Comparison of the blood supply to the articular-epiphyseal growth complex in horse vs. pony foals.

REASONS FOR PERFORMING STUDY: To increase understanding of why the prevalence of clinical/radiographic osteochondrosis (OC) dissecans is high in horses and low in ponies. OBJECTIVES: To investigate whether the clinical difference in OC occurrence between horses and ponies could partly be explained by a difference in: 1) number of patent vessels in the epiphyseal growth cartilage; 2) duration of the presence of patent cartilage canals; or 3) growth cartilage thickness at predilection sites for OC. The hypothesis was that pony foals would have fewer cartilage canals, shorter duration of blood supply and thinner growth cartilage than horse foals. STUDY DESIGN: Observational, cross-sectional study. METHODS: Nine Standardbred foals (horse group) 1-49 days old and 11 Norwegian Fjord foals (pony group) 1-62 days old were included. A total of 15 anatomical locations in the tarsocrural and metatarsophalangeal joints were examined by one or more of the following techniques: arterial perfusion; photography of cleared specimens; microcomputed tomography; radiography; and histology. The number of cartilage canals was counted. Cartilage thickness was measured. Duration of blood supply was assessed in histological sections. RESULTS: Of the 3 common predilection sites for OC investigated, there were significantly fewer vessels (P = 0.003) and thinner cartilage (P = 0.002) at the distal lateral trochlear ridge of the talus in the pony group. There was no difference in the duration of presence of cartilage canals between the groups. CONCLUSION: The hypothesis that pony foals would have fewer cartilage canals and thinner growth cartilage than horse foals was confirmed for the lateral trochlear ridge of the talus. The current results may contribute towards an explanation for the low prevalence of OC at the distal lateral trochlear ridge of the talus in pony foals.

Transection of vessels in epiphyseal cartilage canals leads to osteochondrosis and osteochondrosis dissecans in the femoro-patellar joint of foals; a potential model of juvenile osteochondritis dissecans.

OBJECTIVE: To transect blood vessels within epiphyseal cartilage canals and observe whether this resulted in ischaemic chondronecrosis, an associated focal delay in enchondral ossification [osteochondrosis (OC)] and pathological cartilage fracture [osteochondrosis dissecans (OCD)] in the distal femur of foals, with potential translational value to the pathogenesis of juvenile osteochondritis dissecans (JOCD) in children. METHOD: Ten Norwegian Fjord Pony foals were operated at the age of 13-15 days. Two vessels supplying the epiphyseal growth cartilage of the lateral trochlear ridge of the left distal femur were transected in each foal. Follow-up examination was carried out from 1 to 49 days post-operatively and included plain radiography, macroscopic and histological examination. RESULTS: Transection of blood vessels within epiphyseal cartilage canals resulted in necrosis of vessels and chondrocytes, i.e., ischaemic chondronecrosis, in foals. Areas of ischaemic chondronecrosis were associated with a focal delay in enchondral ossification (OC) in foals examined 21 days or more after transection, and pathological cartilage fracture (OCD) in one foal examined 42 days after transection. CONCLUSION: The ischaemic hypothesis for the pathogenesis of OC has been reproduced experimentally in foals. There are several similarities between OCD in animals and JOCD in children. It should be investigated whether JOCD also occurs due to a focal failure in the cartilage canal blood supply, followed by ischaemic chondronecrosis.