Sinocutaneous fistula repair with a masseter muscle transposition flap combined with wound matrix and cancellous bone graft in a horse: A new technique.

OBJECTIVE To describe a new technique to repair a sinocutaneous fistula with a masseter muscle transposition flap. STUDY DESIGN Case report. ANIMAL One 13-year-old thoroughbred stallion. METHODS One 13-year-old stallion with a 3.5 × 6-cm sinocutaneous fistula over the right caudal maxillary sinus was treated with a transpositional masseter muscle flap. This repair consisted of a commercial wound matrix dressing placed directly over the hole in the maxilla and secured with suture material; a cancellous bone graft collected from the right tuber coxa placed on the dressing; and a portion of the superficial layer of the masseter muscle, with its pedicle at the facial crest, transposed dorsally over the bone graft, followed by a rotational skin flap with skin rostral to the fistula to close the defect. RESULTS Seroma formation and dehiscence of the skin flap occurred, but the transposed muscle flap survived, and the technique resulted in successful closure of the sinocutaneous fistula with excellent cosmetic and functional outcome. CONCLUSION A chronic maxillary sinocutaneous fistula was successfully treated by using a transposition flap of the masseter muscle and a rotational skin flap with minor complications. CLINICAL IMPACT Transposition of the superficial layer of the masseter muscle should be considered for a repair of large maxillary sinocutaneous fistulas in horses.