Increasing Age Alters the Development of Gait Compensations Following Meniscal Injury in Rats

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      Osteoarthritis (OA) is characterized by pathological joint changes that progress to pain and disability. Increasing age and joint injury are risk factors for OA. Cartilage becomes less resilient to OA pathogenesis as age increases; however, pain, not cartilage damage, drives patients to seek treatment. Preclinical OA models can help further understanding of the relationship between OA pathogenesis and pain. Joint pain and dysfunction are often associated with motion, making gait a quantitative measure to detect OA-related behavioral changes. Rodents alter gait patterns to correct mechanical instabilities and protect injured limbs, but it is unknown how age affects these changes. We hypothesized gait compensations following meniscal injury in 3-, 6-, and 9-month rats would be affected by age of injury onset. Rats at 3, 6, and 9 months of age received medial collateral ligament transection plus medial meniscus transection (MCLT+MMT) surgery (n = 8/age group) or a skin incision (n = 8/age group). Gait data was collected at 2, 4, 6, and 8 weeks post-surgery using our lab's novel gait technology. After euthanasia, joints were processed for histology. Our results showed both 6- and 9-month MCLT+MMT rats walked with reduced peak vertical forces in their injured limbs immediately after injury (2 weeks post-surgery), and this decreased loading continued as OA progressed (8 weeks post-surgery). At early time points, stance time tended to be increased in MCLT+MMT animals; however, there were no clear trends in spatiotemporal walking patterns across the different age groups. Finally, histology showed significantly worse cartilage damage in the 6- and 9-month MCLT+MMT animals compared to 3-month MCLT+MMT animals. This data demonstrates age of injury affects joint avoidance behaviors and joint dysfunction in a rodent OA model, with older animals selecting to reduce dynamic limb loading while minimizing changes to the timing of steps and position of paws. This work was supported by the National Institutes of Health under grants R01AR068424 and R01AR071335.
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