L. B. Jeffcott

Equine dyschondroplasia (osteochondrosis)—Histological findings and type VI collagen localization

This study describes (1) the histological appearance of dyschondroplasia, the primary lesion of osteochondrosis, in articular cartilage of the horse and (2) the localization of type VI collagen which is an important constituent of the extracellular matrix (ECM). Dyschondroplastic cartilage was identified on the basis of the presence of cartilage cores (i.e., cartilage extending into the subchondral bone) and confirmed with subsequent histological examination. Full-thickness cartilage samples from 57 horses were collected and paraffin embedded. Histological examination was used to examine the normal architecture of equine growth cartilage and to determine the presence of various pathological changes in dyschondroplastic lesions. Immunolocalization was used to identify type VI collagen in normal and dyschondroplastic lesions. The abnormalities observed in the dyschondroplastic cartilage fell into two groups. In Group A (n = 18) the lesions were associated with a disruption in the normal sequential transition of the chondrocytes through proliferation and maturation resulting in an accumulation of large numbers of small, rounded chondrocytes. A decrease in type VI collagen immunoreactivity compared with normal animals was detected except around chondrocyte clusters. Group B lesions (n = 9) were characterized by an alteration in the staining pattern of the mineralized cartilage and underlying bone. In these lesions type VI collagen immunoreactivity was increased. In both groups the presence of retained blood vessels, chondrocyte clusters, chondronecrosis and fissure formation was detected. These two histologically-distinct groups suggest that equine dyschondroplasia may be comprised of different pathological entities and that it is associated with alterations in the pattern of distribution of an ECM protein.

Osteochondrosis — An international problem for the horse industry

Summary Osteochondrosis is one of the most important skeletalproblems affecting young horses and is one of the conditions included in the syndrome of developmental orthopedic disease. It occurs worldwide in many different breeds and its incidence appears to be steadily increasing. The primary lesion of osteochondrosis is attributed to focal damage of endochondral ossification. When occurring in the articular/epiphyseal cartilage complex, there may be bone formation within the retained cartilage, resulting in “bony fragments.” These are often seen in the tarsocrural articulation on the cranial aspect of the tibia. Focal retention of necrotic cartilage into the subchondral bone may eventually lead to cleft formation resulting in osteochondrosis dissecans. Other lesions associated with osteochondrosis are subchondral cysts, fractures and osteoarthrosis. The definitive cause of osteochondrosis is unknown,but there is evidence that it is the response in growth cartilage to a number of different challenges. It appears to be multifactorial in origin, involving heredity, growth rate, body size, nutrition, mineral imbalance, endocrinological dysfunction and biomechanical trauma. Recent studies have shown cases of osteochondrosis to be preceded by radiographically detectable disturbances of endochondral ossification during the first three months of life. This early appearance of disturbed ossification necessitates further studies into the importance of nutrition/management of the pregnant and lactating mare. Whether these early disturbances will lead to fully developed osteochondrosis or if they will recede obviously depends on a number of factors such as nutrition and exercise. High energy diets have been shown in weaning foals to consistently produce lesions of osteochondrosis. If, however, foals fed a high energy diet are subjected to forced exercise, the incidence of osteochondrosis is reduced dramatically. The prevention of osteochondrosis must rate as a highpriority for the horse industry, but to achieve this more data on the mechanisms of endochondral ossification and how this process is influenced by different intrinsic and environmental factors are required. Recent research into osteochondrosis has involved studies of chondrocyte metabolism in growth cartilage, the influence of growth factors, the extent of degradation of extracellular matrix and endochondral ossification.

Back problems in the horse - a method of clinical examination

THE increased popularity of competitive equine sports in this country over the last 20 years has been accompanied by a rise in the prevalence of spinal injuries in horses. A considerable industry now exists to treat these injuries although little seems to have been done to describe the clinicopathological aspects of the conditions involved. Consequently, the lines of therapy employed are essentially empirical and it is difficult to evaluate the effectiveness of the different techniques available. There have been few detailed reports on the incidence and causes of back disorders in the horse. In a survey carried out by the British Equine Veterinary Association of cases during 1962-63 from general practice, there were 6,588 horses examined for musculoskeletal damage and an incidence of 0.9 per cent of injuries to the back was recorded. No attempt was made to subdivide these into precise entities (Anon 1965). Definitive diagnosis of injuries to the back of the horse is made difficult by the complicated clinical picture often exhibited and by the frequent lack of adequate radiographic facilities for the mid-and caudal regions of the spine. Nevertheless a presumptive diagnosis can often be made in many cases. This paper attempts to describe a practical scheme for clinical evaluation of a horse with a potential back problem. The technique of radiography and radiological interpretation of normal horses and those with a thoracolumbar (TL) disorder have been described in detail elsewhere (Jeffcott, 1979 a, b). The diagnosis of a back problem is frequently achieved by the elimination of conditions with similar signs rather than on the basis of positive findings. A detailed and systematic appi-oach to this type of examination is essential and the protocol employed by the author is summarised in Table 1.