Concentration of methylprednisolone in the centrodistal joint after administration of methylprednisolone acetate in the tarsometatarsal joint.

Summary

# Editorial Summary When treating osteoarthritis of the distal tarsal joints, clinicians have traditionally injected both the tarsometatarsal (TMT) and centrodistal (CD) joints separately with corticosteroids; however, the extent to which methylprednisolone acetate (MPA) diffuses between these anatomically proximate structures remained undocumented. Serena and colleagues administered MPA into the TMT joint of 16 horses and serially sampled the ipsilateral CD joint using synovial fluid aspiration, measuring methylprednisolone concentrations via high-performance liquid chromatography to establish whether therapeutic levels were achievable without direct injection. By 6 hours post-injection, all 10 CD joints sampled at this timepoint contained therapeutic concentrations of methylprednisolone, demonstrating predictable diffusion across the joint capsule. This finding has significant practical implications: clinicians can treat distal hock pain originating from both joints by injecting the TMT joint alone, thereby reducing procedure time, minimising patient stress, and eliminating the technical challenges and potential complications associated with centrodisal arthrocentesis—a notoriously difficult joint to access cleanly. For practices managing hock lameness, this approach streamlines treatment protocols whilst maintaining clinical efficacy.

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Key Findings

• •Methylprednisolone acetate administered into the tarsometatarsal joint diffuses into the centrodistal joint within 6 hours
• •Therapeutic concentrations of methylprednisolone were detected in all 10 centrodistal joints sampled at 6 hours post-injection
• •Single injection into the tarsometatarsal joint can treat osteoarthritis affecting both distal hock joints without separate centesis of the centrodistal joint

Conditions Studied