The equine carpal osteochondral fragment model
Synovial fluid was obtained weekly from nine horses throughout a 70-day study period and subjected to small RNA sequencing. Nine skeletally mature Standardbred trotters (seven mares and two geldings, 2.5-7 years old, weighing 397-528 kg) were included in this study. OA was surgically induced in the left middle carpal joint and the right middle carpal joint underwent sham surgery. Under arthroscopic guidance, an osteochondral fragment was created in the left middle carpal joint by chiselling off a fragment on the dorsodistal surface of the radial carpal bone using an 8 mm curved osteotome. The fragment was left adherent to the joint capsule proximally, and an incongruent defect bed of approximately 15 mm in width was created in the exposed subchondral bone between the fragment and radial carpal bone by drilling with an arthroscopic burr. Debris from the procedure was left inside the joint. Sham surgery (arthroscopy alone) was performed in the right middle carpal joint. All portals were sutured using 2-0 propylene (Surgipro, Medtronic Danmark A/S, Copenhagen, Denmark). Both carpi were bandaged with sterile dressings. Bandages were changed at day 2 and removed at day 5. Sutures were removed 10 days after surgery. From 2 weeks following OA induction and onwards, horses were exercised in 2 min of trot (4.4-5.3 m/sec) , 2 min of fast trot/gallop (9 m/sec) and 2 min of trot (4.4-5.3 m/sec) 5 days a week on a treadmill. The horses were euthanized on day 71 or 72 with an overdose of pentobarbital sodium (140 mg/kg, Euthasol Vet, Dechra Veterinary Products, Uldum, Denmark). One horse, Horse 5, was euthanized according to predefined humane endpoints at day 49, as it became lame at the walk.