Radiation synovectomy with holmium-166 ferric hydroxide macroaggregate in equine metacarpophalangeal and metatarsophalangeal joints.

This research investigates the impact of radiation synovectomy using holmium-166 ferric hydroxide macroaggregate (Ho-166 FHMA) on the synovium and synovial fluid in the metacarpophalangeal and metatarsophalangeal joints of horses. The study found that this procedure can cause inflammation, edema, scar tissue formation, and multifocal necrosis, but may offer benefits for inflamed joints with synovial lining hyperplasia if excessive scar tissue formation can be managed.

Research Methods

• The researchers conducted trials using Ho-166 FHMA, a radioactive compound, or a non-radioactive Ho-165 FHMA on the affected joints for comparison.
• The study involved six mature mixed-breed horses without any sign of disease in the metacarpophalangeal or metatarsophalangeal joints.
• Each joint was injected with a high single dose of Ho-166 FHMA (an average of 1,000 MBq/joint) or a non-radioactive Ho-165 FHMA for the control group.
• The team conducted a clinical examination, arthroscopy, synovial fluid analyses, and histologic studies to identify the effects of radiation synovectomy. They used scintigraphy to determine the intraarticular distribution of Ho-166 FHMA.

Findings

• The administration of Ho-166 FHMA triggered joint inflammation causing regional edema, effusion, and the formation of scar tissue.
• Scintigraphy showed the highest radioactivity intensity in the proximal plantar joint pouch, where the Ho-166 FHMA treatment induced multifocal necrosis.
• The dorsal joint pouch exhibited minimal changes from radiation synovectomy, as evident in arthroscopic and histologic evaluations.
• The researchers discovered no synovium regeneration within two months.
• Synovial fluid protein concentration significantly increased, and residual radioactivity remained five days post Ho-166 FHMA injection.

Conclusion

• The injection of a single high dose of Ho-166 FHMA resulted in multifocal necrosis of the synovium and deep, soft-tissue damage in the equine fetlock joints.
• Inflamed joints with hyperplasia in the synovial lining could benefit from Ho-166 FHMA-induced radiation synovectomy, provided excessive scar tissue formation is controlled.