Morphologic and biochemical changes in cartilage of foals treated with dexamethasone.

This research article focuses on morphologic and biochemical changes observed in the cartilage of pony foals that have been treated with dexamethasone, a type of steroid drug. The primary findings highlight the adverse impacts of administered dexamethasone on articular and epiphyseal cartilages and the resulting initiation of cartilage degeneration.

Methodology and Treatment regimens

• Pony foals were administered intramuscular injections of 0.5 mg dexamethasone per 100 kg of body weight daily for 3, 8 or 11 months. Some were given 5.0 mg per 100 kg for 11 months.
• Horse foals were treated with 5.0 mg dexamethasone per 100 kg for 20 weeks. This group of foals was made a part of the study to gauge the effects of the drug over different durations and dosages in different types of foals.
• The researchers then examined the epiphyseal and articular cartilages of the treated animals.

Changes in Cartilage Morphology and Biochemistry

• Proximal femoral growth plates in the foals revealed increased distances between chondrocyte columns and narrow zones of disorganized columnar and hypertrophic cartilage.
• Other observed abnormalities included abnormal penetration of hypertrophic cartilage by metaphyseal capillaries and retention of cartilage in the spongiosa.
• Destructive articular lesions were observed after three months of dexamethasone treatment at the lower dosage level of 0.5 mg/100 kg. The joint damage originated either at the joint surface or deep within the cartilage.
• Signs of the surface damage included edema, fibrillation, enlargement of lacunae, pitting, shredding, and erosions of cartilage.
• There was a common inactivity in the growth centres of the articular cartilage, where epiphyseal capillaries failed to penetrate the lacunae in the calcified cartilage.
• Chondronecrosis adjacent to the calcification front was accompanied by cartilage ulceration and fracture.
• Intracartilaginous cysts and subchondral chondroid cysts were also observed.
• The healing responses brought about reparative chondrogenesis (focal cartilage hyperplasia), formation of fibrous or fibrocartilaginous “scars”, subchondral osteopetrosis, and epiphyseal marrow petrosis.

Biochemical Changes in Cartilage

• The authors showcase that lactate dehydrogenase specific activities per chondrocyte, 35S uptake per cell, and glycosaminoglycan contents of articular cartilages were all reduced by approximately 55% after 3 months of dexamethasone treatment.
• This inhibition of articular chondrocyte metabolism resulted in the initiation of cartilage degeneration, the onset of destructive surface alterations, and osteochondrosis dissecans (a joint condition in which bone underneath the cartilage of a joint dies due to lack of blood flow).

The study overall provides critical insights into how the use of dexamethasone in young ponies and horses can lead to significant morphologic and biochemical alterations in the animals’ cartilage, initiating degenerative processes.