This paper reports the diagnosis and repair of synovial fistulae between a carpal hygroma and both the antebrachiocarpal (ABC) joint and the extensor carpi radialis (ECR) tendon sheath of the left carpus in a 7-year-old gelding. The communication was confirmed using contrast radiography. Arthroscopy visualised the synovial fistulae and aided in the surgical repair. The gelding made a full athletic and acceptable cosmetic recovery. (2001) Multipotent mesenchymal stem cells from adult human synovial membrane. Arthritis Rheum. 44, 1928-1942. DeLee, J.C. (1985 Complications of arthroscopy and arthroscopic surgery: results of a national survey. Arthroscopy 1, 214-220.