Modified Proximal Interphalangeal Joint Arthrodesis in a Yearling Filly with an Osseous Cyst-Like Lesion in the Proximal Phalanx

SIMPLE SUMMARY: Subchondral cystic lesions are common in young horses, but they can be diagnosed in older horses and often cause lameness. They are most frequently found in the medial femoral condyle, phalanges, elbow, and carpal bones. Lesions that interact with the joint may cause severe lameness and may not respond well to medical treatment. Arthrodesis, or “artificial ankylosis”, of the affected joint can be an effective radical procedure to reduce pain. As a “low motion” joint, the proximal interphalangeal joint has significantly more mobility than the small hock joints. Fusion is impossible to achieve simply by removing the remaining cartilage. To bridge and immobilize the joint, it must be used in conjunction with the surgical placement of screws and plates. This report describes a successful modified surgical method of arthrodesis of the proximal interphalangeal joint and packing with calcium phosphate biocement in a filly with an osseous cyst-like lesion of the proximal phalanx that communicated with the proximal interphalangeal joint. ABSTRACT: After the medial femoral condyle (MFC), the phalanges are the second most common site for osseous cyst-like lesions (OCLLs). Conservative treatment of phalangeal cysts on the convex surface of proximal phalanx presents a technical problem with access to the stoma of the cyst. Surgical therapy options usually aim to avoid cyst enlargement through drilling or screw placement or to encourage lesion filling with osteoconductive material. This paper describes a case of treatment of the OCLL in a yearling Czech warmblood filly with surgical arthrodesis, together with the packing of the OCLL with calcium phosphate biocement (CPB). The filly showed a chronic, moderate to severe, intermittent left hindlimb lameness. Dynamic examination combined with regional anesthesia and radiography confirmed a clinically significant large OCLL on the distal joint surface of the first phalanx. Treatment of the OCLL was performed by surgical arthrodesis of the proximal interphalangeal joint, using two paraxial and one axial crossed lag screw, after curetting of the cyst and filling with CPB.