Bischofberger, A.S.; Fürst, A.; Auer, J.; Lischer, C. Equine Veterinary Journal May 2009 41 5 465-473(9) Reasons for performing study: Osteosynthesis of third metacarpal (McIII) and third metatarsal (MtIII) bone fractures in horses is a surgical challenge and complications surrounding the repair are common. Retrospective studies evaluating surgical repair, complications and outcome are necessary to increase knowledge and improve success of long bone fracture repair in the horse. Objectives: To evaluate clinical findings, surgical repair, post operative complications and outcome of 10 mature horses and 11 foals with McIII or MtIII fractures that were treated with open reduction and internal fixation (ORIF). Methods: Medical records were reviewed and follow-up information obtained by means of radiographs and/or telephone questionnaire. Results: Survival was achieved in 62% of the horses (3 mature/10 foals). On long-term evaluation (>6 months) 11 horses (2 mature/9 foals) were fit for their intended activity, one mature horse had a chronic low grade lameness, and one foal was lost to follow-up because it was sold. The main fracture types were simple transverse (33.3%) or simple oblique (28.6%) and 71.4% of the fractures were open, 3 Type I (one mature/2 foals) and 12 type II (7 mature/5 foals). The preoperative assessment revealed inadequate emergency treatment in 10 horses (5 mature/5 foals; 47.6%). Survival rate of horses with open fractures was 12.5% (1/8) in mature and 85.7% (6/7) in foals. Post operative incisional infection (4 mature, 3 foals) was only managed successfully in 2 foals. Fracture instability related to inadequate fracture fixation technique occurred in 4 horses (all mature) and was always associated with unsuccessful outcome. Conclusions: Age, bodyweight and infection are strongly associated with outcome in treatment of complete McIII/MtIII fractures. Clinical relevance: Rigid fixation using plates and screws can be successful in treatment of closed or open, complete diaphyseal McIII/MtIII fractures in mature horses and foals. Instable fixation, infection and a bodyweight >320 kg are major risk factors for unsuccessful outcome.