Osteoarthritis induction.

Intraarticular injection of MIA into one hindlimb knee was used to induce osteoarthritis. Five dose groups were used, as described previously.²⁸ Briefly, the 5 MIA dose groups were chosen by scaling the doses previously reported in small animal studies according to the difference in total body surface area from rodents to swine.^12,19 Doses comprising 1.2 (n = 9), 4 (n = 12), 12 (n = 2), or 40 (n = 2) mg MIA dissolved in either 2 or 3 mL PBS were injected into one hindlimb knee per animal (n = 25) under ultrasound guidance, as previously described.¹⁵ In MIA-injected animals, the contralateral hindlimb knee received either PBS (n = 10) or no injection (n = 15). Control animals (n = 2) received PBS injected into bilateral hindlimb knees. All procedures were performed under general anesthesia and strict aseptic technique. Anesthesia was induced by using intramuscular tiletamine–zolazepam (5 mg/kg), xylazine (2 mg/kg), and glycopyrrolate (0.01 mg/kg). Swine were then intubated, and anesthesia was maintained by isoflurane (1.5% to 2.5%, titrated to effect) in 50% oxygen. Total duration of anesthesia for osteoarthritis induction was 45 to 60 min per animal. Animals were monitored continuously, and vital signs were documented at least every 15 min for heart rate, respiratory rate, body temperature, ventilation, oxygenation, and depth of anesthesia by eliciting reflex responses. The skin over both knee joints was surgically clipped and scrubbed with 1% chlorhexidine. Under ultrasound guidance, a 23-gauge needle was inserted from lateral to medial into the intraarticular, synovial space between the patella and trochlea. A 100-μL PBS test injection confirmed dispersion of injectate in the synovial space under real-time ultrasound observation. Intraarticular injections were performed in a blinded fashion by a musculoskeletal radiologist during week 0 of the study. The side that received MIA was assigned randomly, and personnel involved in subsequent behavior experiments were blind to the side injected and type of injectate.