Evaluation of samarium-153 for synovectomy in an osteochondral fragment-induced model of synovitis in horses.

Abstract

To determine the effects of intraarticular administration of Samarium-153 (153Sm) bound to hydroxyapatite microspheres (153SmM) on an osteochondral chip-induced synovitis. Sixty days after implantation of autogenous osteochondral fragments in the middle carpal and metacarpophalangeal joints, 153SmM was administered into 1 joint of each type. The contralateral joints were used as untreated controls. Fifteen horses without preexisting joint disease were randomly divided into 2 groups (7 in the carpal group, 8 in the metacarpophalangeal group). Horses had osteochondral fragments that were harvested from the lateral ridge of the trochlea of the talus and implanted bilaterally into a middle carpal joint and a metacarpophalangeal joint; the opposite joint type served as a control. Sixty days later, 10 to 15 mCi of 153SmM (20 to 50 microm diam) was injected into the fragment-implanted joints. Three horses were treated with nonradioactive hydroxyapatite fragments. Horses were examined clinically until they were killed 14 or 30 days later. Control and treated joints were examined grossly and microscopically to determine the effects of 153SmM on synovial membrane and cartilage. Intraarticular 153SmM caused a transient flare with lameness, effusion, and edema for 48 to 72 hours. Implanted osteochondral chips induced a synovitis characterized by variable degrees of joint damage and synovial infiltrate. Use of 153SmM resulted in synovectomy of variable depth and extent. Intraarticular 153SmM may be a useful method for synovectomy of inflamed synovial membrane. With further testing, radioactive pharmaceuticals might become useful clinical treatments for persistent synovitis not responsive to conventional techniques.