EVITA BUSSCHERS, DVM, DEAN W. RICHARDSON, DVM Diplomate ACVS, PATRICIA M. HOGAN, VMD, Diplomate ACVS and MIDGE LEITCH, VMD, Diplomate ACVS Veterinary Surgery December 2008 37 8 771 - 780 Objective—To describe the characteristics of unilateral mid-body proximal sesamoid bone (PSB) fractures, to determine factors associated with the outcome of horses after surgical repair, and to describe a technique for arthroscopically assisted screw fixation in lag fashion. Study Design—Retrospective case series. Animals—Horses (n=25) with unilateral mid-body PSB fracture. Methods—Medical records (1996–2006), radiographs, and arthroscopic videos of horses with surgically repaired unilateral mid-body PSB fractures were reviewed. Retrieved data included signalment, affected limb and PSB, fracture characteristics, and surgical technique. Outcome was established by radiographic assessment of healing and race records; categorical data were analyzed using Fisher's Exact test. Results—Medial forelimb PSBs were most commonly affected (80%). Surgical technique and degree of reduction were significantly associated with outcome; 44% of horses with screw repair and none of the horses with wire fixation raced (P=.047). Factors that may have influenced this outcome were differences in fracture reduction (improved reduction in 22% wire repairs and 88% screw repairs, P=.002) and use of external coaptation (22% wire repair and 88% lag screw repair, P=.002). None of the horses with unimproved reduction raced after surgery. Conclusions—Only 28% of horses with mid-body PSB fractures raced after surgery. Compared with wire fixation, screw fixation in lag fashion resulted in good reduction and is seemingly a superior repair technique. Clinical Relevance—For mid-body PSB fractures, arthroscopically assisted screw fixation in lag fashion and external coaptation for anesthesia recovery and initial support provides the best likelihood of return to athletic use.