Samarium 153-labeled hydroxyapatite microspheres for radiation synovectomyin the horse: A study of the biokinetics, dosimetry, clinical, and morphologic response in normal metacarpophalangeal and metatarsophalangeal joints

Objective-To determine the effects of Samarium-153 bound to hydroxyapatite microspheres ((SmM)-Sm-153) when injected into the metacarpophalangeal and metatarsophalangeal joints of horses. Study Design-Horses were injected with (SmM)-Sm-153 in metacarpophalangeal and metatarsophalangeal joints with the diagonal contralateral joints used as untreated controls. Animals or Sample Population-Twelve adult horses without pre-existing disea se involving the metacarpo/metatarsophalangeal joints. Methods-Horses were divided into three groups: high-dose Samarium-153 (12.5 to 17.0 millicurie [mCi]), intermediate dose (6.5 to 12.0 mCi), and low do se (3.5 to 6.0 mCi). Horses were examined daily for 7 days postinjection fo r clinical abnormalities, lameness, and surface and systemic radiation leve ls. One horse from each group was euthanatized at 14, 30, and 60 days posti njection and the effects of the (SmM)-Sm-153 examined microscopically in th e cartilage and synovial membrane. Results-Intraarticular(153)SmM caused inflammation characterized by lamenes s, effusion, and regional edema for 48 to 72 hours. Minimal levels of activ e (SmM)-Sm-153 were identified in the blood or urine alia were well below t he maximal tolerance of 1 mCi. Microscopically the radiation caused no effe cts on the articular cartilage. The synovectomy created was good but not id eal in that some areas did have necrosis into the subintimal regions and a few islands of intact intimal cells persisted. Conclusions-The use of (SmM)-Sm-153 is an effective means of targeting the synovial intimal cells with minimal extrasynovial leakage of radiation. Clinical Relevance-The metacarpophalangeal and metatarsophalangeal joints o f the horse can be safely treated with (SmM)-Sm-153 without damage to the c artilage or significant extracapsular leakage. (C) Copyright 2000 by The Am erican college of Veterinary Surgeons.