COMPARISON BETWEEN SYNOVIAL FLUID CYTOLOGY AND JOINT CAPSULE HISTOPATHOLOGY IN HORSES WITH CHRONIC OSTEOCHONDRITIS DISSECANS

Abstract

Introduction and objective. The osteochondrosis dissecans (OCD) is a disease that affects humans and animals and its aetiology and pathogenesis have been investigated for long time in human and veterinary medicine. OCD can cause slight changes in viscosity, mild increase in total protein and mild to severe increase in cell count, depending on the stage of the disease, in the synovial fluid of affected joint. Histological examination of the articular cartilage of horses with OCD showed areas of disorganization with reduction of glycosaminoglycans, including chondroitin sulphate, compared to normal horses. The purpose of the present work was to study the relationship between synovial fluid cytology and histopathologic examination of the articular capsule of horses with OCD.

Materials and methods. Fifteen horses of different breed, age and sex with OCD were included in the study and all of them underwent arthroscopy. Synovial fluid samples and osteochondral, or synovial capsule, samples were collected from 22 joints affected by OCD during arthroscopic surgery. For each synovial fluid sample was assessed the following parameters: synovial fluid turbidity, viscosity, mucin clot, total protein, total and differential cell counts. Furthermore, osteochondral or synovial capsule samples were evaluated on histologic examination. The samples were retrospectively divided into two groups according to the results of the synovial fluid cell count: a) group 1: hypocellular synovial fluid (median 200 cells/µL); b) group 2: cellular synovial fluid (median 500 cells/µL). The chi-square test was used to compare synovial fluid turbidity, viscosity and mucin clot test of the two groups.

Results. Ten/22 joint samples were classified into the group 1 and 12/22 into the group 2. No significant differences were found between the 2 groups for turbidity, viscosity and mucin clot. Histological examination was normal in 16/22 joints examined and altered in 6/22.

Conclusions. No differences were observed in synovial fluid turbidity between the two groups. In our study, the total protein concentration was similar between the 2 groups, and always less than 3 g/dl, in agreement with previous studies. The cell count was always less than 600 cell/L and cytology did not show a high percentage of neutrophils, confirming that the synovial fluid was not collected from joints with inflammatory diseases. Confirming the results of previous investigations, our data show the usefulness of laboratory examination for the diagnosis of joint degenerative diseases in the horse and support the greater sensitivity of cytology compared with histopathologic examination.