This paper reports the successful use of a half limb cast to treat prior failures in healing of a synovial hernia in a Thoroughbred yearling. The hernia was due to a nonhealing arthroscopy portal and was confirmed using ultrasonography and positive contrast arthrography to visualise the communication between the metacarpophalangeal joint and subcutaneous space. Surgery was performed 3 times, due to failure of healing of the joint capsule and recurrence of clinical signs. A half limb cast applied following the final surgery effected a repair. At 2 months post surgery there was no recurrence of the subcutaneous swelling and at 3 months post surgery a repeat positive contrast arthrogram confirmed healing of the hernia.