Introduction

• Cause: acute or chronic low-grade synovitis of the tarsocrural joint  → effusion.
• Signs: distended tarsocrural (tibiotarsal) joint       .
• Diagnosis: physical examination, radiography Hindlimb: radiography, arthrocentesis Synovial fluid: collection, arthroscopy Tarsus: arthroscopy.
• Treatment: none; drainage, bandaging, intra-articular anti-inflammatories Dexamethasone.
• Prognosis: guarded.

Pathogenesis

Etiology

• True idiopathic 'bog spavin' is thought to be caused by abnormal biomechanical stress:
  • Conformational faults Musculoskeletal: conformation, eg straight hocks, sickle hocked         or cow hocked   .
  • Lameness in another limb.
  • Intense training.
• Osteochondrosis Bone: osteochondrosis - most common cause in the young animal.
• Hemarthrosis.
• Infection Joint: septic arthritis - adult.
• Osteoarthritis Musculoskeletal: osteoarthritis (joint disease).

Predisposing factors

General

• Poor conformation, eg too straight in the hocks.
• Prolonged periods of being stalled or inactivity.
• Lower hindlimb casts may develop effusion in the immobilized limb. ? due to joint capsule sprain.
• Performance horses, eg dressage, showjumpers, required to perform quick and tight turns and manoeuvres.
• Deficiencies alone or in combination of: phosphorus Phosphorus, calcium Calcium salts Nutrition: minerals, Vitamins A Vitamin A or D Vitamin D3.
• Chronic zinc poisoning.

Pathophysiology

• Biomechanical stress or other tarsal joint pathology, eg osteochondrosis Bone: osteochondrosis → recurring cartilage microtrauma → chronic low grade synovitis → synovial effusion.
• Distension of the joint → increased space between synoviocytes and dilution of hyaluronic acid.
• See synovial joint pathobiology Joint: synovial pathobiology.

Diagnosis

Treatment

Outcomes