Tibial dyschondroplasia (osteochondrosis) in the turkey. A morphologic investigation.

Sixty-seven Broadbreasted White Turkeys, 4 to 137 days old, were included in the investigation. Some were normal, while others were limping, and some had bowed legs. Immediately after destruction of the birds, the arteries of the legs were injected with Colorpaque, using a technique introduced by the author. The proximal part of one or both tibiae were examined radiographically, macroscopically, and microscopically. The microscopic examination included histology, microangiography, and microradiography. The normal development and morphology of the proximal tibia is presented. Thereafter an account is given of development and morphology of the tibia with dyschondroplastic lesions (retained cartilages). It was found that 39 of the 67 birds had some degree of tibial dyschondroplasia. The retained cartilage was seen in the posteromedial part of the proximal tibial metaphysis. The growth plate both of the normal and abnormal birds consisted of 3 layers of cells in order from the epiphysis--the one of proliferating cells, the one of transitional cells, and the one of hypertrophied cells. A main feature in tibial dyschondroplasia is accumulation of transitional cells, which do not have a vascular supply. By microangiographic means it was possible to demonstrate that the retained cartilage is surrounded by numerous vessels, which apparently cannot get into the cartilage. The reason for the loss of normal differentiation of the cartilage cells and concomitant disturbance of the endochondral ossification is obscure. It is speculated that changes on an ultrastructural and biochemical level are responsible for the pathologic condition. When the retained cartilage reaches a certain size, degenerative changes, necrosis, and fissures occur. Complete healing of the lesion was not seen in any of the birds, but partial disappearance of the proximal or distal part of the retained cartilage took place in some birds. It was concluded that the present investigation has shed light on the development and morphology of tibial dyschondroplasia, but it has also brought forward a number of questions about etiology. There seems to be good reason to believe that dyschondroplasia in the turkey is of similar nature as dyschondroplasia in broilers and osteochondrosis in domestic mammals.