Evaluation of Samarium‐153 for Synovectomy in an Osteochondral Fragment‐Induced Model of Synovitis in Horses

Objective— To determine the effects of intraarticular administration of Samarium‐153 ( 153 Sm) bound to hydroxyapatite microspheres ( 153 SmM) on an osteochondral chip–Ninduced synovitis. Study Design— Sixty days after implantation of autogenous osteochondral fragments in the middle carpal and metacarpophalangeal joints, 153 SmM was administered into 1 joint of each type. The contralateral joints were used as untreated controls. Animals or Sample Population— Fifteen horses without preexisting joint disease were randomly divided into 2 groups (7 in the carpal group, 8 in the metacarpophalangeal group). Methods— 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 153 SmM (20 to 50 μm 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 153 SmM on synovial membrane and cartilage. Results— Intraarticular 153 SmM 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 153 SmM resulted in synovectomy of variable depth and extent. Conclusions— Intraarticular 153 SmM may be a useful method for synovectomy of inflamed synovial membrane. Clinical Relevance— With further testing, radioactive pharmaceuticals might become useful clinical treatments for persistent synovitis not responsive to conventional techniques.