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The rat surgical anterior cruciate ligament transection (ACLT) model is commonly used to investigate intra‐articular osteoarthritis (OA) therapies, and histological assessment is often the primary outcome measure. However, histological changes do not always correlate well with clinical outcomes. Therefore, this study evaluated functional outcomes in the rat surgical ACLT model and compared intra‐articular injection volumes ranging from 20 to 50 μl. Unilateral ACLT was surgically induced and static weight‐bearing, mechanical allodynia, motor function, and gait were assessed in four groups of male, Sprague‐Dawley rats (n = 6 per group). Intra‐articular injections of 20 µl Dulbecco's phosphate‐buffered saline (DPBS), 50 µl DPBS, or 50 µl of synthetic biomimetic boundary lubricant were administered once weekly for 3 weeks postoperatively. Structural changes were evaluated histologically at 20 weeks. Rat cadaver knees were injected with 20, 30, 40, or 50 µl of gadolinium solutions and were imaged using magnetic resonance imaging (MRI). Static weight‐bearing, mechanical allodynia, and gait parameters in ACLT groups revealed differences from baseline and naïve controls for 4 weeks post‐ACLT; however, these differences did not persist beyond 6 weeks. Different intra‐articular DPBS injection volumes did not result in functional or histological changes; however, peri‐articular leakage was documented via MRI following 50, 40, and 30 µl but not 20 µl gadolinium injections. Statement of clinical significance: Differences in functional parameters were predominantly restricted to early, postoperative changes in the rat surgical ACLT model despite evidence of moderate histologic OA at 20 weeks. Injection volumes of 20–30 µl are more appropriate for investigating intra‐articular therapies in the rat knee. [ABSTRACT FROM AUTHOR]

As magnetic resonance imaging (MRI) becomes more readily available and more frequently utilized in the assessment of canine carpal lameness, both normal variations and early pathologic conditions must be recognized to optimize patient care and provide accurate diagnosis. On cross sectional studies of the canine carpus, cyst‐like lesions have been detected at the dorsolateral aspect of the intermedioradial carpal bone. The cross‐sectional imaging and histologic properties of these lesions have not been described. The purpose of this observational study is to evaluate the MRI and histologic features of these cyst‐like lesions in a cohort of clinically sound dogs. It was hypothesized that the lesions would show features similar to intraosseous ganglion cysts of the human wrist. Twenty‐five cadaveric canine carpi were obtained and a total of 13 lesions were detected on MRI. Based on MRI, six carpi with lesions of varying size and one normal carpus were submitted for histological evaluation. Five of the abnormal carpi had nonarticular cyst‐like lesions; one specimen with a positive magnetic resonance image for a cyst‐like lesion had no cyst‐like lesion on histology. Conspicuity of a medium‐size lesion as evaluated on radiographs was poor. Given the presence of these nonarticular cyst‐like lesions in a population of clinically sound patients, their clinical importance is uncertain. The development of these lesions may relate to altered mechanics or genetic predispositions, requiring additional study. [ABSTRACT FROM AUTHOR]

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]