CHRISTOPHER R. BYRON, DVM, MS, Diplomate ACVS 1 , BRITANY M. BENSON, DVM 1 , WILLIAM M. KARLIN, DVM 1 , and ALLISON A. STEWART, DVM, MS, Diplomate ACVS 1 1 Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois, Urbana, IL Veterinary Surgery February 2010 39 2 239 - 243 Objective—To report the use of a proximolateral endoscopic portal with a distolateral instrument portal for carpal retinaculum release in a horse clinically affected with carpal canal syndrome. Study Design—Clinical report. Animals—A 4-year-old Thoroughbred female. Methods—Carpal canal syndrome secondary to traumatic suppurative tenosynovitis was treated by accessory carpal bone debridement and carpal retinaculum release using a tenoscopic approach to the carpal flexor synovial sheath through a proximolateral endoscope portal and a distolateral instrument portal. Results—Resolution of carpal sheath effusion and lameness occurred allowing racing 14 months later. Use of a distolateral instrument portal was not associated with complications or iatrogenic damage to neurovascular structures and reduced endoscope and instrument interference and offered easier access to the distal aspect of the carpal sheath. Conclusions—Carpal retinaculum release may be safely accomplished with a distolateral instrument portal when access to the distal aspect of the carpal sheath is needed. Clinical Relevance—The distolateral instrument portal described may be a useful alternative to a proximolateral portal when distal carpal sheath instrument access is necessary or advantageous.