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

The research article investigates the impact of a radioisotope, Samarium-153, bound to hydroxyapatite microspheres when injected into particular joints of horses, examining the resulting alterations in the joints, the presence of any systemic or local radiation, any damage to the cartilage, and therapeutic effectiveness.

Research Methodology

• Twelve adult horses with no pre-existing diseases of certain joints called metacarpophalangeal and metatarsophalangeal were used in this study.
• The horses were divided into three treatment groups: high-dose (12.5 to 17.0 mCi), intermediate dose (6.5 to 12.0 mCi), and low dose (3.5 to 6.0 mCi).
• Samarium-153 microspheres were injected into these joints, using the diagonal contralateral joints as untreated controls.

Monitoring and Analysis

• The horses were daily monitored for any abnormal clinical symptoms, lameness, and local and systemic radiation levels for seven days after injection.
• After specific time intervals (14, 30, and 60 days post injection), one horse from each treatment group was euthanized and their cartilage and synovial membrane were examined microscopically for the radioisotope-induced changes.

Findings

• The injection caused temporary inflammation symptoms such as lameness, joint effusion and regional edema, lasting 48 to 72 hours.
• There were minimal traces of activated Samarium-153 in blood or urine, remaining well below the maximum tolerance level (1 mCi). This suggests minimal extrasynovial leakage of radiation.
• The radioisotope did not cause any noticeable effects on the articular cartilage when observed under a microscope.

Conclusions

• The use of Samarium-153 micropheres proved to be a effective means of targeting synovial intimal cells.
• The metacarpophalangeal and metatarsophalangeal joints in horses can be safely treated with this method without damage to the cartilage or significant risk of extracapsular leakage.