were collected using short tau inversion recovery (STIR) and T1 weighted sequences at 1 and 2 weeks after surgery/loading and histological analysis of the BML was performed after euthanasia to examine tissue microdamage and remodeling. Loaded limbs displayed BMLs while control limbs showed only a small BML-like signal caused by surgery. Histological analysis of the BML at 2 weeks after loading showed increased tissue microdamage (p = 0.03) and bone resorption (p = 0.01) as compared to controls. The model described here displays the hallmarks of load-induced BMLs, supporting the use of the model to examine changes in bone during the development, progression and treatment of BMLs. [ABSTRACT FROM AUTHOR]