Arthroscopic evaluation of the synovial membrane and its relationship with histological changes and biomarkers in equine joint disease

The synovial membrane (SM) presents itself with distinctive characteristics during arthroscopic procedures in cases of osteoarthritis (OA) as well as osteochondritis dissecans (OCD) in horses. Most of the arthroscopic findings of the SM are limited to a description of a nonspecific inflammation state. In the present study, the macroscopic and histological aspects of the SM in OA and OCD horses were compared to those of healthy horses. The expression of interleukin (IL) in SM was also investigated. Besides, the concentrations of ILs and keratan sulfate (KS) in the synovial fluid (SF), and the molecular weights of the SF hyaluronic acid (HA) were also determined and correlated to the macroscopic and histological aspects of SM. This study included 10 healthy horses (control group), 12 horses with OA, and 12 with OCD. Macroscopic scores of the SM were higher in the OA group in comparison to the control and OCD groups. However, histological scores between OA and OCD were not different, and both were higher than the control group. Only in the OA group, there was a correlation between macroscopic and histological aspects of the SM, especially between volume and quantity of villi with perivascular inflammatory cells and synovial proliferation. The OA group has shown decreased expression of IL-10 in the SM, lower IL-10 and KS, and higher IL-1β and IL-6 in the SF in comparison to the control and OCD groups. There was a significant negative correlation between the macroscopic aspect of the SM and the molecular weights AH in the OA group. There was no correlation between the macroscopic aspect of the SM and all dosages in the OA and OCD group. In the OA joints, the evaluation of the shape of the SM during arthroscopy promotes a better indicator for joint inflammatory or tissue repair processes, while in the osteochondritic joints, investigation of the histological aspects are recommended to rule out an incipient OA development process. Both are helpful and should be considered to guide the postoperative treatment. •Arthroscopic images of the synovial membrane can be used as a guide to follow-up treatment.•The shape of the synovial membrane indicates inflammatory or tissue repair processes, and can guide postoperative treatment.•OCD horses that didn’t returned to their physical activities showed a decrease in Keratan Sulfate concentration.•Each increased total macroscopic membrane score, there was a decrease of 7.12% in the Hyaluronic Acid concentration.