Ballybrown Equine Clinic

Talks/Publications:

Treatment of a Subchondral Bone Cyst in an eight-month-old Thoroughbred

INTRODUCTION:

Subchondral bone cysts (SBCs) are produced by an infolding of articular cartilage, as a result of either defective endochondral ossification or traumatic damage leading to ischaemic necrosis, in a focal subchondral area. Affected horses are usually between 6 months and 2 years of age and present with intermittent lameness. The reported incidence in the Thoroughbred is <1%. This report describes a different treatment approach in a case involving an articular cyst in the distal epiphysis of the second phalanx of an eight-month-old flat-bred foal.

MATERIALS AND METHODS:

An eight-month-old weanling filly was presented for assessment of a right forelimb lameness. Regional analgesia was used to locate the painful area and digital radiography revealed the SBC.

TREATMENT:

The Coffin Joint was aseptically medicated with 20mg Methylprednisolone Acetate (Depo-Medrone). A Distal Limb Perfusion (DLP) was also performed, delivering 25mg of Tiludronate (Tildren) directly into the lateral palmar vein at the level of the abaxial surface of the proximal sesamoid bone. The filly was then box rested for 4 weeks. Lameness was still evident at four weeks post-treatment, therefore the joint medication with 20mg Methylprednisolone Acetate was repeated. Following 4 more weeks of rest a slow re-introduction to exercise was initiated. Serial radiographs of the lesion were taken throughout the treatment phase.

RESULTS AND DISCUSSION:

Follow-up radiographs in this case showed a reduction in the lytic appearance of the cyst with a progressive decrease in the diameter and cloaca. The filly remained sound throughout yearling sales preparation and went into training at 21 months. It is intended to race her as a 2-year-old. SBCs are widely accepted as carrying a very poor prognosis for future athletic activity in the Thoroughbred. The most popular current treatment for cysts of this type involves surgical ablation, with or without bone grafting. This approach is not without drawbacks, such as expense, requirement for general anaesthesia, risk of cyst expansion/fracture, likelihood of surgical scar and lengthy convalescence. The reported success of surgery has been as low as 33%. The novel treatment described in this report had two goals: to limit the inflammatory response (Methylprednisolone Intra-Articular injection) and to inhibit active bone resorption (Tiludronate via DLP) within the cyst. The outcome of the treatment in this case would suggest that this protocol could be a viable alternative to surgery.

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