99mTc-DPD uptake in juvenile arthritis. Scintimetry and autoradiography of the knee in dogs.

Unilateral arthritis of the knee was induced in mongrel puppies by intraarticular injections of 1% Carragheenan. Bone metabolism was studied by a scintimetric technique on static 99mTc-diphosphonate bone scans every 2nd week during the induction of arthritis for 3 months and monthly in a postarthritic phase of another 3 months. Changes in uptake of radionuclide were present after 2 weeks. The induction phase was characterized by a decreased uptake in the calcification layer of the juxta-articular growth plates and a moderately increased epiphyseal uptake. The postarthritic phase was characterized by normalization of growth plate uptake and a marked increase in epiphyseal uptake. Using contact autoradiography, the epiphyseal uptake was seen mainly in a narrow subchondral and subsynovial bone layer, around bone cysts and osteophytes, whereas central epiphyseal bone was osteopenic with decreased uptake of tracer. The study suggests that the early scintigraphic appearance of juvenile non-suppurative arthritis may be an overall decrease in uptake of 99mTc-diphosphonate due to a depression of growth plate metabolism.