Background. Sub-trochanteric fractures are challenging to treat due to various anatomical and biomechanical factors. High tensile forces contribute to the challenge of fracture reduction. Intramedullary nailing has become the treatment of choice. If anatomical reduction is not achieved, any mal-alignment will predispose to implant failure. Open reduction with cerclage wires can add to construct stability and improve the quality of reduction. There is no consensus or classification to guide surgeons on when to perform open reduction, which is often performed intra-operatively when closed reduction fails often with no planning. This can lead to intraoperative delays as theatre staff would not have prepared the correct equipment necessary for open reduction. Objectives. The purpose of this study was to assess outcomes of closed and open reduction of traumatic sub-trochanteric fractures treated with intramedullary nailing and to propose a new classification system to dictate management. Methods. After a review of current classification systems, a 3-tier classification was proposed (Type 1, 2 and 3). Type 1 indicated a transverse fracture, Type 2 was a spiral fracture with an intact posterior and medial wall and a Type 3 fracture were fractures with no posterior and/or medial walls. Over a two-year period (2013–2015), patients with sub trochanteric fractures were classified into Type 1, 2 or 3 injuries based on radiographic appearances by two senior clinicians. Patients with Type 3 injuries were divided into two groups based on whether they were treated with open or closed reduction. A clinical and radiographic review was performed. The primary outcome measure was the incidence of implant failure, whereas secondary outcome measures were related to fracture reduction. Statistical analysis was performed using GraphPad Prism Version 6 (GraphPad Software Inc. California, USA). Fisher's exact test was used for independent categorical data and Mann–U Whitney for continuous nonparametric data. Statistical significance was set at p<0.05. Results. 75 patients had intramedullary nailing for subtrochanteric fractures over the study period with a mean age of 82.6 years. There were 48 patients who had a Type 3 fracture pattern with a deficient medial and/or posterior wall. Reduction was achieved open with cerclage wires in 42% of patients (n=20 and closed in 58% (n=28). Overall there were a total of 18 (37.5%) major complications. In patients treated with closed reduction, 9 patients suffered mechanical complications (6 distal locking screw failures, 3 lag screw cut outs). There was a significantly increased risk of implant failure in patients treated with closed reduction compared to open reduction (p=0.006). No cases with cerclage wire had implant failure. Open reduction with cerclage wires improved the quality of reduction (p=0.0001) compared with closed reduction. There was no significant increase in operating time in patients treated with cerclage wires (p=0.4334). Conclusions. Open reduction with cerclage wires should be considered in patients with Type 3 sub-trochanteric fractures as it has shown to significantly reduce the risk of implant failure and improve the quality of reduction with no significant increase in operating time