## 1 Introduction  
Subtochanterior hip fractures account for 5% to 34% of all proximal femoral fractures. [1]. The subtrochanterior region is located between the lesser trochanter of the femur and extends approximately 5 cm below it [2]. It experiences the highest level of mechanical stress in the human skeleton. In this region, the stress distribution is unequal; the medial cortex experiences about 20% more compressive stress (up to 1200 pounds/square inch) than the tensile stress encountered by the lateral cortex, leading to immense stress in this area [3]. The standard treatment for subtrochanterior fractures is intramedullary nailing [2]. Due to the region's anatomy, fractures are often not appropriately reduced in a significant number of cases, which can result in residual displacement (gaps between the ends of the bone) and leave the proximal fragment of the femur in a varus position. Given the high bending forces present in this area, varus malalignment is considered the most critical factor contributing to nonunion [4]. Poor vascularization in this anatomical zone also contributes to the nonunion of these types of fractures. Nevertheless, the advantages of achieving an anatomic bone reduction, or at least restoring a valgus alignment of the fracture, are likely more significant than the potential risks of disrupting the soft tissue and periosteal blood supply during an open surgical approach. Therefore, an anatomic fracture reduction, or at least restoring hip valgus through an open approach, is preferable to achieving varus malalignment through a percutaneous approach [2,4]. The reported nonunion rate for these types of fractures ranges from 4% to 20% [5, 6, 7]. The current approach to treating subtrochanterior nonunion is surgical; exchanging nailing is the most widely used technique [2]. It is mandatory to perform nailing in a static mode (which involves both proximal and distal static locking of the new nail) in conjunction with over-reaming of the canal. This technique has reported good outcomes [8, 9, 10, 11]. However, a valgus restoration of the hip angle becomes essential for achieving bone union in subtrochanterior nonunion when residual varus malalignment is present, and achieving proper valgus hip angle correction can be complex (requiring osteectomies of the fracture) or simply impossible with intramedullary fixation [12]. Open reduction using an extramedullary device and a lateral closing osteotomy appears to be the preferable surgical procedure for restoring a physiological valgus alignment of the hip in a subtrochanterior nonunion in varus [13, 14, 15]. In most cases, anatomical reduction of the bone and rigid fixation (needed to achieve absolute stability and primary bone union) can be quite challenging. Bone defects, technical intraoperative limitations, or the performance of the osteotomy required to restore the physiological valgus of the hip make this optimal surgical fixation impossible, and it is, in fact, poorly documented in the literature [16]. Therefore, secondary bone healing using extramedullary fixation with fixed-angle devices (such as condylar blade plates, condylar locking plates, and 95\({}^{\circ}\) dynamic condylar screw plates) following a valgus lateral closed osteotomy is actually the standard surgical procedure aimed at correcting varus deformities and achieving bone union [8, 9, 14, 15, 16, 17]. None of these allow for dynamic fixation. Condylar blade plates and condylar locking plates are static devices that do not enable interfragmentary dynamic compression of the bone. In contrast, the 95\({}^{\circ}\) dynamic condylar screw plate is a dynamic device; however, in subtrochanterior nonunions, the proximal fragment is fixed in a manner that does not follow the anatomical direction of the neck of the hip, making sliding between the fragments impossible as well.