Experimentally induced arthritis of the equine carpus: histologic and histochemical changes in the articular cartilage.

This research study focuses on inducing arthritis in the carpal joints of ponies to observe the histological and histochemical changes in their articular cartilage. The experiment involved administering twelve injections of the antibiotic filipin, and the changes recorded were likened to the early stages of joint degeneration in horses.

Experimental Procedure

• Arthritis was experimentally induced in the equine carpus (orientations between different bones in the wrist or hand) of a group of adult ponies. This was done with intraarticular injections of 400 micrograms of the polyene antibiotic filipin, combined with 1 milliliter of dimethyl sulfoxide.
• This was administered in twelve consecutive weekly doses, and the ponies were euthanatized four weeks after the last injection.
• During the experiment’s duration, the ponies were required to exercise for an hour each day.
• Following euthanization, articular cartilage specimens from each pony were collected from four different sites in the intercarpal joint and examined histologically (study of the microscopic structure of tissues) and histochemically (chemical analysis of cells).

Techniques Used for Examination

• The histochemical examination involved the usage of safranin O-fast green, Alcian blue in 0.4 M and 0.9 M MgCl2, and Alcian blue 0.9 M MgCl2-Van Gieson matrical staining techniques.
• Selected carpi (plural of carpus) were decalcified, and sagittal sections were examined histologically.

Findings and Conclusions

• Pathological changes found in the joints’ articular cartilage specimens included superficial fibrillation (fine fragmentation) and chondrocyte necrosis (death of cartilage cells).
• These changes were accompanied by a lack of histochemical staining of the intercellular matrix, attributed to the loss of glycosaminoglycans (major components of the cartilage).
• Other observed changes included hypertrophy (enlargement) of the remaining cartilage cells and the formation of chondrones (cartilage nodes).
• On examining the decalcified sections of carpi, both exostoses (benign growths on bone) and marginal osteophytosis (formation of bony outgrowths) were detected.
• Evidence of both intramembraneous and endochondral osteogeneses (bone formation within the membrane and cartilage respectively) was found in the exostoses.
• Comparing these changes to naturally occurring degenerative joint disease in horses revealed similarities, thus validating the experimental model.