A new model of osteoarthritis has been developed that utilizes an extraarticular surgical technique to alter gait and weight-bearing capabilities in the hind limbs of experimental animals. Guinea pigs, averaging 650 gm in weight, were subjected to unilateral resection of a segment of the gluteal muscles at the sacral origin, to section of the infrapatellar ligament, or to both procedures. Progressive changes consistent with osteoarthritis developed over 10-24 weeks as judged by gross, radiologic, and microscopic findings. In addition, an increase in mean cartilage water content and '%Oq-* incorporation into proteoglycans by 10 and 14 weeks, respectively, were consistent with the chemical changes observed in early osteoarthritis. Abnormalities developed not only in the operated hind limb, but in the contralateral, unoperated hind limb at a slightly later time. Thus, this animal model provided the opportunity to evaluate a mild gait abnormality and other biomechanical influences on the evolution of osteoarthritis which is uninfluenced by any intraarticular joint trauma.

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Objectives: Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) and tumor necrosis factor (TNF) blocking agents have been widely used in the treatment of SpA. Recent evidence has shown anti-TNF therapies may induce hepatic injury. Interleukin inhibitors, a newer drug class with potentially lower side effects, have recently been approved for use. We aim to assess the risk of treatment-related liver injury among patients with SpA utilizing real-world data. Methods: A retrospective, claims-based observational study was conducted in a multi-state health system from 2010 to 2017. SpA patients were identified by diagnosis codes and proposed treatment agents, including NSAIDs, anti-TNF agents, and interleukin inhibitors. The primary outcome was 12-month incidence of liver injury after each treatment. Liver injury was evaluated as abnormal liver function test lab values. Results: The majority of patients (98.9%, n=16,348) received NSAIDs only for first-line treatment. Of those, 1.6% (n=259) changed from NSAIDs to second-line monotherapy treatment with anti-TNF agents (n=249) or interleukin inhibitors (n=6), or polytherapy with at least 2 anti-TNFs 6 NSAIDs or anti-TNF + interleukin 6 NSAIDs (n=4). Before the second-line treatment, liver injury rate at first-line was 8.5% (22/259),serving as a benchmark. Patients receiving anti-TNF agents as second-line treatment had a similar incidence of liver injury compared to the benchmark (9.2% vs 8.5%, p=0.768). Patients receiving interleukin inhibitors as second-line treatment did not have any liver injuries incidence, however no statistical significance was found due to the small sample size (0% vs 8.5%, p=1.000). Additionally, patients receiving a polytherapy had a higher incidence of liver injury (50.0% vs 8.5%, p=0.043), and the incidence remained high (33.3%) in clinical perspective after excluding those pre-existing liver injuries at firstline. Conclusions: Treatment with a polytherapy of TNFs and/or interleukin inhibitors might increase the risk of liver injury. Further studies with larger sample sizes are needed to validate these findings.

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